Army ants in four forests: geographic variation in raid rates and species composition

1. The New World army ants are top predators in the litter of tropical forest, but no comprehensive studies exist on variation in assemblage-wide activity and species composition. We used standardized protocols to estimate foraging raid rates and species composition of army ant communities in four Neotropical forests. The study sites spanned approximately 10 degrees latitude, with two sites each in Central and South America. 2. We recorded a total of 22 species of army ants. The four sites varied in observed and estimated species richness. Species overlap was highest between the Central American sites, and lowest between the South American sites. 3. Raid activity varied significantly among sites. Raid activity per kilometre of trail walks was over four times higher at the most active site (Sta. Maria, Venezuela) than at the least active site (Barro Colorado Island, Panama). Furthermore, each site showed a different diel pattern of activity. For example, raid activity was higher during daylight hours in Costa Rica, and higher at night in Venezuela. Raid activity relationships with ambient temperature also varied significantly among sites. 4. The overall rate of army ant raids passing through 1 m(2) plots was 0.73 raids per day, but varied among sites, from 0 raids per day (Panama) to 1.2 raids per day (Venezuela). 5. Primarily subterranean species were significantly more abundant in Venezuela, and above-ground foragers that form large swarm fronts were least abundant in Panama. The site heterogeneity in species abundance and diel activity patterns has implications for army ant symbionts, including ant-following birds, and for the animals hunted by these top predators.     

Honor and Violence

We present a theory of honor violence as a form of costly signaling. Two types of honor violence are identified: revenge and purification. Both types are amenable to a signaling analysis whereby the violent behavior is a signal that can be used by out-groups to draw inferences about the nature of the signaling group, thereby helping to solve perennial problems of social cooperation: deterrence and assurance. The analysis shows that apparently gratuitous acts of violence can be part of a system of norms that are Pareto superior to alternatives without such signals. For societies that lack mechanisms of governance to deter aggression or to enforce contracts, norms of honor can be a rational means of achieving these functions. The theory also suggests that cultures can become trapped in inefficient equilibria owing to path-dependent phenomena. In other words, costly signals of honor may continue to be sent even when they are no longer providing useful information.     

Strategic procurement of fish by the pumé: A South American “fishing culture”

Information is presented on fishing effort, efficiency, techniques, and catch composition for Pumé men, women, and children along with a conceptual model of fishing as a food procurement strategy. The Pumé are a native lowland South American group living in the topical savanna region of southwestern Venezuela characterized by seasonal flooding. Results are discussed in relation to the Pumé environmental and social situation, and briefly compared with results from other lowland South American groups.     

High risk maternal factors related to fetal wastage in rural Bangladesh

An analysis of the relationship between fetal mortality (early fetal death and stillbirth), pregnancy order, maternal age, and previous fetal deaths in a rural Bangladesh population characterized by high fertility and mortality and the virtual absence of obstetric and other medical care indicates that early fetal wastage and stillbirth are higher among pregnancy orders 1 and 6, or higher than among orders 2 and 3, with the increased risk particularly apparent among those pregnancies following 2 or more previous fetal deaths. The data consist of the 21,144 pregnancies that occurred to the women in Matlab, Bangladesh, 1966-1969. By a multiple regression technique allowing for pregnancy order and previous fetal deaths, adjustments were made for age of the mother, and after allowances were made for previous fetal deaths, adjustments were made for pregnancy order. Results show the fewest fetal deaths in 2nd and 3rd pregnancies, and most at the highest parities. 10% of all pregnancy terminations 1966-1969 were registered as fetal deaths. Women in the higher pregnancy orders who have not experienced previous fetal deaths or only 1 fetal death have only a slight increase in the risk of fetal death compared to women in pregnancy orders 2 and 3. It is concluded that the virtual absence of medical care facilities is responsible for the large numbers of fetal deaths due to complications of gestation, delivery, and environmental influences. It also results in a higher maternal mortality of women with pregnancy complications related to fetal deaths. This absence of obstetric care and the high maternal mortality in this population may allow only women without reproductive impairments to reach the higher pregnancy orders.     

