Four’s a crowd: social preferences for larger groups in golden mantella (Mantella aurantiaca) tadpoles

Abstract

Group living results in various benefits and costs, which often depend on group size and ontogenetic state of the individual. Therefore, certain group sizes are favourable over others, often depending on individual age or intrinsic state. Under natural conditions many amphibians can be found in aggregations, especially during the larval stage. Yet, whether these aggregations are the result of active social preferences or are driven by environmental factors has only been tested in a limited number of taxa. This study explores social preferences and group size discrimination in golden mantella (Mantella aurantiaca) tadpoles. We gave tadpoles the choice between different numbers of conspecifics using a two-choice design. To test for general social tendency, tadpoles could either join a group of three or remain solitary (3 vs. 0). To test for group size preferences, we tested tadpoles in two different ratios: 2 vs. 1 and 4 vs. 2 conspecifics. We repeated the trials weekly until metamorphosis to determine potential shifts in preference through ontogeny. Tadpoles preferred being with a group over being alone, and the strength of this preference declined with increasing age. Furthermore, tadpoles preferred to be close to the larger of two groups. This preference was stronger in the 2 vs. 1 treatment. Mantella aurantiaca tadpoles, therefore, show clear social tendencies and possess the ability to spontaneously discriminate between group sizes. The lower preference at higher group sizes might indicate cognitive limitations or lower benefits of choosing the larger of two groups when overall group size is high. These findings are one of the few showing social preferences depending on group size in tadpoles and contribute to our understanding of social behaviour in amphibians in general.