The classification of sympatric forms of bottlenose dolphins (genus Tursiops) in Chinese waters

Abstract

<p>The classification within bottlenose dolphins (genus: Tursiops ) is controversial. The prevalent view is that of a single species. To test this hypothesis, osteological, molecular and external morphological data from two sympatric forms of bottlenose dolphins in Chinese waters were examined. Multivariate cluster analysis of meristic osteological characters identified two distinct groups that were consistent with the field classifications of the specimens into two forms. The main contributor to the separation of the two groups was total number of vertebrae. Cluster analyses of principal components scores for cranial morphometric data resulted in two distinct groups that agreed completely with the meristic analysis and field classifications. A series of discriminant analyses revealed highly significant differences in cranial characters between the two forms, helped to identify important characters for an identification key and generated classification functions for separating the two forms. A portion of the mitochondrial DNA control region (386 base pairs) from 47 specimens was analysed. Separation of the haplotypes of the two forms was revealed independently by maximum likelihood, neighbor-joining and maximum parsimony analyses. Separation of the two forms in Chinese waters was also supported by bootstrap and consensus values, a large divergence of ∼4.4%, and seven fixed site differences. Congruence between the osteological and molecular data provided strong evidence that reproductive isolation between the two sympatric forms exists. According to the Biological Species Concept, the two forms in Chinese waters represent separate species. Furthermore, the results also satisfied the criteria of other species concepts. To determine if these species can be differentiated externally, several morphological characters were subjected to a discriminant analysis. The results were highly significant. Examining individual characters revealed non-overlapping distributions in rostrum length and rostrum length as a proportion of total body length or snout-to-eye length. These characters are potentially useful for identifying free-ranging dolphins.</p>