primary focus in such social endeavors is amply illustrated
by the occurrence of infanticide among close kin in black-
tailed prairie dogs (Hoogland 1985). In killing nieces, co-
terie members enhance their own direct fitness by increas-
ing the probability that their daughters will remain in the
natal area. Such philopatry may also promote the inheri-
tance of resources of the natal area (Harris and Murie
1984; Lindström 1986; Myles 1988).
It is also evident that kinship is not a definitive correlate
of amicable social interactions and advanced sociality in
ground-dwelling squirrels. Hoogland (1986) noted nepo-
tism in general among both male and female black-tailed
prairie dogs, but found that amicable and aggressive be-
havior varied with seasonal differences in competition be-
tween individuals rather than with their coefficient of re-
latedness. Thus neither Hamilton’s (1964) prediction that
the expression of nepotism should vary with the coefficient
of relatedness, nor Altmann’s (1979) prediction that indi-
viduals should direct all beneficent behavior toward their
closest available relative were upheld. Indeed, the killing of
young of closely related females (Hoogland 1985) clearly
indicates that competition to recruit one’s own daughters to
the natal area takes precedence over any component of in-
direct fitness in black-tailed prairie dogs. Similarly, yellow-
bellied marmots limit amicable behavior to uterine kin
(mothers, daughters, and sisters), having a coefficient of
relatedness of 0.5, but are agonistic toward all other con-
specific females, including their more distant relatives (Ar-
mitage 1988). In highly social Olympic marmots, holding
individuals away from the group and reintroducing them at
a later time results in aggression from colony members that
is correlated in its intensity with the duration of the indi-
viduals’ absence, and not contingent upon its relatedness to
those group members (Barash 1973). This finding in itself
suggests that reinforcement of group membership, perhaps
via olfactory contacts in the context of extensive greeting
described by Barash (1973), may in the proximate sense
underlie amicable coloniality. A similar diminution in the
importance of relatedness among members of the society
may also occur in the genus Spermophilus. Columbian
ground squirrels, which were regarded as the most highly
social members of that genus by both Armitage (1981) and
Michener (1983a), and which received the highest social
complexity index of all theSpermophilusspecies considered
by Blumstein and Armitage (1997b, 1998), are amicable to
all familiar conspecifics (Hare 1994) and fail to manifest
kin-differential behavior (see fig. 29.2 and Hare and Mu-
rie 1996). Both Michener (1983a) and Rayor and Armi-
tage (1991) foreshadowed this possibility in noting that
relaxed discrimination among members of neighboring lit-
ters, both in terms of more cohesive behavioral interactions
and increased spatial overlap, accompanied complex soci-
ality in the ground-dwelling squirrels. Even among Bel-
ding’s ground squirrels, where kin discrimination is highly
refined (Holmes 1986b) and nepotism well documented,
Sherman (1980a) noted the adoption of recently emerged
juveniles by nesting adult females, and indicated that as
yearlings the adopted females treated their true littermates
as nonrelatives. Where neighbors are kin, benefits of social
cooperation will accrue via kin selection. Payoffs for coop-
eration, however, are not limited to kin (Trivers 1971; Axel-
rod and Hamilton 1981; Connor 1995), and thus societies
may appear and be maintained by social bonds that tran-
scend lines of kinship. Arguments predicated upon kinship
are not necessary to explain the formation or maintenance
of social groups (Jaisson 1991; Myles 1988; Waser 1988),
and high relatedness in isolation of particular ecological
factors may be insufficient to account for advanced social-
ity (Andersson 1984). To understand sociality, one must
consider all possible levels at which both benefits and costs
may accrue.Additional Factors Contributing to SocialityThe retention of daughters in the natal area clearly pays di-
rect fitness dividends in terms of offspring survival (Armi-
tage 1988). Further, the direct fitness interests of parents
and young alike will be served where offspring inherit ma-
ternal resources (Myles 1988), as would be the case where
daughters inherit burrow systems in their mother’s territory
(Harris and Murie 1984).
Explanations extending beyond direct fitness are typi-
cally invoked to account for behavior that appears to place
the survival and /or reproductive interests of the actor in
jeopardy. Among ground squirrels, such apparent altruism
is most often cited to occur in the alarm-calling system
(Blumstein, chap. 27 this volume), where calling individu-Ecology, Kinship, and Ground Squirrel Sociality: Insights from Comparative Analyses 351Figure 29.2 Highly social Columbian ground squirrel (Spermophilus columbi-
anus) juveniles discriminate group members from other conspecifics but not kin
from nonkin. Photo by J. Hare.