Li Yang, Zhang Jianzhi
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA.
Mol Biol Evol. 2025 Apr 1;42(4). doi: 10.1093/molbev/msaf066.
Adaptive evolution can be described by an uphill walk in a fitness landscape. However, climbing the global peak in a multipeak landscape is improbable because of the high chance of being trapped at a local peak. Nonetheless, over three-quarters of simulated adaptive walks in the fitness landscape of the Escherichia coli dihydrofolate reductase (DHFR) gene were reported to end at the highest 14% of peaks, suggesting that biological systems may be substantially more evolvable than commonly thought. To investigate the cause and generality of this observation, we estimate in empirical and theoretical fitness landscapes the probability of reaching high peaks by adaptive walks (PHP), where high peaks refer to the highest 1, 5, 14, or 25% of all peaks. We find that (i) PHP varies substantially among landscapes, (ii) PHP in empirical landscapes is generally comparable to or smaller than that in same-size Rough Mount Fuji landscapes of similar ruggedness, and (iii) lowering landscape ruggedness boosts PHP. As observed in DHFR, we find in every examined landscape a positive correlation between the fitness of a peak and its basin size, which is the number of genotypes that can reach the peak through adaptive walks. Yet, this correlation does not guarantee a large PHP because of the influences of other factors. We conclude that evolvability depends on the specific fitness landscape and that the large PHP in the DHFR landscape is not a general property of empirical or theoretical fitness landscapes.
适应性进化可以用适应度景观中的上坡行走来描述。然而，在多峰景观中攀登全局峰值是不太可能的，因为被困在局部峰值的可能性很高。尽管如此，据报道，在大肠杆菌二氢叶酸还原酶（DHFR）基因的适应度景观中，超过四分之三的模拟适应性行走在最高的14%的峰值处结束，这表明生物系统的可进化性可能比通常认为的要高得多。为了研究这一观察结果的原因和普遍性，我们在经验和理论适应度景观中估计了通过适应性行走到达高峰值的概率（PHP），其中高峰值指的是所有峰值中最高的1%、5%、14%或25%。我们发现：（i）PHP在不同景观之间有很大差异；（ii）经验景观中的PHP通常与具有相似崎岖度的相同大小的粗糙富士山景观中的PHP相当或更小；（iii）降低景观的崎岖度会提高PHP。正如在DHFR中观察到的那样，我们在每个检查的景观中都发现峰值的适应度与其盆地大小之间存在正相关，盆地大小是指可以通过适应性行走到达该峰值的基因型数量。然而，由于其他因素的影响，这种相关性并不能保证有很大的PHP。我们得出结论，可进化性取决于特定的适应度景观，并且DHFR景观中较大的PHP并不是经验或理论适应度景观的普遍属性。
