Biogeography and Taxonomy of Razor Clams (Bivalvia: Solenidae)

This dissertation describes the taxonomy, biodiversity, biogeography, and current and future predicted distributions of deep-burrowing razor clams of the family Solenidae. Solen species have often been misidentified due to the high similarity in their shell morphology. Principal component analysis (PCA) and discriminant analysis showed that species could not be separated based on the morphometric measurements of the anterior adductor scar length, ligament length, and shell width to shell length ratio. Thus, geometric shape analysis, and DNA-barcoding techniques are recommended to further study the phylogeny and evolution of Solenidae. A bimodal global species richness pattern was discovered resulting from a higher Solenidae species richness at the edges of the tropics than near the equator. This contrasts with the unimodal latitudinal species richness pattern reported so far in most marine taxa with high species richness in the Tropics. There was a non-linear relationship between the Solenidae species richness and mean sea surface temperature values in each 5?? latitude band. The mid-latitude peaks in richness support the hypothesis of speciation in response to temperature variation near the edges of the tropics. Cluster analysis of Solenidae species distribution showed 13 biogeographic regions with no species occurring in polar regions. Most (50-100%) of the species were endemic to, i.e. only occurred in their geographic regions. Suitable environments for Solenidae species were predicted using species distribution modelling techniques based on environmental factors. Maximum Entropy (MaxEnt) was applied to predict the distribution of Solenidae species at present and thus the species??? potential geographic ranges under future climate change scenarios. Distance to land and depth were the most important variables in determining Solenidae distribution. Species distribution models predicted that all species in the northern hemisphere would shift northward, and southern species southward, under future climate change. Models also predicted that 50% of the species would expand their distribution ranges, about 28% would not change their distribution, and about 22% would shrink their distribution ranges under future climate warming. Climate change will likely lead to distribution range changes in Solenidae species richness mostly in the southern hemisphere, especially in Australia.