5种入侵植物补偿反应及其形态可塑性比较

通过模拟刈割试验,研究了5种外来入侵植物(黑麦草、空心莲子草、三叶鬼针草、薇甘菊和胜红蓟)的补偿能力及其形态可塑性。结果表明:多数植物的补偿能力与形态可塑性有一定相关性,刈割和非刈割条件下空心莲子草和薇甘菊都具有较强的形态可塑性,其补偿指数较高,分别为1.65和1.27;多年生黑麦草和三叶鬼针草的形态可塑性在刈割条件下得到增强,补偿指数分别为1.44和1.28;刈割条件下胜红蓟的形态可塑性变化不大或有所降低,其补偿指数最低,为0.82。研究认为,5种植物具有不同的限制其形态可塑性和补偿能力比较理想的刈割时期,薇甘菊攀援生长方式下为30d前和60d后,空心莲子草为60d后,胜红蓟为40～50d,鬼针草为30d前,黑麦草为40～50d。     

Size is not everything: rates of genome size evolution,not C-value,correlate with speciation in angiosperms

Angiosperms represent one of the key examples of evolutionary success, and their diversity dwarfs other land plants; this success has been linked, in part, to genome size and phenomena such as whole genome duplication events. However, while angiosperms exhibit a remarkable breadth of genome size, evidence linking overall genome size to diversity is equivocal, at best. Here, we show that the rates of speciation and genome size evolution are tightly correlated across land plants, and angiosperms show the highest rates for both, whereas very slow rates are seen in their comparatively species-poor sister group, the gymnosperms. No evidence is found linking overall genome size and rates of speciation. Within angiosperms, both the monocots and eudicots show the highest rates of speciation and genome size evolution, and these data suggest a potential explanation for the megadiversity of angiosperms. It is difficult to associate high rates of diversification with different types of polyploidy, but it is likely that high rates of evolution correlate with a smaller genome size after genome duplications. The diversity of angiosperms may, in part, be due to an ability to increase evolvability by benefiting from whole genome duplications, transposable elements and general genome plasticity.     

Correlated evolution of genome size and seed mass

Previous investigators have identified strong positive relationships between genome size and seed mass within species, and across species from the same genus and family. Here, we make the first broad-scale quantification of this relationship, using data for 1222 species, from 139 families and 48 orders. We analyzed the relationship between genome size and seed mass using a statistical framework that included four different tests. A quadratic relationship between genome size and seed mass appeared to be driven by the large genome/seed mass gymnosperms and the many small genome size/large seed mass angiosperms. Very small seeds were never associated with very large genomes, possibly indicating a developmental constraint. Independent contrast results showed that divergences in genome size were positively correlated with divergences in seed mass. Divergences in seed mass have been more closely correlated with divergences in genome size than with divergences in other morphological and ecological variables. Plant growth form is the only variable examined thus far that explains a greater proportion of variation in seed mass than does genome size.     

An assessment of accuracy, error, and conflict with support values from genome-scale phylogenetic data

Despite the importance of molecular phylogenetics, few of its assumptions have been tested with real data. It is commonly assumed that nonparametric bootstrap values are an underestimate of the actual support, Bayesian posterior probabilities are an overestimate of the actual support, and among-gene phylogenetic conflict is low. We directly tested these assumptions by using a well-supported yeast reference tree. We found that bootstrap values were not significantly different from accuracy. Bayesian support values were, however, significant overestimates of accuracy but still had low false-positive error rates (0% to 2.8%) at the highest values (>99%). Although we found evidence for a branch-length bias contributing to conflict, there was little evidence for widespread, strongly supported among-gene conflict from bootstraps. The results demonstrate that caution is warranted concerning conclusions of conflict based on the assumption of underestimation for support values in real data.