Spatiotemporal and genetic contingency of extrapair behaviour in a songbird

It's about Her: Male Within-Season Movements Are Related to Mate Searching in a Songbird

AbstractIn species with resource-defense mating systems (such as most temperate-breeding songbirds), male dispersal is often considered to be limited in both frequency and spatial extent. When dispersal occurs within a breeding season, the favored explanation is ecological resource tracking. In contrast, movements of male birds associated with temporary emigration, such as polyterritoriality (i.e., defense of an additional location after attracting a female in the initial territory), are usually attributed to mate searching. We suggest that male dispersal and polyterritoriality are functionally related and that mate searching may be a unifying hypothesis for predicting the within-season movements of male songbirds. Here, we test three key predictions derived from this hypothesis in Wood Warblers (Phylloscopus sibilatrix). We collected data on the spatial behavior of 107 males between 2017 and 2019 and related male movements to a new territory (in both a dispersal and a polyterritorial context) to mating potential in the current territory. Most males dispersed from their territories within days or weeks after failing to attract a female, despite occupying territories in apparently suitable habitat. Probability of polyterritoriality by paired males increased after the peak fertile period of their mate. Males never dispersed following nest predation if the female remained to renest. Thus, our data are consistent with the hypothesis that both movement types are functionally related to mate searching.

Lead exposure is correlated with reduced nesting success of an urban songbird

Lead exposure is a concern in urban ecosystems, with physiological and behavioral effects well documented in humans. Wildlife inhabiting urban ecosystems are also exposed to lead, yet little work has documented the sublethal effects of lead exposure in urban wildlife. We studied northern mockingbirds (Mimus polyglottos) in three neighborhoods of New Orleans, Louisiana, two with high soil lead and one with low soil lead, to better understand how lead exposure may influence mockingbirds' reproductive biology. We monitored nesting attempts, measured lead concentrations in blood and feathers of nestling mockingbirds, documented egg hatching and nesting success, and assessed rates of sexual promiscuity in relation to neighborhood soil lead levels. We found that nestling mockingbirds' blood and feather lead levels reflected the soil lead levels of their neighborhoods and nestling blood lead levels were similar to those of adult mockingbirds in the same neighborhoods. Nest success, as evaluated by daily nest survival rates, was higher in the lower lead neighborhood. Clutch sizes varied substantially across neighborhoods, but rates of unhatched eggs did not covary with neighborhood lead levels, suggesting that other drivers are influencing variation in clutch sizes and hatching success in urban habitats. At least one-third of nestling mockingbirds were sired by an extra-pair male, and there was no relationship between extra-pair paternity rates and neighborhood lead levels. This study provides insight on how lead contamination may influence reproduction in urban-dwelling wildlife and suggests that nestling birds could serve as useful bioindicators of lead levels in urban neighborhoods.

Mate Choice in Double-Breeding Female Great Tits (Parus Major): Good Males or Compatible Males

Simple Summary

Double breeding is a common reproductive strategy among temperate passerines to increase annual fecundity. To produce two clutches in the same breeding season and to ensure offspring quality, choosing a good mate is important for females. Uncovering the method used in social mate choice for genetic benefits adopted by double-breeding females would provide a better understanding of the life history and rules of female choice. In the present study, we tested the effects of the date of the first egg of the first brood and of female quality on double breeding, and good genes and genetic compatibility hypotheses on mate choice for double breeding female great tits (Parus major) in a population breeding inside nest boxes of Zuojia Natural Reserve in northeast China. The date of the first egg of the first brood did not affect initiation of a second brood, and female individual heterozygosity slightly influenced initiation of a second breeding. Female great tits choose males with both compatible genes and good genes in double-breeding mating. Double-breeding females prefer males with large breast stripes, high heterozygosity, and lower relatedness. The number of offspring of the first clutch did not affect the pairing status of male great tits in double breeding. The genetic quality of offspring from double-breeding pairs was higher than that of those from single-breeding pairs (higher heterozygosity and lower individual F).

