Phylogenetic trends and environmental correlates of nuclear
genome size variation in Helianthus sunflowers

Summary
         Flowering plants serve as a powerful model for studying the evolution of nuclear genome size (GS) given the tremendous GS variation that exists both within and across angiosperm lineages.

        Helianthus sunflowers consist of c. 50 species native to North America that occupy diverse habitats and vary in ploidy level. In the current study, we generated a comprehensive GS database for 49 Helianthus species using flow cytometric approaches. We examined variability across the genus and present a comparative phylogenetic analysis of GS evolution in diploid Helianthus species.

        Results demonstrated that different clades of diploid Helianthus species showed evolutionary patterns of GS contraction, expansion and relative stasis, with annual diploid species evolving smaller GS with the highest rate of evolution. Phylogenetic comparative analyses of  diploids revealed significant negative associations of GS with temperature seasonality and cell  production rate, indicating that the evolution of larger GS in Helianthus diploids may be more  permissible in habitats with longer growing seasons where selection for more rapid growth  may be relaxed.

        The Helianthus GS database presented here and corresponding analyses of environmental
and phenotypic correlates will facilitate ongoing and future research on the ultimate drivers of
GS evolution in this well-studied North American plant genus

    开花植物对研究GS大小的进化提供了一个强有力的模型，因为其在被子植物谱系内外具有巨大的GS变异。

    向日葵属植物在南美具有50个物种，占据了不同的生境且倍性不同。在我们这个研究中我们用流失细胞术产生了49个物种的GS数据库。我们通过整个属的GS变化，对二倍体向日葵属植物的进化进行了系统发育比较分析。

    结果表明，不同的二倍体向日葵属植物进化模式表现为GS的收缩、扩张和相对停滞，一年生二倍体植物进化速度最快，进化幅度较小。二倍体的系统发育比较分析表明，GS与季节性温度和细胞产量呈显著负相关，表明在生长季节较长的生境中，生长速度较快的选择可能较为宽松，更大的GS在向日葵二倍体中可能更容易进化

    向日葵属的GS数据库和环境和表型的相关性分析将促进正在进行和将来南美植物的GS进化的研究。