title: Chela asymmetry in a durophagous crab: predominance of right-handedness and handedness reversal is linked to chela size and closing force.
abstract: The swimming crab Portunus trituberculatus is a durophagous brachyuran. Right-handed crabs are predominant, but left-handed crabs are also found in nature. Left-handedness may arise from loss of the right crusher. We examined whether heterochely (morphology) was correlated with differences in closing force (physical property) and handedness (behaviour). The closing force was stronger in larger chela with greater apodeme height and handedness resided in the chela with stronger closing force. With loss of the right chela (autotomy), handedness transitioned from the right to left chela, and all crabs were left-handed thereafter. Reversed handedness was accompanied with a reduction of size and closing force in the regenerated right chela, and growth of the original left chela. After handedness reversal, dentition on the left dactylus of the newly-converted crusher was close to that of the original right crusher, but did not attain the same shape, even after 10 moults. Left-handed crabs were significantly worse than right-handed crabs at crushing hard-shelled prey. Chela formation was symmetrical in the zoea, and heterochely and right-handedness started in the megalopa, regardless of maternal handedness. Since the left chela is capable of being the crusher, heterochely may be caused by differences in morphogenetic velocity between the right and left chelae, under a signal discriminating right from left. Right-handedness is an attribute of P. trituberculatus, that would be inheritable across generations. It is probable that right-handedness was used in the earliest durophagous crabs, and this trend has been succeeded to extant species.
authors.affiliation: Research Institute for Fisheries Science, Okayama Prefectural Technology Centre for Agriculture, Forestry, and Fisheries, Ushimado 6641-6, Okayama-Setouchi 701-4303, Japan.
authors.forename: Nobufumi
authors.initials: N
authors.lastname: Masunari
authors.affiliation: Research Institute for Fisheries Science, Okayama Prefectural Technology Centre for Agriculture, Forestry, and Fisheries, Ushimado 6641-6, Okayama-Setouchi 701-4303, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Hiro-oku
authors.affiliation: Tamano Laboratory, National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Chikko 5-21-1, Okayama-Tamano 706-0002, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Dan
authors.affiliation: Section of Research and Education, The Biosphere Project (NPO), Tsushima-Fukui 1-8-71, Okayama-Kitaku 700-0080, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Nanri
authors.affiliation: Research Institute for Fisheries Science, Okayama Prefectural Technology Centre for Agriculture, Forestry, and Fisheries, Ushimado 6641-6, Okayama-Setouchi 701-4303, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Kondo
authors.affiliation: Research Institute for Fisheries Science, Okayama Prefectural Technology Centre for Agriculture, Forestry, and Fisheries, Ushimado 6641-6, Okayama-Setouchi 701-4303, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Goto
authors.affiliation: Japan Sea National Fisheries Research Institute, Fisheries Research Agency, Suido-cho 1-5939-22, Niigata 951-8121, Japan.
authors.forename: Yoshitake
authors.initials: Y
authors.lastname: Takada
authors.affiliation: Section of Research and Education, The Biosphere Project (NPO), Tsushima-Fukui 1-8-71, Okayama-Kitaku 700-0080, Japan saigusa@biodiv-p.or.jp.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Saigusa
mesh_terms: D000818:Animals; D003386:Brachyura / Q000254:growth & development / Q000502:physiology*; D005121:Extremities / Q000254:growth & development / Q000502:physiology; D005260:Female; D007839:Functional Laterality; D007814:Larva / Q000254:growth & development / Q000502:physiology; D008297:Male; D009024:Morphogenesis
keywords: Autotomy; Durophagy; Evolution; Handedness reversal; Linked morphogenic and functional regulation; Ontogeny; Portunus trituberculatus