"Hermaphroditic origins of anisogamy"Henshaw, JonathanAnisogamy – the size dimorphism of gametes – is the defining differences between the sexes. In animals, it is often presumed that anisogamy arose in sessile broadcast spawners, and that the earliest anisogamous animals had separate sexes. There is little empirical or theoretical evidence to support this picture. I briefly consider the phylogenetic contexts in which anisogamy has evolved and what we can say for certain about the first anisogamous animals. I then present a model of the origins of anisogamy that allows for both separate sexes and hermaphroditism to evolve directly. Which of these outcomes emerges depends crucially on the population structure during fertilisation. Lastly, I consider how the sex allocation of newly anisogamous hermaphrodites differs from their isogamous ancestors. |
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