Evolution Of Reproductive Strategies Research Articles

A syringe-like love dart injects male accessory gland products in a tropical hermaphrodite.

Sexual conflict shapes the evolution of many behaviours and processes involved in reproduction. Nearly all evidence supporting this comes from species where the sexes are separated. However, a substantial proportion of animals and most plants are hermaphroditic, and theoretical work predicts that sexual conflict plays an important role even when the sexes are joined within one individual. This seems to have resulted in bizarre mating systems, sophisticated sperm packaging and complex reproductive morphologies. By far the best-known example of such a strategy in hermaphrodites is the shooting of so-called love-darts in land snails. All known love darts carry a gland product on their outside and enter this into the partner’s hemolymph by stabbing. Here, we show that species of the snail genus Everettia possess a syringe-like dart that serves as a real injection needle. Their dart is round in cross-section, contains numerous channels, and has perforations along its side. Histology and electron microscopy show that these holes connect to the channels inside the dart and run all the way up to the elaborate mucus glands that are attached to the dart sac. This is the first report on a love dart that is used as a syringe to directly inject the gland product into the partner’s hemolymph. Although the exact use and function of this dart remains to be demonstrated, this clearly adds to the complexity of the evolution of reproductive strategies in hermaphrodites in general. Moreover, the perforations on the outside of the love dart resemble features of other injection devices, thus uncovering common design and repeated evolution of such features in animals.

High reproductive efficiency as an adaptive strategy in competitive environments

Summary Reproductive efficiency (the efficiency of conversion of resources from vegetative tissue to reproductive output) is a central to our understanding of reproductive allocation and the evolution of reproductive strategies in plants. Plant strategy theory predicts that reproductive efficiency should decrease under competition. Short‐lived semelparous species are not predicted to evolve under competition and therefore should not express adaptive responses to the presence of competitors. Long‐lived iteroparous species are predicted to delay reproduction in favour of growth and resource acquisition in the presence of competitors. I use life‐history theory to advance a prediction that reproductive efficiency increases under competition in both short‐lived semelparous and potentially longer‐lived iteroparous species. Contrary to the predictions of plant strategy theory, short‐lived semelparous species are frequently observed to live in highly competitive environments. Further, iteroparous species under intense competition may die long before they reach competitive dominance or an optimal size for reproduction. I surveyed the literature for studies on plant species including measurements of vegetative and reproductive allocation in high and low (or no) competition treatments. Across species, relative reproductive efficiency (reproductive efficiency under high competition/reproductive efficiency under low competition) significantly increased with increasing competition intensity. Patterns of allocation to reproduction under competition support the existence of a competitive annual strategy and a reproductive perennial strategy. Under these strategies, short‐lived semelparous species and long‐lived iteroparous species express high reproductive efficiency under competition as an adaptation to high neighbour density. In addition, some species also expressed patterns of allocation to reproduction consistent with plant strategy theories. Under this interpretation, I predict that competitive strategies, where plants delay reproduction in competitive environments to gain competitive superiority, are favoured not under intense competition but under modest competition. Including a life‐history interpretation in reproductive efficiency under competition provides a much needed predictive framework for strategies of reproduction observed across species.

Nest Survival and Density of Cackling Geese (Branta Hutchinsii) Inside and Outside a Ross's Goose (Chen Rossii) Colony

ABSTRACT. The influence of heterospecifics on successful avian reproduction remains poorly understood, despite the role that such relationships may play in the evolution of reproductive strategies. We estimated nest survival of Cackling Geese (Branta hutchinsii) near McConnell River, Nunavut, in 2004 and 2005 in relation to (1) nest initiation date; (2) nest age; (3) nesting habitat; (4) presence in or absence from a colony composed mainly of Ross's Geese (Chen rossii); and (5) density of neighboring Lesser Snow Geese (C. caerulescens caerulescens) and Ross's Geese. We also assessed whether there was any consistent pattern in nest densities of Cackling Geese inside and outside the colony, using distance sampling methods that account for imperfect detection. Nest survival declined both with later nesting and with increased densities of surrounding Lesser Snow Geese and Ross's Geese, independently of whether or not Cackling Geese nested in the Ross's Goose colony. However, despite these negative interspecif...

Structure and function in mammalian societies.

