Individual-based simulations were conducted to examine the spread of an altruistic allele by group selection. For the simulations, individuals with one locus determining altruistic behaviour were created in an environment with 13 patches. Individual fitness was determined by the number of altruists and the number of total individuals in a patch. Offspring disperse within the natal patch or into neighbouring patches depending on random values with a normal distribution having a zero mean and standard deviation σd (random dispersal model). The probability of the spread of the altruistic allele increased with increasing dispersal distance until a moderately low dispersal distance (σd = 50); thereafter, the probability decreased with increasing dispersal distance. A density-dependent dispersal model in which female offspring tend to disperse to the patch with lowest densities among five candidate dispersal sites was also tested For the density-dependent dispersal model, the chance of spreading the altruistic allele was higher than that of the random dispersal model. The results can be explained by two components of group selection: the extinction of groups with lower frequencies of altruists (selective extinction) and higher frequencies of migrants of altruists due to high productivities of altruistic groups (effective migrants). Evolution of altruism by interdemic group selection only (i.e. by differential extinctions and recolonization of demes) appears unlikely, since it requires high rates of both extinction and recolonization with low migration among surviving demes. However, the present study showed that moderately low migration can create favourable conditions under which both selective extinction and effective migrants simultaneously increase the probability of spreading the altruistic alleles.
|ジャーナル||Evolutionary Ecology Research|
|出版ステータス||出版済み - 1999 10月|