Historical biogeography reveals new independent evolutionary lineages in the Pantosteus plebeius-nebuliferus species-group (Actinopterygii: Catostomidae).

BACKGROUND: The Pantosteus plebeius-nebuliferus species-group is a group of freshwater fishes distributed in endo- and exorheic drainage basins in the Mexican Sierra Madre Occidental mountain range system and central North Mexico. The geological history of this region is considered an important factor in explaining the evolutionary history of low vagility animals like freshwaters fishes. The aim of this study was to examine the phylogenetic relationships and describe the evolutionary history of the species-group. We hypothesized that the genetic structure and distribution of the main clades of Pantosteus plebeius-nebuliferus are associated with the geological history of Northern Mexico. To this end, we obtained DNA sequences of mitochondrial and nuclear genes and performed phylogenetic and phylogeographic analyses. Divergence time estimation and ancestral area reconstruction were also carried out to propose a biogeographical hypothesis, and species boundaries within the species-group were also tested. RESULTS: We identified four clades within the Pantosteus plebeius-nebuliferus species-group in both markers. Divergence ranged from 5.9% to 9.2% for cytb and 0.1% to 0.9% for GHI. We observed significant genetic structure and no shared haplotypes between clades. We estimated that the clades diverged during the last 5.1 Myr, with a biogeographic scenario suggesting eight vicariant and four dispersal events through the historic range of the species-group. We found that the best species-delimitation model is when four species are assumed, which correspond to the main clades. We identified nine evolutionary significance units (ESUs), pertinent to the conservation of the group, each representing populations present in distinct drainage basins. CONCLUSIONS: The evolutionary history of the Pantosteus plebeius-nebuliferus species-group is characterized by vicariant post-dispersal processes, linked to geological changes in the Sierra Madre Occidental and central Northern Mexico since the Pliocene. This is congruent with biogeographic patterns described for other co-distributed fish species. We propose a new phylogenetic hypothesis for the species-group, clarifying the taxonomy of this evolutionarily complex group. Our results suggest that the species-group consists of at least four clades with independent evolutionary histories, two of which may represent new undescribed species. Our identification of ESUs provides a basis upon which conservation measures can be developed for the species-group.

Evolutionary History of the Live-Bearing Endemic Allotoca diazi Species Complex (Actinopterygii, Goodeinae): Evidence of Founder Effect Events in the Mexican Pre-Hispanic Period.

The evolutionary history of Mexican ichthyofauna has been strongly linked to natural events, and the impact of pre-Hispanic cultures is little known. The live-bearing fish species Allotoca diazi, Allotoca meeki and Allotoca catarinae occur in areas of biological, cultural and economic importance in central Mexico: Pátzcuaro basin, Zirahuén basin, and the Cupatitzio River, respectively. The species are closely related genetically and morphologically, and hypotheses have attempted to explain their systematics and biogeography. Mitochondrial DNA and microsatellite markers were used to investigate the evolutionary history of the complex. The species complex shows minimal genetic differentiation. The separation of A. diazi and A. meeki was dated to 400-7000 years ago, explained by geological and climate events. A bottleneck and reduction of genetic diversity in Allotoca diazi was detected, attributed to recent climate fluctuations and anthropogenic activity. The isolation of A. catarinae occurred ~1900 years ago. No geological events are documented in the area during this period, but the date is contemporary with P'urhépecha culture settlements. This founder effect represents the first evidence of fish species translocation by a pre-Hispanic culture of Mexico. The response of the complex to climate fluctuation, geological changes and human activity in the past and the future according to the ecological niches predictions indicates areas of vulnerability and important information for conservation. The new genetic information showed that the Allotoca diazi complex consist of two genetic groups with an incomplete lineage sorting pattern: Pátzcuaro and Zirahuén lakes, and an introduced population in the Cupatitzio River.