Osteological development of a small and fast metamorphic frog, Microhyla fissipes (Anura, Neobatrachia, Microhylidae)

Abstract

Describing osteological development is of great importance for understanding vertebrate phenotypic variations, form‐functional transitions and ecological adaptations. Anurans exhibit dramatic changes in their morphology, habitat preferences, diet and behaviour between the tadpole and frog stages. However, the anatomical details of their cranial and postcranial development have not been extensively studied, especially in Microhylidae. In this work, we studied the microhylid Microhyla fissipes, commonly known as the ornamented pygmy frog, a small‐sized frog with fast metamorphosis. Its osteological development was comprehensively described based on 120 cleared and stained specimens, including six tadpoles for each stage between 28 and 45, six juveniles and six adults. Additionally, 22 osteological traits of these specimens involved in food acquisition, respiration, audition and locomotion were selected and measured to reflect the changes in tadpole ecological functions during metamorphosis. Our study provides the first detailed qualitative and quantitative developmental information about these structures. Our results have confirmed that skeletal elements (viz., neopalatines, omosternum, clavicles and procoracoids) absent in adults are not detected during development. Our data reveal that morphologically, radical transformations of the cranial structures related to feeding and breathing are completed within stages 42–45 (72 h), but the relative length and width of these skeletons have changed in earlier stages. The postcranial skeletons correlated with locomotion are well developed before stage 42 and approach the adult morphology at stage 45. Indeed, the relative length of the pectoral girdle and forelimb reaches the adult level at stage 42 and stage 45, respectively, whereas that of the vertebral column, pelvic girdle and hind limbs increases from their appearance until reaching adulthood. Based on published accounts of 19 species from Neobatrachia, Mesobatrachia and Archaeobatrachia, cranial elements are among the first ossified skeletons in most studied species, whereas sphenethmoids, neopalatines, quadratojugals, mentomeckelians, carpals and tarsals tend to ossify after metamorphosis. These results will help us to better understand the ecomorphological transformations of anurans from aquatic to terrestrial life. Meanwhile, detailed morphological and quantitative accounts of the osteological development of Microhyla fissipes will provide a foundation for further study.

Restricting living space: Development and larval morphology in sticky frogs (Microhylidae: Kalophrynus) with different reproductive modes

“…The morphology of the larval chondrocranium and brachial skeleton of the three Kalophrynus species also differs markedly. In K. interlineatus, these structures are in many aspects similar to those of other pond-dwelling microhylid tadpoles studied to date, in particular, the representatives of the neotropical genera Hamptophryne, Chiasmocleis, Gastrophryne, Dermatonotus, and Elachistocleis (de Sá and Trueb 1991;Vera Candioti 2007;Trueb et al 2011;Fabrezi et al 2012;Ferreira and Weber 2021), as well as the Asian genera Uperodon, Microhyla, and Kaloula (Ramaswami 1940;Haas 2003;Bowatte and Meegaskumbura 2011;Vassilieva 2021;Zhang et al 2021). All of these tadpoles share features such as a generally broad and depressed shape of the skull, an underdeveloped muscular process of the palatoquadrate, well-developed lateral posterior process, and the presence of larval otic and subotic processes; the wide cristae paroticae are mostly characteristic of neotropical microhylids, but in Asian species they are rather reduced.…”

Evolutionary rates and shape variation along the anuran vertebral column with attention to phylogeny, body size, and ecology

“…Larval habitat could also influence the evolution of vertebrae shape because vertebrae begin developing and ossifying prior to metamorphosis (Analía Púgener and Maglia 1997;Haas 1999;Wild 1999;Zhang et al 2021). Although the vertebral column has been characterized as relatively short and inflexible in most anuran adults, it participates in left-right lateral bending in freeswimming anuran larvae (tadpoles), which generates thrust during undular movement (Azizi et al 2007).…”