Evolutionary Perspectives on Pregnancy

Evolutionary Perspectives on Pregnancy

JOHN C. AVISE
ANIMAL DRAWINGS BY TRUDY NICHOLSON
Copyright Date: 2013
Pages: 346
https://www.jstor.org/stable/10.7312/avis16060
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  • Book Info
    Evolutionary Perspectives on Pregnancy
    Book Description:

    Covering both the internal and external incubation of offspring, this book provides a biology-rich survey of the natural history, ecology, genetics, and evolution of pregnancy-like phenomena. From mammals and other live-bearing organisms to viviparous reptiles, male-pregnant fishes, larval-brooding worms, crabs, sea cucumbers, and corals, the world's various species display pregnancy and other forms of parental devotion in surprisingly multifaceted ways. An adult female (or male) can incubate its offspring in a womb, stomach, mouth, vocal sac, gill chamber, epithelial pouch, backpack, leg pocket, nest, or an encasing of embryos, and by studying these diverse examples from a comparative vantage point, the ecological and evolutionary-genetic outcomes of different reproductive models become fascinatingly clear.

    John C. Avise discusses each mode of pregnancy and the decipherable genetic signatures it has left on the reproductive structures, physiologies, and innate sexual behaviors of extant species. By considering the many biological aspects of gestation from different evolutionary angles, Avise offers captivating new insights into the significance of "heavy" parental investment in progeny.

    eISBN: 978-0-231-53145-0
    Subjects: Ecology & Evolutionary Biology, Biological Sciences, Aquatic Sciences

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-xii)
  3. PREFACE
    (pp. xiii-xvi)
  4. ACKNOWLEDGMENTS
    (pp. xvii-xx)
  5. PART I Distribution and Diversity of Pregnancy
    • CHAPTER ONE One Generation Inside Another
      (pp. 3-36)

      Successful reproduction is the name of the evolutionary game for all organisms, but in species that have evolved pregnancy-like phenomena, parents often go to extraordinary lengths in promoting the survival of their young. Pregnancy as a biological syndrome presents several enigmas. The phenomenon is simultaneously the epitome of both self-sacrifice and selfishness because a parent jeopardizes its own health by nurturing embryos inside its body, yet its ulterior evolutionary motive is to cultivate its own personal genetic contribution to succeeding generations. Another paradox is that pregnancy symbolizes safety and danger alike because internal gestation connotes the essence of warmth and...

    • CHAPTER TWO Vertebrate Live-Bearers: The Borne and the Born
      (pp. 37-70)

      This chapter introduces “live-bearing” vertebrates as ambassadors of pregnancy and as exemplars of diverse evolutionary topics that the pregnancy syndrome motivates. In other words, it describes vertebrate creatures in which progeny are borne internally by their mothers before being delivered as free-living beings to the outside world. This overview should prepare readers for later chapters that focus on other manifestations of pregnancy-like phenomena in both vertebrates and invertebrates.

      Viviparity(from “vivi,” meaning “alive,” and “parity,” meaning “borne”) refers to the gestation and subsequent delivery of offspring from within the body of a biological parent. Viviparous species, including Homo sapiens and most...

    • CHAPTER THREE Vertebrate Alternatives to Standard Pregnancy
      (pp. 71-92)

      This chapter introduces vertebrate animals that practice egg laying (oviparity) rather than live birthing (viviparity) and emphasizes that the distinction between these two seemingly distinct methods of procreation can often be somewhat artificial or arbitrary. Although oviparous vertebrates seldom meet the stereotypical criteria for pregnancy, oviparous females do bear their young internally (albeit encased in eggshells) before parturition, and their offspring are of course alive inside the eggs at the time they exit the dam’s body. So, technically, even oviparous species could be deemed live-bearers. Thus, depending on how one defines pregnancy, oviparous vertebrates display reproductive modes that can be...

