Hormonal changes over the spawning cycle in the female three-spined stickleback, Gasterosteus aculeatus

Abstract

Female three-spined sticklebacks are batch spawners laying eggs in a nest built by the male. We sampled female sticklebacks at different time points, when they were ready to spawn and 6, 24, 48 and 72 h post-spawning (hps) with a male. Following spawning, almost all females (15 out of 19) had ovulated eggs again at Day 3 post-spawning (72 hps). At sampling, plasma, brain and pituitaries were collected, and the ovary and liver were weighed. Testosterone (T) and estradiol (E2) were measured by radioimmunoassay. Moreover, the mRNA levels of follicle-stimulating hormone (fsh-beta) and luteinizing hormone (lh-beta) in the pituitary, and of the gonadotropin-releasing hormones (GnRHs: gnrh2, gnrh3) and kisspeptin (kiss2) and its G protein-coupled receptor (gpr54) in the brain were measured by real-time qPCR. Ovarian weights peaked in ready to spawn females, dropped after spawning, before again progressively increasing from 6 to 72 hps. Plasma T levels showed peaks at 24 and 48 hps and decreased at 72 hps, while E2 levels increased already at 6 hps and remained at high levels up to 48 hps. There was a strong positive correlation between T and E2 levels over the spawning cycle. Pituitary lh-beta mRNA levels showed a peak at 48 hps, while fsh-beta did not change. The neuropeptides and gpr54 did not show any changes. The changes in T and E2 over the stickleback spawning cycle were largely consistent with those found in other multiple-spawning fishes whereas the marked correlation between T and E2 does not support T having other major roles over the cycle than being a precursor for E2. Crown Copyright (C) 2017 Published by Elsevier Inc. All rights reserved.