Erik Svensson, a professor at Lund University in Sweden, spoke this past Friday at the weekly Biological Sciences seminar at Dartmouth College. Throughout his lecture, Svensson highlighted the idea that “behavior plays a dual role in evolution and speciation,” which means that the way organisms behave can serve either to increase or decrease the rate at which new species are formed.
Svensson is an evolutionary and ecological biologist who works primarily with damselflies in southern Sweden and elsewhere. Historically, the degree to which behavior influences evolution has been debated. However, Svensson shared several recent studies that showed behavior to act as an “accelerator of speciation,” resulting in the creation of new species more quickly, or as a “constraint on evolution and speciation,” that served to slow down the same process.
Svensson chose to focus largely on sexual selection, and referenced Mark McPeek’s work with damselflies several times throughout the lecture. Svensson noted that preferences in mates can drive the creation of new species even while the new species maintains the same ecological characteristics – the same habits of living and feeding. Sexual selection is important in the creation of new species, and damselflies are a good example of this process, as many different damselfly species cannot mate with each other due to differences in sexual organs. In his own studies in southern Sweden, Svensson has shown that many preferences in mates, such as male body size, can vary greatly from place to place and from season to season. These fluctuations tend to “cancel each other out,” and do not contribute significantly to the process of speciation. “We need to solve that contradiction, if it exists at all,” Svensson said, in reference to the largely separate bodies of evidence showing behavior as both an accelerator and constraint on speciation.
While behavior can both contribute to and hinder speciation, geographic separation between species has also been shown to influence the way in which behavior influences evolution. Svensson and his postdoctoral students have shown that mate preference is different in areas where multiple species of damselflies occur than in those populations where one species of damselfly is isolated. When young damselflies from an area isaolated from other species are placed in an area where other species do occur, they adopt the mating preferences of the damselflies of their own species born in the second area. This suggests that mating preference may be a learned behavior in damselflies, a phenomenon that had only previously been observed in birds that “adopt the behavior of their foster parents if they are placed in another nest as eggs,” according to Svensson.
Over the past years Svensson and others have noted several different effects of behavior on speciation and evolution. Svensson emphasized the need for more research on the topic, and mentioned several methods he and others in the field are using to try to better quantify the connections between behavior and speciation.