School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, USA.
Proc Natl Acad Sci U S A. 2012 Oct 2;109(40):16217-21. doi: 10.1073/pnas.1213621109. Epub 2012 Sep 17.
Fundamental differences in the distribution of oceans and landmasses in the Northern and Southern Hemispheres potentially impact patterns of biological diversity in the two areas. The evolutionary history of conifers provides an opportunity to explore these dynamics, because the majority of extant conifer species belong to lineages that have been broadly confined to the Northern or Southern Hemisphere during the Cenozoic. Incorporating genetic information with a critical review of fossil evidence, we developed an age-calibrated phylogeny sampling ∼80% of living conifer species. Most extant conifer species diverged recently during the Neogene within clades that generally were established during the later Mesozoic, but lineages that diversified mainly in the Southern Hemisphere show a significantly older distribution of divergence ages than their counterparts in the Northern Hemisphere. Our tree topology and divergence times also are best fit by diversification models in which Northern Hemisphere conifer lineages have higher rates of species turnover than Southern Hemisphere lineages. The abundance of recent divergences in northern clades may reflect complex patterns of migration and range shifts during climatic cycles over the later Neogene leading to elevated rates of speciation and extinction, whereas the scattered persistence of mild, wetter habitats in the Southern Hemisphere may have favored the survival of older lineages.
北半球和南半球海洋和陆地分布的基本差异可能会影响这两个地区生物多样性的模式。松柏类植物的进化历史为探索这些动态提供了机会，因为大多数现存的松柏类植物物种属于在新生代广泛局限于北半球或南半球的谱系。我们结合遗传信息和对化石证据的批判性回顾，开发了一个年龄校准的系统发育树，该系统发育树采样了大约 80%的现存松柏类植物物种。大多数现存的松柏类植物物种在新近纪的分支中分化，这些分支通常在中生代后期就已经建立，但主要在南半球多样化的谱系的分化年龄分布明显比它们在北半球的对应谱系古老。我们的树拓扑结构和分化时间也最符合多样化模型，其中北半球松柏类植物谱系的物种更替率高于南半球谱系。北部谱系中最近的分化的大量出现可能反映了在较晚的新生代气候循环中，迁徙和范围转移的复杂模式导致了更高的物种形成和灭绝率，而南半球温和、湿润的栖息地的分散存在则有利于更古老谱系的存活。
