Unraveling cryptic diversity in the Indo-West Pacific gastropod genus Lunella (Turbinidae) using elliptic Fourier analysis

摘要

Morphological variation in shell shape was quantitatively evaluated among newly identified cryptic species in two species complexes (coronata and cinerea groups) belonging to the gastropod genus Lunella (Turbinidae) using elliptic Fourier descriptors (EFDs). Sympatric species of the coronata group show greater phenotypic diversity than the entirely allopatric cinerea group. We suggest that if morphological divergence is driven most strongly in sympatry, cryptic species are more likely to occur in taxa with allopatric speciation. Discriminant analysis showed that one species (L. aff. coronata ophiolite) was significantly different and could be distinguished from its two sister species (L. coronata (Gmelin, 1791), L. aff. coronata Oman) by shell outline with a high degree of success. In pairwise analyses two pairs from the cinerea group were also significantly different and species could be determined with a modest degree of success: L. aff. cinerea Fiji with L. aff. cinerea SW Pacific and L. aff. cinerea Indian Ocean with L. aff. cinerea central Indo-West Pacific (cIWP). The remaining species could not be accurately identified by shell shape alone in this study. We also used a combination of shell shape and shell sculpture to determine that the coronate form of L. coronata, which occurs along the east coast of Africa and along the Arabian Peninsula into India, corresponds to L. coronata sensu stricto. We were unable to assign either a holotype for L. cinerea (Born, 1778) or a figured specimen of L. versicolor (Gmelin, 1791) to genetic lineages with any statistical confidence, although the shell outline of the former is most similar to L. aff. cinerea cIWP and the latter to L. aff. cinerea SW Pacific. Finally, using morphometrics, in combination with other shell characters, two fossil species, one from the cinerea group from the Pleistocene and one Japanese species from the Eocene, were compared with extant species. Using this method in combination with other characters, we suggest that the Japanese L. kurodai Itoigawa, 1955 is most likely a member of the coronata group and the Pleistocene cinerea fossil is most similar to L. cinerea cIWP.