Fishes from the uplands and intermontane basins of Guatemala : revisionary studies and comparative geography. Bulletin of the AMNH ; v. 162, article 5

p. 269-375 : ill., maps ; 26 cm.Includes bibliographical references (p. 374-375)."Continuing studies of the fish fauna of the karst regions of Guatemala along the northern foothills of the sierras have revealed the presence of about two dozen species in thirteen genera and nine families in isolated basins with subterranean outlets. Eleven to thirteen of these species, mostly fishes of the family Poeciliidae, are endemic to the isolated basins; five have been described previously. Among poeciliid fishes, members of the genera Heterandria and Xiphophorus are best represented in the karst regions. Because of similarities in their geography the two genera are reviewed together: nine species of Heterandria are recognized, of which six are new (H. attenuata, H. litoperas, H. obliqua, H. anzuetoi, H. cataractae, H. dirempta); 15 species of Xiphophorus are recognized, of which none is new, although numerous taxa previously recognized as subspecies are treated here as species. Taxonomic decisions concerning recognized species of Xiphophorus are based on a reconsideration of various current species concepts from which it is concluded that the 'biological species' should be rejected as a conceptual tool and the 'subspecies' as a methodological one. Earlier taxonomic accounts of Heterandria and Xiphophorus by the author are found to be unacceptable because they were not rigorously and explicitly based on a search for shared derived characters (synapomorphies). Many of the subgroups recognized in those prior accounts are grade groups based merely on the failure of the included taxa to possess the derived defining characters of other subgroups, therefore suggesting, that they were, in fact defined unacceptably by shared primitive characters (symplesiomorphies). As newly revised on the basis of proposed synapomorphy schemes, and the derivative cladograms of relationship, various members of Heterandria and Xiphophorus are shown to possess a number of cladistic similarities in relation to geography: 1. Mexican and Central American species together form a natural group separated from their sister group to the north by a gap, the southern boundary of which is somewhat to the north of Tampico, Mexico. 2. In Middle America the sister group of a group including many southern Mexican and Central American species is in the region around Tampico. 3. A relatively plesiomorphic species occupies two separate isolated karst basins along the western foothills of the sierras in Guatemala. 4. Less plesiomorphic forms occupy the two southernmost Guatemalan rivers that drain into the Gulf of Honduras as well as Atlantic coastal drainages of Honduras. 5. The most apomorphous sister pair of species includes a widespread species that extends along coastal regions of southern Mexico and parts of the Yucatan Peninsula and a species that is confined to an easterly karst basin. 6. Putative hybrids are present between the distributions of the westerly karst species and the widespread form. A discussion of cladistic theory in relation to hybridization suggests how the cladistic interrelationships of putative parents can resolve whether or not intergradation between species in nature is to be considered secondary (i.e., due to the effects of hybridization). The geographic similarities between Heterandria and Xiphophorus are compared by converting their cladograms of taxa into cladograms of areas. In terms of probability theory, it is concluded that the congruence of their area cladograms at a very high confidence level indicates that the two genera shared, in part, a common history in Middle America"--P. 271