Patterns of Genetic Diversity and Its Loss in Mammalian Populations

Abstract

Policy aimed at conserving biodiversity has focused on species diversity. Loss of genetic diversity, however, can affect population persistence, evolutionary potential, and individual fitness. Although mammals are a well-studied taxonomic group, a comprehensive assessment of mammalian genetic diversity based on modern molecular markers is lacking. We examined published microsatellite data from populations of 108 mammalian species to evaluate background patterns of genetic variability across taxa and body masses. We tested for loss of genetic diversity at the population level by asking whether populations that experienced demographic threats exhibited lower levels of genetic diversity. We also evaluated the effect of ascertainment bias (a reduction in variability when microsatellite primers are transferred across species) on our assessment of genetic diversity. Heterozygosity did not vary with body mass across species ranging in size from shrews to whales. Differences across taxonomic groupings were noted at the highest level, between populations of marsupial and placental mammals. We documented consistently lower heterozygosity, however, in populations that had experienced demographic threats across a wide range of mammalian species. We also documented a significant (p = 0.01) reduction in heterozygosity as a result of ascertainment bias. Our results suggest that populations of both rare and common mammals are currently losing genetic diversity and that conservation efforts focused above the population level may fail to protect the breadth of persisting genetic diversity. Conservation policy makers may need to focus their efforts below the species level to stem further losses of genetic resources.Resumen: Las políticas de conservación de la biodiversidad tradicionalmente se han centrado en la diversidad de especies. Sin embargo, la pérdida de diversidad genética puede impactar al potencial de persistencia y evolutivo, así como a la adaptabilidad individual. Aunque los mamíferos son un grupo taxonómico bien estudiado, se carece de una evaluación integral de la diversidad genética de mamíferos basada en marcadores moleculares. Examinamos datos publicados de microsatélites de poblaciones de 108 especies de mamíferos para evaluar los patrones de variabilidad genética entre los taxa y masas corporales. Probamos la pérdida de variabilidad en el nivel poblacional preguntando si las poblaciones que experimentaron amenazas demográficas exhibieron menores niveles de diversidad genética. También evaluamos el impacto del sesgo de determinación (una reducción en la variabilidad cuando los iniciadores de microsatélites son transferidos a otras especies) sobre nuestro análisis de diversidad genética. La heterocigosidad no varió con la masa corporal en especies que variaron en tamaño desde musarañas hasta ballenas. Las diferencias entre grupos taxonómicos se notaron en el nivel más alto, entre poblaciones mamíferos marsupiales y placentarios. Sin embargo, en un amplio rango de especies de mamíferos consistentemente documentamos ...

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