Mazer Susan J, Delesalle Véronique A, Neal Paul R
Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, 93106.
Biology Department, Gettysburg College, Gettysburg, Pennsylvania, 17325.
Evolution. 1999 Jun;53(3):717-731. doi: 10.1111/j.1558-5646.1999.tb05366.x.
Two widespread assumptions underlie theoretical models of the evolution of sex allocation in hermaphroditic species: (1) resource allocations to male and female function are heritable; and (2) there is an intrinsic, genetically based negative correlation between male and female reproductive function. These assumptions have not been adequately tested in wild species, although a few studies have detected either genetic variation in pollen and ovule production per flower or evidence of trade-offs between male and female investment at the whole plant level. It may also be argued, however, that in highly autogamous, perfect-flowered plant taxa that exhibit genetic variation in gamete production, strong stabilizing selection for an efficient pollen:ovule ratio should result in a positive correlation among genotypes with respect to mean ovule and mean pollen production per flower. Here we report the results of a three-generation artificial selection experiment conducted on a greenhouse population of the autogamous annual plant Spergularia marina. Starting with a base population of 1200 individuals, we conducted intense mass selection for two generations, creating four selected lines (high and low ovule production per flower; high and low anther production per flower) and a control line. By examining the direct and correlated responses of several floral traits to selection on gamete production per flower, we evaluated the expectations that primary sexual investment would exhibit heritable variation and that resource-sharing, variation in resource-garnering ability, or developmental constraints mold the genetic correlations expressed among floral organs. The observed direct and correlated responses to selection on male and female gamete production revealed significant heritabilities of both ovule and anther production per flower and a significant negative genetic correlation between them. When plants were selected for increased ovules per flower over two generations, ovule production increased and anther production declined relative to the control line. Among plants selected for decreased anthers per flower, we observed a decline in anther production and an increase in ovule production relative to the control line. In contrast, the lines selected for low ovules per flower and for high anthers per flower exhibited no evidence for significant genetic correlations between male and female primary investment. Correlated responses to selection also indicate a genetically based negative correlation between the production of normal versus developmentally abnormal anthers (staminoid organs); a positive correlation between the production of ovules versus staminoid organs; and a positive correlation between the production of anthers and petals. The negative relationship between male versus female primary investment supports classical sex allocation theory, although the asymmetrical correlated responses to selection indicate that this relationship is not always expressed.
（1）对雄性和雌性功能的资源分配是可遗传的；（2）雄性和雌性生殖功能之间存在内在的、基于遗传的负相关。尽管有一些研究检测到了每朵花花粉和胚珠产量的遗传变异，或者在整株植物水平上发现了雄性和雌性投资之间权衡的证据，但这些假设在野生物种中尚未得到充分验证。然而，也可以认为，在高度自花授粉、具有完全花的植物类群中，配子产量存在遗传变异，对有效花粉：胚珠比率的强烈稳定选择应该导致基因型之间在每朵花的平均胚珠和平均花粉产量方面呈正相关。在此，我们报告了对自花授粉一年生植物滨海拟漆姑温室种群进行的三代人工选择实验结果。从1200个个体的基础种群开始，我们进行了两代高强度的混合选择，创建了四个选择品系（每朵花胚珠产量高和低；每朵花花药产量高和低）和一个对照品系。通过研究几种花部性状对每朵花配子产量选择的直接和相关反应，我们评估了以下预期：主要性投资将表现出可遗传变异，并且资源共享、资源获取能力的变异或发育限制塑造了花器官之间表达的遗传相关性。观察到的对雄性和雌性配子产量选择的直接和相关反应表明，每朵花的胚珠和花药产量都具有显著的遗传力，并且它们之间存在显著的负遗传相关性。当在两代中选择每朵花胚珠增加的植株时，相对于对照品系，胚珠产量增加而花药产量下降。在选择每朵花花药减少的植株中，相对于对照品系，我们观察到花药产量下降而胚珠产量增加。相比之下，选择每朵花胚珠少和花药多的品系没有显示出雄性和雌性主要投资之间存在显著遗传相关性的证据。对选择的相关反应还表明，正常花药与发育异常花药（雄蕊状器官）的产量之间存在基于遗传的负相关；胚珠与雄蕊状器官的产量之间存在正相关；花药与花瓣的产量之间存在正相关。雄性与雌性主要投资之间的负相关支持了经典的性别分配理论，尽管对选择的不对称相关反应表明这种关系并不总是表现出来。
