Hunter‐gatherers and human evolution

Although few hunter‐gatherers or foragers exist today, they are well documented in the ethnographic record. Anthropologists have been eager to study them since they assumed foragers represented a lifestyle that existed everywhere before 10,000 years ago and characterized our ancestors into some ill‐defined but remote past. In the past few decades, that assumption has been challenged on several grounds. Ethnographically described foragers may be a biased sample that only continued to exist because they occupied marginal habitats less coveted by agricultural people. 3 In addition, many foragers have been greatly influenced by their association with more powerful agricultural societies. 4 It has even been suggested that Holocene foragers represent a new niche that appeared only with the climatic changes and faunal depletion at the end of the last major glaciation. 5 Despite these issues, the ethnographic record of foragers provides the only direct observations of human behavior in the absence of agriculture, and as such is invaluable for testing hypotheses about human behavioral evolution. 6 .     

Heavily male-biased long-distance dispersal of orang-utans (genus: Pongo), as revealed by Y-chromosomal and mitochondrial genetic markers

Mating systems are thought to be an important determinant of dispersal strategies in most animals, including the great apes. As the most basal taxon of all great apes, orang-utans can provide information about the evolution of mating systems and their consequences for population structure in this Family. To assess the sex-specific population structure in orang-utans, we used a combination of paternally transmitted Y-chromosomal genetic markers and maternally transmitted mitochondrial DNA sequences. Markers transmitted through the more philopatric sex are expected to show stronger differentiation among populations than the ones transmitted through the dispersing sex. We studied these patterns using 70 genetic samples from wild orang-utans from seven Bornean and two Sumatran populations. We found pronounced population structure in haplotype networks of mitochondrial sequence data, but much less so for male-specific markers. Similarly, mitochondrial genetic differentiation was twice as high among populations compared to Y-chromosomal variation. We also found that genetic distance increased faster with geographic distance for mitochondrial than for Y-linked markers, leading to estimates of male dispersal distances that are several-fold higher than those of females. These findings provide evidence for strong male-biased dispersal in orang-utans. The transition to predominantly female-biased dispersal in the great ape lineage appears to be correlated with life in multimale groups and may reflect the associated fitness benefits of reliable male coalitions with relatives or known partners, a feature that is absent in orang-utans.     

Estimating dispersal distributions at multiple scales: within‐colony and among‐colony dispersal rates,distances and directions in European Shags Phalacrocorax aristotelis

Knowledge of the rate, distance and direction of dispersal within and among breeding areas is required to understand and predict demographic and genetic connectivity and resulting population and evolutionary dynamics. However dispersal rates, and the full distributions of dispersal distances and directions, are rarely comprehensively estimated across all spatial scales relevant to wild populations. We used re‐sightings of European Shags Phalacrocorax aristotelis colour‐ringed as chicks on the Isle of May (IoM), UK, to quantify rates, distances and directions of dispersal from natal to subsequent breeding sites both within IoM (within‐colony dispersal) and across 27 other breeding colonies covering 1045 km of coastline (among‐colony dispersal). Additionally, we used non‐breeding season surveys covering 895 km of coastline to estimate breeding season detection probability and hence potential bias in estimated dispersal parameters. Within IoM, 99.6% of individuals dispersed between their natal and observed breeding nest‐site. The distribution of within‐colony dispersal distances was right‐skewed; mean distance was shorter than expected given random settlement within IoM, yet some individuals dispersed long distances within the colony. The distribution of within‐colony dispersal directions was non‐uniform but did not differ from expectation given the spatial arrangement of nest‐sites. However, 10% of all 460 colour‐ringed adults that were located breeding had dispersed to a different colony. The maximum observed dispersal distance (170 km) was much smaller than the maximum distance surveyed (690 km). The distribution of among‐colony dispersal distances was again right‐skewed. Among‐colony dispersal was directional, and differed from random expectation and from the distribution of within‐colony dispersal directions. Non‐breeding season surveys suggested that the probability of detecting a colour‐ringed adult at its breeding location was high in the northeastern UK (98%). Estimated dispersal rates and distributions were therefore robust to incomplete detection. Overall, these data demonstrate skewed and directionally divergent dispersal distributions across small (within‐colony) and large (among‐colony) scales, indicating that dispersal could create genetic and demographic connectivity within the study area.     