Traditional interpretations of the evolution of animal societies have suggested that their structure is a consequence of attempts by individuals to maximize their inclusive fitness within constraints imposed by their social and physical environments. In contrast, some recent re-interpretations have argued that many aspects of social organization should be interpreted as group-level adaptations maintained by selection operating between groups or populations. Here, I review our current understanding of the evolution of mammalian societies, focusing, in particular, on the evolution of reproductive strategies in societies where one dominant female monopolizes reproduction in each group and her offspring are reared by other group members. Recent studies of the life histories of females in these species show that dispersing females often have little chance of establishing new breeding groups and so are likely to maximize their inclusive fitness by helping related dominants to rear their offspring. As in eusocial insects, increasing group size can lead to a progressive divergence in the selection pressures operating on breeders and helpers and to increasing specialization in their behaviour and life histories. As yet, there is little need to invoke group-level adaptations in order to account for the behaviour of individuals or the structure of mammalian groups.

Sex, attachment, and the development of reproductive strategies

This target article presents an integrated evolutionary model of the development of attachment and human reproductive strategies. It is argued that sex differences in attachment emerge in middle childhood, have adaptive significance in both children and adults, and are part of sex-specific life history strategies. Early psychosocial stress and insecure attachment act as cues of environmental risk, and tend to switch development towards reproductive strategies favoring current reproduction and higher mating effort. However, due to sex differences in life history trade-offs between mating and parenting, insecure males tend to adopt avoidant strategies, whereas insecure females tend to adopt anxious/ambivalent strategies, which maximize investment from kin and mates. Females are expected to shift to avoidant patterns when environmental risk is more severe. Avoidant and ambivalent attachment patterns also have different adaptive values for boys and girls, in the context of same-sex competition in the peer group: in particular, the competitive and aggressive traits related to avoidant attachment can be favored as a status-seeking strategy for males. Finally, adrenarche is proposed as the endocrine mechanism underlying the reorganization of attachment in middle childhood, and the implications for the relationship between attachment and sexual development are explored. Sex differences in the development of attachment can be fruitfully integrated within the broader framework of adaptive plasticity in life history strategies, thus contributing to a coherent evolutionary theory of human development.

Direct and Indirect Effects of Environmental Temperature on the Evolution of Reproductive Strategies: An Information‐Theoretic Approach

For ectotherms, environmental temperature affects the optimal size and number of offspring via multiple mechanisms. First, temperature influences the performance of offspring, which directly affects the optimal size of offspring. Second, temperature influences maternal body size, which indirectly affects the optimal size and/or number of offspring when larger females acquire more energetic resources or provide better parental care. Although traditional statistical approaches might distinguish the relative importance of these effects, an information-theoretic approach enables one to estimate effects more accurately by identifying the best evolutionary model in a set of candidate models. Here, we use the Akaike Information Criterion to calculate the likelihoods of seven path models, each derived from one or more optimality models of reproduction. Variation in reproductive traits among populations of lizards (Sceloporus undulatus) was used to quantify support for the models. Our results overwhelmingly supported a model based on an indirect effect of temperature that is mediated by maternal size. Path coefficients of this model were consistent with the hypotheses that, first, larger females can acquire more energy for reproduction and, second, the survival of offspring depends on both their size and their density. Our analyses exemplify how information theory can identify evolutionary hypotheses that merit experimental testing.

Patterns of sperm use in the scorpionfly Panorpa germanica L. (Mecoptera: Panorpidae)

Sperm competition can be a powerful selective force in the evolution of reproductive strategies and mating systems. In studies on sperm competition, patterns of sperm use are typically reported as the mean species value of P 2, determined as the proportion of offspring sired by the second male to copulate with a doubly mated female. However, the within-species variance in P 2 has mostly been ignored, although taking this variance into account may be crucial for understanding the underlying mechanisms of sperm competition. Paternity analysis among the offspring of doubly mated females of Panorpa germanica (Mecoptera, Panorpidae) revealed a relationship between relative copulation durations of both males and the proportion of offspring each male will sire. This correlation between proportional copulation durations and paternity suggests mixing of sperm from different males inside the female’s spermatheca. Yet, sperm mixing appears to be incomplete, as paternity was overall slightly shifted towards the second male on average fathering a higher proportion of the offspring than its relative copulation duration would predict in case of complete sperm mixing. For individual males, however, the outcome of sperm competition is rather unpredictable as the intraspecific variance in P 2 was found to be very high, irrespective of copulation durations. Possible causes of the observed variance in P 2 and the partial last male sperm precedence are discussed.

