Temperature-induced elevation of basal metabolic rate does not affect testis growth in great tits

Samuel, P.; Visser, Marcel E.

doi:10.1242/jeb.026344

Cited by 31 publications

(25 citation statements)

References 42 publications

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“…As we detected no such reduction, our observations are consistent with the proposition that testis growth in the Abert's Towhee may not be particularly energetically demanding. This conclusion is consistent with results of a study by Caro & Visser () in which Great Tits Parus major exposed to ambient temperatures of 8 °C or 22 °C during photoperiodically induced reproductive development had different basal metabolic rates, but showed similar testicular growth. We should point out that neither our study nor that of Caro & Visser () can exclude the possibility that testis growth is energetically demanding, but when energy is limited, birds continue to allocate energy to this process at the cost of other processes.…”

Section: Discussionsupporting

confidence: 92%

Food availability, energetic constraints and reproductive development in a wild seasonally breeding songbird

et al. 2015

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Summary In many organisms, food availability is a proximate cue that synchronizes seasonal development of the reproductive system with optimal environmental conditions. Growth of the gonads and secondary sexual characteristics is orchestrated by the hypothalamic–pituitary–gonadal (HPG) axis. However, our understanding of the physiological mechanisms by which food availability modulates activity of the HPG axis is limited.It is thought that many factors, including energetic status, modulate seasonal reproductive activation. We tested the hypothesis that food availability modulates the activity of the HPG axis in a songbird. Specifically, we food‐restricted captive adult male Abert's Towhees Melozone aberti for 2 or 4 weeks during photoinduced reproductive development. A third group (control) received ad libitum food throughout. We measured multiple aspects of the reproductive system including endocrine activity of all three levels of the HPG axis [i.e. hypothalamic gonadotropin‐releasing hormone‐I (GnRH‐I), plasma luteinizing hormone (LH) and testosterone (T)], and gonad morphology. Furthermore, because gonadotropin‐inhibitory hormone (GnIH) and neuropeptide Y (NPY; a potent orexigenic peptide) potentially integrate information on food availability into seasonal reproductive development, we also measured the brain levels of these peptides.At the hypothalamic level, we detected no effect of food restriction on immunoreactive (ir) GnRH‐I, but the duration of food restriction was inversely related to the size of ir‐GnIH perikarya. Furthermore, the number of ir‐NPY cells was higher in food‐restricted than control birds. Food restriction did not influence photoinduced testicular growth, but decreased plasma LH and T, and width of the cloacal protuberance, an androgen‐sensitive secondary sexual characteristic. Returning birds to ad libitum food availability had no effect on plasma LH or T, but caused the cloacal protuberance to rapidly increase in size to that of ad libitum‐fed birds.Our results support the tenet that food availability modulates photoinduced reproductive activation. However, they also suggest that this modulation is complex and depends upon the level of the HPG axis considered. At the hypothalamic level, our results are consistent with a role for the GnIH and NPY systems in integrating information on energetic status. There also appears to be a role for endocrine function at the anterior pituitary gland and testicular levels in modulating reproductive development in the light of energetic status and independently of testicular growth.

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Section: Discussionsupporting

confidence: 92%

Food availability, energetic constraints and reproductive development in a wild seasonally breeding songbird

et al. 2015

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“…This may be mediated physiologically in the gonads by a dampening of the responsiveness to stress hormones and metabolic stress during breeding. Additionally, recrudescence of the gonads represents a higher metabolic cost than simply maintaining large gonads once they have recrudesced (Vezina & Salvante, 2010), although in a study on wild birds housed indoors with ad libitum food, testicular growth was not thought to be energy-demanding (Caro & Visser, 2009). Thus when metabolic fuels are limited, the onset of gonadal growth (which would occur in photosensitive birds) is delayed, but maintenance of gonads (which would occur in photostimulated birds) is not.…”

Section: Discussionmentioning

confidence: 99%

The direct response of the gonads to cues of stress in a temperate songbird species is season-dependent

