Modeling Sexual Differences of Body Size Variation in Ground Beetles in Geographical Gradients: A Case Study of Pterostichus melanarius (Illiger, 1798) (Coleoptera, Carabidae)

The aim of this study was to test the steepness of body size variation in males and females in the widespread ground beetle Pterostichus melanarius in geographical gradients. Beetles were sampled in 15 regions of Europe and Asia, and sampling territories differed 17° in latitude and 121° in longitude. We measured six linear traits in every captured beetle and formed a data set that included 2154 individuals. Body size variation in all traits in general was sawtooth, both in latitude and in longitude gradients. Regression analysis showed slight trends: in the latitude gradient, elytra parameters increased, pronotum length did not change but the width increased, and head parameters decreased. In the longitude gradient, the changes were as follows: elytra length increased, but its width did not change; pronotum length did not change, but its width increased; the head parameters decreased. Thus, we observed the elytra length increase and the head parameters decrease northwards and eastwards. We compared female and male regression curves (trait size on latitude/longitude): p-levels were significant only in four cases out of 12. Thus, we conclude that, in general, there is no evidence for the steepness in trait variation in males compared with females.

Body Size Variation in a Social Sweat Bee, Halictus ligatus (Halictidae, Apoidea), across Urban Environments

High morphological variation is often associated with species longevity, and it is hypothesized that urban-dwelling species may require more plasticity in functional traits such as body size in order to maximize fitness in heterogeneous environments. There has been published research regarding the functional trait diversity of urban bee pollinators. However, no two cities are identical, so the implementation of multi-city studies is vital. Therefore, we compared body size variation in female Halicus ligatus sweat bees from May–October 2016 from three distinct Midwestern United States cities: Chicago, Detroit, and Saint Louis. Additionally, to elucidate potentially influential environmental factors, we assessed the relationship between temperature and measured body size. We collected bees in community gardens and urban farms and measured their head width and intertegular distance as a proxy for overall body size. We utilized an ANCOVA to determine whether body size variation differed significantly across the three surveyed cities. Results indicated that H. ligatus females in Chicago, Detroit, and Saint Louis had significantly different body size ranges. These findings highlight the importance of intraspecific body size variation and support our prediction that bees from different urban environments will have distinct ranges in body size due to local ecological factors affecting their populations. Additionally, we found a significant influence of temperature, though this is probably not the only important ecological characteristic impacting bee body size. Therefore, we also provided a list of predictions for the future study of specific variables that are likely to impact functional trait diversity in urban bees.

Feeding performance of the larval stag beetle Aegus chelifer (Coleoptera: Lucanidae) explains adult body size variation and sexual dimorphism

In stag beetle larvae, food availability is considered a major cause of body size variation in adults, but this has not been explicitly tested. To evaluate wood use and the effects of food quantity on growth and adult body size, the feeding performance of the tropical stag beetle Aegus chelifer MacLeay (Coleoptera: Lucanidae), which is widely distributed in Southeast Asia, was investigated by rearing larvae with different food quantities. Apparent digestibility was approximately 9%, and the efficiency of conversion of ingested food ranged from 0.7% to 1.7%. Feeding period, total food consumption, and adult body size significantly increased alongside food quantity. Males had higher consumption rates than females did at the same larval weight due to shorter food retention time. Males showed greater variation in feeding, growth performance, and adult body size than females. Differences in feeding performance that depend on food availability may enhance their fitness and may further result in sexual differences and adult body size variation.

Mammalian body size is determined by interactions between climate, urbanization, and ecological traits

Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions. Less understood are effects of other human-caused disturbances on body size, such as urbanization. We compiled 140,499 body size records of over 100 North American mammals to test how climate and human population density, a proxy for urbanization, and their interactions with species traits, impact body size. We tested three hypotheses of body size variation across urbanization gradients: urban heat island effects, habitat fragmentation, and resource availability. Our results demonstrate that both urbanization and temperature influence mammalian body size variation, most often leading to larger individuals, thus supporting the resource availability hypothesis. In addition, life history and other ecological factors play a critical role in mediating the effects of climate and urbanization on body size. Larger mammals and species that utilize thermal buffering are more sensitive to warmer temperatures, while flexibility in activity time appears to be advantageous in urbanized areas. This work highlights the value of using digitized, natural history data to track how human disturbance drives morphological variation.

Correcting for Body Size Variation in Morphometric Analysis

Using an allometric growth model to correct for body size variation has been known for many decades to be superior to several other widely used methods such as ratios, analysis of covariance, principal components analysis, and residual analysis. However, this technique remains relatively obscure and rarely applied. We optimize the implementation of this method through a newly developed and easy-to-use R package GroupStruct and use empirical datasets to test its relative efficacy compared to several commonly used methods. Our results demonstrate the superiority of the allometric method and highlights the negative impacts of applying improper body size correction methods.