Repeated evolution of underwater rebreathing in diving Anolis lizards
This repository contains all data used to generate all non-image figures (Figures 2-4, Supplementary figures) in Boccia et al 2021, "Repeated evolution of underwater rebreathing in diving Anolis lizards". Data are divided into behavioural and oxygen trace folders. Please see https://github.com/chrisboccia/anole-rebreathing-curbio for code and the data processing pipeline used. Authors: Christopher K. Boccia, Lindsey Swierk, Fernando P. Ayala-Varela, James Boccia, Isabela L. Borges, Camilo Andres Estupiñán, Alexandra M. Martin, Ramón E. Martínez-Grimaldo, Sebastian Ovalle, Shreeram Senthivasan, Ken S. Toyama, María del Rosario Castañeda, Andrés García, Richard E. Glor, D. Luke Mahler Abstract: Air-based respiration limits the use of aquatic environments by ancestrally terrestrial animals. To overcome this challenge, diving arthropods have evolved to respire without resurfacing using air held between their cuticle and surrounding water. Inspired by natural history observations in Haiti (DLM & REG pers. obs.) and Costa Rica, we conducted experiments documenting routine air-based underwater respiration in several distantly-related semi-aquatic Anolis lizard species. Semi-aquatic anoles live along neotropical streams and frequently dive for refuge or food, remaining underwater for up to 18 minutes. While submerged, these lizards iteratively expire and re-inspire narial air bubbles – underwater “rebreathing.” Rebreathed air is used in respiration, as the partial pressure of oxygen in the bubbles decreases with experimental submersion time in living anoles but not in mechanical controls. Non-aquatic anoles occasionally rebreathe when submerged but exhibit more rudimentary rebreathing behaviors. Anole rebreathing is facilitated by a thin air layer (i.e., a “plastron”, sensu Brocher) supported by the animal’s rugose skin upon submergence. We suggest that hydrophobic skin, which we observed in all sampled anoles, may have been exaptative, facilitating the repeated evolution of specialized rebreathing in species that regularly dive. Phylogenetic analyses strongly suggest that specialized rebreathing is adaptive for semi-aquatic habitat specialists. Air-based rebreathing may enhance dive performance by incorporating dead space air from the buccal cavity or plastron into the lungs, facilitating clearance of carbon dioxide, or allowing uptake of oxygen from surrounding water (i.e., a “physical gill” mechanism).