Universitet Mating behaviour in laevicaudatan clam shrimp ( Crustacea , Branchiopoda ) and functional morphology of male claspers in a phylogenetic context

Clam shrimps are freshwater branchiopod crustaceans which often present complicated breeding systems including asexual reproduction (parthenogenesis) and mixed mating systems (in androdioecious species both selfing and outcrossing occurs due to the co-presence of hermaphrodites and males). Reproductive patterns of Spinicaudata, which contains most clam shrimp species, have received much attention. Another group of clam shrimps, Laevicaudata, which holds a key position in branchiopod phylogeny, has practically not been studied. As a part of the mating process, males clasp to the carapace margin of the females with a pair (or two pairs) of anterior trunk limbs modified as claspers. Previous studies have shown that clasper morphology is important in a phylogenetic context, and that some parts of the claspers in Spinicaudata and Laevicaudata may have undergone a remarkable parallel evolution. Here we have used video microscopy to study aspects of the mating behaviour, egg extrusion, and fertilization in Lynceus brachyurus (Laevicaudata). It is shown that fertilization is likely to be external and that the peculiar tri-lobed lateral lamellae of female’s hind body assist in guiding the egg mass to the exopodal egg carriers where they are collected by their distal setation. The functional morphology of the male claspers was studied in detail by close-up video recordings. The movable ‘‘finger’’ of the clasper bends around the female’s carapace edge and serves to hold the female during mating. The larger palp grasps around the female carapace margin in a way very similar to the movable ‘‘finger’’, possibly indirectly providing sensory input on the ‘‘finger’’ position. A brief comparative study of the claspers of a spinicaudatan clam shrimp showed both similarities and differences to the laevicaudatan claspers. The presence of two pairs of claspers in Spinicaudata seems to give males a better hold of the female which may play a role during extended mate guarding. Citation: Sigvardt ZMS, Olesen J (2014) Mating Behaviour in Laevicaudatan Clam Shrimp (Crustacea, Branchiopoda) and Functional Morphology of Male Claspers in a Phylogenetic Context: A Video-Based Analysis. PLoS ONE 9(1): e84021. doi:10.1371/journal.pone. 0084021 Editor: Andreas Hejnol, Sars International Centre for Marine Molecular Biology, Norway Received October 3, 2013; Accepted November 16, 2013; Published January 2, 2014 Copyright: 2014 Sigvardt, Olesen. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: ‘‘Bøje Benzons støttefond’’ supported the first author’s travel to present the study at a scientific meeting. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: jolesen@snm.ku. dk