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Embryonic Gonadal and Sexual Organ Development in a Small Viviparous Skink, Niveoscincus ocellatus


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Neaves, L, Wapstra, E, Birch, D, Girling, JE and Joss, JMP 2006 , 'Embryonic Gonadal and Sexual Organ Development in a Small Viviparous Skink, Niveoscincus ocellatus' , Journal of Experimental Zoology, vol. 305A , pp. 74-82 , doi: 10.1002/jez.a.249..

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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.

Item Type: Article
Authors/Creators:Neaves, L and Wapstra, E and Birch, D and Girling, JE and Joss, JMP
Journal or Publication Title: Journal of Experimental Zoology
ISSN: 1548-8969
DOI / ID Number: 10.1002/jez.a.249.
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