Population differentiation and historical demography of the threatened snowy plover Charadrius nivosus (Cassin, 1858)

Abstract

Delineating conservation units is a complex and often controversial process that is particularly challenging for highly vagile species. Here, we reassess population genetic structure and identify those populations of highest conservation value in the threatened snowy plover (Charadrius nivosus, Cassin, 1858), a partial migrant shorebird endemic to the Americas. We use four categories of genetic data-mitochondrial DNA (mtDNA), microsatellites, Z-linked and autosomal single nucleotide polymorphisms (SNPs)-to: (1) assess subspecies delineation and examine population structure (2) compare the sensitivity of the different types of genetic data to detect spatial genetic patterns, and (3) reconstruct demographic history of the populations analysed. Delineation of two traditionally recognised subspecies was broadly supported by all data. In addition, microsatellite and SNPs but not mtDNA supported the recognition of Caribbean snowy plovers (C. n. tenuirostris) and Floridian populations (eastern C. n. nivosus) as distinct genetic lineage and deme, respectively. Low migration rates estimated from autosomal SNPs (m < 0.03) reflect a general paucity of exchange between genetic lineages. In contrast, we detected strong unidirectional migration (m = 0.26) from the western into the eastern nivosus deme. Within western nivosus, we found no genetic differentiation between coastal Pacific and inland populations. The correlation between geographic and genetic distances was weak but significant for all genetic data sets. All demes showed signatures of bottlenecks occurring during the past 1000 years. We conclude that at least four snowy plover conservation units are warranted: in addition to subspecies nivosus and occidentalis, a third unit comprises the Caribbean tenuirostris lineage and a fourth unit the distinct eastern nivosus deme.

Allelic diversity and patterns of selection at the major histocompatibility complex class I and II loci in a threatened shorebird, the Snowy Plover (Charadrius nivosus)

“…Across continental populations (subspecies nivosus and occidentalis ), we found a similar number of alleles and nucleotide diversity. This result is consistent with the high gene flow observed among Snowy Plover populations [ 31 , 33 , 54 ]. At MHC I only, we found that the Nayarit population had a lower number of alleles (13 alleles), although this may reflect the sample size, as we only genotyped ten birds from this population.…”

“…We investigated the diversity and organization of the MHC in the Snowy Plover Charadrius nivosus , a member of the Charadriidae [ 30 ]. Until recently, Snowy Plovers were lumped with Kentish Plovers Charadrius alexandrinus and considered to be a cosmopolitan species, but the analysis of genetic and phenotypic traits has shown that the two species are separate and that Snowy Plovers are characterized by low genetic diversity at neutral genetic markers [ 31 – 33 ]. Three Snowy Plover lineages are commonly recognized and distinguishable with genetic markers: Western Snowy Plovers ( C. n. nivosus ) in North America, Cuban Snowy Plovers ( C. n. tenuirostris ) in the Caribbean, and the Peruvian Snowy Plover ( C. n. occidentalis ) in South America [ 31 ].…”

Identification of priority shorebird conservation areas in the Caribbean

“…While some authorities only recognize two subspecies ( C. n. nivosus and C. n. occidentalis ; e.g., Clements et al, 2019 ; Gill, Donsker & Rasmussen, 2020 ), others recognize a third, C. n. tenuirostris ( Andres et al, 2012 ; US Fish and Wildlife Service, 2011 ; Funk, Mullins & Haig, 2007 ). The tenuirortris subspecies was originally thought to include mainland Gulf of Mexico and Caribbean birds, though recent genetic work suggests that continental birds are more similar to nivosus and that the tenuirostris group is limited to the Caribbean ( D’Urban, Jackson & Jackson, 2020 ). Unfortunately, there are no strong morphological differences between these two subspecies, leading them to be indistinguishable in the field, and little information exists about range overlap during migration ( Page et al, 2020 ).…”

“…Recent genetic studies suggest that the C. n. tenuirostris population of Snowy Plovers differs sufficiently from C. n. nivosus and they should be considered separate conservation units ( Funk, Mullins & Haig, 2007 ; D’Urban, Jackson & Jackson, 2020 ). The majority of tissue samples in these studies, however, originated from Puerto Rico; there were two samples each from Turks and Caicos Islands, Bermuda, and Haiti, and none originated from other places Snowy Plovers occupy.…”

“…It is critical to identify where C. n. tenuirostris persists, their complete range, and where they overlap with nivosus to conserve the subspecies. Finally, D’Urban Jackson et al (2020) identified that the eastern United States nivosus population also warrants its own conservation unit status. This is important because migratory mainland birds that use the Caribbean would originate from this unique population.…”