Patch time allocation in male parasitoids

Abstract 1. Patch time allocation has been mostly studied in female parasitoids exploiting patches of hosts. Different parameters such as oviposition, host encounters, patch quality, etc. have been repeatedly shown to modify the time females invest on hosts. 2. Male parasitoids are expected to maximise their lifetime fitness by maximising the number of females inseminated during their life. Because they can be sperm and/or time limited, they should optimise their time allocation on emergence patches. 3. Patch time allocation thus appears to be an important question for both male and female parasitoids. 4. In this study, we determined the parameters used by males of the egg parasitoid Trichogramma turkestanica to decide when to leave the emergence patch. Among the different patch‐leaving parameters tested, only contacts with parasitised hosts and presence of virgin females significantly influenced the patch‐leaving tendency. 5. Our results suggest that males express behaviours that could enable them to optimise their patch exploitation time, as females do, but using different strategies.     

Extracellular superoxide production, viability and redox poise in response to desiccation in recalcitrant Castanea sativa seeds

Reactive oxygen species (ROS) are implicated in seed death following dehydration in desiccation-intolerant 'recalcitrant' seeds. However, it is unknown if and how ROS are produced in the apoplast and if they play a role in stress signalling during desiccation. We studied intracellular damage and extracellular superoxide (O₂^·−) production upon desiccation in Castanea sativa seeds, mechanisms of O₂^·− production and the effect of exogenously supplied ROS. A transient increase in extracellular O₂^·− production by the embryonic axes preceded significant desiccation-induced viability loss. Thereafter, progressively more oxidizing intracellular conditions, as indicated by a significant shift in glutathione half-cell reduction potential, accompanied cell and axis death, coinciding with the disruption of nuclear membranes. Most hydrogen peroxide (H₂O₂)-dependent O₂^·− production was found in a cell wall fraction that contained extracellular peroxidases (ECPOX) with molecular masses of ∼50 kDa. Cinnamic acid was identified as a potential reductant required for ECPOX-mediated O₂^·− production. H₂O₂, applied exogenously to mimic the transient ROS burst at the onset of desiccation, counteracted viability loss of sub-lethally desiccation-stressed seeds and of excised embryonic axes grown in tissue culture. Hence, extracellular ROS produced by embryonic axes appear to be important signalling components involved in wound response, regeneration and growth.     

RELATIONSHIP BETWEEN TASTE AND CHEWING PATTERNS OF VISCO-ELASTIC MODEL FOODS

The jaw movements and muscular activity of masticatory muscles of five assessors, having bitterness thresholds about 8 μM quinine in water, were monitored throughout chewing of similar strength gelatin gels containing 0, 40, 70 or 100 μM quinine. Gel bitterness ratings were not related to sensory texture which was 78kN/m² by shear test. On average, 100 μM quinine gels were as bitter as 7 to 30 μM quinine in water, depending on the assessor. Chewing patterns were not affected by concentration of quinine in the gels. During mastication of acceptable gels, there appears to be no feedback from taste to the motor control of mastication. In gels of the same consistency and the same concentration of quinine, assessors who chewed more rated higher for bitterness. The implications for mimicking mastication by machine and the training of assessors for solid foods are discussed.     

Effects of Joint Space Use and Group Membership on Contact Rates Among White-Tailed Deer

Abstract: Establishment and spread of infectious diseases are controlled by the frequency of contacts among hosts. Although managers can estimate transmission coefficients from the relationship between disease prevalence and age or time, they may wish to quantify or compare contact rates before a disease is established or while it is at very low prevalence. Our objectives were to quantify direct and indirect contacts rates among white-tailed deer (Odocoileus virginianus) and to compare these measures of contact rate with simpler measures of joint space use. We deployed Global Positioning System (GPS) collars on 23 deer near Carbondale, Illinois, USA, from 2002 to 2005. We used location data from the GPS collars to measure pairwise rates of direct and indirect contact, based on a range of proximity criteria and time lags, as well as volume of intersection (VI) of kernel utilization distributions. We analyzed contact rates at a given distance criterion and time lag using mixed-model logistic regression. Direct contact rates increased with increasing VI and were higher in autumn—spring than in summer. After accounting for VI, the estimated odds of direct contact during autumn—spring periods were 5.0–22.1-fold greater (depending on the proximity criterion) for pairs of deer in the same social group than for between-group pairs, but for direct contacts during summer the within:between-group odds ratio did not differ significantly from 1. Indirect contact rates also increased with VI, but the effects of both season and pair-type were much smaller than for direct contacts and differed little as the time lag increased from 1–30 days. These results indicate that simple measures of joint space use are insufficient indices of direct contact because group membership can substantially increase contacts at a given level of joint space use. With indirect transmission, however, group membership had a much smaller influence after accounting for VI. Relationships between contact rates and season, VI, and pair-type were generally robust to changes in the proximity criterion defining a contact, and patterns of indirect contacts were affected little by the choice of time lag from 1–30 days. The use of GPS collars provides a framework for testing hypotheses about the form of contact networks among large mammals and comparing potential direct and indirect contact rates across gradients of ecological factors, such as population density or landscape configuration.     

