Social Isolation Influences Evolution As Much As Interaction
Introverts of the world, celebrate (separately). Your contribution to evolution has been revealed through a review of the way social isolation is driving changes to species as diverse as ants and primates.
Interactions, both within and between species, are key to evolutionary change, and have been studied extensively. Since Darwin biologists have focused on the way sexual behavior produces peacock tails and dung beetle horns. Competition for resources and parental influence after birth have also been studied in detail.
However, Dr Nathan Bailey of the University of St Andrews, Scotland, decided isolation is equally interesting, and much less investigated. As he notes in Trends in Ecology & Evolution, most research on the topic; “Focuses on negative phenotypic consequences of social isolation within individual lifetimes.” It’s also usually on social species such as loneliness-prone rats.
However; “The environment an animal experiences can influence which genes it expresses, when, and how much, so conditions of social isolation might cause expression of different traits,” Bailey said in a statement. Bailey wondered how often this expression would benefit the animals involved.
Among the examples Bailey uncovered was a study of the cane toad, initially from Central America, but most researched in Australia where it has become an invasive species. The toad has already alerted scientists to a previously unrecognized form of evolution known as spatial sorting.
For cane toads absence really does make the heart (or other organs) grow fonder. Inevitably, toads rarely become isolated from other members of their species in areas where they are incredibly common, but this happens often on the toad frontier, where the population is sparse. These pioneer toads are more attracted to members of the opposite sex during encounters, a trait that has promoted the devastating spread of this pest. Similarly, previously isolated female field crickets are less choosy about the quality of mates.
A different benefit comes when dying members of a species isolate themselves from their kin so they can’t pass on transmissible diseases, as observed in the ant Temnothorax unifasciatus. This hastens the death of the sick individual, but helps the colony survive. Many species have also learned to ostracize members of the group that are dangerous, either because of infectious disease or a propensity to free-ride on the work of the pack. There is speculation humans once ostracized narcissistic individuals, although these days we seem to elect them.
Even perceived isolation – like when mutated male crickets have silent wings and can’t produce mating songs – can alter behavior.
“Traits expressed during social interactions might exist because they’ve been shaped by selection, but at the same time, social interactions themselves represent a type of environment that can select and shape how individuals behave,” Bailey said.
The paper sets out proposals for more systematic research into how isolation affects subsequent generations.