Social interactions during the aquatic breeding phase of the family Hynobiidae (Amphibia: Caudata)

Cranial skeletogenesis of one of the largest amphibians, Andrias japonicus, provides insight into ontogenetic adaptations for feeding in salamanders

Skeletal development in salamanders is greatly influenced by their complex life history. Although the relationship between skull development and life history has been investigated in a variety of salamander species, few studies have compared skull development among lineages. Here, we describe the cranial skeletogenesis of the Japanese giant salamander, Andrias japonicus (family Cryptobranchidae), for the first time. To conduct interspecific comparisons, we also describe the cranial skeletogenesis of Hynobius nebulosus (Hynobiidae), Pleurodeles waltl (Salamandridae) and Ambystoma mexicanum (Ambystomatidae). Our comparative analyses reveal interspecific differences in cranial skeletogenesis, particularly in the timing of the onset of ossification, the direction of ossification (e.g. from anterior to posterior) and the ossification pattern of the hyobranchial skeleton. The early onset of jaw ossification, posterior extension of the maxilla and posterolateral inclination of the squamosal in An. japonicus might be adaptations that allow An. japonicus to gulp feed, primarily using the suction force generated by opening the mouth wide, while also supplementing that force by depressing the hyobranchial skeleton. Multivariate regression of skull shape on log10-transformed centroid size revealed that the unique skull shape of adult and subadult An. japonicus forms through hypermorphosis.

Sexual dimorphism in the Chinese endemic species Pachyhynobius shangchengensis Fei, Qu and Wu, 1983 (Urodela: Hynobiidae)

Sexual dimorphism (SD) is a widespread phenomenon in most vertebrate species and is exhibited in a myriad of ways. In amphibians, sexual size dimorphism, in which females are larger than males, is the most common type, and sexual shape dimorphism varies among species. Different selection forces (sexual selection, fecundity selection, and ecological selection) that act differently upon the sexes form the consequence of SD. Thus, studies of SD provide information about the general intersexual divergence of the same species and allow insights into the impact of selective forces on the sexes. In this study, we analyzed morphometric data of the Shangcheng stout salamander, Pachyhynobius shangchengensis, an endemic and poorly known Chinese salamander, to examine sexual dimorphism in size and shape. The morphometric data included 15 characteristics of 68 females and 55 males which were analyzed using univariate and multivariate methods. A significant difference was found between the sexes in terms of both body size (snout-vent length) and some body shapes (e.g., head length and width, tail length and width, distance between limbs, and limb length and width) in this salamander. The longer snout-vent length in males may be attributed to sexual selection, longer and wider head in males may contribute to male-male competition, longer and wider tail in males may be attributed to energy storage and reproductive success, the larger distance between limbs in females is likely due to a fecundity advantage, and longer and more robust limbs in males may be related to reproductive or competitive behaviors. These results demonstrated that sexual dimorphism of different morphological traits is the consequence of different selection forces that act differently upon the sexes.

Comparison of hematological parameters in two different high altitudinal populations of Batrachuperus pinchonii (Amphibian: Urodela)

Hematological parameters are key to reflect the health status of animals and their physiological adaptation to the environment. However, few studies focused on the inter- and intra-specific variations of hematological parameters in hynobiid salamanders. Here, we examined the hematological parameters of the stream salamander,Batrachuperus pinchonii, originating from two different altitudinal populations to explore their intra-specific variation. Sexual dimorphism is only present in the erythrocyte count and males have higher mean values than females. The morphometric values of erythrocyte, hemoglobin concentration, and erythrocyte count of the high altitudinal (Jiajin) population were smaller than those of the lower altitudinal (Sandaoping) population; however, a significant difference between two populations was only revealed in the case of erythrocyte length via ANOVA. The results of linear regression showed that a significant relationship was present between body condition and erythrocyte length as well as the erythrocyte length to erythrocyte width ratio. Our findings suggest that the features of hematological parameters inB. pinchoniiare reflected in the size of erythrocyte, and neither in erythrocyte count nor in hemoglobin concentration. These results provide a foundation for assessing and monitoring the health status of this salamander species, and furthermore, for understanding the physiological basis of altitudinal adaptation.