Major histocompatibility complex monomorphism and low levels of DNA fingerprinting variability in a reintroduced and rapidly expanding population of beavers.

Abstract

Loss of genetic variation due to population bottlenecks may be a severe threat for the survival of endangered species. Assessment and maintenance of genetic variability are thus crucial for conservation programs related to endangered populations. Scandinavian beavers went through an extensive bottleneck during the last century due to overhunting. In Sweden the species became extirpated but in Norway extinction was avoided by legal protection. Following reintroductions of small numbers of remaining Norwegian animals in 1922-1939, the Swedish population has increased tremendously, now harboring 100,000 animals. We show here that this viable population of beavers possesses extremely low levels of genetic variability at DNA fingerprinting loci and monomorphism at major histocompatibility complex (MHC) class I and class II loci. A similar pattern was also evident among Norwegian beavers but low levels of genetic variabilitywere not a characteristic of the species since Russian conspecifics displayed substantial DNA fingerprinting polymorphism. However, the Russian animals were monomorphic at MHC loci, indicating that the European beaver is exceptional in its low level of MHC variability. The results demonstrate that a conservation program can be successful despite low levels of genetic variation in the founder population.

Structure and amount of genetic variation at minisatellite loci within the subspecies complex of Phoca vitulina (the harbour seal)

“…Evidence that reduced genetic variability does not inevitably impair fitness has been observed for a reintroduced population of beavers (Castor fiber) in Sweden. This population shows high viability despite the very low levels of genetic variation (Ellegren et aL, 1993). However, sound empirical data concerning the importance of genetic processes in nature are still lacking and more research on the genetics of endangered species is needed.…”

Low diversity in the major histocompatibility complex class II DRB1 gene of the Spanish ibex, Capra pyrenaica

“…For example, population bottlenecks and genetic drift have been shown to play a major role in shaping MHC diversity of many wild species (Mikko et al, 1999). Natural populations of muskox (Ovibos moschatus), moose (Alces alces), fallow deer (Dama dama), beaver (Castor fiber), Asiatic lion (Panthera leo persica), cotton-top tamarin (Saguinus oedipus) and the cheetah (Acinonyx jubatus), among others, have shown reduced allelic variation or even monomorphism at the MHC loci, indicating that the presence of high genetic diversity is not a universal feature of this genetic system (O'Brien et al, 1987;Yuhki and O'Brien, 1990;Watkins et al, 1991;Ellegren et al, 1993, Mikko et al, 1999. Studying closely related species with different demographic histories (eg, endangered species that have suffered drastic reductions in population size vs populations that have not gone through genetic bottlenecks) may provide insights into the relative importance of selective and stochastic processes shaping the genetic diversity present at the MHC.…”

Phylogeography of the Malagasy ring-tailed mongoose,Galidia elegans, from mtDNA sequence analysis

“…First, pelage variation and low differentiation within the northern-eastern phylogenetic clade could represent clinal or gradual variation in phenotypic characteristics due to slight environmental differences across continuous forest habitats. Alternatively, G. e. dambrensis could represent a recent geographical expansion of or budding from northern populations of G. e. elegans, and, hence, the establishment of a population that potentially experienced reduced genetic variation due to a founder effect, but retained some of the characteristics from the parent population (Ellegren et al 1993;Hansoon et al 2000).…”

“…Mitochondrial (mt) DNA-based phylogeographic studies have made significant contributions to the field of animal conservation by recovering distinct evolutionary lineages in cryptic species and supporting non-molecular designations of species and subspecies (Ellegren et al 1993;Hansoon et al 2000). There are several characteristics that make mtDNA sequence data particularly useful as markers for studying the extent of population differentiation in a species: they are abundant and readily retrieved from tissue samples, they evolve quickly compared with nuclear markers, and they rarely recombine.…”