Synergistic effects of water temperature and dissolved nutrients on litter decomposition and associated fungi

In woodland streams, the decomposition of allochthonous organic matter constitutes a fundamental ecosystem process, where aquatic hyphomycetes play a pivotal role. It is therefore greatly affected by water temperature and nutrient concentrations. The individual effects of these factors on the decomposition of litter have been studied previously. However, in the climate warming scenario predicted for this century, water temperature and nutrient concentrations are expected to increase simultaneously, and their combined effects on litter decomposition and associated biological activity remains unevaluated. In this study, we addressed the individual and combined effects of water temperature (three levels) and nutrient concentrations (two levels) on the decomposition of alder leaves and associated aquatic hyphomycetes in microcosms. Decomposition rates across treatments varied between 0.0041 day^?1 at 5 °C and low nutrient level and 0.0100 day^?1 at 15 °C and high nutrient level. The stimulation of biological variables at high nutrients and temperatures indicates that nutrient enrichment of streams might have a higher stimulatory effect on fungal performance and decomposition rates under a warming scenario than at present. The stimulation of fungal biomass and sporulation with increasing temperature at both nutrient levels shows that increases in water temperature might enhance fungal growth and reproduction in both oligotrophic and eutrophic streams. The stimulation of fungal respiration and litter decomposition with increasing temperature at high nutrients indicates that stimulation of carbon mineralization will probably occur at eutrophied streams, while oligotrophic conditions seem to be ‘protected’ from warming. All biological variables were stimulated when both factors increased, as a result of synergistic interactions between factors. Increased water temperature and nutrient level also affected the structure of aquatic hyphomycete assemblages. It is plausible that if water quality of presently eutrophied streams is improved, the potential stimulatory effects of future increases in water temperature on aquatic biota and processes might be mitigated.     

Convergent evolutionary processes driven by foraging opportunity in two sympatric morph pairs of Arctic charr with contrasting post‐glacial origins

The expression of two or more discrete phenotypes amongst individuals within a species (morphs) provides multiple modes upon which selection can act semi‐independently, and thus may be an important stage in speciation. In the present study, we compared two sympatric morph systems aiming to address hypotheses related to their evolutionary origin. Arctic charr in sympatry in Loch Tay, Scotland, exhibit one of two discrete, alternative body size phenotypes at maturity (large or small body size). Arctic charr in Loch Awe segregate into two temporally segregated spawning groups (breeding in either spring or autumn). Mitochondrial DNA restriction fragment length polymorphism analysis showed that the morph pairs in both lakes comprise separate gene pools, although segregation of the Loch Awe morphs is more subtle than that of Loch Tay. We conclude that the Loch Awe morphs diverged in situ (within the lake), whereas Loch Tay morphs most likely arose through multiple invasions by different ancestral groups that segregated before post‐glacial invasion (i.e. in allopatry). Both morph pairs showed clear trophic segregation between planktonic and benthic resources (measured by stable isotope analysis) but this was significantly less distinct in Loch Tay than in Loch Awe. By contrast, both inter‐morph morphological and life‐history differences were more subtle in Loch Awe than in Loch Tay. The strong ecological but relatively weak morphological and life‐history divergence of the in situ derived morphs compared to morphs with allopatric origins indicates a strong link between early ecological and subsequent genetic divergence of sympatric origin emerging species pairs. The emergence of parallel specialisms despite distinct genetic origins of these morph pairs suggests that the effect of available foraging opportunities may be at least as important as genetic origin in structuring sympatric divergence in post‐glacial fishes with high levels of phenotypic plasticity. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.