Yamauchi Atsushi, Yamamura Norio
Center for Ecological Research, Kyoto University, Hirano 2-509-3, Otsu 520-2113, Japan.
J Theor Biol. 2006 May 7;240(1):24-31. doi: 10.1016/j.jtbi.2005.08.020. Epub 2005 Oct 3.
In eusocial Hymenoptera species, females variably develop into either alate females (queens) or workers, and in most cases, caste differentiation is determined environmentally. Recently, however, female castes in two harvester ant species, Pogonomyrmex rugosus and P. barbatus, were found to be determined genetically in hybrid zones of these two species. In the hybrid populations, homozygous females (e.g. AA or BB) and heterozygous females (AB) develop into alate females and workers, respectively. This genetic caste determination system is called symmetric social hybridogenesis (SSH). It is clear that populations with SSH can persist only if all four genotypes (AA and BB females, and A and B males) coexist simultaneously. However, it is not obvious that these populations are always persistent when the four genotypes simultaneously exist. Here, we examined the stability and persistence of an SSH population using a simple mathematical model. According to the analysis of the model, the SSH population persists only when some conditions are satisfied: (1) each female mates with more than two males, and (2) male production increases less steeply than linearly with increasing numbers of workers in a colony, and alate female production increases more steeply than linearly with increasing numbers of workers, or (2') male production increases more steeply than linearly with increasing numbers of workers in a colony, and alate female production increases much more steeply than male production. Therefore, it is not obvious that SSH populations are maintained and are stable for long periods. We discuss whether these conditions are satisfied in real SSH populations.
在群居性膜翅目物种中，雌性个体可发育为有翅雌性（蚁后）或工蚁，并且在大多数情况下，品级分化由环境因素决定。然而，最近发现，在两种收获蚁物种，即粗糙收获蚁（Pogonomyrmex rugosus）和巴氏收获蚁（P. barbatus）中，雌性品级由这两个物种杂交区域内的基因决定。在杂交种群中，纯合雌性（如AA或BB）和杂合雌性（AB）分别发育为有翅雌性和工蚁。这种基因品级决定系统被称为对称社会杂交生殖（SSH）。显然，只有当所有四种基因型（AA和BB雌性，以及A和B雄性）同时共存时，具有SSH的种群才能持续存在。然而，当这四种基因型同时存在时，这些种群是否总能持续存在并不明显。在此，我们使用一个简单的数学模型研究了SSH种群的稳定性和持续性。根据模型分析，只有在满足某些条件时，SSH种群才能持续存在：（1）每个雌性与多于两个雄性交配，并且（2）雄性数量随蚁群中工蚁数量的增加而增加的斜率小于线性关系，而有翅雌性数量随工蚁数量的增加而增加的斜率大于线性关系，或者（2'）雄性数量随蚁群中工蚁数量的增加而增加的斜率大于线性关系，且有翅雌性数量随工蚁数量的增加而增加的斜率远大于雄性数量增加的斜率。因此，SSH种群能否长期维持并保持稳定并不明显。我们讨论了这些条件在实际的SSH种群中是否得到满足。
