RESUMO
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.
Assuntos
Charadriiformes , Genética Populacional , Antígenos de Histocompatibilidade Classe II/genética , Antígenos de Histocompatibilidade Classe I/genética , Seleção Genética , Alelos , Animais , Charadriiformes/genética , Espécies em Perigo de Extinção , Variação Genética , FilogeniaRESUMO
Shorebirds (part of the order Charadriiformes) have a global distribution and exhibit remarkable variation in ecological and behavioural traits that are pertinent to many core questions in the fields of evolutionary ecology and conservation biology. Shorebirds are also relatively convenient to study in the wild as they are ground nesting and often occupy open habitats that are tractable to monitor. Here we present a database documenting the reproductive ecology of 1,647 individually marked snowy plovers (Charadrius nivosus) monitored between 2006 and 2016 at Bahía de Ceuta (23°54N, 106°57W) - an important breeding site in north-western Mexico. The database encompasses various morphological, behavioural, and fitness-related traits of males and females along with spatial and temporal population dynamics. This open resource will serve as an important data repository for addressing overarching questions in avian ecology and wetland conservation during an era of big data and global collaborative science.
Assuntos
Cruzamento , Charadriiformes/fisiologia , Reprodução , Animais , Feminino , Masculino , México , Dinâmica Populacional , Áreas AlagadasRESUMO
Adult sex ratio (ASR) is a central concept in population biology and a key factor in sexual selection, but why do most demographic models ignore sex biases? Vital rates often vary between the sexes and across life history, but their relative contributions to ASR variation remain poorly understood-an essential step to evaluate sex ratio theories in the wild and inform conservation. Here, we combine structured two-sex population models with individual-based mark-recapture data from an intensively monitored polygamous population of snowy plovers. We show that a strongly male-biased ASR (0.63) is primarily driven by sex-specific survival of juveniles rather than adults or dependent offspring. This finding provides empirical support for theories of unbiased sex allocation when sex differences in survival arise after the period of parental investment. Importantly, a conventional model ignoring sex biases significantly overestimated population viability. We suggest that sex-specific population models are essential to understand the population dynamics of sexual organisms: reproduction and population growth are most sensitive to perturbations in survival of the limiting sex. Overall, our study suggests that sex-biased early survival may contribute toward mating system evolution and population persistence, with implications for both sexual selection theory and biodiversity conservation.
Assuntos
Charadriiformes/fisiologia , Reprodução , Razão de Masculinidade , Comportamento Sexual Animal , Algoritmos , Animais , Biodiversidade , Charadriiformes/genética , Feminino , Humanos , Masculino , México , Modelos Estatísticos , Dinâmica Populacional , Crescimento Demográfico , Caracteres Sexuais , Fatores SexuaisRESUMO
El chorlo nevado es un ave playera endémica de las Americas, la cual tiene tres subespecies. En Sudamerica la subespecie occidentalis se encuentra a lo largo de la costa del océano Pacifico. Aunque se conoce su comportamiento reproductivo, demografía poblacional y éxito reproductivo en Norteamerica, poco se sabe de estos parámetros ecológicos de la subespecie occidentalis. En octubre de 2008 estudiamos la ecología reproductiva del chorlo nevado en la Reserva Nacional de Paracas, Ica, sudoeste del Perú. Los chorlos nevados fueron encontrados en todas las nueve playas arenosas y humedales costeros visitados. De acuerdo con los conteos estimamos que la población en Paracas consiste en por lo menos 500 chorlos nevados. Hubo evidencia de actividad reproductiva en seis de los nueve sitios. La mayoría de la actividad de crianza fue observada en Playón/Mendieta, alrededor de un charco salado temporal. Encontramos dos nidos y diez familias en toda la reserva. En total se capturaron y marcaron 24 polluelos, ocho machos y siete hembras. Las familias eran atendidas por ambos padres. Hasta el final del estudio 21 de los polluelos habían perecido. Durante el período de estudio ninguno de los polluelos marcados alcanzaron la edad de volantón de 25 días y solamente confirmamos que un polluelo en una visita posterior llego a volantón. Nuestras observaciones destacan algunos problemas observados durante el período reproductivo del chorlo nevado, también sugerimos acciones para contrarrestar las amenazas identificadas.