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Examining sources of variation in HPG axis function among individuals and populations of the dark-eyed junco.

ABSTRACT: Gonadal steroids are important mediators of traits relevant to fitness, and thus may be targets of selection. However, more knowledge is needed about sources of variation along the endocrine axes that may contribute to functional variation in steroid levels. In a controlled captive environment, we studied males of two closely related subspecies of the dark-eyed junco (Junco hyemalis) that differ in testosterone-related phenotype, asking whether they also differ in testosterone (T), and assessing the contribution of the sequential links of the hypothalamic-pituitary-gonadal axis. When males of both subspecies were challenged with gonadotropin-releasing hormone (GnRH), they were similar in circulating luteinizing hormone (LH) and T responses. When challenged with exogenous LH, they again produced levels of T similar to one another, and to the levels produced in response to GnRH. However, the smaller, less ornamented, and less aggressive subspecies had greater abundance of mRNA for LH receptor in the testes and for androgen receptor in the rostral hypothalamus, suggesting potential differences in regulatory feedback. We suggest that circulating hormone levels may be less prone to evolutionary change than the responsiveness of individual hormone targets. Among individuals, T titers were highly repeatable whether males were challenged with GnRH or with LH, but LH produced in response to GnRH did not covary with T produced in response to LH. Testis mass, but not LH receptor transcript abundance, predicted individual variation in T responses. These data implicate the gonad, but not the pituitary, as an important source of individual variation in T production.

SUBMITTER: Bergeon Burns CM

PROVIDER: S-EPMC3944345 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Examining sources of variation in HPG axis function among individuals and populations of the dark-eyed junco.

Bergeon Burns Christine M CM Rosvall Kimberly A KA Hahn Thomas P TP Demas Gregory E GE Ketterson Ellen D ED

Hormones and behavior 20131017 2

Gonadal steroids are important mediators of traits relevant to fitness, and thus may be targets of selection. However, more knowledge is needed about sources of variation along the endocrine axes that may contribute to functional variation in steroid levels. In a controlled captive environment, we studied males of two closely related subspecies of the dark-eyed junco (Junco hyemalis) that differ in testosterone-related phenotype, asking whether they also differ in testosterone (T), and assessing ...[more]

PMID: 24140626

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Project description:BACKGROUND:Though genomic-level data are becoming widely available, many of the metazoan species sequenced are laboratory systems whose natural history is not well documented. In contrast, the wide array of species with very well-characterized natural history have, until recently, lacked genomics tools. It is now possible to address significant evolutionary genomics questions by applying high-throughput sequencing to discover the majority of genes for ecologically tractable species, and by subsequently developing microarray platforms from which to investigate gene regulatory networks that function in natural systems. We used GS-FLX Titanium Sequencing (Roche/454-Sequencing) of two normalized libraries of pooled RNA samples to characterize a transcriptome of the dark-eyed junco (Junco hyemalis), a North American sparrow that is a classically studied species in the fields of photoperiodism, speciation, and hormone-mediated behavior. RESULTS:From a broad pool of RNA sampled from tissues throughout the body of a male and a female junco, we sequenced a total of 434 million nucleotides from 1.17 million reads that were assembled de novo into 31,379 putative transcripts representing 22,765 gene sets covering 35.8 million nucleotides with 12-fold average depth of coverage. Annotation of roughly half of the putative genes was accomplished using sequence similarity, and expression was confirmed for the majority with a preliminary microarray analysis. Of 716 core bilaterian genes, 646 (90?%) were recovered within our characterized gene set. Gene Ontology, orthoDB orthology groups, and KEGG Pathway annotation provide further functional information about the sequences, and 25,781 potential SNPs were identified. CONCLUSIONS:The extensive sequence information returned by this effort adds to the growing store of genomic data on diverse species. The extent of coverage and annotation achieved and confirmation of expression, show that transcriptome sequencing provides useful information for ecological model systems that have historically lacked genomic tools. The junco-specific microarray developed here is allowing investigations of gene expression responses to environmental and hormonal manipulations - extending the historic work on natural history and hormone-mediated phenotypes in this system.

