ABSTRACTS

Waage, J.K. 1997. Parental Investment - Minding the kids or keeping control? In: P.A. Gowaty, ed. Feminism and Evolutionary Biology: Boundaries, Intersections and Frontiers. Chapman & Hall, pp. 527-553.

Introduction. Changing perspectives often reveals the ways in which we become trapped by our own ideas and terminology. Here I attempt to look at parental investment and sexual selection from a different perspective. Traditionally, parental investment is viewed as a nearly universal characteristic of females that makes them limited in their rate of reproduction relative to males. As a consequence, so sexual selection theory goes, males have evolved ways to compete for access to females and/or differentially to attract them as mates. The battle between the sexes has been seen as one of males avoiding the costs (to their reproductive potential) of parental investment and females trying to get males to share in the investment. For example,

"The single most important difference between the sexes is the difference in their investment in offspring. The general rule is this: females do all of the investing; males do none of it." (Trivers, 1972, p. 207)

"Although Trivers' general rule has many exceptions, it accurately identifies the primary source of conflict between the sexes; in most sexual organisms most of the energy and time invested in offspring comes from females. From this basic fact it follows that, for males more than females, reproductive success is limited by the number of matings with fertile partners. For females more than males, on the other hand, reproductive success is limited by the time and effort required to garner and transfer energy to offspring and to protect and care for them (Bateman, 1948; Trivers, 1972). Males therefore are usually more eager than females to mate at any time with any partner who may be fertile, while females are usually more careful than males to choose mates who seem likely to provide good genes, protection, parental care, or resources in addition to gametes (Trivers, 1972: Alexander and Borgia. 1979)". (Smuts and Smuts, 1993, p. 1)

Trivers' (1972) sweeping generalization, and the common argument based on it, here made by Smuts and Smuts (1993), expresses the prevailing view of the relationship between parental investment, gender differences in behavior, and sexual selection theory. The importance, perhaps even primacy, of females in reproduction is acknowledged. Then the emphasis shifts to only one phase of reproduction - matings - and focuses on the primacy of male-male competition for matings and cautious choices of females. It is differential parental investment and the resulting competition and choice that are the supposed root of male-female conflicts of interest over reproduction.

The universal pattern of differential contribution to zygotes defines the existence of two sexes and identifies their gender. It also forms the basis for Trivers' explanation of the dynamics of sexual selection. The common argument goes something like, "It follows from the fact that females invest more initially in zygotes than do males, that females have been predisposed to continue and expand on that investment over evolutionary time." It is this ever-widening gap in investment in offspring that allows us to claim that the system is somehow driven by females, whom we can then largely ignore in our efforts to study the effect of this differential investment on male behaviors and traits. The general exception would seem to be female choice. However, female choice in the context of sexual selection has been largely about selection on male traits (discussion to follow). Thus, even here the focus has been largely on males.

Where do these patterns of differential investment come from? Are males simply a successful parasitic gamete tactic that has left females stuck with high parental investment and an inherent need to be choosy? Is there something else we have overlooked that would provide the incentive to reexamine why females seem to invest so much and what that means? I think so.

Using the symposium as a backdrop, I will discuss what seems a fundamental omission in the reasoning paraphrased in the previous quotations --- control over reproduction. Gowaty (1992; this volume) suggested that male-female interac tions over the control of reproduction, rather than male-male competition over mating opportunities, are the primary driving force in evolution of mating sys tems and associated behavior. Males are selected to control female reproduction to their advantage, but females are selected to resist this control. The result is natural and sexual selection on a variety of characters in both sexes related to re productive success.

Gowaty suggested that "perhaps male-male competition is a derivative process ancillary to competition between females and males," and thus that females' access to essential resources is fundamental, even for male reproduction. This fact implies a suite of selective forces, including female-female competition for resources; female choice of mates; antifemale choice behaviors by males, such as sexual coercion (Smuts and Smuts, 1993); resistance by females to coercive control; competition among males for coercive access to females (these male-male interactions are secondary to the coercive interactions between males and females); competition between males and females for control of resources essential to reproduction; and male-male competition for resources. (Gowaty, 1992, pp. 232, 234).

Her perspective is an expansive view of the fundamental conflict of interest between the sexes resulting from differential parental investment.

What if we focus not on the costs to females of relatively high parental investment but on the possible gains to them of making a higher investment? I will argue that females, from their evolutionary origin, have gained and retained an asymmetric degree of influence over reproduction. Male-female conflicts of interest arose not from present-day parental investment patterns, but from the source of those patterns, the origin and maintenance of differential amounts and kinds of contribution to future generations, and of female control over reproduction. From my perspective, the generality of investment asymmetry between the sexes reflects the establishment and maintenance of (1) differential control over reproduction, and (2) differential influence on future generations by females, including genetic and maternal effects. Males are relatively limited in their contribution to the phenotypic characteristics of their offspringlimited basically to contributions through nuclear DNA.

