The study focused on one hundred male specimens of Erebia medusa collected from three sites in the Volovské vrchy and Ondavská vrchovina mountain ranges. The sampling locations were selected to represent a clear elevation gradient: Kojšovská hoľa at 1,246 meters above sea level, Zlatá Idka at 660 meters, and Dobroslava at 335 meters. Each site was visited six times per month between May and July over a three-year period from 2018 to 2020. The researchers captured the butterflies using nets and subsequently prepared the specimens for detailed morphometric analysis. This systematic approach allowed for a robust comparison of physical traits across populations exposed to different climatic conditions.

The mean annual air temperatures at these sites varied significantly, with Kojšovská hoľa recording an average of 5.7 degrees Celsius, Zlatá Idka at 7.4 degrees Celsius, and Dobroslava at 8.9 degrees Celsius. These temperature differences were monitored using dataloggers placed on tree trunks, providing precise data on the environmental conditions experienced by the butterflies. The habitats themselves also differed, with the high-elevation site characterized by sub-alpine conditions and the lower sites featuring mesophilous meadows and forest-steppes. The distinct separation of these habitats by forest fragments further emphasized the ecological isolation of the populations studied.

Traditional morphometric analysis revealed statistically significant differences in wing length and width among the three populations. Butterflies from the warmer, lower-elevation sites of Zlatá Idka and Dobroslava possessed significantly larger wings than those from the cold, high-elevation site of Kojšovská hoľa. Specifically, the mean forewing length at Kojšovská hoľa was 21.73 millimeters, compared to 23.29 millimeters at Zlatá Idka and 23.55 millimeters at Dobroslava. Similarly, the mean forewing width was 12.26 millimeters at the high site, increasing to 13.66 millimeters and 13.75 millimeters at the lower sites. These results align with the converse Bergmann’s rule, which suggests that larger body sizes are favored in environments with longer growing seasons and warmer temperatures.

Geometric morphometric analysis, utilizing sixteen landmarks on the forewing, provided further insight into shape variations. The study found that the forewings of males from the high-elevation site were more angular, elongated, and narrower than the rounder wings observed in lower-elevation populations. Principal component analysis indicated that the first two principal components accounted for a substantial portion of the shape variation, with the high-elevation population clearly differentiated along the first axis. This elongation may be an adaptation to the windy conditions prevalent at higher altitudes, potentially enhancing gliding efficiency and reducing flight costs. The rounder wing shape at lower elevations, conversely, may facilitate better maneuverability and rapid escape from predators in more complex forested environments.

In addition to size and shape, the researchers analyzed the eyespot patterns on the dorsal side of the forewings. The number of both white and black spots was significantly lower in the high-elevation population compared to the lower-elevation groups. Males from Kojšovská hoľa had an average of 2.95 white spots and 4.16 black spots, whereas those from Zlatá Idka and Dobroslava had averages of 3.72 white spots and 4.61 black spots. Statistical tests confirmed that these differences were significant, with the highest disparity observed between the high-elevation site and the middle-elevation site. This reduction in spotting at colder, higher altitudes may be linked to thermoregulatory needs or reduced predation pressure, while the increased spotting in warmer areas could serve as a deflection mechanism for predators or play a role in sexual selection.

The study also noted a temporal shift in the flight period of the butterflies corresponding to elevation. At the high-elevation site, the flight period lasted 18 days, occurring from mid-June to early July. In contrast, at the lower-elevation site of Zlatá Idka, the flight period extended to 22 days, starting at the end of May and ending in mid-June. This earlier onset and longer duration of flight in warmer areas allow for more time for growth and reproduction, contributing to the larger body sizes observed in these populations. The temporal isolation between populations, even within geographically close localities, highlights the significant impact of microclimatic variations on insect life cycles.

The findings of this study underscore the complex interplay between environmental factors and morphological traits in butterflies. The observed changes in wing size, shape, and pattern are likely the result of adaptive responses to varying intensities of environmental pressures, including temperature, wind, and predation. The elongated wings at high elevations may optimize energy efficiency in windy conditions, while the rounder wings at lower elevations enhance agility. The reduction in eyespots at colder sites may reflect a trade-off between thermoregulation and camouflage, whereas the increased spotting in warmer areas could aid in predator deflection. These adaptations demonstrate the plasticity of Erebia medusa in response to local ecological conditions.

Furthermore, the research highlights the importance of considering both abiotic and biotic factors when studying morphological variation in insects. While temperature and elevation were primary drivers of size and shape, the pattern of eyespots may also be influenced by sexual selection and predation dynamics. The study’s use of both traditional and geometric morphometrics provided a comprehensive view of the morphological differences, revealing subtle shape changes that might be missed by simple size measurements. This multi-faceted approach offers valuable insights into the functional and evolutionary significance of wing traits in butterflies.

As climate change continues to alter temperature regimes and habitat conditions, understanding these morphological adaptations becomes increasingly important. The study suggests that Erebia medusa may have limited capacity to adapt to rapid environmental changes, particularly if the growing season does not lengthen sufficiently to support larger body sizes. Continued monitoring of these populations will be essential to track how they respond to ongoing climatic shifts. The findings contribute to the broader field of evolutionary ecology, providing a detailed case study of how local environmental gradients shape the morphology of a widespread butterfly species.

Subject of Research: Morphological variation of Erebia medusa along an elevation gradient

Article Title: Wing morphology and eyespot pattern of Erebia medusa ( Lepidoptera , Nymphalidae ) vary along an elevation gradient in the Carpathian Mountains

Article References: Mikitová, B., Šemeláková, M., & Panigaj, Ľ. (2022). Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains. Nota Lepidopterologica, 45, 233-250. https://doi.org/10.3897/nl.45.68624

Image Credits: AI Generated

DOI: 10.3897/nl.45.68624

Keywords: Erebia medusa, Wing morphology, Elevation gradient, Carpathian Mountains, Butterfly ecology, Geometric morphometrics, Eyespot patterns, Thermoregulation, Converse Bergmann's rule, Insect adaptation, Wing, morphology