Gene flow connects coastal populations of a habitat specialist, the Clapper Rail Rallus crepitans

Abstract

Examining population genetic structure can reveal patterns of reproductive isolation or population mixing and inform conservation management. Some avian species are predicted to exhibit minimal genetic differentiation among populations as a result of the species high mobility, with habitat specialists tending to show greater fine-scale genetic structure. To explore the relationship between habitat specialization and gene flow, we investigated the genetic structure of a saltmarsh specialist with high potential mobility across a wide geographical range of fragmented habitat. Little variation among mitochondrial sequences (620 bp from ND2) was observed among 149 individual Clapper Rails Rallus crepitans sampled along the Atlantic coast of the USA, with the majority of individuals at all sampling sites sharing a single haplotype. Genotyping of nine microsatellite loci across 136 individuals revealed moderate genetic diversity, no evidence of bottlenecks and a weak pattern of genetic differentiation that increased with geographical distance. Multivariate analyses, Bayesian clustering and an AMOVA all suggested a lack of genetic structuring across the Atlantic coast of the USA, with all individuals grouped into a single interbreeding population. Spatial autocorrelation analyses showed evidence of weak female philopatry and a lack of male philopatry. We conclude that high gene flow connecting populations of this habitat specialist may result from the interaction of ecological and behavioural factors that promote dispersal and limit natal philopatry and breeding-site fidelity. As climate change threatens saltmarshes, the genetic diversity and population connectivity of Clapper Rails may promote resilience of their populations. This finding helps inform about potential fates of other similarly behaving saltmarsh specialists on the Atlantic coast.

Landscape features influencing gene flow and connectivity of an endangered passerine

“…The spatial pattern observed where individuals tended to be genetically more similar within a distance of approximately 20-30 km than those further apart strongly supports the proposed steppingstone model of connectivity for Dupont's lark Méndez et al, 2014) instead of more general models based on long dispersal distances (e.g. Coster et al, 2019). This pattern agrees with the genetic structure observed in Spain, where some genetic clusters are not entirely isolated .…”

“…Recent estimations consider less than 2300 males in the whole Spanish population, with an effective population size of around 600–1300 pairs (Reverter et al., 2023 ). Although the impact of habitat degradation on genetic diversity is less evident in birds in comparison with other vertebrate species because of their higher dispersal abilities (Alcaide et al., 2009 ; Burgess & Garrick, 2020 ; Canales‐Delgadillo et al., 2012 ; Coster et al., 2019 ; Ferrer et al., 2016 ; Mulvaney et al., 2021 ), bird species with restricted dispersal and strict habitat requirements are prone to be genetically affected by habitat fragmentation and loss, often exhibiting significant population structure and low genetic variation (Caizergues et al., 2003 ; Jensen et al., 2019 ; Khimoun et al., 2017 ; Klinga et al., 2019 ).…”

Quantitative acoustic differentiation of cryptic species illustrated with King and Clapper rails

“…Recordings were taken using a Song Meter SM3 (Wildlife Acoustics, Maynard, MA, USA) at 24 kHz and 16‐bit deployed in rotation between 15 random locations within the marsh, each one at least 400 m from every other survey location (Conway, ), at least 50 m from marsh edge, and easily accessible by boat from the Pamunkey River. Animal capture and population genetic surveying of the marsh confirmed that Clapper rails were the only Rallus species found within the marsh (Coster et al, ; G. Costanzo and S. Harding unpublished data).…”