Organisms are expected to invest less in reproduction in response to a stressor, but theory predicts that this effect should depend on the frequency and duration of stressors in the environment. Here, we investigated how an acute stressor affected testes function in a songbird, and how chronic stressors influenced the acute stress response. We exposed male dark-eyed juncos () either to chronic or minimal (control) disturbance during testicular recrudescence, after which we measured baseline testosterone, testosterone after an acute handling stressor, and capacity to produce testosterone after hormonal stimulation. In a 2×2 design, we then killed males from the two chronic treatment groups either immediately or after an acute stressor to investigate the effect of long- and short-term stressors on the testicular transcriptome. We found that chronically disturbed birds had marginally lower baseline testosterone. The acute stressor suppressed testosterone in control birds, but not in the chronic disturbance group. The ability to elevate testosterone did not differ between the chronic treatments. Surprisingly, chronic disturbance had a weak effect on the testicular transcriptome, and did not affect the transcriptomic response to the acute stressor. The acute stressor, on the other hand, upregulated the cellular stress response and affected expression of genes associated with hormonal stress response. Overall, we show that testicular function is sensitive to acute stressors but surprisingly robust to long-term stressors, and that chronic disturbance attenuates the decrease in testosterone in response to an acute stressor.

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Organisms are expected to invest less in reproduction in response to a stressor, but theory predicts that this effect should depend on the frequency of stressors in the environment. Here we investigated how an acute stressor affected gonadal function in a songbird, and how long-term differences in the stress environment influenced these acute stress responses. We exposed male Dark-eyed Juncos (Junco hyemalis) either to chronic or minimal (control) disturbance during gonadal recrudescence, after which we measured baseline testosterone, testosterone after an acute handling stressor, and the ability to elevate testosterone in response to hormonal stimulation. In a 2x2 design, we then euthanized males from the two chronic treatment groups either immediately or after an acute stressor to investigate the effect of these treatments on the gonadal transcriptome. We found that chronically disturbed birds had marginally lower testosterone. The acute stressor suppressed testosterone in control birds, but not in the chronic disturbance group. The ability to elevate testosterone did not differ between the chronic treatments. Surprisingly, chronic disturbance had a weak effect on the testicular transcriptome, and did not affect transcriptomic response to the acute stressor. The acute stressor, on the other hand, upregulated cellular stress response, and affected expression of genes associated with hormonal stress-response. Overall, we show that both chronic and acute stressors affect reproductive function, and that chronic stress changes how acute stressors affect testosterone physiology. Our findings also suggest that acute and chronic stressors affect testes differently, and that gonadal function is relatively robust to long-term stressors.Summary statementAn acute stressor downregulated testosterone production, but this effect was absent in chronically disturbed birds. The acute stressor had a strong effect on the gonadal transcriptome, whereas chronic disturbance had a negligible effect.