ARTICLES
The first known case of Eggs plus Live Birth from One Pregnancy
in a tiny Lizard
Welcome to the world, little lizard. A three-toed skink (Saiphos equalis) hatching from an egg
Author
Oviparous species are egg-layers; the eggs may undergo
external fertilisation, such as in spawning fish, or are fertilised
and shelled internally, like those of reptiles and birds. Oviparous
embryos rely on egg yolk as a source of nutrition to continue
development until hatching.
1. Melanie Laird is a Postdoctoral Fellow at the University of
Otago;
2. Camilla Whittington is a Senior Lecturer at the University of
Sydney.
This article was first published in ‘The Conversation’ on 3rd April,
2019.
In contrast, viviparous species are live bearers that carry their
young to term. Some live-bearing species, including humans,
support embryonic development internally via a placenta. Egg-
laying is ancestral, meaning that modern live-bearers have
descended from egg-laying ancestors.
For most animals, reproduction is straightforward: some species
lay eggs, while others give birth to live babies, however, our
recent research uncovered a fascinating mix between the two
modes of reproduction. In an Australian skink, we observed the
first example of both egg-laying and live-bearing within a single
litter for any backboned animal.
Physiologically, the evolution of live birth from egg-laying is no
mean feat. This transition requires a whole suite of changes,
sometimes including the evolution of a placenta, an entirely new
specialist organ, as well as the loss of the hard outer eggshell,
and keeping the embryo inside the body for a longer time.
This suggests some lizards can “hedge their bets” reproductively,
taking a punt on both eggs and live-born babies to improve
overall survival chances for offspring.
Making reproductive leaps
Most vertebrate species (animals with a backbone) fall neatly into
one of two distinctly different reproductive categories.
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SCIENCE EDUCATIONAL NEWS VOL 68 NO 3