Textbook story of how humans populated America is “biologically unviable”, study finds
By tdk25 from University of Cambridge - Department of Zoology. Published on Aug 10, 2016.
The established theory about how Ice Age peoples first reached the present-day United States has been challenged by an unprecedented study which concludes that their supposed entry route was “biologically unviable”.
The first people to reach the Americas crossed via an ancient land bridge between Siberia and Alaska but then, according to conventional wisdom, had to wait until two huge ice sheets that covered what is now Canada started to recede, creating the so-called “ice-free corridor” which enabled them to move south.
In a new study published in the journal Nature, however, an international team of researchers used ancient DNA extracted from a crucial pinch-point within this corridor to investigate how its ecosystem evolved as the glaciers began to retreat. They created a comprehensive picture showing how and when different flora and fauna emerged and the once ice-covered landscape became a viable passageway. No prehistoric reconstruction project like it has ever been attempted before.
The researchers conclude that while people may well have travelled this corridor after about 12,600 years ago, it would have been impassable earlier than that, as the corridor lacked crucial resources, such as wood for fuel and tools, and game animals which were essential to the hunter-gatherer lifestyle.
If this is true, then it means that the first Americans, who were present south of the ice sheets long before 12,600 years ago, must have made the journey south by another route. The study’s authors suggest that they probably migrated along the Pacific coast.
Who these people were is still widely disputed. Archaeologists agree, however, that early inhabitants of the modern-day contiguous United States included the so-called “Clovis” culture, which first appear in the archaeological record over 13,000 years ago. And the new study argues that the ice-free corridor would have been completely impassable at that time.
The research was led by Professor Eske Willerslev, an evolutionary geneticist in the Department of Zoology and Fellow of St John’s College, University of Cambridge, who also holds posts at the Centre for GeoGenetics, University of Copenhagen, and the Wellcome Sanger Institute in Cambridge.
“The bottom line is that even though the physical corridor was open by 13,000 years ago, it was several hundred years before it was possible to use it,” Willerslev said.
“That means that the first people entering what is now the US, Central and South America must have taken a different route. Whether you believe these people were Clovis, or someone else, they simply could not have come through the corridor, as long claimed.”
Mikkel Winther Pedersen, a PhD student at the Centre for GeoGenetics, University of Copenhagen, who conducted the molecular analysis, added: “The ice-free corridor was long considered the principal entry route for the first Americans. Our results reveal that it simply opened up too late for that to have been possible.”
The corridor is thought to have been about 1,500 kilometres long, and emerged east of the Rocky Mountains 13,000 years ago in present-day western Canada, as two great ice sheets – the Cordilleran and Laurentide, retreated.
On paper, this fits well with the argument that Clovis people were the first to disperse across the Americas. The first evidence for this culture, which is named after distinctive stone tools found near Clovis, New Mexico, also dates from roughly the same time, although many archaeologists now believe that other people arrived earlier.
“What nobody has looked at is when the corridor became biologically viable,” Willerslev said. “When could they actually have survived the long and difficult journey through it?”
The conclusion reached by Willerslev and his colleagues is that the journey would have been impossible until about 12,600 years ago. Their research focused on a “bottleneck”, one of the last parts of the corridor to become ice-free, and now partly covered by Charlie Lake in British Columbia, and Spring Lake, Alberta – both part of Canada’s Peace River drainage basin.
The team gathered evidence including radiocarbon dates, pollen, macrofossils and DNA taken from lake sediment cores, which they obtained standing on the frozen lake surface during the winter season. Willerslev’s own PhD, 13 years ago, demonstrated that it is possible to extract ancient plant and mammalian DNA from sediments, as it contains preserved molecular fossils from substances such as tissue, urine, and faeces.
Having acquired the DNA, the group then applied a technique termed “shotgun sequencing”. “Instead of looking for specific pieces of DNA from individual species, we basically sequenced everything in there, from bacteria to animals,” Willerslev said. “It’s amazing what you can get out of this. We found evidence of fish, eagles, mammals and plants. It shows how effective this approach can be to reconstruct past environments.”
This approach allowed the team to see, with remarkable precision, how the bottleneck’s ecosystem developed. Crucially, it showed that before about 12,600 years ago, there were no plants, nor animals, in the corridor, meaning that humans passing through it would not have had the resources that were essential for their survival.
Around 12,600 years ago, steppe vegetation started to appear, followed quickly by animals such as bison, woolly mammoth, jackrabbits and voles. Importantly 11,500 years ago, the researchers identified a transition to a “parkland ecosystem” – a landscape densely populated by trees, as well as moose, elk and bald-headed eagles, which would have offered crucial resources for migrating humans.
Somewhere in between, the lakes in the area were populated by fish, including several identifiable species such as pike and perch. Finally, about 10,000 years ago, the area transitioned again, this time into boreal forest, characterised by spruce and pine.
The fact that Clovis was clearly present south of the corridor before 12,600 years ago means that they could not have travelled through it. David Meltzer, an archaeologist at Southern Methodist University and a co-author on the study, said: “There is compelling evidence that Clovis was preceded by an earlier and possibly separate population, but either way, the first people to reach the Americas in Ice Age times would have found the corridor itself impassable.”
“Most likely, you would say that the evidence points to their having travelled down the Pacific Coast,” Willerslev added. “That now seems the most likely scenario.”
The paper Postglacial viability and colonization in North America's ice-free corridor is published in the journal Nature on 10. August 2016. DOI: 10.1038/nature19085
Inset images: Map outlining the opening of the human migration routes in North America revealed by the results presented in this study. / Mikkel W. Pedersen and colleague preparing for coring of the lake sediments. All images provided by Mikkel Winther Pedersen, Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen.
Using ancient DNA, researchers have created a unique picture of how a prehistoric migration route evolved over thousands of years – revealing that it could not have been used by the first people to enter the Americas, as traditionally thought.
‘Red gene’ in birds and turtles suggests dinosaurs had bird-like colour vision
By fpjl2 from University of Cambridge - Department of Zoology. Published on Aug 03, 2016.
Earlier this year, scientists used zebra finches to pinpoint the gene that enables birds to produce and display the colour red.
