Clasp and dance: Mating mode promotes variable sexual size and shape
dimorphism trajectories in crocodile newts (Caudata: Salamandridae)
Sexual dimorphism (SD) is a main source of intraspecific morphological
variation, however sexual shape dimorphism (SShD) was long time
neglected in evolutionary research. Especially in cold-blooded animal
groups only subtle shape differences are expressed between males and
females and the selective forces behind it are poorly understood.
Crocodile newts of the genera Echinotriton and Tylototriton are highly
polymorphic in their reproductive ecology and hence, are a highly
suitable model system to investigate potential evolutionary forces
leading to SShD differences. We applied 3D geometric morphometrics to
the cranial and humerus morphology of nine species of crocodile newts to
investigate patterns of SShD in relation to the different mating modes.
Trajectories of shape differences between males and females differ in
both, cranium and humerus but mating mode does explain differences in
SShD trajectories between species only in cranial morphology.
Nevertheless, cranial morphology shape differed between the amplecting
and circle dancing species. Hence, other selective forces must act here.
Variable interspecific allometric trajectories are a potential source of
shape differences whereas these trajectories are quite stable for the
sexes irrespective of the species.