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Avian Research 2022, 13(3): 100037 https://doi.org/10.1016/j.avrs.2022.100037
Research Article | Open Access | Issue | Published: 18 May 2022

Seasonal variations in gonad morphology and hypothalamic GnRH-I and GnIH in Eurasian Tree Sparrow, a multi-brooded passerine

Show Author's Information Limin Wanga,1,  Ghulam Nabia,1,  Li Zhanga,  Dan Liua,  Mo Lia,  Juyong Lia,  Kaixin Shia,  Ibrahim M. Ahmada,  Yuefeng Wua,  John C. Wingfieldb,  Dongming Lia( )
Ministry of Education Key Laboratory of Molecular and Cellular Biology, Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, 050024, China
Department of Neurobiology, Physiology and Behavior, University of California, Davis, CA, USA

1 These two authors contributed equally to this work.

Keywords:
Seasonality, Eurasian Tree Sparrow, Reproduction, Gonads, Hypothalamus
Cite this article:
Wang L, Nabi G, Zhang L, et al. Seasonal variations in gonad morphology and hypothalamic GnRH-I and GnIH in Eurasian Tree Sparrow, a multi-brooded passerine. Avian Research, 2022, 13(3): 100037. https://doi.org/10.1016/j.avrs.2022.100037
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Abstract Full text About this article

The hypothalamic-pituitary-gonadal (HPG) axis ubiquitously regulates seasonal reproduction, following the rhythmicity of a suite of environmental cues. Birds display prominent seasonal variations in gonad size regulated by two hypothalamic peptides, gonadotropin-releasing hormone-1 (GnRH-I) and gonadotropin-inhibiting hormone (GnIH). How multi-brooded avian species adjust GnRH-I and GnIH to regulate gonadal morphology seasonally remains largely unknown. Here, we studied the variations in the hypothalamic immunoreactivity (ir) of GnRH-I and GnIH, gonadal proliferation, and apoptosis in a typical multi-brooded species, the Eurasian Tree Sparrow (Passer montanus), across the pre-breeding (PB), first breeding (FB), second breeding (SB), pre-basic molt (PM), and wintering stages (WS). Our results showed that both sexes had higher preoptic area (POA)-GnRH-I-ir but lower paraventricular nucleus (PVN)-GnIH-ir neurons during the breeding stages (FB and SB) relative to other life-history stages, with no significant differences between two broods. The testes and ovaries were significantly larger during the breeding stages. Testicular volume increased during the two broods due to anincreased diameter of seminiferous tubules. Furthermore, there were more testicular apoptotic cells in PB and WS stages than in breeding stages, and in PB stage than in PM stage. Males had higher POA-GnRH-I expression than females during the breeding stages, but both sexes had comparable PVN-GnIH expression throughout the annual cycle. Both sexes of the sparrows may undergo a similar pattern of life-history stage-dependent variation in the hypothalamic GnRH-I, GnIH, and gonadal morphology, except that during breeding stages, males may display higher expression of POA-GnRH-I relative to females. The higher expression of POA-GnRH-I-ir in breeding male sparrows may be critical for male-dependent parental care.


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About this article

Seasonal variations in gonad morphology and hypothalamic GnRH-I and GnIH in Eurasian Tree Sparrow, a multi-brooded passerine

Show Author's information Limin Wanga,1, Ghulam Nabia,1, Li Zhanga, Dan Liua, Mo Lia, Juyong Lia, Kaixin Shia, Ibrahim M. Ahmada, Yuefeng Wua, John C. Wingfieldb, Dongming Lia( )
Ministry of Education Key Laboratory of Molecular and Cellular Biology, Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, 050024, China
Department of Neurobiology, Physiology and Behavior, University of California, Davis, CA, USA

1 These two authors contributed equally to this work.

Abstract

The hypothalamic-pituitary-gonadal (HPG) axis ubiquitously regulates seasonal reproduction, following the rhythmicity of a suite of environmental cues. Birds display prominent seasonal variations in gonad size regulated by two hypothalamic peptides, gonadotropin-releasing hormone-1 (GnRH-I) and gonadotropin-inhibiting hormone (GnIH). How multi-brooded avian species adjust GnRH-I and GnIH to regulate gonadal morphology seasonally remains largely unknown. Here, we studied the variations in the hypothalamic immunoreactivity (ir) of GnRH-I and GnIH, gonadal proliferation, and apoptosis in a typical multi-brooded species, the Eurasian Tree Sparrow (Passer montanus), across the pre-breeding (PB), first breeding (FB), second breeding (SB), pre-basic molt (PM), and wintering stages (WS). Our results showed that both sexes had higher preoptic area (POA)-GnRH-I-ir but lower paraventricular nucleus (PVN)-GnIH-ir neurons during the breeding stages (FB and SB) relative to other life-history stages, with no significant differences between two broods. The testes and ovaries were significantly larger during the breeding stages. Testicular volume increased during the two broods due to anincreased diameter of seminiferous tubules. Furthermore, there were more testicular apoptotic cells in PB and WS stages than in breeding stages, and in PB stage than in PM stage. Males had higher POA-GnRH-I expression than females during the breeding stages, but both sexes had comparable PVN-GnIH expression throughout the annual cycle. Both sexes of the sparrows may undergo a similar pattern of life-history stage-dependent variation in the hypothalamic GnRH-I, GnIH, and gonadal morphology, except that during breeding stages, males may display higher expression of POA-GnRH-I relative to females. The higher expression of POA-GnRH-I-ir in breeding male sparrows may be critical for male-dependent parental care.

Keywords: Seasonality, Eurasian Tree Sparrow, Reproduction, Gonads, Hypothalamus

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Acknowledgements
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Publication history

Received: 18 March 2022
Revised: 05 May 2022
Accepted: 08 May 2022
Published: 18 May 2022
Issue date: September 2022

Copyright

© 2022 The Authors.

Acknowledgements

We thank Shuo Cui, Yinchao Hao, Xuelu Liu, Yaqing Li, Chenyang Hao for their assistance with sample collection in the field. This work was supported by the National Natural Science Foundation of China (NSFC, 31971413) to DL and NSFC (31770445) to YW, the Natural Science Foundation of Hebei Province, China (NSFHB, C2020205038) to DL, and NSFHB (C2020205005), and the Postdoctoral Research Foundation of China (PRFC, 2020M670685) to LW.

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This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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