Context-dependent sexual mimicry in the viviparous fish Girardinichthys multiradiatus

Abstract

Male Girardinichthys multiradiatus display a black spot around the vent that resembles the “pregnancy” spot of females belonging to the families Poeciliidae and Goodeidae. This spot is usually very pale/absent in dominant males, and becomes apparent upon losing an agonistic encounter. Males which exhibited the spot when in isolation (when they were socially dominant) were more likely to lose fights than males without this colour pattern when isolated. Subordinate males with experimentally enhanced spots (E) were as likely to engage in fights with the other males as males with concealed spots (C). However, of all the agonistic interactions involving an experimental male (C or E) and either the dominant or the other experimental male (E or C) a significantly larger proportion was initiated by the E than by the C male, implying that, compared to C males, fish with enhanced black spots were less often perceived as rivals by the other males. With manipulation of the patch courtship displays to subordinate males by the dominant male increased significantly more for E than for the C males. We argue that by displaying the black spot, males with low resourceholding power increase their probability of being regarded as females by other fish, and may thus gain access to defended females and courtship arenas.