    • CHAPTER FOUR Nonvertebrate Brooders
      (pp. 93-124)

      Although many invertebrate organisms manifest one or another version of viviparity, it is customary to refer to these species as internally producing their offspring rather than as giving birth by standard means of pregnancy.This chapter discusses the diverse expressions of internal (and external) brooding by invertebrate animals. Furthermore, among the external brooders are invertebrate species that retain embryos at one place or another on their bodies, plus other species that encase their embryos in special off-body capsules.Figure 4.1 introduces some of the rationales for including all of these categories of endogenous and exogenous brooding in a book on pregnancy. Pregnancy-like...

    • CHAPTER FIVE Human Pregnancy in Mythology and in Real Life
      (pp. 125-148)

      Each human pregnancy technically begins when a sperm cell and an ovum unite inside a woman and produce a fertilized egg or zygote, whose nucleus contains 2 nearly matched sets of genetic material, one from the father and the other from the mother. This never-before-seen mixture of genes interacts to help direct the progeny’s biological life—from preembryo to the person’s death perhaps decades later. However, in the first 2–4 rounds of cell division, most of the RNA and protein molecules that orchestrate ontogeny are maternal holdovers that the mother produced and deposited into the egg’s cytoplasm. Much of...

  6. PART II Evolutionary Ramifications of Pregnancy
    • CHAPTER SIX Natural Selection During Mammalian Pregnancy
      (pp. 151-184)

      Pregnancy unleashes powerful forms of natural selection during the gestational phase of the mammalian life cycle. From the outset, however, I want to emphasize that not all expressions of mammalian pregnancy necessarily register adaptations shaped by natural selection. Thus there is no need to invoke adaptive justifications for all empirical facets of mammalian pregnancies. Indeed, chapter 5 noted that human pregnancy is often maladaptive (even lethal) to the participants. Here we take a broader evolutionary look at how natural selection both shapes and can be directed by mammalian-style viviparity. I first discuss natural selection’s likely influence (or sometimes lack thereof)...

    • CHAPTER SEVEN Sexual Selection and Piscine Pregnancy
      (pp. 185-218)

      Sexual selection arises from the differential ability of individuals to obtain sexual partners and fertilize gametes. It is the “other form” of selection explicated by Darwin (1871). Unlike natural selection (Darwin 1859), which tends to forge adaptations in response to environmental demands, sexual selection tends to mold behaviors and other phenotypes to meet mating demands. As Darwin recognized, sexual selection is tightly interwoven with many other reproductive topics, including mating behaviors, mating systems, sex ratios, and sexual dimorphism. Even a century and a half after Darwin (Avise and Ayala 2009), modern extensions of sexual-selection theory continue to present empirical and...

    • CHAPTER EIGHT Pregnancy in a Comparative Light
      (pp. 219-240)

      We learned in chapters 1 and 7 that anisogamy (the larger size and lower motility of female gametes) initiated an evolutionary cascade of gender biases with respect to potential fertilities, variances in reproductive success, intensities of mate competition, the nature and direction of sexual selection, the elaboration of secondary sexual traits, magnitudes of parental investment in progeny, proclivities for pregnancy and brooding, and assurances of biological parentage for particular offspring. We also learned that female pregnancy in viviparous taxa then often amplifies these sexual biases by further curbing female fecundity and making each female even more limiting as a reproductive...

  7. EPILOGUE
    (pp. 241-242)

    I hope that this book has opened readers’ eyes to the incredibly diverse ways in which parents in nature gestate their young. Pregnancy from an evolutionary perspective might seem to be strikingly different from the loving and cooperative venture that most people probably have in mind when they think about motherhood. However, cooperation and conflict (much like loyalty and enmity) are much like the opposite sides of a coin and thus may not be quite so disconnected as they at first appear. Regardless of how we might wish to view pregnancy and related gestational phenomena, the fact remains that Mother...

  8. APPENDIX: MOLECULAR-GENETIC PARENTAGE ANALYSIS
    (pp. 243-254)
  9. GLOSSARY
    (pp. 255-274)
  10. REFERENCES CITED
    (pp. 275-312)
  11. INDEX
    (pp. 313-326)