Investigating the role of enemies in temporal dynamics: Differential sensitivity, competition and stable coexistence

The impact of herbivores and other pests on plants varies greatly from year to year. Here we develop an analytical model of a temporal niche dynamic as a tool to examine how natural fluctuations in pest (enemy) levels may determine coexistence in competing annual plant species when one but not the other is affected by the pest. We show that the probability and speed with which the resistant drives out the sensitive species, coexists with it, or is driven out by its sensitive competitor depends on the cost of pest-resistance to the unaffected species, the frequency of high pest levels in the habitat and the competitive advantage of the sensitive species when the pest is not actively present. The interaction is regulated primarily by pest impact on relative seedling survival of the two, with relative yield per capita of seeds viable into the following season (effective fecundity) the next most vulnerable life-cycle stage.     

Changes in the functional efficiency of flight muscle sarcosomes during heat death of adult Calliphora erythrocephala

The temperature sensitivity of flight muscle mitochondria from adult Calliphora erythrocephala has been studied. Intact flies were treated to sublethal and lethal high temperatures, their sarcosomes were isolated and the efficiency of the coupling of oxidation and phosphorylation was measured. The temperature sensitivity of sarcosomes is correlated with the heat death point of the intact animal and the impairment of oxidative phosphorylation with α-glycerophosphate suggests that a breakdown in ATP synthesis may be one of the causes of heat death. Restitution of enzyme activity was observed in mitochondria isolated from flies recovering from sublethal heat treatment. The results suggest that the impairment of membrane-enzyme complexes may be important lesions in heat death.     

Correlates of substitution rate variation in mammalian protein-coding sequences

Background  

Rates of molecular evolution in different lineages can vary widely, and some of this variation might be predictable from aspects of species' biology. Investigating such predictable rate variation can help us to understand the causes of molecular evolution, and could also help to improve molecular dating methods. Here we present a comprehensive study of the life history correlates of substitution rate variation across the mammals, comparing results for mitochondrial and nuclear loci, and for synonymous and non-synonymous sites. We use phylogenetic comparative methods, refined to take into account the special nature of substitution rate data. Particular attention is paid to the widespread correlations between the components of mammalian life history, which can complicate the interpretation of results.