Now, a new study shows the same ‘red gene’ is also found in turtles, which share an ancient common ancestor with birds. Both share a common ancestor with dinosaurs.
The gene, called CYP2J19, allows birds and turtles to convert the yellow pigments in their diets into red, which they then use to heighten colour vision in the red spectrum through droplets of red oil in their retinas.
Birds and turtles are the only existing tetrapods, or land vertebrates, to have these red retinal oil droplets. In some birds and a few turtle species, red pigment produced by the gene is also used for external display: red beaks and feathers, or the red neck patches and rims of shells seen in species such as the painted turtle.
The scientists mined the genetic data of various bird and reptile species to reconstruct an evolutionary history of the CYP2J19 gene, and found that it dated back hundreds of millions of years in the ancient archelosaur genetic line - the ancestral lineage of turtles, birds and dinosaurs.
The findings, published today in the journal Proceedings of the Royal Society B, provide evidence that the ‘red gene’ originated around 250 million years ago, predating the split of the turtle lineage from the archosaur line, and runs right the way through turtle and bird evolution.
Scientists say that, as dinosaurs split from this lineage after turtles, and were closely related to birds, this strongly suggests that they would have carried the CYP2J19 gene, and had the enhanced ‘red vision’ from the red retinal oil.
This may have even resulted in some dinosaurs producing bright red pigment for display purposes as well as colour vision, as seen in some birds and turtles today, although researchers say this is more speculative.
“These findings are evidence that the red gene originated in the archelosaur lineage to produce red for colour vision, and was much later independently deployed in both birds and turtles to be displayed in the red feathers and shells of some species, going from seeing red to being red,” says senior author Dr Nick Mundy, from the University of Cambridge’s Department of Zoology.
“This external redness was often sexually selected as an ‘honest signal’ of genuine high quality in a mate,” he says.
The previous research in zebra finches showed a possible link between red beaks and the ability to break down toxins in the body, suggesting external redness signals physiological quality, and there is some evidence that colouration in red-eared terrapins is also linked to honest signalling.
“The excellent red spectrum vision provided by the CYP2J19 gene would help female birds and turtles pick the brightest red males,” says Hanlu Twyman, the PhD student who is lead author on the work.
The structure of retinas in the eye includes cone-shaped photoreceptor cells. Unlike mammals, avian and turtle retinal cones contain a range of brightly-coloured oil droplets, including green, yellow and red.
These oil droplets function in a similar way to filters on a camera lens. “By filtering the incoming light, the oil droplets lead to greater separation of the range of wavelengths that each cone responds to, creating much better colour sensitivity,” explains Mundy.
“Humans can distinguish between some shades of red such as scarlet and crimson. However, birds and turtles can see a host of intermediate reds between these two shades, for example. Our work suggests that dinosaurs would have also had this ability to see a wide spectrum of redness,” he says.
Over hundreds of millennia of evolution, the CYP2J19 gene was independently deployed to generate the red pigments in the external displays of some bird species and a few turtle species. The scientists say their data indicate that co-option of CYP2J19 for red colouration in dinosaurs would also have been possible.
The ancestral lineage that led to scaly lizards and snakes split from the archosaur line before turtles, and, as the findings suggest, before the origin of the red gene. These reptiles either lack retinal oil droplets, or have yellow and green but not red.
However, the crocodilian lineage split from the archelosaur line after turtles, yet crocodiles appear to have lost the CYP2J19 gene, and have no oil droplets of any colour in their retinal cones.
Mundy says there is some evidence that oil droplets were lost from the retinas of species that were nocturnal for long periods of their genetic past, and that this hypothesis fits for mammals and snakes, and may also be the case with crocodiles.
A gene for red colour vision that originated in the reptile lineage around 250m years ago has resulted in the bright red bird feathers and ‘painted’ turtles we see today, and may be evidence that dinosaurs could see as many shades of red as birds - and perhaps even displayed more red than we might think.
How humans and wild birds collaborate to get precious resources of honey and wax
By amb206 from University of Cambridge - Department of Zoology. Published on Jul 22, 2016.
Humans have trained a range of species to help them find food: examples are dogs, falcons and cormorants. These animals are domesticated or taught to cooperate by their owners. Human-animal collaboration in the wild is much rarer. But it has long been known that, in many parts of Africa, people and a species of wax-eating bird called the greater honeyguide work together to find wild bees’ nests which provide a valuable resource to them both.
Honeyguides give a special call to attract people’s attention, then fly from tree to tree to indicate the direction of a bees’ nest. We humans are useful collaborators to honeyguides because of our ability to subdue stinging bees with smoke and chop open their nest, providing wax for the honeyguide and honey for ourselves.
Experiments carried out in the Mozambican bush now show that this unique human-animal relationship has an extra dimension: not only do honeyguides use calls to solicit human partners, but humans use specialised calls to recruit birds’ assistance. Research in the Niassa National Reserve reveals that by using specialised calls to communicate and cooperate with each other, people and wild birds can significantly increase their chances of locating vital sources of calorie-laden food.
In a paper (Reciprocal signaling in honeyguide-human mutualism) published in Science today (22 July 2016), evolutionary biologist Dr Claire Spottiswoode (University of Cambridge and University of Cape Town) and co-authors (conservationists Keith Begg and Dr Colleen Begg of the Niassa Carnivore Project) reveal that honeyguides are able to respond adaptively to specialised signals given by people seeking their collaboration, resulting in two-way communication between humans and wild birds.
This reciprocal relationship plays out in the wild and occurs without any conventional kind of ‘training’ or coercion. “What’s remarkable about the honeyguide-human relationship is that it involves free-living wild animals whose interactions with humans have probably evolved through natural selection, probably over the course of hundreds of thousands of years,” says Spottiswoode, a specialist in bird behavioural ecology in Africa.
“Thanks to the work in Kenya of Hussein Isack, who electrified me as an 11-year-old when I heard him speak in Cape Town, we’ve long known that people can increase their rate of finding bees’ nests by collaborating with honeyguides, sometimes following them for over a kilometre. Keith and Colleen Begg, who do wonderful conservation work in northern Mozambique, alerted me to the Yao people’s traditional practice of using a distinctive call which they believe helps them to recruit honeyguides. This was instantly intriguing – could these calls really be a mode of communication between humans and a wild animal?”
