Speciation and Gene Flow in the Open Ocean: the Phylogeography of an Oceanic Copepod Family

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

This project will develop a model system for the study of speciation in marine holozooplankton populations, to examine the biogeographic and ecological factors important during speciation in the open ocean. The calanoid copepod family Eucalanidae is oceanic in distribution, and component species are likely to have evolved entirely in the open ocean. The 23 extant species in this family will serve as our model system. The research will consist of two parts. First, a species level molecular phylogeny based on one mitochondrial (16s rDNA) and one nuclear (Elongation Factor-1-a) gene locus will be developed, including all known species within the family. Sister species pairs will be identified based on the phylogeny. Three central hypotheses are being tested regarding the comparative biogeographic distributions, morphological characteristics, and genetic diversity of these sister species pairs. Results will elucidate patterns in the extent of biogeographic range overlap, post-speciational range evolution, divergence in reproductive morphological characteristics, divergence in ecological characteristics, and differences in historical population sizes. Such results will provide insight into those factors that play a role in the speciation process. The second, intraspecific, part of the study will examine geographic distributions of genetic lineages in circumglobal Eucalanus hyalinus s.l. and Rhincalanus nasutus s.l. This component will identify oceanographic features that create boundaries to gene flow between conspecific populations on a global scale. Intraspecific haplotype networks will be generated based on the mitochondrial gene locus Cytochrome Oxidase I (COI). The goal of this second portion of the research is to understand how populations undergo the initial differentiation process, a step critical to speciation models. Initial results demonstrate the tremendous potential value of the proposed work. At least three previously cryptic species have been uncovered within the family, and current understanding of the biogeographic distributions of existing species has been modified. Half of the DNA sequencing for the mtDNA molecular phylogeny has been completed, and most of the specimens required for this work have already been collected. The sequences resulting from this research will be deposited in GenBank, and thus disseminated broadly to all interested parties. The proposed research is the doctoral study. In addition to answering the specific questions posed, this proposal will contribute to the training of a new generation of oceanographers with abilities in systematics and modern molecular techniques.