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    <title>UTas ePrints - Embryonic Gonadal and Sexual Organ Development in a Small Viviparous Skink, Niveoscincus ocellatus</title>
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<meta content="Embryonic Gonadal and Sexual Organ Development
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<meta content="The majority of research into the timing of gonad differentiation (and sex
determination) in reptiles has focused on oviparous species. This is largely because: (1) most reptiles
are oviparous; (2) it is easier to manipulate embryonic developmental conditions (e.g., temperature)
of eggs than oviductal embryos and (3) modes of sex determination in oviparous taxa were thought
to be more diverse since viviparity and environmental sex determination (ESD)/temperaturedependent
sex determination (TSD) were considered incompatible. However, recent evidence
suggests the two may well be compatible biological attributes, opening potential new lines of enquiry
into the evolution and maintenance of sex determination. Unfortunately, the baseline information
on embryonic development in viviparous species is lacking and information on gonad differentiation
and sexual organ development is almost non-existent. Here we present an embryonic morphological
development table (10 stages), the sequence of gonad differentiation and sexual organ development
for the viviparous spotted snow skink (Niveoscincus ocellatus). Gonad differentiation in this species
is similar to other reptilian species. Initially, the gonads are indifferent and both male and female
accessory ducts are present. During stage 2, in the middle third of development, differentiation
begins as the inner medulla regresses and the cortex thickens signaling ovary development, while the
opposite occurs in testis formation. At this point, the Mu¨llerian (female reproductive) duct regresses
in males until it is lost (stage 6), while females retain both ducts until after birth. In the later stages
of testis development, interstitial tissue forms in the medulla corresponding to maximum
development of the hemipenes in males and the corresponding regression in the females. 
" name="eprints.abstract" />
<meta content="2006" name="eprints.date" />
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<meta content="Austin HB. 1988. Differentiation and development of the
reproductive system in the iguanid lizard, Sceloporus
undulatus. Gen Comp Endocrinol 72:351–363.
Blackburn DG. 2000. Reptilian viviparity: past research,
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Physiol A 127:391–409.
Bull JJ. 1980. Sex determination in reptiles. Quart Rev Biol
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Ganesh S, Choudhary B, Raman R. 1999. Temporal differences
between testis and ovary determinations with possible
involvement of testosterone and aromatase in gonadal
differentiation in TSD lacking lizard, Calotes versicolor.
J Exp Zool 283:600–607.
Greenbaum E, Carr JL. 2001. Sexual differentiation in the
spiny softshell turtle (Apalone spinifera), a species with
genetic sex determination. J Exp Zool 290:190–200.
Hewavisenthi S, Parmenter CJ. 2002. Thermosensitive period
for sexual differentiation of the gonads of the flatback turtle
(Natator depressus Garman). Aust J Zool 50:521–527.
Janzen FJ, Paukstis GL. 1991. Environmental sex determination
in reptiles: ecology, evolution, and experimental design.
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Jones SM, Wapstra E, Swain R. 1997. Asynchronous male and
female gonadal cycles and plasma steriod concentrations
in a viviparous lizard, Niveoscincus ocellatus (Scincidae),
from Tasmania. Gen Comp Endocrinol 108:271–281.
Melville J, Swain R. 2000a. Evolutionary relationships
between morphology, performance and habitat openness
in the lizard genus Niveoscincus (Scincidae: Lygosiminae).
Biol J Linn Soc 70:667–683.
Melville J, Swain R. 2000b. Mitochondrial DNA-sequence
based phylogeny and biogeography of the snow skinks
(Squamata: Scincidae: Niveoscincus) of Tasmania. Herpetologica
55:196–208.
Merchant-Larios H, Ruiz-Ramirez S, Moreno-Mendoza N,
Marmolejo-Valencia A. 1997. Correlation among themosensitive
period, estradiol response, and gonad differentiation
in the sea turtle Lepidochelys olivacea. Gen Comp Endocrinol
107:373–385.
Morrish BC, Sinclair AH. 2002. Vertebrate sex determination:
many means to an end. Reproduction 124:447–457.
Olsson M, Shine R. 2001. Facultative sex allocation in snow
skink lizards (Niveoscincus microlepidotus). J Evol Biol 14:
120–128.
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in reptiles. Bioessays 18:19–26.
Pieau C, Dorizzi M, Richard-Mercier N. 1999. Temperaturedependent
sex determination and gonadal differentiation in
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genital system. In: Gans C, Billet F, editors. Biology of
reptiles, Vol. 15. New York: Liss. p 149–301.