With the help of honey-hunters from the local Yao community, Spottiswoode carried out controlled experiments in Mozambique’s Niassa National Reserve to test whether the birds were able to distinguish the call from other human sounds, and so to respond to it appropriately. The ‘honey-hunting call’ made by honey-hunters, and passed from generation to generation, is a loud trill followed by a short grunt: ‘brrr-hm’.
To discover whether honeyguides associate ‘brrr-hm’ with a specific meaning , Spottiswoode made recordings of this call and two kinds of ‘control’ sounds : arbitrary words called out by the honey-hunters and the calls of another bird species. When these sounds were played back in the wild during experimental honey-hunting trips, birds were much more likely respond to the ‘brrr-hm’ call made to attract them than they were to either of the other sounds.
“The traditional ‘brrr-hm’ call increased the probability of being guided by a honeyguide from 33% to 66%, and the overall probability of being shown a bees’ nest from 16% to 54% compared to the control sounds. In other words, the ‘brrr-hm’ call more than tripled the chances of a successful interaction, yielding honey for the humans and wax for the bird,” says Spottiswoode.
“Intriguingly, people in other parts of Africa use very different sounds for the same purpose – for example, our colleague Brian Wood’s work has shown that Hadza honey-hunters in Tanzania make a melodious whistling sound to recruit honeyguides. We’d love to know whether honeyguides have learnt this language-like variation in human signals across Africa, allowing them to recognise good collaborators among the local people living alongside them.”
The greater honeyguide is widely found in sub-Saharan Africa, where its unassuming brown plumage belies its complex interactions with other species. Its interactions with humans to obtain food are mutually beneficial, but to obtain care for its young it is a brutal exploiter of other birds.
“Like a cuckoo, it lays its eggs in the nests of other birds, and its chick hatches equipped with sharp hooks at the tips of its beak. Only a few days old, the young honeyguide uses these built-in weapons to kill its foster siblings as soon as they hatch,” says Spottiswoode. “So the greater honeyguide is a master of deception and exploitation as well as cooperation – a proper Jekyll and Hyde of the bird world.”
Human cooperation is crucial to honeyguides because bees’ nests are often hidden in inaccessible crevices high up in trees – and honeybees sting ferociously. Therefore the honeyguide waits while an expert human undertakes the dangerous tasks of subduing the bees (by smoking them out using a flaming bundle of twigs and leaves hoisted high into the tree) and extracting the honey from within, usually by felling the entire tree. There is no competition for the prize: the honey-hunters harvest the honey and honeyguides devour the wax combs left behind.
Co-author Dr Colleen Begg adds: “The Niassa National Reserve is as much about people as it is about wildlife, and this is really exemplified by these human-honeyguide interactions that have been forged over thousands of years of coexistence. While many people consider wilderness not to have people in it, at Niassa people are an essential part of the landscape.”
This foraging partnership was recorded in print as early as 1588, when a Portuguese missionary in what is now Mozambique observed a small brown bird slipping into his church to nibble his wax candles. He described how this bird had another remarkable habit: it led men to bees’ nests by calling and flying from tree to tree. Once the nest was located, he wrote in his account of life on the eastern African coast in the 17th century, Ethiopia Oriental, the men harvested the honey and the bird fed on the wax.
“What João dos Santos described was what we now call a mutualism between species. Mutualisms are crucial everywhere in nature, but to our knowledge, the only comparable foraging partnership between wild animals and our own species involves free-living dolphins who chase schools of mullet into fishermen’s nets and in so doing manage to catch more for themselves. It would be fascinating to know whether dolphins respond to special calls made by fishermen, as Pliny the Elder asserted nearly two thousand years ago,” says Spottiswoode.
“Back in Africa, we’re fascinated by the evolution of the honeyguide-human mutualism and, as a next step, we want to test whether young honeyguides learn to recognise local human signals, creating a mosaic of honeyguide cultural variation that reflects that of their human partners. Sadly, the mutualism has already vanished from many parts of Africa. The world is a richer place for wildernesses like Niassa where this astonishing example of human-animal cooperation still thrives.”
The project was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) in the UK and the DST-NRF Centre of Excellence at the FitzPatrick Institute in South Africa.
Inset images: Yao honey-hunter Orlando Yassene harvests honeycombs from a wild bees’ nest in the Niassa National Reserve, Mozambique (Claire Spottiswoode); Yao honey-hunter Orlando Yassene holds a female greater honeyguide temporarily captured for research in the Niassa National Reserve, Mozambique (Claire Spottiswoode); Yao honey-hunter Orlando Yassene chops open a bees’ nest in a felled tree in the Niassa National Reserve, Mozambique (Claire Spottiswoode); Yao honey-hunter Orlando Yassene holds a wax comb (honeyguide food) from a wild bees’ nest harvested in the Niassa National Reserve, Mozambique (Claire Spottiswoode); Claire Spottiswoode interviewing honey-hunter Issufo "Kambunga" Jaime (Mbumba Marufo).
By following honeyguides, a species of bird, people in Africa are able to locate bees’ nests to harvest honey. Research now reveals that humans use special calls to solicit the help of honeyguides and that honeyguides actively recruit appropriate human partners. This relationship is a rare example of cooperation between humans and free-living animals.
A billion-year history of movement, from bacteria to Olympic athletes
From Department of Zoology. Published on Jul 19, 2016.
Sir Quentin Blake reveals new artwork at Cambridge's Museum of Zoology
From Department of Zoology. Published on Jul 12, 2016.
Darwin’s 'true century' was delayed until animal biographies illuminated social evolution
By fpjl2 from University of Cambridge - Department of Zoology. Published on Jun 14, 2016.
All animals live in a form of society, and the structures of these societies have been as important for the course of evolution as their physical environment because they steer the drive to reproduce, says Professor Tim Clutton-Brock, author of the first major synthesis of mammalian social behaviour.
