Visiting Professor of Biology Simon Coppard recently published an article titled “Phylogeography of the sand dollar genus Encope: implications regarding the Central American Isthmus and rates of molecular evolution” in Nature - Scientific Reports.
The paper presents a fossil calibrated phylogeny of the new world sand dollar genus Encope, based on one nuclear and four mitochondrial genes, calibrated with fossils at multiple nodes.
Coppard’s research shows that present day distributions of Encope are likely the result of multiple range contractions and extinction events. Most species are now endemic to a single region, but one widely distributed species occurs in the Pacific Ocean and another in the Atlantic Ocean. Each of these is composed of morphotypes previously described as separate species, which appear to correspond with ecophenotypic variation.
An important finding of the research shows that the most recent separation between eastern Pacific and Caribbean extant clades occurred at 4.90 Million years ago, which pre-dates the final closure of the Central American Isthmus, but postdates the recently proposed ancient blockage of seaways. This provides another piece of evidence that genetic (and thus water) connections between oceans were strong until the Pliocene.
Coppard also reports that the rate of evolution of mitochondrial genes in Encope has been 10 times slower than in the closely related genera Mellita and Lanthonia. This large difference in rates suggests that splits between eastern Pacific and Caribbean biota, dated on the assumption of a “universal” mitochondrial DNA clock are not valid.