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Temperature-induced physiological stress and reproductive characteristics of the migratory seahorse Hippocampus erectus during a thermal stress simulation - PubMed

  • ️Mon Jan 01 2018

Temperature-induced physiological stress and reproductive characteristics of the migratory seahorse Hippocampus erectus during a thermal stress simulation

Geng Qin et al. Biol Open. 2018.

Abstract

Inshore-offshore migration occurs frequently in seahorse species, either because of prey opportunities or because they are driven by reproduction, and variations in water temperature may dramatically change migratory seahorse behavior and physiology. The present study investigated the behavioral and physiological responses of the lined seahorse Hippocampus erectus under thermal stress and evaluated the potential effects of different temperatures on its reproduction. The results showed that the thermal tolerance of the seahorses was time dependent. Acute thermal stress (30°C, 2-10 h) increased the basal metabolic rate (breathing rate) and the expression of stress response genes (Hsp genes) significantly and further stimulated seahorse appetite. Chronic thermal treatment (30°C, 4 weeks) led to a persistently higher basal metabolic rate, higher stress response gene expression and higher mortality rates, indicating that the seahorses could not acclimate to chronic thermal stress and might experience massive mortality rates due to excessively high basal metabolic rates and stress damage. Additionally, no significant negative effects on gonad development or reproductive endocrine regulation genes were observed in response to chronic thermal stress, suggesting that seahorse reproductive behavior could adapt to higher-temperature conditions during migration and within seahorse breeding grounds. In conclusion, this simulation experiment indicates that temperature variations during inshore-offshore migration have no effect on reproduction, but promote significantly high basal metabolic rates and stress responses. Therefore, we suggest that the observed high tolerance of seahorse reproduction is in line with the inshore-offshore reproductive migration pattern of lined seahorses.This article has an associated First Person interview with the first author of the paper.

Keywords: Migration; Reproduction; Reproductive endocrine regulation; Seahorse; Temperature.

© 2018. Published by The Company of Biologists Ltd.

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Conflict of interest statement

Competing interestsThe authors declare no competing or financial interests.

Figures

Fig. 1.
Fig. 1.

Seahorse ventilation rate in response to acute thermal stress over 10 h, when the temperature was increased from 22°C to 32°C.

Fig. 2.
Fig. 2.

Hsp60 and Hsp70 expression in seahorse livers in response to acute thermal stress. (A) Hsp60 gene expression. (B) Hsp70 gene expression. Different letters indicate significant differences between the different groups.

Fig. 3.
Fig. 3.

Ventilation rate (A), mortality rate (B) and growth (C) of seahorses in response to chronic thermal stress.

Fig. 4.
Fig. 4.

Feeding behavior and related gene expression of seahorses in response to thermal stress. (A,B) Feeding frequency (A) and defecation frequency (B) over 4 weeks of thermal stress. (C,D) leptin expression in the seahorses’ brains after 10 h (C) or 4 weeks (D) of thermal stress. Different letters indicate significant differences between different groups.

Fig. 5.
Fig. 5.

Hsp gene expression in response to chronic thermal stress (4 weeks of thermal stress) and room-temperature acclimatization (4 additional weeks of normal temperature acclimation). (A) Hsp60 gene expression. (B) Hsp70 gene expression. Different letters indicate significant differences between different groups.

Fig. 6.
Fig. 6.

Ovary development of Hippocampus erectus seahorses under different chronic thermal treatments.

Fig. 7.
Fig. 7.

Reproductive endocrine responses of seahorses in response to chronic thermal stress. (A) Sex hormone levels. (B) Reproductive regulation-related genes in brain and pituitary gland in response to chronic thermal stress. Different letters indicate significant differences between different groups.

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