Our lab studies the ecology, evolution, and development of anatomical traits in amphibians (frogs, salamanders, & caecilians). Our research aims to link phylogenetic patterns and underlying developmental mechanisms to better understand the evolutionary processes that generate phenotypic variation. Some of the current projects in the lab are highlighted below. Our work integrates anatomy (via micro-computed tomography scanning of museum specimens and histology), phylogenetic comparative methods, natural history data, and developmental genetics to test macroevolutionary questions. Interested in learning more? Contact me at daniel.j.paluh@gmail.com!

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Current projects

Investigating the underlying mechanisms of convergent tooth loss in frogs​
Teeth are present in most living vertebrates, but complete tooth loss has evolved in a few groups of fishes, reptiles, and mammals. The dental diversity of amphibians has been poorly studied, but recent work in our lab has demonstrated that frogs have lost teeth more than 20 times. With phylogenetically widespread tooth loss and separate evolutionary losses on upper and lower jaws, frogs offer an unparalleled opportunity for investigating the mechanisms of convergent evolution. We our conducting in situ hybridization experiments in the lab to characterize dental development in amphibians and assess if different signals arrest tooth development among species that have independently lost teeth. The aim of this project is to determine if tooth development is disrupted across toothless species by a single conserved or several novel mechanisms.

​Evaluating the evidence for the re-evolution of lost mandibular teeth in frogs
Dollo’s law of irreversibility states that once a complex structure is lost over evolutionary time, it cannot be regained in the same form. Several exceptions to Dollo’s law have been proposed, but the development of these regained traits are often poorly understood. A single frog species, Gastrotheca guentheri, is renowned as the only anuran with teeth on the lower jaw. Previous work in our lab has assessed the dental anatomy of this species using micro-computed tomography and histology, confirming the longstanding assumption that true mandibular teeth are present. We hypothesize that an ancestral tooth development pathway has been conserved but suppressed in the lower jaw since the origin of frogs, providing a possible mechanism underlying the re-evolution of lost mandibular teeth. We are using RNAseq and in situ hybridizations to evaluate whether there is evidence for the induction of teeth on the developing lower jaw of frog species that lack mandibular teeth.  These results will provide a framework for better understanding the underlying mechanisms responsible for the evolutionary loss and potential regain of complex traits.

Exploring the evolution and development of tadpole keratinized mouthparts
The development of the keratinized mouthparts in tadpoles (sheaths and keratodonts) is poorly understood, likely because these traits are absent in the model frog species, Xenopus laevis. The evolutionary origin of these novel structures is also largely unknown, in part because tadpoles are poorly documented in the fossil record. We hypothesize that a genetic regulatory network governing development may be shared between the keratinized mouthparts of tadpoles and true teeth in frogs, similar to previous suggestions that a deep homology may exist between the keratinized teeth of cyclostomes (lamprey & hagfish) and the true teeth of jawed vertebrates. We are examining the developmental genetics of tadpole mouthparts to identify the genes that govern the initiation, development, and replacement of the keratinized sheaths (i.e., beaks) and keratodonts (i.e., labial teeth).

Modeling dental diversity evolution across amphibians
Teeth are critical for capturing prey and also are important for defense, competition, and communication. Because these functions are essential for survival and reproduction, the dentition of vertebrates is generally thought to be under intense evolutionary selection. Amphibians exhibit a wide variety of dental patterns along with significant diversity in body size, life history, diet, ecology, and behavior, making them an excellent clade for evaluating how patterns of dental diversity corresponds to evolutionary history and other biological factors. Yet, the teeth of amphibians have been poorly studied relative to other vertebrate groups. Using phylogenetic comparative methods and quantitative data collected from microCT scans, we are assessing the evolution of tooth number, size, and location across all extant frog, salamander, and caecilian genera. We are also testing whether body size, diet, and life history variation influence patterns of tooth morphology.
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