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Overripening of eggs and changes in reproductive hormones in the threespine stickleback, Gasterosteus aculeatus
Stockholm Univ, Dept Zool, SE-10691 Stockholm, Sweden..
Ctr Environm Fisheries & Aquaculture Sci Cefas, Weymouth, England..
Ctr Environm Fisheries & Aquaculture Sci Cefas, Weymouth, England..
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Physiology.
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2016 (English)In: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 17, no 3, 583-601 p.Article in journal (Refereed) PublishedText
Abstract [en]

Background: Female threespine sticklebacks, Gasterosteus aculeatus, are batch spawners. As in most teleosts, the ovulated eggs are kept in the ovarian cavity until spawning. If spawning or spontaneous release of the eggs does not take place, they can become overripe and harden, and in most cases remain in the ovary. The overripe eggs are lost for reproduction and also block further spawnings. Reproductive hormones regulate egg production and may be involved in the mechanism of overripening. Question: What are the reproductive endocrinological parameters characterizing overripening of ovulated eggs in the threespine stickleback? Organism: Wild-caught adult threespine sticklebacks from the southern Baltic at Skare in southern Sweden and the island of Asko in northwestern Baltic Proper in Sweden. Experiments: We collected blood samples for hormone measurements, as well as pituitaries and brains for measurement of mRNA from both sexually mature non-overripe (non-ovulated and/or ovulated) and overripe (egg-bound) females. For the Skare fish, sexual maturation was induced under laboratory conditions by exposure to a long photoperiod and we compared the non-overripe (including non-ovulated, with oocytes in different maturing or ripening stages, and ovulated females) with the overripe females. The Asko fish were sampled directly from nature, during the natural summer breeding season and we compared the non-overripe (including non-ovulated, with oocytes in different maturing or ripening stages, and ovulated females) with the overripe females. Methods: In the fish collected from Skare, we used radioimmunoassay to measure the plasma levels of four steroids: testosterone, estradiol, 17,20 beta-dihydroxypregn-4-en-3-one (17,20 beta-P), and 17,20 beta, 21-trihydroxypregn-4-en-3-one (17,20 beta,21-P). We also measured the mRNA levels of gonadotropins [GTHs: follicle-stimulating hormone (fsh-beta) and luteinizing hormone (lh-beta)] in the pituitary, and of gonadotropin-releasing hormones (GnRHs: gnrh2, gnrh3) and kisspeptin (kiss2) and its G protein-coupled receptor (gpr54) in the brain by real-time quantitative PCR. In the fish collected from Asko, we measured only progestogens (17,20 beta-P and 17,20 beta,21-P). Results: In the fish from Skare, overripe female sticklebacks had significantly lower levels of circulating plasma steroid hormones (testosterone, estradiol, 17,20 beta-P), as well as of pituitary lh-beta and brain kiss2 and gpr54 mRNA than the non-overripe females. In the fish caught from Asko, overripe females had lower 17,20 beta-P levels than the non-overripe non-ovulated females, but there was no difference between the non-overripe ovulated and the overripe females. The 17,20 beta,21-P plasma levels were under the limit of detection in all groups.

Place, publisher, year, edition, pages
2016. Vol. 17, no 3, 583-601 p.
Keyword [en]
testosterone, estradiol, 17, 20 beta-dihydroxypregn-4-en-3-one, 17, 20 beta, 21-trihydroxypregn-4-en-3-one, fsh-beta, lh-beta, gnrh2, gnrh3, kiss2, gpr54, ovulation, spawning, overripe, reproduction, stickleback, teleosts
National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:uu:diva-299701ISI: 000378168800008OAI: oai:DiVA.org:uu-299701DiVA: diva2:950025
Funder
Knut and Alice Wallenberg Foundation
Available from: 2016-07-26 Created: 2016-07-26 Last updated: 2016-07-26Bibliographically approved

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Mustafa, ArshiSchmitz, Monika
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