Patterns of cranial sexual dimorphism in the yellow-bellied toad (Bombina variegata, Bombinatoridae)

Abstract

This study provides first insight into patterns of adult cranial size and shape sexual dimorphism in the yellow-bellied toad (Bombina variegata). Our results revealed significant cranial sexual size and shape differences in this species, with a very small impact of allometry on the shape diversity. The pattern of cranial sexual dimorphism indicates early differentiation of the sexes followed by parallel growth trajectories. Males have a larger cranium than females. Shape differences between the sexes are pronounced in the trophic part of the cranium. In comparison to females males have the lateral part of the nasal displaced posteriorly, a shorter anterior pterygoid process and the posterior part of the quadratojugal and pterygoid displaced toward the snout. Therefore, males have a wider but shorter posterior part of the cranium. Adaptation to divergent trophic niches driven by natural selection rather than sexual selection could have led to sexual size and shape differences in the yellow-bellied toad. However, further analysis of cranial variation patterns including ontogenetic aspects of cranial variation and ecological niche analyses are crucial to elucidate how different developmental and evolutionary mechanisms act on the cranium and result in size and shape sexual dimorphism.