Ferrer Miriam M, Good-Avila Sara V, Montaña Carlos, Domínguez César A, Eguiarte Luis E
Departmento de Ecología, Universidad Autónoma de Yucatán, Km. 15.5 Carretera Mérida Xtmacuil, Mérida, Yucatán, México.
Ann Bot. 2009 May;103(7):1077-89. doi: 10.1093/aob/mcp033. Epub 2009 Feb 14.
Selection may favour a partial or complete loss of self-incompatibility (SI) if it increases the reproductive output of individuals in the presence of low mate availability. The reproductive output of individuals varying in their strength of SI may also be affected by population density via its affect on the spatial structuring and number of S-alleles in populations. Modifiers increasing levels of self-compatibility can be selected when self-compatible individuals receive reproductive compensation by, for example, increasing seed set and/or when they become associated with high fitness genotypes.
The effect of variation in the strength of SI and scrub density (low versus high) on seed set, seed germination and inbreeding depression in seed germination (delta(germ)) was investigated in the partially self-incompatible species Flourensia cernua by analysing data from self-, cross- and open-pollinated florets.
Examination of 100 plants in both high and low scrub densities revealed that 51% of plants were strongly self-incompatible and 49 % varied from being self-incompatible to self-compatible. Seed set after hand cross-pollination was higher than after open-pollination for self-incompatible, partially self-incompatible and self-compatible plants but was uniformly low for strongly self-incompatible plants. Strongly self-incompatible and self-incompatible plants exhibited lower seed set, seed germination and multiplicative female fitness (floral display x seed set x seed germination) in open-pollinated florets compared with partially self-incompatible and self-compatible plants. Scrub density also had an effect on seed set and inbreeding depression: in low-density scrubs seed set was higher after open-pollination and delta(germ) was lower.
These data suggest that (a) plants suffered outcross pollen limitation, (b) female fitness in partially self-incompatible and self-compatible plants is enhanced by increased mate-compatibility and (c) plants in low-density scrubs received higher quality pollen via open-pollination than plants in high-density scrubs.
如果在配偶可利用性较低的情况下，选择能够提高个体的繁殖输出，那么它可能会有利于自交不亲和性（SI）的部分或完全丧失。SI强度不同的个体的繁殖输出也可能受到种群密度的影响，因为种群密度会影响种群中S等位基因的空间结构和数量。当自交亲和的个体通过增加结实率等方式获得繁殖补偿，或者当它们与高适合度基因型相关联时，增加自交亲和水平的修饰基因就可能被选择。
通过分析自花授粉、异花授粉和开放授粉小花的数据，研究了部分自交不亲和物种弗洛伦西亚卷毛菊中SI强度变化和灌丛密度（低与高）对结实率、种子萌发和种子萌发中的近交衰退（delta(germ)）的影响。
对高、低灌丛密度下的100株植物进行检查发现，51%的植物具有强烈的自交不亲和性，49%的植物自交不亲和性程度不同，从自交不亲和到自交亲和。对于自交不亲和、部分自交不亲和和自交亲和的植物，人工异花授粉后的结实率高于开放授粉后的结实率，但对于强烈自交不亲和的植物，结实率始终较低。与部分自交不亲和和自交亲和的植物相比，强烈自交不亲和和自交不亲和的植物在开放授粉小花中表现出较低的结实率、种子萌发率和雌性繁殖适合度（花展示×结实率×种子萌发率）。灌丛密度也对结实率和近交衰退有影响：在低密度灌丛中，开放授粉后的结实率较高，delta(germ)较低。
这些数据表明，（a）植物遭受异交花粉限制，（b）部分自交不亲和和自交亲和植物的雌性适合度通过增加配偶亲和性而提高，（c）低密度灌丛中的植物通过开放授粉比高密度灌丛中的植物获得更高质量的花粉。
