The origins and diversification of C4 grasses and savanna-adapted ungulates
The origins and diversification of C4 grasses and savanna-adapted ungulates
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DOI：
10.1111/j.1365-2486.2009.01860.x
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发表时间：
2009-10-01
影响因子：
11.6
通讯作者：
Savolainen, Vincent
中科院分区：
文献类型：
--
作者：
Bouchenak-Khelladi, Yanis;Verboom, G. Anthony;Savolainen, Vincent
C-4草类是热带稀树草原的主要组成部分，在其他干燥的热带生态系统中也很普遍，它们是放牧动物的主要食物。在驱动禾本科植物C-4进化的潜在因素中，禾本科植物和食草动物之间的相互作用尚未得到研究。为了评估，如果增加放牧压力可能选择了更高的叶片二氧化硅生产的草分歧，我们重建了所有800属的禾本科植物的分子（结合多质体DNA区域）和形态特征。使用分子钟，我们还计算了C-4分支的起源的年龄和数量，发现从3090万年前开始，从C-3到C-4光合作用至少发生了12次，并发现证据表明，渐新世晚期（3300万年前至3000万年前）大气中二氧化碳最严重的下降与Chloridoideae中C-4光合作用的第一个起源相匹配。通过结合化石和有蹄类动物的系统发育数据，并实施随机化程序，我们的研究结果表明，C-4草分支和有蹄类动物适应C-4占主导地位的栖息地的外观匹配显着的时间。硅体的叶表皮密度的增加被发现对应于中新世晚期多样化率的假设变化[在2300万年至370万年前检测到24个显著的多样化变化（P < 0.05）]。在中新世晚期，对于类草和类草，放牧压力的增加可能选择了更高的叶表皮二氧化硅产量。
C-4 grasses constitute the main component of savannas and are pervasive in other dry tropical ecosystems where they serve as the main diet for grazing animals. Among potential factors driving C-4 evolution of grasses, the interaction between grasses and grazers has not been investigated. To evaluate if increased grazing pressure may have selected for higher leaf silica production as the grasses diverged, we reconstructed the phylogeny of all 800 genera of the grass family with both molecular (combined multiplastid DNA regions) and morphological characters. Using molecular clocks, we also calculated the age and number of origins of C-4 clades and found that shifts from C-3 to C-4 photosynthesis occurred at least 12 times starting 30.9 million years ago and found evidence that the most severe drop in atmospheric carbon dioxide in the late Oligocene (between 33 and 30 million years ago) matches the first origin of C-4 photosynthesis in Chloridoideae. By combining fossil and phylogenetic data for ungulates and implementing a randomization procedure, our results showed that the appearance of C-4 grass clades and ungulate adaptations to C-4-dominated habitats match significantly in time. An increase of leaf epidermal density of silica bodies was found to correspond to postulated shifts in diversification rates in the late Miocene [24 significant shifts in diversification (P < 0.05) were detected between 23 and 3.7 million years ago]. For aristidoid and chloridoid grasses, increased grazing pressure may have selected for a higher leaf epidermal silica production in the late Miocene.