Differences in perceived predation risk associated with variation in relative size of extra‐pair and within‐pair offspring

Abstract

Extra‐pair paternity (EPP) is a widespread phenomenon in birds. Researchers have long hypothesized that EPP must confer a fitness advantage to extra‐pair offspring (EPO), but empirical support for this hypothesis is definitively mixed. This could be because genetic benefits of EPP only exist in a subset of environmental contexts to which a population is exposed. From 2013 to 2015, we manipulated perceived predator density in a population of tree swallows (Tachycineta bicolor) breeding in New York to see whether fitness outcomes of extra‐pair and within‐pair offspring (WPO) varied with predation risk. In nests that had been exposed to predators, EPO were larger, longer‐winged and heavier than WPO. In nonpredator nests, WPO tended to be larger, longer‐winged and heavier than EPO, though the effect was nonsignificant. We found no differences in age, morphology or stress physiology between extra‐pair and within‐pair sires from the same nest, suggesting that additive genetic benefits cannot fully explain the differences in nestling size that we observed. The lack of an effect of predator exposure on survival or glucocorticoid stress physiology of EPO and WPO further suggests that observed size differences do not reflect more general variation in intrinsic genetic quality. Instead, we suggest that size differences may have arisen through differential investment into EPO and WPO by females, perhaps because EPO and WPO represent different reproductive strategies, with each type of nestling conferring a fitness advantage in specific ecological contexts.

Investigating a trade-off between the quality of nest grown feathers and pace of development in an altricial bird

“…Rather, any perceived threat would have occurred through the indirect effect of subsequent parental behavior. In contrast, previous studies targeting nestlings have manipulated cues (e.g., auditory or visual presentations) that nestlings could perceive directly (Hallinger et al, 2019;LaManna & Martin, 2016). In our study, nestlings in the predation treatment group showed a positive correlation between body size and breast feather density (the opposite to that predicted if predation threat increased relative investment in growth or decreased acquisition of resources).…”

“…Adult and nestling blood samples were stored in lysis buffer (Seutin et al 1991) in the field and DNA was extracted using Qiagen DNeasy Blood & Tissue Kit spin columns following the standard kit protocol. We amplified a set of 9 variable microsatellite loci that have been previously used in this population (Makarewich et al 2009;Hallinger et al 2019). Our amplification protocol exactly followed that described in (Hallinger et al, 2019) and details on primer sequences, reaction volumes, cycling conditions, and fragment analysis can be found there.…”

“…We amplified a set of 9 variable microsatellite loci that have been previously used in this population (Makarewich et al 2009;Hallinger et al 2019). Our amplification protocol exactly followed that described in (Hallinger et al, 2019) and details on primer sequences, reaction volumes, cycling conditions, and fragment analysis can be found there. We determined nest of origin by comparing nestlings to their putative mothers (the females from the 2-3 nests in each cross-fostering pair).…”

Developmental stage-dependent effects of perceived predation risk on physiology and fledging success of tree swallows (Tachycineta bicolor)

“…We used blood samples from nestlings to determine the nest of origin using a previously validated set of 9 microsatellite markers (Hallinger et al, 2019;Makarewich et al, 2009). For the Color and stress manipulations: effects on nestlings purposes of this study, we were only interested in assigning nestlings to their correct mother from 2-3 possible females.…”

Immediate predation risk alters the relationship between potential and realised selection on male traits in the Trinidad guppy Poecilia reticulata

“…Non-lethal effects of predation are increasingly more often recognised as relevant drivers of changes in prey populations (1)(2)(3). Perception of predator cues can affect provisioning of offspring, ultimately determining their fitness (4)(5)(6). Other non-lethal effects consist of changes in mating behaviour in both males and females, with the potential to impact sexual selection trajectories.…”