Comparative skeletogenesis of the Oriental Tree Frog Hyla orientalis (Anura: Hylidae)

The ontogeny of skeletal development of the Oriental Tree Frog, Hyla orientalis (Bedriaga, 1890), is followed from tadpole to froglet and compared with four other hylid species i.e., Hypsiboas lanciformis, Hypsiboas pulchellus, Phyllomedusa vaillanti and Pseudis platensis. Our analysis and comparison is based on cleared and double-stained specimens. The parasphenoid is the first skeletal element that ossified in Hyla orientalis is followed by the exoocipital, prootic, axial and appendicular skeletal elements, frontoparietal, nasal, upper jaw, squamosal, pterygoid, lower jaw, vomer and quadratojugal. Ossification initiated at early Stage 33 in Hyla orientalis whereas in other hylids it begins after Stage 37. Major transformations of the larval jaw were visible after Stage 42. Cranial ossifications were completed after appendicular and axial ossifications of Hyla orientalis. All skeletal elements ossified before the end of the metamorphosis, a unique feature of Hyla orientalis in comparison to the other hylids studied here.     

Chimpanzees Differentially Produce Novel Vocalizations to Capture the Attention of a Human

Chimpanzees produce numerous species-atypical signals when raised in captivity. Here we report contextual elements of the use of two captivity-specific vocal signals, the "raspberry" and the extended grunt. Results demonstrate that these vocalizations are not elicited by the presence of food; rather the data suggest that these vocalizations function as attention-getting signals. These findings demonstrate a heretofore underappreciated category of animal signals: novel signals invented in novel environmental circumstances. The invention and use of species-atypical signals, considered in relation to group differences in signaling repertoires in apes in their natural habitats, may index a generative capacity in these hominoid species without obvious corollary in other primate species.     

Parallel changes in mate-attracting calls and female preferences in autotriploid tree frogs

For polyploid species to persist, they must be reproductively isolated from their diploid parental species, which coexist at the same time and place at least initially. In a complex of biparentally reproducing tetraploid and diploid tree frogs in North America, selective phonotaxis--mediated by differences in the pulse-repetition (pulse rate) of their mate-attracting vocalizations--ensures assortative mating. We show that artificially produced autotriploid females of the diploid species (Hyla chrysoscelis) show a shift in pulse-rate preference in the direction of the pulse rate produced by males of the tetraploid species (Hyla versicolor). The estimated preference function is centred near the mean pulse rate of the calls of artificially produced male autotriploids. Such a parallel shift, which is caused by polyploidy per se and whose magnitude is expected to be greater in autotetraploids, may have facilitated sympatric speciation by promoting reproductive isolation of the initially formed polyploids from their diploid parental forms. This process also helps to explain why tetraploid lineages with different origins have similar advertisement calls and freely interbreed.     

Polystoma gallieni: Experimental evidence for chemical cues for developmental plasticity

Among monogeneans that display direct life cycles, plastic developmental strategies may have been selected to counter the lack of transmission opportunities. Within amphibian polystomatids, some species of the genus Polystoma develop into two different phenotypes depending on the host physiological stage to which free swimming larvae attach. When oncomiracidia infest old tadpoles, they develop slowly and migrate during host metamorphosis towards the bladder where they reach maturity. On the other hand when larvae infest young tadpoles, they develop rapidly into neotenic phenotypes that reproduce in the branchial chamber. These alternative developments are explored through experimental infestations with Polystoma gallieni, the specific polystome of the stripeless tree frog Hyla meridionalis. When oncomiracidia were left for 6 h in water in which young tadpoles had been previously maintained for one day, they mainly developed into the neotenic phenotype regardless of the tadpole stage they encountered later. This indicates that P. gallieni could collect released host-derived signals before physical contact with its host.     

Serous cutaneous glands of the Pacific tree-frog Hyla regilla (Anura, Hylidae): patterns of secretory release induced by nor-epinephrine

The serous (poison) cutaneous glands of the Pacific tree-frog Hyla regilla were induced to release their product by 10(-3)M nor-epinephrine stimulation. After discharge structural and ultrastructural features of the cutaneous glands involved in release were observed. Furthermore, the discharged product, consisting of discrete, secretory granules, was collected and processed for transmission electron microscope analysis. As indicated by patterns found in the myoepithelium encircling the syncytial secretory unit, gland discharge is caused by contraction of the peripheral myocytes. Muscle cell compression dramatically affects the syncytium and results in degenerative changes, including expulsion of the secretory unit nuclei. Therefore, the structural collapse in depleted glands has been ascribed to the mechanical activity performed by the myoepithelium during discharge, rather than cytoplasm involution described in conventional, holocrine glands. TEM investigation revealed that the secretory granules collected after discharge maintain their peculiar traits: they consist of recurrent patterns of thin subunits, acquired during serous maturation and provided with remarkable structural stability.