Land, language, and loci: mtDNA in Native Americans and the genetic history of Peru

Despite a long history of complex societies and despite extensive present-day linguistic and ethnic diversity, relatively few populations in Peru have been sampled for population genetic investigations. In order to address questions about the relationships between South American populations and about the extent of correlation between genetic distance, language, and geography in the region, mitochondrial DNA (mtDNA) hypervariable region I sequences and mtDNA haplogroup markers were examined in 33 individuals from the state of Ancash, Peru. These sequences were compared to those from 19 American Indian populations using diversity estimates, AMOVA tests, mismatch distributions, a multidimensional scaling plot, and regressions. The results show correlations between genetics, linguistics, and geographical affinities, with stronger correlations between genetics and language. Additionally, the results suggest a pattern of differential gene flow and drift in western vs. eastern South America, supporting previous mtDNA and Y chromosome investigations.     

Phylogeography of the bushmaster (Lachesis tnuta: Viperidae): implications for neotropical biogeography, systematics, and conservation

We used mitochondrial gene sequences to reconstruct phylogenetic relationships among subspecies of the bushmaster, Lachesis muta. These large vipers are widely distributed in lowland tropical forests in Central and South America, where three of four allopatric subspecies are separated by montane barriers. Our phylogeny indicates that the four subspecies belong to two clades, the Central American and South American lineages. We use published molecular studies of other taxa to estimate a 'reptilian mtDNA rate' and thus temporal boundaries for major lineage divergences in Lachesis. We estimate that the Central and South American forms diverged 18-6 Mya, perhaps due to the uplifting of the Andes, whereas the two Central American subspecies may have diverged 11-4 Mya with the uprising of the Cordillera de Talamanca that separates them today. South American bushmasters from the Amazon Basin and the Atlantic Forest are not strongly differentiated, perhaps due to episodic gene flow during the Pleistocene, when suitable habitat for this species was at times more continuous. Our results agree with previous evidence that genetic divergence among some neotropical vertebrates pre-dated Pleistocene forest fragmentation cycles and the appearance of the Panamanian Isthmus. Based on morphological, behavioral, and molecular evidence, we recognize three species of Lachesis. In addition to L. muta, the widespread South American form, the Central American forms are treated as distinct species (L. meknocephak and L. stenophrys), each deserving of special conservation status due to restricted distribution and habitat destruction.     

Fitness costs of worker specialization for ant societies

Division of labour is of fundamental importance for the success of societies, yet little is known about how individual specialization affects the fitness of the group as a whole. While specialized workers may be more efficient in the tasks they perform than generalists, they may also lack the flexibility to respond to rapid shifts in task needs. Such rigidity could impose fitness costs when societies face dynamic and unpredictable events, such as an attack by socially parasitic slavemakers. Here, we experimentally assess the colony-level fitness consequences of behavioural specialization in Temnothorax longispinosus ants that are attacked by the slavemaker ant T. americanus. We manipulated the social organization of 102 T. longispinosus colonies, based on the behavioural responses of all 3842 workers. We find that strict specialization is disadvantageous for a colony''s annual reproduction and growth during slave raids. These fitness costs may favour generalist strategies in dynamic environments, as we also demonstrate that societies exposed to slavemakers in the field show a lower degree of specialization than those originating from slavemaker-free populations. Our findings provide an explanation for the ubiquity of generalists and highlight their importance for the flexibility and functional robustness of entire societies.     

Culturally transmitted paternity beliefs and the evolution of human mating behaviour

Recent anthropological findings document how certain lowland South American societies hold beliefs in 'partible paternity', which allow children to have more than one 'biological' father. This contrasts with Western beliefs in 'singular paternity', and biological reality, where children have just one father. Here, mathematical models are used to explore the coevolution of paternity beliefs and the genetic variation underlying human mating behaviour. A gene-culture coevolutionary model found that populations exposed to a range of selection regimes typically converge on one of two simultaneously stable equilibria; one where the population is monogamous and believes in singular paternity, and the other where the population is polygamous and believes in partible paternity. A second agent-based model, with alternative assumptions regarding the formation of mating consortships, broadly replicated this finding in populations with a strongly female-biased sex ratio, consistent with evidence for high adult male mortality in the region. This supports an evolutionary scenario in which ancestral South American populations with differing paternity beliefs were subject to divergent selection on genetically influenced mating behaviour, facilitated by a female-biased sex ratio, leading to the present-day associations of female control, partible paternity and polygamy in some societies, and male control, singular paternity and monogamy in others.     

