Bachelor Thesis

Color variation along an altudinal gradient of ground beetles (Carabidae) in Central Europe

Dorothee Stiller (08/2015-09/2015)

Support: Carl Beierkuhnlein, Andreas Schweiger

Elevational gradients offer a great opportunity to study ecologically relevant factors, as there are steep alterations of environmental parameters within short distances. Temperature is one of the most influential ecological variables for organisms and varies considerably along elevational gradients. Ectotherms, which rely upon external heat sources, need to compensate cold air temperatures in high elevations through thermal benefits. The thermal melanism hypothesis assumes that ectotherms tend to be darker at high elevation to increase heat gain, as different color morphs have different thermoregulatory properties and a dark cuticle improves heat absorbance and accelerates heat transmission. In this study the darkness of 766 ground beetles (Carabidae) distributed in Central Europe is investigated along an elevational gradient. It is hypothesized that darkness increases with elevation, as a consequence of a thermal advantage evoked by decreasing temperatures. The elevational distribution of every beetle species was generated by various literature and the matching color information comes from an online data bank with digital photographs (http://www.eurocarabidae.de/). Mean elevation was used to determine the relation between darkness and elevation. It was revealed that darkness increases with elevation but mean elevation is less crucial for the development of darkness and consequently, giving some support to the thermal melanism hypothesis. In further investigations lifestyle (below or above ground) showed almost no influence on dark coloration. The trophic level of the ground beetles, but particularly the eye size were found to be more decisive. It is supposed that the eye size of the carabids correlates with their body size, and could be connected with darkness in terms of the heat balance hypothesis.