Rising levels of carbon dioxide are impacting more than just our climate; they’re also changing the chemical composition of our oceans. When saltwater takes in carbon dioxide, it becomes more acidic, which can disrupt the ecosystem for marine life. But how does this ocean acidification influence species whose sex can change based on their surroundings? A recent study sheds light on this issue, specifically looking at oysters.
Rising levels of carbon dioxide are impacting more than just our climate; they’re also changing the chemical composition of our oceans. When saltwater takes in carbon dioxide, it becomes more acidic, which can disrupt the ecosystem for marine life. But how does this ocean acidification influence species whose sex can change based on their surroundings? A recent study published in ACS’ Environmental Science & Technology explores this question specifically through the lens of oysters.
Oysters differ from mammals and birds in that they do not possess chromosomes that establish their sex at fertilization. Instead, these bivalves depend on environmental factors to activate genetic signals that determine whether they develop as male or female. This process is referred to as environmental sex determination. While past research has investigated how factors like temperature and food availability influence the ratio of males to females in aquatic species, the effects of changing pH levels have been largely ignored. To address this gap, a research team led by Xin Dang and Vengatesen Thiyagarajan looked into how ocean acidification might alter the sex ratios of oysters across generations, both in hatcheries and natural settings.
The researchers gathered the first generation of oysters from the wild and placed them in two separate tanks: one with neutral pH and another with slightly more acidic water to simulate the effects of ocean acidification. The offspring of these wild oysters (second generation) in the acidic tank exhibited a higher ratio of females to males compared to those spawned in the neutral pH tank.
Following this, the team transplanted the second-generation oysters from the acidic tank into two different natural environments: one with neutral pH and the other with acidic pH. In both habitats, the third-generation oysters displayed elevated female-male ratios, which demonstrated that the pH influence on sex determination can be passed down across generations in oysters.
In a similar fashion, the control group oysters also showed pH-mediated shifts in sex ratios. When the second generation of control-group oysters was placed in acidic environments, their offspring produced higher female-male ratios compared to those moved into neutral pH settings.
The researchers also conducted a genetic analysis to examine the connection between pH levels and sex determination. They discovered that certain genes associated with female development were activated in response to acidic pH, while different genes related to male development were suppressed. These findings reveal a new mechanism for environmental sex determination in oysters.
“This study is the first to document a shift in sex ratio toward females over several generations, driven by low pH exposure,” states Dang. “The findings broaden our understanding of environmental sex determination and emphasize the potential effects of future global changes on the reproductive dynamics of mollusks and other marine organisms.”
The research team plans to investigate this phenomenon in additional marine species to gain a clearer understanding of genetic regulation in the context of climate change, as well as to explore the implications of pH-based sex determination in oyster aquaculture.
The authors acknowledge support from the University Grants Committee General Research Fund, Hong Kong’s Sustainable Fisheries Development Fund, China’s National Key Research and Development Program, the National Science Foundation of China, and the Nansha District Science and Technology Program in Key Areas.
