RESUMO
In the present study we evaluate the population structure and potential colonization routes of the silverside Chirostoma humboldtianum through approximate Bayesian computations. Six microsatellite loci were amplified in a total of 288 individuals from six different locations covering the complete geographic distribution of the species. Additionally, two mitochondrial DNA markers, a D loop control region and cytochrome b were amplified in a subset of 107 individuals. The results found with microsatellites allow recovering well-structured populations that have experienced a drastic reduction in the effective population size. On the other hand, mtDNA sequences showed a moderate phylogeographic structure with shared haplotypes between geographic localities and signalsof a slight increase in the effective population size. Finally, the approximate Bayesian computation analysis performed with both datasets suggested a west-to-east colonization route for the species in Central Mexico.
Assuntos
Peixes/fisiologia , Genética Populacional , Filogeografia , Animais , Teorema de Bayes , Citocromos b/genética , DNA Mitocondrial/genética , Peixes/classificação , Peixes/genética , Marcadores Genéticos/genética , Variação Genética , Haplótipos , México , Repetições de Microssatélites/genética , Densidade DemográficaRESUMO
Successful invasive species can overcome or circumvent the potential genetic loss caused by an introduction bottleneck through a rapid population expansion and admixture from multiple introductions. We explore the genetic makeup and the timing of a species introduction to Santa Cruz Island in the Galápagos archipelago. We investigate the presence of processes that can maintain genetic diversity in populations of the broad-nosed weevil Galapaganus howdenae howdenae. Analyses of combined genotypes for 8 microsatellite loci showed evidence of past population size reductions through moment and likelihood-based estimators. No evidence of admixture through multiple introductions was found, but substantial current population sizes (N0 298, 95% credible limits 50-2300), genetic diversity comparable with long-established endemics (Mean number of alleles = 3.875), and lack of genetic structure across the introduced range (F ST = 0.01359) could suggest that foundations are in place for populations to rapidly recover any loss of genetic variability. The time estimates for the introduction into Santa Cruz support an accidental transfer during the colonization period (1832-1959) predating the spurt in human population growth. Our evaluation of the genetic status of G. h. howdenae suggests potential for population growth in addition to our field observations of a concurrent expansion in range and feeding preferences towards protected areas and endemic host plants.