Why do good hunters have higher reproductive success?

Anecdotal evidence from many hunter-gatherer societies suggests that successful hunters experience higher prestige and greater reproductive success. Detailed quantitative data on these patterns are now available for five widely dispersed cases (Ache, Hadza, !Kung, Lamalera, and Meriam) and indicate that better hunters exhibit higher age-corrected reproductive success than other men in their social group. Leading explanations to account for this pattern are: (1) direct provisioning of hunters’ wives and offspring, (2) dyadic reciprocity, (3) indirect reciprocity, (4) costly signaling, and (5) phenotypic correlation. I examine the qualitative and quantitative evidence bearing on these explanations and conclude that although none can be definitively rejected, extensive and apparently unconditional sharing of large game somewhat weakens the first three explanations. The costly signaling explanation has support in some cases, although the exact nature of the benefits gained from mating or allying with or deferring to better hunters needs further study. For comments on earlier drafts, I thank Monique Borgerhoff Mulder, Mike Gurven, Ray Hames, Kristen Hawkes, Kim Hill, Robert Kelly, Frank Marlowe, John Patton, and Polly Wiessner. Rebecca Bliege Bird and Douglas W. Bird invited me to collaborate in the Meriam research and (along with Del Passi of Mer) collected the data on Meriam demography. Geoff Kushnick and Matt Wimmer ably assisted with coding and statistical analysis of these data. Eric Alden Smith (PhD 1980, Cornell University) is a professor of anthropology at the University of Washington, Seattle. His research interests include the links between production and reproduction, the ecology and evolution of collective action, and politics in small-scale societies. He has conducted fieldwork among Inuit on Hudson Bay, Meriam in Torres Strait, and Mardu Aborigines in the Australian Western Desert.     

The transvestite serpent: why do male garter snakes court (some) other males?

In large mating aggregations of red-sided garter snakes, Thamnophis sirtalis parietalis, in Manitoba, male courtship is directed not only to females, but also to other males with female-like skin lipids ('she-males'). We show that 'she-maleness' is an intrinsic property of a male rather than an artefact of lipid transfer from females, and that male-male courtship is very common in the field. She-males were distinctive in terms of appearance (they were heavier than other males and more often covered with mud), behaviour (they were inactive and rarely courted females) and performance (they were slow crawlers, ineffective courters and easily outcompeted by other males in mating trials). 'She-maleness' was not a characteristic of a particular subset of males, as envisaged in previous work; instead, it was a transitory phase that most (perhaps all) male snakes passed through soon after they first emerged from the winter den. Recently emerged males spent their first day or two relatively inactive, while restoring physiological functions (including locomotor performance and courtship ability). Experimental application of female skin lipids on to males dramatically decreased courtship levels of the recipient snakes. Thus, recently emerged males may derive two kinds of benefit from mimicking female skin lipids. First, female mimicry 'switches off' the male's own (energetically expensive) courtship at a time when that courtship would be unproductive. Second, it may disadvantage his rivals by distracting them from females, and increasing their energy expenditure. Copyright 2000 The Association for the Study of Animal Behaviour.     

Fungal pathogen species richness: why do some plant species have more pathogens than others?

Variation among plant species in the number of associated herbivore and pathogen species is predicted to fit a species-area relationship in which the area or biomass embodied by a plant species is a function of individual size and geographic range size. This hypothesis is tested using published estimates of geographic range, individual size, and species richness of fungal pathogens for 490 plant species occurring in the United States and controlling for sampling intensity and phylogenetic effects. The number of pathogens found on a plant species increases with the metrics of area and/or habitat diversity of plant species, and their effects are similar between gymnosperm and angiosperm lineages. The strength of this pattern across a diverse set of plant lineages suggests that accumulation and persistence of pathogen species on plant species are governed by similar processes among temperate plants.     

Bumblebee sex ratios: why do bumblebees produce so many males?

Sex investment ratios in populations of bumblebees are male biased, which contradicts theoretical predictions. Male-biased investment ratios in eusocial Hymenoptera are assumed to be non-stable for both the queen and her workers. In this paper, we show that male-biased sex allocation does not necessarily decrease fitness in the bumblebee Bombus terrestris. A male-biased investment ratio can be the result of an optimal allocation of resources when resources are scarce if (i) there is a large cost difference between male and female production, (ii) there is uncertainty about the amount of resources a colony can invest, and (iii) only a proportion of the investment made in an individual can be reused. This resource allocation then leads to split sex ratios depending on the amount of resources available to a bumblebee colony: colonies under low resource conditions will show a male-biased investment ratio, whereas colonies under high resource conditions allocate more resources towards females. However, the extent to which bumblebee populations show a male-biased sex allocation cannot be explained by cost differences between male and female production alone. In a recent paper, A. F. G. Bourke argued that male-biased investment ratios in bumblebee populations are a by-product of the occurrence of protandry (males emerge before females). Here we will extend Bourke''s argument and show that within a protandrous population, both protandrous and protogynous (females emerge before males) colonies exist. The existence of protandrous and protogynous colonies results in split sex ratios in time, because protogynous colonies rely on males produced by protandrous colonies (partial protandry).     

