Continuous paleoenvironmental records covering the period prior to the Last Glacial Maximum in northeastern Beringia are sparse. This study presents a multi-proxy analysis of a 35-m-high yedoma exposure located on the right bank of the Itkillik River in Alaska. The exposure accumulated over 39 thousand years (kyr) during the Middle Wisconsinan Interstadial and the Late Wisconsinan glacial advance. We identified five stratigraphic units based on pollen, carbon and ice content, and isotopic composition (δ 18 O) of the sediments. Middle Wisconsinan climate in northern Alaska promoted peat accumulation prior to 33.6 cal kyr BP (calibrated kyr before present). Reconstructed July air temperatures were 1-2°C lower than current at 34.8 cal kyr BP, consistent with the timing of the interstadial climatic optimum in interior Alaska and Yukon. Colder (by up to 4°C) and drier conditions characterize the transition from interstadial to glacial conditions between 33.6 and 29.8 cal kyr BP. Late Wisconsinan (29.8-17.9 cal kyr BP) July air temperatures were 2-3°C lower than today, with grassland vegetation dominated by Poaceae, Artemisia and forbs, in contrast to the modern Cyperaceae dominance. Moister and warmer environmental conditions after 17.9 cal kyr BP correspond to the Late Glacial to Early Holocene interval.
Gonadotropin-releasing hormone (GnRH) is the primary neuropeptide controlling reproduction in vertebrates. GnRH stimulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) synthesis via a G protein-coupled receptor, GnRHR, in the pituitary gland. In mammals, GnRHR lacks a C-terminal cytosolic tail (Ctail) and does not exhibit homologous desensitization. This might be an evolutionary adaptation that enables LH surge generation and ovulation. To test this idea, we fused the chicken GnRHR Ctail to the endogenous murine GnRHR in a transgenic model. The LH surge was blunted, but not blocked in these mice. In contrast, they showed reductions in FSH production, ovarian follicle development, and fertility. Addition of the Ctail altered the nature of agonist-induced calcium signaling required for normal FSH production. The loss of the GnRHR Ctail during mammalian evolution is unlikely to have conferred a selective advantage by enabling the LH surge. The adaptive significance of this specialization remains to be determined.
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