Robert KA, Thompson MB. 2001. Viviparous lizard selects
sex of embryos. Nature 412:698–699.
Scherer G. 1999. Introduction: vertebrate sex determination
and gonadal differentiation. Cell Mol Life Sci 55:821–823.
Shine R. 1995. A new hypothesis for the evolution of viviparity
in reptiles. Am Nat 145:809–823.
Shine R. 1999. Why is sex determined by nest temperature
in many reptiles? Trends Ecol Evol 14:186–189.
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phenotypes via nest-site selection in an oviparous lizard.
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(advantages of temperature-determined sex). Nature 378:
451–452.
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in a lizard population. Ecol Lett 5:486–489.
Smith CA, Joss JMP. 1993. Gonadal sex differentiation in
Alligator mississippiensis, a species with temperaturedependent
sex determination. Cell Tissue Res 273:149–162.
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CR. 2002. Evolution of viviparity: what can Australian
lizards tell us? Comp Biochem Physiol B 131:631–643.
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Austr Ecol 26:179–186.
Wapstra E, Swain R. 2001a. Geographic and annual variation
in life history traits in a small Australian skink. J Herpetol
35:194–203.
Wapstra E, Swain R. 2001b. Reproductive correlates of
abdominal fat body mass in a small skink with an
asynchronous reproductive cycle. J Herpetol 35:403–409.
Wapstra E, Swain R, Jones SM, O’Reilly J. 1999. Geographic
and annual variation in reproductive cycles in the Tasmanian
spotted snow skink, Niveoscincus ocellatus (Squamata:
Scincidae). Aust J Zool 47:539–550.
Wapstra E, Swain R, O’Reilly JM. 2001. Geographic variation
in age and size at maturity in a small Australian viviparous
skink. Copeia 2001:646–655.
Wapstra E, Olsson M, Shine R, Edwards A, Swain R. 2003.
Selection of offspring sex by a viviparous lizard: evidence
for an adaptive explanation. Third International Symposium
on Vertebrate Sex Determination, Kona, Hawaii, March
24–28.
Wapstra E, Olsson M, Shine R, Edwards A, Swain R. 2004.
Maternal basking behaviour determines offspring sex in a
viviparous reptile. Proc R Soc, Lond B (Biol Lett) 271:
S230–S232.
Wibbels T, Bull JJ, Crews D. 1991. Chronology and morphology
of temperature-dependent sex determination. J Exp
Zool 260:371–381.
Wibbels T, Wilson C, Crews D. 1999. Mu¨llerian duct development
and regression in a turtle with temperature-dependent
sex determination. J Herpetol 33:149–152.
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of eggs than oviductal embryos and (3) modes of sex determination in oviparous taxa were thought
to be more diverse since viviparity and environmental sex determination (ESD)/temperaturedependent
sex determination (TSD) were considered incompatible. However, recent evidence
suggests the two may well be compatible biological attributes, opening potential new lines of enquiry
into the evolution and maintenance of sex determination. Unfortunately, the baseline information
on embryonic development in viviparous species is lacking and information on gonad differentiation
and sexual organ development is almost non-existent. Here we present an embryonic morphological
development table (10 stages), the sequence of gonad differentiation and sexual organ development
for the viviparous spotted snow skink (Niveoscincus ocellatus). Gonad differentiation in this species
is similar to other reptilian species. Initially, the gonads are indifferent and both male and female
accessory ducts are present. During stage 2, in the middle third of development, differentiation
begins as the inner medulla regresses and the cortex thickens signaling ovary development, while the
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    <h1 class="ep_tm_pagetitle">Embryonic Gonadal and Sexual Organ Development in a Small Viviparous Skink, Niveoscincus ocellatus</h1>
