Latitudinal cline in weapon allometry and phenology of the European stag beetle

Abstract

Animal body size commonly exhibits a remarkable variation in response to environmental conditions. Latitude, when correlated with temperature, rainfall and seasonality, represents one of the main determinants of variation in body size, as well as in allometry. It has long been recognised that populations of larger body size are found in colder environments (Bergmann's Rule), a cornerstone of evolutionary ecology. However, the way in which latitude might influence investment in exaggerated weapons of animals has received little attention. The European stag beetle Lucanus cervus (Linnaeus, 1758) is the focus of this study. Males of this species exhibit exaggerated mandibles, mainly used as weapons during intra-sexual conflicts. Five populations ranging from northern Italy to the southern limit of the distribution of L. cervus were analysed. Combining morphological and phenological data, latitudinal variation in body size, weapon investment and activity period of the adults were evaluated. The analysis of the allometry of mandibles strongly supported the presence of two male morphs. Large males (major morph) invest significantly more in weapons compared to males of the minor morph. Consistent with Bergmann's Rule, these results confirmed that

Latitudinal variation and coevolutionary diversification of sexually dimorphic traits in the false blister beetle Oedemera sexualis

“…Although trait variation across geographic regions is a fundamental subject with a long history in evolutionary biology, the processes responsible for geographic variation in sexual traits are still only partially understood (Hasegawa & Arai, 2013 2011; Painting et al, 2014;Romiti et al, 2017). In this study, we ob- hind leg was bigger and the hind tibia relatively slenderer at lower latitudes than at higher latitudes.…”

“…Although trait variation across geographic regions is a fundamental subject with a long history in evolutionary biology, the processes responsible for geographic variation in sexual traits are still only partially understood (Hasegawa & Arai, ; Kelly, Folinsbee, Adams, & Jennions, ; Monteiro & Lyons, ; Outomuro & Johansson, ; Painting et al, ; Romiti et al, ). In this study, we observed remarkable variation in body size, the dimensions of sexually dimorphic hind legs, and their allometric slopes across populations of O. sexualis .…”

“…Unlike population means of the traits, however, allometric slopes of male and female hind leg dimensions in O. sexualis were not clearly associated with latitude. In recent examples of latitudinal cline in exaggerated male traits used as weaponry in male–male combat, allometric slopes were associated with latitude (Painting et al, ; Romiti et al, ). Processes responsible for the differentiation of allometric slopes of sexual traits may differ between male–male competition and intersexual selection or sexual conflict.…”

“…Since the estimated slopes were strongly correlated between OLS and SMA in all traits ( r 19 = 0.76–0.97, p < 0.001), only the SMA results are shown. SMA has been frequently used in recent studies on the latitudinal cline of sexual traits (Painting et al, ; Romiti et al, ) and is thus useful for making comparisons.…”

“…Latitudinal clines in body size are found in various groups of animals (e.g., crustaceans, Timofeev, ; insects, Cushman, Lawton, & Manly, ; Sota, Takami, Kubota, & Ishikawa, ; Sota, Takami, Kubota, Ujiie, & Ishikawa, ; fish, Belk & Houston, ; Estlander et al, ; amphibians, Adams & Church, ; Ashton, ; and reptiles, Ashton & Feldman, ). However, latitudinal variation in sexual traits has rarely been explored (Painting, Buckley, & Holwell, ; Romiti et al, ).…”