Biology Reference
In-Depth Information
does especially well. Because each type does better when rare, this will tend to maintain
the behavioural polymorphism (Fitzpatrick
et al
., 2007). This topic is discussed further
in Chapter 5.
The same
foraging
gene,
for
, regulates age changes in foraging worker honeybees,
Apis
mellifera
. When they are young, adult worker bees perform various tasks inside the hive,
such as storing food and caring for the brood. Then, when they are about three weeks
old, they begin to go off on long foraging flights to collect pollen and nectar for the
colony. This marked change from 'sitting at home' to 'roving for food' involves changes
in the expression of
for
, with foragers having increased production of the enzyme PKG.
When young workers were induced to switch to foraging earlier (one week of age) by
removal of older workers, these precocious foragers also had increased
for
expression.
Therefore, expression of
for
was related to social information (presence or absence of
older workers), which then influenced foraging activities; it was not just a response to
age. Finally, experimental elevation of PKG activity in young workers also led to a switch
to foraging behaviour (Ben-Shahar
et al
., 2002).
Thus, in
Drosophila
different individual foraging behaviours are caused by differences
in alleles of the
for
gene, while in honeybees the switch in behaviour within individuals
is caused by changes in
for
gene expression.
Single gene differences can also cause differences in
Drosophila
courtship song. Males
produce a courtship song by vibrating their wings and the temporal pattern of the song
varies between species. Breeding experiments and molecular genetic analysis reveal
that these differences in song structure are caused by differences in the
period
gene.
Transfer of a small piece of the
period
gene from
D. simulans
to
D. melanogaster
causes
melanogaster
males to produce the
simulans
song rather than
melanogaster
song (Wheeler
et al
., 1991).
Gene expression
and behaviour
changes with age
in honeybees
Drosophila
courtship song
MC1R: mate choice and camouflage
The lightness or darkness of skin, hair or feathers depends primarily on the amount of
a pigment, melanin, produced by specialised skin cells (melanocytes). The MC1R gene
(melanocortin-1 receptor) encodes a receptor that is expressed in melanocytes. The
activity of this receptor regulates the amount and type of melanin synthesis. Point
mutations in this gene are associated with colour variation in fish, reptiles, birds and
mammals, so this gene has been conserved through a long evolutionary history.
In lesser snow geese (
Anser chen caerulescens
) there are two colour morphs, white and
blue. Individuals that are homozygous for one variant allele at MC1R are white, while
those that are heterozygous or homozygous for the other allele are blue. Curiously, there
is no evidence for any selective advantage in being either white or blue. However, colour
influences the choice of mate. There is assortative mating by colour (white with white,
blue with blue) and young goslings imprint on their parents' colour and then favour a
mate of the same colour (Mundy
et al
., 2004).
Variation in the same gene controls colour in the rock pocket mouse (
Chaetodipus
intermedius
). In the Pinacate desert of Arizona, the mouse occurs in two colour forms.
Dark, melanic mice live on black lava flows while sandy-coloured mice live in sandy,
desert habitat. There is selective predation by owls against mice which do not match
their background (Nachman
et al
., 2003).
A gene
influencing
melanin
