Ant-plants as oases: Colonies of Cladomyrma sirindhornae (Hymenoptera, Formicidae) thrive in their host plants Sphenodesme pentandra in both the wet and dry seasons

Seasonal changes affect the distribution and behavior of animals. Ant societies are strongly affected by the dry season: they suffer from high temperatures and desiccation, but also from the lower availability of insect prey. However, some species of ants are involved in mutualistic relationships with myrmecophytic plants that provide a moist nesting space and nutrition. The effects of seasonal changes on such ant-plant symbioses are poorly understood. In this study, we report the nesting habits, colony composition and reproductive status of a plant-ant species, Cladomyrma sirindhornae Jaitrong, Laedprathom & Yamane, 2013 in the wet and dry seasons in Thailand. C. sirindhornae nested inside vines of Sphenodesme pentandra Jack, a pioneer species found in secondary dry evergreen forests and at forest edges which provides naturally hollowed stems for ant colonies. Among the 243 observed vines in this study, 223 vines (92%) were inhabited by C. sirindhornae while only 11 (4.5%) were occupied by other ant species, suggesting a high specialization of the ant-plant mutualism. C. sirindhornae nested within the cavities of the host plant, extending throughout the stems and branches from the base to the canopy. A comparison of ten colonies collected in the dry season and ten in the wet season showed no effects of seasonality on colony size and proportion of larvae, worker pupae and scale insects. However, sexual pupae and adults were more abundant in the wet season than in the dry season. Our results suggest that myrmecophytes buffer seasonal variations, allowing plant-ant colonies to grow year-round, while reproductives are produced only when conditions outside are favorable for colony founding.