Morphology and reproduction in the Hapalocarcinus marsupialis Stimpson, 1859 species complex (Decapoda: Brachyura: Cryptochiridae)

Susanne Bähr, Magnus L. Johnson, Michael L. Berumen, Royale Hardenstine, Walter A. Rich, Sancia E.T. van der Meij

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Symbiotic relationships contribute considerably to the high biodiversity found on coral reefs. Coral-dwelling gall crabs (Cryptochiridae) represent a prime example of coral-associated invertebrates that exhibit obligate relationships with their host. The induction of a skeletal modification in the coral, used as a dwelling by the crab, is the most remarkable aspect of this close association. Here we examined Hapalocarcinus marsupialisStimpson, 1859, collected from Pocillopora and Stylophora corals in the Saudi Arabian Red Sea. Specimens were DNA barcoded, and five distinct clades were revealed, providing further evidence for the hypothesis that H. marsupialis is a species complex. Divergence (COI) between the clades ranged from 3.2 to 15.7%. The putative species were tested for differences in morphology and reproduction. Crabs were examined regarding morphometric characters (carapace length and width, pleon (abdomen), chelae, and growth patterns) and reproductive traits. The data were pooled and analysed by host genus and putative species, which revealed significant differences for most of the measured variables in female crabs. Specimens retrieved from Pocillopora were significantly larger (up to 49 %) and had higher fecundity than those inhabiting Stylophora. For reproductive output (RO) no differences at species- or host-genus level were detected. The average RO of ∼70% over all specimens is high compared to other brachyurans, supporting the assumption that symbiotic brachyurans invest more energy in reproduction than their free-living counterparts. Discrepancies with published data on growth and reproduction of Hapalocarcinus are discussed. Our results demonstrate the usefulness of morphometric traits and fecundity in separating the clades in the H. marsupialis complex, and prepare the ground for further morphometric studies on the genus and other symbiotic brachyurans. Moreover, it highlights the need to check for the presence of cryptic species when studying aspects of the biology of a species.
Original languageEnglish (US)
JournalJournal of Crustacean Biology
Issue number3
StatePublished - Sep 30 2021

Bibliographical note

KAUST Repository Item: Exported on 2021-11-29
Acknowledgements: We thank Irene Salinas, Matt Tietbohl, Claire Shellem, and Morgan Bennett-Smith for the collection of additional Hapalocarcinus marsupialis specimens during the Eid Cruises 2018/19 undertaken by the King Abdullah University of Science and Technology. We would like to extend our gratitude to Jorn Claassen (University of Groningen, The Netherlands) for obtaining additional H. marsupialis sequences for the phylogenetic analysis and Jan Veldsink (University of Groningen) for help with the laboratory work. We thank two anonymous reviewers and the Editor-in-Chief for their constructive comments.


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