Butterfly contests and flight physiology: why do older males fight harder?

The males of many butterfly species compete for territoriesvia conspicuous aerial wars of attrition, in which the determinantsof persistence ability are largely unclear. Flight performancefeatures, such as stamina, acceleration, and maneuverability,are often assumed to be important in this context, yet thereis no direct evidence by which to evaluate these possibilities.Recent research has indicated that competitive ability increaseswith age in a notably territorial species, Hypolimnas bolina,which could arise from lifetime morphological or physiologicalchanges that directly affect flight performance. I evaluatedthis hypothesis by investigating how size-independent variancein body composition, energy stores, flight muscle ratio (FMR),and wing condition change with age in this species. Males infive age categories (spanning the functional life span of territorialindividuals) were sampled from encounter sites in tropicalAustralia. Analysis of body composition with respect to anestimate of eclosion mass (forewing length) indicated thattotal body mass, abdomen mass, and wing area decrease throughoutan individual's lifetime, but thorax mass remains unchanged.Wing loading (the ratio of wing area to body mass) is lowestin intermediately aged individuals, but FMR and energetic statusremain largely similar regardless of age. On average, therefore,the energetic cost of sustained flight should first decrease,then increase, with age in a male H. bolina (of standardizedbody size), while available energy reserves decline slightly. Acceleration and maneuverability should remain relatively constant.These results, coupled with the fact that body size is unrelatedto contest success in this territorial butterfly, fail to supportthe idea that age-related competitive ability is mediated simplyby energetics or flight performance.     

How does Merendera montana (L.) Lange (Liliaceae) benefit from being consumed by mole-voles?

The relationships between a geophyte (Merendera montana (L.) Lange – Liliaceae) and a mole-vole (Microtus duodecimcostatus de Sélys-Longchamps) in the Spanish Pyrenees were investigated by analysing plant density, asexual reproductive strategies, and chemical composition of M. montana, and by observing the feeding behavior of M. duodecimcostatus in captivity. We found that M. montana contains toxic alkaloids, the concentration of which varies throughout the year; being minimal at the end of the vegetative period. Alkaloids are stored in the whole plant, particularly in the leaves which are scarcely consumed by herbivores. Nevertheless, mole-voles eat this plant profusely both in the field and in captivity, where they showed preference for the corm. The corm has lower alkaloid concentration and higher levels of energetic substances than the other plant parts, particularly leaves. Although corm consumption causes plant death, M. montana grows more abundantly in areas colonized by mole-voles than in undisturbed grasslands with high plant cover and absence of mole-vole populations. Both asexual reproduction and seedlings of this species are more frequent in highly disturbed areas. Results strongly suggest a protocooperative relationship between mole-voles and this geophyte: the burrowing behavior of mole-voles favours dispersal and reproductive success of the plant, enhancing its habitat availability; the plant in turn supplies abundant and nutritious food at a low and "acceptable" toxicity cost.     

Immune dysregulation and self-reactivity in schizophrenia: do some cases of schizophrenia have an autoimmune basis?

Schizophrenia affects 1% of the world's population, but its cause remains obscure. Numerous theories have been proposed regarding the cause of schizophrenia, ranging from developmental or neurodegenerative processes or neurotransmitter abnormalities to infectious or autoimmune processes. In this review, findings suggestive of immune dysregulation and reactivity to self in patients with schizophrenia are examined with reference to criteria for defining whether or not a human disease is autoimmune in origin. Associations with other autoimmune diseases and particular MHC haplotypes, increased serum levels of autoantibodies, and in vivo and in vitro replication of some of the functional and ultrastructural abnormalities of schizophrenia by transfer of autoantibodies from the sera of patients with schizophrenia suggest that, in some patients at least, autoimmune mechanisms could play a role in the development of disease. Recent findings regarding specific autoimmune responses directed against neurotransmitter receptors in the brain in patients with schizophrenia will also be reviewed.     

Individuality in nest building: do southern masked weaver (Ploceus velatus) males vary in their nest-building behaviour?

