净多样化速率和进化时间对虎耳草目科间物种多样性差异的影响

Influence of net diversification rate and evolutionary time on the differences in species richness among families of order Saxifragales

关键词:  虎耳草目, 物种多样性, 系统发育, 多样化速率, 宏观演化

Key words:  Saxifragales, species diversity, phylogeny, diversification rate, macroevolution

摘要:

不同生物类群包含的物种数目常存在巨大差异,这是生态学和生物学研究中普遍观察到的现象。然而,这一现象产生的原因仍然是未解之谜。从宏观进化的角度,进化时间假说和多样化速率假说是两个比较流行的假说。进化时间假说认为类群的演化时间越长,积累的物种丰富度越高; 而多样化速率假说认为类群的净多样化速率越快,则其物种丰富度越高。为验证这两个假说,该文以一棵包含1 539个物种化石定年的虎耳草目系统发育树为基础,通过宏观进化分析获取了虎耳草目内15个科的物种形成和灭绝速率,并计算了每个科的平均多样化速率。结果表明:(1)虎耳草目的物种多样化速率有着增加的趋势,并且多样化速率的增加主要出现在温带和高山类群,如茶藨子科、景天科和芍药科等。(2)采用系统发育广义最小二乘模型(PGLS)和线性回归模型(LM)结果表明,虎耳草目15个科的物种丰富度与科的分化时间和科内物种的最近共同祖先年龄都没有显著相关关系,而与净多样化速率显著正相关(R² =0.380,P<0.05)。该研究支持了多样化速率假说,认为不同科的净多样化速率的差异是导致虎耳草目科间物种数目差异的主要原因之一。全球气候变冷可能为虎耳草目中草本、落叶乔木和灌木等能够适应寒冷环境的类群提供了分布范围扩张和物种快速多样化的机会。该研究表明在温带和高山扩张类群中,物种净多样化速率可能是导致不同类群物种数目差异的主要原因。

Abstract:

The differences in the species richness among different biological taxonomic groups often vary greatly, which is a phenomenon commonly observed in ecological and biological studies. However, the underlying mechanisms of this pattern are still in hot debate. From the perspective of macroevolution, time-for speciation hypothesis and diversification rate hypothesis are two popular hypotheses. Time-for speciation hypothesis suggesting that the time-for-speciation is the primary driver of diversity variation among groups by species accumulation along time, while diversification rate hypothesis suggesting that the groups with high species number resulted from their high net diversification rates. To test these two hypotheses, we studied species variation among 15 families of order Saxifragales based on a fossil-calibrated phylogenetic tree containing 1 539 species. We obtained the rates of speciation and extinction of 15 families and calculated the average diversification rate of each family through macroevolutionary analysis. The results are as follows:(1)The species diversification rate of order Saxifragales shows an increasing trend, and the increase of diversification rate mainly occurred in temperate and alpine groups, such as Grossulariaceae, Crassulaceae and Paeoniaceae.(2)The results of phylogenetic generalized least squares(PGLS)and linear regression model(LM)show that the species richness of the 15 families is not significantly correlated with the age of family differentiation or the age of the most recent common ancestor, but it is positively correlated with the net diversification rate(R²=0.380, P<0.05). These results support the diversification rate hypothesis, suggesting that the diversification rate is a primary evolutionary driver of the variation of species richness among families of order Saxifragales. Global cooling may provide opportunities for the expansion of distribution and rapid species diversification of herbaceous, deciduous trees and shrubs those can adapt to cold conditions. The study show that in temperate and alpine spreading groups, the net diversification rate may be the main reason for the differences in species numbers of different taxonomic groups.