McGuire

Koh

Bentley

2013

PeerJ

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The gonadotropin releasing hormone (GnRH) system in the hypothalamus is often considered the final point in integration of environmental cues as they pertain to the reproductive axis. However, cues such as stress and food availability are detectable in the plasma (as glucocorticoid and metabolic fuel fluctuations). Vertebrate gonads express glucocorticoid receptor, therefore we hypothesized that the gonads can detect and respond directly to cues of stress. We provide evidence here that, in addition to regulation by the brain, the gonads of European starlings (Sturnus vulgaris) respond directly to fluctuations in corticosterone and metabolic fuels by modulating sex steroid secretion. Using a 4-h gonad culture, we show that physiologically-relevant concentrations of corticosterone and metabolic stress (via use of the glucose utilization inhibitor 2-deoxy-D-glucose and the fatty acid oxidation inhibitor ethyl 2-mercaptoacetate (2DG/MA)) can directly decrease testosterone and estradiol secretion from luteinizing hormone and follicle-stimulating hormone (LH/FSH)-stimulated testes and ovaries. This effect is regulated seasonally. Prior to the breeding season, testes and ovaries respond to corticosterone and 2DG/MA by significantly decreasing gonadal steroid release. Within the breeding season, the testes do not respond to these cues of stress, while the ovaries respond only to corticosterone. This seasonal difference in response may be due in part to the influence of these cues of stress on gonadal neuropeptide expression: corticosterone upregulates GnIH expression in the testes while metabolic stress upregulates GnIH in the ovaries. Thus the gonads can directly respond to fluctuations in corticosterone and metabolic fuels during a time of critical importance to the onset of breeding.

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“…For example, cold-acclimated (5°C) house finches, Carpodacus mexicanus, exhibited a 15% increase in BMR above that of warm-acclimated (25˚C) birds (O'Connor et al, 2000), while cold-acclimation (to 8˚C) in great tits (Parus major) induced a 21% increase in MR above warm-acclimated (to 22°C) BMR (Caro and Visser, 2009). Similarly, winter-acclimatized American goldfinches (Carduelis tristis) demonstrated 23% and 46% higher BMR than spring-and summer-acclimatized birds (Liknes et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

Evidence for within-individual energy reallocation in cold-challenged, egg-producing birds

Salvante

Vézina

Williams

2010

Journal of Experimental Biology

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SUMMARYRecent studies have shown that the metabolic cost of avian egg production involves a 16-27% increase in metabolic rate (MR) above non-reproductive basal or resting values (BMR and RMR, respectively). To determine how the metabolic cost of egg production interacted with the costs of other essential processes (such as cold acclimation and active heat production), we measured the MR of non-breeding and egg-producing zebra finches (Taeniopygia guttata) while (a) warm-acclimated (to 19-21°C) and measured within their thermoneutral zone (at 35°C), (b) cold-acclimated (to 7°C) and measured at thermoneutrality (at 35°C, i.e. not actively producing heat), and (c) cold-acclimated and measured below thermoneutrality (at 7°C) (i.e. during active heat production). The metabolic cost of egg production was small (24% above BMR) compared with the additive costs of cold acclimation and active heat production (224% above BMR). Exposure to low ambient temperatures was accompanied by an increase in seed consumption (by 72%) and a decrease in locomotor activity (by 72%) compared with warm-acclimated, nonbreeding values. By contrast, egg production in heat-producing females was associated with an 11% decrease in MR and a 22% decrease in seed consumption compared with non-breeding thermoregulating values. Our data suggest that while the increase in MR associated with egg production is small in relation to the birds' capacity to increase MR in response to other energetically demanding processes, the addition of egg production to these metabolically costly activities may be enough to necessitate the use of energy-saving strategies, such as internal energy reallocation, to cope with the additional energetic demands.

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Temperature-induced elevation of basal metabolic rate does not affect testis growth in great tits

Cited by 31 publications

References 42 publications

Food availability, energetic constraints and reproductive development in a wild seasonally breeding songbird

Food availability, energetic constraints and reproductive development in a wild seasonally breeding songbird

The direct response of the gonads to cues of stress in a temperate songbird species is season-dependent

Evidence for within-individual energy reallocation in cold-challenged, egg-producing birds

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