While Darwin initially recognised the importance of social behaviour in his 1871 masterpiece The Descent of Man, biologists focused on anatomy rather than behaviour for many decades. In his new book Mammal Societies, Clutton-Brock argues that the “true century of Darwin was delayed for nearly 100 years” as a consequence.
Field studies of animal behaviour began with the ringing of birds in the 1930s. But it was the arrival of cheap air travel in the 1960s that fuelled behavioural fieldwork of mammals, says Clutton-Brock, as it enabled scientists to conduct long-term studies of natural populations of the larger, long-lived mammals in Africa and Asia – from gorillas to big cats.
Pioneers such as Jane Goodall and Dian Fossey, both of whom studied at Cambridge under famed zoologist Robert Hinde (as did Clutton-Brock) set up primate field studies in the 1960s and 70s which continue today.
These researchers and others began to follow animal communities over entire lives and then generations, recording a detailed ‘life history’ of each animal. In doing so, they revealed how foraging strategies affect group dynamics, how reproductive behaviour creates breeding systems, and how these create networks of kinship and sociality.
This shifted how scientists viewed wild animals: as individuals with personality traits that hold positions – some fluid, some stable – in often complex hierarchies. These societies influence who gets to breed, who gets to survive, and consequently how animals evolve.
“Darwin’s message was that selection works through differences in breeding success between individuals, not between species or populations, and the success of individuals is determined by their position in the societies they live in,” says Clutton-Brock, one of the world’s leading behavioural ecologists from Cambridge’s Zoology Department.
“That’s why it is important to be able to recognise and follow individuals. If you see a field full of rabbits, for example, you can’t tell sex, age, kinship, dominance – all of which is crucial to understanding what they are doing. This only comes alive once you follow individuals over significant periods of their lives. Long-term studies can get at questions that nothing else can answer.”
Long-term studies also allowed the wider public to identify with individual animals. The killing of studied animals – such as Digit the gorilla from Fossey’s study, or the recent hunting of Cecil the lion – provoked outcry, which in turn raised awareness of the need for conservation.
Clutton-Brock has worked on Kalahari meerkats for the last twenty years, and the lives of his study animals were featured in the popular TV series ‘Meerkat Manor’. When a dominant female, Flower, succumbed to snakebite in 2007, fans of the show grieved publicly on internet forums. Clutton-Brock wrote a book that told the true story of Flower’s life from birth to death – the first complete biography of a wild animal.
Now, across twenty chapters in Mammal Societies, he brings together decades of accrued knowledge from observations and experiments on social behaviour right across the field, much of which is the result of the thousands of animal life histories collected from long-term studies over the last fifty years.
While there have been reviews of social organisation for birds and ants, this is the first synthesis of sociality across mammals. The new book is set to become a milestone in the literature of evolution, covering social behaviour from baboons to bears, zebra to squirrels, and ending in the most successful mammal society of all: ours.
For Clutton-Brock, part of the excitement of pulling back to view such an extraordinary sweep of social behaviour is the generalities that start to appear. For example, much of the book is divided between the sexes.
“When viewing the whole scope of behaviour, what emerges is that females are distributed in relation to food, which they process into offspring, and males are adapted to adjust themselves to the distribution of females – or, more precisely, to the distribution of unfertilised ova that they can turn into babies,” he says.
Behaviours examined in the book range from extremes of competition, such as infanticide committed by baboons to increase their own breeding prospects, and hyena cubs, born with a full set of sharp teeth, who will sometimes kill their own siblings. But also extremes of cooperation: female meerkats helping each other through birth; male chimpanzees caring for orphaned juveniles.
The final chapters focus on human social progress, from our hominin ancestors’ journey through the polygynous breeding societies still seen in the great apes, to the unique cooperation with strangers and kin alike that defines us as a species.
If you want to put human society and evolution in perspective, says Clutton-Brock, it is the other mammals which provide it, and generalisations drawn from across mammalian social behaviour feed into our understanding of humanity.
“Though modern humans are mostly monogamous, we carry the legacy of past polygyny, as our ancestors lived in societies where a single male dominates several females. In polygynous mammals such as red deer, males only breed for a short time, as competition is so fierce and often brutal. This may relate to the shorter lifespan and larger bodies we see in men,” he explains.
Clutton-Brock has led a study of red deer on the Isle of Rum for over forty years which often feature on the BBC’s Spring and AutumnWatch, as well as the famous meerkats, and his studies have trained large numbers of young biologists in fieldwork.
The meerkat project has taken a dozen interns each year (“I don’t take anyone for less than a year”) for the last twenty years. Many go on to do PhDs, starting field studies of their own. Clutton-Brock admits he had to learn the hard way. “I did my PhD on forest monkeys – what a disaster. The animals were a hundred feet above you eating leaves, and urinated in your face as you watched them from below.”
Mammal Societies, a project that has taken some ten years to complete, ends with the mammal that has come to dominate the planet. Clutton-Brock offers suggestions to arguably the central question of human evolution: ‘Why us?’
“Many of the characteristics of higher primates may have facilitated the evolution of our own unusual traits,” he says. “They live in complex societies with many competitors and rely on support from other individuals to breed and protect their offspring. The difficult social decisions they have to take has probably played an important role in the evolution of our large brains and understanding of cause and effect.”
The book closes with a warning to our species: that controlling population growth and preventing environmental destruction requires cooperation on a global scale – a feat no animal has managed. “This would be a novel development in mammals, and it remains to be seen whether humans are able to meet this challenge.”
Inset images: babysitting meerkats, credit - Kalahari Meerkat Project. Red Deer, credit - Mick Lobb.
Over the last fifty years, long-term studies following individual animals over entire lifespans have allowed insight into the evolutionary influence of social behaviour – finally fulfilling the holistic approach to evolution first suggested by Darwin, argues the author of a new milestone work on mammal societies.
Genetic switch that turned moths black also colours butterflies
By tdk25 from University of Cambridge - Department of Zoology. Published on Jun 02, 2016.
The same gene that enables tropical butterflies to mimic each other’s bright and colourful patterning also caused British moths to turn black amid the grime of the industrial revolution, researchers have found.
Writing in the journal Nature, a team of researchers led by academics at the Universities of Cambridge and Sheffield, report that a fast-evolving gene known as “cortex” appears to play a critical role in dictating the colours and patterns on butterfly wings.
