Population Genetics of the Galápagos Hawk (Buteo Galapagoensis): Genetic Monomorphism Within Isolated Populations

Because of their smaller size and isolation, island populations tend to be more divergent and less genetically variable than mainland populations. We collected DNA samples from nine Galápagos Hawk (Buteo galapagoensis) island populations, covering the species’ entire range. Neutral minisatellite DNA markers were used to calculate within-island genetic diversity and between-island genetic differentiation (FST). Typically, these markers mutate too quickly to be informative in such studies. However, in very small, isolated populations, concerns about high mutational rate are obviated by the relative force of genetic drift. Individuals within islands had the highest levels of reported genetic uniformity of any natural bird population, with mean within-population band-sharing similarity values ranging from 0.693 to 0.956, increasing with decreasing island size. Galápagos Hawks exhibit cooperative polyandry to varying degrees across islands; however, we did not find an association between degree of polyandry and genetic variability. Between-island FST values ranged from 0.017 to 0.896, with an overall archipelago value of 0.538; thus, most populations were genetically distinct. Also, we documented higher levels of genetic similarity between nearby populations. Our results indicated negligible gene flow among most Galápagos Hawk populations, and genetic drift has played a strong role in determining structure at these minisatellite loci. Genética de Poblaciones de Buteo galapagoensis: Monomorfismo Genético dentro de Poblaciones Aisladas

Variation in Morphology and Mating System Among Island Populations of GaláPagos Hawks

Interspecific variation in sexual size dimorphism has commonly been attributed to variation in social mating system, with dimorphism increasing as intrasexual competition for mates increases. In birds, overall body size has also been found to correlate positively with size dimorphism. In this study, we describe variation in morphology and mating system across six populations of the endemic Galápagos Hawk (Buteo galapagoensis). Galápagos Hawks exhibit cooperative polyandry, a mating system in which long-term social groups contain a single female and multiple males. Comparisons among islands revealed significant differences in overall body size for both adults and immatures. Populations ranged from completely monogamous to completely polyandrous, with varying mean group sizes. Data did not support our prediction that sexual size dimorphism would increase with the degree of polyandry (number of males per group) or with body size; there was no correlation between mating system and sexual dimorphism. We did find a significant negative relationship between degree of polyandry and body size among islands, opposite of the pattern predicted. Variación en Morfología y Sistema de Apareamiento entre Poblaciones de Buteo galapagoensis Resumen. Variación interespecífica en dimorfismo sexual ha sido atribuída comúnmente a variaciones del sistema social de apareamiento, de tal manera que el dimorfismo aumenta conforme aumenta la competencia intrasexual por parejas reproductivas. También se ha encontrado que el tamaño corporal se correlaciona positivamente con el dimorfismo. En este estudio describimos la variación morfológica y el grado de poliandría de seis poblaciones de Buteo galapagoensis, una especie que exhibe un sistema de apareamiento denominado poliandría cooperativa. En este sistema los grupos de individuos reproductivos incluyen una sola hembra y múltiples machos. Se comprobó que existen diferencias significativas en el tamaño del cuerpo de adultos y juveniles entre islas. Las poblaciones muestreadas variaron entre monógamas y completamente poliándricas, y el tamaño promedio de los grupos fue variable. Los datos no apoyaron las predicciones establecidas inicialmente pues el grado de dimorfismo sexual no aumentó con el nivel de poliandría (número de machos por grupo) ni con el tamaño corporal, ni hubo una correlación entre el sistema de apareamiento y el dimorfismo sexual. La relación entre el tamaño corporal y el sistema de apareamiento fue contraria a la que se predijo: hubo una correlación negativa significativa entre el grado de poliandría y el tamaño corporal entre islas.

Serial Polyandry and Alloparenting in Long-Eared Owls

We used DNA fingerprinting to document serial polyandry in a double-brooded female Long-eared Owl (Asio otus) in western Montana. We also determined that an extra male that helped provision offspring at a nest was a close relative of the female parent. The nest had split paternity, and it is not clear whether the helper was the sire or brother of two of the four nestlings. These data constitute the first known cases of serial polyandry and alloparenting in Long-eared Owls and leave open the question of whether cooperative polyandry also occurs in this species. Poliandría en Serie y Alopaternidad en Asio otus Resumen. Empleamos huellas dactilares genéticas (i.e., DNA fingerprinting) para documentar poliandría en serie en una hembra de Asio otus que presentó dos nidadas, en el oeste de Montana. También determinamos que un macho extra-pareja que ayudó a abastecer a los pichones en un nido era un pariente cercano de la madre. El nido presentó paternidad compartida y no está claro si el ave que ayudaba era el padre o el hermano de dos de los cuatro polluelos. Estos datos representan el primer caso conocido de poliandría en serie y alopaternidad en Asio otus, y deja abierta la pregunta si en esta especie también ocurre poliandría cooperativa.