Low Endosymbiont Incidence in Drosophila Species Across Peninsula Thailand

Arthropods are known to harbor several endosymbionts, such as Cardinium, Rickettsia, Spiroplasma, and Wolbachia. Wolbachia, for example, are the most widespread known endosymbionts in the world, which are found in about half of all arthropod species. To increase their transmission, these endosymbionts must manipulate their hosts in several ways such as cytoplasmic incompatibility and male killing. In tropical regions, endosymbiont diversity has not been studied exhaustively. Here, we checked four endosymbionts, including Cardinium, Rickettsia, Spiroplasma, and Wolbachia, in eleven Drosophila species found in Thai Peninsula. The Wolbachia strain wRi-like was found in all populations of Drosophila ananassae and Drosophila simulans. Furthermore, we found two new strains, wMalA and wMalB, in two populations of Drosophila malerkotliana. Besides Wolbachia, we did not find any of the above endosymbionts in all fly species. This work reveals the hidden diversity of endosymbionts in Drosophila and is the first exhaustive study on Drosophila in the region.

Cuticular protein genes involve heat acclimation of insect larvae under global warming

Cuticular proteins (CPs) play important roles in insect growth and development. However, it is unknown whether CPs are related to heat tolerance. Cnaphalocrocis medinalis, a serious pest of rice, occurs in summer and exhibits strong adaptability to high temperature, but the underlying mechanism is unclear. Here, the role of CP genes in heat acclimation was studied. Heat tolerance of the heat-acclimated larvae was significantly stronger than the unacclimated larvae. The cuticular protein content in the heat-acclimated larvae was higher than that of the unacclimated larvae. 191 presumed CP genes of C. medinalis (CmCPs) were identified. Expression patterns of 14 CmCPs were different between the heat acclimated (S39) and unacclimated (S27) larvae under heat stress. CmCPs were specifically expressed in epidermis and the head except CmCPR20 mainly expressed in Malpighian tubules. CmCPR20 was upregulated in S39 while downregulated in S27, but CmTweedle1 and CmCPG1 were upregulated in S27 and downregulated in S39. RNAi CmTweedle1 or CmCPG1 remarkably decreased heat tolerance and cuticular protein content of the heat-acclimated larvae but not the unacclimated larvae. RNAi CmCPR20 decreased heat tolerance and cuticular protein content of the unacclimated larvae but not the heat-acclimated larvae. CmTweedle1 and CmCPG1 genes involve heat acclimation of C. medinalis.

Responses to Developmental Temperature Fluctuation in Life History Traits of Five Drosophila Species (Diptera: Drosophilidae) from Different Thermal Niches

Temperature has profound effects on biochemical processes as suggested by the extensive variation in performance of organisms across temperatures. Nonetheless, the use of fluctuating temperature (FT) regimes in laboratory experiments compared to constant temperature (CT) regimes is still mainly applied in studies of model organisms. We investigated how two amplitudes of developmental temperature fluctuation (22.5/27.5 °C and 20/30 °C, 12/12 h) affected several fitness-related traits in five Drosophila species with markedly different thermal resistance. Egg-to-adult viability did not change much with temperature except in the cold-adapted D. immigrans. Developmental time increased with FT among all species compared to the same mean CT. The impact of FT on wing size was quite diverse among species. Whereas wing size decreased quasi-linearly with CT in all species, there were large qualitative differences with FT. Changes in wing aspect ratio due to FT were large compared to the other traits and presumably a consequence of thermal stress. These results demonstrate that species of the same genus but with different thermal resistance can show substantial differences in responses to fluctuating developmental temperatures not predictable by constant developmental temperatures. Testing multiple traits facilitated the interpretation of responses to FT in a broader context.

