Tada Yasuhiro, Nishida Chizuko, Katakura Haruo
1 Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan.
Zoolog Sci. 2014 Feb;31(2):71-6. doi: 10.2108/zsj.31.71.
We examined whether the ploidy level of eggs from sexual and parthenogenetic females of the weevil Scepticus insularis changes when field-collected, egg-bearing females are exposed to low temperature, as suggested by a previous study. We observed no change in ploidy level in eggs laid by sexual females (n = 15) treated by low temperature (1.1-6.7°C). In contrast, eggs laid by parthenogenetic females were not stable in ploidy level, as 11 of 16 females tested laid both diploid and triploid eggs even before the low-temperature treatment. After the low-temperature treatment, the proportion of triploid eggs to total eggs increased in nine individuals and decreased in the rest, and the effect of the treatment on the overall change in frequency was significant. Our results thus show that exposure to cold does not induce a change in egg ploidy in the sexual form of S. insularis, although cold may affect ploidy levels in the eggs of parthenogens. Additionally, eggs laid by laboratory-reared, virgin sexual females (n = 13) did not hatch after the low-temperature treatment, indicating that the treatment did not induce parthenogenetic reproduction in normally sexually reproducing females of S. insularis. We also examined the effect of low temperature on the ploidy level of eggs from parthenogenetic females (n = 4) of another weevil species, Catapionus gracilicornis, and confirmed that the proportion of triploid eggs steeply decreased and that of diploid eggs increased after exposure to cold, being consistent with those of previous studies.
正如之前一项研究所表明的，我们研究了野外采集的携带虫卵的海岛象甲雌性个体（包括有性生殖和孤雌生殖的雌性）暴露于低温环境时，其产出的卵的倍性水平是否会发生变化。我们观察到，经低温处理（1.1 - 6.7°C）的有性生殖雌性（n = 15）所产的卵，其倍性水平没有变化。相比之下，孤雌生殖雌性所产的卵在倍性水平上不稳定，因为在16只受试雌性中，有11只在低温处理前就产出了二倍体和三倍体的卵。低温处理后，9只个体的三倍体卵占总卵数的比例增加，其余个体则下降，且该处理对频率总体变化的影响显著。因此，我们的结果表明，暴露于寒冷环境不会导致海岛象甲有性生殖形式的卵的倍性发生变化，尽管寒冷可能会影响孤雌生殖者的卵的倍性水平。此外，实验室饲养的未交配的有性生殖雌性（n = 13）所产的卵在低温处理后未孵化，这表明该处理不会诱导海岛象甲正常有性生殖的雌性进行孤雌生殖。我们还研究了低温对另一种象甲细角隐头象甲（Catapionus gracilicornis）孤雌生殖雌性（n = 4）所产的卵的倍性水平的影响，并证实暴露于寒冷环境后，三倍体卵比例急剧下降，二倍体卵比例上升，这与之前的研究结果一致。