    <p style="margin-bottom: 1em" class="not_ep_block"><span class="person_name">Neaves, Linda</span> and <span class="person_name">Wapstra, Erik</span> and <span class="person_name">Birch, Debra</span> and <span class="person_name">Girling, Jane E.</span> and <span class="person_name">Joss, Jean M.P.</span> (2006) <xhtml:em>Embryonic Gonadal and Sexual Organ Development in a Small Viviparous Skink, Niveoscincus ocellatus.</xhtml:em> Journal of Experimental Zoology, 305A . pp. 74-82. ISSN 1548-8969</p><p style="margin-bottom: 1em" class="not_ep_block"></p><table style="margin-bottom: 1em" class="not_ep_block"><tr><td valign="top" style="text-align:center"><a href="http://eprints.utas.edu.au/2190/1/Embryonic_Gonadal.pdf"><img alt="[img]" src="http://eprints.utas.edu.au/style/images/fileicons/application_pdf.png" class="ep_doc_icon" border="0" /></a></td><td valign="top"><a href="http://eprints.utas.edu.au/2190/1/Embryonic_Gonadal.pdf"><span class="ep_document_citation">PDF</span></a> - Full text restricted - Requires a PDF viewer<br />439Kb</td><td><form method="get" accept-charset="utf-8" action="http://eprints.utas.edu.au/cgi/request_doc"><input accept-charset="utf-8" value="2755" name="docid" type="hidden" /><div class=""><input value="Request a copy" name="_action_null" class="ep_form_action_button" onclick="return EPJS_button_pushed( '_action_null' )" type="submit" /> </div></form></td></tr></table><p style="margin-bottom: 1em" class="not_ep_block">Official URL: <a href="http://dx.doi.org/10.1002/jez.a.249">http://dx.doi.org/10.1002/jez.a.249</a></p><div class="not_ep_block"><h2>Abstract</h2><p style="padding-bottom: 16px; text-align: left; margin: 1em auto 0em auto">The majority of research into the timing of gonad differentiation (and sex&#13;
determination) in reptiles has focused on oviparous species. This is largely because: (1) most reptiles&#13;
are oviparous; (2) it is easier to manipulate embryonic developmental conditions (e.g., temperature)&#13;
of eggs than oviductal embryos and (3) modes of sex determination in oviparous taxa were thought&#13;
to be more diverse since viviparity and environmental sex determination (ESD)/temperaturedependent&#13;
sex determination (TSD) were considered incompatible. However, recent evidence&#13;
suggests the two may well be compatible biological attributes, opening potential new lines of enquiry&#13;
into the evolution and maintenance of sex determination. Unfortunately, the baseline information&#13;
on embryonic development in viviparous species is lacking and information on gonad differentiation&#13;
and sexual organ development is almost non-existent. Here we present an embryonic morphological&#13;
development table (10 stages), the sequence of gonad differentiation and sexual organ development&#13;
for the viviparous spotted snow skink (Niveoscincus ocellatus). Gonad differentiation in this species&#13;
is similar to other reptilian species. Initially, the gonads are indifferent and both male and female&#13;
accessory ducts are present. During stage 2, in the middle third of development, differentiation&#13;
begins as the inner medulla regresses and the cortex thickens signaling ovary development, while the&#13;
opposite occurs in testis formation. At this point, the Mu¨llerian (female reproductive) duct regresses&#13;
in males until it is lost (stage 6), while females retain both ducts until after birth. In the later stages&#13;
of testis development, interstitial tissue forms in the medulla corresponding to maximum&#13;
development of the hemipenes in males and the corresponding regression in the females. &#13;
</p></div><table style="margin-bottom: 1em" cellpadding="3" class="not_ep_block" border="0"><tr><th valign="top" class="ep_row">Item Type:</th><td valign="top" class="ep_row">Article</td></tr><tr><th valign="top" class="ep_row">Additional Information:</th><td valign="top" class="ep_row">see individual journal copyright transfer agreements</td></tr><tr><th valign="top" class="ep_row">Subjects:</th><td valign="top" class="ep_row"><a href="http://eprints.utas.edu.au/view/subjects/270604.html">270000 Biological Sciences &gt; 270600 Physiology &gt; 270604 Comparative Physiology</a></td></tr><tr><th valign="top" class="ep_row">ID Code:</th><td valign="top" class="ep_row">2190</td></tr><tr><th valign="top" class="ep_row">Deposited By:</th><td valign="top" class="ep_row"><span class="ep_name_citation"><span class="person_name">Dr Erik Wapstra</span></span></td></tr><tr><th valign="top" class="ep_row">Deposited On:</th><td valign="top" class="ep_row">15 Oct 2007 09:07</td></tr><tr><th valign="top" class="ep_row">Last Modified:</th><td valign="top" class="ep_row">09 Jan 2008 02:30</td></tr><tr><th valign="top" class="ep_row">ePrint Statistics:</th><td valign="top" class="ep_row"><a target="ePrintStats" href="/es/index.php?action=show_detail_eprint;id=2190;">View statistics for this ePrint</a></td></tr></table><p align="right">Repository Staff Only: <a href="http://eprints.utas.edu.au/cgi/users/home?screen=EPrint::View&amp;eprintid=2190">item control page</a></p>
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