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 (
Geographic variation in bird song has received much attention in evolutionary studies, yet few consider components within songs that may be subject to different constraints and follow different evolutionary trajectories. Here, we quantify patterns of geographic variation in the socially transmitted “whistle” song of Albert's lyrebirds (
- Award ID(s):
- 1755132
- NSF-PAR ID:
- 10453366
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 11
- Issue:
- 6
- ISSN:
- 2045-7758
- Page Range / eLocation ID:
- p. 2701-2716
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract 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. -
more » « less
Geographic variation in song is widespread among birds, particularly in species that learn vocalizations. The relationship between geographic distance and song variation is likely related to the degree of isolation between populations. To assess this effect of geographic isolation on song divergence, we examined patterns of geographic song variation in four species of Australian fairy‐wrens (
Malurus ), two with suspected histories of geographic isolation and two without. Song variation in all four species was consistent with patterns of isolation by distance, and allopatric subspecies in two species were more divergent in song than predicted by distance alone. Each species’ pattern was unique, and some interspecific variation could not be explained by geographic distance. These results indicate that patterns of geographic variation can be influenced by more than geographic distance and historical isolation alone. We suggest that morphological constraints, environmental influences, and sexual selection may all contribute to the variation observed for each species. -
null (Ed.)Abstract Many animals learn to produce acoustic signals that are used to attract mates and defend territories. The structure of these signals can be influenced by external features of the environment, including the anthropogenic soundscape. In many sedentary species, habitat features and soundscape appears to influence the cultural evolution of songs, often with tradeoffs for better transmission over sexually selected song structure. However, none have investigated whether noise on the wintering grounds affects song structure, which for long-distance migrants may result in an acoustic ‘mismatch’ when returning to a breeding ground. This study investigates urban noise effects on song structure in a long-distance migrant, Zonotrichia leucophrys gambelii, on the wintering grounds in the Fresno Clovis Metropolitan Area and in outlying non-urban areas. Songs and background noise levels were recorded concurrently, and song measurements of frequency and duration were examined differences across noise levels and habitats . We found that the buzz and trill decrease in bandwidth in the presence of noise. The length of the whistle and buzz portion of the song also tends to decreases with noise in urban habitats. This trend toward short, pure tones in noisy areas may transmit better in noisy urban winter habitats, but may not be adaptive on quieter breeding grounds. We suggest that future studies should consider whether winter auditory feedback and song learning environments have consequences for song crystallization and breeding success for long-distance migrants.more » « less
-
more » « less
Abstract Human commensal species such as rodent pests are often widely distributed across cities and threaten both infrastructure and public health. Spatially explicit population genomic methods provide insights into movements for cryptic pests that drive evolutionary connectivity across multiple spatial scales. We examined spatial patterns of neutral genomewide variation in brown rats (
Rattus norvegicus ) across Manhattan, New York City (NYC ), using 262 samples and 61,401SNP s to understand (i) relatedness among nearby individuals and the extent of spatial genetic structure in a discrete urban landscape; (ii) the geographic origin ofNYC rats, using a large, previously published data set of global rat genotypes; and (iii) heterogeneity in gene flow across the city, particularly deviations from isolation by distance. We found that rats separated by ≤200 m exhibit strong spatial autocorrelation (r = .3,p = .001) and the effects of localized genetic drift extend to a range of 1,400 m. Across Manhattan, rats exhibited a homogeneous population origin from rats that likely invaded from Great Britain. While traditional approaches identified a single evolutionary cluster with clinal structure across Manhattan, recently developed methods (e.g., fineSTRUCTURE,sPCA ,EEMS ) provided evidence of reduced dispersal across the island's less residential Midtown region resulting in fine‐scale genetic structuring (F ST -
more » « less
Premise Divergence depends on the strength of selection and frequency of gene flow between taxa, while reproductive isolation relies on mating barriers and geographic distance. Less is known about how these processes interact at early stages of speciation. Here, we compared population‐level differentiation in floral phenotype and genetic sequence variation among recently diverged
Castilleja to explore patterns of diversification under different scenarios of reproductive isolation.Methods Using target enrichment enabled by the Angiosperms353 probe set, we assessed genetic distance among 50 populations of four
Castilleja species. We investigated whether patterns of genetic divergence are explained by floral trait variation or geographic distance in two focal groups: the widespreadC. sessiliflora and the more restrictedC. purpurea species complex.Results We document that
C. sessiliflora and theC. purpurea complex are characterized by high diversity in floral color across varying geographic scales. Despite phenotypic divergence, groups were not well supported in phylogenetic analyses, and little genetic differentiation was found across targeted Angiosperms353 loci. Nonetheless, a principal coordinate analysis of single nucleotide polymorphisms revealed differentiation withinC. sessiliflora across floral morphs and geography and less differentiation among species of theC. purpurea complex.Conclusions Patterns of genetic distance in
C. sessiliflora suggest species cohesion maintained over long distances despite variation in floral traits. In theC. purpurea complex, divergence in floral color across narrow geographic clines may be driven by recent selection on floral color. These contrasting patterns of floral and genetic differentiation reveal that divergence can arise via multiple eco‐evolutionary paths.
