Photoperiod-Independent Hypothalamic Regulation of Luteinizing Hormone Secretion in a Free-Living Sonoran Desert Bird, the Rufous-Winged Sparrow <i>(Aimophila carpalis)</i>

Abstract

We investigated the regulation of luteinizing hormone (LH) in the male Rufous-winged Sparrow,Aimophila carpalis, a resident of the Sonoran desert that breeds after irregular summer rains. Although the testes develop in March due to increasing photoperiod and regress in September due to decreasing photoperiod, LH does not consistently increase in the spring as in other photoperiodic birds. However, throughout the year increased plasma LH is correlated with rainfall. To investigate this rainfall-associated regulation of LH secretion, we quantified immunocytochemical labeling for gonadotropin-releasing hormone I (GnRH-I), proGnRH (the GnRH precursor), and gonadotropin-inhibitory hormone (GnIH) in the hypothalamus of free-living adult males caught before (low LH), and during (high LH) the monsoon rainy season. Compared to pre-monsoon birds, birds caught during the monsoon season had larger immunoreactive GnRH-I (GnRH-I-ir) and proGnRH-ir cell bodies, as well as fewer, less densely labeled proGnRH-ir cell bodies. Birds caught during the monsoon had fewer, less densely labeled GnIH-ir cell bodies than birds caught before the monsoon. Further, there was no GnIH-ir labeling in the median eminence on either capture dates, suggesting that GnIH is not released to the pituitary gland via the portal vein at this time of year, but there were fewer GnIH-ir fibers in the preoptic area of birds caught during the monsoon season. Our data support the hypothesis that environmental factors associated with increased rainfall during the monsoon season stimulate GnRH synthesis and release to increase LH secretion. These data also suggest that GnIH could inhibit GnRH neuronal activity prior to the monsoon season.

Spring phenology does not affect timing of reproduction in the great tit (Parus major)

“…As the development of the male reproductive system precedes that of the female, it is less likely that males will show an adaptive response to phenological cues to fine-tune gonadal development. Yet, in an opportunistic breeder, the rufous-winged sparrow (Aimophila carpalis), environmental factors associated with summer rains stimulated both gonadotropinreleasing hormone (GnRH) synthesis and LH secretion in males, which was, however, unrelated to gonadal growth earlier in the season ( Small et al, 2008). Similarly, the higher LH concentrations reported by Visser and colleagues did not induce a greater increase in testis size (Visser et al, 2002); also, in the present experiment there was only a weak correlation between female LH concentrations and actual laying date.…”

“…In non-equatorial birds, lengthening photoperiod in spring provides the principal cue for the timing of seasonal breeding (Dawson et al, 2001;Farner, 1985;Follett et al, 1985;Sharp, 2005;Silverin et al, 1993), but supplementary cues derived from rainfall, ambient temperature and phenology are available to increase the precision of a timing decision (Dawson, 2008;Hau et al, 2004;Perfito et al, 2005;Salvante et al, 2007;Schaper et al, 2011;Small et al, 2008;Visser et al, 2009;Wingfield et al, 1992) (but see Visser et al, 2011). The aims of this study were, firstly, to re-evaluate evidence for the involvement of phenological cues in the onset of egg laying in opportunistic and strictly seasonally breeding birds, and, secondly, to assess experimentally whether there is a causal relationship between phenological cues provided by leafing birch and caterpillars and the onset of reproduction in a seasonal breeder, the great tit (Parus major L.).…”

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

“…In contrast to testicular size, cloacal protuberance growth in finches was not affected by food availability. Cloacal protuberance size usually varies in parallel with testis size (Perfito et al, 2005;Small et al, 2008) and both are influenced by circulating testosterone levels (Deviche and Cortez, 2005). Although food-restricted finches had lower plasma testosterone than ad libitum-fed finches, it appears that the precise relationship between plasma testosterone and cloacal protuberance growth is somewhat dissociated, an observation that is not without precedent (Wingfield et al, 2012).…”

“…Between two and four assays were performed for each neuropeptide, with birds from each treatment group equally represented on each assay. Immunocytochemical labeling was done using a previously published procedure (Deviche et al, 2000;Small et al, 2008). Briefly, free-floating sections were washed three times for 20 min in 0.1 mol l −1 PB, incubated in 0.36% hydrogen peroxide, washed 3 times for 5 min in 0.1 mol l −1 PB, incubated for 1 h in normal blocking serum, and incubated overnight at 4°C in primary antibody.…”

Individual variation in avian reproductive physiology does not reliably predict variation in laying date

“…For example, it has been shown that LH levels in male songbirds, even though primarily regulated by photoperiod, increase in response to environmental stimuli, such as the onset of rain [35], or the presence of leafing birch branches [44], but see [28]. Furthermore, if LH plasma concentrations are only loosely regulating gonadal development, the question remains which external or internal information is reflected in elevated LH concentrations, and which mechanisms might be affected further downstream.…”