129-70 Morphometric Variation in Neothauma tanganyicense from Lake Tanganyika, East Africa

Abstract:

Neothauma tanganyicense is a freshwater gastropod endemic to Lake Tanganyika. There are extensive unconsolidated shell beds of N. tanganyicense on the modern lake floor that exhibit time averaged accumulations from 200-3000 years old. They are a crucial part of the lake environment as they support a littoral ecosystem for many fish and invertebrate species. The shells exhibit geographically related morphological variation. Historically there has been considerable scientific debate over the taxonomic designation of the genus Neothauma and whether the differences in morphology could be considered different species. The most recent analysis was published in 1953 by Eugene Leloup and consolidated Neothauma into the single species based primarily on collections from the western side of the lake. Additionally, morphometric studies on newer collections of Neothauma from the eastern coast of the lake have been conducted, providing a wider scope of data. Advances in quantitative morphometric methods and evolving taxonomic concepts have provided new ways to evaluate the taxonomy of this species since this previous work.

 This study statistically compares morphological measurements of snails collected from museum specimens from the western coast of the lake to measurements from the newer collections from the east side of the lake. To re-examine the questions regarding species designation(s), we analyzed over 1200 shells using a combination of 2d geometric morphometrics of the plane of the aperture and traditional morphometrics including categorizing differences in keeling and sutures through character data. These morphological data, analyzed in R and PAST using multivariate statistical methods, allow testing of whether geographically distinct samples form distinct taxonomic groups or a scale of variation. The results will provide the first quantitative analysis of Neothauma taxonomy in over 70 years and are timely because recent studies have indicated that populations of live Neothauma have decreased over the last 100 years: a change that may profoundly affect the lake’s ecosystem. Future conservation actions will depend on sound taxonomy of the affected taxa/taxon.

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