Morphological and genetic evolution in eastern populations of the Macrhybopsis aestivalis complex (Cypriniformes: Cyprinidae), with the descriptions of four new species.

For many years the North American cyprinid fish Macrhybopsis aestivalis (common name: Speckled Chub) was regarded as a single widespread and morphologically variable species, occurring in rivers throughout much of the Mississippi Valley and geographically adjacent eastern Gulf slope drainages, west to the Rio Grande basin in Texas, New Mexico, and Mexico. Eisenhour (1997) completed a morphological study of western populations of the Speckled Chub, the results of which appeared thereafter in published form (Eisenhour 1999, 2004). He demonstrated the existence of five valid species west of the Mississippi River (aestivalis, marconis, australis, tetranema, hyostoma), of which the name aestivalis was shown to be restricted to the population occurring in the Rio Grande and the geographically adjacent Rio San Fernando system, in northeastern Mexico. Eisenhour (2004) considered populations throughout the middle Mississippi Valley and its major tributaries to be a single morphologically variable species (hyostoma), and he also indicated that populations of Macrhybopsis from eastern Gulf slope drainages may represent a complex of species. Genetic confirmation of Eisenhour's conclusions regarding western species appeared in the publication by Underwood et al. (2003), who also showed that western populations of M. hyostoma, as presently recognized, are genetically much more complex than previously considered.     Meanwhile, the present authors were involved in a companion study of eastern populations of Macrhybopsis, for which a genetic summary of the eastern Gulf coast species was published by Mayden & Powers (2004). Based on their findings, four species were recognized from southeastern drainages (identified as species A-D), although no formal taxonomic descriptions were included. Their genetic data, in combination with meristic, morphometric and other morphological data presented herein, form the basis for a revised classification of eastern Macrhybopsis populations, including formal descriptions of the four new species from eastern Gulf coast drainages.

Genetic Structure of Pacific Trout at the Extreme Southern End of Their Native Range.

Salmonid fishes are cold water piscivores with a native distribution spanning nearly the entire temperate and subarctic northern hemisphere. Trout in the genus Oncorhynchus are the most widespread salmonid fishes and are among the most important fish species in the world, due to their extensive use in aquaculture and valuable fisheries. Trout that inhabit northwestern Mexico are the southernmost native salmonid populations in the world, and the least studied in North America. They are unfortunately also facing threats to their continued existence. Previous work has described one endemic species, the Mexican golden trout (O. chrysogaster), and one endemic subspecies, Nelson's trout (O. mykiss nelsoni), in Mexico, but previous work indicated that there is vastly more biodiversity in this group than formally described. Here we conducted a comprehensive genetic analysis of this important group of fishes using novel genetic markers and techniques to elucidate the biodiversity of trout inhabiting northwestern Mexico, examine genetic population structure of Mexican trout and their relationships to other species of Pacific trout, and measure introgression from non-native hatchery rainbow trout. We confirmed substantial genetic diversity and extremely strong genetic differentiation present in the Mexican trout complex, not only between basins but also between some locations within basins, with at least four species-level taxa present. We also revealed significant divergence between Mexican trout and other trout species and found that introgression from non-native rainbow trout is present but limited, and that the genetic integrity of native trout is still maintained in most locations. This information will help to guide effective conservation strategies for this important group of fishes.

Phylogeography of Pteronotropis signipinnis, P. euryzonus, and the P. hypselopterus Complex (Teleostei: Cypriniformes), with Comments on Diversity and History of the Gulf and Atlantic Coastal Streams.

The cyprinid genus Pteronotropis is endemic to southeastern Gulf of Mexico and Atlantic Ocean of North America. Never before has the genus been demonstrated to be monophyletic. We investigate both the phylogenetic relationships and the phylogeography of some species in the genus using mitochondrial ND2 sequences. In no analysis is the genus resolved as monophyletic if Notropis harperi is not included in the genus. Biogeographic and phylogeographic evaluations are conducted with Pteronotropis, including P. signipinnis, P. euryzonus, and the P. hypselopterus complex. Patterns of relationships and population genetic analyses support divergences within multiple clades both at the species level and within species that are tied to abiotic changes in the region. Replicated patterns across clades are observed, as well as patterns previously found in other taxa. Pteronotropis hypselopterus is likely not a natural grouping as populations from some drainages form clades more closely related to other species of the genus. The general patterns of relationships indicate likely cryptic species not currently recognized. Finally, the patterns of species relationships and clades and population structuring within species serve as another example of replicated divergences in the biodiversity east and west of the Mobile Bay.

