Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Biol Lett. 2012 Apr 23;8(2):245-8. doi: 10.1098/rsbl.2011.0950. Epub 2011 Nov 2.
Variation in the timing of reproductive functions in dioecious organisms may result in adaptive changes in the direction of sexual dimorphism during the breeding season. For plants in which both pollen and seeds are wind-dispersed, it may be advantageous for male plants to be taller when pollen is dispersed and female plants to be taller when seeds are dispersed. We examined the dynamics of height dimorphism in Rumex hastatulus, an annual, wind-pollinated, dioecious plant from the southern USA. A field survey of seven populations indicated that females were significantly taller than males at seed maturity. However, a glasshouse experiment revealed a more complex pattern of height growth during the life cycle. No dimorphism was evident prior to reproduction for six of seven populations, but at flowering, males were significantly taller than females in all populations. This pattern was reversed at reproductive maturity, consistent with field observations. Males flowered later than females and the degree of height dimorphism was greater in populations with a later onset of male flowering. We discuss the potential adaptive significance of temporal changes in height dimorphism for pollen and seed dispersal, and how this may be optimized for the contrasting reproductive functions of the sexes.
雌雄异体生物生殖功能的时间变化可能导致繁殖季节中性别二态性的方向发生适应性变化。对于花粉和种子都通过风传播的植物来说，当花粉传播时雄性植物更高大，当种子传播时雌性植物更高大可能是有利的。我们研究了来自美国南部的一年生、风媒传粉、雌雄异株的酸模属植物 Rumex hastatulus 中高度二态性的动态。对七个种群的实地调查表明，在种子成熟时，雌性明显比雄性高大。然而，温室实验揭示了在生命周期中更复杂的高度生长模式。在六个种群中，在繁殖前没有明显的二态性，但在所有种群中，雄性在开花时明显比雌性高大。这种模式在生殖成熟时发生了逆转，与野外观察结果一致。雄性比雌性开花晚，而且雄性开花时间较晚的种群的高度二态性程度更大。我们讨论了高度二态性随时间变化在花粉和种子传播中的潜在适应性意义，以及如何优化性别之间的对比生殖功能。
