More acidic oceans can affect oyster sex. newswise

More acidic oceans can affect oyster sex. newswise


Rising carbon dioxide levels affect more than just climate; They also affect the chemistry of the oceans. When salt water absorbs carbon dioxide, it becomes acidic, which alters the aquatic animal ecosystem. But how does ocean acidification affect animals whose genetic makeup can shift based on environmental cues? A study published in ACS’ Environmental Science and Technology Addresses this question through the “eyes” of the oyster.

Unlike mammals and birds, oysters do not have chromosomes that determine their sex at the point of fertilization. Diatoms rely on environmental factors to trigger genetic signals that determine whether they are male or female – a mechanism known as environmental sex determination. Previous studies have shown how environmental cues such as temperature and food availability can alter female-to-male ratios for aquatic animals, but shifting pH levels has been overlooked. So, a research team led by Xin Dang and Vengetsen Thiarajan investigated how ocean acidification might affect the sex ratio of oysters across generations, both in hatcheries and in the wild.

The researchers collected the first generation of oysters studied from the wild and placed them in two separate tanks, one with a neutral pH and the other with slightly more acidic water to mimic ocean acidification. The progeny (second generation) of wild oysters in the acidic tank had a higher female-to-male ratio than those spawned in the neutral pH tank.

Next, they transplanted second-generation oysters from the acidic tank into two different natural habitats: one with a neutral pH and one with an acidic pH. Third generation oysters had higher female-to-male ratios regardless of habitat pH, indicating that pH-mediated sex determination may be transgenerational for oysters.

Similarly, pH-mediated sex determination also occurred in the control-group offspring. When second-generation control-group oysters were transplanted into acidic natural habitats, their offspring had higher female-to-male ratios than control-group oysters that were transplanted into neutral pH natural habitats.

The team also explored the relationship between pH and sex determination through genetic analysis. The results indicated that a series of genes involved in female development turned on in response to acidic pH, while a different set of genes involved in male development turned off. These results highlight a new trigger for environmental sex determination in oysters.

“This study is the first to document a biased sex ratio across multiple generations toward women exposed to low pH,” says Dang. “The results expand our understanding of environmental sex determination and highlight the potential impact of future global changes on the reproduction and population dynamics of mollusks and other marine organisms.”

The researchers’ next steps include exploring this phenomenon in other marine animals to better understand genetic regulation in response to climate change and testing the application of pH sex determination in oyster aquaculture.

The authors acknowledge funding in key areas from the General Research Fund of the University Grants Committee, the Sustainable Fisheries Development Fund of Hong Kong, the National Science Foundation of China, the National Science Foundation of China and the Nansha District Science and Technology Program.

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