Paradoxical associations between fitness components and behavioural phenotype in a wild bird

Individually consistent behavioural phenotypes persist in a diversity of populations, despite the expec-tation that selection would reduce their prevalence. The life-history trade-off between current and future reproduction, combined with individual variation in age or condition and therefore in residual repro-ductive value, may explain this apparent paradox. Specifically, individuals that are old or of low condition and therefore of low residual reproductive value should take risks and thus elevate current reproduction at the expense of future reproduction. The opposite should be true for individuals that are young or of high condition and therefore of high residual reproductive value, which should be risk averse. Over the course of a long-term study on Lincoln's sparrows, Melospiza lincolnii, we discovered a behavioural phenotype based on trappability that predicts both condition (but not age) and current reproductive success but, surprisingly, in a way that was not expected based on our assumption of how this phenotype is associated with risk taking. We found that, relative to individuals that did not enter traps (the nontrap phenotype, assumed as risk averse), those of the trap phenotype (assumed as risk taking) showed elevated indices of energetic condition and, for females, reduced reproductive success. Assortative mating may be a proximate mechanism for the populationwide maintenance of multiple behavioural phenotypes, and we found that assortative pairings based on trappability phenotype occurred more frequently than random pairing would predict. However, assortative pairing, when compared to dis-assortative pairing, did not affect reproductive success. Nevertheless, the contrasting relationships be-tween current reproductive success and condition that we found for each phenotype are consistent with life-history theory. However, our results are not consistent with the assumption that the trap phenotype is a manifestation of risk-taking behaviour and may, in fact, arise from just the opposite: a risk-averse, shy or neophobic behaviour for the trap phenotype.(c) 2023 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.