Abstract
Colophon is an understudied, rare and endangered stag beetle genus with all species endemic to isolated mountain peaks in South Africa’s Western Cape. Geometric morphometrics was used to analyse intersexual and interspecific variation of size and shape in the mandibles, heads, pronota and elytra of two sympatric species: Colophon haughtoni and Colophon kawaii. All measured structures showed significant sexual dimorphism, which may result from male-male competition for females. Female mandibles were too small and featureless for analysis, but male Colophon beetles possess large, ornate mandibles for fighting. Males had significantly larger heads and pronota that demonstrated shape changes which may relate to resource diversion to the mandibles and their supporting structures. Females are indistinguishable across species, but males were accurately identified using mandibles, heads and pronota. Male C. kawaii were significantly larger than C. haughtoni for all structures. These results support the species status of C. kawaii, which is currently in doubt due to its hybridisation with C. haughtoni. We also demonstrate the value of geometric morphometrics as a tool which may aid Colophon conservation by providing biological and phylogenetic insights and enabling species identification.
Highlights
Colophon Gray, 1832, is a genus of endangered montane stag beetles (subfamily Lucaninae Latreille, 1804 (Kim and Farrell 2015)) endemic to the Western Cape Province of South Africa (Fig. 1) (Geertsema and Owen 2007; Switala et al 2015)
The mandible principal component analysis (PCA) shows two distinct clusters for C. haughtoni and C. kawaii when PC1 is plotted against PC2 (Fig. 3a)
This study has made the first exploration of Colophon morphology using geometric morphometrics
Summary
Colophon Gray, 1832, is a genus of endangered montane stag beetles (subfamily Lucaninae Latreille, 1804 (Kim and Farrell 2015)) endemic to the Western Cape Province of South Africa (Fig. 1) (Geertsema and Owen 2007; Switala et al 2015). All species are slow-moving and flightless, with adult activity spanning October to March (Barnard 1929; Endrödy-Younga 1986; Geertsema and Owen 2007). They inhabit montane fynbos habitats and are closely associated with Restionaceae bushes (Barnard 1929; Brinck 1956). Little else is known about the ecology, demography, physiology or behaviour of the genus (Geertsema and Owen 2007; Roets et al 2013)
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