The various and shared roles of lncRNAs during development

lncRNAs, genes transcribed but not translated, longer than 200 nucleotides, are classified as a separate class of nonprotein coding genes. Since their discovery, largely from RNAseq data, a number of pioneer studies have begun to unravel its myriad functions, centered on gene expression regulation, suggesting developmental and evolutionary conservation. Since they do not code for proteins and have no open reading frames, their functional constraints likely differ from that of protein coding genes, or of genes where the majority of the nucleotide sequence is required for function, like tRNAs. This has complicated assessment of both developmental and evolutionary conservation, and the identification of homologs in different species. Here we argue that other characteristics: general synteny and particular chromosomal placement regardless of sequence, sequence micro-motifs, and secondary structure allow for "homologs" to be identified and compared, confirming developmental and evolutionary conservation of lncRNAs. We conclude exemplifying a case in point: that of the evolutionarily conserved lncRNA acal, characterized and required for embryogenesis in Drosophila.

Plasticity and cross-tolerance to heterogeneous environments: divergent stress responses co-evolved in an African fruit fly

Plastic adjustments of physiological tolerance to a particular stressor can result in fitness benefits for resistance that might manifest not only in that same environment but also be advantageous when faced with alternative environmental stressors, a phenomenon termed 'cross-tolerance'. The nature and magnitude of cross-tolerance responses can provide important insights into the underlying genetic architecture, potential constraints on or versatility of an organism's stress responses. In this study, we tested for cross-tolerance to a suite of abiotic factors that likely contribute to setting insect population dynamics and geographic range limits: heat, cold, desiccation and starvation resistance in adult Ceratitis rosa following acclimation to all these isolated individual conditions prior to stress assays. Traits of stress resistance scored included critical thermal (activity) limits, chill coma recovery time (CCRT), heat knockdown time (HKDT), desiccation and starvation resistance. In agreement with other studies, we found that acclimation to one stress typically increased resistance for that same stress experienced later in life. A more novel outcome, however, is that here we also found substantial evidence for cross-tolerance. For example, we found an improvement in heat tolerance (critical thermal maxima, CT_max ) following starvation or desiccation hardening and improved desiccation resistance following cold acclimation, indicating pronounced cross-tolerance to these environmental stressors for the traits examined. We also found that two different traits of the same stress resistance differed in their responsiveness to the same stress conditions (e.g. HKDT was less cross-resistant than CT_max ). The results of this study have two major implications that are of broader importance: (i) that these traits likely co-evolved to cope with diverse or simultaneous stressors, and (ii) that a set of common underlying physiological mechanisms might exist between apparently divergent stress responses in this species. This species may prove to be a valuable model for future work on the evolutionary and mechanistic basis of cross-tolerance.

Water loss in tree weta (Hemideina): adaptation to the montane environment and a test of the melanisation-desiccation resistance hypothesis

Montane insects are at a higher risk of desiccation than their lowland counterparts and are expected to have evolved reduced water loss. Hemideina spp. (tree weta; Orthoptera: Anostostomatidae) have both lowland (Hemideina femorata, Hemideina crassidens and Hemideina thoracica) and montane (Hemideina maori and Hemideina ricta) species. H. maori has both melanic and yellow morphs. We use these weta to test two hypotheses: that montane insects lose water more slowly than lowland species, and that cuticular water loss rates are lower in darker insects than lighter morphs, because of incorporation of melanin in the cuticle. We used flow-through respirometry to compare water loss rates among Hemideina species and found that montane weta have reduced cuticular water loss by 45%, reduced respiratory water loss by 55% and reduced the molar ratio of V̇H2 O:V̇CO2  by 64% compared with lowland species. Within H. maori, cuticular water loss was reduced by 46% when compared with yellow morphs. Removal of cuticular hydrocarbons significantly increased total water loss in both melanic and yellow morphs, highlighting the role that cuticular hydrocarbons play in limiting water loss; however, the dark morph still lost water more slowly after removal of cuticular hydrocarbons (57% less), supporting the melanisation-desiccation resistance hypothesis.