CSIRO Land and Water, Black Mountain, Canberra, ACT, 2601, Australia.
Applied BioSciences, Macquarie University, Macquarie Park, Sydney, NSW, 2109, Australia.
BMC Genet. 2020 Dec 18;21(Suppl 2):132. doi: 10.1186/s12863-020-00936-1.
Bactrocera tryoni and Bactrocera neohumeralis mate asynchronously; the former mates exclusively around dusk while the latter mates during the day. The two species also differ in the colour of the post-pronotal lobe (callus), which is predominantly yellow in B. tryoni and brown in B. neohumeralis. We have examined the genetic relationship between the two characters in hybrids, backcrosses and multigeneration hybrid progeny.
Our analysis of the mating time of the parental species revealed that while B. tryoni mate exclusively at dusk, B. neohumeralis females pair with B. neohumeralis males during the day and with B. tryoni males at dusk. We found considerable variance in mating time and callus colour among hybrid backcross individuals of both sexes but there was a strong although not invariant trend for callus colour to co-segregate with mating time in both sexes. To genetically separate these two phenotypes we allowed the interspecific F1 hybrids to propagate for 25 generations (F25) without selection for mating time or callus colour, finding that the advanced hybrid population had moved towards B. tryoni phenotypes for both traits. Selection for day mating in replicate lines at F25 resulted in significant phenotypic shifts in both traits towards B. neohumeralis phenotypes in F26. However, we were unable to completely recover the mating time profile of B. neohumeralis and relaxation of selection for day mating led to a shift back towards dusk mating, but not yellow callus colour, by F35.
We conclude that the inheritance of the two major species-defining traits is separable but tightly linked and involves more than one gene in each case. It also appears that laboratory conditions select for the B. tryoni phenotypes for mating time. We discuss our findings in relation to speciation theory and the likely effects of domestication during the generation of mass release strains for sterile insect control programmes.
地中海实蝇和南亚果实蝇交配不同步；前者仅在黄昏交配，而后者在白天交配。这两个物种在后胸叶突（胼胝体）的颜色上也有所不同，地中海实蝇的颜色主要是黄色，而南亚果实蝇的颜色是棕色。我们已经检查了杂种、回交和多代杂种后代中这两个特征之间的遗传关系。
我们对亲本物种交配时间的分析表明，虽然地中海实蝇仅在黄昏交配，但南亚果实蝇的雌性在白天与南亚果实蝇的雄性交配，在黄昏与地中海实蝇的雄性交配。我们发现，雌雄两性的杂交回交个体在交配时间和胼胝体颜色上有相当大的差异，但胼胝体颜色与交配时间在两性中强烈但并非不变的趋势存在很强的相关性。为了在遗传上分离这两种表型，我们让种间 F1 杂种在没有选择交配时间或胼胝体颜色的情况下繁殖 25 代（F25），发现先进的杂交种群在两个性状上都向地中海实蝇表型移动。在 F25 时对重复线进行日交配选择，导致两个性状的表型向南亚果实蝇表型显著转移，但 F35 时不再完全恢复南亚果实蝇的交配时间模式，且对日间交配的选择放松导致回交向黄昏交配，但胼胝体颜色不是黄色。
我们得出结论，两个主要的物种定义特征的遗传是可分离的，但紧密相连，每个特征涉及不止一个基因。似乎实验室条件选择了地中海实蝇的交配时间表型。我们讨论了我们的发现与物种形成理论的关系，以及在为不育昆虫控制计划生成大规模释放菌株的过程中驯化的可能影响。
