Sex-biased Natal Dispersal Research Articles

Do larids exhibit sex-biased natal dispersal? A case study of a southwest Florida population of Black Skimmers ( Rynchops niger )

Do larids exhibit sex-biased natal dispersal? A case study of a southwest Florida population of Black Skimmers ( Rynchops niger )

Sex-biased natal dispersal in Hokkaido brown bears revealed through mitochondrial DNA analysis

Understanding natal dispersal patterns is fundamental in the ecology and conservation biology of large wild carnivores. In this study, we used two approaches to determine genetic variation and dispersal patterns of brown bears in the Shiretoko Peninsula, eastern Hokkaido, Japan. The first approach was a large-scale genetic analysis. We analyzed haplotypes from the mitochondrial DNA (mtDNA) control region of 760 individual samples collected throughout the peninsula during 1998–2016. We detected seven haplotypes, including two that were confirmed for the first time. In females, the distribution of haplotypes was geographically structured, whereas haplotypes in males were distributed widely throughout the peninsula. Only some males in the lower peninsula had haplotypes that were not detected within the peninsula. The second approach was a local-scale genetic analysis, including intensive focal sampling in the Rusha area, a special wildlife protection area on the peninsula. Proportions of mtDNA haplotypes in adult bears were investigated and compared between the sexes. Although more than half of the females had the same haplotype, males had more diverse haplotypes, suggesting that they came to the Rusha area from other regions. Thus, our study revealed that mtDNA haplotype distribution has been maintained by female philopatry, and that bears exhibit male-biased dispersal. Furthermore, the lower peninsula appears to act as a contact zone between the peninsula and mainland Hokkaido, which is important for maintaining genetic diversity.

The Evolution of Male-Biased Dispersal under the Joint Selective Forces of Inbreeding Load and Demographic and Environmental Stochasticity.

Sex-biased natal dispersal is widespread, and its significance remains a central question in evolutionary biology. However, theory so far fails to predict some of the most common patterns found in nature. To address this, we present novel results from an individual-based model investigating the joint roles of inbreeding load, demographic stochasticity, environmental stochasticity, and dispersal costs for the evolution of sex-biased dispersal. Most strikingly, we found that male-biased natal dispersal evolved in polygynous systems as a result of the interplay between inbreeding avoidance and stochasticity, whereas previous theory, in contrast to empirical observations, predicted male philopatry and female-biased natal dispersal under inbreeding load alone. Furthermore, the direction of the bias varied according to the nature of stochasticity. Our results therefore provide a unification of previous theory, yielding a much better qualitative match with empirical observations of male-biased dispersal in mate defense mating systems.

The enduring question of sex-biased dispersal: Paul J. Greenwood's (1980) seminal contribution

In 1980, Paul J. Greenwood published a review of dispersal in birds and mammals that has been widely cited. The review evaluated possible explanations for sex-biased natal dispersal. It concluded that female-biased dispersal occurred in socially monogamous birds because males were using territorial resources to attract mates. In mammals, polygynous and polygynandrous males compete directly for and defend groups of females, and thus males more often disperse to find opportunities to sequester such groups. Thus, the primary difference between birds and mammals in sex-bias of dispersal appeared to be one of resource defence and mate defence mating systems. What made this review so seminal and what is the fate of his research question today? I begin with the excitement of the ‘sociobiology’ revolution and the fundamental nature and importance of the topic of dispersal. Furthermore, as all living things disperse, the topic of dispersal is central to many fields of study in behaviour, ecology, conservation and evolutionary biology. The hypotheses to explain dispersal that Greenwood reviewed (competition for resources, competition for mates and inbreeding avoidance) have been augmented, primarily by interest in lowered local kin competition as a fitness advantage for dispersers and kin cooperation as a reason not to disperse (viz. to remain philopatric in or near the natal area, particularly for female mammals). Current studies of Greenwood's question about sex biases in dispersal focus on testing the effects of local kin competition and on phylogenetic comparisons that reveal evidence of independent evolution of alternative dispersal patterns.

