The consequences of winter flock demography for genetic structure and inbreeding risk in vinous-throated parrotbills, Paradoxornis webbianus

Abstract

The adaptive significance of flocking behaviour has been intensively studied, especially among birds, but the demography and genetic structure of winter flocks is poorly understood, despite their importance for many biological processes. For three successive winters, we studied the demography and genetic structure of winter flocks in a small passerine, the vinous-throated parrotbill Paradoxornis webbianus. Our objectives were to determine the match between observed demography and the genetic structure of winter flocks, and to investigate the consequences of kin structure for the risk of inbreeding during the breeding season. The size of five main study flocks ranged from 60 to 120 individuals. The sex ratio of each flock did not deviate from parity and survival rates of adults were moderately low (36 and 17% in 2 years). Adults showed strong fidelity to a winter flock not only within a season but also between years. As expected from observational data, we found significant genetic differentiation and isolation by distance among males and females in winter flocks at a fine spatial scale. Likewise, relatedness among individuals within a winter flock was significantly greater than between flocks. Despite these demographic and genetic circumstances, the inbreeding rate was relatively low (4%). We conclude that fine-scale genetic structure occurs in the winter flocks of birds as a result of demographic processes without physical barriers. This genetic structure introduced a risk of inbreeding, but our evidence on whether individuals avoided incest was equivocal.

Extremely reduced dispersal and gene flow in an island bird

“…This was found in wild populations of great tits (Parus major) separated by distances of o3 km (Garant et al, 2005;Shapiro et al, 2006;Björklund et al, 2010), and also in song sparrows (Melospiza melodia) with five subspecies coexisting in a restricted area made of various microhabitats (Chan and Arcese, 2003). However, the latter results were not associated with significant neutral genetic differentiation, which suggests that genetic drift was not strong enough to generate neutral genetic differentiation (but also refer to the studies by Senar et al (2006), Lee et al (2010) and Rutz et al (2012)). There is no evidence from previous studies that populations belonging to one particular colour form of the Réunion grey white-eye and being as geographically close as those used in this study show any sign of niche differentiation (Gill, 1971(Gill, , 1973, suggesting that this explanation is unlikely.…”

Trophic niche width increases with bill‐size variation in a generalist passerine: a test of niche variation hypothesis

“…Although we could not discern flock membership of the individuals used in this study, within‐flock genetic structures in P. webbianus were found to be seasonally unstable and were not strong enough to create inbreeding (Lee et al . , ). In addition, home ranges of neighbouring P. webbianus flocks could overlap extensively with membership changes under some circumstances (e.g.…”

Females may not obtain indirect genetic benefits from extra-pair paternity in vinous-throated parrotbills, Paradoxornis webbianus

“…However, I found patchy distribution of EPP among females, and in three nests with multiple EPY there was only one extra-pair male per brood. Interestingly, Lee et al (2010) reported that winter flocks of vinous-throated parrotbills where pairing occurs are genetically structured. Even males and females within the same flocks showed a higher degree of genetic relatedness than those between flocks.…”

“…In order to identify juvenile recruitment, I also caught birds at the surrounding area in the second and third wintering seasons (16 flocks with 30-160 individuals, capture rate: [60% in most flocks; see Lee et al 2010 for the map of flock locations). Almost all birds caught in winter were ringed with metal rings and given unique combinations of color rings.…”