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Journal of Molluscan Studies Advance Access





Published: Tue, 14 Nov 2017 00:00:00 GMT

Last Build Date: Mon, 13 Nov 2017 23:48:48 GMT

 



Gametogenesis, sex ratio and energy metabolism in Ostrea angasi : implications for the reproductive strategy of spermcasting marine bivalves

2017-11-14

ABSTRACT
Spermcasting is an unusual reproductive strategy in some aquatic species in which functional males release gametes to fertilize eggs inside the body cavity of functional females. As some spermcasting bivalves have high ecological and economical importance, the understanding of their reproductive strategy is crucial for aquaculture, fisheries and conservation. This study investigates gametogenesis, sex ratio and energy metabolism in Ostrea angasi to elucidate the reproductive strategy of spermcasting bivalves. Gonad histology indicated asynchronous development of spermatozeugmata, but synchronous development of oocytes within an individual. The hermaphroditic individuals released spermatozeugmata before egg ovulation. The population of 2–3 year old oysters comprised 46.7% hermaphrodites and showed a highly skewed male to female ratio of 7:1. This species primarily metabolized glycogen as the energy source for gametogenesis, with an overlapping period of energy storage and utilization. This pattern of gametogenesis suggests multiple production of spermatozeugmata in a reproductive season in male and hermaphroditic oysters, but a single episode of egg ovulation in female and hermaphroditic oysters. The dynamics of energy metabolism indicate that O. angasi follows a strategy for energy metabolism that is intermediate between those of conservative and opportunistic species. This study suggests that unsynchronized gamete development, skewed sex ratio and intermediate energy metabolism are adaptive strategies in the reproduction of spermcasting bivalve species.









Phylogeography of the pelagic snail Limacina helicina (Gastropoda: Thecosomata) in the subarctic western North Pacific

2017-11-10

Abstract
The genetic diversity of one of the most abundant species in the Arctic and subarctic oceans, the pelagic snail Limacina helicina, has not yet been characterized in the north Pacific. This species has different ‘forma’ (L. helicina forma helicina, acuta, pacifica and ochotensis), but whether or not the morphological differences between these forma are caused by phenotypic plasticity or genetic differentiation remains unclear. Here, we analysed partial nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I gene in L. helicina from the subarctic western North Pacific Ocean (SWNP; L. helicina f. acuta) and compared them with those from Svalbard (L. helicina f. helicina) and other localities (Beaufort Sea, eastern Pacific, northern Sea of Japan and western Atlantic). The results show clear genetic differentiation between populations in the SWNP and Svalbard (ΦCT = 0.59282, P < 0.001). These genetic differences are consistent with the previous description of the two forma L. h. f. acuta (SWNP) and L. h. f. helicina (Svalbard) based on shell morphology.