A parallel paper in the same journal by researchers from the University of Liverpool shows that this same gene also caused the peppered moth to turn black during the mid-19th century, when it evolved to find new ways to camouflage itself; a side-effect of industrial pollution at the time.
The finding offers clues about how genetics plays a role in making evolution a predictable process. For reasons the researchers have yet to understand in full, the cortex gene, which helps to regulate cell division in butterflies and moths, has become a major target for natural selection acting on colour and pattern on the wings.
Chris Jiggins, Professor of Evolutionary Biology and a Fellow of St John’s College, University of Cambridge, said: “What’s exciting is that it turns out to be the same gene in both cases. For the moths, the dark colouration developed because they were trying to hide, but the butterflies use bright colours to advertise their toxicity to predators. It raises the question that given the diversity in butterflies and moths, and the hundreds of genes involved in making a wing, why is it this one every time?”
Dr Nicola Nadeau, a NERC Research Fellow from the University of Sheffield added: “It’s amazing that the same gene controls such a diversity of different colours and patterns in butterflies and a moth. Our study, together with the findings from the University of Liverpool, shows that the cortex gene is important for colour and pattern evolution in this whole group of insects.”
Butterflies and moths comprise the order of insects known as Lepidoptera. Nearly all of the 160,000 types of moth and 17,000 types of butterfly have different wing patterns, which are adapted for purposes like attracting mates, giving off warnings, camouflage (also known as “crypsis”), and thermal regulation.
These wing patterns are actually made up of tiny coloured scales arranged like tiles on a roof. Although they have been studied by biologists for over a century, the molecular mechanisms which control their development are only now starting to be uncovered.
The peppered moth is one of the most famous examples of evolution by natural selection. Until the 19th Century, peppered moths were predominantly pale-coloured, and used this to camouflage themselves against lichen-covered tree trunks, which made them almost invisible to predators.
During the industrial revolution, however, the lichen on trees in some parts of the country was killed by pollution, and soot turned the trunks black. A corresponding change was seen in the in peppered moths which turned black as well, helping them to remain camouflaged from birds. The process is known as industrial melanism – melanism meaning the development of dark coloured pigmentation.
The Liverpool-led team found that this colour change was produced by a mutation in the cortex gene, which occurred during the mid 1800s, just before the first reported sighting of black peppered moths. Fascinatingly, however, the Cambridge-Sheffield study has now shown that exactly the same gene also influences the extremely bright and colourful patterns of Heliconius – the name given to about 40 different closely-related species of beautiful, tropical butterflies found in South America.
Heliconius colour patterns are used to send a signal to potential predators that the butterflies are toxic if eaten, and different types of Heliconius butterfly mimic one another by using their bright colours as warning signals. Unlike the dark colouring of the peppered moth, it is therefore an evolutionary development that is meant to be seen.
The researchers carried out fine-scale mapping, looking for parts of the DNA sequence that were specifically different in butterflies with different patterns, in three different Heliconius species, and in each case the cortex gene was found to be responsible for this adaptation in their patterning.
Because Heliconius species are extremely diverse, the study of what causes variations in their patterning can provide more general clues about the genetic switches that control diversification in species.
In most cases, the genes responsible for these processes are known as “transcription factors” – meaning that they are responsible for turning other genes on and off. Intriguingly, what made cortex such an elusive switch to spot was the fact that it does not do this. Instead, it is a cell cycle regulator, which means that it controls when cells divide and thus when different coloured scales develop within a butterfly wing.
“It’s a different gene to the one we might have expected and we still need to do more to understand exactly what it’s doing, and how it’s doing it,” Jiggins said. Dr Nadeau added “Our results are even more surprising because the cortex gene was previously thought to only be involved in producing egg cells in female insects, and is very similar to a gene that controls cell division in everything from yeast to humans.”
Nadeau N. et al. The gene cortex controls mimicry and crypsis in butterflies and moths. Nature, 2 June 2016; DOI: 10.1038/nature17961
Additional image: The study reveals that the black colour of the moth (above) and the yellow patches on the butterfly (below) were caused by the same gene, known as “cortex”. Credits: Yikrazuul and Loz, both via Wikimedia Commons.
Heliconius butterflies have evolved bright yellow colours to deter predators, while peppered moths famously turned black to hide from birds. A new study reveals that the same gene causes both, raising fascinating questions about how evolution by natural selection occurs in these species.
Tim Clutton-Brock's latest book 'Mammal Societies' is published
From Department of Zoology. Published on May 31, 2016.
Female meerkats compete to outgrow their sisters
By Anonymous from University of Cambridge - Department of Zoology. Published on May 26, 2016.
Meerkats live in groups of up to 50 individuals, yet a single dominant pair will almost completely monopolise reproduction, while subordinates help to raise offspring through feeding and babysitting. Since only a small minority of individuals ever get to be dominants, competition for the breeding role is intense in both sexes and females are unusually aggressive to each other.
Within groups, subordinate females are ranked in a hierarchy based on age and weight, forming a “reproductive queue”. When dominant females die, they are usually replaced by their oldest and heaviest daughter, though younger sisters sometimes outgrow their older sisters and can replace them in breeding queues.
University of Cambridge scientists working on wild Kalahari meerkats identified pairs of sisters and artificially increased the growth of the younger member of each pair by feeding them three times a day with hard-boiled egg.
The scientists weighed them and their (unfed) older sisters daily for three months. The results, published today in the journal Nature, show that the increased growth of younger females stimulated their older sisters to increase their daily food intake and weight gain in an attempt to outgrow their rivals.
Tellingly, the extent to which the older sister increased her weight was greater when her younger sister’s weight gain was relatively large than when it was slight.
These results suggest that subordinate meerkats are continually keeping tabs on those nearest them in the breeding queue, and make concerted efforts to ensure they are not overtaken in size and social status by younger and heavier upstarts.
But competitive growth does not stop there. If a female meerkat gets to be a dominant breeder, her period in the role (and her total breeding success) is longer if she is substantially heavier than the heaviest subordinate in her group.
