Demographic and reproductive associations with nematode infection in a long-lived mammal

Infection by macroparasites, such as nematodes, varies within vertebrate host systems; elevated infection is commonly observed in juveniles and males, and, for females, with different reproductive states. However, while such patterns are widely recognized in short-lived model systems, how they apply to long-lived hosts is comparatively understudied. Here, we investigated how infection varies with host age, sex, and female reproduction in a semi-captive population of individually marked Asian elephants Elephas maximus. We carried out 1,977 faecal egg counts (FECs) across five years to estimate nematode loads for 324 hosts. Infection patterns followed an established age-infection curve, whereby calves (5 years) exhibited the highest FECs and adults (45 years) the lowest. However, males and females had similar FECs across their long lifespan, despite distinct differences in life-history strategy and clear sexual dimorphism. Additionally, although mothers invest two years in pregnancy and a further three to five years into lactation, nematode load did not vary with four different measures of female reproduction. Our results provide a much-needed insight into the host-parasite dynamics of a long-lived host; determining host-specific associations with infection in such systems is important for broadening our knowledge of parasite ecology and provides practical applications for wildlife medicine and management

Network theory may explain the vulnerability of medieval human settlements to the Black Death pandemic

Epidemics can spread across large regions becoming pandemics by flowing along transportation and social networks. Two network attributes, transitivity (when a node is connected to two other nodes that are also directly connected between them) and centrality (the number and intensity of connections with the other nodes in the network), are widely associated with the dynamics of transmission of pathogens. Here we investigate how network centrality and transitivity influence vulnerability to diseases of human populations by examining one of the most devastating pandemic in human history, the fourteenth century plague pandemic called Black Death. We found that, after controlling for the city spatial location and the disease arrival time, cities with higher values of both centrality and transitivity were more severely affected by the plague. A simulation study indicates that this association was due to central cities with high transitivity undergo more exogenous re-infections. Our study provides an easy method to identify hotspots in epidemic networks. Focusing our effort in those vulnerable nodes may save time and resources by improving our ability of controlling deadly epidemics

Excretion patterns of coccidian oocysts and nematode eggs during the reproductive season in Northern Bald Ibis (Geronticus eremita)

Individual reproductive success largely depends on the ability to optimize behaviour, immune function and the physiological stress response. We have investigated correlations between behaviour, faecal steroid metabolites, immune parameters, parasite excretion patterns and reproductive output in a critically endangered avian species, the Northern Bald Ibis (Geronticus eremita). In particular, we related haematocrit, heterophil/lymphocyte ratio, excreted immune-reactive corticosterone metabolites and social behaviour with parasite excretion and two individual fitness parameters, namely, number of eggs laid and number of fledglings. We found that the frequency of excretion of parasites’ oocysts and eggs tended to increase with ambient temperature. Paired individuals excreted significantly more samples containing nematode eggs than unpaired ones. The excretion of nematode eggs was also significantly more frequent in females than in males. Individuals with a high proportion of droppings containing coccidian oocysts were more often preened by their partners than individuals with lower excretion rates. We observed that the more eggs an individual incubated and the fewer offspring fledged, the higher the rates of excreted samples containing coccidian oocysts. Our results confirm that social behaviour, physiology and parasite burden are linked in a complex and context-dependent manner. They also contribute background information supporting future conservation programmes dealing with this critically endangered species

Social networks in primates: smart and tolerant species have more efficient networks

Network optimality has been described in genes, proteins and human communicative networks. In the latter, optimality leads to the efficient transmission of information with a minimum number of connections. Whilst studies show that differences in centrality exist in animal networks with central individuals having higher fitness, network efficiency has never been studied in animal groups. Here we studied 78 groups of primates (24 species). We found that group size and neocortex ratio were correlated with network efficiency. Centralisation (whether several individuals are central in the group) and modularity (how a group is clustered) had opposing effects on network efficiency, showing that tolerant species have more efficient networks. Such network properties affecting individual fitness could be shaped by natural selection. Our results are in accordance with the social brain and cultural intelligence hypotheses, which suggest that the importance of network efficiency and information flow through social learning relates to cognitive abilities

Shallow divers, deep waters, and the rise of behavioural stochasticity

International audienceLittle penguins (Eudyptula minor) have oneof the widest geographic distributions among penguins,exposing them to variable ecological constraints acrosstheir range, which in turn can affect their foraging behaviour.Presumably, behavioural flexibility exists to allowanimals to adapt to prevailing environmental conditionsthroughout their foraging range. This study examinedwhether complexity in the temporal organization of foragingsequences corresponds to characteristics of the foragingarea across four colonies geographically distributed alongthe entire species’ range. Complexity and fractal scalingin spatiotemporal patterns of foraging behaviour havebeen theoretically linked to foraging efficiency in heterogeneousenvironments. Using fractal time series methods(detrended fluctuation analysis), we found that foragingcomplexity along a stochastic–deterministic gradient was associated with bathymetry in local foraging areas; littlepenguins foraging in deeper waters produced more stochastic/less deterministic foraging sequences than thoseforaging in shallower waters. Corresponding data on fledgingsuccess suggest that little penguins foraging in deeperwaters also experienced reduced reproductive success. Aprincipal component analysis further showed that our fractalscaling index, which specifically measured the degree towhich sequences are long-range dependent (a deterministicphenomenon), correlated positively with foraging efficiency(prey encounter per unit time) and negatively withforaging effort (total time underwater). Our statistical modelsshowed that production of complex foraging sequenceswith high degrees of stochasticity appears to be energyintensive. However, we could not determine which strategywould have maximized foraging success, a variable wecould not measure, under the conditions observed. We proposethat increasing stochastic elements in foraging behaviourmay be necessary under challenging environmentalconditions, but it may not be sufficient to match fitnessgains attained under more favourable conditions

Hydrodynamic handicaps and organizational complexity in the foraging behavior of two free-ranging penguin species

International audienceBackground: Animal movement exhibits self-similarity across a range of both spatial and temporal scales reminiscentof statistical fractals. Stressors are known to induce changes in these statistical patterns of behavior, although thedirection and interpretation of such changes are not always clear. We examined whether the imposition of knownhydrodynamic disruptors, bio-logging devices and flipper bands, induces changes in the temporal organization(complexity) of foraging sequences in two penguin species, little penguins (Eudyptula minor) and Adélie penguins(Pygoscelis adeliae).Results: Detrended fluctuation analysis showed that foraging sequences produced by little penguins carrying largerloggers were more complex, i.e., were more erratic tending toward greater stochasticity, than those carrying smallerloggers. However, logger size did not affect complexity in foraging sequences of Adélie penguins. Logger positionwas associated only weakly with altered complexity in little penguins, with individuals carrying loggers in the middleof their backs displaying slightly more complex dive sequences than those carrying loggers lower on their backs.Finally, despite their known negative effects on penguin fitness, flipper bands were not associated with dive sequencecomplexity in little penguins.Conclusions: Despite that externally attached devices can disrupt certain behavioral parameters in diving seabirds,we found mixed evidence in support of the hypothesis that such devices significantly disrupt the time-structuredorganizational properties of foraging sequences in the two penguin species investigated. However, smaller speciescarrying larger loggers, and perhaps those positioned higher on their backs, may experience an added element ofnoise in their behavioral sequences that may indicate a departure from foraging behavior observed under normal,unburdened conditions