Bebbington Kat, Fairfield Eleanor A, Spurgin Lewis G, Kingma Sjouke A, Dugdale Hannah, Komdeur Jan, Richardson David S
School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, UK.
Behavioural Ecology and Physiological Group, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, The Netherlands.
Behav Ecol. 2018 Jan-Feb;29(1):169-178. doi: 10.1093/beheco/arx137. Epub 2017 Oct 20.
Competition between offspring can greatly influence offspring fitness and parental investment decisions, especially in communal breeders where unrelated competitors have less incentive to concede resources. Given the potential for escalated conflict, it remains unclear what mechanisms facilitate the evolution of communal breeding among unrelated females. Resolving this question requires simultaneous consideration of offspring in noncommunal and communal nurseries, but such comparisons are missing. In the Seychelles warbler we compare nestling pairs from communal nests (2 mothers) and noncommunal nests (1 mother) with singleton nestlings. Our results indicate that increased provisioning rate can act as a mechanism to mitigate the costs of offspring rivalry among nonkin. Increased provisioning in communal broods, as a consequence of having 2 female parents, mitigates any elevated costs of offspring rivalry among nonkin: per-capita provisioning and survival was equal in communal broods and singletons, but lower in noncommunal broods. Individual offspring costs were also more divergent in noncommunal broods, likely because resource limitation exacerbates differences in competitive ability between nestlings. It is typically assumed that offspring rivalry among nonkin will be more costly because offspring are not driven by kin selection to concede resources to their competitors. Our findings are correlational and require further corroboration, but may help explain the evolutionary maintenance of communal breeding by providing a mechanism by which communal breeders can avoid these costs.
后代之间的竞争会极大地影响后代的适应性和父母的投资决策，尤其是在群居繁殖者中，非亲属竞争者让出资源的动机较小。鉴于冲突升级的可能性，目前尚不清楚哪些机制促进了非亲属雌性之间群居繁殖的进化。要解决这个问题，需要同时考虑非群居和群居育雏环境中的后代，但目前缺少这样的比较。在塞舌尔莺中，我们将群居巢穴（2只雌性）和非群居巢穴（1只雌性）中的雏鸟对与单独的雏鸟进行了比较。我们的结果表明，提高育雏率可以作为一种机制来减轻非亲属后代竞争的成本。由于有2只雌性亲代，群居巢穴中育雏率的提高减轻了非亲属后代竞争中任何增加的成本：群居巢穴中的雏鸟和单独雏鸟的人均育雏量和存活率相等，但非群居巢穴中的较低。在非群居巢穴中，单个后代的成本差异也更大，这可能是因为资源限制加剧了雏鸟之间竞争能力的差异。通常认为，非亲属后代之间的竞争成本会更高，因为后代不会受到亲缘选择的驱动而将资源让给竞争对手。我们的发现是相关性的，需要进一步证实，但可能有助于解释群居繁殖的进化维持机制，即群居繁殖者可以通过这种机制避免这些成本。
