DOI: 10.5061/dryad.sbcc2fr3n
title: Divergent adaptations in resource-use traits explain how pikas thrive on the roof of the world

description: Life in extreme environments is possible through multilevel adaptations to
 physical and biotic stresses. At high elevations, species face numerous
 challenges, besides low oxygen levels, but previous studies have focused
 on genetic and physiological adaptations to chronic hypoxia while
 overlooking other key strategies for thriving in alpine landscapes. Here,
 we investigate resource-use trait adaptations to extreme elevations using
 pikas as a model, lagomorphs distributed up to 6200 metres and reaching
 maximum diversity on the Qinghai-Tibet plateau, the highest plateau on
 Earth. Specifically, we assess cranial evolution in pikas using geometric
 morphometric and phylogenetic comparative techniques to determine whether
 adaptations among high-elevation biota shown at the molecular and
 physiological levels also occur in resource-use traits. We further explore
 the roles of two contrasting lifestyles (burrowing and rocky-dwelling) in
 cranial evolution. We found that alpine species exhibit striking
 phenotypic specialization to distinct microhabitats. Contrary to
 physiological and genetic adaptive convergence, we show that the cranium
 has undergone adaptive divergence likely reflecting past resource
 competition in highlands and long-term association with alpine landscapes.
 Our analyses also reveal that the evolution of burrowing lifestyle allows
 high-elevation pikas to explore novel niches and boosts their phenotypic
 diversification. In addition to cold and hypoxia tolerance, high cranial
 specialization, the appearance of burrowing habits, and strong niche
 separation explain how pikas overcome alpine stresses and flourish on the
 highest plateau on Earth. By contrast, when moving to spatially complex
 and heterogeneous vegetation zonation, pikas exhibit generalist skull
 forms able to exploit diverse habitats. These findings mirror previously
 reported intraspecific patterns in mammals, suggesting a general
 morphological response in resource-exploiting traits to cope with distinct
 selection pressures across elevation zones. Phenotypic diversity is
 further constrained by rocky habitats, resulting in convergent skulls. Our
 study highlights that adaptations to extreme environments occur at
 multiple levels of organization, but can lead to distinct evolutionary
 paths depending on which selective forces they respond to. The evolution
 of burrowing behaviour represents a landmark in the evolutionary history
 of pikas. We further show that rocky habitats impose strong ecological
 pressures, leading to convergent responses in resource-use traits, which
 is rarely documented in mammals.
description: <strong>Ochotona_landmarks_157ind.TPS</strong> This file contains the landmarks of 157 individuals of <em>Ochotona</em> used to perform the geometric morphometric analyses. <strong>Ochotona_traits.csv</strong> This file contains species, subgenus, elevation zone and lifestyle information for the 157 individuals of <em>Ochotona</em> <strong>Ochotona_phylogeny_31species.tre</strong> Tree with 31 pika species based on four genes (cytb, COI and ND4, ILRPB1).