During the three months after acquiring their new status, dominant females gain further weight to reduce the risk of being usurped. Regular weighing sessions of newly established dominants showed that that, even if they were already adult, they increased in weight during the first three months after acquiring the dominant position – and that the magnitude of their weight increase was greater if the heaviest subordinate of the same sex in their group was close to them in weight.
This is the first evidence for competitive growth in mammals. The study’s authors suggest that other social mammals such as domestic animals, primates and even humans might also adjust their growth rates to those of competitors, though these responses may be particularly well developed in meerkats as a result of the unusual intensity of competition for breeding positions.
“Size really does matter and it is important to stay on top,” said senior author Professor Tim Clutton-Brock, who published the first major overview of research on mammalian social evolution this month in the book Mammal Societies (Wiley).
“Our findings suggest that subordinates may track changes in the growth and size of potential competitors through frequent interactions, and changes in growth rate may also be associated with olfactory cues that rivals can pick up,” Clutton-Brock said.
“Meerkats are intensely social and all group members engage in bouts of wrestling, chasing and play fighting, though juveniles and adolescents play more than adults. Since they live together in such close proximity and interact many times each day, it is unsurprising that individual meerkats are able to monitor each other’s strength, weight and growth.”
Male meerkats leave the group of their birth around the age of sexual maturity and attempt to displace males in other groups, and here, too, the heaviest male often becomes dominant. The researchers found a similar strategy of competitive weight-gain in subordinate males.
The data was collected over the course of twenty years and encompassed more than forty meerkat groups, as part of the long-term study of wild meerkats in the Southern Kalaharu at the Kuruman River Reserve, South Africa, which Clutton-Brock began in 1993. In the course of the study, the team have followed the careers of several thousand individually-recognisable meerkats – some of which starred in the award winning docu-soap Meerkat Manor, filmed by Oxford Scientific Films.
The meerkats were habituated to humans and individually recognisable due to dye marks. Most individuals were trained to climb onto electronic scales for their weigh-ins, which occurred at dawn, midday and dusk, on ten days of every month throughout their lives. This is the first time it has been feasible to weigh large numbers of wild mammals on a daily basis.
Weighing meerkats. Image credit: Tim Clutton-Brock
Latest research shows subordinate meerkat siblings grow competitively, boosting their chance of becoming a dominant breeder when a vacancy opens up by making sure that younger siblings don’t outgrow them.
Genes discovered that enable birds to produce the colour red
By fpjl2 from University of Cambridge - Department of Zoology. Published on May 20, 2016.
Right across the bird and animal kingdoms, the colour red is used for communication, often to attract mates, and zebra finches are no different: the males have a distinctive red beak, which is a sexually selected trait - as females prefer males with redder beaks.
New research on zebra finches has identified for the first time the genes that allow some bird species to produce the red pigment that plays such a critical role in attraction and mating.
The genes belong to a wider family of genes that also play an important role in detoxification, suggesting how heightened redness may be a sign of mate quality: it indicates a bird's ability to cleanse harmful substances from its body.
This could explain what's known as 'honest signaling': where an evolved trait is a genuine sign of better, fitter genes - in this case the ability to better deal with anything toxic.
The research is published today in the journal Current Biology.
Birds such as the zebra finch obtain yellow pigments, known as carotenoids, from their diet of seeds, or insects in the case of other bird species.
Prior to the latest findings, it was known that such birds must have a way of converting these yellow dietary pigments into the red pigments - the ketocarotenoids - that colour the beaks, feathers or bare skin of many species. However, the mechanism for this process was unclear.
Nick Mundy from Cambridge's Department of Zoology, along with colleagues including Staffan Andersson from the University of Gothenburg and Jessica Stapley from the University of Sheffield, compared the gene sequences of wild, red-beaked zebra finches with captive finches that had a mutant, recessive gene causing yellow beaks.
They identified a cluster of three genes in the wild finches that were either missing or mutated in this genetic region in the 'yellowbeak' birds.
These genes encode enzymes called cytochrome P450s, which play an important role in breaking down and metabolising toxic compounds, primarily in the liver of vertebrates. In humans, these enzymes are well-studied, as they are strongly associated with drug metabolism.
"It was known that birds have an unusual ability to synthesize red ketocarotenoids from the yellow carotenoids that they obtain in their diet, but the enzyme, gene or genes, and anatomical location have been obscure," said Mundy. "Our findings fill this gap and open up many future avenues for research on the evolution and ecology of red coloration in birds."
Red colour in birds is thought to signal individual genetic quality, and the researchers argue that one way it can do this is if the amount of red colour relates to other beneficial physiological processes, such as detoxification.
"Our results, which link a detoxification gene to carotenoid metabolism, shed new light on this old hypothesis about the honesty of signalling," said co-author Staffan Andersson.
The researchers found the specific expression of one or more of the identified 'red' gene cluster in the tissues where the red pigments were deposited: the beak, the tarsus in the bird's feet - as well as in the retina.
The structure of retinas in the eye includes cone-shaped photoreceptor cells. Unlike mammals, avian retinal cones contain a range of brightly-coloured oil droplets, including green, yellow and red. These oil droplets allow birds to see many more colours than mammals.
Mundy says that the newly-discovered genetic links between red beaks and feathers and the internal red retina droplets suggest that producing red pigment evolved for colour vision before it developed a function for external display - as, while red oil eye droplets are ubiquitous across bird species, external reds are only patchily distributed.
"It was quite a surprise that the same genes are involved both in seeing red colours and making red coloration," said Mundy.
Mundy says he and his colleagues are now working on the genetics of red coloration in African widowbirds and bishops, which show "spectacular differences among different species."
Latest research suggests a new mechanism for how sexual displays of red beaks and plumage might be ‘honest signals’ of mate quality, as genes that convert yellow dietary pigments into red share cofactors with enzymes that aid detoxification – hinting that redness is a genetic sign of the ability to better metabolise harmful substances.
Natural selection sculpts genetic information to limit diversity
By tdk25 from University of Cambridge - Department of Zoology. Published on May 13, 2016.
A study of tropical butterflies has added to growing evidence that natural selection reduces species’ diversity by moulding parts of their genetic structure, including elements that have no immediate impact on their survival.
