Seasonal constraints on the mandible allometry of Lucanus cervus (Coleoptera: Lucanidae)

Abstract

Abstract. In insects, allometries of exaggerated traits such as horns or mandibles are often considered species specific and constant during a season. However, given that constraints imposed by the advancing season affect the developmental processes of organisms, these allometries may not be fixed, and the switch point between morphs may vary between populations and within populations during a season. The hypothesis of such a seasonal variation in exaggerated traits was tested using the dimorphic males of the beetle Lucanus cervus. The remains of specimens killed by predators were collected along forest tracks from mid May to late August 2008 in a protected lowland forest in northern Italy. The largest beetles were collected in mid May and average size thereafter decreased. Males collected early in the season mostly had large mandibles (i.e. they belonged to the major morph). In contrast, late in the season the probability of finding males with large mandibles was very low. The threshold body size determining morph expression also shifted during the season. Early in the season, the threshold pronotum width for a 50% chance of developing into the major morph was 1.74 cm, whereas later in the season it was 1.90 cm. This shift in the threshold body size was interpreted as the effect of phenotypic plasticity in a population exposed to constraints imposed by the advancing season.

Exaggerated allometric structures in relation to demographic and ecological parameters inLucanus cervus(Coleoptera: Lucanidae)

“…Our results indicated that there is no phenological difference among live individuals of the two morphological classes, but minor males turned out to be more preyed on, during the flight season. On the contrary, Hardersen et al () detected a decrease in mean male fragments body size, indicating that major males were preyed mostly in the first period of the flight season. It can be hypothesized that due to the greater strength of major male mandibles and their aggressive behavior (Lagarde et al, ), some birds could be discouraged to prey (feed) on them.…”

“…To investigate if males exhibit a seasonal difference in size, the sampling season was divided in five periods (2 daily surveys for each period), with the following number of captured individuals: I ( N = 11); II ( N = 14); III ( N = 54); IV ( N = 18); V ( N = 10). Periods with less than 10 measured males, corresponding to the beginning and the end of the sampling period (i.e., from May 28 to June 13, and from July 12 to July 27) were excluded according to Hardersen et al (). The variation in body size between periods was analyzed by assessing differences in mean elytron length (LnEL) and in mean LnBM using a one‐way ANOVA and Tukey HSD posthoc tests.…”

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

“…For the allometric analysis of male mandibles, the elytron length was used as an independent variable, mainly for three reasons: (i) its proven high correlation coefficient with mandible length (Romiti et al 2015); (ii) the comparability with previous morphometric studies which used linear distances for L. cervus (Harvey and Gange 2006, Hardersen et al 2011, Chiari et al 2014, Romiti et al 2015 and (iii) to avoid scale dependence issues in comparing traits with different units (e.g., mm vs g) which could affect the data despite the log transformation (Warton et al 2006). The pooled dataset was used to analyse the allometric relationship between the mandible length (LnML) and the elytron length (LnEL) of L. cervus males.…”

“…Recently, in studying the exaggerated rostrum of the New Zealand giraffe weevil Lasiorhynchus barbicornis (Fabricius, 1775), Painting et al (2014) linked the latitudinal cline in body size with allometry (sensu Huxley and Teissier 1936). The European stag beetle, Lucanus cervus (Linnaeus, 1758), like many other species of Lucanidae, shows remarkable sexual dimorphism in mandible size and shape (Franciscolo 1997) and a great variation amongst males for this characteristic (Clark 1977, Harvey et al 2011, Hardersen et al 2011, Romiti et al 2015. The mandibles of L. cervus males can be considered as secondary sexual characteristics (SSC) that are used as weapons in intra-sexual combats (Darwin 1871, Arrow 1951, Mathieu 1969, Otte and Staymen 1979, Lagarde et al 2005.…”

When morphological identification meets genetic data: the case of Lucanus cervus and L. tetraodon (Coleoptera, Lucanidae)

“…; Harvey and Gange ; Hardersen et al. ). These morphological differences are influenced by the quantity/quality of food during the larval stages and by other seasonal constraints (Paulian and Baraud ; Paulian ; Baraud ; Harvey and Gange ; Hardersen et al.…”