Patterns of livestock depredation and cost‐effectiveness of fortified livestock enclosures in northern Tanzania

Human–carnivore conflicts and retaliatory killings contribute to carnivore populations' declines around the world. Strategies to mitigate conflicts have been developed, but their efficacy is rarely assessed in a randomized case–control design. Further, the economic costs prevent the adoption and wide use of conflict mitigation strategies by pastoralists in rural Africa. We examined carnivore (African lion [Panthera leo], leopard [Panthera pardus], spotted hyena [Crocuta crocuta], jackal [Canis mesomelas], and cheetah [Acinonyx jubatus]) raids on fortified (n = 45, total 631 monthly visits) and unfortified (traditional, n = 45, total 521 monthly visits) livestock enclosures (“bomas”) in northern Tanzania. The study aimed to (a) assess the extent of retaliatory killings of major carnivore species due to livestock depredation, (b) describe the spatiotemporal characteristics of carnivore raids on livestock enclosures, (c) analyze whether spatial covariates influenced livestock depredation risk in livestock enclosures, and (d) examine the cost‐effectiveness of livestock enclosure fortification. Results suggest that (a) majority of boma raids by carnivores were caused by spotted hyenas (nearly 90% of all raids), but retaliatory killings mainly targeted lions, (b) carnivore raid attempts were rare at individual households (0.081 raid attempts/month in fortified enclosures and 0.102 raid attempts/month in unfortified enclosures), and (c) spotted hyena raid attempts increased in the wet season compared with the dry season, and owners of fortified bomas reported less hyena raid attempts than owners of unfortified bomas. Landscape and habitat variables tested, did not strongly drive the spatial patterns of spotted hyena raids in livestock bomas. Carnivore raids varied randomly both spatially (village to village) and temporally (year to year). The cost‐benefit analysis suggest that investing in boma fortification yielded positive net present values after two to three years. Thus, enclosure fortification is a cost‐effective strategy to promote coexistence of carnivores and humans.     

Experience of violence and socioeconomic position in South Africa: a national study

Background

Violence is a leading cause of morbidity and mortality in South Africa and needs to be researched from a public health perspective. Typically in violence research, socioeconomic position is used in the analysis to control for confounding. Social epidemiology approaches this variable as a primary determinant of interest and is used in this research to better understand the aetiology of violence in South Africa. We hypothesised that measures of socioeconomic position (employment, education and household wealth) would be inversely related to violence at the individual and household levels.

Methodology/Principal Findings

Data came from the1998 South African Demographic and Health Survey (SADHS). Measures of socioeconomic position used were employment, education and household wealth. Eighty-eight people (0.2%) received treatment for a violent injury in the previous 30 days and 103 households (0.9%) experienced a violent death in the previous year. Risk factors for violence at the individual level included employment (41% of those who experienced violence were employed vs. 27% of those who did not, p = 0.02), and education (those who experienced violence had on average, one year more education than those who did not, p = 0.04). Belonging to a household in the wealthiest quintile was protective against violence (OR: 0.32; 95% CI: 0.12–0.89). In contrast, at the household level all three measures of socioeconomic position were protective against the experience of a violent death. The only association to persist in the multivariate analysis was that between the wealth of the household and violence at the individual level.

Conclusions/Significance

Our hypothesis was supported if household wealth was used as the measure of socioeconomic position at the individual level. While more research is needed to inform the conflicting results observed between the individual and household levels, this analysis has begun to identify the disparities across the socioeconomic structure with respect to violent outcomes.     

Evaluating completeness of maternal mortality reporting in a rural health and social affairs unit in Vellore, India, 2004

Health systems in developing countries infrequently implement and evaluate maternal death surveillance. This study identified under-reported and misclassified maternal deaths among women of reproductive age between 1999 and 2004 in a rural service unit in Vellore, India. In-depth interviews, semi-structured interviews and structured questionnaires were used to identify maternal deaths known to health care providers and community leaders who regularly come in contact with pregnant women. Eighteen under-reported and misclassified cases--or 50% of maternal deaths--were reported. These included 29% of abortion-related and 7% of domestic violence-related deaths. Based on this study's fieldwork, the existing death surveillance system detected 100% of the maternal deaths reported by hospital staff; however, it missed most maternal deaths reported by community workers. The latter are more likely than deaths reported by hospital workers to result from abortion and family violence. The existing surveillance system should be augmented with a community-based death surveillance system. This comprehensive approach identified twice as many maternal deaths than previously recorded and could be applied in other settings. Appropriate public health interventions should be initiated to prevent maternal deaths in this community.     

