Behavioral mechanisms of reproductive isolation in avian hybrid zones

Sexual signals and mating behaviors influence whether sympatric species interbreed, and can therefore promote or impede behavioral reproductive isolation between species in secondary contact. Traditionally, research on sexual selection and hybridization has focused on the importance of interspecific mate choice and species discrimination from the perspective of choosy females, and competition from the lens of aggressive and indiscriminate males. I examined two different avian systems to compare the role of male and female competition on hybridization: white-crowned sparrows on the west coast of the US, and sex-role reversed jacanas in Panama. Using genomics and experimental field techniques, I tested morphological, behavioral, and historical factors that influence patterns of gene flow between lineages. I found that contrary to traditional expectations, divergence in male competitive signals can promote reproductive isolation, and female competition can facilitate hybridization

Multimodal models of animal sex in scientific literature: breaking binaries leads to a better understanding of ecology and evolution

‘Sex’ is often used to describe a suite of phenotypic and genotypic traits of an organism related to reproduction. However, not all these traits are necessarily linked, and the rhetorical collapse of variation into a single term elides much of the complexity inherent in reproductive phenotypes. We conducted a meta-analysis of scientific literature to investigate how terminology related sexual phenotypes changes over time. We find that the conflation of gender and sex has increased, and there is a mammalian bias in this conflation. We highlight how a more inclusive and expansive framework for sex can clarify studies of sexual diversity

When females compete and males care: Phenotypic differences in the spotted sandpiper

Ecology can shape variation in mating systems. Spotted sandpipers (Actitis macularius) are migratory shorebirds with a sequentially polyandrous mating system. Females compete for multiple mates, and males care for offspring, including through incubation and chick care. A study of a Midwestern population found that females have larger body mass and feather spots, but we do not know whether this pattern extends to other populations of this species. We studied a California population of spotted sandpipers surrounding Mono Lake. We used PCR to determine genetic sex from blood samples, and we used R to compare morphological traits between females and males. We find sexual dimorphism in several morphological traits, including tarsus, wing, and bill length, as well as body mass, suggesting the Midwestern and California populations have evolved similarly, and both have sexually dimorphic morphology

Behavioural response to song and genetic divergence in two subspecies of white-crowned sparrows (Zonotrichia leucophrys)

© 2016 John Wiley & Sons Ltd Divergence in sexual signals may drive reproductive isolation between lineages, but behavioural barriers can weaken in contact zones. Here, we investigate the role of song as a behavioural and genetic barrier in a contact zone between two subspecies of white-crowned sparrows (Zonotrichia leucophrys). We employed a reduced genomic data set to assess population structure and infer the history underlying divergence, gene flow and hybridization. We also measured divergence in song and tested behavioural responses to song using playback experiments within and outside the contact zone. We found that the subspecies form distinct genetic clusters, and demographic inference supported a model of secondary contact. Song phenotype, particularly length of the first note (a whistle), was a significant predictor of genetic subspecies identity and genetic distance along the hybrid zone, suggesting a close link between song and genetic divergence in this system. Individuals from both parental and admixed localities responded significantly more strongly to their own song than to the other subspecies song, supporting song as a behavioural barrier. Putative parental and admixed individuals were not significantly different in their strength of discrimination between own and other songs; however, individuals from admixed localities tended to discriminate less strongly, and this difference in discrimination strength was explained by song dissimilarity as well as genetic distance. Therefore, we find that song acts as a reproductive isolating mechanism that is potentially weakening in a contact zone between the subspecies. Our findings also support the hypothesis that intraspecific song variation can reduce gene flow between populations

SNP calls for Zonotrichia leucophrys nuttalli x Z. l. pugetensis hybrid zone

Dataset includes 6419 SNP loci for 169 individuals across the Zonotrichia leucophrys nuttalli x Z. l. pugetensis hybrid zone. Sampling information, including individual ID, locality, lat/long, sex, and whether song data is available is also provided. Songs are archived at the Borror Laboratory of Bioacoustics at Ohio State University

Seasonal fluctuations in population size and habitat segregation of Kittlitz’s Plover Charadrius pecuarius at Barberspan Bird Sanctuary, North West province, South Africa