The research, by a University of Cambridge-led team of academics, focused on genetic data from South American Heliconius butterflies. It showed that when these butterflies develop a beneficial adaptation through a mutation in their DNA, other parts of the same chromosome – the long strings of DNA that make up the butterfly’s genome – may end up being defined by the fact that they are “linked” to the point where the mutation took place. Natural selection ends up influencing the fate of these linked sites, even though they have no impact on the species’ fitness and long-term survival prospects.
As the adaptation is passed down through the generations as a result of natural selection, this collection of linked genetic sites can be passed on intact, removing genetic variation that previously existed in the population at these sites. This effectively limits the overall amount of variation in the butterfly population.
The study complements similar findings in other species, including humans and fruit flies, which together offer one possible solution to a long-standing paradox in population genetics. This is the fact that while species with bigger populations should be more genetically diverse – because there is more potential for new mutations to occur – in practice they often only exhibit as much diversity as smaller populations.
For example, in the Cambridge-led study, the researchers found that the genetic diversity of Heliconius butterflies is very similar to that of fruit flies, even though fruit flies are far more numerous. They also estimated that the amount of adaptation within Heliconius butterflies caused by natural selection is probably about half that of fruit flies. In other words, because natural selection affects the fruit flies more, reducing variation, they end up exhibiting roughly the same amount of genetic diversity, even though there are more of them.
The researchers stress that this explanation for variable levels of genetic diversity between different species is still, at the moment, a theory. Not all scientists are convinced that natural selection has this effect and argue that the variable diversity of species relative to population size may well have other causes.
Understanding more about what these causes are will, however, help to answer even more fundamental scientific questions – such as how and why species vary in the first place, and when they can really be said to have become distinct enough from their ancestors to represent a species in their own right.
Dr Simon Martin, a Research Fellow at St John’s College, Cambridge, who led the study, said: “We will only be able to understand this fully if we can compare results from across different species. Extending our knowledge to butterflies is a step towards explaining these much broader patterns in nature; it’s only by doing this kind of research that we will know whether these ideas are right or not.”
Martin and his colleagues examined a very large data set of 79 whole genome sequences representing 12 related species of Heliconius butterfly. This large-scale data has only become available in recent years, as a result of advances in genome sequencing which have made the process both easier and more affordable.
The study involved scouring the sequences for an apparent pattern of association between particular sites within the genome and low variation. “That acts as a kind of signature,” Martin said. “If you can see that in a genome, then as far as we can tell it is an indication of selection.”
In addition, the researchers compared the number of variations in the parts of the genome where proteins are coded – and therefore may be responsible for adaptations – with the number of variations in other parts of the genome. It is possible to predict what this ratio would be if variations only occurred by chance. The difference between that prediction, and the actual statistics, suggests the extent to which natural selection has shaped species differences.
The study estimated that around 30% of the protein differences between species of Heliconius are adaptations caused by natural selection. In keeping with theories about diversity in the population of other species, this turned out to be about half the number of protein variations in fruit flies – a larger population with less genetic diversity overall.
Intriguingly, the study effectively suggests that natural selection could limit a species' ability to adapt to future environmental change by removing linked variations that, despite having no immediate beneficial impact on the species, could become relevant to its survival and capacity to cope with its environment in the future.
“Variation is a kind of raw material and you don’t necessarily use it all at any one time,” Martin explained. “It’s something that could be used to adapt and change in the future.”
“Something that has turned up during the last few years in research of this kind is a phenomenon where we see that a species has adapted, and we discover, when we look for the origin of that adaptation, that the mutation was not actually new. Instead, it was a variation that previously existed in the population. So while we cannot forecast the future, an emerging idea is that mutations that have no effect on survival today may be a source of beneficial variation in the future.”
The study appears in the May 2016 issue of Genetics.
A study of butterflies suggests that when a species adapts, other parts of its genetic make-up can be linked to that adaptation, limiting diversity in the population.
Youngest Ancient Egyptian human foetus discovered in miniature coffin at the Fitzwilliam Museum
By fpjl2 from University of Cambridge - Department of Zoology. Published on May 12, 2016.
A miniature ancient Egyptian coffin measuring just 44cm in length has been found to contain the youngest ever example of a human foetus to be embalmed and buried in Egyptian society. This discovery is the only academically verified specimen to exist at only sixteen to eighteen weeks of gestation.
This landmark discovery from the Fitzwilliam Museum in Cambridge, is remarkable evidence of the importance that was placed on official burial rituals in ancient Egypt, even for those lives that were lost so early on in their existence. Curators at the Fitzwilliam made the discovery, during their research for the pioneering bicentennial exhibition Death on the Nile: Uncovering the afterlife of ancient Egypt.
The tiny coffin was excavated at Giza in 1907 by the British School of Archaeology and came into the collection at the Fitzwilliam Museum the same year. It is a perfect miniature example of a wooden coffin of the ancient Egyptian ‘Late Period’ and may date to around 664-525 BC. The lid and box are both made from cedar wood. Although the coffin is deteriorated, it is clear that the wood was carefully carved on a painstakingly small scale and decorated. This gave the curators at the Fitzwilliam the first very clear indication of the importance given to the coffin’s contents at this time in ancient Egyptian society.
The diminutive wrapped package inside was carefully bound in bandages, over which molten black resin had been poured before the coffin was closed. For many years it was thought that the contents were the mummified remains of internal organs that were routinely removed during the embalming of bodies.
Examination using X-ray imaging at the Fitzwilliam Museum was inconclusive, but suggested that it may contain a small skeleton. It was therefore decided to micro CT (computed tomography) scan the tiny bundle at Cambridge University’s Department of Zoology. The cross-sectional images this produced gave the first pictures of the remains of a tiny human body held within the wrappings, which remain undisturbed.
Dr Tom Turmezei, recently Honorary Consultant Radiologist at Addenbrooke’s Hospital in Cambridge collaborated with the Fitzwilliam Museum, alongside Dr. Owen Arthurs, Academic Consultant Paediatric Radiologist at Great Ormond Street Hospital, London. The ground-breaking results were based on their extensive knowledge of CT imaging and paediatric autopsy.
