ARTICLES
The first known case of Eggs plus Live Birth from One Pregnancy in a tiny Lizard (continued)
Being able to switch between reproductive modes may be
advantageous, particularly in changing or uncertain environments.
For example, extreme cold, drought or the presence of predators
can be risky for vulnerable eggs exposed to the environment,
meaning that mothers that can carry offspring to term may have
the upper hand.
By contrast, lengthy pregnancies can be taxing on the mother, so
depositing offspring earlier as an egg may be beneficial in some
situations.
Egg coverings of S. equalis consist of an outer crust (C) and
an inner shell membrane (SM). We compared the structure and
thicknesses of these layers of both egg-laying (A) and live-
bearing (B) S. equalis to identify similarities with our ‘unusual’
embryos (C).
We suggest that other species in which live birth has evolved from
egg-laying relatively recently may also use flexible reproductive
tactics.
Further research into this small Australian lizard, which seems to
occupy the grey area between live birth and egg-laying, will help
us determine how and why species make major reproductive
leaps.
We compared the structure and thicknesses of these layers
of both egg-laying (A) and live-bearing (B) Saiphos equalis to
identify similarities with our ‘unusual’ embryos (C).
How evolution works
We still don’t know the trigger that caused this female to lay eggs
and give birth to a live baby from the same pregnancy, however,
our findings suggest that species “in transition” between egg-
laying and live bearing may hedge their bets reproductively
before a true transition to live birth evolves.
The three-toed skink lives in eastern Australia.
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SCIENCE EDUCATIONAL NEWS VOL 68 NO 3