Biology Reference
In-Depth Information
(a)
(b)
70
60
50
40
30
20
10
125
127.5
130
132.5
135
137.5
140
142.5
145
147.5
150
152.5
Mean area of father's eye spot (mm
2
)
Fig. 7.11
(a) Male peacock displaying. Photo © Marion Petrie. (b) Males with larger eyespots on their tails sired
offspring that survived better. From Petrie (1994).
Peacocks
The extraordinary tail of the male Indian peafowl
Pavo cristatus
has often been regarded
as the pinnacle of sexual selection. The train comprises numerous elongated upper tail
coverts, with blue-centred green and copper ocelli, and males erect these to form a
shimmering fan in their display to females (Fig. 7.11a). Marion Petrie tested whether
this spectacular display signalled a male's genetic quality. She studied a feral population
of peafowl in Whipsnade wildlife park, southern England. Firstly, she showed that the
number of eyespots in the train predicted a male's mating success and that experimental
reduction of eyespot numbers led to a reduction in male mating success between years
(Petrie
et al
., 1991). Then she performed an experiment in which females were paired
at random with males of different natural tail ornamentation. The eggs were all
collected and raised by chickens under standard conditions, and the peafowl chicks
were then given food ad libitum in aviaries. Petrie (1994) found that both the sons and
the daughters of males with the more ornamented tails grew better. Furthermore,
when they were released into the park they survived better to two years of age
(Fig. 7.11b). This suggests that in this population females obtained more viable young
through choosing the most ornamented males. In another study in Japan, however,
there was no evidence that females preferred males with more elaborate trains
(Takahashi
et al
., 2008). Perhaps, like the guppies, female choice varies in different
ecological conditions.
By choosing more
ornamented
males, females
gain more viable
offspring
Sticklebacks
Testing the Hamilton-Zuk hypothesis is by no means straightforward. For example, it is
not sufficient to show merely that females prefer males with lower parasite burdens.
They may do this not because they are shopping for good genes for their offspring but
simply because they want to avoid infection during the act of mating, or because they
Difficulties of
testing female
choice for disease
resistance
