Geometric morphometric analysis reveals that the shells of male and female siphon whelks Penion chathamensis are the same size and shape

ABSTRACT

Secondary sexual dimorphism can make the discrimination of intra and interspecific variation difficult, causing the identification of evolutionary lineages and classification of species to be challenging, particularly in palaeontology. Yet sexual dimorphism is an understudied research topic in dioecious marine snails. We use landmark-based geometric morphometric analysis to investigate whether there is sexual dimorphism in the shell morphology of the siphon whelk Penion chathamensis. In contrast to studies of other snails, results strongly indicate that there is no difference in the shape or size of shells between the sexes. A comparison of P. chathamensis and a related species demonstrates that this result is unlikely to reflect a limitation of the method. The possibility that sexual dimorphism is not exhibited by at least some species of Penion is advantageous from a palaeontological perspective as there is a rich fossil record for the genus across the Southern Hemisphere.

KEYWORDS:

• Buccinulidae
• conchology
• fossil
• geometric morphometrics
• mating
• paleontology
• reproduction
• secondary sexual dimorphism
• snail
• true whelk

Acknowledgements

We are grateful for the constructive criticism provided by the reviewer Liew Thor Seng and the editor Winston F. Ponder. This work was supported by the Royal Society of New Zealand Te Apārangi Marsden Fund grant (12-MAU-008). We are incredibly grateful to the following researchers who provided us with help, hospitality and permission to access the museum collections at the listed institutions: Heidi Schlumpf, Wilma Blom, Severine Hannam (Auckland War Memorial Museum); Chris Rowley (Museum Victoria); Amanda Reid (Australian Museum); and Neville Hudson (University of Auckland). We also thank Katie S. Collins (Victoria University of Wellington) for her assistance with geometric morphometric analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Felix Vaux http://orcid.org/0000-0002-2882-7996