Behavioral repeatability in dung beetles is not limited to subsocial and sexual horn dimorphic species: the case of Geotrupes mutator (Coleoptera, Geotrupidae).

The study of temperament and behavioral syndromes in insects is still in its early stage, and research conducted to date has mainly focused on locomotor activity and thanatosis. Dung beetles have been the subject of extensive behavioral studies; however, very few studies have addressed the expression of temperament. Those doing so only looked at subsocial and sexual horn dimorphic species, suggesting subsociality and/or sexual horn-dimorphism as possible facilitators of temperament expression. To test this assumption, we conducted a temperament study in a hornless, non-subsocial species, namely Geotrupes mutator (Marsham, 1802). We set up laboratory tests to evaluate 3 behaviors (activity, thanatosis, and distress calls) through the measurement of 7 distinct behavioral traits (3 activity-, 1 thanatosis-, and 3 call-related traits). We found high levels of individual repeatability in all activity- and thanatosis-related traits. We also identified behavioral differences between individuals, which may reflect differences in temperament. Statistical analyses revealed a negative correlation between activity and thanatosis. These results show that the temperament and behavioral syndromes related to activity and thanatosis may also be expressed in dung beetle species that are neither subsocial nor sexual horn dimorphic. By contrast, we only found one of 3 sound-related traits tested (frequency) to be clearly repeatable. Males and females presented a different structure of the stridulatory apparatus, suggesting that morphology may affect the frequency of sounds emitted. These results indicate that certain sound traits might not be good descriptors of individual temperament revealing the need for future research addressing the role of bioacoustics.