Dudley Leah S, Galen Candace
Institute of Ecology and Biodiversity, Facultad de Ciencias, University of Chile, Santiago, Chile.
Oecologia. 2007 Aug;153(1):1-9. doi: 10.1007/s00442-007-0712-4. Epub 2007 Apr 4.
Females and males of sexually dimorphic species have distinct resource demands due to differential allocation to reproduction. Sexual allocation theory predicts that functional traits will diverge between sexes to support these demands. However, such dimorphism may be masked by the impact of current reproduction on source-sink interactions between vegetative and reproductive organs. We ask whether natural selection has led to genetic dimorphism in homologous physiological traits between sexes of the dioecious willow shrub, Salix glauca. In a common garden experiment we compared physiological responses to drought stress by male and female ramets in the absence of confounding demands from reproductive structures. Ramets experienced similar pre-dawn leaf water status (Psi(l)) as parental genets in flower within the natural population, indicating that experimental dry-down mirrored environmental conditions in nature. Male and female ramets achieved similar instantaneous water use efficiency, based on the ratio of carbon gain to water loss, under wet and dry conditions. However, female ramets experienced greater water stress (i.e., more negative Psi(l)) than males under dry conditions. Lower Psi(l) for female ramets may partly reflect the maintenance of conductance under drought; males, in contrast, maintain Psi(l) under drought by reducing conductance. Differences between sexes in terms of conductance and leaf water status of the vegetative ramets were absent in a concomitant comparison of parental flowering plants. Our results show (1) genetic divergence in physiology between sexes of S. glauca occurs in the absence of gender-specific reproductive sinks, (2) males are the more physiologically plastic sex with respect to water use, and (3) paradoxically, divergence in water relations between sexes is not detectable at sexual maturity under natural conditions.
由于在繁殖方面的分配差异，两性异形物种的雌性和雄性有不同的资源需求。性分配理论预测，功能性状将在两性之间产生分化以支持这些需求。然而，这种二态性可能会被当前繁殖对营养器官和生殖器官之间源 - 库相互作用的影响所掩盖。我们研究自然选择是否导致了雌雄异株柳树灌木（Salix glauca）两性之间同源生理性状的遗传二态性。在一个共同花园实验中，我们比较了在没有生殖结构带来的混杂需求情况下，雄性和雌性分株对干旱胁迫的生理反应。分株在黎明前的叶片水势（Psi(l)）与自然种群中开花的亲本植株相似，这表明实验性的干旱模拟了自然环境条件。基于碳同化与水分损失的比率，雄性和雌性分株在湿润和干燥条件下都实现了相似的瞬时水分利用效率。然而，在干燥条件下，雌性分株比雄性分株经历了更大的水分胁迫（即Psi(l)更负）。雌性分株较低的Psi(l)可能部分反映了其在干旱条件下对导度的维持；相比之下，雄性在干旱条件下通过降低导度来维持Psi(l)。在对亲本开花植株的同步比较中，营养分株在导度和叶片水势方面的性别差异并不存在。我们的结果表明：（1）在没有性别特异性生殖库的情况下，Salix glauca两性之间在生理上存在遗传分化；（2）就水分利用而言，雄性是生理可塑性更强的性别；（3）矛盾的是，在自然条件下性成熟时，两性之间水分关系的差异无法检测到。
