If you are hidden, how will I know what you feel?: the role of tarantula burrows in buffering the external climatic conditions

Abstract

Context. Thermal refuges, such as burrows, play a crucial role in the survival of ectothermic species by buffering environmental temperature fluctuations. The burrowing tarantula Grammostola vachoni inhabits rocky outcrops in central grassland of Argentina. Considering the importance of refuges for ectotherms, the significant differences between microhabitat and external environmental conditions, and the limited information available on tarantula habitats, understanding microclimate variations within burrows is crucial. Aims. We investigated the temperature and humidity dynamics inside the burrows of G. vachoni in relation to the surrounding environment. We characterized microhabitat temperature and humidity in adjacent habitats, evaluated the stability of environmental conditions inside and outside the burrow, and analyzed these findings in relation to the known thermal limits of the species. Methods. We conducted the study in the Ventania System (Argentina), measuring temperature and humidity throughout an entire year. Environmental parameters were recorded using a HOBO data logger, whereas burrow parameters were measured using iButton data loggers placed inside burrows occupied by adult females of G. vachoni. We also analyzed the stability of environmental and burrow conditions, the distribution of extreme temperatures, humidity variability, and the rates of cooling and heating. Key results. We found that burrows exhibit greater thermal and hydric stability than the external environment, with temperatures inside remaining above 0°C during winter. Cooling and heating rates inside the burrows were slower, which allowed the spiders to avoid rapid and harmful temperature fluctuations. Humidity levels inside the burrows were consistently higher than outside, particularly during the warmer months. Conclusions. Our results highlighted the importance of monitoring microhabitat conditions not only during the species’ activity periods, because burrows play a determinant role in other phases of the life cycle. Whereas burrows provide some level of thermal refuge, the increasing frequency and intensity of heatwaves could challenge the species’ thermal resilience. The fact that burrow temperatures can exceed both optimal temperature and critical thermal maximum, particularly in the warmer months, raises concerns about the suitability of these refuges in the face of climate change. Implications. Understanding these microhabitat conditions is essential to grasp the fine-scale relationship between the organism and its environment.