Brief communication: physiological stress in the Florida Archaic-enamel hypoplasia and patterns of developmental insult in early North American hunter-gatherers

We examined the prevalence and developmental timing of linear enamel hypoplasias (LEHs) in an early Archaic Floridian population from Windover (8,120-6,980 (14)C years B.P. uncorrected). Using digital images, mandibular and maxillary canines were analyzed for defect prevalence and timing of insults. Although overall prevalence was very weakly correlated with earlier defect timing, there were significant differences in defect prevalence that varied by sex and tooth type. The mean LEH count in male mandibular canines was far higher than in male maxillary canines or in female mandibular or maxillary canines. We examined defect timing as a possible predictor of the sex differences in LEH prevalence. There were no significant sex differences in the developmental timing of the earliest defects in either tooth class. Developmental timing is not responsible for the sex differences seen in defect prevalence in mandibular canines.     

Complex mating system and dispersal patterns in a social lizard, Egernia whitii

In contrast to the polygynous mating systems typically displayed by most reptilian taxa, long-term genetic monogamy appears to be widespread within a lineage of group-living Australian scincid lizards, the Egernia group. We have recently shown that White's skink, Egernia whitii, lives in small but temporally stable social aggregations. Here, we examine the mating system, spatial organization, and dispersal patterns of E. whitii using behavioural field studies and data from four microsatellite loci. Parentage analysis of E. whitii litters revealed that its mating system is characterized by both polygyny and monogamy. Polygyny was the predominant mating system but within-season social and genetic monogamy was common (36-45% of breeding pairs). The incidence of between-season monogamy in E. whitii was rare compared to that reported for its congeners. Low levels of multiple paternity (12% of litters) and extra-group paternity (16%) were detected. Social groups are generally comprised of closely related individuals, but breeding pairs were not more closely related compared to other potential mates. Spatial autocorrelation analyses revealed significant positive local genetic structure over 50 m, which was consistent for all age-sex classes. There was no clear and consistent evidence for sex-biased dispersal, with assignment tests (mean assignment index) and relatedness analyses suggesting female-biased dispersal, but spatial autocorrelation analyses indicating a trend for male-biased dispersal. We discuss the implication of our results in regard to the factors promoting the evolution of monogamy within the Egernia group.     

Differential dispersal patterns of male and female masu salmon fry

Behavioural experiments using artificial and natural stream channels were undertaken to determine whether there were differences in dispersal between newly emerged male and female masu salmon. Eyed eggs from a cross with wild spawners were planted in the middle pool of an artificial channel. After emergence, more males than females moved into an upstream trap, while fewer males moved downstream. In a natural stream, eyed eggs were marked with alizarin complexone to distinguish them from naturally spawned eggs and these were planted into artificial redds. More newly emerged male fry remained at the planted site than female fry. In contrast, more females moved downstream than males. These results imply that differences in dispersal patterns between male and female masu salmon fry are genetically controlled.     

Reproductive consequences of natal dispersal in a highly philopatric seabird

Natal and breeding dispersal have a major impact on gene flowand population structure. We examined the consequences of nataldispersal on the reproductive success (proportion of pairs rearingchicks) of colonial-breeding Thick-billed murres (Uria lomvia).Reproductive success increased with distance dispersed for thefirst and second breeding attempt. The increase in breedingsuccess leveled off at natal dispersal distances above 7 m.Our results were consistent with the idea that the relationshipbetween dispersal and reproductive success is caused by siteavailability and mate choice as birds willing to disperse fartherhad a greater choice of potential sites and mates. This hypothesiswas supported by the fact that birds dispersing farther weremore likely to pair with an experienced breeder, which increasesthe likelihood of breeding success for young breeders. Explanationsfor increasing breeding success with increased dispersal basedon inbreeding effects were unlikely because most breeding failureswere caused by egg loss rather than infertility or nestlingdeath. However, we could not explain why >50% of birds returnwithin 3 m of the natal site, despite having an up to 50% lowerreproductive success than birds dispersing 7 m or more.     

