4.3
Where Males & Females Co-reside (Polygynandry; Multi-male, Multi-female Groups): Mammals
More
than one reproductive males cohabiting in stable groups with
reproductive females are virtually limited to mammals (Wilson 1975,
Brown 1975), and most empirical reports of these structures remain
descriptive (e.g., Garber and Kowalewski 2013) rather than
theoretical or empirical, including, experimental. A paucity of
studies is available to describe degrees of relatedness, intrasexual
competition, or tendencies for these males to exhibit mate “choice”.
Additionally, systematic research on the stability of
“fission-fusion” dynamics, frequently characterizing
multimale-multifemale and “nested” reproductive groups, has not
been conducted. In both multimale-multifemale (Packer and Pusey
1982, Jones 1980, 1985) and “nested” societies (Wiszniewski et
al. 2012a), males demonstrate coalitions and alliances, but mammalian
males rarely, if ever, demonstrate altruism, achievable only via
a subsocial route of evolution involving vertical transmission of
reproductive benefits (Chapters 1 and 2).
Recent
reports on polygynandrous lions (Mosser and Packer 2009) and
hierarchically-organized bottleneck dolphins (Wiszniewski et al.
2012b) suggested that defense of reproductive females may explain
benefits to related (via
subsocial route) or unrelated (via
semisocial route) males from collaboration and/or cooperation. The
latter reports indicated, as well, that (presumably, up to some
optimal limit) larger group sizes are associated with greater
reproductive benefits to males from kinship or from shared interests
other than kinship (“shared fates”). Discussing eusocial
bathyergids, Lewis and Pusey (1997) reported that higher infant
mortality was associated with larger groups, a trend that, if common
among mammals, would oppose Allee effects whereby female reproductive
success increases with an increase in group size. Compared to
sociality among females, the scientific literature on sociality among
mammalian males is limited, a topic in need of systematic study,
particularly, variations in tactics and strategies for the management
of competition attendant to reproductive conflicts of interest, as
well as differential behaviors and network characteristics of related
and unrelated reproductive males.
In
multimale-multifemale groups, accurate discrimination of mates is a
component of their survival and fitness, but discrimination often
involves a tradeoff between efficiency and flexibility. The tactics
and strategies employed by females have received relatively little
systematic study by social biologists, particularly in regard to
conflicts of reproductive interest among potential mates. In some
patches, females will benefit most from maximizing the genetic
heterogeneity of a litter of their lifetime reproductive output,
conditions favoring disassortative mating (mating with the most
divergent genotypes). Similar to the effects of polyandry,
disassortative mating by females may also reduce the intensity of
sexual selection on males by decreasing competition for mates by
unrelated males in a group.
The
latter scenario may give rise to sociality via
a parasocial route, a condition likely to maintain benefits from
dispersal for mammalian males, generating conditions within groups
characterized by high asymmetries between chronic states of genetic
asymmetries. In these conditions, sequential female “decisions”
(“female choice”) effectively manage conflicts of interest among
males. In mammals, because of high levels of intrasexual selection
attendant to female philopatry, this condition may drive the
evolution of sociality among females as a mechanism to manage
male-male competition, and it is well-documented that females in many
multimale-multifemale mammalian groups, express an array of social
behaviors, particularly, grooming, allomothering, and adoption. The
aforementioned and related topics deserve systematic study by social
biologists because Hamilton’s rule subsumes the resolution of
interindividual conflicts of interest. Thus, mechanisms to
coordinate and control competition within and between groups may
reflect tradeoffs between reproductive conflict and cooperation.