Aims Our aim was to uncover and describe patterns of historical biogeography of the main river basins in central Mexico, based on a secondary Brooks parsimony analysis (BPA) of goodeine fishes, and to understand the processes that determine them with respect to the molecular clock of the goodeines and the geological events that have taken place in the region since the Miocene.
Location The region covered in this study includes central Mexico, mostly the so-called Mesa Central of Mexico, an area argued to be a transitional zone comprising several major river drainages from their headwaters at high elevations along the Transmexican Volcanic Belt to the coast of the Gulf of Mexico and the Pacific Ocean.
Methods Based on a previous phylogenetic hypothesis regarding the Goodeidae, we built a data matrix using additive binary coding. First, we conducted a primary BPA to provide general explanations of the historical biogeography of Central Mexico. As ambiguity was found, a secondary BPA was conducted, and some areas were duplicated in order to explain the reticulated history of the area. Area cladograms were obtained by running a parsimony analysis. Instances of vicariance and non-vicariance processes were described with reference to the cladogram obtained from secondary BPA.
Results The study area was divided into 18 discrete regions. Primary BPA produced nine equally parsimonious cladograms with 129 steps, and a consistency index (CI) of 0.574. A strict consensus cladogram shows low resolution among some areas, but other area relationships are consistent. For secondary BPA, five of the 18 regions were duplicated (LEA, COT, AYU, CUT, PAN); one was triplicated (BAL); and one was quadruplicated (AME), suggesting that the pattern of distribution of species in these areas reflects multiple independent events. These areas correspond with the regions exhibiting the highest levels of diversification and the most complex geological history, and those for which river piracy events or basin connections have been proposed. The secondary BPA produced a single most parsimonious cladogram with 118 steps, and a CI of 0.858. This cladogram shows that none of the duplicated areas are nested together, reinforcing the idea of a reticulated history of the areas and not a single vicariant event.
Main conclusions Although our results are preliminary and we cannot establish this as a general pattern, as the BPA is based on a single-taxon cladogram, resolution obtained in the secondary BPA provides some insights regarding the historical biogeography of this group of fishes in river basins of central Mexico. Secondary BPA indicates that the historical biogeography of central Mexico, as shown by their goodeine freshwater fishes, is complex and is a result of a series of vicariant and non-vicariant events such as post-dispersal speciation and post-speciation dispersal.