The Role of Host Traits, Season and Group Size on Parasite Burdens in a Cooperative Mammal

The distribution of parasites among hosts is often characterised by a high degree of heterogeneity with a small number of hosts harbouring the majority of parasites. Such patterns of aggregation have been linked to variation in host exposure and susceptibility as well as parasite traits and environmental factors. Host exposure and susceptibility may differ with sexes, reproductive effort and group size. Furthermore, environmental factors may affect both the host and parasite directly and contribute to temporal heterogeneities in parasite loads. We investigated the contributions of host and parasite traits as well as season on parasite loads in highveld mole-rats (Cryptomys hottentotus pretoriae). This cooperative breeder exhibits a reproductive division of labour and animals live in colonies of varying sizes that procreate seasonally. Mole-rats were parasitised by lice, mites, cestodes and nematodes with mites (Androlaelaps sp.) and cestodes (Mathevotaenia sp.) being the dominant ecto- and endoparasites, respectively. Sex and reproductive status contributed little to the observed parasite prevalence and abundances possibly as a result of the shared burrow system. Clear seasonal patterns of parasite prevalence and abundance emerged with peaks in summer for mites and in winter for cestodes. Group size correlated negatively with mite abundance while it had no effect on cestode burdens and group membership affected infestation with both parasites. We propose that the mode of transmission as well as social factors constrain parasite propagation generating parasite patterns deviating from those commonly predicted

Developmental temperatures and phenotypic plasticity in reptiles: a systematic review and meta-analysis

Early environments can profoundly influence an organism in ways that persist over its life. In reptiles, early thermal environments (nest temperatures) can impact offspring phenotype and survival in important ways, yet we still lack an understanding of whether general trends exist and the magnitude of impact. Understanding these patterns is important in predicting how climate change will affect reptile populations and the role of phenotypic plasticity in buffering populations. We compiled data from 175 reptile studies to examine, and quantify, the effect of incubation temperature on phenotype and survival. Using meta-analytic approaches (standardized mean difference between incubation treatments, Hedges' g), we show that across all trait types examined there is, on average, a moderate to large magnitude of effect of incubation temperatures (absolute effect: |g| = 0.75). Unsurprisingly, this influence was extremely large for incubation duration, as predicted, with warmer temperatures decreasing incubation time overall (g = −8.42). Other trait types, including behaviour, physiology, morphology, performance, and survival experienced reduced, but still mostly moderate to large effects, with particularly strong effects on survival. Moreover, the impact of incubation temperature persisted at least one-year post-hatching, suggesting that these effects have the potential to impact fitness in the long term. The magnitude of effect increased as the change in temperature increased (e.g. 6°C versus 2°C) in almost all cases, and tended to decrease when temperatures of the treatments fluctuated around a mean temperature compared to when they were constant. The effect also depended on the mid-temperature of the comparison, but not in consistent ways, with some traits experiencing the greatest effects at extreme temperatures, while others did not. The highly heterogeneous nature of the effects we observe, along with a large amount of unexplained variability, indicates that the shape of reaction norms between phenotype and temperature, along with ecological and/or experimental factors, are important when considering general patterns. Our analyses provide new insights into the effects of incubation environments on reptile phenotype and survival and allow general, albeit coarse, predictions for taxa experiencing warming nest temperatures under climatic change

Future climate alleviates stress impact on grassland productivity through altered antioxidant capacity

Predicting future ecosystem functioning requires a mechanistic understanding of how plants cope with different stressors under future climate conditions with elevated CO2 concentrations and warmer temperatures. Nonetheless, studies of stress responses under combined elevated CO2 and warming remain scarce.We assembled grassland communities in sunlit, climate-controlled greenhouses and subjected these to three stressors (drought, zinc toxicity, nitrogen limitation) and their combinations. Half of the communities were exposed to ambient climate conditions (current climate) and the other half were continuously kept at 3°C above ambient temperatures and at 620ppm CO2 (future climate).Across all stressors and their combinations, future climate-grown plants coped better with stress, i.e. above-ground biomass production was reduced less in future than in current climate. Among several tested potential biochemical and ecophysiological stress-relief mechanisms, we found three mutually non-exclusive mechanisms underpinning an improved stress protection under future climate conditions: (i) altered sugar metabolism; (ii) up-regulated levels of total antioxidant capacity and polyphenols; and (iii) more efficient use of ascorbate and glutathione as antioxidants. © 2013 Elsevier B.V