Mena-Ali Jorge I, Keser Lidewij H, Stephenson Andrew G
Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.
BMC Evol Biol. 2008 Jan 16;8:10. doi: 10.1186/1471-2148-8-10.
Solanum carolinense (horsenettle) is a highly successful weed with a gametophytic self-incompatibility (SI) system. Previous studies reveal that the strength of SI in S. carolinense is a plastic trait, associated with particular S-alleles. The importance of this variation in self-fertility on the ability of horsenettle to found and establish new populations will depend, to a large extent, on the magnitude of inbreeding depression. We performed a series of greenhouse and field experiments to determine the magnitude of inbreeding depression in S. carolinense, whether inbreeding depression varies by family, and whether the estimates of inbreeding depression vary under field and greenhouse conditions. We performed a series of controlled self- and cross-pollinations on 16 genets collected from a large population in Pennsylvania to obtain progeny with different levels of inbreeding. We grew the selfed and outcrossed progeny in the greenhouse and under field conditions and recorded various measures of growth and reproductive output.
In the greenhouse study we found (1) a reduction in flower, fruit and seed production per fruit in inbred (selfed) progeny when compared to outbred (outcrossed) progeny; (2) a reduction in growth of resprouts obtained from rhizome cuttings of selfed progeny; and (3) an increase in the ability to self-fertilize in the selfed progeny. In the field, we found that (1) outcrossed progeny produced more leaves than their selfed siblings; (2) herbivory seems to add little to inbreeding depression; and (3) outcrossed plants grew faster and were able to set more fruits than selfed plants.
Solanum carolinense experiences low levels of inbreeding depression under greenhouse conditions and slightly more inbreeding depression under our field conditions. The combined effects of low levels of inbreeding depression and plasticity in the strength of SI suggest that the production of selfed progeny may play an important role in the establishment of new populations of S. carolinense.
卡罗来纳茄（刺萼龙葵）是一种极为成功的杂草，具有配子体自交不亲和（SI）系统。先前的研究表明，卡罗来纳茄中自交不亲和的强度是一个可塑性性状，与特定的S等位基因相关。这种自交育性的变异对刺萼龙葵建立新种群能力的重要性，在很大程度上取决于近交衰退的程度。我们进行了一系列温室和田间实验，以确定卡罗来纳茄的近交衰退程度、近交衰退是否因家系而异，以及近交衰退的估计值在田间和温室条件下是否不同。我们对从宾夕法尼亚州一个大种群中收集的16个基因型进行了一系列控制自交和异交授粉，以获得不同近交水平的后代。我们在温室和田间条件下种植自交和异交后代，并记录了各种生长和繁殖输出指标。
在温室研究中，我们发现：（1）与异交（杂交）后代相比，自交后代的花、果实和每个果实的种子产量减少；（2）自交后代根茎插条产生的新芽生长减少；（3）自交后代的自交能力增强。在田间，我们发现：（1）异交后代比其自交的同胞产生更多的叶子；（2）食草作用似乎对近交衰退影响不大；（3）异交植物比自交植物生长得更快，能够结更多的果实。
卡罗来纳茄在温室条件下近交衰退水平较低，在我们的田间条件下近交衰退略多。低水平的近交衰退和自交不亲和强度的可塑性共同作用表明，自交后代的产生可能在卡罗来纳茄新种群的建立中发挥重要作用。
