Prof. Jinzhong Fu and his students find genetic signals of high-altitude adaption in amphibians
Modern evolutionary biology seeks to understand the genetic basis of adaptation and high-altitude environments provide an excellent system for studying how organisms cope with a multitude of stresses such as low levels of oxygen, low temperature, high levels of UV radiation, and strong seasonality.
Physiological adaptation to high-altitude environments have been well documents in endothermic vertebrates (organisms that can control their internal body temperature, i.e. birds and mammals) where improved response to hypoxia (oxygen deficiency) play a large role in their ability to adapt to high altitudes.
Poikilotherms (organisms that cannot regulate their body temperature, e.g. lizards, amphibians) on the other hand are not as well understood due to limitations in genomic technology. However, they are expected to have evolved different adaptive mechanisms to high altitudes due to physiological differences, such as lower and more variable body temperatures and they do not use internal processes to maintain them.
Advances in genome-wide scans have allowed Dr. Fu and his colleagues to study the genetic signals of high-altitude adaptation of an amphibian, the Asiatic Toad (Bufo gargarizans), using transcriptome sequences. This species is a useful source of study because it has a large altitudinal distribution range and phenotypic differences along altitudinal gradients that are well-documented.
While comparative analyses of high-altitude vs. low-altitude populations are common, Dr. Fu and his team also incorporated transcriptome data from another high-altitude amphibian, the plateau brown frog (Rana kukunoris) and its low-altitude relative, the Chinese brown frog (Rana chensinensis) to support his findings.
Results showed strong genetic signals of accelerated evolution and positive selection for genes associated with nutrient metabolic functions such as carbohydrate binding, electron carrier activity and lipid metabolic process and metabolic pathways such as insulin signaling, fat digestion and absorption.
This indicates that modifications of genes associated with nutrient metabolism have likely played a major role in the adaptation process of adult toads. The fact that two species of two independent lineages showed largely similar patterns between them further reinforces their conclusions.
They also did not detect any positively selected genes associated with responses to hypoxia which represents a significant difference from endotherms suggesting that amphibians likely use different genetic mechanisms for high-altitude adaptation compared to endotherms.
Moving forward, they plan to explore adaptive variations at the gene expression level.
Poikilotherms represent the majority of animal diversity and they hope that their study can provide useful directions for future studies.