The evolutionary demise of a social interaction: social partners differ in the rate at which interacting phenotypes are lost

Abstract

Phenotypic plasticity enables animals to flexibly adjust their behaviour to their social environment – sometimes through the expression of adaptive traits that have not been exhibited for several generations. We investigated how long social adaptations can usefully persist when they are not routinely expressed by using experimental evolution to document the loss of social traits associated with the supply and demand of parental care. Populations of burying beetles Nicrophorus vespilloides were evolved over 48 generations – in "Full Care" populations traits associated with the supply and demand of care were expressed, whereas in "No Care" populations we prevented expression of these traits experimentally. We then revived trait expression in the No Care populations at generations 24, 43 and 48 by allowing parents to supply post-hatching care, and compared these social traits with those expressed by the Full Care populations. We found that offspring demands for care decayed in the No Care populations more rapidly than a parent's capacity to supply care. Furthermore, male care decayed faster than female care. We suggest that this reflects differences in the strength of selection on offspring, males and females, for the expression of alternative traits which are more likely to enhance fitness when post-hatching care is disrupted.