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The potentially devastating effects of climate change have raised awareness of the need to understand how the biology of wild animals is influenced by extreme-weather events. We investigate how a wild arctic-breeding bird, the Lapland longspur (Calcarius lapponicus), responds to different environmental perturbations and its coping strategies. We explore the transcriptomic response to environmental adversity during the transition from arrival at the breeding grounds to incubation on the Arctic tundra. The effects of an extremely cold spring on arrival and a severe storm during incubation are examined through RNA-seq analysis of pertinent tissues sampled across the breeding cycle. The stress response, circadian rhythms, reproduction, and metabolism are all affected. A key gene of the Hypothalamic-Pituitary-Adrenal axis, FKBP5, was significantly up-regulated in hypothalamus. The genome assembly and gene expression profiles provide comprehensive resources for future studies. Our findings on different coping strategies to chronic and acute stressors will contribute to understanding the interplay between changing environments and genomic regulation. Response strategies to acute and chronic environmental stress in Arctic-breeding Lapland longspurs highlight key adaptive changes, including activation of the HPA axis, regulation of energy, and reproductive functions. [ABSTRACT FROM AUTHOR]

Circulating sex steroid concentrations vary dramatically across the year in seasonally breeding animals. The ability of circulating sex steroids to effect muscle function can be modulated by changes in intracellular expression of steroid metabolizing enzymes (e.g., 5α-reductase type 2 and aromatase) and receptors. Together, these combined changes in plasma hormones, metabolizing enzymes and receptors allow for seasonally appropriate changes in skeletal muscle function. We tested the hypothesis that gene expression of sex steroid metabolizing enzymes and receptors would vary seasonally in skeletal muscle and these changes would differ between a migrant and resident life history strategy. We quantified annual changes in plasma testosterone and gene expression in pectoralis and gastrocnemius skeletal muscles using quantitative polymerase chain reaction (qPCR) in free-living migrant (Zonotrichia leucophrys gambelii) and resident (Z. l. nuttalli) subspecies of white-crowned sparrow during breeding, pre-basic molt, and wintering life history stages. Pectoralis muscle profile was largest in migrants during breeding, while residents maintained large muscle profiles year-round. Circulating testosterone peaked during breeding in both subspecies. Pectoralis muscle androgen receptor mRNA expression was lower in females of both subspecies during breeding. Estrogen receptor-α expression was higher in the pectoralis muscle, but not gastrocnemius, of residents throughout the annual cycle when compared to migrants. Pectoralis aromatase expression was higher in resident males compared to migrant males. No differences were observed for 5α-reductase 2. Between these two subspecies, patterns of plasma testosterone and androgen receptors appear to be conserved, however estrogen receptor gene expression appears to have diverged. [ABSTRACT FROM AUTHOR]