No abstract

Aim Geomorphic evolution of river basins can shape the structure and diversity of aquatic communities, but understanding the biological significance of basin evolution can be challenging in semi-arid regions with ephemeral or endorheic conditions and complex drainage configurations such as the Sierra Madre Occidental (SMO) in North America. In this study, we characterized range-wide patterns of genetic variation in the Mexican stoneroller (Campostoma ornatum) to infer how orogenic and erosional influences on river basin connectivity have given rise to the diverse and largely endemic freshwater communities across the SMO region.Location Twelve drainage basins across northern Mexico and the south-western United States, centred on the SMO.Methods We collected 202 specimens from 98 localities across the range of C. ornatum. We performed phylogenetic analyses of DNA sequences from one mitochondrial (cytochrome b) and one nuclear (intron S7) gene. Phylogenetic trees were estimated for each data set using maximum likelihood and Bayesian inference.Results Phylogenetic analyses consistently resolved a monophyletic C. ornatum composed of multiple evolutionary lineages within two markedly divergent clades that differentiate northern drainages from southern drainages in the SMO region. Within-clade patterns of divergence corresponded to fine-scale geographic structure within and among SMO drainage basins. However, the geographic distribution of evolutionary lineages within the northern and southern clades did not always correspond to the geographic configuration of drainage basins. Some subclades encompassed multiple drainages, and individuals from a single drainage were sometimes recovered in multiple subclades. Main conclusions Our findings indicate that a common ancestor of MexicanCampostoma is likely to have entered north-west Mexico through an ancient Rio Grande system that extended as far south as the Rio Nazas and Rio Aguanaval. The geographic orientation of the two strongly divergent clades recovered within C. ornatum provides evidence of long-standing isolation of southern basins from northern basins within the ancestral Rio Grande system, possibly due to the combined influence of tectonic events and increasing regional aridity. Geographic patterns of genetic variation also provide evidence of range expansion from Atlantic to Pacific drainages due to drainage evolution and river capture events, as well as further inter-basin exchange via more recent headwater capture events, hydrological connections and possible anthropogenic introductions.

This study represents a thorough analysis of Codoma, a monotypic genus endemic to north‐western Mexico. A previous morphological analysis of the species concluded that there exists several morphological groups in Codoma ornata, suggesting diversity in Codoma could be underestimated. No studies have examined the genetic diversity in Codoma ornata to test this hypothesis and identify independent lineages. We present a phylogeographic analysis using one mitochondrial and two nuclear genes, and specimens from across nine major drainages in both the Chihuahuan Desert and the Sierra Madre Occidental of western Mexico. All genes and analyses recovered populations of Codoma in a well‐supported clade and sister to Tampichthys, and this clade sister to Cyprinella. Analyses of both mitochondrial and nuclear genes indicated Codoma is not monotypic and recover more diversity in the genus than currently recognized. The four (mitochondrial) and five (nuclear) genetically distinct lineages are consistent with those groups outlined in the prior morphological study of the genus. Composition and distribution of these major lineages is also consistent with prior biogeographic hypothesis for other fishes in the region, supporting an ancestral Rio Grande system extending south towards central Mexico. Fragmentation of this paleosystem was followed by allopatric speciation in the Chihuahuan Desert. These results suggest a scenario of long‐term isolation in four major regions (upper Conchos, lower Conchos, Nazas, upper Mezquital). Resolution of the diversity and biogeography of these lineages has many implications for various biological disciplines, especially for evolutionary and conservation studies.

In this paper we analyse the degree of concordance in species richness and taxonomic distinctness (diversity) patterns among different freshwater taxonomic groups in order to test three long held patterns described in Mexican freshwater biogeography: 1. The aquatic biota of Mexico includes two distinct faunas, a rich Neotropical component in the south and a south-eastern region and a less rich Nearctic component towards central and northern latitudes of the country. 2. A hotspot of species richness and diversity has been recorded in the Usumacinta, including the Yucatan Peninsula. 3. The presence of two distinct biotas in Mexico, an eastern one distributed along the Gulf of Mexico slope, and a western one associated to the Pacific versant. We use species richness and taxonomic distinctness to explore patterns of diversity and how these patterns change between zoogeographical regions. This paper points out a clear separation between Neotropical and Nearctic drainage basins but also between eastern (Gulf of Mexico) and western (Pacific) drainage basins. Present data gives additional empirical support from freshwater biota for three long held beliefs regarding distributional patterns of the Mexican biota. The neotropical basins of Mexico are generally host to a richest and more diversified fauna, that includes more families, genera and species, compared to the less rich and less diverse fauna in the nearctic basins.

One of the problems that arose from the meetings of the Barcode in Mexico project was the urgency of having a method in which Mexican authorities could trust for detecting shark finning. This study examined DNA barcoding as a method to identify 14 dried shark fins confiscated by the Mexican Government in two exportation shipments in Mazatlán and Manzanillo ports. Fins were DNA barcoded using the COI mitochondrial gene and provided matching sequences of six species: Prionace glauca, Carcharhinus falciformis, Carcharhinus limbatus, Alopias pelagicus, Mustelus henlei and Rhizoprionodon longurio. There is no information on DNA barcoding sharkfin trade in the Mexican Pacific and this is the first group effort with Mexican Government Agencies for the conservation of sharks.