Author Hasni Hamin
Title Morphological and molecular discrimination of Uca species on Pulau Hantu.

Academic Exercise (B.Sc. Hons.) National Institute of Education, Nanyang Technological University

Year 2002
Supervisor Chia, Tet Fatt
Call no. QL444.M33 Has

Uca species, a complex group of crabs, have complicated diagnostic features. In this study, four morphological characters were used for instant identification of a community of two sympatric species, Uca annulipes and U. vocans on Pulau Hantu: the colour and granularity of the major cheliped of male crabs; carapace colour; carapace shape and eye width.

Generally, the colour and granularity of the major cheliped were reliable characters observable in male crabs. Colour variation in the carapace being highly plastic was not found to be useful in differentiating the species. Morphometric data analyses showed that carapace shape and eye width were good measures of species identification. However, an unknown crab specimen (labelled U40) was found, which could not be identified as either Uca annulipes or U. vocans with any certainty as it had some morphological features that were similar to both, and yet at the same time. it had unique features of its own.

Further methods of species identification using molecular methods to study the variation in the partial sequence of  mitochondria1 16s ribosomal RNA gene of Uca annulipes, U. vocans and U40 were conducted. The gene was amplified using the universal primers, 16Sar and 16Sbr. Results showed that a stretch of five bases at position 274, three bases at position 284, and a six-base gap at position 385 could be used as genetic yardsticks in differentiating between U. annulipes and U. vocans.

The sequences for U40 yielded interesting results: out of 99 base differences in its 16s mitochondrial rRNA gene, 51 were similar to U. vocans and 16 of the differences were similar to U. annulipes. Thirty-two bases in the 16s rRNA gene were unique to itself. It was hypothesized that U40 is a new species that is genetically more similar to U. vocans than U. annulipes. xviii.