Phylogenetic relationships of North American western chubs of the genus Gila (Cyprinidae, Teleostei), with emphasis on southern species.

Species of Gila comprise a heterogeneous and widespread group of freshwater fishes inhabiting drainage systems of western North America. The classification of species of Gila and relatives has been complicated and sometimes compromised by differences in body shapes, sizes, habitats, variable taxonomic placement by early taxonomists, and instances of hypothesized hybridization. While most attention on Gila has focused on hybridization in USA, little is actually know about their intra and intergeneric relationships. We present a molecular phylogeny using 173 specimens for all 19 recognized species of Gila, covering their entire distributions in 31 major drainages. Using one mitochondrial and three nuclear genes, specimens of Gila were analyzed with 10 other North American genera that comprise the Revised Western Clade. All analyses identified most species of Gila in a lineage that always included the monotypic genera Moapa and Acrocheilus, and we recommend the synonymy of both genera with Gila. The composition of this Gila lineage varied depending on the genes analyzed. Within the Gila lineage, similar morphotypes (forms adapted to fast currents vs. general forms) were not resolved as closest relatives. Analyses of mitochondrial DNA resolved all species of Gila from Mexico in reciprocally monophyletic clades except G. modesta. Most species of Gila in the USA were nested in 3 major clades, potentially indicating some level of historic or contemporary interspecific hybridization. Herein, we redefine the ranges for all species of Gila in Mexico. Relevant taxonomic and conservation implications stemming from the results are discussed.

Phylogeny, diversity, and species delimitation of the North American Round-Nosed Minnows (Teleostei: Dionda), as inferred from mitochondrial and nuclear DNA sequences.

Accurate delimitation of species is a critical first step in protecting biodiversity. Detection of distinct species is especially important for groups of organisms that inhabit sensitive environments subject to recent degradation, such as creeks, springs, and rivers in arid or semi-desert regions. The genus Dionda currently includes six recognized and described species of minnows that live in clear springs and spring-fed creeks of Texas, New Mexico (USA), and northern Mexico, but the boundaries, delimitation, and characterization of species in this genus have not been examined rigorously. The habitats of some of the species in this genus are rapidly deteriorating, and many local populations of Dionda have been extirpated. Considering the increasing concerns over degradation of their habitat, and pending a more detailed morphological revision of the genus, we undertook a molecular survey based on four DNA regions to examine variation over the range of the genus, test species boundaries, and infer phylogenetic relationships within Dionda. Based on analyses of two mitochondrial (cytb and D-loop) and two nuclear (Rag1 and S7) DNA regions from specimens collected throughout the range of Dionda, we identified 12 distinct species in the genus. Formerly synonymized names are available for two of these species, and four other species remain undescribed. We also redefine the known range of six species. The limited distribution of several of the species, coupled with widespread habitat degradation, suggests that many of the species in this genus should be targets for conservation and recovery efforts.

Molecular evolution of southern North American Cyprinidae (Actinopterygii), with the description of the new genus Tampichthys from central Mexico.

Most of the recognized species of the genus Dionda inhabit drainages of the Gulf of Mexico from central Mexico to central Texas, USA, and have been considered a monophyletic group based on morphological, osteological, and allozyme investigations. Phylogenetic relationships of 15 species of Dionda and 34 species from closely related genera were inferred from one mitochondrial (cytb) and three nuclear gene sequences (S7, Rhodopsin, Rag1) totaling 4487 nucleotides. Separate analyses of all four genes yield congruent phylogenies; however the 15 putative species of Dionda evaluated were never recovered as a monophyletic group when species from nine related genera were included in the analyses. Among the ingroup taxa, one well-supported and highly divergent clade is consistently recognized and consists of six recognized and three undescribed northern species currently recognized in the genus Dionda. These nine species inhabit present or past tributaries of the Rio Grande basin of northern Mexico and southern USA, and were recovered as a basal clade in all analyses. Another large, also strongly supported clade, consisting of seven genera, include five southern recognized species currently in the genus Dionda, forming the sister group to the Codoma clade. These five species comprise the "Southern Dionda clade" and inhabit headwaters of the Pánuco-Tamesí drainage and some adjacent coastal rivers in the Tampico Embayment. The consistent and repeated identification of eight different clades recovered in most of the separate gene analyses strongly supports a division of the non-natural genus Dionda. A new genus, Tampichthys, is proposed for the clade of species endemic to east-central Mexico and formerly in Dionda. Tampichthys and the putative monotypic genus Codoma are more related to Mexican species of the genera Cyprinella and Notropis than to other species referred to Dionda sensu stricto.