Abstract

Producing two broods within the same season may be a good strategy by which short-lived species can maximize reproductive success. To produce two clutches in the same breeding season and to ensure offspring quality, choosing a good mate is important for females. Previous studies on double breeding focused on the associated influencing factors, and few studies examined how females choose social mates. Good genes and genetic compatibility are the two main hypotheses of the genetic benefit that females obtain from choosing mates. Uncovering the method used in mate choice for genetic benefits adopted by double-breeding females would provide a better understanding of the life history and rules of female choice. The great tit is an optionally double-breeding species in temperate-latitude populations. Here, we used a dataset for a Chinese population monitored between 2014 and 2016 to test two hypotheses on double-breeding female mate choice. A total of 30.1% of the breeding pairs initiated second breeding attempts, always remating with the same mate. The date of the first egg of the first brood did not affect initiation of a second brood, and female individual heterozygosity slightly influenced initiation of a second breeding. Female great tits choose males with both compatible genes and good genes in double-breeding mating. Double-breeding females prefer males with large breast stripes, high heterozygosity, and lower relatedness, while tarsus length, repertoire size, and individual F are not the main factors considered by females when selecting males for double breeding. The number of offspring of the first clutch did not affect the pairing status of male great tits in double breeding. The genetic quality of offspring from double-breeding pairs was higher than that of those from single-breeding pairs (higher heterozygosity and lower individual F). Taken together, our results showed that double breeding female great tits adopt multiple methods for genetic benefits to choose mates.

Brood-tending males in a biparental fish suffer high paternity losses but rarely cuckold

Extra‐pair paternity within socially monogamous mating systems is well studied in birds and mammals but rather neglected in other animal taxa. In fishes, social monogamy has evolved several times but few studies have investigated the extent to which pair‐bonded male fish lose fertilizations to cuckolders and gain extra‐pair fertilizations themselves. We address this gap and present genetic paternity data collected from a wild population of Variabilichromis moorii, a socially monogamous African cichlid with biparental care of offspring. We show that brood‐tending, pair‐bonded males suffer exceptionally high paternity losses, siring only 63% of the offspring produced by their female partners on average. The number of cuckolders per brood ranged up to nine and yet, surprisingly, brood‐tending males in the population were rarely the culprits. Brood‐tending males sired very few extra‐pair offspring, despite breeding in close proximity to one another. While unpaired males were largely responsible for the cuckoldry, pair‐bonded males still enjoyed higher fertilization success than individual unpaired males. We discuss these results in the context of ecological and phenotypic constraints on cuckoldry and the fitness payoffs of alternative male tactics. Our study provides new insights into how pair‐bonded males handle the trade‐off between securing within‐pair and extra‐pair reproduction.

Polygamy slows down population divergence in shorebirds

Sexual selection may act as a promotor of speciation since divergent mate choice and competition for mates can rapidly lead to reproductive isolation. Alternatively, sexual selection may also retard speciation since polygamous individuals can access additional mates by increased breeding dispersal. High breeding dispersal should hence increase gene flow and reduce diversification in polygamous species. Here, we test how polygamy predicts diversification in shorebirds using genetic differentiation and subspecies richness as proxies for population divergence. Examining microsatellite data from 79 populations in 10 plover species (Genus: Charadrius) we found that polygamous species display significantly less genetic structure and weaker isolation-by-distance effects than monogamous species. Consistent with this result, a comparative analysis including 136 shorebird species showed significantly fewer subspecies for polygamous than for monogamous species. By contrast, migratory behavior neither predicted genetic differentiation nor subspecies richness. Taken together, our results suggest that dispersal associated with polygamy may facilitate gene flow and limit population divergence. Therefore, intense sexual selection, as occurs in polygamous species, may act as a brake rather than an engine of speciation in shorebirds. We discuss alternative explanations for these results and call for further studies to understand the relationships between sexual selection, dispersal, and diversification.

Problem-solving performance and reproductive success of great tits in urban and forest habitats

Success in problem solving, a form of innovativeness, can help animals exploit their environments, and recent research suggests that it may correlate with reproductive success. Innovativeness has been proposed to be especially beneficial in urbanized habitats, as suggested by superior problem-solving performance of urban individuals in some species. If there is stronger selection for innovativeness in cities than in natural habitats, we expect problem-solving performance to have a greater positive effect on fitness in more urbanized habitats. We tested this idea in great tits (Parus major) breeding at two urban sites and two forests by measuring their problem-solving performance in an obstacle-removal task and a food-acquisition task. Urban pairs were significantly faster problem-solvers in both tasks. Solving speed in the obstacle-removal task was positively correlated with hatching success and the number of fledglings, whereas performance in the food-acquisition task did not correlate with reproductive success. These relationships did not differ between urban and forest habitats. Neophobia, sensitivity to human disturbance, and risk taking in the presence of a predator did not explain the relationships of problem-solving performance either with habitat type or with reproductive success. Our results suggest that the benefit of innovativeness in terms of reproductive success is similar in urban and natural habitats, implying that problem-solving skills may be enhanced in urban populations by some other benefits (e.g. increased survival) or reduced costs (e.g. more opportunities to gain practice with challenging tasks).