Sunday, May 31, 2015

[Herpetology • 2015] Patterns of Reproductive-Mode Evolution in Old World Tree Frogs (Anura, Rhacophoridae)


life-history characteristics: blue – fully aquatic development (AB); red – terrestrial, gel-encapsulated eggs laid over water with initial phases of larval development in the egg and later stages in the water (GN); yellow – terrestrial eggs in foam nest over water with later stages of larval development in the water (FN); green – fully terrestrial development (DD)
Figure 1.
 — B. The proportionate number of all known rhacophorid species characterized by AB (10 spp.), GN (54 spp), FN (134 spp.) and DD (189 spp.); (i) Buergeria sp. eggs in water; (ii) Gracixalus lumarius eggs above a tree hole; (iii) Gracixalus quangi tadpoles on leaf overhanging water; (iv–vii) Raorchestes resplendens embryonic stages and fully developed metamorphs; (viii) Rhacophorus lateralis and (ix) Rhacophorus malabaricus foam nests (FN).


The Old World tree frogs (Anura: Rhacophoridae), with 387 species, display a remarkable diversity of reproductive modes – aquatic breeding, terrestrial gel nesting, terrestrial foam nesting and terrestrial direct development. The evolution of these modes has until now remained poorly studied in the context of recent phylogenies for the clade. Here, we use newly obtained DNA sequences from three nuclear and two mitochondrial gene fragments, together with previously published sequence data, to generate a well-resolved phylogeny from which we determine major patterns of reproductive-mode evolution. We show that basal rhacophorids have fully aquatic eggs and larvae. Bayesian ancestral-state reconstructions suggest that terrestrial gel-encapsulated eggs, with early stages of larval development completed within the egg outside of water, are an intermediate stage in the evolution of terrestrial direct development and foam nesting. The ancestral forms of almost all currently recognized genera (except the fully aquatic basal forms) have a high likelihood of being terrestrial gel nesters. Direct development and foam nesting each appear to have evolved at least twice within Rhacophoridae, suggesting that reproductive modes are labile and may arise multiple times independently. Evolution from a fully aquatic reproductive mode to more terrestrial modes (direct development and foam nesting) occurs through intermediate gel nesting ancestral forms. This suggests that gel nesting is not only a possible transitional state for the evolution of terrestriality, but also that it is a versatile reproductive mode that may give rise to other terrestrial reproductive modes. Evolution of foam nesting may have enabled rhacophorids to lay a larger number of eggs in more open and drier habitats, where protection from desiccation is important. Terrestrial direct development allows frogs to lay eggs independent of bodies of water, in a diversity of humid habitats, and may represent a key innovation that facilitated the evolution of nearly half of all known rhacophorid species.

Figure 1.A. 50% majority-rule consensus tree from the Bayesian analysis. Major developmental modes of Rhacophoridae indicating Bayesian ancestral-trait reconstruction probabilities for the following life-history characteristics: blue – fully aquatic development (AB); red – terrestrial, gel-encapsulated eggs laid over water with initial phases of larval development in the egg and later stages in the water (GN); yellow – terrestrial eggs in foam nest over water with later stages of larval development in the water (FN); green – fully terrestrial development (DD). The basal life-history strategy for rhacophorids was AB; GN arose multiple times, subsequently giving rise to FN twice and DD two or three times.
B. The proportionate number of all known rhacophorid species characterized by AB (10 spp.), GN (54 spp), FN (134 spp.) and DD (189 spp.); (i) Buergeria sp. eggs in water; (ii) Gracixalus lumarius eggs above a tree hole; (iii) Gracixalus quangi tadpoles on leaf overhanging water; (iv–vii) Raorchestes resplendens embryonic stages and fully developed metamorphs; (viii) Rhacophorus lateralis and (ix) Rhacophorus malabaricus foam nests (FN).
CE. Worldwide distribution of AB, GN, FN and DD. FN is the most widespread, whereas AB is the least.


Madhava Meegaskumbura, Gayani Senevirathne, S. D. Biju, Sonali Garg, Suyama Meegaskumbura, Rohan Pethiyagoda, James Hanken and Christopher J. Schneider. 2015. Patterns of Reproductive-Mode Evolution in Old World Tree Frogs (Anura, Rhacophoridae).
Zoological Scripta. DOI: 10.1111/zsc.12121


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