This study investigated how infant pigtailed macaque monkeys performed on two separate learning assessments, two-object discrimination/reversal and Hamilton search learning. Although the learning tasks have been tested on several species, including non-human primates, there have been no normative results reported for young macaque monkeys. The present study provides normative results for these learning tasks in very young captive pigtailed macaques and investigates the degree to which performances on these assessments are related. In addition, an error analysis was conducted to understand the choice patterns of the animals on each task. It was found that males took longer to reach criterion than females on the two-object reversal task. Performance and latency on the discrimination task predicted performance and latency on the reversal task. Performance on Hamilton Search Set-Breaking negatively predicted performance on the later Hamilton Search Forced Set-Breaking task. Finally, latency on reversal significantly predicted the latency on the Hamilton search task. These data provide strong evidence of a relationship between performance on discrimination and reversal. This study shows that, otherwise, each task assesses a different cognitive function.     

Relationships between body size and sound‐producing structures in crickets: do large males have large harps?

Abstract. Male crickets produce conspicuous acoustic signals to attract mates and deter potential rivals. These signals are created when a male cricket closes his wings rapidly and a file and scraper mechanism causes several areas of the wing to vibrate. The harp is an area of the wing that is part of the resonating structure. Because the harp acts as part of a mechanical resonator, changes in harp area or mass could influence the frequency of sound produced. Because females exhibit stabilizing selection on the frequency used in male songs, we hypothesized that there would be a negative allometric relationship between body size and harp area. In addition, we examined the degree of asymmetry in the harp, wing, and tibia. We examined this in four different species of cricket: Acheta domesticus, Gryllus bimaculatus, Gryllus rubens , and Teleogryllus oceanicus. For each species, we measured pronotum width as an index of body size, tibia length, and the area of the forewing and harp. There were significant differences among species in their morphological characteristics. We observed consistent directional asymmetry in the harp area but not in the total wing area. When wings did exhibit directional asymmetry, it was in the opposite direction of the directional asymmetry observed in the harp. Within species, larger males typically had larger harps and the relationship between harp area and body size exhibited negative allometry. Wing area exhibited an isometric relationship with body size. Our data provide a potential mechanism linking decreases in song frequency with body size in male crickets, and suggest that sensory constraints might influence the morphology of signaling structures in a similar fashion as genitalia.     

Evolution of genital masculinization: why do female hyaenas have such a large 'penis'?

In place of a 'normal' external vagina, female spotted hyaenas bear a fully erectile, penis-sized clitoris through which they mate and give birth. Early hypotheses on the evolution of this organ have focused on its signal function, because the erect phallus is used by both sexes as part of submission or appeasement displays. However, a quite different hypothesis is suggested by recent data on the ecological function of female aggressiveness, and on the role of androgens in the development of aggressiveness and male genital development. In this view, the female phallus may have originated as an unselected side effect of selection for androgen-mediated bellicosity, a major advantage in the extraordinarily competitive hyaena social system.     

Vitamin D regulation of immune function in the gut: why do T cells have vitamin D receptors?

Low vitamin D status is associated with an increased risk of immune-mediated diseases like inflammatory bowel disease (IBD) in humans. Experimentally vitamin D status is a factor that shapes the immune response. Animals that are either vitamin D deficient or vitamin D receptor (VDR) deficient are prone to develop IBD. Conventional T cells develop normally in VDR knockout (KO) mice but over-produce IFN-γ and IL-17. Naturally occurring FoxP3+ regulatory T cells are present in normal numbers in VDR KO mice and function as well as wildtype T regs. Vitamin D and the VDR are required for the development and function of two regulatory populations of T cells that require non-classical MHC class 1 for development. The two vitamin D dependent cell types are the iNKT cells and CD4/CD8αα intraepithelial lymphocytes (IEL). Protective immune responses that depend on iNKT cells or CD8αα IEL are therefore impaired in the vitamin D or VDR deficient host and the mice are more susceptible to immune-mediated diseases in the gut.     

Oxysterols in human circulation: which role do they have?

Oxysterols are oxygenated derivatives of cholesterol that are intermediates in cholesterol excretion pathways. They may also be regarded as transport forms of cholesterol and introduction of an additional hydroxyl group facilitates flux of cholesterol across cell membranes and the blood-brain barrier. According to current concepts, oxysterols are also mediating a number of cholesterol-induced metabolic effects. The recent discovery of nuclear receptors with an affinity for oxysterols has given support to this concept. Nuclear receptors such as liver X receptor alpha do have a role in cholesterol homeostasis, but there is still only indirect evidence that oxysterols are the physiological ligands. In this overview we report some recent advancements in our knowledge about the origin and metabolic fate of the quantitatively most important oxysterols occurring in the circulation. In addition, we discuss the possibility that some of these oxysterols may activate liver X receptors and regulate cholesterol homeostasis.     

