Day/night upper thermal limits differ within Ectatomma ruidum ant colonies
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In the tropics, daily temperature fluctuations can pose physiological challenges for ectothermic organisms, and upper thermal limits may affect foraging activity over the course of the day. Variation in upper thermal limits can occur among and within species, and for social insects such as ants, within colonies. Within colonies, upper thermal limits may differ among individuals or change for an individual throughout the day. Daytime foragers of the Neotropical ant Ectatomma ruidum have higher critical thermal maxima (CTmax) than nocturnal foragers, but whether these differences occur among or within colonies was not previously known. We investigated the potential mechanisms accounting for day/night variation in CTmax of E. ruidum foragers by testing whether CTmax varied among or within colonies or due to individuals within colonies acclimating to changes in temperature over a short time scale (3 h). We found within- but not among-colony differences in CTmax on a diel cycle, and we found no evidence for among- or within-colony partitioning of foraging times by individual workers. Individuals did not acclimate to experimental manipulations of temperature, although additional experiments with more ecologically relevant temperature manipulations are needed to rule out this mechanism. In summary, we have shown that day/night differences in upper thermal limits can occur within ant colonies, but further investigation is needed to elucidate the mechanisms driving this variation.
KeywordsDiel variation Maximum critical temperature Intra-colony variation Acclimation
We thank the Organization for Tropical Studies (OTS) and the La Selva Biological Station for facilitating and funding this research. Field supplies and equipment were made available from the Tropical Ecology Mentorship Program, NSF Grant no. OISE-1130156. Research was conducted under a course research permit from the Costa Rican government (MINAET/SINAC). A. Nelson was funded by the OTS, the Ayala School of Biological Sciences at the University of California, Irvine, and the National Science Foundation Graduate Research Fellowship Program under Grant no. DGE-1321846. M. Barczyk received funding from two student organizations, Fundacja Bratniak and Fundusz im. J. Kochanowskiego. M. Janowiecki was supported by the Urban Entomology Endowment at Texas A&M University. A. Figueiredo was supported by funding from the OTS and the Whitney R. Harris World Ecology Center at the University of Missouri St. Louis.
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