The effect of Wolbachia on diapause, fecundity, and clock gene expression in Trichogramma brassicae (Hymenoptera: Trichogrammatidae)

Common Ground between Biological Rhythms and Forensics

Simple Summary

Biological clocks regulate the timing of numerous body functions in adaption to daily repeating cycles in the environment, such as the sleep–wake phases that are trained by the cycling changes of night and day light. The identification of a deceased victim is a critical component in a forensic investigation, but it can be significantly hampered by the condition of the dead body and the lack of personal records and documents. This review links current knowledge on the molecular mechanisms of biological rhythms to forensically relevant aspects, including the time period since death, cause of death, the use of insects for forensics, sex and age of a person, ethnic background and development. Putting these findings in context demonstrates how the analysis of molecular clock analysis could be used as tool for future personal identification in forensic investigations.

Abstract

Biological clocks set the timing for a large number of essential processes in the living human organism. After death, scientific evidence is required in forensic investigations in order to collect as much information as possible on the death circumstances and personal identifiers of the deceased victim. We summarize the associations between the molecular mechanisms of biological rhythms and forensically relevant aspects, including post-mortem interval and cause of death, entomological findings, sex, age, ethnicity and development. Given their importance during lifetime, biological rhythms could be potential tools to draw conclusions on the death circumstances and the identity of a deceased person by mechanistic investigations of the different biological clocks in a forensic context. This review puts the known effects of biological rhythms on the functions of the human organism in context with potential applications in forensic fields of interest, such as personal identification, entomology as well as the determination of the post-mortem interval and cause of death.

Endosymbionts Reduce Microbiome Diversity and Modify Host Metabolism and Fecundity in the Planthopper Sogatella furcifera

Endosymbionts can strongly affect bacterial microbiota in pests. The white-backed planthopper Sogatella furcifera, a notorious pest in rice, is usually co-infected with Cardinium and Wolbachia, but the effects of these endosymbionts together or individually on the host microbiome and fecundity are unclear. Here, we established three S. furcifera lines (Cardinium and Wolbachia double-infected, Cardinium single-infected, and both-uninfected lines) backcrossed to a common nuclear background and found that single and double infections reduced bacterial diversity and changed bacterial community structure across nymph and adult stages and across adult tissues. The endosymbionts differed in densities between adults and nymphs as well as across adult tissues, with the distribution of Cardinium affected by Wolbachia. Both the single infection and particularly the double infection reduced host fecundity. Lines also differed in levels of metabolites, some of which may influence fecundity (e.g., arginine biosynthesis and nicotinamide metabolism). Cardinium in the single-infected line upregulated metabolic levels, while Wolbachia in the double-infected line appeared to mainly downregulate them. Association analysis pointed to possible connections between various bacteria and differential metabolites. These results reveal that Cardinium by itself and in combination with Wolbachia affect bacterial microbiota and levels of metabolites, with likely effects on host fecundity. Many of the effects of these metabolically limited endosymbionts that are dependent on the hosts may be exerted through manipulation of the microbiome.

IMPORTANCE Endosymbionts can profoundly affect the nutrition, immunity, development, and reproduction of insect hosts, but the effects of multiple endosymbiont infections on microbiota and the interaction of these effects with insect host fitness are not well known. By establishing S. furcifera lines with different endosymbiont infection status, we found that Cardinium and the combined Cardinium + Wolbachia infections differentially reduced bacterial diversity as well as changing bacterial community structure and affecting metabolism, which may connect to negative fitness effects of the endosymbionts on their host. These results established the connections between reduced bacterial diversity, decreased fecundity and metabolic responses in S. furcifera.

Effects of Thelytokous Parthenogenesis-Inducing Wolbachia on the Fitness of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) in Superparasitised and Single-Parasitised Hosts

