Specificity of the crowding response in the Brachionus
plicatilis species complex  Stelzer, Claus-Peter, Terry W. Snell
Limnol. Oceanogr., 51(1), 2006, 125-130 | DOI:
10.4319/lo.2006.51.1.0125  ABSTRACT: Crowding chemicals
influence a wide variety of life history traits in zooplankton
communities. In the rotifer Brachionus, sexual reproduction
(mixis) is induced by a chemical signal produced by the rotifers
that accumulates during population growth. The specificity of
the reaction to the mixis induction signal could play a central
role in maintaining reproductive barriers between closely
related sympatric species. Using cross-induction assays between
different species, we tested whether this signal has diversified
in the Brachionus plicatilis species complex. We found that
closely related, as well as more distant species in this
complex, could induce mixis in each other. This suggests that
there are no species barriers in sex induction and that the
mixis signal did not diversify for several million years dur