The impact of male-killing bacteria on the evolution of aphidophagous coccinellids

Many aphidophagous coccinellids harbour male-killing bacteria. These maternally inherited bacteria kill males early in embryogenesis, female offspring of infected mothers gaining a large resource advantage from the consumption of their dead brothers. In this paper, the diversity of male-killing bacteria and their coccinellid hosts will be briefly reviewed. Thereafter, the impact that invasion by male-killers has on coccinellid hosts will be addressed in two ways. First, the selective effects due to the loss of male progeny, and the intra-genomic conflict resulting from the cytoplasmic inheritance of the bacteria will be considered. Reduc- tions in mitochondrial diversity, effects on clutch sizes and the evolution of male-killer suppresser systems will be discussed. Second, the impact of female biased population sex ratios on the evolution of reproductive strategies and the primary sex ratio will be investigated. Preliminary results suggesting changes in male investment per copulation, reductions in female testing behaviour of males, and male biases in the progenic sex ratios of some uninfected male lines will be presented. Avenues for future work will be outlined.

HAVE MALE AND FEMALE GENITALIA COEVOLVED? A PHYLOGENETIC ANALYSIS OF GENITALIC MORPHOLOGY AND SEXUAL SIZE DIMORPHISM IN WEB-BUILDING SPIDERS (ARANEAE: ARANEOIDEA)

Sexual size dimorphism (SSD) can strongly influence the evolution of reproductive strategies and life history. If SSD is extreme, and other characters (e.g., genitalic size) also increase with size, then functional conflicts may arise between the sexes. Spiders offer an excellent opportunity to investigate this issue because of their wide range of SSD. By using modern phylogenetic methods with 16 species of orb-weaving spiders, we provide strong evidence for the "positive genitalic divergence" model, implying that sexual genitalic dimorphism (SGD) increases as SSD increases. This pattern is supported by an evolutionary mismatch between the absolute sizes of male and female genitalia across species. Indeed, our findings reveal a dramatic reversal from male genitalia that are up to 87x larger than female genitalia in size-monomorphic species to female genitalia that are up to 2.8x larger in extremely size-dimorphic species. We infer that divergence in SGD could limit SSD both in spiders, and potentially in other taxa as well. Further, male and female body size, as well as male and female genitalia size, are decoupled evolutionarily. Finally, we show a negative scaling (hypoallometry) of male and female genitalic morphology within sexes. Evolutionary forces specific to each sex, such as larger female size (increased fecundity) or smaller male size (enhanced mate-searching ability), may be balanced by stabilizing selection on relative genitalic size.

MULTIPLE ORIGIN OF VIVIPARITY IN SOUTHEAST ASIAN GASTROPODS (CERITHIOIDEA: PACHYCHILIDAE) AND ITS EVOLUTIONARY IMPLICATIONS

This study aims at a better understanding of the evolutionary significance of viviparity in some freshwater gastropods. We use a phylogeny based on partial sequences of the mitochondrial 16S gene of representatives of the limnetic and pantropical Pachychilidae to infer the relationships within this particular group of cerithioideans and the evolution of reproductive strategies. The phylogeny presented herein implies a new systematization and suggests that viviparity has appeared three times among the Pachychilidae. This is supported by the finding of very distinct reproductive morphologies in different lineages of viviparous taxa that are exclusively found in Southeast Asia. Based on the observation that oviparity is the ancestral character state in this freshwater family, we conclude that viviparity has evolved subsequent to the exploration of freshwater. We present data showing that all Pachychilidae produce considerably larger but fewer egg capsules compared to most marine snails. In other studies on freshwater gastropods, this has been discussed as an adaptation to freshwater environments. In this context we hypothesize that the increased parental investment involved in the enlargement of eggs in concert with the reduction of clutch sizes was the driving factor that ultimately lead to the evolution of viviparity in the Asian taxa. Consequently, although not directly correlated with the colonization of the new adaptive zone, viviparity is strongly favored by other consequences of this step. Hence, we hypothesize that the production of large eggs, which is necessitated by the exploration of freshwater, represents a preadaptation existing in those ancestors from which viviparous pachychilid lineages eventually evolved in Southeast Asia.

