Identification of Main Oyster Species and Comparison of Their Genetic Diversity in Zhejiang Coast, South of Yangtze River Estuary

Oysters are an important aquaculture species distributed worldwide, including in Zhejiang Province, located on the east coast of China. Because of the high diversity and complicated introduction history of oysters and their seedlings, there has been much disagreement regarding the origin of each species, and the dominant and indigenous species remain unclear. We sampled 16 batches of oysters from seven sites in three aquaculture bays and found two main oyster species, Crassostrea sikamea and Crassostrea angulata. The former occupied the higher intertidal zone and comprised more than 70% of the cultured oysters. Based on the cytochrome oxidase C subunit I (COI) and mitochondrial noncoding region (MNR), C. sikamea showed higher genetic diversity than C. angulata. The analysis of molecular variance among COI sequences of these species from the Xiangshan Bay populations were comparable to those of other populations and showed that most of the molecular variance was within groups, which was consistent with the low pairwise fixation index FST values. The neutrality test revealed that C. sikamea experienced population expansion events, whereas for C. angulata, the significant Fu’s Fs and non-significant Tajima’s D test results may indicate a possible population expansion event, implying that C. sikamea is likely an indigenous species. The method established based on internal transcribed spacer 1 digestion by the HindIII restriction enzyme is useful for identifying C. sikamea and C. angulata in the local region. The specific primers on the MNR sequence show potential for distinguishing C. sikamea from four other important Crassostrea oysters. These results highlight the abundance of C. sikamea on the Zhejiang coast and lay the foundation for protecting and utilizing the local oyster germplasm resources and for the sustainable development of the oyster industry.

Adapting to Change in Australian Estuaries

In the 1880s, Eastern Australian estuaries supported thriving oyster industries. They supplied lime for building early in Australia’s development, but as cities and towns grew, it was the briny salty taste for this delicacy that saw the growth of the sector. When the oyster beds at the east coast of Australia became depleted, fishermen looked to New Zealand, where the same Oyster species grew, to supply cultivation stock for the Australian market. It was presumed that transfers would have the same impact as those already being moved within the Australian ecological networks. That is: it would present no problem at all. What was overlooked in this intercolonial exchange was the presence of the mudworm in the New Zealand estuaries. Mudworm co-habitats with oysters without killing them, but impedes the healthy development of the oysters making them inedible. This chapter places the mudworm at the center of a new narrative in the ecological networks of oysters. Rather than articulating the mudworm as a damaging invasive species, it argues that the mudworm was an agent of change that caused the fishermen to adjust their methods of oyster cultivation.

Evolutionary trade-offs between baseline and plastic gene expression in two congeneric oyster species

Organismal responses to environmental stresses are a determinant of the effect of climate change. These can occur through the regulation of gene expression, involving genetic adaptation and plastic changes as evolutionary strategy. Heat shock protein ( hsp ) family genes are extensively expanded and play important roles in thermal adaptation in oysters. We investigated expression of all heat-responsive hsp s in two allopatric congeneric oyster species, Crassostrea gigas and C. angulata , which are respectively distributed along the northern and southern coasts of China, using common garden and reciprocal transplant experiments. Our results showed that hsp s in C. gigas have evolved higher basal levels of expression under ambient conditions at each field site, with lower expression plasticity in response to heat stress in comparison to C. angulata , which exhibited lower baseline expression but higher expression plasticity. This pattern was fixed regardless of environmental disturbance, potentially implying genetic assimilation. Our findings indicate divergent adaptive strategies with underlying evolutionary trade-offs between genetic adaptation and plasticity at the molecular level in two oyster congeners in the face of rapid climate change.