The failure to completely realize just how female behavior and parental investment relates to reproduction and evolution has caused us to focus primarily on "reproductive opportunity" (how male-male and female-male interactions influence matings and fertilizations) while tending to ignore the broader issue of "reproductive success" (how female-male and female-female interactions affect the outcome of matings and fertilizations). Parental care, female reproductive competition, life history tactics, and social development have been seen as secondary or even separate topics. As was pointed out in a variety of talks (e.g., see Altman, Gowaty, this volume) the uncoupling of sexual selection (the study of male actions and traits that allow them differential access to fertilizations) from natural selection, social selection (West-Eberhard, 1979), or maternal selection (Kirkpatrick and Lande, 1989) on reproduction has produced a large part of the male bias that until very recently has dominated the behavioral ecology literature. There is clearly more to the story than simply saying that female investment limits male reproduction.

Antoinette Blackwell Brown (1875/1976) argued a long time ago that Darwin had not paid as much attention to how selection has shaped females and their behavior. I suggest that the emphasis on parental investment and the view of sexual selection now primary in the literature has perpetuated the imbalance she identified. A reexamination of reproduction in the expanded context of control and non-Mendelian influence on offspring may help us to overcome this imbalance.

I do not suggest that the importance of female reproduction has been ignored. The female perspective in the context of reproduction has indeed become increasingly popular (see, e.g., Birkhead and Moller, 1993; Hrdy and Williams, 1983; Rosenqvist and Berglund, 1992). The view that is emerging is not of females as the simple, relatively static, underlying cause of the evolution of male traits, but as a dynamically evolving, diverse set of tactics for balancing survival and reproduction across life spans through cooperative and competitive interactions not only with males but with other females. However, like others in this book (e.g., Altman, Gowaty, Stamps), I suggest that sexual selection theory remains too strongly focused on the issue of fecundity (matings obtained or zygotes fertilized), even when the quality of those offspring is directly (e.g., good genes models of female choice) or indirectly (e.g., natural selection on female reproduction) acknowledged. It is also not my intention to discard differential parental investment as an important concept or heuristic in sexual selection theory. I merely want to emphasize that there is much more to the dynamics of male-female interaction than simply acknowledging that females make high investments and studying how this affects males.

The speakers at this symposium made it clear that a feminist perspective in behavioral ecology and evolutionary biology goes beyond simply paying more attention to female behaviors because they are understudied. That would merely be adding to the existing male perspectives to make the story balanced. What is called for is a shift in our perspective. There is a need to rethink the entire question of the actions and interactions of females and males during reproduction or, indeed, the patterns of gender difference and similarity across evolutionary time.

Fincke, O.M., J.K. Waage, and W.D. Koenig. 1997. Natural and Sexual Selection Components of Odonate Behavior. In: J. Choe and B.J. Crespi, eds. The Evolution of Mating Systems in Insects and Arachnids. Cambridge University Press.

Abstract: Traditionally, students of odonate reproductive behavior have focussed on how males compete for access to mates and fertilizations. This tendency has yielded considerable information on male reproductive strategies and on the proximate and ultimate mechanisms involved in male-male competition, but has left numerous gaps in our knowledge of other aspects of odonate mating systems.

We review relevant aspects of odonate biology and examine the extent to which current data on mating patterns support predictions arising from sexual selection theory. Although long-term studies offer some such support, they also indicate that natural selection for longevity and stochastic factors such as weather play critical roles in influencing reproductive success. Relatively little of the variance in male reproductive success in odonates has been traced to variance in male phenotype.

We emphasize the role of females as determinants of odonate mating patterns and discuss sexual conflicts of interest over mating, fertilization, and oviposition decisions. Finally, we explore ways in which natural selection underlies female mating decisions and how larval and adult ecology interact to influence adult reproductive behavior.

Marden, J.H. and J.K. Waage. 1990. Escalated damselfly territorial contests are energetic wars of attrition. Animal Behavior 39: 954-959.

Abstract. Thirteen pairs of neighbouring Calopteryx maculata (Odonata: Calopterygidae) males were manipulated such that members of each pair became residents in the same territory, thereby removing the normal resident-intruder asymmetry and permitting direct analysis of the physical and energetic factors affecting the outcomes of the prolonged, escalated contests that resulted. Energy reserves (fat remaining at the end of contests) were more often correlated with winning these contests than size or physical attributes related to flight ability. This pattern was also true for I I natural contests in which persistent intruders displaced residents. Fat content varied with age, being lowest in immature (teneral) and older males. and highest in young males first appearing at the water. Our results indicate that escalated territorial contests in C. maculata favour males with the greatest energy reserves. High fat content in some males, especially young ones, may allow them to overcome the normal resident-intruder asymmetry and displace established territory residents. Since males rarely feed while at their territories and since territories are important for obtaining and protecting mates, energy reserves may be crucial to reproductive success and escalated fights may be especially costly.

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