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

Anidación del chorlo nevado (Charadrius nivosus) en Atotonilco, Jalisco, México

El chorlo nevado (Charadrius nivosus) es una de las aves playeras menos abundantes. Es una especie amenazada cuyas poblaciones se encuentran en constante declive. México es importante para las poblaciones de esta especie, pero existe poca información sobre su reproducción y amenazas. Con el objetivo obtener datos sobre su anidación y potenciales amenazas existentes, realizamos un monitoreo de la población del chorlo nevado en la laguna de Atotonilco durante la temporada reproductiva (marzo-julio) del año 2020. Efectuamos conteos de individuos y nidos, tamaño de nidada, fecha aproximada de puesta de los huevos y observaciones sobre las amenazas presentes durante este periodo. Los machos representaron el 85% (n = 140) de la población total y el mes con la mayor cantidad de nidos fue mayo (n = 15). El tamaño promedio de la nidada fue de 2.5 huevos. La superficie de agua fue variable durante los meses de muestreo, pero no se comprobó estadísticamente que a mayor desecación el tamaño de la nidada disminuyera (p = 0.09). Las principales amenazas identificadas fueron los vehículos motorizados y la ganadería. La laguna de Atotonilco es un sitio clave para la reproducción del chorlo nevado y se deben implementar acciones de manejo que permitan ampliar la presencia de agua y regulen las actividades humanas.

The taxonomic basis of subspecies listed as threatened and endangered under the endangered species act

More than 170 subspecies are listed as threatened or endangered under the US Endangered Species Act. Most of these subspecies were described decades ago on the basis of geographical variation in morphology using relatively primitive taxonomic methods. The US Fish and Wildlife Service defaults to subspecies descriptions by taxonomists working with specific groups of organisms, but there is no single definition of subspecies across plants and animals. Valid tests today usually entail molecular analyses of variation within and among populations, although there is no reason that behavioral, ecological or molecular characters could not be used, and include tests for significant differences between samples of the putative endangered subspecies and its nearest geographic relatives. We evaluated data gathered since subspecies listed under the ESA were described finding about one-third are valid (distinct evolutionary taxa), one-third are not, and one-third have not been tested. Therefore, it should not be assumed that because a subspecies occurs in a checklist, it is taxonomically valid. If the US Fish and Wildlife Service intends to continue listing subspecies, we suggest that they convene taxonomic experts representing various groups of organisms to provide a minimal set of criteria for a subspecies to be listed under the ESA.

Identification of priority shorebird conservation areas in the Caribbean

Despite being geographically central to the Atlantic Americas Flyway for migratory birds, the Caribbean is often overlooked or underappreciated when addressing the conservation of North American shorebirds. To our knowledge, this is the first Caribbean-wide assessment of shorebird use in the region. We analyzed 211,013 shorebird species observations in the insular Caribbean from 2010–2019, representing 78,794 eBird checklists and cumulative total of 2.1 million shorebirds of 45 species. We conclude that priority areas for shorebird conservation include Humedal Sur de Pinar del Río (Humedal Sur de Los Palacios) in Cuba, and Monte Cristi in the Dominican Republic as they each likely support more than 20,000 shorebirds annually, and they host large abundances of geographic populations for particular taxa. Specifically, the former site hosts >10% of Short-billed Dowitchers (Limnodromus griseus griseus/hendersoni), and >1% of Black-bellied Plovers (Pluvialis squatarola cynosurae) and Wilson’s Plovers (Charadrius wilsonia wilsonia), while the latter site supports large numbers of Black-necked Stilts (Himantopus mexicanus). We also identified at least 15 additional sites that likely cross the 1% population threshold for one or more shorebird taxa. These sites may qualify for special international designations such as Important Bird and Biodiversity Areas or as part of the Western Hemisphere Shorebird Reserve Network; 11 of the 17 sites we identified do not hold either of these titles. Data on subspecific or geographic distributions of three species, Snowy Plover (C. nivosus), Black-necked Stilt, and Killdeer (C. vociferous), are insufficient to reveal if the sites with the highest abundances were mostly comprised of Caribbean populations or migrants, but the limited information suggests that they also likely exceed 1% thresholds on several islands. Based on our results, we recommend more extensive systematic surveys of shorebirds in the Caribbean, including research on turnover rates and movements between islands, as well as assimilation of shorebird survey data not yet included in the eBird portal.

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)

Background

Understanding the structure and variability of adaptive loci such as the major histocompatibility complex (MHC) genes is a primary research goal for evolutionary and conservation genetics. Typically, classical MHC genes show high polymorphism and are under strong balancing selection, as their products trigger the adaptive immune response in vertebrates. Here, we assess the allelic diversity and patterns of selection for MHC class I and class II loci in a threatened shorebird with highly flexible mating and parental care behaviour, the Snowy Plover (Charadrius nivosus) across its broad geographic range.

Results

We determined the allelic and nucleotide diversity for MHC class I and class II genes using samples of 250 individuals from eight breeding population of Snowy Plovers. We found 40 alleles at MHC class I and six alleles at MHC class II, with individuals carrying two to seven different alleles (mean 3.70) at MHC class I and up to two alleles (mean 1.45) at MHC class II. Diversity was higher in the peptide-binding region, which suggests balancing selection. The MHC class I locus showed stronger signatures of both positive and negative selection than the MHC class II locus. Most alleles were present in more than one population. If present, private alleles generally occurred at very low frequencies in each population, except for the private alleles of MHC class I in one island population (Puerto Rico, lineage tenuirostris).

Conclusion

Snowy Plovers exhibited an intermediate level of diversity at the MHC, similar to that reported in other Charadriiformes. The differences found in the patterns of selection between the class I and II loci are consistent with the hypothesis that different mechanisms shape the sequence evolution of MHC class I and class II genes. The rarity of private alleles across populations is consistent with high natal and breeding dispersal and the low genetic structure previously observed at neutral genetic markers in this species.