PHYLOGENETIC HISTORIES OF CENTRAL AMERICAN TURRITELLINE GASTROPODS

Despite the abundance and usefulness of turritellines (family Turritellidae, subfamily Turritellinae), a diverse group of marine snails in the fossil record, placing turritelline species into a phylogenetic context is difficult due to the lack of morphological (shell) characters available. In this study we construct evolutionary phylogenies of fossil and recent turritellines from the Eastern Pacific and Western Atlantic oceans in the Central American Isthmus region. Outline-based methods, which generate continuous characters using eigenshape analysis, were devised to increase resolution in conjunction with traditional, discrete characters. While the eigenshape analysis improves phylogenetic resolution by decreasing polytomies, incongruence was found to be high between our morphological and molecular datasets. Morphological data consisted of a total evidence matrix of 7 discrete and 19 continuous characters; molecular data was derived from concatenated sequences of mtDNA 16S and COI genes. We measured similarity between trees using several methods. The Robinson-Foulds metric (RF) was 0.75 for morphological versus molecular analysis in extant species, and the Incongruence Length Difference (ILD) test was measured to be p = 0.0049 for the extant dataset and p = 0.0069 for the dataset including fossils, indicating that the molecular and morphological datasets are significantly different. Adding fossils to the extant morphological dataset resulted in lower but not significantly different (t-Test, p = 0.86) CI and RI scores. All fossils fell into one stem group in the total evidence tree, which also identifies two geminate species pairs. Placement of one geminate pair, sister to the stem group, indicates that at least two major divergences occurred. These results highlight the complex nature of transisthmian evolution and agree with findings in other taxa that resolving phylogenetic history may not be straightforward.