“It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change.”
– Leon C. Megginson (1963)
This quote is often attributed to Charles Darwin, but it actually originated from a speech by Leon C. Megginson. Whoever said it, adaptation is a key concept in evolutionary biology and scientists are still trying to figure out how it happens. The main prerequisite seems to be the presence of advantageous alleles. The sources of these alleles are new mutations, gene flow from other species (i.e. adaptive introgression) or standing genetic variation. The latter refers to ancestral variation that is already present in the population and can be utilized immediately. A recent study in PNAS argues that this standing genetic variation has been the main source for adaptation in the vinous-throated parrotbill (Sinosuthora webbiana).
High and Low
The vinous-throated parrotbill is a small songbird from East Asia. You can find it on the Asian mainland and on the island of Taiwan. There, it occurs up to 3100 meters above sea level. Yu-Ting Lai and colleagues collected 40 individuals from four populations in Taiwan, two from the lowlands and two from the highlands (situated in the Central Mountain Range). Next, they sequenced the genomes of these birds and started comparing their genetic variants, namely single-nucleotide polymorphisms (SNPs).
The researchers looked for genomic regions that were different between the high- and lowland populations. This search uncovered 24 candidate regions which harbored several genes related to adaptation to high and low altitudes, particularly the use of oxygen and thermoregulation.
Interestingly, the SNPs in these regions were not located within these genes but rather in the regions between the genes (i.e. intergenic regions) or in the non-coding parts of the genes (i.e. introns). This suggests that adaptation might be due to regulatory changes because the switches that control gene expression are generally located in these intergenic and intronic sections of the genome.
Next, the researchers sequenced the genomes of 40 parrotbills from the mainland. If the candidate SNPs from the Taiwanese populations are absent from the mainland, then they are probably due to new mutations. However, if the candidate SNPs are shared between the island and the mainland, it points to standing genetic variation. And indeed, most of the candidate SNPs were also found in the mainland population, indicating that standing genetic variation is the main source for adaptation to different altitudes on Taiwan.
The use of standing genetic variation allows for rapid adaptation to changing environments. This is relevant given global climate change and habitat loss. The authors write that “these findings provide important context for understanding adaptation and conservation of species in the Anthropocene.” Although I am not a big fan of the term Anthropocene (it still feels like a trick to “sell” your papers), understanding how species adapt to rapidly changing environments is crucial if we want to protect them.
Lai, Y.T., Yeung, C.K., Omland, K.E., Pang, E.L., Hao, Y., Liao, B. Y., Cao, H.F., Zhang, B.W., Yeh, C.F., Hung, C.M., Hung, H.Y., Yang, M.Y., Liang, W., Hsu, Y.C., Yao, C.T., Dong, L., Lin, K. & Hung, H. Y. (2019). Standing genetic variation as the predominant source for adaptation of a songbird. Proceedings of the National Academy of Sciences, 116(6), 2152-2157.