Relative fitness of two hermaphroditic mating types in the androdioecious clam shrimp, Eulimnadia texana

Androdioecy (populations of males and hermaphrodites) is a rare reproductiv e form, being described from only a handful of plants and animals. One of t hese is the shrimp Eulimnadia texana, which has populations comprised of th ree mating types: two hermaphroditic types (monogenics and amphigenics) and males. In a recent study, the amphigenic hermaphrodites were found to be i n greater abundance than that predicted from a model of this mating system. Herein, we compare the relative fitness of offspring from amphigenic and m onogenic siblings, attempting to understand the greater relative abundance of the former. Populations started with offspring from self ed monogenic he rmaphrodites had a net reproductive rate (R) 87% that of offspring from the ir amphigenic siblings. Additionally, within populations of amphigenic offs pring (which included males, monogenics and amphigenics), amphigenics survi ved longer than monogenics. These differences help to explain the increased relative abundance of amphigenics in natural populations, but amphigenics continue to be more abundant than expected.