Intraspecific karyotypic variation in the silverside fish Chirostoma humboldtianum (Atheriniformes: Atherinopsidae)

Abstract

Within its genus, Chirostoma humboldtianum is one of the species with the widest distribution, inhabiting lake and pond environments along the Lerma-Santiago basin in the Mexican Plateau. Although the species is of great ichthyological, economic, and cultural relevance, factors related to human activity such as habitat loss, pollution, overfishing, and introduction of non-native fish have played important roles in the decline and disappearance of populations. With the aim of describing the karyotype of the species, 22 specimens of C. humboldtianum were collected and their chromosomes obtained from gills based on Denton (1973). Here we reveal intraspecific chromosome variation, characterized by five cytotypes found in four studied populations: 1) Las Tazas, Tiacaque dam (2n = 48, FN = 58) with chromosome formula 6m + 4sm + 38t; 2); Villa Victoria dam (2n = 48, FN = 54) 2m + 2sm + 2st + 42t; 3) Tepuxtepec dam, with two cytotypes (2n = 48, FN = 50) 8m + 2sm + 38t and (4n = 96, FN = 116) 8m + 2st + 38t; 4) and San Pedro Lagunillas lagoon (2n = 48, FN = 58) 8m + 2sm + 38t. We observed chromosome variation in the morphology of pairs 1, 2, 4, and 5. Results allow us to suggest that pericentric inversions are the source of intraspecific chromosome variation. Comparative analyses support the hypothesis that the karyotype of the population from Villa Victoria dam represents the primitive form for the species.

Isolation and characterization of microsatellite loci in the Charal de Xochimilco Chirostoma humboldtianum

“…Likewise, decrease in observed heterozygosity suggests nonrandom mating and genetic drift (Loew et al, 2005), due that genetic drift causes random fixation and loss of alleles within population. In contrast, heterozygote excess appears to be due to the presence of hybrids within the sample (Pitchar et al, 2007) as has been earlier suggested for species of the genus (Barriga-Sosa et al, 2001). Translocations among populations and hybridization have been reported for this and others species of the genus (Alaye, 1996;Barriga-Sosa et al, 2001), however, this issues needs to be punctually addressed in further studies.…”

“…In contrast, heterozygote excess appears to be due to the presence of hybrids within the sample (Pitchar et al, 2007) as has been earlier suggested for species of the genus (Barriga-Sosa et al, 2001). Translocations among populations and hybridization have been reported for this and others species of the genus (Alaye, 1996;Barriga-Sosa et al, 2001), however, this issues needs to be punctually addressed in further studies. These 8 microsatellite loci are the first developed for C. humboldtianum and will be useful in investigating population genetics, conservation, and management of this and closely related species.…”