Maeno Koutaro Ould, Piou Cyril, Leménager Nicolas
Japan International Research Center for Agricultural Sciences (JIRCAS), Livestock and Environment Division, Ohwashi 1-1, Tsukuba, Ibaraki 305-8686, Japan.
CIRAD, UMR CBGP, INRAE, Institut Agro, IRD, Université Montpellier, F-34398 Montpellier, France.
J Insect Physiol. 2023 Mar;145:104467. doi: 10.1016/j.jinsphys.2022.104467. Epub 2022 Dec 14.
Phenotypic plasticity in body size is a product of modification of the developmental pathway. Although hatchlings of the desert locust, Schistocerca gregaria, show egg size-dependent plasticity in body size, it remains unclear how embryogenesis during egg development regulates final embryonic body size. To determine the developmental pathway causing body size variation at hatching, we examined egg and embryonic development at the early, middle, and late egg developmental stages in S. gregaria by comparing small and large eggs. Crowd-reared females produced larger eggs than isolated-reared females. The daily egg developmental rate was similar between small and large eggs: eggs dramatically absorbed external water after days 3 to 7 and nearly doubled the initial egg weight at the late stage of day 12. Morphological measurements of eggs and embryos at different days after oviposition revealed that large eggs were longer than small eggs throughout developmental stages. However, embryo length was similar between small and large eggs at the early stage (anatrepsis). Embryos begin to absorb yolk into their bodies after blastokinesis. The size of large-egg embryos increased significantly from the middle stage (katatrepsis) due to absorption of more yolk than small eggs. Egg length and embryo length were conspicuously larger in large eggs than in small eggs on day 12 of late katatrepsis. These results suggest that egg size did not influence the egg developmental rate and initial embryo size. Large eggs had more yolk and space, resulting in larger final embryos than small eggs. The amount of yolk and size of eggshells during katatrepsis could play a key role in determining hatchling body size in S. gregaria.
体型的表型可塑性是发育途径改变的产物。尽管沙漠蝗虫（Schistocerca gregaria）的幼体在体型上表现出卵大小依赖性可塑性，但卵发育过程中的胚胎发生如何调节最终胚胎体型仍不清楚。为了确定导致孵化时体型变化的发育途径，我们通过比较小卵和大卵，研究了沙漠蝗虫卵发育早期、中期和晚期的卵和胚胎发育情况。群体饲养的雌性产生的卵比单独饲养的雌性产生的卵更大。小卵和大卵的每日卵发育速率相似：卵在第3至7天后显著吸收外部水分，并在第12天后期使初始卵重几乎翻倍。产卵后不同天数对卵和胚胎的形态测量表明，在整个发育阶段，大卵比小卵更长。然而，在早期（原肠胚形成前期），小卵和大卵的胚胎长度相似。胚胎在胚动后开始将卵黄吸收到体内。由于吸收的卵黄比小卵多，大卵胚胎的大小从中期（原肠胚形成后期）开始显著增加。在原肠胚形成后期第12天，大卵中的卵长和胚胎长度明显大于小卵。这些结果表明，卵大小不影响卵发育速率和初始胚胎大小。大卵有更多的卵黄和空间，导致最终胚胎比小卵更大。原肠胚形成后期的卵黄量和卵壳大小可能在决定沙漠蝗虫幼体体型方面起关键作用。
