Reproductive polymorphism in Daphnia pulex
Daphnia are facultative parthenogens, meaning they can switch between asexual and sexual reproduction. When they choose to reproduce asexually, they make the additional choice of whether to produce clonal females or males. The ability to switch is often environmentally dependent and the capacity and cues required to switch are subject to local adaptation. Clones can vary in their sensitivity to switching to sex, as well as to what extent they make males. However, the stability of these types of reproductive polymorphisms, and how this stability is influenced by ecology is uncertain.
We work in a metapopulation of European D. pulex in the southern UK, which consists of a series of intermittently connected small ponds, that vary in their ephemerality. DBunk appears to dry every year, D8 dries some years, but not others, and DCat is deepest and appears most permanent. In line with this observed variation in ephemerality, clonal lineages are never observed over more than one growing season in DBunk, but are observed over multiple growing seasons in D8 and DCat. Within D8, two dominant clones were observed to co-exist over multiple growing seasons. Phenotyping assays in the lab established that one of these clones was male limited, while the other produced ample males. A similar reproductive polymorphism does not currently appear to be present in DCat and DBunk.