Five digits on both hands and feet and the long bones of the legs and arms were all clearly visible. Although the soft skull and pelvis were found to be collapsed the categorical consensus was that inside the bundle was a human foetus estimated to be of no more than eighteen weeks gestation. It was impossible to give a gender to the specimen and it is thought that the foetus was probably the result of a miscarriage, as there were no obvious abnormalities to explain why it could not have been carried to full-term.
From the micro CT scan it is noticeable that the foetus has its arms crossed over its chest. This, coupled with the intricacy of the tiny coffin and its decoration, are clear indications of the importance and time given to this burial in Egyptian society.
"CT imaging has been used successfully by the museum for several projects in recent years, but this is our most successful find so far," Dr. Tom Turmezei explained. "The ability of CT to show the inner workings of such artefacts without causing any structural damage proved even more invaluable in this case, allowing us to review the foetus for abnormalities and attempt to age it as accurately as possible."
Julie Dawson, Head of Conservation at the Fitzwilliam Museum said, "Using non-invasive modern technology to investigate this extraordinary archaeological find has provided us with striking evidence of how an unborn child might be viewed in ancient Egyptian society. The care taken in the preparation of this burial clearly demonstrates the value placed on life even in the first weeks of its inception."
Tutankhamun’s tomb contained two small foetuses that had been mummified and placed in individual coffins, but these infants were both significantly more developed, at about 25 weeks and 37 weeks into gestation. Very few other examples of burials of miscarried babies have so far been identified from ancient Egypt.
The miniature coffin is currently on display as part of the exhibition Death on the Nile: Uncovering the Afterlife of ancient Egypt until 22nd May 2016 at the Fitzwilliam Museum Cambridge.
Inset image: Micro CT scan image of the upper limbs
Tiny coffin excavated at Giza in 1907 is remarkable evidence of importance placed on official burial rituals in ancient Egypt.
Opinion: There’s a reason why Africa’s migratory songbirds sing out of season
By Anonymous from University of Cambridge - Department of Zoology. Published on May 09, 2016.
Bird song has fascinated scientists for decades. Songs can be intricate, loud and, as it turns out, very important for reproductive success. In many species the males with the most complex songs secure the highest quality breeding territories and mates, and end up producing the most young. For species that spend their summers in Europe, almost every hour of daylight is crammed full with energetic and often very loud song.
For songbirds that have migrated to Africa at the end of the breeding season, singing shouldn’t be on their to-do list. Singing requires a big energetic investment and increases vulnerability to predators. The only time males should be willing to pay these costs is when there is a good chance of attracting females as mates, and that is not going to happen in Africa outside of the breeding season.
Despite this, several species of migratory songbirds, from Wood Warblers to Nightingales, are known to sing a great deal in Africa. This prompted us to ask: what is the purpose of singing in Africa, when the breeding grounds are thousands of kilometres away? To answer this question, we focused on a drab-looking but raucous singer, the Great Reed Warbler. This species breeds in Europe and spends the northern winter in the wet grasslands and savannahs of sub-Saharan Africa.
Testing a long-held hypothesis
We began by testing a long-held hypothesis for the persistence of singing in Africa. Perhaps singing is being used as a means to defend individual winter-feeding territories. It might be acting as a “keep out” sign to other individuals encroaching on the territory holder’s space.
In territorial systems, distinct boundaries are expected between the spaces used by each individual in combination with an aggressive reaction when that territorial boundary is breached. We used radio transmitters to track bird movements through the tall grasses of the study site in Zambia, and used models of Great Reed Warblers with recorded song to simulate territory intrusions. We found no support for the expectations of territoriality. Great Reed Warblers overlapped widely in their use of space, and individuals were unperturbed by other birds in their space.
Given that Great Reed Warblers did not have a territorial system, this long-held hypothesis of singing for territorial protection didn’t hold up.
Singing for song improvement
Next, we tackled an intriguing but yet untested hypothesis. Perhaps, given the importance of song quality for males during breeding, they were using their downtime in Africa to improve the quality of their songs.
To find out, we combed through the literature and spoke to other researchers in Africa to determine which of the 57 migratory songbird species that migrate from Europe sing while in Africa and, importantly, how much. If this hypothesis is true, the benefits of singing in Africa should be most important for species in which song is especially valued when choosing a mate. Those should be species with the most complex songs, but conversely with the dullest appearance. So, when males are drab, females are expected to pay more attention to flashy song rather than flashy plumage.
Sure enough, we found that species with more complex songs, and those with drab plumage colouration, sing most often when in Africa. We argue that the costs associated with practice are probably well worth the investment for those species that stand to benefit most from producing the highest-quality songs.
A final piece of evidence comes from the Great Reed Warblers themselves. If songs function to defend territories, then they should sing the short territorial warnings they use to defend their breeding territories. But instead, recordings from Zambia showed that African songs are much more like those sung during mate attraction on the breeding grounds, when attracting a female is paramount. But there are a couple of important differences.
In Africa, songs are much longer and with many more switches between syllables than those sung in Europe. Given that songs in Africa are sung without a female receiver in mind, this may be the best way to practice. In Europe, when songs are mixed amongst the racket from competing males, repeating complex syllables up to five times is important to ensure that they are received loud and clear by females.
With the evidence tallied, both from Great Reed Warblers and across the dozens of songbird species that migrate between Africa and Europe, this puzzling non-breeding singing behaviour appears best explained as a rehearsal period before the big show the following spring.
To conclusively test this hypothesis, researchers would need to follow individual birds between their breeding and non-breeding grounds and monitor changes to their song and their breeding success. But this is close to impossible given the current tracking devices available. For now, this study points towards an intriguing new explanation for this previously unstudied behaviour. It also offers insight into the lives of migratory songbirds during the lengthy, but little-known part of their lives spent in Africa.
The opinions expressed in this article are those of the individual author(s) and do not represent the views of the University of Cambridge.
Claire Spottiswoode (Department of Zoology) and Marjorie Sorensen (Goethe University Frankfurt am Main) discuss why several species of migratory songbirds sing a great deal in Africa when their breeding grounds are thousands of kilometres away.
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