Fragment: Inferences from West-Eberhard (1975) pertinent to Mammals (Clara B. Jones)

2.4 Inferences Pertinent To Mammalian Sociality Can Be Drawn From West-Eberhard (1975)

West-Eberhard’s (1975) summary of general models of social evolution reducible to mechanisms dependent upon inclusive-fitness maximizing is useful as a reminder that Hamilton’s rule is manifested in several ways, dependent upon local condition, sex, role (e.g., reproductive or helper), and lineage. It is noteworthy that each of the six strategies (1a – 3b) is, in one manner or another, applicable to social mammals and to mammalian females living mutualistically or cooperatively in groups. In insects and most mammals, olfaction is the primary mechanism of communication. Thus, coordination and control of conspecifics is expected to be constrained by the spatiotemporal dynamics of chemical properties (rapid delivery, relatively rapid decay, pheromonal repression of selfishness). Despite interspecific similarities, it is possible to derive inferences from West-Eberhard’s (2005) outline that may pertain, especially, to social mammals.

Inference 1: Because the variance on reproductive success is lower among females than among males, ceteris paribus (Trivers 1972), mammalian females will be more closely related, on average, to other females in their group or population than will males be, on average, to each other, to group or population females, and to each other’s offspring. For the same reasons, a mammalian population is likely to include more females than males, and females are more likely to exhibit sociality.

Inference 2: Trivers’ (1972) model, fundamentally, concerns differential energetic investments by males and females and the life-history trajectories deriving from polymorphic allocation patterns. Thus, because female “fitness budgets” are more constrained energetically that those of males, the reproductive female component of a group or population is expected to be more stable, spatiotemporally, than the dispersion of males in the same population. For the same reason, on average, female turnover is likely to be lower, female survivorship higher, female emigration rates lower than for males.

Verbal Model I was advanced by Trivers (1972) and was not, originally, presented as a general model of social evolution. However, this author predicts that social evolution will be biased by initial reproductive allocations or energetic investments (Schoener, 1971). This verbal model is not limited to evolution by sex, encompasses all conditions in which organisms make (“Hebbian”) “decisions”, including, decisions to join (group-formation), or, remain in (group-maintenance), groups, and has the potential to be developed, qualitatively, and, expressed, quantitatively, as a synthetic formulation.

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Inference 3: On average, since females are “energy-maximizers”, “inclusive-fitness maximizing” is expected to mitigate energy losses, and, on average, females should benefit from transferring some component “fitness budget” to others. Thus, females and their female offspring are likely to be the major donors and beneficiaries of the benefits of cooperation and altruism, and, relative to males in her population, an adult female has more to gain in her reproductive lifetime from facilitation.

Inference 4: Since males, “time-minimizers”, are expected to favor direct over indirect reproduction, “inclusive-fitness maximizing”, a relatively time-intense strategy, is unlikely to characterize reproductive males, on average.

Inference 4: Ceteris paribus, and, depending upon threshold reproductive effects relative to ecological conditions, where males cannot discriminate their own young, they should be indiscriminately selfish, concentrating on mating allocation strategies rather than facilitation of conspecifics.

Inference 5: It follows from “parental manipulation” and “maternal control” models that females can discriminate their mothers and, there own offspring, where females are not “promiscuous” and do not express “favoritism” of a single male during an estrus cycle. On the other hand, cortical circuitry may be favored, permitting females to make “decisions” based on likelihoods of paternity. In order for this neurophysiological strategy to be favored by selection, losses from error must not, on average, compromise relative reproductive success (of the pertinent genotype). It is important to note that “decisions” based on kinship may yield lower group sizes than those based on selfish strategies (Hamilton 1964); thus, the Malthusian optimum for a reproductive female may not concord with idealized mean fitness of her population.

Inference 6: Following from previous inferences, a reproductive female, on average, is expected to lose less from probabilistic tactics and strategies than will a reproductive male of the same population. Related to the previous inference, “inclusive-fitness maximizing” is expected to mitigate the maternal investment : ageing tradeoff for tactical and strategic females, on average, possibly explaining the reproductive advantage of extended post-reproductive lifespan in humans and killer whales: ////.

The previous discussion of West-Eberhard’s (1975) classification (1a-3b) suggests that “inclusive-fitness maximizing” should be more characteristic of reproductive females, on average, than of reproductive males in the same conditions. It is hypothesized that this condition obtains since, theoretically, females are expected to be “energy-maximizers”. The latter life-history strategy should privilege time-intense (“non-damaging”) rather than energy-intense (“damaging”) strategies, theoretically, characteristic of males. Should the aforementioned allocation (thermal) trajectories withstand quantitative, including, experimental, testing, each of them will yield information pertinent to the evolution of mammalian sociality. In particular, on average, each reproductive morph in the same population will respond differentially to density effects that are expected to impact “energy-maximizers” to a greater degree than “time-minimizers” since an increase in population density should correlate positively, ceteris paribus, with increased intensities of competition. Under these regimes, reproductive females should “switch” to or increase dependence upon, time-intense, energy-saving, helper tactics and strategies, including, in some regimes, self- (suicide, “give-up” points) or offspring-elimination (foetal resorbtion, abortion).

Fragment: Where males & females co-reside (Clara B. Jones)

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.