A review of the reproductive behavior of Polyphemus pediculus (L.) Müller (Crustacea: Branchiopoda)

The reproductive behavior of Polyphemus pediculus (L.) includes mating, laying of resting eggs and giving birth to juveniles. All these forms of behavior are performed in a population daily and simultaneously by means of individual and social actions. Individual behavior is manifested by certain sets of stereotyped movements which can be observed at any time of the day and at any location in a water body. Individual behavior has an episodic, stable character and low intensity. Social behavior is accomplished by specimens of similar physiological state who form transitory swarms. They form within the main continually existing main swarms of the population. Social behavior is rhythmic and of high intensity. Reproductive parthenogenetic swarms first form around dawn and later during the day: about noon in May–July and before sunset in Autumn. As swarms of parthenogenetic females disintegrate, swarms of old gamogenetic females form and mass laying of resting eggs begins. Young gamogenetic females and males swarm only when resting-egg-laying swarms disintegrate. Parthenogenetic reproduction peaks in northern Russia in May and August and persists until late September. Swarms of resting-egg-laying females form once a day around dawn, from May to September. Mating swarms form in summer in midmorning, at twilight and on moonlit nights. In Autumn, there is only one peak of mating, in midmorning. Intensity, duration and time of manifestation of different forms of social behavior change from spring to autumn. Location and character of their manifestation are predictable.     

Do highly ornamented and less parasitized males have high quality sperm? – an experimental test for parasite-induced reproductive trade-offs in European minnow (Phoxinus phoxinus)

Parasites take their resources from hosts and thus directly reduce available resources for hosts’ own body functions, such as growth and reproduction. Furthermore, parasite infections cause significant indirect costs to their hosts in terms of increased investments on immune defense. In this study, we investigated the impact of parasite infection on the sperm quality and expression of secondary sexual ornamentation (saturation of the red abdominal colouration and number of breeding tubercles) in the Eurasian minnow (Phoxinus phoxinus). We exposed minnows to a high and low dose of common nonspecific fish ectoparasite, the glochidia larvae of duck mussel (Anodonta anatina) and tested whether parasite infection leads to trade‐off in sperm quality and/or ornamental expression. We found that glochidia infection reduces the curvature of the sperm swimming trajectory, number of breeding tubercles, and possibly male competitive ability, but does not affect expression of male color ornamentation. Furthermore, glochidia infection was found to reduce sperm motility, but only when all the noninfected individuals were excluded from the model. Supporting one of the predictions by phenotype‐linked fertility hypothesis both in high‐infection and low‐infection group male breeding colouration was positively associated with sperm quality. Our results suggest that although glochidia infection may have negative impact on male reproductive success, parasite‐induced costs may not create strong trade‐off between breeding colouration and sperm quality or that such trade‐off become detectable only in resource‐limited conditions.     

Rabbit (Oryctolagus cuniculus) abundance and protected areas in central-southern Spain: why they do not match?

European rabbits (Oryctolagus cuniculus), a keystone species in the Iberian Mediterranean ecosystem, are the staple prey of the Iberian lynx (Lynx pardinus) and the Spanish imperial eagle (Aquila adalberti). These predators require medium to high rabbit densities and a low degree of human disturbance. We compared rabbit abundances in areas of central-southern Spain under three levels of protection and management: protected areas, intensively managed (nonprotected) hunting estates, and other nonprotected areas. We used pellet abundance indices to estimate rabbit density in 118 surveys conducted during the summers of 2002 and 2003. We observed greater rabbit abundance in intensively managed hunting estates compared to protected areas and other nonprotected areas, perhaps because policy makers did not consider rabbit numbers when selecting priority areas. Alternatively, differences in game management practices (e.g., predator control or habitat management) may explain the higher rabbit densities observed in managed hunting estates. Our results suggest that the best feeding conditions for the Iberian lynx and the Spanish imperial eagle occur in intensively managed hunting areas, where such predators are frequently persecuted. The conservation of these endangered predators may require efforts to increase rabbit densities in protected areas.     

Toads in the backyard: why do invasive cane toads (Rhinella marina) prefer buildings to bushland?