Genetic structure of a Virginia opossum (Didelphis virginiana) population inhabiting a fragmented agricultural ecosystem

Fragmentation has drastically altered the quality of habitats throughout numerous ecosystems, often leading to dramatic changes in the composition of wildlife communities. The ecology and associated movement behavior of a species may also be modified as a result of forest fragmentation, resulting in changes in genetic composition of the affected species. In this research, we evaluated the genetic structure of the Virginia opossum ( Didelphis virginiana Kerr, 1792) at the landscape and local scales in a fragmented, agricultural ecosystem in northern Indiana using 13 microsatellite loci. We examined 290 samples from opossums inhabiting 28 discrete habitat patches, and evaluated partitioning of genetic variation of opossums among and within habitat patches. We observed low but significant levels of genetic structure (FST = 0.005) overall, and pairwise comparisons of FSTvalues among habitat patches also were relatively low. Relatedness within patches was highly variable (–0.077 ≤ rxy ≤ 0.060), with a few patches exhibiting significantly higher levels of relatedness than random expectations, and we detected no evidence of sex-biased natal dispersal. These results contrast with previous field studies that documented male-biased dispersal in the Virginia opossum, indicating dispersal in this species is plastic and dependent upon local environmental conditions.

Sex biased natal dispersal is not a fixed trait in a stable population of Seychelles warblers

We observed a change in the sex-specific rate of delayed natal dispersal in a stable population of Seychelles warblers over a period of 20 years. At first, females were more likely to delay dispersal in their first year of life than were males, whereas later there was no sex bias in the rate of delayed natal dispersal. Similarly, the female-bias in helping-at-the-nest and the male-bias in floating have also weakened over time. These changes may have resulted from the decrease in variation in territory quality observed in the population over the study period. Our findings strengthen the view that natal dispersal is a highly plastic response to local ecological and social circumstances, and clearly show that rates of sex-biased dispersal cannot be considered a species or population constant. Our study also highlights the importance of collecting long-term datasets to understand complex behaviour such as natal dispersal.

Sex-specific shifts in natal dispersal dynamics in a reintroduced hihi population

Sex-biased natal dispersal is prevalent in many avian species, with females typically dispersing further than males. We examined natal dispersal patterns in an growing reintroduced population of hihi (stitchbird, Notiomystis cincta) on Tiritiri Matangi Island in New Zealand. Hihi nest almost exclusively in the nest boxes provided throughout the island, and breeding locations have been recorded since the 1997–1998 season. The population grew from 16 to 170 birds in the 10 years since establishment in 1995, and also experienced substantial changes in adult sex ratio over this period. We calculated distances from natal to breeding locations to examine the dynamics of natal dispersal with sex, population density and sex ratio, and maternal and environmental effects. Overall, females dispersed significantly further than males, with permutation tests indicating that mean female dispersal distance was significantly higher than expected if they selected boxes at random, and male mean dispersal distance was significantly less than expected if they selected boxes at random. General linear mixed modelling also revealed sex-specific changes in dispersal behaviour over time that were correlated with changes in population density and sex ratio, and a strong effect of the maternal females' identity. The mean dispersal distance of males decreased with density, with the number of the juveniles in the cohort as the best correlate. We suggest that males are able to disperse further to gain the highest quality open territories at lower population densities, whereas dispersal distances become increasingly constrained by territory availability, and possibly variation in mating strategy, at higher densities. In contrast, female dispersal showed a weak positive density-dependent relationship, but was more strongly influenced by sex ratio, with dispersal distances decreasing with an increasing male bias in the population. We also found a strong effect of the maternal female that could not be explained solely by nest box location. Overall, these results imply a critical role of social context, including population size, density, and sex ratio in influencing natal dispersal dynamics in a closed, insular population of hihi, and have important conservation management applications for future translocation design and implementation for this endangered species.

Sex‐biased natal dispersal and inbreeding avoidance in American black bears as revealed by spatial genetic analyses