Seasonal fluctuations in population size reflect breeding patterns and movements of birds, but distinguishing residents from itinerant birds is difficult with partially migratory species such as Kittlitz’s Plover. We determined changes in the size of Kittlitz’s Plover populations in two microhabitats (Goose Point and Sandy Beach) at Barberspan Bird Sanctuary, North West province, South Africa, where we ringed waders between February 2008 and May 2010. Using a Bayesian model, we estimated the population of this species at these two sites from capture–recapture data gathered in eight 3- to 12-day collection periods. The estimated adult population at Goose Point peaked at 161 in October 2009, but decreased to about 40 in March 2009 and March 2010. The immature population peaked at 119 in January–February 2010. This, along with observations of nests and chicks, suggests that residents bred at Goose Point from September to March. The estimated number of adults at Sandy Beach increased from 48 in March 2010 to 380 in April 2010. Adults captured there in April 2010 formed feeding flocks and were heavier than the resident birds at Goose Point. These results suggest that Barberspan Bird Sanctuary supports resident and itinerant populations that are partially segregated in different microhabitats.OSTRICH 2011, 82(3): 207–21

Data from: Behavioral response to song and genetic divergence in two subspecies of white-crowned sparrows (Zonotrichia leucophrys)

Divergence in sexual signals may drive reproductive isolation between lineages, but behavioral barriers can weaken in contact zones. Here, we investigate the role of song as a behavioral and genetic barrier in a contact zone between two subspecies of white-crowned sparrows (Zonotrichia leucophrys). We employed a reduced genomic dataset to assess population structure and infer the history underlying divergence, gene flow and hybridization. We also measured divergence in song and tested behavioral responses to song using playback experiments within and outside the contact zone. We found that the subspecies form distinct genetic clusters, and demographic inference supported a model of secondary contact. Song phenotype, particularly length of the first note (a whistle), was a significant predictor of genetic subspecies identity and genetic distance along the hybrid zone, suggesting a close link between song and genetic divergence in this system. Individuals from both parental and admixed localities responded significantly more strongly to their own song than to the other subspecies song, supporting song as a behavioral barrier. Putative parental and admixed individuals were not significantly different in their strength of discrimination between own and other songs; however, individuals from admixed localities tended to discriminate less strongly, and this difference in discrimination strength was explained by song dissimilarity as well as genetic distance. Therefore, we find that song acts as a reproductive isolating mechanism that is potentially weakening in a contact zone between the subspecies. Our findings also support the hypothesis that intra-specific song variation can reduce gene flow between populations

Differential introgression of a female competitive trait in a hybrid zone between sex-role reversed species

Mating behavior between recently diverged species in secondary contact can impede or promote reproductive isolation. Traditionally, researchers focus on the importance of female mate choice and male-male competition in maintaining or eroding species barriers. Although female-female competition is widespread, little is known about its role in the speciation process. Here, we investigate a case of interspecific female competition and its influence on patterns of phenotypic and genetic introgression between species. We examine a hybrid zone between sex-role reversed, Neotropical shorebird species, the northern jacana (Jacana spinosa) and wattled jacana (J. jacana), in which female-female competition is a major determinant of reproductive success. Previous work found that females of the more aggressive and larger species, J. spinosa, disproportionately mother hybrid offspring, potentially by monopolizing breeding territories in sympatry with J. jacana. We find a cline shift of female body mass relative to the genetic center of the hybrid zone, consistent with asymmetric introgression of this competitive trait. We suggest that divergence in sexual characteristics between sex-role reversed females can influence patterns of gene flow upon secondary contact, similar to males in systems with more typical sex roles

Individual sample information

Data file includes information on sample ID, sex, age, date collected, geographic locality, morphological measurements, genomic hybrid index, and species identification

Data from: Differential introgression of a female competitive trait in a hybrid zone between sex-role reversed species

Mating behavior between recently diverged species in secondary contact can impede or promote reproductive isolation. Traditionally, researchers focus on the importance of female mate choice and male-male competition in maintaining or eroding species barriers. Although female-female competition is widespread, little is known about its role in the speciation process. Here, we investigate a case of interspecific female competition and its influence on patterns of phenotypic and genetic introgression between species. We examine a hybrid zone between sex-role reversed, Neotropical shorebird species, the northern jacana (Jacana spinosa) and wattled jacana (J. jacana), in which female-female competition is a major determinant of reproductive success. Previous work found that females of the more aggressive and larger species, J. spinosa, disproportionately mother hybrid offspring, potentially by monopolizing breeding territories in sympatry with J. jacana. We find a cline shift of female body mass relative to the genetic center of the hybrid zone, consistent with asymmetric introgression of this competitive trait. We suggest that divergence in sexual characteristics between sex-role reversed females can influence patterns of gene flow upon secondary contact, similar to males in systems with more typical sex roles