title: Thyroid hormone modulates offspring sex ratio in a turtle with temperature-dependent sex determination.
abstract: The adaptive significance of temperature-dependent sex determination (TSD) has attracted a great deal of research, but the underlying mechanisms by which temperature determines the sex of a developing embryo remain poorly understood. Here, we manipulated the level of a thyroid hormone (TH), triiodothyronine (T3), during embryonic development (by adding excess T3to the eggs of the red-eared slider turtle Trachemys scripta, a reptile with TSD), to test two competing hypotheses on the proximate basis for TSD: the developmental rate hypothesis versus the hormone hypothesis Exogenous TH accelerated embryonic heart rate (and hence metabolic rate), developmental rate, and rates of early post-hatching growth. More importantly, hyperthyroid conditions depressed expression of Cyp19a1 (the gene encoding for aromatase) and levels of oestradiol, and induced more male offspring. This result is contrary to the direction of sex-ratio shift predicted by the developmental rate hypothesis, but consistent with that predicted by the hormone hypothesis Our results suggest an important role for THs in regulating sex steroid hormones, and therefore, in affecting gonadal sex differentiation in TSD reptiles. Our study has implications for the conservation of TSD reptiles in the context of global change because environmental contaminants may disrupt the activity of THs, and thereby affect offspring sex in TSD reptiles.
authors: Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, People's Republic of China.
authors: Bao-Jun
authors: 0000-0002-7318-6059
authors: BJ
authors: Sun
authors: Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, People's Republic of China.
authors: Teng
authors: T
authors: Li
authors: Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, People's Republic of China.
authors: Yi
authors: Y
authors: Mu
authors: Science and Health Hawkesbury Institute, University of Western Sydney, New South Wales 2751, Australia.
authors: Jessica K
authors: JK
authors: McGlashan
authors: Institute for Applied Ecology, University of Canberra, Australian Capital Territory 2601, Australia.
authors: Arthur
authors: A
authors: Georges
authors: School of Life and Environmental Sciences A08, University of Sydney, New South Wales 2006, Australia.
authors: Richard
authors: 0000-0001-7529-5657
authors: R
authors: Shine
authors: Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, People's Republic of China duweiguo@ioz.ac.cn.
authors: Wei-Guo
authors: 0000-0002-1868-5664
authors: WG
authors: Du
mesh_terms: D000818:Animals; D005260:Female; D018507:Gene Expression Regulation, Developmental; D008297:Male; D010063:Ovum / Q000502:physiology; D019849:Sex Determination Processes; D012733:Sex Differentiation; D012744:Sex Ratio; D013696:Temperature; D013963:Thyroid Hormones / Q000502:physiology*; D014426:Turtles / Q000502:physiology*
chemical_list: D013963:Thyroid Hormones
keywords: embryonic development; sex determination; thyroid hormone; turtle