We tested the hypothesis that sex-biased natal dispersal reduces close inbreeding in American black bears, a solitary species that exhibits nearly complete male dispersal and female philopatry. Using microsatellite DNA and spatial data from reproductively mature bears (>or= 4 years old), we examined the spatial genetic structure of two distinct populations in New Mexico from 1993 to 2000. As predicted, relatedness (r) and the frequency of close relationships (parent-offspring or full siblings) decreased with distance among female dyads, but little change was observed among male or opposite-sex dyads. Neighbouring females were more closely related than neighbouring males. The potential for inbreeding was low. Most opposite-sex pairs that lived sufficiently close to facilitate mating were unrelated, and few were close relatives. We found no evidence that bears actively avoided inbreeding in their selection of mates from this nearby pool, as mean r and relationship frequencies did not differ between potential and actual mating pairs (determined by parentage analysis). These basic patterns were apparent in both study areas despite a nearly two-fold difference in density. However, the sex bias in dispersal was less pronounced in the lower-density area, based on proportions of bears with male and female relatives residing nearby. This result suggests that male bears may respond to reduced competition by decreasing their rate or distance of dispersal. Evidence supports the hypothesis that inbreeding avoidance is achieved by means of male-biased dispersal but also indicates that competition (for mates or resources) modifies dispersal patterns.

Sex biased natal dispersal in a closed, saturated population of Seychelles warblersAcrocephalus sechellensis

The distances that individuals disperse, from their natal site to the site of first breeding and between breeding sites, have important consequences for the dynamics and genetic structure of a population. Nearly all previous studies on dispersal have the problem that, because the study area encompassed only a part of the population, emigration may have been confounded with mortality. As a result long‐distance dispersers may have been overlooked and dispersal data biased towards short distances. By studying a virtually closed population of Seychelles warblersAcrocephalus sechellensiswe obtained almost unbiased results on several aspects of dispersal. As in the majority of other avian species, natal dispersal distance was female biased in the Seychelles warbler. Female offspring also forayed further from the natal territory in search of breeding vacancies than male offspring. The sex bias in natal dispersal distance did, however, depend on local breeding density. In males, dispersal distance decreased as the number of territories bordering the natal territory increased, while in females, dispersal distance did not vary with local density. Dispersal by breeders was rare and, unlike in most species, distances did not differ between the sexes. We argue that our results favour the idea that the sex bias in natal dispersal distance in the Seychelles warbler is due to inbreeding avoidance and not resource competition or intrasexual competition for mates.

Sex biased natal dispersal in a closed, saturated population of Seychelles warblers Acrocephalus sechellensis

Sex biased natal dispersal in a closed, saturated population of Seychelles warblers Acrocephalus sechellensis

KIN RECOGNITION IN GROUND SQUIRRELS AND OTHER RODENTS

Significant advances have been made in understanding kin recognition as it pertains to nepotism (preferential treatment of kin) and mate choice (optimization of inbreeding and outbreeding). Yet complementary knowledge about how animals discriminate conspecifics on the basis of genetic relatedness remains unclear for most species. Because of the diversity of their scent sources and highly developed olfactory systems, rodents present a unique opportunity for examining chemical communication and kin recognition as a function of sociality. I review general processes of kin recognition and summarize mechanisms of recognition used by rodents. As a case study, I also examine recognition systems of ground squirrels, relating odor production and perception to differences in patterns of nepotism. Belding’s ground squirrels ( Spermophilus beldingi) produce $2 odors (from oral and dorsal glands) that correlate with relatedness (kin labels), and they are able to use these odors to make precise discriminations among their unfamiliar relatives. Thus, S. beldingi can recognize their distant female kin and male kin, even though these kin are not treated nepotistically (e.g., through cooperative territory defense or alarm call production). Furthermore, S. beldingi use these kin labels and recognition abilities to interact differentially with conspecifics as a function of relatedness. In ground squirrels and in other rodents, components of the kin recognition process (production of recognition cues, discrimination of these cues, and differential treatment of conspecifics) have evolved differentially among even closely related species. Kin recognition abilities in the absence of nepotism might reflect selection for inbreeding avoidance mechanisms, in addition to sex-biased natal dispersal. Together, data and the review demonstrate that recognition abilities cannot be predicted on the basis of sociality alone and suggest that comparative analyses, by multiple assays of discrimination, might be necessary to understand variation in the function of kin recognition within and across species.

