The Role of Historical Barriers in the Diversification Processes in Open Vegetation Formations during the Miocene/Pliocene Using an Ancient Rodent Lineage as a Model

Abstract

The Neotropics harbors a high diversity of species and several hypotheses have been proposed to account for this pattern. However, while species of forested domains are frequently studied, less is known of species from open vegetation formations occupying, altogether, a larger area than the Amazon Forest. Here we evaluate the role of historical barriers and the riverine hypothesis in the speciation patterns of small mammals by analyzing an ancient rodent lineage (Thrichomys, Hystricomorpha). Phylogenetic and biogeographic analyses were carried out with mitochondrial and nuclear DNA markers to analyze the evolutionary relationships between Thrichomys lineages occurring in dry domains along both banks of the Rio São Francisco. This river is one of the longest of South America whose course and water flow have been modified by inland tectonic activities and climate changes. Molecular data showed a higher number of lineages than previously described. The T. inermis species complex with 2n = 26, FN = 48 was observed in both banks of the river showing a paraphyletic arrangement, suggesting that river crossing had occurred, from east to west. A similar pattern was also observed for the T. apereoides complex. Thrichomys speciation occurred in Late Miocene when the river followed a different course. The current geographic distribution of Thrichomys species and their phylogenetic relationships suggested the existence of frequent past connections between both banks in the middle section of the Rio São Francisco. The extensive palaeodune region found in this area has been identified as a centre of endemism of several vertebrate species and is likely to be a center of Thrichomys diversification.

Geographic variation in skull shape of the water rat Scapteromys tumidus (Cricetidae, Sigmodontinae): isolation-by-distance plus environmental and geographic barrier effects?

“…Geographic barriers are known to play an essential role in rodent genetic and morphological differentiation (Colombi et al 2010, Nascimento et al 2013). The populations analyzed in the present study are distributed in areas that are part of Precambrian to Holocene geological formations (Bossi and Navarro 1988, Philipp et al 2000, Tomazelli and Villwock 2000.…”

Seasonally flooded stepping stones: emerging diversity of small mammal assemblage in the Amazonia-Cerrado ecotone, central Brazil

“…Although a growing number of studies have been focused on the small mammal fauna in Cerrado (for review see Carmignotto et al 2012), further studies should be focused on understanding the role of geographic barriers and/or the contribution of different floristic structures within the Cerrado biome to the differentiation of small mammal assemblages (e.g. Nascimento et al 2011Nascimento et al , 2013.…”

Late Pleistocene echimyid rodents (Rodentia, Hystricognathi) from northern Brazil

“…Currently, T. pachyurus is distributed to the east and south of the studied area, while T. aff. inermis is found to the north (Nascimento et al 2013). Fossils of Thrichomys have been found in the intertropical region of Brazil (Table I) Figure 3); this feature differentiates it from Thrichomys, which in a similar wear stage has the metafossette more reduced or absent.…”