Data from: Biparental care is more than the sum of its parts: experimental evidence for synergistic effects on offspring fitness

Despite an extensive body of theoretical and empirical literature on
biparental cooperation, it is still unclear whether offspring fare
equally, better, or worse when receiving care by two parents versus a
single parent. Some models predict that parents should withhold the amount
of care they provide due to sexual conflict, thereby shifting as much of
the workload as possible to their partner. This conflict should lead to
offspring faring worse with two parents. Yet, other models predict that
when parents care for their offspring together, their individual
contributions can have synergistic (more than additive) effects on
offspring fitness. Under this scenario, biparental cooperation should lead
to offspring faring better with two parents. We address this fundamental
question using a unique experimental design where we compared offspring
fitness when the two parents worked together (biparental treatment) and
when the two parents worked separately (uniparental treatment), while
keeping constant the amount of resources and number of offspring per
parent across treatments. This made it possible to directly compare the
biparental treatment to the sum of the male and female contributions in
the uniparental treatment. Our main finding was that offspring grew larger
and were more likely to survive to adulthood when reared by both parents
than a single parent. This is the first empirical evidence for a
synergistic effect of biparental cooperation on offspring fitness and
could provide novel insights into the conditions favouring the evolution
of biparental cooperation.