MULTIPLE ORIGIN OF VIVIPARITY IN SOUTHEAST ASIAN GASTROPODS (CERITHIOIDEA: PACHYCHILIDAE) AND ITS EVOLUTIONARY IMPLICATIONS

This study aims at a better understanding of the evolutionary significance of viviparity in some freshwater gastropods. We use a phylogeny based on partial sequences of the mitochondrial 16S gene of representatives of the limnetic and pantropical Pachychilidae to infer the relationships within this particular group of cerithioideans and the evolution of reproductive strategies. The phylogeny presented herein implies a new systematization and suggests that viviparity has appeared three times among the Pachychilidae. This is supported by the finding of very distinct reproductive morphologies in different lineages of viviparous taxa that are exclusively found in Southeast Asia. Based on the observation that oviparity is the ancestral character state in this freshwater family, we conclude that viviparity has evolved subsequent to the exploration of freshwater. We present data showing that all Pachychilidae produce considerably larger but fewer egg capsules compared to most marine snails. In other studies on freshwater gastropods, this has been discussed as an adaptation to freshwater environments. In this context we hypothesize that the increased parental investment involved in the enlargement of eggs in concert with the reduction of clutch sizes was the driving factor that ultimately lead to the evolution of viviparity in the Asian taxa. Consequently, although not directly correlated with the colonization of the new adaptive zone, viviparity is strongly favored by other consequences of this step. Hence, we hypothesize that the production of large eggs, which is necessitated by the exploration of freshwater, represents a preadaptation existing in those ancestors from which viviparous pachychilid lineages eventually evolved in Southeast Asia.

Novel reproductive modes in freshwater clams: brooding and larval morphology in Southeast Asian taxa of Corbicula (Mollusca, Bivalvia, Corbiculidae)

AbstractWhile the majority of marine bivalves are oviparous, the two freshwater families among the order Veneroida, i.e. Corbiculidae and Sphaeriidae, comprise species with ovoviviparous and viviparous reproduction. Within the Corbiculidae, the genus Corbicula, which is well‐known for its invasive and, thus, ecologically important representatives, is characterized by (i) a wide range of limnic habitats, inhabiting both brackish water and freshwater environments, and (ii) contrasting modes of reproduction, including ‘planktonic’ development via a free‐swimming larva vs. intrabranchial incubation (brooding) of shelled juveniles. The present investigation of five species of Corbicula from the Indonesian islands Sumatra and Sulawesi, which were hitherto not studied anatomically, adds to the diversity in reproductive patterns in this genus. As a unique feature among Corbicula we here report on two newly observed modes of brooding in species endemic to Sulawesi, (i) tetragenous brooding (i.e. in both demibranchs) in Corbicula possoensis Sarasin & Sarasin, 1898 from Lake Poso, and (ii) prolonged incubation in the maternal gills, with juvenile shells reaching up to 1.3 mm in length and with a well‐developed hinge in C. linduensis Bollinger, 1914 from the Lindu River system. In contrast, a third method is seen in the following taxa that incubate their young in their inner demibranchs only until the stage of juveniles with straight‐hinged shells (D‐shaped): C. matannensis Sarasin & Sarasin, 1898 from Lake Matano and Lake Mahalona, C. loehensis Kruimel, 1913 from Lake Masapi (all on Sulawesi) and C. moltkiana Prime, 1878 from Lakes Maninjau and Singkarak (on Sumatra). Details of the anatomical and histological features of ctenidia are described for each type of brooding, and some trends in the evolution of reproductive strategies within the Corbiculidae are discussed, comparing them with those known from other limnic molluscs.

Rem sleep, early experience, and the development of reproductive strategies.

We hypothesize that rapid eye movement or REM sleep evolved, in part, to mediate sexual/reproductive behaviors and strategies. Because development of sexual and mating strategies depends crucially on early attachment experiences, we further hypothesize that REM functions to mediate attachment processes early in life. Evidence for these hypotheses comes from (1) the correlation of REM variables with both attachment and sexual/reproductive variables; (2) attachment-related and sex-related hormonal release during REM; (3) selective activation during REM of brain sites implicated in attachment and sexual processes; (4) effects of maternal deprivation on REM; (5) effects of REM deprivation on sexual behaviors; and (6) the REM-associated sexual excitation. To explain why we find associations among REM sleep, attachment, and adult reproductive strategies, we rely on recent extensions of parent-offspring conflict theory. Using data from recent findings on genomic imprinting, Haig (2000) and others suggest that paternally expressed genes are selected to promote growth of the developing fetus/child at the expense of the mother, while maternally expressed genes counter these effects. Because developmental REM facilitates attachment-related outcomes in the child, developmental REM may be regulated by paternally expressed genes. In that case, REM may have evolved to support the "aims" of paternal genes at the expense of maternal genes.

Quantitative genetics of life-history traits in a long-lived wild mammal.

