Supplemental Data Files for: Male color polymorphism in populations of Reef Geckos (Sphaerodactylus notatus) reduces the utility of visual signals in sex recognition

Sexually dichromatic signals can identify the sex of a conspecific, facilitating decisions to initiate agonistic or courtship displays at the onset of social interactions. The utility of sex-specific signals, however, may be reduced when polymorphism evolves and these signals become variable. To explore the impact of polymorphism in the utility of sex-specific signals, we studied Floridian and Bahamian populations of the Reef Gecko, Sphaerodactylus notatus, which vary in the presence of polymorphic males (i.e., populations with monomorphic males that are sexually dichromatic from females; polymorphic with dichromatic and female-like males; polymorphic with dichromatic and intermediate males). We staged encounters between same-sex and different sex pairs on opposite sides of transparent barriers to measure response to visual signals, quantifying agonistic and courtship behavior. For geckos from the monomorphic population, opposite sex pairs consistently initiated courtship displays, and same-sex pairs initiated agonistic displays. In contrast, both polymorphic populations lacked consistent sex-specific response to visual signal, and the population with dichromatic and female-like males showed similar responses in both same-sex and opposite-sex pairings, failing to distinguish sex even when interacting with dichromatic males. When individuals from this polymorphic population were tested with the transparent barrier removed to allow olfactory signaling, we found clear courtship and agonistic responses between opposite sex and same-sex pairs, respectively. Our study suggests that loss of signal reliability when a trait becomes polymorphic can lead to reduction of signal utility, even when the signal remains present in some individuals and still conveys the sex of conspecifics.