Distribution patterns and dispersal strategies of Galiciales

In Caliciales both passive and active spore dispersal occurs. A review of the distribution of 162 species is given. Species with small spores have wider distribution than species with large spores, irrespective of dispersal strategy. In antitropical species there is only rarely a differentiation between Northern and Southern Hemisphere populations. It is concluded that in several small-spored genera long-distance dispersal has been instrumental in dispersing the species and range extensions have been much more frequent than in large-spored species for which vicariance explanations are more appropriate. Comparisons with bryophyte distributions show differences in dispersal strategies and distribution patterns.     

Synchrony between growth and reproductive patterns in human females: Early investment in growth among Pumé foragers

Life history is an important framework for understanding many aspects of ontogeny and reproduction relative to fitness outcomes. Because growth is a key influence on the timing of reproductive maturity and age at first birth is a critical demographic variable predicting lifetime fertility, it raises questions about the synchrony of growth and reproductive strategies. Among the Pumé, a group of South American foragers, young women give birth to their first child on average at age 15.5. Previous research showed that this early age at first birth maximizes surviving fertility under conditions of high infant mortality. In this study we evaluate Pumé growth data to test the expectation that if early reproduction is advantageous, then girls should have a developmental trajectory that best prepares them for young childbearing. Analyses show that comparatively Pumé girls invest in skeletal growth early, enter puberty having achieved a greater proportion of adult body size and grow at low velocities during adolescence. For early reproducers growing up in a food‐limited environment, a precocious investment in growth is advantageous because juveniles have no chance of pregnancy and it occurs before the onset of the competing metabolic demands of final reproductive maturation and childbearing. Documenting growth patterns under preindustrial energetic and demographic conditions expands the range of developmental variation not otherwise captured by normative growth standards and contributes to research on human phenotypic plasticity in diverse environments. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Contemporary pollen and seed dispersal in a Prunus mahaleb population: patterns in distance and direction

Pollination and seed dispersal determine the spatial pattern of gene flow in plant populations and, for those species relying on pollinators and frugivores as dispersal vectors, animal activity plays a key role in determining this spatial pattern. For these plant species, reported dispersal patterns are dominated by short-distance movements with a significant amount of immigration. However, the contribution of seed and pollen to the overall contemporary gene immigration is still poorly documented for most plant populations. In this study we investigated pollination and seed dispersal at two spatial scales in a local population of Prunus mahaleb (L.), a species pollinated by insects and dispersed by frugivorous vertebrates. First, we dissected the relative contribution of pollen and seed dispersal to gene immigration from other parts of the metapopulation. We found high levels of gene immigration (18.50%), due to frequent long distance seed dispersal events. Second, we assessed the distance and directionality for pollen and seed dispersal events within the local population. Pollen and seed movement patterns were non-random, with skewed distance distributions: pollen tended moved up to 548 m along an axis approaching the N-S direction, and seeds were dispersed up to 990 m, frequently along the SW and SE axes. Animal-mediated dispersal contributed significantly towards gene immigration into the local population and had a markedly nonrandom pattern within the local population. Our data suggest that animals can impose distinct spatial signatures in contemporary gene flow, with the potential to induce significant genetic structure at a local level.     

