Victoria C. Giménez Gómez

Global warming is expected to strongly impact insect populations, particularly in montane environments where elevational gradients impose steep climatic variation. Insects in these systems are thought to be especially vulnerable because upward range shifts reduce available habitat. However, few studies have considered the combined influence of temperature and aridity on thermal tolerance at the intraspecific level. Here, we examined physiological and morphological variation in populations of the carabid beetle (Coleoptera) Baripus nevado along an altitudinal gradient (2380, 2644 and 2959 m) in Cerro Nevado, Argentina, an arid mountain system. We measured upper thermal limits (CTmax and upper lethal temperature [ULT]), body size and water loss. Our results revealed significant intraspecific variation: CTmax, ULT, body size and water loss/body size all declined with elevation. Low‐elevation populations exhibited the highest thermal limits and body mass, consistent with adaptations to endure greater aridity and desiccation stress. These patterns contrast with previous studies reporting conserved upper thermal limits within species across elevations, highlighting the role of water availability as an additional selective pressure. Our findings suggest that physiological and morphological diversity within species can buffer climate change impacts, but also indicate that increasing aridity may pose critical challenges even for heat‐tolerant populations. Overall, we demonstrate that intraspecific variation in thermal physiology is shaped by the interaction between temperature and aridity, and that this variation could be key for the persistence of montane insects under climate change.

Insects, particularly dung beetles, are highly sensitive to environmental changes due to their dependence on climatic variables like temperature and humidity. These variables control numerous physiological and biochemical functions, making the study of insect ecophysiology crucial for understanding their spatial and temporal distribution. Dung beetles play vital roles in ecosystems, such as nutrient recycling, soil aeration, greenhouse gas mitigation, seed dispersal, and improving livestock health. Due to their sensitivity to environmental changes and antiparasitic drugs excreted in cattle feces, they serve as excellent bioindicators. Extensive studies worldwide have examined the ecophysiological responses of dung beetles to temperature, humidity, residues of veterinary medications excreted in cattle dung, and trophic preferences, revealing significant impacts on their survival and ecosystem functions. In Argentina, although some local and regional studies have explored some of these aspects, comprehensive ecophysiological research remains limited. Future studies in Argentina should focus on the effects of temperature, humidity, antiparasitic drugs, and trophic resources, to enhance the understanding of dung beetles' ecophysiological responses. Such research is essential for developing effective conservation strategies, particularly in regions with high cattle production and diverse dung beetle populations, ensuring the maintenance of their important ecological functions.

Physiological traits in insects are useful to understand their distribution at different spatial scales, their presence and abundance, and the use of different habitats. This study explored physiological parameters of dung beetles in two contrasting ecoregions of Argentina: Paranaense Forest and Dry Chaco. We capture dung beetles from both regions and habitats with different degrees of disturbance within each region, and performed lab experiments on metabolic rate and thermal tolerance. This study revealed that dung beetles inhabiting regions or habitats with higher temperatures (Dry Chaco and open pastures) showed greater temperature tolerance compared to those inhabiting regions or habitats with lower temperatures (Paranaense Forest and habitats preserving tree canopy). Furthermore, in the Dry Chaco, more species exploit open disturbed habitats, indicating less physiological sensitivity to temperature changes than dung beetles in the Paranaense Forest. This study is the first to compare dung beetle assemblages at both regional and local scales. The findings highlight the importance of preserving tree canopy in land use planning to mitigate microclimatic changes, especially in humid forests, to support dung beetle populations and their crucial ecosystem roles in the face of climate change.

Dung beetles exhibit a wide range of trophic preferences, including soft and hard resources. The study of mouthparts associated with these resources is extensive, and mouthparts of these insects have generally been described as membranous, hairy, and poorly adapted to cutting hard food. In this study, we compare the mouthparts (epipharynx, labium, and hypopharynx) of five species of Dichotomius Hope from Argentina that show differences in their trophic preferences, to evaluate if these structures also differ according to their feeding habit. We found epipharyngeal teeth, hypopharyngeal teeth, and more sclerotized structures in species that consume hard resources [Dichotomius carbonarius (Mannerheim)] and the absence or reduction of these structures in species that consume soft resources [Dichotomius sericeus (Harold), Dichotomius nisus (Olivier), Dichotomius mormon (Ljungh), and Dichotomius depressicollis (Harold)]. On the other hand, the latter species have hairier and softer mouth structures associated with these soft resources. According to these results, a detailed study of the macrostructures of mouthparts could indicate a priori the resource state consumed by a dung beetle species: the presence or absence of teeth and sclerotized structures would be associated with hard or soft food as the main resource, respectively, despite the occasional use of other resources in the field.

Functional diversity approaches, which are based on an organism's trait pattern, are of increasing interest in ecological studies. However, there are no rules setting the number or kinds of traits that should be assessed; hence, researchers are left to make their own decisions in this regard. Moreover, in some cases, the same trait could be assessed using different procedures, making comparisons between studies potentially difficult. Such is the case of dung beetle body size. We found that it was measured by using eight different methods in the literature. Using three scarabaeine dung beetle species (Canthon quinquemaculatus Castelnau, Deltochilum komareki Balthasar, and Eurysternus parallelus Castelnau), eight methods of measuring dung beetle body size (wet weight, dry weight, wet weight × clypeal-pygidial length, clypeal-pygidial length, pronotal-pygidial length, clypeal-elytral length, pronotal-elytral length, and elytral width × pronotal-elytral length) were compared to determine if they are equivalent. Using a Spearman correlation coefficient, not all the measurement methods were found to be equivalent. Wet and dry weight were the least correlated with all other methods. Hence, to standardize measurement methods in future studies, dry body weight is suggested for use, which also has the advantage of being an easy method to use. Standardization will allow more reliable and accurate comparisons between studies.

The authors investigated the role of thermoregulation mechanisms and thermal limits on thermal niche differentiation in two hierarchical similar Eucraniini dung beetle assemblages inhabiting arid environments in north‐western Argentina. Both dung beetle assemblages showed temporal and thermal niche segregation between all sympatric species, minimising overlap during their daily activity and soil temperature preferences. Thermal tolerance of Eucraniini species was partially modulated by behavioural adaptations and complementary thermoregulatory mechanisms related to eliminating the temperature excess, increasing the metabolic rate promoting an effective regulation of the excess heat that permitted a decrease in their body temperature by evaporative cooling. Based on the physiological syndromes obtained, the authors found a greatest interspecific differentiation that allows us to differentiate each species using ecophysiological traits. Interspecific body size differences in sympatric Eucraniini contributed greatly to the metabolic capacity of individuals to thermoregulate. Eucranium species, the largest species showed the lowest capacity to respond to thermal stress decreasing heat excess temperature, presenting the lowest thermal limit values coinciding with a ‘minithermy’ strategy that explains the preferred lower soil temperatures around 30°C. On the contrary, Anomiopsoides species showed a clear adaptation to being active during periods of the day in which the soil temperature reached over 50°C, adopting a strategy of ‘maxithermy’ by foraging when temperatures are closer to their thermal limits. In conclusion, it can be determined that ecophysiological syndromes related to thermal stress regulation and thermal limits allowed a displacement in thermal niche dimension, minimising interspecific competition and so allowing species coexistence in Eucraniini dung beetles.