Mating Behaviour in Laevicaudatan Clam Shrimp (Crustacea, Branchiopoda) and Functional Morphology of Male Claspers in a Phylogenetic Context: A Video-Based Analysis

Abstract

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.

Male claspers in clam shrimps (Crustacea, Branchiopoda) in the light of evolution: A case study on homology versus analogy

“…). The function of the different parts of the clasper has been studied in detail for a laevicaudatan by Sigvardt and Olesen (). No such studies are available for spinicaudatans or cyclestheridans, but it has been suggested that stout spines on the tip of the movable finger in some spinicaudatans play a role in mate recognition (Schwentner et al, ).…”

Functional morphology of amplexus (clasping) in spinicaudatan clam shrimps (Crustacea, Branchiopoda) and its evolution in bivalved branchiopods: A video-based analysis

“… “Type 2 thrusting” after Weeks et al () and Weeks and Benvenuto (), “brushing movements” after Sigvardt and Olesen (). Male succeeds in getting its hind body in contact with the female hind body.…”

A new species of Lynceus Müller, 1776 from New Caledonia (Crustacea: Branchiopoda: Laevicaudata) from dolines, with remarks on zoogeography

“…10 pairs, first pair modified as claspers. Right and left claspers equal in size and shape, of typical Lynceus form (clasper terminology follows Sigvardt &Kaji et al 2014). Endite 1 of clasper limb typical for genus, lobiform, margined with short setae.…”

“…Endite 3 broad, oval, laterally compressed, with proximal anterior margin bearing patch of fine plumose setae. Median margin or "palm" region ("gripping area") of clasper with slender, relatively short setae (~100 μm) bearing sparse lateral setulae (type 3 or 4 setae of Sigvardt & Olesen 2014), positioned in semicircular arrangement leaving glabrous area under endopod apex. Anterior margin of glabrous area partially obscured by endopod, with short row of 4 cylindrical peglike spines (type 2 setae of Sigvardt & Olesen 2014).…”

“…Median margin or "palm" region ("gripping area") of clasper with slender, relatively short setae (~100 μm) bearing sparse lateral setulae (type 3 or 4 setae of Sigvardt & Olesen 2014), positioned in semicircular arrangement leaving glabrous area under endopod apex. Anterior margin of glabrous area partially obscured by endopod, with short row of 4 cylindrical peglike spines (type 2 setae of Sigvardt & Olesen 2014). Endite 4 (small palp) lobiform proximally, with dorsal branch bearing five long (~100-400 μm) setae, each margined with sparse long setules along anterior margin to apex, and additional ~20 setae of varying length along posterior margin.…”