ABSTRACT
Morphological variation is often maintained by complex and interrelated factors, complicating the identification of underlying drivers. Comprehensive understanding of the evolution of morphological traits thus requires the use of integrative methods that can simultaneously investigate potentially interacting drivers.
Tadpole oral morphology is one such trait that may be driven by the direct and indirect effects of the environment and variation in developmental processes. Although many studies have investigated tadpole oral morphological diversity among species, few have sought to understand the drivers that underlie intraspecific variation.
In this study, we investigated potential drivers of labial tooth number variation among populations of two species of tailed frogs, the Rocky Mountain tailed frog (Ascaphus montanus) and the Coastal tailed frog (A. truei). We used an integrative eco-evo-devo framework to test the direct and indirect effects of developmental processes (population variation in size by developmental stage) and environmental selection (temperature) on labial tooth number across three tooth rows in 240 tadpoles.
Using this framework, we explained 64-81% of the variation in labial tooth number variation in three labial tooth rows for A. montanus and 37-54% of the variation in labial tooth number in the same tooth rows for A. truei. Apart from the consistent effects of tadpole length on labial tooth number, we found strong support for temperature as a direct driver for increased labial tooth number, supporting our eco-evo hypothesis in both species. In A. montanus, we also found strong support for variation in our proxy for developmental processes influencing labial tooth number variation (devo-evo), as well as the interacting effects of temperature and this developmental process proxy (i.e., developmental plasticity; eco-devo). In A. truei, we found mixed support for these latter two drivers among labial tooth rows.
We conclude that labial tooth number variation in tailed frogs is driven by complex and interacting environmental and developmental factors. Without the use of an interdisciplinary framework, these relationships may not have been uncovered and our ability to explain the variation in this morphological trait would have been limited.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Data Availability Statement Data for this manuscript will be deposited to Dryad upon acceptance.
New analytical framework; author order revised.
