Thread: Macroscincus coctei (underlined) oviparous or viviparous?

Leeway Corucia Research Center (LCRC)

It has been mentioned that the extinct Scincidae species: Macroscincus coctei (underlined) laid eggs (Andreone, 1998). However, if one looks at photographs of Macroscincus coctei (underlined) (Pether, 2003) - Reptiles Magazine "In search of Macroscincus") pickled specimens of this species show a 'belly - button slit' indicative of viviparous matrotrophy. Perhaps Macroscincus was capable of both methods. It is not without precident. In the January 2003 issue of Reptiles Magazine, Bill Love mentions the Sheen Skink (Eugongylus albofasciolatus) from the Solomon Islands uses both forms of reproduction. Not only the species but a single Sheen female can switch from vivipararism to oviparism and vica versa. Several Museums supposedly had eggs and individual Macroscincus specimens by the turn of the century. Dr. Andreone reported Macroscincus eggs are housed at the Museo Regionali Di Torino.

Brian
LCRC

Is this versatility reserved to reptiles only? What are the factors that promote live birth vs. egg-bearing?

I'm assuming that the incubation of an egg takes slightly longer than the gestation of live young, so I'd guess an environemnt with scarce resources would favour the egg. If rain comes before the egg hatches the young may emerge to a favourable environment than the one their parents knew.

On the other hand an egg requires all its resources in in one go, so a mother gestating live young would be able to replenish scant resources over a longer period.

Hello,

Selective pressure against hungry mauraders along with other things.

Many animals including fish, amphibians, and insects are viviparous but generally ovoviviparous (The young hatch from eggs within the mother). Even some plants reproduce by viviparity such as the red mangrove (Rhizophora genus). No birds do.

What is rarer is true viviparity by means of a placenta. Corucia zebrata(underlined) produces a placenta connected by the female to the embryo very similar to placental mammals.

Sincerely,
Brian
LCRC

One reference on this subject is also found in Recommendations for the Care of Amphibians and Reptiles in Academic Institutions by F. Harvey Pough

He writes "...Viviparity has evolved at least 45 times among lizards, and another 35 times among snakes (Blackburn, 1982, 1985). Modes of fetal nutrition among vivparous reptiles encompasses a spectrum from lecithotrophy (nutrients deposited in the yolk vitellogenesis) to matrotrophy (nutrients supplied throughout development via a placenta). The skink Mabuya heathi (underlined), a Brazilian lizard, exhibits a nearly mammilian level of matrotrophy (Blackburn et al., 1984). The newly ovulated egg is only 1 mm in diameter, and placental transport accounts for more than 99 percent of the dry mass of the fetus at birth. Another skink, Chalcides chalcides (underlined), a species that is used in biological studies, may also rely primarily on matrotrophy during embryonic development: the ova of C. chalcides (underlined) are less than 3 mm in diameter at ovulation (Blackburn et al., 1984). For these skinks, and for other reptiles with high levels of material input to the fetus, the nutrition of a female during embryonic development may influence the size and viability of the young she produces."

Chalcides chalcides (underlined) speaking of biological studies was used in the SENI biometric studies mentioned in this forum.

Don't be embarrassed if this subject is new to you. There are many people unfamiliar with placental viviparity in non mammalian species. In fact, when I was having a scientific paper reviewed one time that mentioned a brief sentence on this subject, one reviewer kicked back the paper with a circle of red and wrote "How can that be! Only Mammals produce any kind of Placenta." Obviously, his field of expertize did not lie strongly in the biological sciences of reproduction. Once the proper references were produced, both he and the editor apologized.

I hope this was of help to you.

Sincerely,
Brian
LCRC