Support for a role of colour vision in mate choice in the nocturnal European treefrog (Hyla arborea)

Although nocturnal anurans use vision for reproductive communication, it remains unknown whether they see colours at night. Here, we explored this question in the European treefrog (Hyla arborea), by conducting two mate choice experiments under controlled light conditions. Experiments involved static male models with identical calls but different vocal sac colouration combining chromatic (red/orange) and brightness (dark/light) information. We found that females preferred dark red over light orange, evidencing for the first time a visually-guided mate choice in nocturnal diffuse light conditions. Conversely, females did not discriminate between dark orange and light red. The preference for dark over light in the first but not in the second experiment suggested that females had not only access to brightness cues but also to chromatic cues. The absence of preference may originate from females choosing at random in a situation where colour and brightness cues may convey contradictory information about male quality or from individual heterogeneity in the type of cues used for mate choice. Overall, these experiments provide the first support for the use of colour vision in a nocturnal amphibian.