Species recognition is the ability of animals to discriminate among their own and another species. Evolutionary theory suggests that this ability is particularly important for females as they normally invest much more in reproduction than males. Natural selection should therefore avoid costly interbreeding and favor the evolution of animal signals that can be used to avoid mating with another species (heterospecific mating).
Species recognition is the ability of animals to discriminate among their own and another species.
Animals use a variety of different signals for species recognition. Olfactory signals are known to be used for species recognition in some species of bats and fish, whereas acoustic signals are used in many species of frogs and birds, and also in some mammals. Facial cues as a form of visual signals are considered to be particularly relevant for species recognition in non-human primates.
Our experiments
In our study we investigated the importance of facial cues for species recognition for the red-fronted lemur from Madagascar. We wanted to “ask” the animals themselves, if facial differences among species actually have a real relevance for the animals in terms of reproductive isolation and if they can discriminate among pictures of their own and those of other closely related species. In an experiment we presented pictures of faces of different species of the genus Eulemur to males and females of free-ranging Red-fronted lemurs in Kirindy Forest, Western Madagascar, and measured the time the lemurs spent looking at the pictures.
Red-fronted lemurs looked longer at pictures of their own species than at pictures of others. Females also showed a more pronounced response than males. This may indicate that female red-fronted lemurs perceive and respond to differences in fur patterns and coloration to recognize viable mates from their own species, enabling them to avoid costly interbreeding.
In a previous study, we found no such ability for discriminating among acoustic signals of different species. Interestingly, the animals also showed increased sniffing behavior towards pictures of their own species. This might indicate that they use two different modalities at the same time, but this (cross-modal recognition) needs to be tested in the future.
Interesting new questions
Our findings are particularly interesting because these animals mate with individuals from other species in nature – they hybridize even though they are able to recognize individuals of their own species. It might therefore be interesting to conduct future studies in hybrid zones, where two or more species occur together in order to examine whether experience with closely related species affects their ability to discriminate between species.
Our results also suggest an effect of sexual variation in color vision. In fact, male red-fronted lemurs are always dichromatic, whereas females can be dichromatic or trichromatic, allowing some of them to see more colors than males. Future studies require genetic tests to test the significance of color vision polymorphism and its role for species recognition in red-fronted lemurs.
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