Thelytokous Wolbachia-infected Trichogramma species have long been considered as biological control agents against lepidopteran pests in agriculture and forestry. Wolbachia has been suggested to increase the probability of the superparasitism of Trichogramma, but the fate of infected offspring in the superparasitised host is still unknown. The present study aimed to evaluate the fitness of thelytokous Wolbachia-infected (TDW) and bisexual Wolbachia-free (TD) Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) lines in superparasitised or single-parasitised hosts. The results showed that irrespective of whether Trichogramma wasps were developed from superparasitised or single-parasitised hosts, the TDW line was characterized by reduced fitness, including lower fecundity, shorter longevity, and smaller body size of F1 offspring, and lower emergence rate of F2 offspring than the TD line. This was not true for the survival rate and developmental time of F1 offspring. Additionally, the fitness parameters of T. dendrolimi that developed from superparasitised hosts were lower compared with that of T. dendrolimi that developed from single-parasitised hosts. Interestingly, Wolbachia-infected females had higher dispersal capacity than bisexual females when they developed from superparasitised hosts. The results indicated that Wolbachia negatively affects fitness of T. dendrolimi, but enhance dispersal capacity of T. dendrolimi females in superparasitism condition. Further studies need to be carried out to select the best line that will allow Wolbachia and their host Trichogramma to be better adapted to one another.

Animal-Microbe Interactions in the Context of Diapause

Dormancy and diapause are key adaptations in many organisms, enabling survival of temporarily or seasonally unsuitable environmental conditions. In this review, we examine how our understanding of programmed developmental and metabolic arrest during diapause intersects with the increasing body of knowledge about animal co-development and co-evolution with microorganisms. Host-microbe interactions are increasingly understood to affect a number of metabolic, physiological, developmental, and behavioral traits and to mediate adaptations to various environments. Therefore, it is timely to consider how microbial factors might affect the expression and evolution of diapause in a changing world. We examine how a range of host-microbe interactions, from pathogenic to mutualistic, may have an impact on diapause phenotypes. Conversely, we examine how the discontinuities that diapause introduces into animal host generations can affect the ecology of microbial communities and the evolution of host-microbe interactions. We discuss these issues as they relate to physiology, evolution of development, local adaptation, disease ecology, and environmental change. Finally, we outline research questions that bridge the historically distinct fields of seasonal ecology and host-microbe interactions.

Identification of Wolbachia-Responsive miRNAs in the Small Brown Planthopper, Laodelphax striatellus

Laodelphax striatellus is naturally infected with the Wolbachia strain wStri, which induces strong cytoplasmic incompatibility of its host. MicroRNAs (miRNAs) are a class of endogenous non-coding small RNAs that play a critical role in the regulation of gene expression at post-transcriptional level in various biological processes. Despite various studies reporting that Wolbachia affects the miRNA expression of their hosts, the molecular mechanism underlying interactions between Wolbachia and their host miRNAs has not been well understood. In order to better understand the impact of Wolbachia infection on its host, we investigated the differentially expressed miRNAs between Wolbachia-infected and Wolbachia-uninfected strains of L. striatellus. Compared with uninfected strains, Wolbachia infection resulted in up-regulation of 18 miRNAs and down-regulation of 6 miRNAs in male, while 25 miRNAs were up-regulated and 15 miRNAs were down-regulated in female. The target genes of these differentially expressed miRNAs involved in immune response regulation, reproduction, redox homeostasis and ecdysteroidogenesis were also annotated in both sexes. We further verified the expression of several significantly differentially expressed miRNAs and their predicted target genes by qRT-PCR method. The results suggested that Wolbachia appears to reduce the expression of genes related to fertility in males and increase the expression of genes related to fecundity in females. At the same time, Wolbachia may enhance the expression of immune-related genes in both sexes. All of the results in this study may be helpful in further exploration of the molecular mechanisms by which Wolbachia affects on its hosts.

Abiotic and biotic factors influence diapause induction in sexual and asexual strains of Trichogramma brassicae (Hym: Trichogrammatidae)

The effects of some abiotic (maternal photoperiod and offspring developmental temperature) and biotic (host quality during both maternal and offspring generations) factors on diapause induction were investigated for two sympatric strains of Trichogramma brassicae Bezdenko (Hym: Trichogrammatidae) differing by infection status with regard to Wolbachia. The mode of reproduction, developmental temperature, maternal photoperiod and the quality of the host significantly affected diapause induction. The highest percentage of diapausing individuals were observed with the sexual strain reared at 14 °C using a “high quality” host and after a long photophase during the maternal generation. Environment-by-Environment, as well as Genotype-by-Environment interactions, was observed. All these patterns were discussed with the goal of providing relevant protocols for the commercial mass-rearing of such biocontrol agents. A successful diapause in beneficial insects could affect the efficiency of mass rearing by increasing the duration of storage conditions based on a high percent emergence and providing a large number of individuals at the appropriate time in the field season.