Phylogenetic relationships of members of the subfamily Poeciliinae (Cyprinodontiformes) are investigated to test alternate hypotheses of diversification resulting from the assembly of the Central America and the Caribbean from the Cretaceous period onwards. We use 4333 aligned base pairs of mitochondrial DNA and 1549 aligned base pairs of nuclear DNA from 55 samples representing 48 ingroup and seven outgroup species to test this hypothesis. Mitochondrial genes analyzed include those encoding the 12S and 16S ribosomal RNAs; transfer RNAs coding for valine, leucine, isoleucine, glutamine, methionine, tryptophan, alanine, asparagine, cysteine and tyrosine; and complete cytochrome b and NADH dehydrogenase subunit I and II; nuclear gene analyzed included the third exon of the recombination activation gene 1 (RAG1). Analyses of combined mtDNA and nuclear DNA data sets result in a well-supported phylogenetic hypothesis. This hypothesis is in conflict with the classical taxonomic assignment of genera into tribes and phylogenetic hypotheses based on the taxonomy; however, the molecular hypothesis defines nine clades that are geographically restricted and consistent with the geological evolution of Central America and the Caribbean. Our analyses support multiple colonization events of Middle America followed by a mix of vicariance and dispersal events.

Species of the genus Xiphophorus (swordtails and platies) are of great interest for the study of evolution of sexually selected traits like the sword, which is an elongation of ventral fin rays of the male caudal fin, that has evolved in several species within this genus. The detection of 10 microsatellites within the genus Xiphophorus will enable studies about the correlation of this trait with sexual reproductive success of males possessing swords of different lengths. These microsatellites will also be useful in determining population structure and enable paternity analysis in these species, where sperm storage is widespread. The 22 species of platies and swordtails belong to the genus Xiphophorus . This genus is one of the 22 genera composing the family Poeciliidae, a widespread and diverse group of small-sized fishes that are endemic to the New World. Poeciliids have internal fertilization and bear live young (except for one species, which is a facultative livebearer), hence their common name, the livebearers. Xiphophorids are model organisms in several biological subdisciplines, such as research on sexual selection, particularly mating preference (Basolo 1990(Basolo , 1991(Basolo , 1995, and cancer research (Schartl et al . 1999). Phylogenetic studies have largely resolved evolutionary relationships among species within Xiphophorus (Meyer et al . 1994;Meyer 1997), but no genetic work at the population level has been conducted. KeywordsIn this note we present 10 microsatellite loci that will aid further genetic studies of these fish and their relatives. Up to now, there is no information concerning the population structure or mating systems in Xiphophorus . Female choice experiments demonstrate that females spend more time in courtship behaviour with males possessing longer swords (Basolo 1995). Moreover, platy females seem to prefer heterospecific males with swords over their conspecific swordless males (Basolo 1990). Paternity analysis using microsatellites could resolve remaining questions about the fitness of swords in males. Microsatellites can also provide information about population structure, variability in natural populations and even about mating systems. Microsatellite studies offer many opportunities for future behavioural and ecological studies of species of the genus Xiphophorus .Genomic DNA from Xiphophorus montezumae was used to screen for microsatellites. DNA from a single fish was extracted, following a general phenol-chloroform extraction protocol and stored in ddH 2 O. DNA was digested with the restriction enzyme Sau3AI and fragments of a size of 300-1000 bp were ligated into the bluescript vector pBS (Stratagene), and the vectors transfected into electrocompetent bacteria. Microsatellites were screened with dioxygenin-labeled di-/tri-and tetranucleotide-repeats. Plasmids from positive clones were extracted with a plasmid extraction kit (Quiagen), and the inserts were sequenced with universal primers M13F and M13R.The primers for the amplification of Xiphophorus DNA were designe...