Data from: Local gamete competition explains sex allocation and fertilization strategies in the sea

Within and across taxa, there is much variation in the mode of
fertilization, i.e. whether eggs and/or sperm are released or kept inside
or on the surface of the parent's body. Although the evolutionary
consequences of fertilization mode are far reaching, transitions in the
fertilization mode itself have largely escaped theoretical attention. Here
we develop the first evolutionary model of egg retention and release,
which also considers transitions between hermaphroditism and dioecy as
well as egg size evolution. We provide a unifying explanation for reported
associations between small body size, hermaphroditism, and egg retention
in marine invertebrates that have puzzled researchers for over three
decades. Our model, by including sperm limitation, shows that all these
patterns can arise as an evolutionary response to local competition
between eggs for fertilization. This can provide a general explanation for
three empirical patterns: Sperm casters tend to be smaller than related
broadcast spawners, hermaphroditism is disproportionately common in sperm
casters, and offspring of sperm casters are larger. Local gamete
competition also explains a universal sexual asymmetry: females of some
species retain their gametes while males release theirs, but the opposite
('egg casting') lacks evolutionary stability and is apparently
not found in nature.