Biology Reference
In-Depth Information
matings with females, whilst the other male is a subordinate who appears to obtain no
mates. Given this, why do the subordinates remain in the coalition? Alan Krakauer
(2005) examined whether this cooperative courtship could be explained as altruistic
cooperation between kin. In order to do this, he estimated the three parameters of
Hamilton's rule:
r
,
B
and
C
(Table 11.2). Firstly, he used microsatellite markers to
estimate relatedness, and found
that the mean relatedness between
males in coalitions was
r
Wild turkeys:
brothers form
display
partnerships to
attract females
0.42, and
not significantly different from that
expected if they were full siblings
(
r
=
0.5).
Krakauer then went on to estimate
the costs to the subordinate and
benefits to the dominant of this
cooperative courtship. To estimate
the benefit,
B
, he compared the
reproductive success of dominant
males and non-cooperating solitary
males. Dominant paired males
mated with more females and, on
average, produced 6.1 more off-
spring than solitary males. To
estimate the cost,
C
, he compared
the reproductive success of sub-
ordinate males and non-cooperating
solitary males. While solitary males
=
Fig. 11.2
A pair of male wild turkeys,
Meleagris gallopavo,
that have formed a
coalition to court females. Photo by
Maslowski/National Wild Turkey Federation.
Variable
Description
Calculation
Value
Table 11.2
Parameterizing
Hamilton's rule
with wild turkeys
(Krakauer, 2005).
B
and
C
are
measured in units
of offspring per
male.
r
Coefficient of
relatedness
Mean pairwise relatedness of
subordinates to their
dominant display partner
0.42
B
Benefit to dominant
(number of extra young
produced due to
subordinate male's help)
(Mean number of offspring
produced per dominant male)
- (Mean number of offspring
produced per solitary male)
6.1
C
Cost to subordinate
(number of own young
sacrificed in order to
help dominant male)
(Mean number of offspring
produced per solitary male) -
(Mean number of offspring
produced per subordinate
male)
0.9
rB
−
C
Is Hamilton's rule
satisfied?
(0.42
×
6.1) − 0.9
+
1.7 (
>
0)
