Raisa A. Sukhodolskaya, Viktor V. Aleksanov, Teodora M. Teofilova, Vladimir Langraf, Aleksander G. Borisovsky, Alexander B. Ruchin, Sergey L. Luzyanin, Olga A. Neverova, Sergey E. Shchetinin, Igor A. Solodovnikov, Chiara Ferracini, Dominik Stočes, Roman P. Gorbunov

Carabus granulatus (Coleoptera, Carabidae) body size becomes less dependent on habitat latitude as soil organic carbon increases across mid-latitude zone

Introduction

Carabus granulatus (coleoptera, carabidae) body size becomes less dependent on habitat latitude as soil organic carbon increases across mid-latitude zone. Research reveals Carabus granulatus body size dependence on habitat latitude lessens with higher soil organic carbon. Explores sex differences and implications for ecological monitoring.

Abstract

The study examined the relationship between soil quality and the size characteristics of ground beetle Carabus granulatus as bioindicators of ecosystem health. Soil quality is defined by its ability to sustain biological productivity, the surrounding environment, and the health of living organisms, with biological (especially soil invertebrates), chemical, and physical soil properties playing a key role. The aim of the research was to identify the influence of soil factors on the size variability of ground beetles. Using regression analysis, we studied the dependence of beetle size on organic carbon content in the soil (0–5 cm layer) and the geographical latitude of the habitat, taking into account the sex of the insects. Carbon content data were extracted from an existing global distribution map generated using machine learning. A total of 8107 specimens from 13 regions (42,9–56,8° N) were examined. The findings revealed a statistically significant influence of both latitude and organic carbon content on beetle size, with an interaction effect identified. It was established that males are 1 mm smaller than females. Additionally, for each degree increase in latitude, the length of the elytra decreases by 0.13 mm, and for each tonne of organic carbon in the 5 cm soil layer, it decreases by 0.14 mm. The results demonstrate a compensatory effect: as organic carbon content increases, the influence of habitat latitude on insect size weakens. These findings expand our understanding of the mechanisms shaping insect size variability in relation to soil conditions and geographical location, which is important for ecological monitoring and bioindication.

Review

This study presents a compelling investigation into the intricate relationship between soil quality, geographical latitude, and the body size of *Carabus granulatus* ground beetles, a recognized bioindicator species. The research addresses a pertinent ecological question regarding how environmental factors shape insect morphology, with significant implications for ecosystem health assessment. The central contribution is the identification of a novel compensatory effect, demonstrating that the dependence of beetle body size on habitat latitude diminishes as soil organic carbon content increases across the mid-latitude zone. This finding provides valuable insights into the complex interplay of environmental drivers influencing biological traits. The methodology employed is robust, utilizing regression analysis to explore the influence of organic carbon content, geographical latitude, and insect sex on beetle size. A notable strength is the substantial dataset, comprising 8107 specimens collected from 13 regions spanning a considerable latitudinal range (42.9–56.8° N). The analysis revealed statistically significant influences from both latitude and organic carbon, alongside an identified interaction effect. Quantitatively, the study established that males are consistently smaller than females, and both increasing latitude and higher organic carbon content are associated with a decrease in elytra length. Crucially, the core finding is that elevated soil organic carbon content acts to weaken the typically observed latitudinal influence on insect size, suggesting a buffering capacity of higher soil quality. The study's large sample size and clear identification of quantitative relationships enhance the credibility and generalizability of its findings. The discovery of this compensatory mechanism significantly advances our understanding of the multi-faceted environmental determinants of insect body size, moving beyond simple linear relationships. This work is particularly relevant for ecological monitoring and the effective use of bioindicators, as it suggests that the interpretation of latitudinal size gradients in *Carabus granulatus* might need to account for varying soil organic carbon levels. This research represents a significant step forward in understanding insect adaptability to changing environmental conditions and offers valuable insights for conservation efforts.

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