Ctenomys magellanicus, Bennett, 1836

Fasanella, Mariana, Bruno, Cecilia, Cardoso, Yamila & Lizarralde, Marta, 2013, Historical demography and spatial genetic structure of the subterranean rodent Ctenomys magellanicus in Tierra del Fuego (Argentina), Zoological Journal of the Linnean Society 169 (3), pp. 697-710 : 707

OF C. MAGELLANICUS

Genetic differentiation studies in fragmented landscapes are useful in the identification of appropriate management units and the determination of independent genetic units ( Shaffer et al., 2000; Cegelski et al., 2003). Evolutionarily significant units (ESUs) are, according to Ryder (1986), population units that merit their own management and have a high conservation priority. By contrast, Moritz (1994) defines an ESU as a group of individuals or populations that present reciprocal monophyly for mitochondrial markers, and significant divergences in the allele frequencies of nuclear loci, attributable to populations, species, or subspecies, and also considering the kind of isolation of such populations. The concept of a management unit (MU; Moritz, 1994) was established for those cases in which reciprocal monophyly was not reached among lineages. This concept was originally defined for populations (or groups of populations) identified by a significant divergence in the allele frequencies of neutral loci (nuclear or mitochondrial), independently of the phylogenetic relationships between the alleles. Therefore, MUs are a group of individuals with a sufficiently low degree of ecological and genetic connectivity, which justifies a separate monitoring and management for each group (subpopulation; Palsbøll, Berubé & Allendorf, 2006).

The concepts discussed here might be applied to the conservation of C. magellanicus . In that sense, it has been suggested that each region (north and south) might be considered an ESU, given their high degree of isolation, the fact that no mitochondrial haplotypes are shared, and that they present different chromosomal number and nuclear differentiation. Therefore, and given that C. magellanicus presents two chromosomal forms, it should be necessary to conserve individuals in both regions. Appropriate MUs could be defined within each ESU for the conservation of these rodents in Tierra del Fuego.

Our results demonstrate that C. magellanicus presents a significant genetic and population structure, with limited genetic flow between the two regions and with differences within each, indicating that the south population is more genetically structured than the north population. Therefore, in the south, each subpopulation might be defined as an MU, given that they present high F st values between them (i.e. great divergence between subpopulations; all divergence values between subpopulations were> 0.3). Moreover, the four subpopulations of the south presented unique haplotypes that were not shared either by subpopulations within the same region or with the north region (i.e. haplotypes 2 and 3 were only found in subpopulation C; haplotype 8 in subpopulation D; haplotype 9 in subpopulation E; and haplotype 4 in subpopulation F). Therefore, if any of these subpopulations disappeared, then these unique haplotypes would also disappear. On the other hand, given that subpopulation B is likely to have arisen from subpopulation A and that in the north the degree of divergence is not high ( Fasanella, 2012a,b), we can considering population A as an MU for the north and thereby reduce conservation efforts.

Future management and conservation plans for this species should contemplate the genetic differentiation aspects presented in this study. If any of the five MUs identified by this study should become extinct, a great part of the genetic pool of the species would be lost.