Mortality in Iraq Associated with the 2003–2011 War and Occupation: Findings from a National Cluster Sample Survey by the University Collaborative Iraq Mortality Study

Background

Previous estimates of mortality in Iraq attributable to the 2003 invasion have been heterogeneous and controversial, and none were produced after 2006. The purpose of this research was to estimate direct and indirect deaths attributable to the war in Iraq between 2003 and 2011.

Methods and Findings

We conducted a survey of 2,000 randomly selected households throughout Iraq, using a two-stage cluster sampling method to ensure the sample of households was nationally representative. We asked every household head about births and deaths since 2001, and all household adults about mortality among their siblings. We used secondary data sources to correct for out-migration. From March 1, 2003, to June 30, 2011, the crude death rate in Iraq was 4.55 per 1,000 person-years (95% uncertainty interval 3.74–5.27), more than 0.5 times higher than the death rate during the 26-mo period preceding the war, resulting in approximately 405,000 (95% uncertainty interval 48,000–751,000) excess deaths attributable to the conflict. Among adults, the risk of death rose 0.7 times higher for women and 2.9 times higher for men between the pre-war period (January 1, 2001, to February 28, 2003) and the peak of the war (2005–2006). We estimate that more than 60% of excess deaths were directly attributable to violence, with the rest associated with the collapse of infrastructure and other indirect, but war-related, causes. We used secondary sources to estimate rates of death among emigrants. Those estimates suggest we missed at least 55,000 deaths that would have been reported by households had the households remained behind in Iraq, but which instead had migrated away. Only 24 households refused to participate in the study. An additional five households were not interviewed because of hostile or threatening behavior, for a 98.55% response rate. The reliance on outdated census data and the long recall period required of participants are limitations of our study.

Conclusions

Beyond expected rates, most mortality increases in Iraq can be attributed to direct violence, but about a third are attributable to indirect causes (such as from failures of health, sanitation, transportation, communication, and other systems). Approximately a half million deaths in Iraq could be attributable to the war. Please see later in the article for the Editors'' Summary     

Elevational and geographic variation in army ant swarm raid rates

Geographic and elevational variation in the local abundance of swarm-raiding army ants has implications for the population dynamics of their prey, as well as affecting the profitability of army-ant-following behavior for birds. Here, we analyze systematically collected data on E. burchellii and L. praedator raid rates from geographically and elevationally wide-ranging sites, from lowland to montane forests. We show that raids of each species, and of both species pooled, reach peak densities at intermediate (premontane) elevations. These patterns suggest that army ant swarm raids are relatively abundant in Neotropical montane forests. Therefore, a paucity of ant raids does not explain the absence of obligate ant-following bird species, particularly true antbirds (Thamnophilidae), from montane forests. As army ant raids are relatively common at middle elevations, opportunities exist for other montane bird taxa to exploit army ant raids as a food source.     

Hormonal Mechanisms for Regulation of Aggression in Human Coalitions

Coalitions and alliances are core aspects of human behavior. All societies recognize alliances among communities, usually based in part on kinship and marriage. Aggression between groups is ubiquitous, often deadly, fueled by revenge, and can have devastating effects on general human welfare. Given its significance, it is surprising how little we know about the neurobiological and hormonal mechanisms that underpin human coalitionary behavior. Here we first briefly review a model of human coalitionary behavior based on a process of runaway social selection. We then present several exploratory analyses of neuroendocrine responses to coalitionary social events in a rural Dominican community, with the objective of understanding differences between in-group and out-group competition in adult and adolescent males. Our analyses indicate: (1) adult and adolescent males do not elevate testosterone when they defeat their friends, but they do elevate testosterone when they defeat outsiders; (2) pre-competition testosterone and cortisol levels are negatively associated with strength of coalitionary ties; and (3) adult males usually elevate testosterone when interacting with adult women who are potential mates, but in a striking reversal, they have lower testosterone if the woman is a conjugal partner of a close friend. These naturalistic studies hint that reciprocity, dampening of aggression, and competition among friends and allies may be biologically embedded in unique ways among humans.     