Delayed dispersal and the costs and benefits of different routes to independent breeding in a cooperatively breeding bird

Why sexually mature individuals stay in groups as nonreproductive subordinates is central to the evolution of sociality and cooperative breeding. To understand such delayed dispersal, its costs and benefits need to be compared with those of permanently leaving to float through the population. However, comprehensive comparisons, especially regarding differences in future breeding opportunities, are rare. Moreover, extraterritorial prospecting by philopatric individuals has generally been ignored, even though the factors underlying this route to independent breeding may differ from those of strict philopatry or floating. We use a comprehensive predictive framework to explore how various costs, benefits and intrinsic, environmental and social factors explain philopatry, prospecting, and floating in Seychelles warblers (Acrocephalus sechellensis). Not only floaters more likely obtained an independent breeding position before the next season than strictly philopatric individuals, but also suffered higher mortality. Prospecting yielded similar benefits to floating but lower mortality costs, suggesting that it is overall more beneficial than floating and strict philopatry. While prospecting is probably individual‐driven, although limited by resource availability, floating likely results from eviction by unrelated breeders. Such differences in proximate and ultimate factors underlying each route to independent breeding highlight the need for simultaneous consideration when studying the evolution of delayed dispersal.     

Demographic parameters and life history of chimpanzees at Bossou, Guinea

Demographic parameters of wild chimpanzees at Bossou, Guinea, are presented and compared with those of other populations. The population size of Bossou chimpanzees has been stable over the last 26 years, except during two incidents of partial deforestation. The annual birth rate for a female (mean = 0.194, but 0.165 when the infant survived more than 4 years) and interbirth interval are not much different from those of other study sites. The primiparous age of Bossou chimpanzees, however, is far younger (mean = 10.9 years) than for all other known wild chimpanzee populations. The infant and juvenile survival rate is also the highest (female = 0.64, male = 0.52 for the first 8 years). As a result, the lifetime reproductive success of Bossou chimpanzees is estimated to be highest among long-term study sites. The rate of disappearance from Bossou dramatically increases during the adolescent stage, and most young chimpanzees disappear before or around maturation. Probably because the environmental capacity for chimpanzees at Bossou is at its limit, many young independent males, as well as females, have to disperse, though others may die. For chimpanzee alpha males of other populations, mature males may be needed as collaborators to defend resources. In the case of Bossou, however, a lack of adjacent groups, conspecific competitors, predators, and perhaps medium-sized mammals as prey for group hunting may eliminate this need of the alpha male for other males. The reasons why all males of other chimpanzee populations persist in being philopatric for life and maintain kin-related male bonds differing from most mammal species, including humans, are discussed.     

Gene dispersal and outbreeding in a philopatric mammal

Extensive mark-recapture data from banner-tailed kangaroo rats, Dipodomys spectabilis, have shown that both males and females are highly philopatric and suggest the possibility of close inbreeding. However, indirect analyses based on genetic structure appear to contradict direct observations, suggesting longer dispersal distances. Using microsatellite genotypes from most members of a banner-tailed kangaroo rat population during five successive breeding seasons, we ask how relatedness is influenced by dispersal and how it in turn influences mating patterns. The data confirm that, because of philopatry, neighbours are often close relatives. However, patterns of parentage also show that the average distance between mates is large relative to natal dispersal distances and larger than the average distance between nearest opposite-sexed neighbours. Females' mates were often not their nearest male neighbour and many were less related than the nearest male neighbour. We detected multiple paternity in some females' litters; both sexes produce offspring with multiple mates within and between breeding seasons. At the population level, heterozygosities were high and estimates of F were low, indicating that levels of inbreeding were low. Using individual inbreeding coefficients of all juveniles to estimate their parents' relatedness, we found that parental relatedness was significantly lower than relatedness between nearest opposite-sexed adult neighbours. Thus in philopatric populations, long breeding forays can cause genes to move further than individuals disperse, and polyandry may serve to reduce relatedness between mates.     

