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

我们利用野外淡水蜗牛(Physa Acta)研究了栖息地空间结构对有害突变积累的影响。钉螺来自两个不同的栖息地：(1)(大稳定种群)稻田，那里的水位可能稳定，蜗牛可能在大种群中杂交；(2)(交替混合种群)暂时孤立的小水池，有时在暴雨中变成大池塘。在交替混合种群中，钉螺可能在孤立的小水池中以高密度近亲繁殖，而在大而稳定的种群中，钉螺可能以低密度近亲繁殖。因此，可以预测，在高密度下，交替混合种群钉螺的近亲繁殖抑制可能较低。结果表明，以产卵量和适合度(卵数×存活率)为指标的交错混交钉螺在高密度条件下的近交抑制程度低于大密度稳定钉螺，而在低密度条件下两种种群钉螺的近交抑制程度无显着差异。结果与上述预测一致。此外，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累积和灭绝风险的影响。结果表明，总群体大小和遗传邻域大小独立地线性影响累积的纯合子有害基因座数。此外，栖息地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.