Hunter–Gatherer population structure and the evolution of contingent cooperation

Unlike other vertebrates, humans cooperate in large groups with unrelated individuals. Many authors have argued that the evolution of such cooperation has resulted from reciprocity and other forms of contingent cooperation. This argument is not well supported by existing theory. The theory of contingent cooperation in pairs is well developed: reciprocating strategies are stable when common, and can increase when rare as long as population structure leads to modest levels of relatedness. In larger groups, however, it is not clear whether contingent cooperation can increase when rare. Existing work suggests that contingent strategies cannot increase unless relatedness is high, but depends on unrealistic assumptions about the effects of population structure. Here we develop and analyze a model incorporating a two level population structure that captures important features of human hunter–gatherer societies. This model suggests that previous work underestimates the range of conditions under which contingent cooperation can evolve, but also predicts that cooperation will not evolve unless (1) social groups are small, and (2) the relatedness within ethnolinguistic groups is at the high end of the range of empirical estimates.     

Recent diversification in African greenbuls (Pycnonotidae: Andropadus) supports a montane speciation model

It is generally accepted that accentuated global climatic cycles since the Plio-Pleistocene (2.8 Ma ago) have caused the intermittent fragmentation of forest regions into isolated refugia thereby providing a mechanism for speciation of tropical forest biota contained within them. However, it has been assumed that this mechanism had its greatest effect in the species rich lowland regions. Contrary evidence from molecular studies of African and South American forest birds suggests that areas of recent intensive speciation, where mostly new lineages are clustered, occur in discrete tropical montane regions, while lowland regions contain mostly old species. Two predictions arise from this finding. First, a species phylogeny of an avian group, represented in both lowland and montane habitats, should be ordered such that montane forms are represented by the most derived characters. Second, montane speciation events should predominate within the past 2.8 Ma. In order to test this model I have investigated the evolutionary history of the recently radiated African greenbuls (genus Andropadus), using a molecular approach. This analysis finds that montane species are a derived monophyletic group when compared to lowland species of the same genus and recent speciation events (within the Plio-Pleistocene) have exclusively occurred in montane regions. These data support the view that montane regions have acted as centres of speciation during recent climatic instability.     

The role of immigrants in the assembly of the South American rainforest tree flora

The Amazon lowland rainforest flora is conventionally viewed as comprising lineages that evolved in biogeographic isolation after the split of west Gondwana (ca. 100 Myr ago). Recent molecular phylogenies, however, identify immigrant lineages that arrived in South America during its period of oceanic isolation (ca. 100-3 Myr ago). Long-distance sweepstakes dispersal across oceans played an important and possibly predominant role. Stepping-stone migration from Africa and North America through hypothesized Late Cretaceous and Tertiary island chains may have facilitated immigration. An analysis of inventory plot data suggests that immigrant lineages comprise ca. 20% of both the species and individuals of an Amazon tree community in Ecuador. This is more than an order of magnitude higher than previous estimates. We also present data on the community-level similarity between South American and palaeotropical rainforests, and suggest that most taxonomic similarity derives from trans-oceanic dispersal, rather than a shared Gondwanan history.     

Epidemiology of sudden cardiac death in rural South India - insights from the andhra pradesh rural health initiative

Background

Sudden cardiac death (SCD) is a common initial presentation of coronary artery disease (CAD). Despite the growing epidemic of CAD in India, the epidemiology of SCD is largely unknown.

Objective

The objective of the study was to define the prevalence and determinants of sudden cardiac deaths in rural South India.

Methods

Prospective mortality surveillance was conducted in 45 villages (180,162 subjects) in rural South India between January 2006 and October 2007. Trained multipurpose health workers sought to do verbal autopsies within 4 weeks of any death. Detailed questionnaires including comorbidities and circumstances surrounding death were recorded. SCD was adjudicated using the modified Hinkle-Thaler classification.

Results

A total of 1916 deaths occurred in the study population over the 22 month time period and verbal autopsy was obtained in 1827 (95%) subjects. Overall mean age of the deceased was 62 ± 20 years and 1007 (55%) were men. Cardiovascular and cerebrovascular diseases together accounted for 559 deaths (31%), followed by infectious disease (163 deaths, 9%), cancer (126 deaths, 7%) and suicide (93 deaths, 5%).Of the 1827 deaths, after excluding accidental deaths (89 deaths), 309 deaths (17%) met criteria for SCD. Cardiovascular disease was the underlying causes in the majority of the SCD events (231/309 (75%)). On multivariate analyses, previous MI/CAD (p < 0.001, OR 14.25), hypertension (p < 0.001, OR 1.84), and age groups between 40-60 yrs (p=0.029) were significantly associated with SCD.

Conclusion

Sudden cardiac death accounted for up to half of the cardiovascular deaths in rural Southern India. Traditional cardiovascular risk factors were strongly associated with SCD.