|Figure 1. Appearance of caruncles in dorsal (top row), lateral (middle row), and frontal (bottom row) views of the four species of Limnonectes; Limnonectes dabanus (Smith, 1922), Limnonectes gyldenstolpei (Andersson, 1916), Limnonectes macrognathus (Boulenger, 1917), and Limnonectes plicatellus (Stoliczka, 1873)|
Only the dorsal images are to scale. Scale bar: 1 cm.
The males of four species of the Asian frog genus Limnonectes [Limnonectes dabanus (Smith, 1922a), Limnonectes gyldenstolpei (Andersson, 1916), Limnonectes macrognathus (Boulenger, 1917), and Limnonectes plicatellus (Stoliczka, 1873)] exhibit remarkable ornamentation in the form of a swollen, or cap-like, structure (caruncle) on the top of their heads. These caruncles vary in their appearance among species, and neither their function nor their actual systematic value is known. We compared their anatomy via dissections, morphometrics, radiography, and histology, and analysed the available mitochondrial DNA sequences as well as new data to place these species within the context of a larger phylogenetic hypothesis for Limnonectes. Despite the externally different morphology, the underlying histological structure is virtually identical. Beneath skin that is densely packed with mucous glands lies a pad of connective tissue overlaying the parietal bone. The actual function of the caruncle, however, remains enigmatic. In addition to the presence of the caruncle, independent evidence from osteological characters and molecular data support the monophyly of a clade comprising of L. dabanus, L. gyldenstolpei, L. macrognathus, and L. plicatellus. The caruncles are therefore interpreted as a robust autapomorphy for this clade, and suggest that the subgenus Elachyglossa should be restricted to the four species in question.
Keywords: Elachyglossa; functional morphology; integrative taxonomy; Limnonectes dabanus; Limnonectes gyldenstolpei; Limnonectes macrognathus; Limnonectes plicatellus; phylogeny; Ranoidea; Southeast Asia
|Figure 2. Head of a male Limnonectes gyldenstolpei, mediosagittally split. The actual specimen is shown on the left, whereas the right-hand image shows the H&E stained surface of the corresponding view. Note the flap-like caudad curve of the posterior margin of the caruncle (ca).|
Abbreviations: br, brain; ca, caruncle; to, tongue. Scale bar: 1 cm.
|Figure 6. Simplified phylogram demonstrating the relationships among the caruncle-bearing Limnonectes, within the context of the genus Limnonectes and the Limnonectes kuhlii complex, based on a Bayesian analysis of 16S mtDNA sequences. Numbers above branches are Bayesian posterior probabilities.|
Fejervara limnocharis (Gravenhorst, 1829), Hoplobatrachus rugulosus (Wiegmann, 1834), and Occidozyga laevis (Günther, 1858) were used to root the tree (not shown).
Markus Lambertz, Timo Hartmann, Shannon Walsh, Peter Geissler and David S. McLeod. 2014. Anatomy, Histology, and Systematic Implications of the Head Ornamentation in the Males of Four Species of Limnonectes (Anura: Dicroglossidae). Zoological Journal of the Linnean Society. DOI: 10.1111/zoj.12171
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