Department of Zoology, Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia.
Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic.
PLoS One. 2019 Apr 23;14(4):e0215317. doi: 10.1371/journal.pone.0215317. eCollection 2019.
Sex-specific mechanisms of the determination of insect body sizes are insufficiently understood. Here we use the common heath moth, Ematurga atomaria (Lepidoptera: Geometridae) to examine how larval growth trajectories differ between males and females. We monitored the development of 1379 larvae in controlled laboratory conditions. Sexually dimorphic development times during the first four instars were associated with sexual size dimorphism (SSD) in the beginning of the fifth (last) instar, when females were on average 15% heavier than males. Similarly, the duration of the last instar was about 13% longer in females. Further, we specifically focussed on the estimates of differential (instantaneous) growth rates of the larvae based on 24h mass increments of the 2nd, 3rd, 4th and 5th day in the beginning of the last instar. We calculated 'allometric' differential growth rates as the per-day increase in cube-root-transformed mass of the larvae. We found that allometric growth rates were slightly but significantly larger in females than in males. As this measure of growth rate (in contrast to the relative growth rate, based on the ratio of masses recorded at consecutive measurements) did not depend on body size, it allows an unambiguous separation of the effects of sex and size. We conclude that in accordance with an emerging general pattern, larger female body size in E. atomaria is achieved primarily by means of a longer growth period. Furthermore, our study shows that the differential growth rate can also be sexually dimorphic and contribute to SSD. This contribution, however, is lower than that of the development time by an order of magnitude. In addition to development periods and growth rates, other parameters of the non-linear growth curves of insect larvae also need to be considered in the context of SSD determination. In particular, weight loss prior to pupation was shown to be considerably larger in females than in males.
昆虫体型的性别决定机制尚不完全清楚。在这里，我们使用常见的 Heath 蛾 Ematurga atomaria（鳞翅目：尺蛾科）来研究幼虫的生长轨迹如何在雄性和雌性之间存在差异。我们在受控的实验室条件下监测了 1379 只幼虫的发育情况。在前四个龄期中存在性别二型的发育时间与第五个（最后一个）龄期开始时的性别体型二型（SSD）有关，此时雌性的平均体重比雄性重 15%。同样，最后一个龄期的持续时间在雌性中大约长 13%。此外，我们特别关注基于第五个龄期开始时第二天、第三天、第四天和第五天 24 小时质量增量对幼虫的差异（瞬时）生长率的估计。我们计算了幼虫的“分形”差异生长率，作为幼虫质量立方根转化后每天的增加量。我们发现，雌性的分形生长率略高于雄性，但具有统计学意义。由于这种生长率的测量方法（与相对生长率不同，后者基于连续测量记录的质量比）不依赖于体型，因此可以明确区分性别和体型的影响。我们得出的结论是，与新兴的一般模式一致，E. atomaria 中较大的雌性体型主要通过更长的生长时间来实现。此外，我们的研究表明，差异生长率也可能具有性别二型性，并有助于 SSD。然而，这种贡献比发育时间低一个数量级。除了发育时间和生长率之外，昆虫幼虫非线性生长曲线的其他参数也需要在 SSD 确定的背景下进行考虑。特别是，与雄性相比，雌性在化蛹前的体重损失明显更大。
