Biology Reference
In-Depth Information
Female ground
squirrels
recognize kin
partly by learning
…
… and partly by
'phenotype
matching'
together were no more aggressive to one another than true siblings reared together.
This suggests, therefore, that individuals learn who are their kin from association in
early life.
However, it was also found that among animals reared apart, genetic siblings were
less aggressive to one another in an arena test than unrelated individuals (Fig. 11.5a).
Interestingly, this effect only occurred among females; thus, true sisters reared apart
were less aggressive to each other than unrelated females reared apart but genetic
relatedness did not affect aggression between male-male or male-female pairs. Only
females, the sex that behaves altruistically in the field, show evidence of being able to
recognize unfamiliar, but genetically related, kin.
Of course, sisters reared apart may still learn to 'recognize' each other because of
prenatal experience in their mother's uterus. Field observations by Paul Sherman,
however, suggest that this may not be the whole story. Female Belding's ground squirrels
mate with up to eight different males (mean 3.3 males) on the one afternoon they are
sexually receptive in spring. Analysis of polymorphic blood proteins collected from
mothers, potential fathers and their offspring, showed that 78% of the litters were sired
by more than one male (Hanken & Sherman, 1981; this method of assessing probable
paternity is rather like the old use of blood groups to settle paternity disputes in court
cases). The exciting discovery was that littermates who were full sisters (same mother,
same father) were less aggressive to one another and more cooperative than half-sisters
(same mother, different father, i.e. half-sisters arise because of multiple matings). For
example, when establishing nest burrows and defending territories full sisters fought and
chased less often when they encountered each other than did half-sisters (Figs. 11.5b
and 11.5c).
Littermates all share the same nest burrow and the same uterus, whether they are full
sisters or half-sisters, so some mechanism other than this common experience must be
involved. More recent experiments by Jill Mateo have shown that odours from oral and
dorsal glands play a mechanistic role in kin discrimination. She collected the scents of
different animals by rubbing a plastic cube over mouth corners or dorsal glands, and then
tested how individuals adjusted their behaviour when given cubes from different animals.
She found a strong response to relatedness, with individuals spending less time investigating
cubes which had been rubbed over more closely related individuals (Fig. 11.6).
In conclusion, a female Belding's ground squirrel seems to categorize others in two
ways. Firstly, she recognizes and cooperates with individuals she shared a burrow with
as opposed to those she did not; the former will be full siblings or half-siblings. Secondly,
she may be particularly cooperative with nest mates who are like herself phenotypically,
and hence more likely to be full siblings rather than half-siblings.
Odours from oral
and dorsal glands
act as a cue of
relatedness.
Kin selection doesn't need kin
discrimination
Behavioural
problems can be
solved by either
fixed or
conditional
strategies
In the above examples we have examined how individuals vary their behaviour depending
upon their relatedness to other individuals. Consequently, we have been examining
whether individuals show kin discrimination (a conditional strategy). However, kin
selection can also be important without kin discrimination. If kin discrimination were
