Getting in shape: adaptation and phylogenetic inertia in morphology of Australian anuran larvae

Abstract

The external morphology of frog larvae is predicted to vary among habitats, for a variety of functional reasons. I performed a phylogenetic comparative study to test whether correlations between habitat and the shape of the tadpole and its oral disc are adaptive in 82 species from south‐eastern Australia in the families Hylidae and Myobatrachidae. Habitat distributions and phylogenetic relationships were compiled from the literature and shape was quantified using geometric morphometric analysis of published drawings. Results indicate that shape evolved towards different optima in different habitats while also showing appreciable levels of phylogenetic inertia. Within myobatrachids, evolution of terrestrial tadpoles was associated with a short and shallow head/body and a shallow tail. In aquatic species, the use of benthic microhabitats was correlated with a long shallow tail, dorsal eye position, shallow head/body and ventral mouth with robust jaw sheaths. Even traits with evidence for adaptation evolved slowly in response to habitat shifts, usually requiring ≥10 million years to evolve half‐way to a new optimum. Although these findings support adaptive evolution of tadpole body form, they also highlight a strong influence of ancestral character states and indicate that phenotypes in extant species are partly maladaptive.

Where to Live? How Morphology and Evolutionary History Predict Microhabitat Choice by Tropical Tadpoles

“…Thus, it is possible that niche conservatism is not an assemblage property but a lineage property, i.e ., some species in an assemblage could have shared preferences due to niche conservatism while others have shared preferences due to convergence. Van buskirk () and Eterovick and Fernandes () have presented similar conclusions for assemblages of Australian tadpoles and in Brazilian montane meadows. Our results also reflect how little we know about the behavior of tadpoles, since we can include only general behavioral categories, ecomorphological guilds, or presence and absence data.…”

“…The external morphology of tadpoles shows high phenotypic plasticity; although the plasticity should result from evolution, morphological variation is driven by the ecological context including the effect of forest canopy and the presence or absence of predators or competitors ( e.g ., McIntyre et al . , Van buskirk ). Thus, morphology, and especially morphological variation, can be used as surrogate for ecological signal after having controlled for the phylogenetic effect.…”

“…We obtained 101 tadpole characterizations in lateral view and 68 in dorsal view. We used these characterizations to define 23 landmarks that describe tadpole morphology in the lateral view (modified from Van buskirk ), and 18 landmarks in the dorsal view (Appendix S3). Geometric morphometrics describe the variation in shape of an organism, excluding the effect of size, position, and rotation (Zelditch et al .…”

“…The source of the adaptations of organisms to their environment, and how morphological and ecological characteristics evolved, remain widely discussed issues in evolutionary biology (Peres‐neto , Lande , Griffen & Mosblack ). An ecomorphological approach tries to explain and measure the relationships between morphology ( i.e ., phenotype) and ecology ( e.g., variation in the use of resources) in communities, guilds, populations, and individuals (Peres‐neto , Van buskirk , Griffen & Mosblack ). Using this approach, we can detect morphological differences among species and associate these differences with environmental pressures and ecological factors (Irschick & Losos ).…”

Comparative feeding kinematics of tropical hylid tadpoles

“…Amphibian biologists have long noted correlations between the oral morphology of tadpoles and their habitats (e.g. Noble, 1931), and the study of tadpole ecomorphological diversity continues to be an active field of research (Van Buskirk, 2009;Vera Candioti and Altig, 2010). However, despite nearly a century of research on tadpole ecomorphology, we have (at best) a very limited understanding of how variation in tadpole oral morphology relates explicitly to feeding.…”