Postfledging parental care in Savannah sparrows: sex, size and survival

We investigated postfledging parental care in a philopatric population of Savannah sparrows,Passerculus sandwichensis , breeding on Kent Island, New Brunswick, Canada in an effort to understand the factors influencing adult birds' decisions about parental investment in offspring. Brood division was not based on offspring sex: male and female parents were equally likely to care for sons or daughters. The total duration of parental care, from hatching to independence, was similar for sons and daughters (median=23 days), regardless of the sex of the care-giving parent. The duration of parental care also corresponded closely to the time required for juveniles to acquire basic foraging skills. Despite high levels of extrapair paternity, male Savannah sparrows invested as much in postfledging care and were as effective as females in caring for fledglings, based on recruitment of fledglings into the breeding population the following year. Male parents were more likely to care for smaller fledglings and for offspring from early broods (presumably to enable females to dedicate their efforts towards second clutches). Caring for fledglings was costly for parents: survivorship decreased as a function of the duration of postfledging parental care and the number of fledglings cared for. Parental survivorship, however, was not affected by the sex of the fledglings cared for. This study suggests that sex-biased provisioning may be unlikely except in species with strongly sexually dimorphic offspring, biased offspring sex ratios and sex-biased natal dispersal. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Costs and benefits of female-biased natal philopatry in the common goldeneye

Sex-biased natal dispersal in long-lived species may result in interactions between parents and mature young of the philopatric sex. To investigate the evolutionary basis of natal philopatry in a noncooperative species, the common goldeneye Bucephala clangula, we studied possible costs and benefits of simultaneous breeding of females and philopatric daughters. We did not find any fitness consequences of a daughter's breeding on their mother's breeding in terms of nest-site selection, body weight, clutch size, hatching date, or hatching success. Our results, therefore, did not support the assumption of the local resource competition hypothesis, that the natally philopatric sex should be more costly to a breeding parent. As possible benefits for daughters returning to their natal area, we tested inheritance of nest sites from mothers and explored whether daughters utilize the presence of their mother by parasitically sneaking into her mother's nest. Daughters' nest-site selection was not associated with the presence of their mothers. A comparison between daughters and control females revealed that daughters chose their nest site closer to their natal nest than expected by nest-site availability alone. Daughters could not expect to inherit a nest site from their mother, and we did not find other indications of cooperation between relatives either. The mother's clutch size did not increase in the year breeding with the daughter, indicating daughters do not parasitize their mother's nest. We suggest that benefits such as decreased nest predation risk associated with nesting close to the natal nest site may be important in the natal philopatric behavior of the species.

Natal Dispersal of Snowshoe Hares during a Cyclic Population Increase

We used radiotelemetry to monitor movements of 35 juvenile snowshoe hares ( Lepus amer-icanus ) from weaning until their first breeding season (June 1995–April 1996). Juveniles born on control or food-addition areas were assigned to one of three cohorts of litters. We calculated natal dispersal distances (distance from nest site to breeding location) and frequencies of emigration (proportion dispersing more than twice the home-range diameter of adults) and determined ages and dates at emigration. Natal dispersal distances ranged from 23 m to > 16 km. Fifty percent (9/18) of juveniles that survived until their first breeding season emigrated. Juveniles from the third litter dispersed at an older age than those from first or second litters. We detected no statistically significant effect of food addition on dispersal distance. With our small sample, we did not find statistical evidence of sex-biased natal dispersal (7 of 12 males and 2 of 6 females dispersed).

Patterns of natal dispersal, turnover and dispersal costs in eastern bluebirds

Most hypotheses explain dispersal patterns in vertebrate populations based upon an assumption that individuals incur costs when moving away from their natal territories. The geometric distribution of dispersal distances that typically reflects observed dispersal, however, may also be modelled from the basic structure and demographic parameters of the resident population, independent of costs to dispersers. For example, sex-biased natal dispersal might then be explained by differential turnover rates of adult males and females. Patterns of natal dispersal were determined for a South Carolina population of eastern bluebirds, Sialia sialis, from 1985 to 1991 and relationships between different measures of dispersal and initial reproductive success, survival of parents and availability of nest sites were subsequently examined. Females settled significantly further from the natal territory than did males and were more likely to emigrate from the local population. In addition, immigrant females outnumbered immigrant males within local populations. The initial reproductive success of philopatric and dispersing second-year males and females did not differ, but the possibility of high dispersal costs associated with mortality alone could not be excluded. Adult turnover rates did not affect dispersal of individual offspring or general philopatry rates within local populations (as a factor determining overall territory availability). Therefore, alternative factors, such as competitive interactions or intrinsic mechanisms, may be more likely proximate causes of natal dispersal patterns than adult survivorship.