Miller Jill S, Kamath Ambika, Husband Brian C, Levin Rachel A
Department of Biology, Amherst College, Amherst, MA 01002 USA,
Department of Biology, Amherst College, Amherst, MA 01002 USA, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA and.
Ann Bot. 2016 Feb;117(2):307-17. doi: 10.1093/aob/mcv167. Epub 2015 Nov 5.
Polyploidy has important effects on reproductive systems in plants and has been implicated in the evolution of dimorphic sexual systems. In particular, higher ploidy is associated with gender dimorphism across Lycium species (Solanaceae) and across populations within the species Lycium californicum. Previous research on the association of cytotype and sexual system within L. californicum sampled a limited portion of the species range, and did not investigate evolutionary transitions between sexual systems. Lycium californicum occurs in arid regions on offshore islands and mainland regions in the south-western United States and Mexico, motivating a more comprehensive analysis of intraspecific variation in sexual system and cytotype across the full range of this species.
Sexual system (dimorphic vs. cosexual) was determined for 34 populations across the geographical range of L. californicum using field observations of pollen production, and was confirmed using morphological measurements and among-plant correlations of primary sexual traits. Ploidy was inferred using flow cytometry in 28 populations. DNA sequence data from four plastid and two nuclear regions were used to reconstruct relationships among populations and to map transitions in sexual system and ploidy.
Lycium californicum is monophyletic, ancestrally diploid and cosexual, and the association of gender dimorphism and polyploidy appears to have two evolutionary origins in this species. Compared with cosexual populations, dimorphic populations had bimodal anther size distributions, negative correlations between male and female floral traits, and larger coefficients of variation for primary sexual traits. Flow cytometry confirmed tetraploidy in dimorphic populations, whereas cosexual populations were diploid.
Tetraploidy and gender dimorphism are perfectly correlated in L. californicum, and the distribution of tetraploid-dimorphic populations is restricted to populations in Arizona and the Baja California peninsula. The analysis suggests that tetraploidy and dimorphism likely established in Baja California and may have evolved multiple times.
多倍体对植物的生殖系统具有重要影响，并且与两性异形性系统的进化有关。特别是，更高的倍性与枸杞属（茄科）物种间以及加州枸杞物种内不同种群的性别二态性相关。先前关于加州枸杞细胞型与性系统关联的研究仅在该物种分布范围的有限区域进行采样，且未调查性系统之间的进化转变。加州枸杞生长在美国西南部和墨西哥的近海岛屿及大陆地区的干旱区域，这促使我们对该物种整个分布范围内性系统和细胞型的种内变异进行更全面的分析。
通过对花粉产生的实地观察确定了加州枸杞地理分布范围内34个种群的性系统（两性异形与雌雄同体），并通过形态测量和主要性特征的植株间相关性进行了确认。使用流式细胞术推断了28个种群的倍性。利用来自四个质体和两个核区域的DNA序列数据重建种群间的关系，并绘制性系统和倍性的转变图谱。
加州枸杞是单系的，祖先为二倍体且雌雄同体，性别二态性与多倍体的关联在该物种中似乎有两个进化起源。与雌雄同体种群相比，两性异形种群的花药大小分布呈双峰，雄性和雌性花部特征之间呈负相关，主要性特征的变异系数更大。流式细胞术证实两性异形种群为四倍体，而雌雄同体种群为二倍体。
四倍体与性别二态性在加州枸杞中完全相关，四倍体 - 两性异形种群的分布仅限于亚利桑那州和下加利福尼亚半岛的种群。分析表明，四倍体和二态性可能在下加利福尼亚形成，并且可能已经多次进化。
