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; Ibn Zohr University, Agadir, Morocco; Centre National de Lutte Antiacridienne (CNLAA), Aït-Melloul, BP 125, Inezgane, Agadir, Morocco.
J Insect Physiol. 2022 Jan;136:104331. doi: 10.1016/j.jinsphys.2021.104331. Epub 2021 Nov 25.
The desert locust, Schistocerca gregaria, shows a density-dependent reproductive trade-off by laying fewer but larger eggs in crowded conditions (gregarious phase) than in isolated conditions (solitarious phase). However, the physiological mechanisms controlling reproductive resource allocation remain unclear. We examined how egg production processes, including ovulation timing (i.e., oogenesis period), oocyte and ovarian growth rates, and oosorption rate (resorbing developing terminal oocytes), regulate reproductive outputs (egg biomass per clutch, egg size, and clutch size) during a reproductive cycle in S. gregaria by rearing them either under isolated or crowded conditions. We observed a common density-dependent negative correlation between egg size and clutch size, with no significant difference in egg biomass between the two rearing conditions. Dissection of female locusts after different days of oviposition revealed that the daily oocyte growth rate was almost similar between the two rearing conditions, but crowd-reared females ovulated later than isolated-reared ones, resulting in further oocyte growth in the former. Terminal oocytes were renewed by previous penultimate oocytes at the onset of a new reproductive cycle, and oosorption mainly occurred at an early stage in both rearing conditions; however, crowd-reared locusts displayed higher levels of oosorption compared to their isolated-reared counterparts. Crowding induced a high oosorption rate, resulting in a reduced clutch size and a prolonged oogenesis period, which in turn allowed oocytes to intake more yolk, which was probably recycled via oosorption. These results suggest that the length of the oogenesis period and oosorption rate are manipulated by maternal density, and these physiological modifications interactively regulate reproductive trade-off in S. gregaria.
沙漠蝗，Schistocerca gregaria，在密集条件下（群居阶段）比在隔离条件下（独居阶段）产卵更少但更大，表现出密度依赖的生殖权衡。然而，控制生殖资源分配的生理机制仍不清楚。我们通过在隔离或密集条件下饲养它们，研究了产卵过程（即卵发生期）、卵母细胞和卵巢生长率以及卵吸收率（吸收发育中的终末卵母细胞）如何调节 S. gregaria 生殖周期中的生殖产出（每卵群的卵生物质、卵大小和卵群大小）。我们观察到在生殖周期中，卵大小和卵群大小之间存在一种共同的密度依赖的负相关，而在两种饲养条件下，卵生物质没有显著差异。对不同产卵日的雌性蝗虫进行解剖发现，两种饲养条件下的每日卵母细胞生长率几乎相似，但群居饲养的雌性蝗虫比独居饲养的雌性蝗虫排卵晚，导致前者的卵母细胞进一步生长。终末卵母细胞在新的生殖周期开始时由前一个次末卵母细胞更新，卵吸收主要发生在两种饲养条件的早期；然而，群居饲养的蝗虫比独居饲养的蝗虫表现出更高水平的卵吸收。密集饲养诱导高卵吸收率，导致卵群大小减少和卵发生期延长，这反过来又允许卵母细胞摄入更多的卵黄，这些卵黄可能通过卵吸收回收。这些结果表明，卵发生期的长度和卵吸收率受母体密度的操纵，这些生理变化相互作用调节 S. gregaria 的生殖权衡。
