Birds do it, bees do it, and oysters do it too, but in a different way. Oysters are marine bivalves that live on the bottom of the ocean by cementing themselves permanently to a hard surface. They do not actually mate as most terrestrial animals do. Instead, oysters broadcast their gametes in the water, and fertilization takes place outside of their bodies. Oysters also have two separate sexes, males and females. However, oysters can completely change their sex between mating seasons! Juvenile oysters usually mature as males first and then change to females later in life. Occasionally, one oyster can function as both female and male at the same time, a condition known as hermaphroditism.
Crassostrea virginica spawning --->
The coexistence of separate sexes, sex-change, and hermaphroditism within the same species raises an interesting question. Is such a system under genetic control? Although interest in the sexuality of oysters dates back over a century, the inability to make pair-matings has prohibited in-depth analysis of sex determination. It is commonly believed that oysters have a protandric (mature as males first) alternative sexuality, and that sex is determined by environmental factors such as food supply and water temperature. Involvement of genetic factors was suspected, but supporting evidence has been scarce.
A recent study published by HSRL scientists and colleagues at the University of California at Davis and the University of Washington has shed some light on genetic determinants of sex in oysters (Guo et al, 1998). By analyzing sex-ratios in pair-mated families, they found strong evidence for genetic control of sex in the Pacific oyster. Furthermore, the sex-ratio of a family is primarily determined by the father, but not the mother. It seems that there are two types of males: true males that do not change sex and males that do. All females can change sex, and the rate of sex-change may be influenced by secondary genes and/or environmental factors. This study raises more questions. If sex is genetically controlled, why is there no strict-genic determination of sexes like most other animals have? Why do oysters change sex at all? Is this an adaptation to the unique life history of oysters or a phylogenic mishap that oysters are trapped in? Answers to these questions would enhance our understanding of how sex has evolved.
Crassostrea virginica spawning --->
The coexistence of separate sexes, sex-change, and hermaphroditism within the same species raises an interesting question. Is such a system under genetic control? Although interest in the sexuality of oysters dates back over a century, the inability to make pair-matings has prohibited in-depth analysis of sex determination. It is commonly believed that oysters have a protandric (mature as males first) alternative sexuality, and that sex is determined by environmental factors such as food supply and water temperature. Involvement of genetic factors was suspected, but supporting evidence has been scarce.
A recent study published by HSRL scientists and colleagues at the University of California at Davis and the University of Washington has shed some light on genetic determinants of sex in oysters (Guo et al, 1998). By analyzing sex-ratios in pair-mated families, they found strong evidence for genetic control of sex in the Pacific oyster. Furthermore, the sex-ratio of a family is primarily determined by the father, but not the mother. It seems that there are two types of males: true males that do not change sex and males that do. All females can change sex, and the rate of sex-change may be influenced by secondary genes and/or environmental factors. This study raises more questions. If sex is genetically controlled, why is there no strict-genic determination of sexes like most other animals have? Why do oysters change sex at all? Is this an adaptation to the unique life history of oysters or a phylogenic mishap that oysters are trapped in? Answers to these questions would enhance our understanding of how sex has evolved.
joscelyne:
Fascinating! Some fish and shrimp do that, too, but not in the exact way that oysters do. Change their sex, I mean.
Fascinating! Some fish and shrimp do that, too, but not in the exact way that oysters do. Change their sex, I mean.