Burrowing habit in Smilisca frogs as an adaptive response to ecological niche constraints in seasonally dry environments

Alondra Encarnación-Luévano,A Townsend Peterson,Octavio R Rojas-Soto

doi:10.21425/f5fbg50517

Abstract

As environmental conditions change over time, some species can follow the spatial footprint of their ecological niches or can adapt physiologically to the new conditions; modifying behavior can offer an alternative means of adapting to novel environments. The burrowing habit allows organisms to avoid adverse climatic conditions during part of the year by remaining inside burrows. Smilisca fodiens and S. dentata are two burrowing hylid frogs that inhabit areas beyond the northernmost distributional limits of the other six arboreal species of their genus, and indeed beyond of most American hylids. In this study, we tested whether burrowing habit allows these species to adapt to drier conditions while conserving the climatic niche of the arboreal species. We compared the annual niches of the arboreal species to those of the burrowing species under two assumptions: true seasonal niches and full annual niches. Through ecological niche similarity tests, we performed 24 comparisons in both geographic and environmental spaces. In geographic space, when considering burrowing annual niches, only five of 24 tests indicated similarity, yet as regards seasonal niche, 18 of 24 tests indicated similarity. In environmental space, all tests failed to reject null hypotheses. The analyses showed clearly that burrowing and arboreal species were closer in environmental space when seasonal niches of the burrowing species were used, rather than annual niches. That is, climatic conditions in seasonal niches of burrowing species resemble the annual niches of arboreal species, supporting the proposition that reduction of activity to certain periods of the year is a strategy in burrowing species to conserve their tropical niches while living in dry regions.

Highlights

In amphibians, species’ presence in permanent populations at higher latitudes is limited by narrow physiological tolerances with respect to temperature and precipitation since the annual variation of these parameters is more significant within temperate regions than in tropical regions (Janzen 1967, Ghalambor et al 2006, Hua and Wiens 2009, Sunday et al 2010, Sunday et al 2019)
We found that seasonal niches of burrowing species showed reduced environmental distances in relation to the remaining species of the Smilisca group, supporting the hypothesis that they evolved a novel behavior while maintaining physiological conservatism
Of the six arboreal species, only S. baudinii occurs in xeric environments, overlapping with the southernmost parts of the range of S. fodiens

Summary

Introduction

Species’ presence in permanent populations at higher latitudes is limited by narrow physiological tolerances with respect to temperature and precipitation since the annual variation of these parameters is more significant within temperate regions than in tropical regions (Janzen 1967, Ghalambor et al 2006, Hua and Wiens 2009, Sunday et al 2010, Sunday et al 2019). Despite its ecological, biogeographic, and evolutionary importance, the relationship between these behavioral traits and adaptation to dry climates has not been analyzed in detail (Encarnación-Luévano et al 2013) This discussion leads us to consider that burrowing habit in Smilisca species constitutes a behavioral adaptation that permits populations to inhabit drier regions while retaining the same physiological constraints for climatic conditions as the tropical species. Actual tolerance limits, reflecting the fundamental ecological niche of a species, are physiological characteristics that can be assessed fully only via physiological measurements Those characteristics can be studied via coarseresolution associations with environments manifested across their geographic distributions (Grinnell 1917, Soberón and Peterson 2005, Soberón 2007, Barve et al 2014). We employed ecological niche similarity tests in geographic and environmental spaces to assess niche similarity and difference patterns

Materials and Methods

Results

Discussion