TY - JOUR

T1 - An evolutionary switch from sibling rivalry to sibling cooperation, caused by a sustained loss of parental care

AU - Rebar, Darren

AU - Jarrett, Benjamin

AU - Bailey, Nathan

AU - Kilner, Rebecca

PY - 2020/1/21

Y1 - 2020/1/21

N2 - Sibling rivalry is commonplace within animal families, yet off- spring can also work together to promote each other’s fitness. Here we show that the extent of parental care can determine whether siblings evolve to compete or to cooperate. Our experi- ments focus on the burying beetle Nicrophorus vespilloides, which naturally provides variable levels of care to its larvae. We evolved replicate populations of burying beetles under two different re- gimes of parental care: Some populations were allowed to supply posthatching care to their young (Full Care), while others were not (No Care). After 22 generations of experimental evolution, we found that No Care larvae had evolved to be more cooperative, whereas Full Care larvae were more competitive. Greater levels of cooperation among larvae compensated for the fitness costs caused by parental absence, whereas parental care fully compen- sated for the fitness costs of sibling rivalry. We dissected the evo- lutionary mechanisms underlying these responses by measuring indirect genetic effects (IGEs) that occur when different sibling social environments induce the expression of more cooperative (or more competitive) behavior in focal larvae. We found that indirect genetic effects create a tipping point in the evolution of larval social behavior. Once the majority of offspring in a brood start to express cooperative (or competitive) behavior, they induce greater levels of cooperation (or competition) in their siblings. The resulting positive feedback loops rapidly lock larvae into evolving greater levels of cooperation in the absence of parental care and greater levels of rivalry when parents provide care.

AB - Sibling rivalry is commonplace within animal families, yet off- spring can also work together to promote each other’s fitness. Here we show that the extent of parental care can determine whether siblings evolve to compete or to cooperate. Our experi- ments focus on the burying beetle Nicrophorus vespilloides, which naturally provides variable levels of care to its larvae. We evolved replicate populations of burying beetles under two different re- gimes of parental care: Some populations were allowed to supply posthatching care to their young (Full Care), while others were not (No Care). After 22 generations of experimental evolution, we found that No Care larvae had evolved to be more cooperative, whereas Full Care larvae were more competitive. Greater levels of cooperation among larvae compensated for the fitness costs caused by parental absence, whereas parental care fully compen- sated for the fitness costs of sibling rivalry. We dissected the evo- lutionary mechanisms underlying these responses by measuring indirect genetic effects (IGEs) that occur when different sibling social environments induce the expression of more cooperative (or more competitive) behavior in focal larvae. We found that indirect genetic effects create a tipping point in the evolution of larval social behavior. Once the majority of offspring in a brood start to express cooperative (or competitive) behavior, they induce greater levels of cooperation (or competition) in their siblings. The resulting positive feedback loops rapidly lock larvae into evolving greater levels of cooperation in the absence of parental care and greater levels of rivalry when parents provide care.

U2 - 10.1073/pnas.191167711

DO - 10.1073/pnas.191167711

M3 - Article

VL - 117

SP - 2544

EP - 2550

JO - Proceedings of the National Academy of Sciences of the USA

JF - Proceedings of the National Academy of Sciences of the USA

SN - 0027-8424

ER -