Project description:Plumage color plays a prominent role in reproductive isolation and thus understanding the genetic basis of pigmentation patterns can provide critical insight into speciation. Subspecies of the dark-eyed junco (Junco hyemalis) show marked differences in melanic plumage coloration known to have evolved rapidly since the Last Glacial Maximum just 18,000 years ago. To understand this rapid radiation we studied the pigment composition and the genetic basis of coloration in two divergent subspecies, the slate-colored and Oregon juncos. We used HPLC and light microscopy to investigate pigment deposition patterns in feathers from four body areas. RNA-seq data generated under common garden experimental conditions were then used to compare the relative roles of differential gene expression in growing feathers and sequence divergence in loci expressed during feather development. Junco feathers were found to differ in eumelanin and pheomelanin content and distribution, producing a range of black, gray and brown colors. Transcriptomic data revealed marked regulatory differences among subspecies and among body-parts within subspecies in known melanin-pathway genes (including PMEL, TYR, TYRP1, OCA2, MLANA), but also in several novel or poorly known loci (EDAR, VPS33B, HPS1). Within subspecies, lighter feathers expressed less melanin synthesis genes, more ASIP, and showed differential expression of Wnt signaling genes. Feathers from different body regions also showed differential expression of Hox genes. The two subspecies differed in expression of ASIP and three other genes (MFSD12, KCNJ13, HAND2) previously associated with color development. Sequence variation in the expressed genes was not related to color differences between junco subspecies. Our findings suggest that differential expression of a few genes can account for marked differences in plumage color and pattern, a mechanism that can account for the rapid diversification of juncos. Several novel candidate pigmentation genes found in juncos may contribute to the expression of melanic coloration in other vertebrates.

Project description:Affective disorders show sex-specific differences in prevalence, symptoms, and complications. One hypothesis for this discrepancy is the interaction between the hypothalamic-pituitary-adrenal (HPA) axis and hypothalamic-pituitary-gonadal (HPG) axis. The present study investigates the influence of androgen on the behavioral phenotype and explores how it interacts with HPA axis genes. Gonadectomized (GDX) and GDX rats treated with testosterone propionate (T) were tested for learned helplessness (LH) behavior and compared with tested controls (TC). Prefrontal cortex was used for analyses of HPG- axis-related genes (androgen receptor, (Ar); estrogen receptor-? (Er-?)) and HPA axis-related genes (corticotropin-releasing hormone, (Crh); glucocorticoid receptor, (Nr3c1); corticotropin-releasing hormone receptor 1, (Crhr1); corticotropin-releasing hormone receptor 2, (Crhr2); FK506 binding protein 5, (Fkbp5)). Promoter-specific CpG methylation in the Crh gene was determined by bisulfite sequencing. Chromatin immunoprecipitation (ChIP) assay was used for determining ER-? binding on the proximal promoter region of Crh gene. Serum testosterone levels confirmed a testosterone-depleted GDX group, a group with supraphysiological levels of testosterone (T) and another group with physiological levels of testosterone (control (C)). Unlike GDX rats, T group exhibited significantly higher LH score when compared with any other group. Crh and Fkbp5 genes were significantly upregulated in GDX group compared with controls, whereas Er-? showed a significant downregulation in the same group. Methylation analysis showed no significant differences in-between groups. ChIP assay was unable to determine a significant change in ER-? binding but revealed a notable contrast in Crh promoter occupancy between T and GDX groups. Altogether, the present study reveals an increased susceptibility to depression-like behavior due to chronic supraphysiological level of androgen via HPA axis inhibition.

Dataset Information

Examining sources of variation in HPG axis function among individuals and populations of the dark-eyed junco.

Publications

Examining sources of variation in HPG axis function among individuals and populations of the dark-eyed junco.

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