Abstract
Geographic barriers and elevational gradients have long been recognized as important in species diversification. Here, we illustrate an example where both mechanisms have shaped the genetic structure of the Neotropical rainfrog, Pristimantis ornatissimus, which has also resulted in speciation. This species was thought to be a single evolutionary lineage distributed throughout the Ecuadorian Chocó and the adjacent foothills of the Andes. Based on recent sampling of P. ornatissimus sensu lato, we provide molecular and morphological evidence that support the validity of a new species, which we name Pristimantis ecuadorensis sp. nov. The sister species are elevational replacements of each other; the distribution of Pristimantis ornatissimus sensu stricto is limited to the Ecuadorian Chocó ecoregion (< 1100 m), whereas the new species has only been found at Andean localities between 1450–1480 m. Given the results of the Multiple Matrix Regression with Randomization analysis, the genetic difference between P. ecuadorensis and P. ornatissimus is not explained by geographic distance nor environment, although environmental variables at a finer scale need to be tested. Therefore this speciation event might be the byproduct of stochastic historic extinction of connected populations or biogeographic events caused by barriers to dispersal such as rivers. Within P. ornatissimus sensu stricto, morphological patterns and genetic structure seem to be related to geographic isolation (e.g., rivers). Finally, we provide an updated phylogeny for the genus, including the new species, as well as other Ecuadorian Pristimantis.
Highlights
Species diversification is important to understanding the great diversity of organisms in nature
Further morphological and molecular analyses indicate that highland populations represent a new species that we describe and that variation observed among lowland populations seem to be the result of different degrees of geographic isolation
Independent analyses of the three genes (Fig 4) show that the species currently recognized as Pristimantis ornatissimus is composed of two clearly differentiated lineages, one from lowland localities (< 1100 m: Reserva Otokiki, Reserva Canande, Milpe, Reserva de Biodiversidad Mashpi, La Florida, La Mana), which corresponds to P. ornatissimus Despax, 1991, sensu stricto, and the other from highlands (> 1400 m: Las Pampas) that we describe as a new species below
Summary
Species diversification is important to understanding the great diversity of organisms in nature. The mechanisms by which this diversity has arisen has been a long-standing question since the seminal works of Darwin and Wallace [1,2,3]. There are numerous hypotheses to explain the factors involved in speciation, and for the majority of species, the most likely scenario includes the geographic separation of an ancestral population into two or more lineages, resulting in allopatric speciation [4,5,6]. When sister species occur parapatrically along elevational gradients, speciation has been hypothesized to include the following steps: (1) an ancestral population colonizes a new environment, (2) gene flow becomes restricted between populations, and (3) separate lineages evolve and are maintained [15]. Ecological speciation may occur across an environmental gradient, in which divergent ecological selection results in reproductive isolation, for example through pleiotropy or close genetic linkage between traits involved in local adaptation and mate choice [16,17]
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