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Jones SM. Variations upon a theme: Australian lizards provide insights into the endocrine control of vertebrate reproductive cycles. Gen Comp Endocrinol 2017; 244:60-69. [PMID: 26342969 DOI: 10.1016/j.ygcen.2015.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2015] [Revised: 08/13/2015] [Accepted: 09/01/2015] [Indexed: 11/28/2022]
Abstract
Australian lizards exhibit a broad array of different reproductive strategies and provide an extraordinary diversity and range of models with which to address fundamental problems in reproductive biology. Studies on lizards have frequently led to new insights into hormonal regulatory pathways or mechanisms of control, but we have detailed knowledge of the reproductive cycle in only a small percentage of known species. This review provides an overview and synthesis of current knowledge of the hormonal control of reproductive cycles in Australian lizards. Agamid lizards have provided useful models with which to test hypotheses about the hormonal regulation of the expression of reproductive behaviors, while research on viviparous skinks is providing insights into the evolution of the endocrine control of gestation. However, in order to better understand the potential risks that environmental factors such as climate change and endocrine disrupting chemicals pose to our fauna, better knowledge is required of the fundamental characteristics of the reproductive cycle in a broader range of lizard species.
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Affiliation(s)
- Susan M Jones
- School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
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Anderson L, Cree A, Towns D, Nelson N. Modulation of corticosterone secretion in tuatara (Sphenodon punctatus): Evidence of a dampened stress response in gravid females. Gen Comp Endocrinol 2014; 201:45-52. [PMID: 24713446 DOI: 10.1016/j.ygcen.2014.03.035] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 03/08/2014] [Accepted: 03/11/2014] [Indexed: 11/15/2022]
Abstract
Baseline and stress response glucocorticoid (GC) secretion can be modulated by individuals to support activities and physiological functions connected with reproduction (migration, mating, oviposition and/or parturition, care of young). Corticosterone (CORT) is the primary GC in reptiles and, in accordance with other vertebrates, an adrenocortical stress response is observed. Modulation of CORT secretion occurs in several reptile species, such that elevated baseline CORT concentration and/or a dampened CORT response are common during reproductive life-history events. We investigated CORT secretion after 24 h capture-restraint in the oviparous tuatara (Sphenodon punctatus), the last living rhynchocephalian, and tested whether gravid females have a dampened CORT response compared with non-gravid females. We also included males as a comparison. We confirmed that gravid females have significantly higher baseline plasma CORT concentrations than non-gravid females, suggesting increased CORT secretion during nesting. Furthermore, we found that gravid females exhibit a dampened CORT response compared to non-gravid females and males. Our results demonstrate that female reproductive condition influences CORT secretion in tuatara, and suggest that gravid females modulate CORT secretion during nesting to maintain homeostasis, effectively increasing chances of reproductive success and promoting overall fitness.
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Affiliation(s)
- Lindsay Anderson
- Allan Wilson Centre for Molecular Ecology and Evolution, School of Biological Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand.
| | - Alison Cree
- Department of Zoology, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.
| | - David Towns
- Ecosystem Development Team, Science and Technical Group, Department of Conservation, Private Bag 68-908 Newton, Auckland 1145, New Zealand.
| | - Nicola Nelson
- Allan Wilson Centre for Molecular Ecology and Evolution, School of Biological Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand.
