RESUMO
Carlos P. Muñoz-Ramírez, Evelyn Habit, Peter J. Unmack, Jerald B. Johnson, and Pedro F. Victoriano (2016) Despite the fundamental importance of the family Diplomystidae for understanding catfish evolution, its species are poorly known and most of them endangered. Diplomystes camposensis, restricted to a single river basin in southern Chile, is perhaps the most vulnerable species due to its small geographic range and imminent habitat alterations by dam constructions. Using mitochondrial DNA sequences, we describe the genetic diversity across its entire distribution in the Valdivia basin and test hypotheses related to the impact of glacial cycles on the genetic diversity and structure. We found that Diplomystes camposensis has low genetic diversity and structure across the entire Valdivia basin along with a pattern of decreasing nucleotide and haplotype diversity from West to East. Demographic analyses showed evidence of population expansion in agreement with the glaciated history of the basin. Analyses of population structure showed no evidence of population subdivision. However, coalescent analyses indicated that very recent subdivision (in the last 50 years) cannot be ruled out. Low genetic diversity and genetic structure across the entire basin suggest that the species might be highly vulnerable to habitat fragmentation. Thus, the imminent construction of hydropower dams represents a serious threat to its conservation. Our results suggest that the low genetic diversity can be the product of the glaciated history of the basin, although the influence of species-specific biological traits may also add to this condition. Despite the overall low genetic diversity, higher diversity was found in the central portion of the basin suggesting high priority of conservation for this area as it might be used as a source population in case translocations are required among potential management plans.
RESUMO
Southern South America provides a set of unusual geographic features that make it particularly interesting for studying phylogeography. The Andes Mountains run along a north-to-south axis and act as a barrier to gene flow for much of the biota of this region, with southern portions experiencing extensive historical glaciation. Geological data reveal a series of drainage reversals, shifting from Pacific Ocean outlets to Atlantic Ocean outlets because of glacier formation that dammed and reversed rivers. Once glaciers melted around 13 000 years ago, drainages returned to the Pacific Ocean. This geologic history predicts that aquatic organisms in Pacific rivers should have their closest relationships to their counterparts in Atlantic rivers immediately to their east. We tested this prediction in the trichomycterid catfish Hatcheria macraei from 38 locations using the mitochondrial cytochrome b gene. Our results show that most populations found in Pacific rivers were closely related to fish found in the adjacent Atlantic draining Río Chubut. Surprisingly, one documented drainage reversal (from Río Deseado into Río Baker) did not result in movement of H. macraei. Overall, we found the lowest levels of genetic structure between most Pacific rivers that are adjacent to the Atlantic draining Río Chubut. We also found low levels of population structuring among three of four contemporary river basins that drain to the Atlantic Ocean. Our findings suggest that drainage basin boundaries have historically not played an important long-term role in structuring between nine of 11 drainages, an unusual finding in freshwater biogeography.
Assuntos
Peixes-Gato/genética , Genética Populacional , Fenômenos Geológicos , Filogeografia , Animais , Argentina , Oceano Atlântico , Peixes-Gato/classificação , Chile , DNA Mitocondrial/genética , Fluxo Gênico , Variação Genética , Haplótipos , Dados de Sequência Molecular , Oceano Pacífico , Rios , Análise de Sequência de DNARESUMO
BACKGROUND: Understanding how freshwater assemblages have been formed and maintained is a fundamental goal in evolutionary and ecological disciplines. Here we use a historical approach to test the hypothesis of codivergence in three clades of the Chilean freshwater species assemblage. Molecular studies of freshwater crabs (Aegla: Aeglidae: Anomura) and catfish (Trichomycterus arealatus: Trichomycteridae: Teleostei) exhibited similar levels of genetic divergences of mitochondrial lineages between species of crabs and phylogroups of the catfish, suggesting a shared evolutionary history among the three clades in this species assemblage. RESULTS: A phylogeny was constructed for Trichomycterus areolatus under the following best-fit molecular models of evolution GTR + I + R, HKY + I, and HKY for cytochrome b, growth hormone, and rag 1 respectively. A GTR + I + R model provided the best fit for both 28S and mitochondrial loci and was used to construct both Aegla phylogenies. Three different diversification models were observed and the three groups arose during different time periods, from 2.25 to 5.05 million years ago (Ma). Cladogenesis within Trichomycterus areolatus was initiated roughly 2.25 Ma (Late Pliocene-Early Pleistocene) some 1.7-2.8 million years after the basal divergences observed in both Aegla clades. These results reject the hypothesis of codivergence. CONCLUSIONS: The similar genetic distances between terminal sister-lineages observed in these select taxa from the freshwater Chilean species assemblage were formed by different processes occurring over the last ~5.0 Ma. Dramatic changes in historic sea levels documented in the region appear to have independently shaped the evolutionary history of each group. Our study illustrates the important role that history plays in shaping a species assemblage and argues against assuming similar patterns equal a shared evolutionary history.