The effects of habitat spatial structure on the accumulations of deleterious mutations : using freshwater snails

我们研究了生境空间结构的影响，对有害突变的积累，使用现场淡水螺（Physa acta）。钉螺采集自两种不同的生境：（1）（大稳定种群）水位稳定的稻田，钉螺可能在大种群内杂交;（2）（交替混合种群）小的暂时孤立的水池，有时在大雨中变成大池塘。螺类在交替混合种群中，在小的隔离水池中可能发生高密度的近亲繁殖;而在大的稳定种群中，螺类可能发生低密度的近亲繁殖。因此，可以预测，在高密度下，来自交替混合种群的钉螺的近交衰退可能较低。结果表明，在高密度下，由螺卵数和适合度（螺卵数×存活率）估算的近交衰退率，交替混合种群低于大稳定种群，但在低密度下，两种群间的近交衰退率无显著差异。结果与上述预测相一致。此外，还进行了基于个体的模拟，考察了遗传邻域大小和栖息地形状对有害突变积累和灭绝风险的影响。结果表明，总群体大小和遗传邻域大小对累积的纯合有害位点数有独立的线性影响。此外，生境的形状显著影响有害突变的积累和灭绝概率。

We examined the effects of habitat spatial structure on the accumulations of deleterious mutations using field freshwater snails (Physa acta). The snails were collected from two different habitat : (1) (Large stable population) Rice fields in which the water levels might be stable and the snails might interbreed within large populations ; (2) (Alternate mixing populations) Small isolated temporally water pools which sometimes become large ponds in a heavy rain. Snails might inbreed at high densities in small isolated water pools in alternate mixing population ; while snails might inbreed at low densities in the large stable population. Thus, it can be predicted that inbreeding depression of snails from the alternate mixing populations might be low at high densities. The results showed that the inbreeding depression estimated from the number of eggs and the fitness (number of eggs x survival rates) was lower in the snails form the alternate mixing populations than those from the large stable populations at high densities but there was no significant differences in inbreeding depression between snails from two populations at low densities. The results were consistent with the above predictions.Furthermore, the individual -based simulations were conducted to examine the effects of the genetic neighborhood size and the shape of habitat on the accumulations of deleterious mutation and the risk of extinction. The results indicated that the total population size and the genetic neighborhood size affect linearly the numbers of accumulated homozygotic deleterious loci independently. In addition, the shape of habitat significantly affect the accumulation of deleterious mutations and the extinction probability.