Habitat-Dependent Species Recognition in Hybridizing Newts

Many species breed in heterogeneous environments where conditions affecting signaling fidelity may vary. Species recognition may be impaired under particular environmental conditions enhancing the hybridization risk. We investigated the influence of habitat on species recognition efficiency in two hybridizing newts, Lissotriton vulgaris and L. helveticus. The former is considered to be an open habitat species where the two species are in sympatry, whereas the latter also breeds in forest ponds where dissolved humic acids attenuate wavelength transmission, especially in the UV range. Because UV sexual signalling occurs in L. vulgaris, we predicted that species recognition would be reduced in water stained by humic acids. We conducted two-choice preference tests in males and females in stained and clear water. Females of both species preferred the conspecific male in clear water but not in stained water. Males did not show species recognition in either treatment. In both newts, visual species recognition is likely to depend upon habitat. Resorting to chemical communication may offset the loss of visual information but the same environmental factors that affect the transmission of visual signal can also affect the transmission of chemical signals. This environmental disruption of species recognition may account for the general avoidance of forest ponds by L. vulgaris in sympatry with L. helveticus. Stochastic variations of visual conditions in ponds may also explain the ongoing hybridization between two long diverged species that exhibit many and well differentiated sexual ornaments, and more generally between taxa naturally experiencing strong variations of their sensory environment.