The ability of sensitive rainforest species to evolve in response to climate change is largely unknown. We show that the Australian tropical rainforest fly Drosophila birchii exhibits clinal variation in desiccation resistance, but the most resistant population lacks the ability to evolve further resistance even after intense selection for over 30 generations. Parent-offspring comparisons indicate low heritable variation for this trait but high levels of genetic variation for morphology. D. birchii also exhibits abundant genetic variation at microsatellite loci. The low potential for resistance evolution highlights the importance of assessing evolutionary potential in targeted ecological traits and species from threatened habitats.

Clines for size and stress resistance traits have been described for several Drosophila species and replicable clines across different species may indicate climatic selection. Here we consider clines in stress resistance traits in an Australian endemic species, D. serrata, by comparing levels of variation within and among isofemale lines initiated with flies collected from the eastern coast of Australia. We also consider clinical variation in chill coma recovery, a trait that has recently been shown to exhibit high levels of variation among Drosophila species. Patterns were compared with those in the cosmopolitan species D. melanogaster from the same area. Both desiccation and starvation resistance showed no clinical pattern despite heritable variation among isofemale lines. In contrast chill coma resistance exhibited a linear cline in the anticipated direction, resistance increasing with latitude. Body size was measured as wing length and body weight. Both traits showed geographic variation and strong non-linear clines with a sharp reduction in size in the tropics. These results are discussed in the context of climatic selection and evolutionary processes limiting species borders.

Clinal variation has been described in many invertebrates including drosophilids but usually over broad geographical gradients. Here we describe clinal variation in the rainforest species Drosophila birchii from Queensland, Australia, and potential confounding effects of laboratory adaptation. Clinal variation was detected for starvation and development time, but not for size or resistance to temperature extremes. Starvation resistance was higher at southern locations. Wing shape components were not associated with latitude although they did differ among populations. Time in laboratory culture did not influence wing size or heat knockdown resistance, but increased starvation resistance and decreased recovery time following a cold shock. Laboratory culture also increased development time and altered wing shape. The results indicate that clinal patterns can be detected in Drosophila over a relatively narrow geographical area. Laboratory adaptation is unlikely to have confounded the detection of geographical patterns.

The wheat curl mite (WCM), Aceria tosichella Keifer, is an eriophyoid pest of cereals, and the vector responsible for transmitting wheat streak mosaic virus. Several authors have suggested cryptic species of this mite identified through morphological variation, but this has never been conclusively demonstrated. Here, we use the mitochondrial 16S rRNA gene and two nuclear markers (internal transcribed spacer 1 and adenine nucleotide translocase) to show that WCM from Australia consists of at least two separate lineages that may represent putative species. In our study, both WCM variants were widespread and the only eriophyoids found on wheat varieties. The WCM variants were also found on alternate host plants, including some plants not known to host WCM. These results have implications for the control of this pest within Australian cereal crops.

Wolbachia infections have been described in several Drosophila species but relatively few have been assessed for phenotypic effects. Cytoplasmic incompatibility (CI) is the most common phenotypic effect that has been detected, while some infections cause male killing or feminization, and many Wolbachia infections have few host effects. Here we describe two new infections in a recently described species, D. pandora, one of which causes near-complete CI and near-perfect maternal transmission (the “CI” strain). The other infection is a male killer (the “MK” strain), which we confirm by observing re-initiation of male production following tetracycline treatment. No incompatibility was detected in crosses between CI strain males and MK strain females, and rare MK males do not cause CI. Molecular analyses indicate that the CI and MK infections are distantly related and the CI infection is closely related to the wRi infection of D. simulans. Two population surveys indicate that all individuals are infected with Wolbachia, but the MK infection is uncommon. Given patterns of incompatibility among the strains, the infection dynamics is expected to be governed by the relative fitness of the females, suggesting that the CI infection should have a higher fitness. This was evidenced by changes in infection frequencies and sex ratios in population cages initiated at different starting frequencies of the infections.

The analysis of interaction networks across spatial environmental gradients is a powerful approach to investigate the responses of communities to global change. Using a combination of DNA metabarcoding and traditional molecular methods we built bipartite Drosophila – parasitoid food webs from six Australian rainforest sites across gradients spanning 850 m in elevation and 5°C in mean temperature. Our cost‐effective hierarchical approach to network reconstruction separated the determination of host frequencies from the detection and quantification of interactions. The food webs comprised 5–9 host and 5–11 parasitoid species at each site, and showed a lower incidence of parasitism at high elevation. Despite considerable turnover in the relative abundance of host Drosophila species, and contrary to some previous results, we did not detect significant changes to fundamental metrics of network structure including nestedness and specialisation with elevation. Advances in community ecology depend on data from a combination of methodological approaches. It is therefore especially valuable to develop model study systems for sets of closely‐interacting species that are diverse enough to be representative, yet still amenable to field and laboratory experiments.

Wolbachia bacteria are common insect endosymbionts transmitted maternally and capable of spreading through insect populations by cytoplasmic incompatibility (CI) when infected males cause embryo death after mating with uninfected females. Selection in the Wolbachia endosymbiont occurs on female hosts and is expected to favour strong maternal transmission to female offspring, even at the cost of reduced CI. With maternal leakage, nuclear genes are expected to be selected to suppress cytoplasmic incompatibility caused by males while also reducing any deleterious effects associated with the infection. Here we describe a new type of Wolbachia strain from Drosophila pseudotakahashii likely to have arisen from evolutionary processes on host and/or Wolbachia genomes. This strain is often absent from adult male offspring, but always transmitted to females. It leads to males with low or non-detectable Wolbachia that nevertheless show CI. When detected in adult males, the infection has a low density relative to that in females, a phenomenon not previously seen in Wolbachia infections of Drosophila. This Wolbachia strain is common in natural populations, and shows reduced CI when older (infected) males are crossed. These patterns highlight that endosymbionts can have strong sex-specific effects and that high frequency Wolbachia strains persist through effects on female reproduction. Female-limited Wolbachia infections may be of applied interest if the low level of Wolbachia in males reduces deleterious fitness effects on the host.

No abstract