Microhabitat selection and thermoregulation in amazonian dragonflies

Abstract

Insect eco-physiological traits are important for understanding their distribution and habitat selection, especially in the face of land use change. We estimated the average temperature of the thoracic surface of 20 Odonata (Insecta) species and classified them into thermoregulation categories according to their preferences for sunny or shaded habitats to assess their temperature variation. We tested the influence of air temperature and six morphological metrics related to thorax and abdomen size. We expected that: (i) heliothermic species would have higher thoracic temperatures compared to thermoconformer species; (ii) Zygopterans, due to their smaller body size, are less efficient at maintaining a constant body temperature relative to the air when compared to anisopterans; (iii) thorax volume would cause an increase in Odonata thoracic temperature, and abdomen length would cause a decrease. The study was conducted at 18 Amazonian streams in Eastern Amazonia. We observed differences of 2.5 °C in thoracic temperature between heliothermic and thermoconformer species, as predicted in the first hypothesis. Both suborders, Zygoptera and Anisoptera, use different morphological and environmental variables to control temperature. While Zygoptera thoracic temperature oscillated near and below air temperature (−1.28 ± 0.62), Anisoptera maintained temperatures above air temperature (1.81 ± 1.96). Air temperature influenced only the increase in Zygoptera thoracic temperature, supporting our second hypothesis. The third hypothesis was corroborated for order Odonata, but partially for its suborders. Zygoptera thoracic temperature was only related to abdomen length, which was proportional to a temperature decrease. Anisoptera temperature showed a relationship only with thoracic metrics, especially thorax volume, which had a significant contribution to temperature increase. Despite the observed differences, which varied according to size, we noted exceptions in the thermal characteristics of some species that deviated from these predictions. Therefore, we emphasize the importance of considering the interaction of other eco-physiological aspects in dragonfly temperature regulation.