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Parsley LM, Wapstra E, Jones SM. Placental and embryonic tissues exhibit aromatase activity in the viviparous lizard Niveoscincus metallicus. Gen Comp Endocrinol 2014; 200:61-6. [PMID: 24631640 DOI: 10.1016/j.ygcen.2014.02.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Revised: 02/03/2014] [Accepted: 02/10/2014] [Indexed: 11/26/2022]
Abstract
Aromatase is a key regulator of circulating testosterone (T) and 17-β-oestradiol (E2), two steroids which are critical to the development, maintenance and function of reproductive tissues. The role of aromatase in sexual differentiation in oviparous (egg-laying) reptiles is well understood, yet has never been explored in viviparous (live-bearing) reptiles. As a first step towards understanding the functions of aromatase during gestation in viviparous reptiles, we measured aromatase activity in maternal and embryonic tissues at three stages of gestation in the viviparous skink, Niveoscincus metallicus. Maternal ovaries and adrenals maintained high aromatase activity throughout gestation. During the early phases of embryonic development, placental aromatase activity was comparable to that in maternal ovaries, but declined significantly at progressive stages of gestation. Aromatase activity in the developing brains and gonads of embryos was comparable with measurements in oviparous reptiles. Aromatase activity in the developing brains peaked mid development, and declined to low levels in late stage embryos. Aromatase activity in the embryonic gonads was low at embryonic stage 29-34, but increased significantly at mid-development and then remained high in late stage embryos. We conclude that ovarian estrogen synthesis is supplemented by placental aromatase activity and that maternal adrenals provide an auxiliary source of sex steroid. The pattern of change in aromatase activity in embryonic brains and gonads suggests that brain aromatase is important during sexual differentiation, and that embryonic gonads are increasingly steroidogenic as development progresses. Our data indicate vital roles of aromatase in gestation and development in viviparous lizards.
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Affiliation(s)
- Laura M Parsley
- School of Zoology, University of Tasmania, Sandy Bay Campus, Private Bag 5, 7000 Tasmania, Australia.
| | - Erik Wapstra
- School of Zoology, University of Tasmania, Sandy Bay Campus, Private Bag 5, 7000 Tasmania, Australia
| | - Susan M Jones
- School of Zoology, University of Tasmania, Sandy Bay Campus, Private Bag 5, 7000 Tasmania, Australia
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Yolk contributes steroid to the multidimensional endocrine environment of embryos of Niveoscincus metallicus, a viviparous skink with a moderately complex placenta. Comp Biochem Physiol A Mol Integr Physiol 2014; 171:51-6. [DOI: 10.1016/j.cbpa.2014.02.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Revised: 02/10/2014] [Accepted: 02/14/2014] [Indexed: 02/05/2023]
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Schuett GW, Repp RA, Hoss SK, Herrmann HW. Environmentally cued parturition in a desert rattlesnake,Crotalus atrox. Biol J Linn Soc Lond 2013. [DOI: 10.1111/bij.12166] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Gordon W. Schuett
- Department of Biology and Center for Behavioral Neuroscience; Georgia State University; 33 Gilmer Street, SE, Unit 8 Atlanta GA 30303-3088 USA
| | - Roger A. Repp
- National Optical Astronomy Observatory; 950 North Cherry Avenue Tucson AZ 85719 USA
| | - Shannon K. Hoss
- Department of Biology; San Diego State University; 5500 Campanile Drive San Diego CA 92182-4614 USA
| | - Hans-Werner Herrmann
- School of Natural Resources and the Environment; University of Arizona; Tucson AZ 85721 USA
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Smith CF, Schuett GW, Hoss SK. Reproduction in female copperhead snakes (Agkistrodon contortrix): plasma steroid profiles during gestation and post-birth periods. Zoolog Sci 2012; 29:273-9. [PMID: 22468838 DOI: 10.2108/zsj.29.273] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We investigated levels of plasma progesterone (P4), 17β-estradiol (E2), testosterone (T), and corticosterone (CORT) during gestation and post-birth periods in wild-collected female copperhead snakes (Viperidae; Agkistrodon contortrix). We also sought to determine whether CORT levels at (or near) birth dramatically increase and were correlated with duration of labor and litter size. Specifically, pregnant subjects (N = 14) were collected during early- to mid-gestation, held in the laboratory, and repeatedly bled to obtain plasma for steroid analyses. Progesterone showed significant changes during gestation, with the highest levels at the onset of sampling (circa 50 days prior to birth); P4 progressively declined up to parturition, and basal levels were observed thereafter. At the onset of sampling, E2 was at peak levels and fell sharply at circa 30 days prior to birth, a trend observed throughout the post-birth sampling period. Throughout the entire sampling period, T was undetectable. Although CORT showed no significant changes during gestation and several days following parturition, there was a highly significant peak at the time of birth. Our findings mirror the results of previous studies on pregnancy and steroid hormones of other live-bearing snakes, lizards, and mammals. As expected, there was a significant relationship between duration of labor and litter size; however, although levels of CORT did not achieve significance, there was a positive trend with litter size. We suggest that elevation of CORT at birth is involved in the mobilization and regulation of energy stores necessary for the physiological process of parturition and as a possible mechanism to trigger birth.
