Data from: Dwarf brooder versus giant broadcaster: combining genetic and reproductive data to unravel cryptic diversity in an Antarctic brittle star

Poecilogony, or multiple developmental modes in a single species, is
exceedingly rare. Several species described as poecilogenous were later
demonstrated to be multiple (cryptic) species with a single developmental
mode. The Southern Ocean is known to harbor a high proportion of brooders
(Thorson's Rule) but with an increasing number of counter examples
over recent years. Here we evaluated poecilogony versus crypticism in the
brittle star Astrotoma agassizii across the Southern Ocean. This species
was initially described from South America as a brooder before some
pelagic stages were identified in Antarctica. Reproductive and
mitochondrial data were combined to unravel geographic and genetic
variation of developmental modes. Our results indicate that A. agassizii
is composed of seven well supported and deeply divergent clades (I:
Antarctica and South Georgia; II: South Georgia and Subantarctic locations
including Kerguelen, Patagonian shelf, and New Zealand; III-VI-VII:
Patagonian shelf, IV-V: South Georgia). Two of these clades demonstrated
strong size dimorphism when in sympatry and can be linked to differing
developmental modes (Clade V: dwarf brooder versus Clade I: giant
broadcaster). Based on their restricted geographic distributions and on
previous studies, it is likely that Clades III-VI-VII are brooders. Clade
II is composed of different morphological species, A. agassizii and A.
drachi, the latter originally used as the outgroup. By integrating
morphology, reproductive and molecular data we conclude that the variation
identified in A. agassizii is best described as crypticism rather than
poecilogony.