Hylidae

Abstract: A phylogenetic analysis of sequences from 503 species of hylid frogs and four outgroup taxa resulted in 16,128 aligned sites of 19 genes. The molecular data were subjected to a maximum likelihood analysis that resulted in a new phylogenetic tree of treefrogs. A conservative new classification based on the tree has (1) three families composing an unranked taxon, Arboranae, (2) nine subfamilies (five resurrected, one new), and (3) six resurrected generic names and five new generic names. Using the results of a maximum likelihood timetree, times of divergence were determined. For the most part these times of divergence correlated well with historical geologic events. The arboranan frogs originated in South America in the Late Mesozoic or Early Cenozoic. The family Pelodryadidae diverged from its South American relative, Phyllomedusidae, in the Eocene and invaded Australia via Antarctica. There were two dispersals from South America to North America in the Paleogene. One lineage was the ancestral stock of Acris and its relatives, whereas the other lineage, subfamily Hylinae, differentiated into a myriad of genera in Middle America.

Abstract: Species distributed across vast continental areas and across major biomes provide unique model systems for studies of biotic diversification, yet also constitute daunting financial, logistic and political challenges for data collection across such regions. The tree frog Dendropsophus minutus (Anura: Hylidae) is a nominal species, continentally distributed in South America, that may represent a complex of multiple species, each with a more limited distribution. To understand the spatial pattern of molecular diversity throughout the range of this species complex, we obtained DNA sequence data from two mitochondrial genes, cytochrome oxidase I (COI) and the 16S rhibosomal gene (16S) for 407 samples of D. minutus and closely related species distributed across eleven countries, effectively comprising the entire range of the group. We performed phylogenetic and spatially explicit phylogeographic analyses to assess the genetic structure of lineages and infer ancestral areas. We found 43 statistically supported, deep mitochondrial lineages, several of which may represent currently unrecognized distinct species. One major clade, containing 25 divergent lineages, includes samples from the type locality of D. minutus. We defined that clade as the D. minutus complex. The remaining lineages together with the D. minutus complex constitute the D. minutus species group. Historical analyses support an Amazonian origin for the D. minutus species group with a subsequent dispersal to eastern Brazil where the D. minutus complex originated. According to our dataset, a total of eight mtDNA lineages have ranges >100,000 km2. One of them occupies an area of almost one million km2 encompassing multiple biomes. Our results, at a spatial scale and resolution unprecedented for a Neotropical vertebrate, confirm that widespread amphibian species occur in lowland South America, yet at the same time a large proportion of cryptic diversity still remains to be discovered.

Abstract: Phenotypically plastic responses to environmental change are typically com- partmentalized by the type of environmental cues that cause the induction (e.g., temperature, light), but different types of environmentally induced responses might very well be related to each other. I used a number of experiments to document competitor-induced behavior and morphology in wood frog tadpoles (Rana sylvatica), to quantify how competitor-induced changes affected subsequent competitive ability, and to investigate the cues responsible for the competitor-induced response. Competitors induced wood frogs to increase their activity and generally develop larger bodies and smaller tails. Further, wood frogs were able to discriminate between intraspecific and interspecific competitors. Whereas behavioral re- sponses to competitors are well documented, the widespread morphological responses are a new discovery; these responses are particularly intriguing because they are in the opposite direction of predator-induced responses in tadpoles. The competitor-induced phenotypes are not simply an allometric effect, but appear to be adaptive responses to competitors; competitor-induced wood frogs experienced higher relative growth rates than noninduced wood frogs in subsequent performance trials, but past studies suggest that the competitor- induced phenotype should experience higher predation risk. When responding to compe- tition, wood frogs were not responding only to reduced food. They were able to sense changes in both the per capita food levels and changes in density (per unit volume) that were independent of per capita food level. Thus, these animals have an amazing ability to sense changes in their environments and respond in very precise ways. When one considers competitor-induced responses in light of past studies on predator- induced phenotypes in larval anurans, one sees that predator-induced traits provide indi- viduals with increased predator resistance but decreased competitive ability, whereas com- petitor-induced traits provide individuals with. increased competitive ability but decreased predator resistance. This suggests that predator- and competitor-induced plasticity have evolved an intricate link that presents a trade-off between competitive ability and predator resistance ability. This trade-off is common across species and makes sense in light of the environments in which wood frogs live, ranging from ponds with high densities of predators and few tadpoles competing to ponds with few predators and extremely high densities of tadpoles competing. Further, there is evidence that this type of plasticity trade-off might be quite common in other phenotypically plastic taxa.