Population structure, patterns of natal dispersal and demographic history in a declining aerial insectivore, the purple martin Progne subis

Abstract

Genetic variation is a fundamental component of biodiversity, and studying population structure, gene flow and demographic history can help guide conservation strategies for many species. Like other aerial insectivores, the purple martin Progne subis is in decline, and yet their genetic background remains largely unknown. To address this knowledge gap, we assessed population structure in the nominate eastern subspecies (P. s. subis) with relation to natal dispersal and examined historical genetic patterns in all three subspecies (P. s. subis, P. s. arboricola, P. s. hesperia) across their North American breeding range by estimating effective population sizes over time. We used next‐generation sequencing strategies for genomic analyses, integrating whole‐genome resequencing data with continent‐wide band encounter records to examine natal dispersal. We documented population structure across P. s. subis, with the highest differentiation between the northern (Alberta) and more southern colonies and following patterns of isolation‐by‐distance. Consistent with spatial patterns of genetic differentiation, we also found greater longitudinal than latitudinal natal dispersal distances, signifying potential latitudinal constraints on gene flow. Earlier contractions in effective population sizes in the western P. s. arboricola and P. s. hesperia compared to the eastern P. s. subis subspecies suggest these subspecies originated from two different glacial refugia. Together, these findings support latitudinal distinction in P. s. subis, and elucidate the origin of subspecies differentiation, highlighting the importance of conserving populations across the range to maximize genetic diversity and adaptive potential in the purple martin.

Fine-scale genetic structure and phenotypic divergence of a passerine bird population inhabiting a continuous Mediterranean woodland

“…Widespread highly mobile species are likely to experience several environmental conditions and geographical barriers, and thus, they are expected to experience genetic population structure at large geographical scales [70][71][72][73], often following an isolation-by-distance pattern (e.g. [3,72,74]). However, genetic structure can be observed at small spatial scales depending on the landscape composition and environmental conditions [8], which can restrict dispersal and gene flow among populations when organisms match habitat selection to natal conditions [75].…”

Spring departure date, not en route conditions, drive migration rate and arrival timing in a long-distance migratory songbird

“…In cliff swallows (Petrochelidon pyrrhonota), Brown and Brown (1999) found a large shift in arrival dates in the year after an extreme selection event (early cold snap), providing evidence for short-term shifts in optimal timing. Moreover, timing phenotypes in purple martins are associated with genomic variation, suggesting phenological microevolution (de Greef et al, 2022). However, the repeat tracking of individual purple martins shows individual variability in timing (Fraser et al, 2019).…”

Revealing the Demographic History of the European nightjar (Caprimulgus europaeus).

“…However, the samples contributing to Schweizer et al's (2020) work spanned a much broader latitudinal range (encompassing W Europe to Asia) than those in our study and likely represented a deeper divergence. Much of the structure in contemporary Palearctic and Nearctic animal populations are fundamentally linked to past glacial and interglacial cycles, which have led to the contraction of temperate breeding populations into Southern refugia, and subsequent northward recolonisation during warmer interglacial periods (Hewitt, 2004;Nadachowska-Brzyska et al, 2016;Yao et al, 2022;de Greef et al, 2022). Previously panmictic populations may become isolated from one another in different refugia, during periods of glaciation, leading to genetic differentiation post-interglacial expansion (Hewitt et al, 2001).…”

“…Restriction to different glacial refugia and subsequent northward expansion during interglacial periods have been linked to contemporary population structure and subspecies divergence in multiple species, including birds and aerial insects (e.g. Schmitt, 2007;Hansson et al, 2008;Nadachowska-Brzyska et al, 2016;de Greef et al, 2022). Occupation of separate glacial refugia by different populations is thought to have driven spatial patterns of genetic differentiation in temperate species, with many Palearctic birds exhibiting contemporary East -West patterns in genetic structure and speciation (e.g.…”