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Theory of the Evolution of Sexes Tested with Algae

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The varied sex lives of a type of green algae have enabled an Adelaide researcher to test a theory for why distinct males and females evolved.

“Why would a situation evolve where some individuals produce small gametes that are motile or capable of motion (the males) and others produce large, non-motile gametes (the females)?” asks Dr Jack da Silva of The University of Adelaide. “Sexual reproduction does not require males and females. All it requires is the fusion of sex cells from two different mating types.”

The Disruptive Selection Theory was proposed in the 1970s to describe how a population evolves from different mating types producing same-sized sex gametes to distinct males and females producing different-sized gametes. da Silva has provided the first test specific to this theory. “The theory is that as organisms evolve to be larger, the single-celled embryo (or zygote) is selected to be larger as well. This necessitates larger gametes to store more nutrients to give the embryo a head-start in development,” da Silva says.

“Organisms have a limited budget for producing gametes. So if there are more they will be smaller; if there are less they will be larger. Because greater numbers of gametes gives one mating type a selective advantage – more chance of successful fertilisation – the other mating type will be forced to produce larger, and...

The full text of this article can be purchased from Informit.