Reaney Ashley M, Saldarriaga-Córdoba Mónica, Pincheira-Donoso Daniel
Laboratory of Evolutionary Ecology of Adaptations, School of Life Sciences, University of Lincoln, Brayford Campus, Lincoln, Lincolnshire, LN6 7DL, UK.
Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK.
BMC Evol Biol. 2018 Feb 6;18(1):16. doi: 10.1186/s12862-018-1133-1.
Life diversifies via adaptive radiation when natural selection drives the evolution of ecologically distinct species mediated by their access to novel niche space, or via non-adaptive radiation when new species diversify while retaining ancestral niches. However, while cases of adaptive radiation are widely documented, examples of non-adaptively radiating lineages remain rarely observed. A prolific cold-climate lizard radiation from South America (Phymaturus), sister to a hyper-diverse adaptive radiation (Liolaemus), has extensively diversified phylogenetically and geographically, but with exceptionally minimal ecological and life-history diversification. This lineage, therefore, may offer unique opportunities to investigate the non-adaptive basis of diversification, and in combination with Liolaemus, to cover the whole spectrum of modes of diversification predicted by theory, from adaptive to non-adaptive. Using phylogenetic macroevolutionary modelling performed on a newly created 58-species molecular tree, we establish the tempo and mode of diversification in the Phymaturus radiation.
Lineage accumulation in Phymaturus opposes a density-dependent (or 'niche-filling') process of diversification. Concurrently, we found that body size diversification is better described by an Ornstein-Uhlenbeck evolutionary model, suggesting stabilizing selection as the mechanism underlying niche conservatism (i.e., maintaining two fundamental size peaks), and which has predominantly evolved around two major adaptive peaks on a 'Simpsonian' adaptive landscape.
Lineage diversification of the Phymaturus genus does not conform to an adaptive radiation, as it is characterised by a constant rate of species accumulation during the clade's history. Their strict habitat requirements (rocky outcrops), predominantly invariant herbivory, and especially the constant viviparous reproduction across species have likely limited their opportunities for adaptive diversifications throughout novel environments. This mode of diversification contrasts dramatically with its sister lineage Liolaemus, which geographically overlaps with Phymaturus, but exploits all possible microhabitats in these and other bioclimatic areas. Our study contributes importantly to consolidate these lizards (liolaemids) as promising model systems to investigate the entire spectrum of modes of species formations, from the adaptive to the non-adaptive extremes of the continuum.
当自然选择驱动生态上不同的物种通过进入新的生态位空间而进化时，生命通过适应性辐射实现多样化；或者当新物种在保留祖先生态位的同时实现多样化时，通过非适应性辐射实现多样化。然而，虽然适应性辐射的案例有广泛记录，但非适应性辐射谱系的例子仍然很少被观察到。来自南美洲的一种多产的寒冷气候蜥蜴辐射类群（肥尾守宫属）是高度多样化的适应性辐射类群（鬃狮蜥属）的姐妹群，在系统发育和地理上已经广泛分化，但生态和生活史的分化异常微小。因此，这个谱系可能为研究多样化的非适应性基础提供独特机会，并与鬃狮蜥属相结合，涵盖理论预测的从适应性到非适应性的整个多样化模式范围。利用在新构建的包含58个物种的分子树上进行的系统发育宏观进化建模，我们确定了肥尾守宫属辐射的多样化速度和模式。
肥尾守宫属的谱系积累与密度依赖（或“生态位填充”）的多样化过程相反。同时，我们发现体型多样化用奥恩斯坦 - 乌伦贝克进化模型能更好地描述，这表明稳定选择是生态位保守性（即维持两个基本体型峰值）的潜在机制，并且在“辛普森式”适应景观上主要围绕两个主要适应峰值进化。
肥尾守宫属的谱系多样化不符合适应性辐射，因为其特征是在进化枝历史中物种积累速率恒定。它们对严格栖息地（岩石露头）的要求、主要不变的食草习性，尤其是整个物种中恒定的胎生繁殖，可能限制了它们在新环境中进行适应性多样化的机会。这种多样化模式与其姐妹谱系鬃狮蜥属形成了鲜明对比，鬃狮蜥属在地理上与肥尾守宫属重叠，但利用了这些以及其他生物气候区域内所有可能的微生境。我们的研究对于巩固这些蜥蜴（鬃狮蜥科）作为研究物种形成模式全谱（从适应性到非适应性连续统的极端情况）的有前景的模型系统做出了重要贡献。
