臺灣地區入侵紅火蟻巢內親族關係及小地理尺度族群遺傳結構之研究

Abstract

Remarkable genetic changes of Solenopsis invicta have been reported in US. The post-invasion turnover seems unfailing but lacks further evidence from other introduced areas. Two social forms of fire ant in Taiwan provide a great opportunity to test the genetic change in different levels of hierarchical structure. At colony level, data from multiple microsatellite loci reveal that nestmate relatedness for monogyne invariably overlaps with 0.75 and is similar to those in US as well as its native range South America, suggesting that social organization of this form remains stable whether the population is native or introduced. In contrast, the nestmate relatedness of polygyne tends to be binomial; that is, one group possesses much higher value while the other one overlaps with zero. By keeping surveying one “higher” site, the significant decline of relatedness observed during successive collections from gives a direct evidence that sites belong to the “zero” group might have been invaded much longer than others from ‘‘higher’’ group. This pattern somehow parallels patterns in US and might be explained by adoption of unrelated alates driven by ecological constraints (e.g. habitat saturation) as the habitat ages. At microgeographical level, significant genetic differentiation is seen between sympatric forms in mtDNA but not microsatellite, which can be explained by the limited male mediated interform gene flow model. Subsequent genetic analyses show significant differentiation and strong isolation by distance (IBD) among polygyne sites but not monogyne, indicating restricted inter-site gene flow by polygyne queens, who usually expand by budding or local mating. On the other hand, the ability of monogyne queens to conduct distant mating flights appears to be the force homogenizing the genetic structure in a kilometer-scale. Results from the present study in population genetic give a indirect evidence to the form-specific biology of different Solenopsis invicta social organization. In colony level, the observation of changes in relatedness is generally consistent with ecological constraint hypothesis and provide direct evidence that the invasive fire ants did underwent rapid social evolution associated with invasion given they were estimated to have arrived into Taiwan within the last decade.