Biology Reference
In-Depth Information
A. LIZARDS, CROCODILES
B. TURTLES
1.0
1.0
0.5
0.5
+
0
0
16
20
24
28
32
36
16
20
24
28
32
36
C. SNAPPING TURTLE
1.0
0.5
+
0
16
20
24
28
32
36
° C
Fig. B10.1.2
Example sex ratio responses to incubation temperature in reptiles with
temperature-dependent sex determination. Different lines represent different species.
From Bull (1980).
In haplodiploid species, such as ants, bees, wasps and some beetles, sex is
determined by whether or not an egg is fertilized. Fertilized eggs are diploid
and develop as females, whereas unfertilized eggs are haploid and develop
as males. This allows a female to control the sex of her offspring, by whether
or not she fertilizes an egg. In some wasp species, an observer can even
determine the sex of an egg as it is laid, because there is a visible pause,
while the female fertilizes it.
In species with environmental sex determination, some feature of the
environment such as temperature or day length determines sex. This occurs in
a range of species including some turtles, crocodiles, shrimps and worms. For
example, in turtles, males are produced at relatively low temperatures and
females at relatively high temperatures. In contrast, the opposite pattern occurs
with many lizards and crocodiles, with males being produced at relatively high
temperatures. (Fig. B10.1.2).
