Kamping A, Van Delden W
Department of Genetics, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands.
Heredity (Edinb). 1999 Oct;83 ( Pt 4):460-8. doi: 10.1038/sj.hdy.6885980.
In order to explain the worldwide latitudinal distribution and seasonal fluctuations in In(2L)t frequencies in Drosophila melanogaster, fitness differences among In(2L)t and Standard (ST ) homo- and heterokaryotypes under high-temperature conditions were determined. Viabilities were measured for high-temperature treatment started at different juvenile stages. The capacity to restore fertility after high-temperature treatment was measured for adults and juveniles. Furthermore, genetic adaptation for increased temperature resistance for these traits was determined for strains which were reared at 33 degrees C for 10 generations. Whereas larva-pupa survival rates were high, highest juvenile mortalities and strongest karyotypic effects were observed during the pupal stage when preceding larval stages were reared at 33 degrees C. ST karyotypes showed lowest viabilities. Although mating rate was hardly influenced, sterility was induced for females and males after high-temperature treatment of adults as well as juveniles. Subsequent transfer to 25 degrees C, however, resulted in restored fertility in some of the individuals, depending on the length of the recovery period. Fertility restoration was significantly higher for heterokaryotype males and females. Heterokaryotype superiority for restored fertility as well as for viability was positively correlated with severity of the treatment. Ten generations of selection at 33 degrees C resulted in significant improvement of juvenile survival and fertility restoration for all karyotypes. These fitness components were positively correlated (r=0.91; P < 0.001), which might suggest pleiotropic effects. It is concluded that the capacity to restore fertility after heat stress is an important fitness component, especially with respect to the In(2L)t polymorphism. The observed heterokaryotypic superiority fits with the idea that the latitudinal distribution of In(2L)t frequencies is maintained by balancing selection, with equilibrium values decreasing with latitude.
为了解释黑腹果蝇中In(2L)t频率的全球纬度分布和季节性波动，我们测定了In(2L)t与标准（ST）同核型和异核型在高温条件下的适合度差异。测量了在不同幼虫阶段开始高温处理后的活力。测定了成虫和幼虫在高温处理后恢复生育能力的能力。此外，还测定了在33℃饲养10代的品系对这些性状的耐热性遗传适应性。虽然幼虫-蛹的存活率较高，但当幼虫前期在33℃饲养时，在蛹期观察到最高的幼虫死亡率和最强的核型效应。ST核型的活力最低。虽然交配率几乎不受影响，但成虫和幼虫经高温处理后均诱导了雌性和雄性的不育。然而，随后转移到25℃，部分个体的生育能力得以恢复，这取决于恢复期的长短。异核型雄性和雌性的生育能力恢复率明显更高。异核型在生育能力恢复和活力方面的优势与处理的严重程度呈正相关。在33℃下进行十代选择，所有核型的幼虫存活率和生育能力恢复均得到显著改善。这些适合度成分呈正相关（r = 0.91；P < 0.001），这可能表明存在多效性效应。结论是，热应激后恢复生育能力的能力是一个重要的适合度成分，特别是对于In(2L)t多态性而言。观察到的异核型优势符合这样一种观点，即In(2L)t频率的纬度分布是通过平衡选择维持的，平衡值随纬度降低。