Like many invasive species, cane toads (Rhinella marina) in Australia concentrate in the disturbed habitats created by human activity, rather than in pristine areas. We surveyed cane toads in the wet–dry tropics of the Northern Territory to assess the abundances, body sizes, sexes, behaviour, hydration state and feeding rates of toads around buildings compared to those in areas remote from buildings, and conducted experimental trials to assess the effects of building-related variables (lights and increased toad densities) on the foraging success of toads. Toads around buildings were smaller than bushland conspecifics, and adult sex-ratios were female-biased. Toads were more sedentary around buildings than in the bush, but their feeding rates (based on direct observations and faeces production post-capture) were similar. That similarity, despite twofold-higher densities of competing toads around building, reflected the strong enhancement of feeding rates due to artificial lights attracting insects (in our experimental trials, a threefold increase regardless of the number of competing toads). Toads collected from around buildings were apparently in better hydric condition. Thus, access to water also may attract toads to buildings. The relative scarcity of adult male toads around buildings likely reflects waterbody-centred reproductive activities, whereas the concentration of females and juveniles around buildings is driven largely by access to the insects attracted by artificial light. We conclude that buildings enhance the persistence of cane toad populations and may facilitate their spread.     

Monophyly of Anthozoa (Cnidaria): why do nuclear and mitochondrial phylogenies disagree?

The phylum Cnidaria is usually divided into five classes: Anthozoa, Cubozoa, Hydrozoa, Scyphozoa and Staurozoa. The class Anthozoa is subdivided into two subclasses: Hexacorallia and Octocorallia. Morphological and molecular studies based on nuclear rDNA and recent phylogenomic studies support the monophyly of Anthozoa. On the other hand, molecular studies based on mitochondrial markers, including two recent studies based on mitogenomic data, supported the paraphyly of Anthozoa, and positioned Octocorallia as sister group to Medusozoa (the monophyletic group of Cubozoa, Hydrozoa and Scyphozoa). On the basis of 51 nuclear orthologs from four hexacorallians, four octocorallians, two hydrozoans and one scyphozoan (with poriferans and Homo sapiens as out‐groups), we built a multilocus alignment of 9 873 amino acids, which aimed at minimizing missing data and hidden paralogy, in order to understand the discrepancy between nuclear and mitochondrial phylogenies. Our phylogenetic analyses strongly supported the monophyly of Anthozoa. We compared the level of substitution saturation between our data set, the data sets of two recent phylogenomic studies and one of a mitogenomic study. We found that mitochondrial DNA is more saturated than nuclear DNA at all the phylogenetic levels studied. Our results emphasize the need for a good evaluation of phylogenetic signal.     

Size-dependent gender modification in Lilium apertum (Liliaceae): does this species exhibit gender diphasy?

Background and Aims

Variation in the relative female and male reproductive success of flowering plants is widespread, despite the fundamental hermaphroditic condition of the majority of species. In many hermaphroditic populations, environmental conditions and their influence on development and size can influence the gender expression of individuals through the formation of hermaphroditic and unisexual flowers. This study investigates the hypothesis that the bulbous, animal-pollinated, perennial Lilium apertum (Liliaceae) exhibits a form of size-dependent gender modification known as gender diphasy, in which the sexual expression of individuals depends on their size, with plants often changing sex between seasons.

Methods

Variation in floral traits was examined in relation to their size using marked individuals in natural populations, and also under glasshouse conditions. Measurements were taken of the height, flower number, floral sex expression, flower size, flower biomass and pollen production of individuals over consecutive years between 2009 and 2012 in seven populations in south-west China.

Key Results

Flowers of L. apertum are either perfect (hermaphroditic) or staminate (male) and, in any given season, plants exhibit one of three sex phenotypes: only hermaphrodite flowers, a mixture of hermaphroditic and male flowers, or only male flowers. Transitions between each of these sex phenotypes were observed over consecutive years and were commonly size-dependent, particularly transitions from small plants bearing only male flowers to those that were taller with hermaphroditic flowers. Hermaphroditic flowers were significantly larger, heavier and produced more pollen than male flowers.

Conclusions

The results for L. apertum are consistent with the ‘size advantage hypothesis’ developed for animal species with sex change. The theory predicts that when individuals are small they should exhibit the sex for which the costs of reproduction are less, and this usually involves the male phase. L. apertum provides an example of gender diphasy, a rare sexual system in flowering plants.     

Epigenetics’ Role in the Common Bean (Phaseolus vulgaris L.) and Soybean (Glycine max (L.) Merr.) Nodulation: a Review

Plant Molecular Biology Reporter - Nitrogen-fixing bacteria establish symbiosis with legumes for the biological nitrogen fixation process in specific root structures called nodules. Among these...