The role of body size and nesting strategy on ant resistance to environmental conditions
Cristian Luan Klunk, Cristian Luan Klunk , Marcio Roberto Pie
Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Brazil; Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Brazil ; Departamento de Zoologia, Universidade Federal do Paraná, Curitiba, Brazil
Ants nest in a variety of structures, being subject to a variety of microclimates. In addition, workers differ considerably in body size, a key trait affecting their physiological responses. In this study we tested how interspecific variation in resistance to desiccation and low/high temperatures is influenced by body size (Weber’s length) and nesting strategy (soil, twig or tree). We collected ants in fragments of Atlantic Forest in southern Brazil and subjected them to tests within 48 h after collection. We use 20 ant workers per species for each test whenever possible. To evaluate the resistance to high temperature, we placed workers individually in micro tubes and put them in an aluminum bowl filled with 40ºC water. We raised temperature by gradually adding boiled water and recorded their corresponding lethal temperatures. We also exposed workers to ice for 30 minutes and compute time until recovery from chill coma to evaluate cold resistance. Finally, we placed workers in micro tubes filled with 0.08g of silica gel and computed the time until death to assess desiccation resistance. We tested 44 ant species and analyzed the results with Cox proportional regression. Twig ant species are more prone to death at high temperatures (HR=2.2). Tree ant species performed best at recover for chill coma (HR= 1.5) and smaller workers recover faster than larger ones (HR=1.1). Soil (HR=1.3) and smaller (HR=1.7) workers are more prone to desiccation. Being large is a obviously advantage in drier conditions due to water storage, and is expected that larger organisms perform best at cold conditions, in accordance with what we found here. Tree ant species are more resistant to high and low temperatures, which is not surprisingly since this ants are more exposed to shifts in temperature, due to the low buffering capacity of them nesting structures, which also explain why twig ant species dealt best with drier conditions.