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Affiliation(s)
- Charles F Smith
- Department of Ecology and Evolutionary Biology, The University of Connecticut, Storrs, Connecticut 06269-3043, USA.
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Itonaga K, Wapstra E, Jones SM. Evidence for placental transfer of maternal corticosterone in a viviparous lizard. Comp Biochem Physiol A Mol Integr Physiol 2011; 160:184-9. [DOI: 10.1016/j.cbpa.2011.05.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Revised: 05/25/2011] [Accepted: 05/26/2011] [Indexed: 10/18/2022]
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Hamlin HJ, Lowers RH, Albergotti LC, McCoy MW, Mutz J, Guillette LJ. Environmental Influence on Yolk Steroids in American Alligators (Alligator mississippiensis)1. Biol Reprod 2010; 83:736-41. [DOI: 10.1095/biolreprod.110.085142] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
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Hare KM, Cree A. Incidence, causes and consequences of pregnancy failure in viviparous lizards: implications for research and conservation settings. Reprod Fertil Dev 2010; 22:761-70. [PMID: 20450828 DOI: 10.1071/rd09195] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2009] [Accepted: 11/21/2009] [Indexed: 11/23/2022] Open
Abstract
Research on the causes of pregnancy failure in vertebrates has historically been mammal-focussed. However, live-birth (viviparity) has evolved multiple times, and is present in all other vertebrate taxa except Aves and Agnatha. Viviparous lizards (O. Squamata, excluding snakes and amphisbaenians) provide a valuable experimental group when studying major evolutionary events and some are also species of high conservation value. Consequently, both researchers and herpetoculturists often require high reproductive output from captive-held lizards. We reviewed the literature to determine potential or known causes of pregnancy failure for captive lizards. Pregnancy success across species averages approximately 86%, but varies extensively and does not appear to be related to embryonic stage when brought into captivity or level of placentation. Causes of pregnancy failure also vary among species, but correct thermal environments are vital to success, and providing adequate nutrition before vitellogenesis increases the number of viable offspring. A coordinated sequence of hormonal changes involving both pro-pregnancy and pro-labour factors is important for successful pregnancies, although uncertainty remains around the maternal concentrations of corticosterone that allow successful development. Several research areas commonly studied in mammals have yet to be explored or fully addressed in pregnant lizards, including impacts of toxins, parasites, UV light and nutritional quality. As viviparity has evolved over 100 times in lizards, and many different levels of placentation exist, pregnant lizards provide valuable models for studies in ecology and evolution and offer a useful comparison for studies on other viviparous vertebrates.
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Affiliation(s)
- Kelly M Hare
- Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
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While GM, Uller T, Wapstra E. Offspring performance and the adaptive benefits of prolonged pregnancy: experimental tests in a viviparous lizard. Funct Ecol 2009. [DOI: 10.1111/j.1365-2435.2009.01544.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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While GM, Wapstra E. Are there benefits to being born asynchronously: an experimental test in a social lizard. Behav Ecol 2007. [DOI: 10.1093/beheco/arm124] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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WHILE GM, JONES SM, WAPSTRA E. Birthing asynchrony is not a consequence of asynchronous offspring development in a non-avian vertebrate, the Australian skink Egernia whitii. Funct Ecol 2007. [DOI: 10.1111/j.1365-2435.2007.01272.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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