Interannual Variability of Human Plague Occurrence in the Western United States Explained by Tropical and North Pacific Ocean Climate Variability

Plague is a vector-borne, highly virulent zoonotic disease caused by the bacterium Yersinia pestis. It persists in nature through transmission between its hosts (wild rodents) and vectors (fleas). During epizootics, the disease expands and spills over to other host species such as humans living in or close to affected areas. Here, we investigate the effect of large-scale climate variability on the dynamics of human plague in the western United States using a 56-year time series of plague reports (1950–2005). We found that El Niño Southern Oscillation and Pacific Decadal Oscillation in combination affect the dynamics of human plague over the western United States. The underlying mechanism could involve changes in precipitation and temperatures that impact both hosts and vectors. It is suggested that snow also may play a key role, possibly through its effects on summer soil moisture, which is known to be instrumental for flea survival and development and sustained growth of vegetation for rodents.     

Competition among fishermen and fish causes the collapse of Barents Sea capelin

The vast majority of the world's fisheries are typically managed within a single-species perspective, ignoring the dynamic feedback mechanisms generated by the ecological web of which they are a part. Here we show that the dynamics of the Barents Sea capelin (Mallotus villosus), the world's largest stock of this species, is strongly influenced by both within-system ecological feedback mechanisms and the impact of harvesting. Both overexploitation and predation by herring (Clupea harengus) can cause the population to collapse, whereas predation by cod (Gadus morhua) is demonstrated a delay in the stock's recovery after a collapse. Such collapses, which have occurred twice in 20 years, affect the entire Barents Sea ecosystem, a region that for ages has provided food for all of Europe.     

Protective efficacy of vaccines of the Korea national antigen bank against the homologous H5Nx clade 2.3.2.1 and clade 2.3.4.4 highly pathogenic avian influenza viruses

The occurrence of severe outbreaks of highly pathogenic avian influenza in Korea led to establishment of a national antigen bank for emergency preparedness. Here, we developed five vaccines for this bank (clade 2.3.2.1C, clade 2.3.4.4A, B, C, and D) by reverse genetics, inactivated them with formalin, and evaluated the protective efficacy and potency of serial dilutions against lethal homologous challenge in specific-pathogen-free chickens. After vaccination with one dose, each vaccine resulted in 100% survival, with no clinical symptoms, or lack of detectable virus shedding, and high levels of pre-challenge protective immunity (8.4–10.2 log₂). After vaccination with one-tenth of the full dose, protection was similar to that with the full dose. After vaccination with one-hundredth of the initial dose, survival was 20–80%, and all vaccines showed virus shedding. Four vaccines (excluding clade 2.3.2.1C) had satisfactory potency. In antibody-persistence tests, all vaccines maintained long-lasting protective immunity. Our results suggest that inactivated reverse-genetics vaccines genetically matched to outbreak viruses provide adequate protection after a single vaccination.     

Covariation between human pelvis shape,stature, and head size alleviates the obstetric dilemma

