Evaluating proximate causes of longevity in ant queens by RNA-sequencing

Why organisms age and why some species do so at a faster rate than others are fundamental questions in biology. The queens of perennial eusocial insects (ants, honeybees and termites) are extraordinarily long-lived compared with females of solitary insects. Similar to the reproductive females of eusocial mammals, they do not exhibit signs of functional senescence and terminate reproduction only shortly before they die. In contradiction to the widespread fecundity/longevity trade-off, lifespan and reproductive success seem to be positively associated in eusocial animals. Evolutionary theories explain the long lifespan of queens from their low extrinsic mortality. They live in sheltered, often subterraneous nests, and are cared for by the workers. Furthermore, the queens of eusocial insects use the sperm of only one or a few males to fertilize all their eggs. The lifelong pair bond between males and females predicts that both partners benefit from an increased lifespan of the queen. If and how the reproductive females of eusocial insects avoid the costs of reproduction are open questions. In this study, the myrmicine ant Cardiocondyla obscurior served as a model to investigate the regulation of queen longevity on the proximate level. Due to their relative short life expectancy, the survival and lifetime reproductive success of C. obscurior queens could be monitored in the laboratory. This study is the first to report age-related changes in the transcriptome of mature social insect queens and shows that these changes are exactly opposite to what has previously been reported to aging females of fruit flies, Drosophila melanogaster. The results match the opposing reproductive and mortality patterns observed in social and solitary species and provide a first mechanistic explanation for the simultaneous increase of fecundity and longevity in ant queens (chapter 2). The compensation of putative reproductive costs has not been thoroughly investigated in social insect queens. To test the prediction that reproduction competes for energy and nutrients with other processes, ant queens were forced to increase their investment into somatic repair. This experiment provides clear evidence on the phenotypic and transcriptome level that queens reallocate resources between the reproductive and immune systems (chapter 3). The positive effect of mating on queen longevity was addressed in three analyses (chapter 2, 4 and 5). Physiological changes could be identified which are attributable to mating independent of reproduction (chapter 2) and the male type with whom the queen had mated (chapter 4 and 5). In conclusion, this study suggests an alternative regulation of the conserved pathways that mediate the interplay among reproduction, metabolism and longevity. Queens might not avoid the costs of reproduction, but the costs of self-maintenance which are possibly borne by the workers

Molecular phylogeography reveals multiple Pleistocene divergence events in estuarine crabs from the tropical West Pacific

Due to the lack of visible barriers to gene flow, it was a long-standing assumption that marine coastal species are widely distributed, until molecular studies revealed geographically structured intraspecific genetic differentiation in many taxa. Historical events of sea level changes during glacial periods are known to have triggered sequential disjunctions and genetic divergences among populations, especially of coastal organisms. The Parasesarma bidens species complex so far includes three named plus potentially cryptic species of estuarine brachyuran crabs, distributed along East to Southeast Asia. The aim of the present study is to address phylogeography and uncover real and hidden biological diversity within this complex, by revealing the underlying genetic structure of populations and species throughout their distribution ranges from Japan to West Papua, with a comparison of mitochondrial COX1 and 16S rRNA gene sequences. Our results reveal that the P. bidens species complex consists of at least five distinct clades, resulting from four main cladogenesis events during the mid to late Pleistocene. Among those clades, P. cricotum and P. sanguimanus are recovered as monophyletic taxa. Geographically restricted endemic clades are encountered in southeastern Indonesia, Japan and China respectively, whereas the Philippines and Taiwan share two clades. As individuals of the Japanese clade can also be found in Taiwan, we provide evidence of a third lineage and the occurrence of a potential cryptic species on this island. Ocean level retreats during Pleistocene ice ages and present oceanic currents appear to be the main triggers for the divergences of the five clades that are here addressed as the P. bidens complex. Secondary range expansions converted Taiwan into the point of maximal overlap, sharing populations with Japan and the Philippines, but not with mainland China

Mimicking superinfection exclusion disrupts alphavirus infection and transmission in the yellow fever mosquito Aedes aegypti

Multiple viruses, including pathogenic viruses, bacteriophages, and even plant viruses, cause a phenomenon termed superinfection exclusion whereby a currently infected cell is resistant to secondary infection by the same or a closely related virus. In alphaviruses, this process is thought to be mediated, at least in part, by the viral protease (nsP2) which is responsible for processing the nonstructural polyproteins (P123 and P1234) into individual proteins (nsP1–nsP4), forming the viral replication complex. Taking a synthetic biology approach, we mimicked this naturally occurring phenomenon by generating a superinfection exclusion-like state in Aedes aegypti mosquitoes, rendering them refractory to alphavirus infection. By artificially expressing Sindbis virus (SINV) and chikungunya virus (CHIKV) nsP2 in mosquito cells and transgenic mosquitoes, we demonstrated a reduction in both SINV and CHIKV viral replication rates in cells following viral infection as well as reduced infection prevalence, viral titers, and transmission potential in mosquitoes.</p

Transcriptomic response to injury sheds light on the physiological costs of reproduction in ant queens

The trade-off between reproduction and longevity is widespread among multicellular organisms. As an important exception, the reproductive females of perennial social insects (ants, honeybees, termites) are simultaneously highly fertile and very long-lived relative to their nonreproductive nestmates. The observation that increased fecundity is not coupled with decreased lifespan suggests that social insect queens do not have to reallocate resources between reproduction and self-maintenance. If queens have to compensate for the costs of reproduction on the level of the individual, the activation of other energy-demanding physiological processes might force them to reduce the production of eggs. To test this hypothesis in ant queens, we increased immunity costs by injury and measured the effect of this treatment on egg-laying rates and genomewide gene expression. Amputation of both middle legs led to a temporary decrease in egg-laying rates and affected the expression of 947 genes corresponding to 9% of the transcriptome. The changes comprised the upregulation of the immune and wound healing response on the one hand, and the downregulation of germ cell development, central nervous system development and learning ability on the other hand. Injury strongly influenced metabolism by inducing catabolism and repressing amino acid and nitrogen compound metabolism. By comparing our results to similar transcriptomic studies in insects, we found a highly consistent upregulation of immune genes due to sterile and septic wounding. The gene expression changes, complemented by the temporary decline of egg-laying rates, clearly reveal a trade-off between reproduction and the immune response in social insect queens

Cross_species_comparisons

Cross-species comparison matrix (Camponotus & Drosophila studies

Fecundity

Egg counts from RNA-seq queens and queens which were monitored for 4 week

RNA-seq

Gene counts and DESeq2 analysis resul

Script_RNA-seq

R script for RNA-seq analysi