Measuring dispersal and detecting departures from a random walk model in a grasshopper hybrid zone

Abstract. 1. The grasshopper species Chorthippus brunneus and C. jacobsi form a complex mosaic hybrid zone in northern Spain. Two mark–release–recapture studies were carried out near the centre of the zone in order to make direct estimates of lifetime dispersal.
2. A model framework based on a simple random walk in homogeneous habitat was extended to include the estimation of philopatry and flying propensity. Each model was compared with the real data, correcting for spatial and temporal biases in the data sets.
3. All four data sets (males and females at each site) deviated significantly from a random walk. Three of the data sets showed strong philopatry and three had a long dispersal tail, indicating a low propensity to move further than predicted by the random walk model.
4. Neighbourhood size estimates were 76 and 227 for the two sites. These estimates may underestimate effective population size, which could be increased by the long tail to the dispersal function. The random walk model overestimates lifetime dispersal and hence the minimum spatial scale of adaptation.
5. Best estimates of lifetime dispersal distance of 7–33 m per generation were considerably lower than a previous indirect estimate of 1344 m per generation. This discrepancy could be influenced by prezygotic isolation, an inherent by-product of mosaic hybrid zone structure.     

Genetic evidence for male-biased dispersal in the Siberian jay (Perisoreus infaustus) based on autosomal and Z-chromosomal markers

Sex-bias in natal dispersal patterns can have important genetic and evolutionary consequences; however, reliable information about sex-biased dispersal can be difficult to obtain with observational methods. We analysed the sex-specific patterns of genetic differentiation among three Siberian jay (Perisoreus infaustus) populations, using 11 autosomal and six Z-chromosomal microsatellite markers. Irrespective of marker-type and indices used (viz. F(ST), average pairwise relatedness and effective number of immigrants), all analyses provided strong evidence for male-biased dispersal. Population structuring at autosomal loci (F(ST) =0.046, P<0.05) exceeded that at Z-chromosomal loci (F(ST) =0.033, P<0.05), and levels of introgression were inferred to be significantly higher for Z-chromosomal when compared to autosomal loci. Of the three populations studied, levels of genetic variability were the lowest in the southernmost fringe population, despite the fact that it harboured a group of divergent Z-chromosomal haplotypes that were not found in the other two populations. In general, the results provide strong genetic evidence for male-biased dispersal in Siberian jays, where observational data have previously suggested male philopatry. The results also highlight the utility of Z-chromosomal markers for gaining insights into the genetic diversity and structuring of populations.     

Oral microbiomes from hunter‐gatherers and traditional farmers reveal shifts in commensal balance and pathogen load linked to diet

Maladaptation to modern diets has been implicated in several chronic disorders. Given the higher prevalence of disease such as dental caries and chronic gum diseases in industrialized societies, we sought to investigate the impact of different subsistence strategies on oral health and physiology, as documented by the oral microbiome. To control for confounding variables such as environment and host genetics, we sampled saliva from three pairs of populations of hunter‐gatherers and traditional farmers living in close proximity in the Philippines. Deep shotgun sequencing of salivary DNA generated high‐coverage microbiomes along with human genomes. Comparing these microbiomes with publicly available data from individuals living on a Western diet revealed that abundance ratios of core species were significantly correlated with subsistence strategy, with hunter‐gatherers and Westerners occupying either end of a gradient of Neisseria against Haemophilus, and traditional farmers falling in between. Species found preferentially in hunter‐gatherers included microbes often considered as oral pathogens, despite their hosts' apparent good oral health. Discriminant analysis of gene functions revealed vitamin B5 autotrophy and urease‐mediated pH regulation as candidate adaptations of the microbiome to the hunter‐gatherer and Western diets, respectively. These results suggest that major transitions in diet selected for different communities of commensals and likely played a role in the emergence of modern oral pathogens.     

Nest‐site fidelity in parental male bluegill Lepomis macrochirus: spatial patterns and the influence of prior mating success

A 4 year mark–recapture study examined the pattern of nesting site fidelity of parental‐type male bluegill Lepomis macrochirus. The study results indicated that iteroparous male L. macrochirus choose new nest sites near their own previously used sites. The scale of site fidelity varied, but generally males choose to renest within shoreline areas rather than specific or exact nest locations (94% within‐year, 86% among‐years). Iteroparous males also displayed no preference to nest in proximity to neighbouring males from previous colonies to suggest social fidelity. Contrary to expectation, manipulating males' reproductive success had no significant effect on the pattern or scale of male reproductive site fidelity.