Botany, University of New England, Armidale, NSW 2351, Australia.
Ann Bot. 2012 Feb;109(3):521-30. doi: 10.1093/aob/mcr163. Epub 2011 Aug 10.
Sexually dimorphic populations are often located in drier habitats than cosexual populations. Gender plasticity (GP), whereby hermaphrodites alter female and male functions depending on resources, and sex-differential plasticity (SDP) between hermaphrodites and unisexuals are predicted to affect sexual system stability. Here, GP and SDP are evaluated in cosexual and gynodioecious Wurmbea biglandulosa and sub-dioecious and dioecious W. dioica.
GP was evaluated under two resource conditions, compared among sexual systems and assessed as to whether (1) males produced perfect flowers and (2) hermaphrodites altered investment in perfect (female function) and total (male function) flowers. SDP was assessed within sexual systems as differences between sex functions of hermaphrodites vs. unisexuals. Males and hermaphrodites were compared to assess whether size thresholds for female function differed among sexual systems. Plasticity costs were evaluated using correlations between female function and male traits in hermaphrodites, and in W. dioica by comparing hermaphrodite and male regressions between plant size and pollen production.
In dioecious W. dioica no males exhibited GP, whereas 100 % did in gynodioecious and cosexual W. biglandulosa. In sub-dioecious W. dioica, resources affected GP (high, 66 %; low, 42 %). Hermaphrodites in all sexual systems reduced perfect but not total flowers under low resources. Unisexuals were unaffected, demonstrating SDP for female function only. Thresholds for female function were greater in sub-dioecious W. dioica than in W. biglandulosa. Plasticity costs were detected only in sub-dioecious W. dioica.
SDP for female function could assist female establishment in cosexual populations and maintain females in gynodioecious and sub-dioecious populations. Although the absence of male SDP should stabilize sub-dioecy, plasticity costs would render sub-dioecy unstable, favouring canalized males over hermaphrodites. This study highlights the importance of interactions between environmental conditions and hermaphrodite sex expression for the stability of dimorphic sexual systems.
性二态种群通常位于比同性别种群更干燥的栖息地。性别可塑性（GP），即雌雄同体根据资源改变雌性和雄性功能，以及雌雄同体和雌雄异体之间的性别差异可塑性（SDP），预计会影响性系统的稳定性。在这里，评估了同性别和雌雄异株的 Wurmbea biglandulosa 以及亚雌雄同株和雌雄异株的 W. dioica 中的 GP 和 SDP。
在两种资源条件下评估 GP，比较不同性系统之间，并评估（1）雄性是否产生完美花朵，以及（2）雌雄同体是否改变对完美（雌性功能）和总（雄性功能）花朵的投资。在性系统内评估 SDP，作为雌雄同体与雌雄异体之间性功能的差异。比较雄性和雌雄同体，以评估雌性功能的大小阈值是否在性系统之间存在差异。通过比较亚雌雄同株和雌雄异株中植物大小和花粉产量之间的雌雄同体回归，以及在雌雄异株 W. dioica 中比较雌雄同体和雄性回归，评估可塑性成本。
在雌雄异株的 W. dioica 中，没有雄性表现出 GP，而在雌雄异株和同性别 W. biglandulosa 中，100%的雄性表现出 GP。在亚雌雄同株的 W. dioica 中，资源影响 GP（高，66%；低，42%）。在低资源下，所有性系统中的雌雄同体都减少了完美但不是总花朵。雌雄异体不受影响，仅表现出雌性功能的 SDP。亚雌雄同株的 W. dioica 中雌性功能的阈值大于 W. biglandulosa。仅在亚雌雄同株的 W. dioica 中检测到可塑性成本。
雌性功能的 SDP 可以帮助同性别种群中的雌性建立，维持雌雄异株和亚雌雄同株种群中的雌性。尽管缺乏雄性 SDP 应该稳定亚雌雄同株，但可塑性成本会使亚雌雄同株不稳定，有利于雌雄同体而不是雌雄同体。本研究强调了环境条件与雌雄同体性别表达之间的相互作用对二态性系统稳定性的重要性。
