The effect of chronic and acute stressors, and their interaction, on testes function: an experimental test during testicular recrudescence

Abstract

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.

Wildfire affects expression of male sexual plumage through suppressed testosterone circulation in a tropical songbird

“…Furcular fat stores did not appear to be sensitive to fire in either the comparison to previous study years or in the paired pre fire versus post fire analysis, suggesting that males did not suffer from diminished body condition in response to fire. Finally, we did not find a relationship between corticosterone and testosterone in our dataset (Supporting information), thus adding to a growing list of studies in birds suggesting an absence of antagonism between these two hormones (Davies et al 2016, Deviche et al 2017, Abolins‐Abols et al 2018).…”

Wildfire affects circulating hormone levels and the expression of male sexual plumage in a tropical songbird

“…In addition, this limited sampling window could have kept us from detecting diminished fat stores following fire (Table 1). Finally, we did not find a relationship between corticosterone and testosterone in our dataset ( Figure S1), thus adding to a growing list of studies in birds suggesting an absence of antagonism between these two hormones (Davies et al 2016, Deviche et al 2017, Abolins-Abols et al 2018.…”

Chronic disturbance induces attenuation of the acute glucocorticoid response in an urban adapter, the dark-eyed junco

“…Alternatively, the exercise of flying and hopping during disturbances may have interfered with mass gain in the disturbance group. A companion study of these same birds found that frequently-disturbed birds were equally reproductively ready as control birds: groups did not differ in testes mass or testosterone in response to GnRH, and cloacal protuberance size was larger in the disturbance group, although baseline testosterone was lower in the disturbance group (Abolins-Abols et al, 2018). These results indicate that birds in the chronic disturbance treatment were likely not in homeostatic overload (Romero et al, 2009), and were instead able to achieve reproductive readiness despite disturbances, suggesting that the phenotypic flexibility we observed was adaptive (Ghalambor et al, 2007).…”