VIVIPARITY IN SNAKES – HISTOLOGICAL STUDY OF THE RELATIONSHIP BETWEEN FETUS, FETAL MEMBRANES AND OVIDUCT IN EMERALD TREE BOA (Corallus caninus)

Abstract

Viviparity is an important reproductive mode in reptiles from an evolutionary perspective. Viviparous reproduction is associated with certain physiological changes, probably in response to inadequate environmental conditions for egg development. Unlike in oviparous species, embryos remain and develop in the oviduct until birth. In order for the developing embryo to exchange respiratory gasses, water, and food, a placenta is required, which consists of fetal membranes that interact with the maternal oviduct. About 20% of squamates (snakes and lizards) are viviparous, but the morphology of the snake placenta has been studied only in the subfamilies Thamnophiinae and Hydrophiinae. Our objective was to study the structure of the placental layers and fetus in situ in the maternal oviduct of a 6-year-old Emerald tree boa (Corallus caninus). Five fertilized and three unfertilized slugs were found in the uterus during post mortem examination. The average mass of the slug with the fetus (48 mm length x 26 width) was 55-65 g and that of the unfertilized slug was 15-35 g. The fetal membranes and two fetuses were examined by light microscopy. Multiple projections of the tissue samples were made and cut into 5 µm thick paraffin tissue sections, which were stained with Haematoxylin-eosin, Toluidine blue, Goldner’s Trichrome and assessed immunohistochemically with monoclonal antibodies for cytokeratin. The morphology of the fetal membranes was described and found to have an anatomy similar to that of most squamates: a type I allantoplacenta.  Th structure of the oviduct and of the fertilized and unfertilized slug was described. This case report provides a better understanding of placental morphology in boids and expands the spectrum of viviparous squamate species described. VIVIPARNOST PRI KAČAH – HISTOLOŠKA POVEZAVA PLODU, PLODOVIH OVOJEV IN JAJCEVODA PRI PASJEGLAVEM UDAVU (Corallus caninus) Izvleček: Viviparnost (živorodnost) je z evolucijskega vidika pomemben način razmnoževanja pri plazilcih. Takšen način razmnoževanja je povezan z določenimi fiziološkimi spremembami, verjetno kot odziv na neustrezne okoljske razmere za razvoj jajc. V nasprotju z oviparnimi vrstami se zarodki do rojstva razvijajo in se zadržijo v jajcevodu. Razvijajoči se zarodek potrebuje način za izmenjavo dihalnih plinov, vode in hrane. Za to potrebuje placento, ki jo sestavljajo plodove membrane in jajcevod matere. Približno 20 odstotkov luskarjev (Squamata) (kuščarjev in kač) je živorodnih, morfologijo placente pa so proučevali predvsem pri rodovih Thamnophiinae in Hydrophinae. Namen naše raziskave je bil proučiti strukturo placente in situ v jajcevodu 6-letne samice pasjeglavega udava (Corallus caninus). Pri sekciji smo našli 5 oplojenih in 3 neoplojena jajca. Povprečna masa jajca s plodom (48 mm dolžine x 26 širine) je bila 55–65 g, neoplojenega jajca pa 15–35 g. Fetalne membrane in dva ploda pasjeglavega udava smo pregledali s svetlobno mikroskopijo. Narejenih je bilo več 5 µm debelih parafinskih tkivnih rezin, ki so bile obarvane s hematoksilinom in eozinom, toluidinskim modrilom, trikromnim barvanjem po Goldnerju ter s pomočjo imunohistokemičnega barvanja citokeratina in dezmina. Opazovali smo položaj in strukturo plodovih ovojev in situ. Morfologija plodovih ovojev je pokazala, da pri pasjeglavem udavu najdemo tip I alantoplacente. Opisali smo tudi strukturo jajcevoda, oplojenega in neoplojenega jajca. Raziskava je omogočila boljše razumevanje morfologije placente pri kačah in razširila spekter opisanih živorodnih vrst luskarjev. Ključne besede: živorodnost; kače; placenta; histologija; imunohistokemija; Corallus caninus