The role of warm tropical waters in the Eastern Pacific: What has been the historical pattern of gene flow in Pollicipes elegans

The latitudinal gradient in species diversity suggests that tropical regions may act as a diversity engine that supplies the planet with novel animal and plant diversity. Despite that great advancement has been made identifying the mechanisms promoting speciation, not enough effort has been place on evaluating the role of latitudinal thermal gradients in the process of genetic differentiation and adaptation on marine species. I investigated the genetic variation in one mitochondrial and two nuclear genes of the Eastern Pacific barnacle P. elegans to evaluate the role of warm tropical waters in population connectivity of tropical and extra-tropical regions. Results based on the mitochondrial gene supported two main haplogroups with a strong break at North of El Salvador. Extra-tropical populations were highly differentiated at the mitochondrial gene (ø_ST=0.594), and moderate and low differentiated by the nuclear genes (ø_ST=0.189 and 0.043). Coalescent analyses based on the isolation with migration model shown that tropical effective population sizes were bigger than extra-tropical ones, supporting a tropical origin of the extra-tropical populations. Time since divergence indicates that all populations originated during the Pleistocene (time since divergence =~155,594 yr.), when sea water temperature was 4 to 5 degrees cooler than today. Warm tropical waters had a major influence shaping the genetic structure of P. elegans isolating populations. Additional studies in tropical and extra-tropical marine species are necessary to better understand the mechanisms of speciation and thermal adaptation, information that is crucial to predict the effects of global warming in marine species.