de Jong T J, van der Meijden E
Institute of Biology, Leiden University, P.O. Box 9516, 2300 RA Leiden, The Netherlands.
Plant Biol (Stuttg). 2004 Sep;6(5):616-20. doi: 10.1055/s-2004-821177.
In dioecious plants the fraction of males among flowering plants in the field (the secondary sex ratio) is the result of the fraction of males in the seeds (the primary sex ratio) and the subsequent survival and age at first reproduction of the two genders. It has been assumed that survival and age at first reproduction are the main determinants of biased secondary sex ratio but, especially for long-lived perennials, few data are available. We address this issue for natural populations of four long-lived perennials in a dune area. In Asparagus officinale and Bryonia dioica, the secondary sex ratio was unbiased. In Salix repens the secondary sex ratio was female-biased (0.337). Hippophae rhamnoides populations were male-biased; the average sex ratio of flowering plants was 0.658, while the fraction of males varied between 0.39 near the sea to 0.84 at the inland side of the dunes. The primary sex ratio was estimated by germinating seeds and growing plants under favourable conditions with minimal mortality. In S. repens the primary sex ratio in seeds was variable among mother plants and was, on average, female-biased (0.289). This is close to the secondary sex ratio, suggesting that the female bias already originates in the seed stage. In Hippophae rhamnoides the primary sex ratio was slightly male-biased (0.564). We argue that in this species, apart from the primary sex ratio, higher mortality and a later age at first reproduction for females contribute to the strong male bias among flowering plants in the field.
在雌雄异株植物中，田间开花植物中雄性的比例（次生性别比）是种子中雄性比例（初生性别比）以及随后两种性别的存活情况和首次繁殖年龄的结果。人们一直认为，存活情况和首次繁殖年龄是次生性别比偏差的主要决定因素，但特别是对于长寿多年生植物而言，可用数据很少。我们针对沙丘地区四种长寿多年生植物的自然种群解决了这个问题。在芦笋和白泻根中，次生性别比无偏差。在匍匐柳中，次生性别比偏向雌性（0.337）。沙棘种群偏向雄性；开花植物的平均性别比为0.658，而雄性比例在沙丘近海一侧为0.39，在内陆一侧为0.84之间变化。通过在有利条件下使种子发芽并种植植物，将死亡率降至最低来估计初生性别比。在匍匐柳中，种子的初生性别比在母株之间存在差异，平均而言偏向雌性（0.289）。这与次生性别比接近，表明雌性偏差在种子阶段就已产生。在沙棘中，初生性别比略微偏向雄性（0.564）。我们认为，在这个物种中，除了初生性别比之外，雌性较高的死亡率和较晚的首次繁殖年龄导致了田间开花植物中强烈的雄性偏差。