Quantitative genetic studies of life-history traits in wild populations are very rare, yet variance/covariance estimates of these traits are crucial to understanding the evolution of reproductive strategies. We estimated heritabilities (h2) of several life-history traits (longevity, age and mass at primiparity, and reproductive traits) in two bighorn sheep (Ovis canadensis) populations, and both phenotypic (rP) and genetic (rA) correlations between life-history traits in one population. We included adult mass in our analyses because it is related to several life-history traits. We used the mother-daughter regression method and resampling tests based on data from long-term monitoring of marked females. Contrary to the theoretical prediction of low heritability for fitness-related traits, heritability estimates in the Ram Mountain population ranged from 0.02 to 0.81 (mean of 0.52), and several were different from zero. Coefficients of variation tend to support the hypothesis of a higher environmental influence on life-history traits. In contrast, at Sheep River we found low heritabilities of life-history traits. Phenotypic correlations varied between -0.09 and 0.95. Several genetic correlations were strong, particularly for different reproductive traits that are functionally related, and ranged from -0.34 to 1.71. Overall, genetic and phenotypic correlations between the same variables were similar in magnitude and direction. We found no phenotypic or genetic correlations suggesting trade-offs among life-history traits. Bighorn sheep may not form the large, outbred populations at equilibrium that are assumed by both Fisher's fundamental theorem and by theories predicting antagonistic pleiotropy between life-history traits. Alternatively, the absence of negative genetic correlations may result from genetic variation in ability to acquire resources or from novel environmental conditions existing during the study period.

The relationship of neonate mass and incubation temperature to embryonic development time in a range of animal taxa

AbstractEmbryonic development time has been of long‐standing interest to physiologists and ecologists because of its importance in understanding the behaviour and ecology of reproduction, and the evolution of reproductive strategies in animals. Yet, the relationship of embryonic development time to both neonate mass and incubation temperature remains poorly understood for most taxonomic groups. Here we define the relationship of embryonic development time to neonate mass (embryo mass at birth) and incubation temperature for a broad range of animals, ectothermic and endothermic, invertebrate and vertebrate, microscopic and gigantic. We begin by establishing the relationship of embryonic development time to neonate mass for a broad array of zooplankton, fishes and amphibians for temperatures from 5 to 20°C. Next, we compare the relationships of embryonic development time to neonate mass in these aquatic ectotherms to those for terrestrial ectotherms (reptiles) and endotherms (birds and mammals) in terms of degree‐days. The similar nature of these relationships allows us to define embryonic development time as a function of neonate mass for many of the species considered here with a single equation in terms of degree‐days for incubation temperatures ranging from 5 to 38°C. This relationship establishes a basis by which to compare differences in embryonic development time among species.

The relationship of neonate mass and incubation temperature to embryonic development time in a range of animal taxa

Embryonic development time has been of long-standing interest to physiologists and ecologists because of its importance in understanding the behaviour and ecology of reproduction, and the evolution of reproductive strategies in animals. Yet, the relationship of embryonic development time to both neonate mass and incubation temperature remains poorly understood for most taxonomic groups. Here we define the relationship of embryonic development time to neonate mass (embryo mass at birth) and incubation temperature for a broad range of animals, ectothermic and endothermic, invertebrate and vertebrate, microscopic and gigantic. We begin by establishing the relationship of embryonic development time to neonate mass for a broad array of zooplankton, fishes and amphibians for temperatures from 5 to 20°C. Next, we compare the relationships of embryonic development time to neonate mass in these aquatic ectotherms to those for terrestrial ectotherms (reptiles) and endotherms (birds and mammals) in terms of degree-days. The similar nature of these relationships allows us to define embryonic development time as a function of neonate mass for many of the species considered here with a single equation in terms of degree-days for incubation temperatures ranging from 5 to 38°C. This relationship establishes a basis by which to compare differences in embryonic development time among species.

Reproductive endocrinology of female elasmobranchs: Lessons from the little skate (Raja erinacea) and spiny dogfish (Squalus acanthias)

Conventional classification of reproductive modes in female elasmobranchs fails to account for the diversity in ovarian dynamics that operate during oviparous and viviparous cycles. Delineating this diversity is crucial for understanding the endocrine regulation of the manifold physiological mechanisms utilized to retain and protect eggs and developing embryos, to fuel embryogenesis, and to manage the intrauterine milieu. Oocyte development and follicular steroidogenesis overlap with egg retention and pregnancy in some species, whereas in others the follicular phase of the cycle is temporally separated from the gravid period. A luteal phase predominates the post-ovulatory period in viviparous species. In oviparous species, the luteal phase overlaps with the follicular cycle. This heterogeneity in ovulatory cycles suggests that the endocrine system evolved a transmutable system for regulating steroidogenesis and the control of the reproductive events. The reproductive biology and endocrinology of the oviparous little skate and lecithotrophic viviparous spiny dogfish are reviewed in order to derive a working hypothesis that explains the complex nature of endocrine patterns observed in species utilizing disparate reproductive modes. An understanding of the adaptations in ovarian dynamics to particular ovulatory cycles is key to developing theories about the evolution of reproductive strategies in female elasmobranchs. J. Exp. Zool. 284:557–574, 1999. © 1999 Wiley-Liss, Inc.

