Abstract
BackgroundMarine allopatric speciation involves interplay between intrinsic organismal properties and extrinsic factors. However, the relative contribution of each depends on the taxon under study and its geographic context. Utilizing sea catfishes in the Cathorops mapale species group, this study tests the hypothesis that both reproductive strategies conferring limited dispersal opportunities and an apparent geomorphologic barrier in the Southern Caribbean have promoted speciation in this group from a little studied area of the world.Methodology/Principal FindingsMitochondrial gene sequences were obtained from representatives of the Cathorops mapale species group across its distributional range from Colombia to Venezuela. Morphometric and meristic analyses were also done to assess morphologic variation. Along a ∼2000 km transect, two major lineages, Cathorops sp. and C. mapale, were identified by levels of genetic differentiation, phylogenetic reconstructions, and morphological analyses. The lineages are separated by ∼150 km at the Santa Marta Massif (SMM) in Colombia. The northward displacement of the SMM into the Caribbean in the early Pleistocene altered the geomorphology of the continental margin, ultimately disrupting the natural habitat of C. mapale. The estimated ∼0.86 my divergence of the lineages from a common ancestor coincides with the timing of the SMM displacement at ∼0.78 my.Main Conclusions/SignificanceResults presented here support the hypothesis that organismal properties as well as extrinsic factors lead to diversification of the Cathorops mapale group along the northern coast of South America. While a lack of pelagic larval stages and ecological specialization are forces impacting this process, the identification of the SMM as contributing to allopatric speciation in marine organisms adds to the list of recognized barriers in the Caribbean. Comparative examination of additional Southern Caribbean taxa, particularly those with varying life history traits and dispersal capabilities, will determine the extent by which the SMM has influenced marine phylogeography in the region.
Highlights
Whereas there is tremendous evidence documenting the processes promoting isolation, and speciation, in terrestrial and freshwater organisms, how such mechanisms operate in marine habitats can be puzzling [1,2,3]
Sample size within the C. mapale group consisted of 17 individuals from each lineage collected at 10 locations along its distributional range, with a focus on neighboring localities from either side of the Parque Nacional Natural Tayrona (PNNT) in Santa Marta, Colombia (Fig. 1; Table S1), which represents the distributional breakpoint between the lineages
Defining biogeographic breaks at regional scales may be complex as a result of the varying dispersal capabilities among marine organisms [9,10]
Summary
Whereas there is tremendous evidence documenting the processes promoting isolation, and speciation, in terrestrial and freshwater organisms, how such mechanisms operate in marine habitats can be puzzling [1,2,3]. Allopatric speciation models are difficult to invoke for marine organisms given the limited opportunities for geographic isolation in a continuous environment and an elevated potential for dispersal due to pelagic broadcast spawning [1,4]. Extrinsic factors such as circulation patterns, temperature regimes, and coastal geomorphology may act as barriers restricting gene flow in marine environments [2,5,6]. Studying the genetic structure of additional species with limited dispersal abilities can provide further insights into the mechanisms driving marine allopatric speciation as well as the relative contribution of extrinsic and intrinsic factors to this process. Utilizing sea catfishes in the Cathorops mapale species group, this study tests the hypothesis that both reproductive strategies conferring limited dispersal opportunities and an apparent geomorphologic barrier in the Southern Caribbean have promoted speciation in this group from a little studied area of the world
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