An organism's fitness is highly dependent on resource quality. The diet of saprobiotic organisms often comprises a variety of microorganisms. Saprophagous Drosophila melanogaster Meigen (Diptera: Drosophilidae) is known to feed on various yeast species, both as larva and adult. The yeasts encountered by the insects may differ in composition and quality, and thus in their influence on larval and adult performance. Our study explores life-history consequences of larval diet on selected larval and adult traits, as well as larval and adult food choice and egg-laying behaviour. The chosen yeast species could be shown to influence several life-history traits of D. melanogaster, such as survival, development time, and adult body weight. Additionally, the amount of yeast biomass initially fed to the larvae significantly influenced development time and adult body weight, whereby the effect depended on the yeast species offered. There were also yeast-specific influences on the measured fitness traits when larvae were reared at different densities. Larvae exhibited a preference for those yeast species that had shown to favour most of the measured life-history traits. Adults, on the other hand, exhibited a different preference. Contrary to our expectation based on the preference-performance hypothesis, female adult flies did not prefer to lay their eggs on substrates inoculated with yeast species that had been shown to favourably influence larval development time. Possible reasons for this seemingly 'bad mother'-behaviour are being discussed.

Nutrition fuels any activity performed by an organism and has been shown to affect its ability to withstand pathogens and parasites. Furthermore, animals over a wide range of taxa have been shown to exhibit a choice of foods and nutrients that are beneficial to their fitness. Saprophagous animals most often feed on microorganisms growing on dead organic matter rather than the organic matter itself. Various yeast species play an important role in both larval and adult nutrition of saprophagous Drosophila melanogaster. We hypothesised the dietary microbial species to affect life‐history traits of D. melanogaster, including the ability to fend offparasitoids, and larvae to prefer to devour those yeast species beneficial to their development and immunocompetence. Particular yeast species known to be associated with D. melanogaster could be shown to have a substantial influence on various larval and adult fitness traits including the ability to encapsulate eggs of the parasitoid wasp Asobara tabida. It also turned out that larvae chose to devour those yeast species which supported their ability to encapsulate parasitoid eggs. Which yeast species was preferred and had a beneficial impact on encapsulation ability, was subject to inter‐individual variability within the investigated population, hinting at the existence of an adaptive heritable variability regarding individual choice and salubriousness of food. The results suggest that the dietary microbial species of saprophagous insects may influence the resistance against parasitoid attacks and thus the outcome of the interaction between a saprophagous host and its parasitoids.

For the coconut crab Birgus latro, Christmas Island in the Indian Ocean may be one of the last retreats where populations of this declining species are not threatened by overharvesting, as on many other mostly tropical Indo-Pacific islands within the species’ wide range. Nevertheless, the population on Christmas Island has experienced severe losses during the past decade owing to habitat destruction and road mortality. To assess the population’s evolutionary potential and identify the number of conservation units, we conducted a combined morphometric and population genetic analysis using microsatellite markers. The findings suggest that the population is genetically diverse and panmictic. Neither genetic nor morphometric analyses revealed any population substructuring. There was no genetic evidence for sex-biased dispersal. Single-sample estimators for the effective population size (Ne) ranged from 492 to infinity, with very wide confidence intervals; they should therefore be viewed with caution. It would be advisable to reanalyse Ne, preferably by temporal methods. Despite mixed results, there is stronger evidence against rather than for the occurrence of a recent genetic bottleneck. So far, the population of B. latro on Christmas Island may be considered as a single conservation management unit, this way simplifying future conservation efforts taken for this magnificent species.