ABSTRACT

Dioecy, the separation of sexes into different male and female plants, can enable sexes to independently develop optimal strategies for the sex-linked allocation of reproductive resources. Understanding how dioecious species vary as conditions become more or less favourable may affect conservation and revegetation efforts in arid environments. Our study investigated sex-related resource allocation in the Australian native shrub, Pimelea microcephala subsp. microcephala (Thymelaeaceae) at four sites across an annual rainfall gradient of 250–390 mm in semi-arid South Australia. The study measured 25 male and 25 female individuals for plant height, plant diameter, the number of inflorescences per plant, number of flowers per inflorescence and the ratio of reproductive to vegetative biomass. Significant differences in the ratio of biomass allocated to reproduction between sexes (p < 0.05) were detected at three of the four sites, with sex-related differences increasing with decreased annual rainfall. Female reproductive allocation was two to five times greater, and was less variable than males at all sites except the highest rainfall site (p < 0.05), while male reproductive allocation decreased with average annual rainfall (p < 0.05). Growth outcomes of males and females were equal and female reproductive traits were mostly consistent between sites and were not associated with rainfall, therefore population structure may remain stable for P. microcephala subsp. microcephala as habitats become drier, so long as pollen limitation does not occur.

摘要

雌雄同体，将两性分离成不同的雄性和雌性植物，可以使两性独立地制定最佳策略，以进行生殖资源的性别相关分配。了解雌雄异体物种如何随着条件变得或多或少有利而变化，可能会影响干旱环境中的保护和植被恢复工作。我们的研究调查了澳大利亚本土灌木Pimelea microcephala subsp 中与性相关的资源分配。小头动物（百里香科）在半干旱的南澳大利亚年降雨量梯度为 250-390 毫米的四个地点。该研究测量了 25 个雄性和 25 个雌性个体的株高、株径、每株植物的花序数、每个花序的花数以及生殖生物量与营养生物量的比率。 在四个站点中的三个站点检测到分配给两性繁殖的生物量比率存在显着差异 ( p < 0.05)，与性别相关的差异随着年降雨量的减少而增加。除了降雨量最高的地点 ( p  < 0.05) 外，所有地点的雌性生殖分配比雄性多两到五倍，而且变化较小 ( p < 0.05)，而雄性生殖分配随着年平均降雨量的增加而减少 ( p < 0.05)。雄性和雌性的生长结果相等，雌性生殖特征在不同地点之间基本一致，与降雨无关，因此P. microcephala亚种的种群结构可能保持稳定。只要不发生花粉限制，栖息地就会变得干燥。