Compared with other primates, childbirth is remarkably difficult in humans because the head of a human neonate is large relative to the birth-relevant dimensions of the maternal pelvis. It seems puzzling that females have not evolved wider pelvises despite the high maternal mortality and morbidity risk connected to childbirth. Despite this seeming lack of change in average pelvic morphology, we show that humans have evolved a complex link between pelvis shape, stature, and head circumference that was not recognized before. The identified covariance patterns contribute to ameliorate the “obstetric dilemma.” Females with a large head, who are likely to give birth to neonates with a large head, possess birth canals that are shaped to better accommodate large-headed neonates. Short females with an increased risk of cephalopelvic mismatch possess a rounder inlet, which is beneficial for obstetrics. We suggest that these covariances have evolved by the strong correlational selection resulting from childbirth. Although males are not subject to obstetric selection, they also show part of these association patterns, indicating a genetic–developmental origin of integration.Childbirth is remarkably difficult in humans because of the tight fit of the human neonate through the maternal birth canal (1, 2). Obstructed labor occurs in 3–6% of all births and is thought to be globally responsible for 8% of all maternal deaths today (3–5). The most frequent cause of obstructed labor is cephalopelvic disproportion—a mismatch between the fetal head and the mother’s pelvis (5). Without effective medical intervention, maternal mortality due to childbirth is estimated to be 1.5% (6), but many more women experience acute or chronic morbidity and develop lasting disabilities as a consequence of obstructed labor (4, 7). In evolutionary terms, there have been incredible fitness costs associated with childbirth in humans throughout modern human evolution, yet the birth canal has not become sufficiently wider.This “obstetric dilemma” (8) is considered to be a consequence of the conflicting demands on the human pelvis imposed by bipedal locomotion and a large brain size. The shape of the human pelvis is assumed to be a compromise solution. Human pelvises are shaped for upright walking, but at the same time, they must remain wide enough for giving birth to large-headed neonates (1, 2, 9–12). Upright walking evolved at least 4–5 million years ago and required major skeletal adjustments (9, 13, 14). Only in the late Pleistocene (600,000–150,000 B.P.) did a major increase in brain size evolve (13), and the increasingly large-headed neonates had to be delivered through a pelvis that had earlier been adapted to bipedalism. The obstetric dilemma might further be aggravated by a higher infant survival rate for heavier neonates (15), implying that a higher birth weight is favored by selection. However, a recent study showed that neonatal size and human gestation length are limited not only by pelvic dimensions but also by maternal metabolic capacity (16). Phenotypic plasticity of pelvic dimensions and head size in response to changes in nutrition, poor food availability, and infectious disease burden, among others, might influence the severity of the obstetric dilemma (17–19).Despite the effect of environmental factors, pelvic dimensions are highly heritable in human populations (most pelvic traits have heritabilities in the range of 0.5–0.8) (20) (SI Text and Table S1). It has further been claimed that low levels of integration in the pelvis enable high evolvability (14, 21, 22), yet pelvis shape has seemingly not sufficiently responded to the strong selection pressure imposed by childbirth. Despite insufficient change in average pelvic morphology, selection might have shaped the covariation between pelvic morphology and other body dimensions to ameliorate the consequences of pelvic constraints on childbirth. Cephalopelvic disproportion is determined by the mother’s pelvic dimensions relative to the size of the fetal head, implying that pelvis and head are subject to correlational selection. A twin study (23) reported a heritability of 0.73 for intracranial volume, despite the apparent plasticity in head shape due to cranial deformations during birth (resulting in a heritability of 0.14 for neonatal head circumference but of 0.90 for head circumference of infants aged 4–5 mo) (24) (SI Text and Table S1). Because of the considerable heritabilities for head size and pelvic dimensions, we predict that females with a larger head have evolved a birth canal that can better accommodate large-headed neonates, compared with females with a smaller head, who are likely to give birth to children with smaller heads.Similarly, the risk of birth complications increases if the father is much taller than the mother (25). A short woman with a small pelvis might give birth to a large neonate with a large head, inherited from a much taller father. As this suggests, shorter women, on average, have harder births than taller women (25–30). Given the high heritability of stature (24, 31, 32), we therefore also predict that the stronger obstetric selection pressure on shorter women has led to a pelvis with a birth canal that is more shaped toward obstetric demands in comparison with taller women.We suggest that the optimal compromise between a large birth canal and a narrow pelvis is not uniform across a population but rather depends on both head size and stature. Hence, correlated variation between pelvic form, head size, and stature would reduce cases of obstructed labor and increase the human population’s mean fitness. The joint selection regimes might have led to an adaptive integration (covariation) between pelvis shape, head circumference, and stature within human populations. To detect such integration patterns within the human body, we assess the covariation between human pelvis shape, head circumference, and stature in males and females by applying geometric morphometrics to fine-resolution 3D landmark data (Fig. 1 and Table S2) from 99 human skeletons.Open in a separate windowFig. 1.Pelvic landmarks. The full set of 126 3D pelvic landmarks measured on each pelvis, shown as red spheres on the mean pelvis shape, are shown in (A) anterior, (B) superior, and (C) lateral view. The mean pelvis shape was computed as the average shape of all individuals in our dataset.     

Seasonality, density dependence, and population cycles in Hokkaido voles

Voles and lemmings show extensive variation in population dynamics regulated across and within species. In an attempt to develop and test generic hypotheses explaining these differences, we studied 84 populations of the gray-sided vole (Clethrionomys rufocanus) in Hokkaido, Japan. We show that these populations are limited by a combination of density-independent factors (such as climate) and density-dependent processes (such as specialist predators). We show that density-dependent regulation primarily occurs in winter months, so that populations experiencing longer winters tend to have a stronger delayed density-dependence and, as a result, exhibit regular density cycles. Altogether, we demonstrate that seasonality plays a key role in determining whether a vole population is cyclic or not.     

Mushroom fruiting and climate change

Many species of fungi produce ephemeral autumnal fruiting bodies to spread and multiply. Despite their attraction for mushroom pickers and their economic importance, little is known about the phenology of fruiting bodies. Using approximately 34,500 dated herbarium records we analyzed changes in the autumnal fruiting date of mushrooms in Norway over the period 1940-2006. We show that the time of fruiting has changed considerably over this time period, with an average delay in fruiting since 1980 of 12.9 days. The changes differ strongly between species and groups of species. Early-fruiting species have experienced a stronger delay than late fruiters, resulting in a more compressed fruiting season. There is also a geographic trend of earlier fruiting in the northern and more continental parts of Norway than in more southern and oceanic parts. Incorporating monthly precipitation and temperature variables into the analyses provides indications that increasing temperatures during autumn and winter months bring about significant delay of fruiting both in the same year and in the subsequent year. The recent changes in autumnal mushroom phenology coincide with the extension of the growing season caused by global climate change and are likely to continue under the current climate change scenario.     

The effect of climate variation on agro-pastoral production in Africa

Using national crop and livestock production records from 1961-2003 and satellite-derived data on pasture greenness from 1982-2003 we show that the productivity of crops, livestock, and pastures in Africa is predictably associated with the El Ni?o Southern Oscillation and the North Atlantic Oscillation. The causal relations of these results are partly understandable through the associations between the atmospheric fluctuations and African rainfall. The range of the explained among-year variation in crop production in Africa as a whole corresponds to the nutritional requirements for approximately 20 million people. Results suggest reduced African food production if the global climate changes toward more El Ni?o-like conditions, as most climate models predict. Maize production in southern Africa is most strongly affected by El Ni?o events. Management measures include annual changes in crop selection and storage strategies in response to El Ni?o Southern Oscillation-based and North Atlantic Oscillation-based predictions for the next growing season.