Engelbrecht Hanlie M, Branch William R, Tolley Krystal A
School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, Gauteng, South Africa.
Kirstenbosch Research Centre, South African National Biodiversity Institute, Cape Town, Western Cape, South Africa.
PeerJ. 2021 Aug 6;9:e11728. doi: 10.7717/peerj.11728. eCollection 2021.
The African continent is comprised of several different biomes, although savanna is the most prevalent. The current heterogeneous landscape was formed through long-term vegetation shifts as a result of the global cooling trend since the Oligocene epoch. The overwhelming trend was a shift from primarily forest, to primarily savanna. As such, faunal groups that emerged during the Paleogene/Neogene period and have species distributed in both forest and savanna habitat should show a genetic signature of the possible evolutionary impact of these biome developments. and (Colubridae) are excellent taxa to investigate the evolutionary impact of these biome developments on widespread African colubrid snakes, and whether timing and patterns of radiation are synchronous with biome reorganisation.
A phylogenetic framework was used to investigate timing of lineage diversification. Phylogenetic analysis included both genera as well as other Colubridae to construct a temporal framework in order to estimate radiation times for and . Lineage diversification was estimated in Bayesian Evolutionary Analysis Sampling Trees (BEAST), using two mitochondrial markers (cyt-, ND4), one nuclear marker (c-mos), and incorporating one fossil and two biogeographical calibration points. Vegetation layers were used to classify and confirm species association with broad biome types ('closed' = forest, 'open' = savanna/other), and the ancestral habitat state for each genus was estimated.
showed an ancestral state of closed habitat, but the ancestral habitat type for was equivocal. Both genera showed similar timing of lineage diversification diverging from their sister genera during the Oligocene/Miocene transition (. 25 Mya), with subsequent species radiation in the Mid-Miocene. appeared to have undergone allopatric speciation during Mid-Miocene forest fragmentation. Habitat generalist and open habitat specialist species emerged as savanna became more prevalent, while at least two forest associated lineages within moved into Afromontane forest habitat secondarily and independently.
With similar diversification times, but contrasting ancestral habitat reconstructions, we show that these genera have responded very differently to the same broad biome shifts. Differences in biogeographical patterns for the two African colubrid genera is likely an effect of distinct life-history traits, such as the arboreous habits of compared to the terrestrial lifestyle of .
非洲大陆由几种不同的生物群落组成，尽管稀树草原最为普遍。当前这种异质景观是由于自渐新世以来全球变冷趋势导致的长期植被变化而形成的。总体趋势是从主要的森林转变为主要的稀树草原。因此那些在古近纪/新近纪时期出现且物种分布在森林和稀树草原栖息地的动物类群，应该会显示出这些生物群落发展可能产生的进化影响的基因特征。锦蛇属（游蛇科）是研究这些生物群落发展对广泛分布的非洲游蛇科蛇类的进化影响，以及辐射时间和模式是否与生物群落重组同步的优良分类单元。
利用系统发育框架来研究谱系分化的时间。系统发育分析包括这两个属以及其他游蛇科动物，以构建一个时间框架，从而估计锦蛇属和瘦蛇属的辐射时间。在贝叶斯进化分析采样树（BEAST）中，使用两个线粒体标记（细胞色素b、ND4）、一个核标记（c - mos），并纳入一个化石和两个生物地理校准点来估计谱系分化。利用植被层对物种与广泛的生物群落类型（“封闭” =森林，“开阔” =稀树草原/其他）的关联进行分类和确认，并估计每个属的祖先栖息地状态。
锦蛇属显示出封闭栖息地的祖先状态，但瘦蛇属的祖先栖息地类型不明确。两个属在渐新世/中新世过渡时期（约2500万年前）与其姐妹属分道扬镳，显示出相似的谱系分化时间，随后在中新世中期出现物种辐射。锦蛇属似乎在中新世中期森林碎片化期间经历了异域物种形成。随着稀树草原变得更加普遍，栖息地泛化种和开阔栖息地特化种出现，而锦蛇属内至少有两个与森林相关的谱系后来独立地迁入了东非山地森林栖息地。
尽管分化时间相似，但祖先栖息地重建情况不同，我们表明这些属对相同的广泛生物群落变化的反应非常不同。这两个非洲游蛇科属的生物地理模式差异可能是不同生活史特征的结果，比如锦蛇属的树栖习性与瘦蛇属的陆栖生活方式形成对比。
