Food restriction negatively affects multiple levels of the reproductive axis in male house finches, Haemorhous mexicanus

Abstract

Nutrition influences reproductive functions across vertebrates, but the effects of food availability on the functioning of the hypothalamicpituitary-gonadal (HPG) axis in wild birds and the mechanisms mediating these effects remain unclear. We investigated the influence of chronic food restriction on the HPG axis of photostimulated house finches, Haemorhous mexicanus. Food-restricted birds had underdeveloped testes with smaller seminiferous tubules than ad libitum-fed birds. Baseline plasma testosterone increased in response to photostimulation in ad libitum-fed but not in food-restricted birds. Food availability did not, however, affect the plasma testosterone increase resulting from a gonadotropin-releasing hormone-I (GnRH) or a luteinizing hormone (LH) challenge. The number of hypothalamic GnRH immunoreactive (ir) but not proGnRH-ir perikarya was higher in food-restricted than in ad libitum-fed finches, suggesting inhibited secretion of GnRH. Hypothalamic gonadotropin-inhibitory hormone (GnIH)-ir and neuropeptide Y (NPY)-ir were not affected by food availability. Plasma corticosterone (CORT) was also not affected by food availability, indicating that the observed HPG axis inhibition did not result from increased activity of the hypothalamic-pituitaryadrenal (HPA) axis. This study is among the first to examine multilevel functional changes in the HPG axis in response to food restriction in a wild bird. The results indicate that food availability affects both hypothalamic and gonadal function, but further investigations are needed to clarify the mechanisms by which nutritional signals mediate these effects.

Changes in brain peptides associated with reproduction and energy homeostasis: Putative roles of gonadotrophin‐releasing hormone‐II and tyrosine hydroxylase in determining reproductive performance in response to daily food availability times in diurnal zebra finches

“…9,52 We caution, however, that changes in the hypothalamic perikarya number, as measured in the present study, might not account for all the food-induced reproductive effects by themselves because food cues could affect also the release of hypothalamic neuropeptides in the median eminence, and the sensitivity of the anterior pituitary to GnRH/ GnIH, or of gonads to luteinising hormone. 9,12,26 Regardless of the possibility for more than one end point of the food-induced effects, the overall hypothalamic reproductive peptide levels in the current study correlated with earlier reported adverse effects of Figure 1. Values indicate the resuls of the two-way ANOVA (FA, food availability).…”

“…Nevertheless, several bird studies have shown a negative impact of food deprivation on the hypothalamic‐pituitary‐gonadal (HPG) axis . For example, food availability affected circulating oestradiol levels in broiler hens and testosterone levels in male house finches ( Haemorhous mexicanus ) and Abert's towhees . Recently, Mishra and Kumar reported reduced oestradiol and mesotocin levels but not thyroxin and triiodothyronine levels in female zebra finches with access to food for 4 hours compared to food available ad lib., suggesting a negative effect of food restriction on the reproductive, not general, health, of breeding zebra finches …”

The quantity-quality trade-off: differential effects of daily food times on reproductive performance and offspring quality in diurnal zebra finches

“…starvation) could have a direct effect by triggering a cascade of hypothalamic releases which negatively impact the activity of the hypothalamicpituitary-gonadal axis (Lynn et al, 2015;Davies et al, 2015;Rønning et al, 2009). This is evidenced by a food availabilityinduced alteration in the plasma levels of oestradiol in broiler hens (Onagbesan et al, 2006), testosterone in male house finches (Haemorhous mexicanus; Valle et al, 2015) and Abert's towhees (Davies et al, 2015) and thyroid hormones in Japanese quails, Coturnix c. japonica (Rønning et al, 2009). Consistent with this, food deprivation increased gonadotropin inhibiting hormone levels in zebra finches (Taeniopygia guttata; Lynn et al, 2015) and Pekin duck (Anas platyrhynchos domestica; Fraley et al, 2013).…”

Effects of temperature on the timing of breeding and molt transitions in house finches

“…Enzyme immunoassay kits from Enzo Life Sciences (Farmingdale, NY, USA) were used to measure plasma testosterone (ADI-901-065) and corticosterone (ADI-900-097). These assays have been validated for house finches (Deviche and Cortez, 2005;Valle et al, 2015).…”

“…For the testosterone assay, samples were run at a 1:15 dilution with 1% (of raw plasma volume) steroid displacement buffer (following Valle et al, 2015). Samples were run in duplicate, with samples assigned randomly across multiple plates except that all samples for a given individual were run on a single plate.…”