Evolution of reproductive strategies and male sexual ornaments in poeciliid fishes as inferred by mitochondrial 16 rRNA gene phylogeny

Poeciliid fishes have been widely used as a model system in the study of sexual selection mechanisms. In several species belonging to the genera Xiphophorus and Poecilia males show conspicuous ornaments and use courtship display to obtain female cooperation during mating. Conversely most of the remaining poeciliids are drab and achieve copulation mainly through gonopodial thrusting, a fertilization strategy that bypasses the female's consent. We sequenced a portion of the large (16S) mitochondrial ribosomal RNA gene to estimate the phylogenetic relationships among the five tribes of the subfamily Poeciliinae (ROSEN & BAYLEY 1963) and we used the molecular phylogeny to reconstruct the origin of male ornaments and the evolutionary history of the reproductive strategies in this family. Gambusiini were found to be the basal tribe in the subfamily Poeciliinae. In our phylogeny, Xiphophorus and Poecilia were not closely related thus suggesting that the tribe Poeciliini is not a monophyletic group. Gonopodial thrusting was probably the primitive mating strategy of the poeciliids. Sexual ornaments and elaborate courtship behaviour apparently evolved more recently in the genus Xiphophorus and independently in the genus Poecilia.

CLUTCH SIZE AND EGG SIZE IN FREE-LIVING AND PARASITIC COPEPODS: A COMPARATIVE ANALYSIS.

The evolution of reproductive strategies and the trade-off between number and size of eggs were investigated in a comparative analysis of free-living and parasitic copepods. Data from 1038 copepod species were used to obtain family averages for 105 families; the phylogenetic relationships among these families include 94 branching events or 94 independent contrasts on which the analysis was based. Transition from a free-living existence to parasitism on invertebrates resulted in small increases in body size. Transition from parasitism on invertebrates to parasitism on fish was associated with greater increases in body size. After controlling for body size, a switch to fish hosts resulted in an increase in the number of eggs produced and a reduction in egg size. Among all contrasts, there was a negative relationship between changes in relative clutch size and changes in relative egg size, suggesting the existence of a trade-off between egg size and numbers. However, opposite changes in these measures of clutch size and egg size were not quite more frequent than expected by chance, therefore indicating that investments into egg numbers are not necessarily made at the expense of egg size, and vice versa. Latitude affected copepod body size, clutch size, and egg size, whereas the effects of freshwater colonization or size of the fish host were not significant. Comparative analyses at either the genus or species levels within given taxa of copepods parasitic on fish provided limited support for a trade-off between clutch size and egg size, but were hampered by the small number of independent phylogenetic contrasts available. From the family-level comparative analysis, it appears that the evolutionary transition from a free life to parasitism on invertebrates, and the transition from parasitism on invertebrates to parasitism on fish, have led to changes in life-history traits in response to the different selective pressures associated with the different modes of life.

Death, Hope, and Sex: Life-History Theory and the Development of Reproductive Strategies [and Comments and Reply

Many social scientists reject evolutionary views of human behavior because of their supposed genetic determinism. To establish that not all evolutionary models are inherently deterministic the author first reviews the perennial adaptationist-mechanist controversy in evolutionary biology. He then outlines life-history theory a burgeoning field of biology devoted to the study of reproduction growth and development and ecology in an evolutionary context. He undertakes next to show how life-history theory can provide a satisfactory resolution to the adaptationist-mechanist debate. Combining Promislow and Harveys arguments about the role of mortality rates in the evolution of life-history traits with Belsky Steinberg and Drapers attachment-theory model of the development of alternative reproductive strategies in humans the author proposes that the allocation of reproductive (mating and parenting) effort in adults may be partially contingent on their early experience with the causes and correlates of local high death rates. The author concludes with a discussion of some implications of this proposal for the emerging field of evolutionary psychology. (authors)