摘要: Eusocial insects display a caste system in which different castes are morphologically and physiologically specialized for different tasks. Recent studies have revealed that epigenetic modifications, including DNA methylation and histone modification, mediate caste determination and differentiation, longevity, and polyethism in eusocial insects. Although there has been a growing interest in the relationship between epigenetic mechanisms and phenotypic plasticity in termites, there is little information about differential expression levels among castes and expression sites for these genes in termites. Here we show royal-tissue-specific expression of epigenetic modification genes in the termite Reticulitermes speratus. Using RNA-seq, we identified 74 genes, including three DNA methyltransferases, seven sirtuins, 48 Trithorax group proteins, and 16 Polycomb group proteins. Among these genes, 15 showed king-specific expression, and 52 showed age-dependent differential expression in kings and queens. Quantitative real-time PCR revealed that DNA methyltransferase 3 is expressed specifically in the king's testis and fat body, whereas some histone modification genes are remarkably expressed in the king's testis and queen's ovary. These findings imply that epigenetic modification plays important roles in the gamete production process in termite kings and queens.

摘要: Environmental cues, mainly photoperiod and temperature, are known to control female adult reproductive diapause in several insect species. Diapause enhances female survival during adverse conditions and postpones progeny production to the favorable season. Male diapause (a reversible inability to inseminate receptive females) has been studied much less than female diapause. However, if the males maximized their chances to fertilize females while minimizing their energy expenditure, they would be expected to be in diapause at the same time as females. We investigated Drosophila montana male mating behavior under short-day conditions that induce diapause in females and found the males to be reproductively inactive. We also found that males reared under long-day conditions (reproducing individuals) court reproducing postdiapause females, but not diapausing ones. The diapausing flies of both sexes had more long-chain and less short-chain hydrocarbons on their cuticle than the reproducing ones, which presumably increase their survival under stressful conditions, but at the same time decrease their attractiveness. Our study shows that the mating behavior of females and males is well coordinated during and after overwintering and it also gives support to the dual role of insect cuticular hydrocarbons in adaptation and mate choice.

摘要: Seminal gifts range from important material donations to items that provide little direct benefit to females. Promiscuous, female silk corn flies Euxesta eluta expel and consume male ejaculates immediately after mating. The evolution and function of this peculiar behavior are currently unknown. We performed a series of experiments aimed to: determine if females under different dietary regimes derive nutrients or water for survival and/or reproduction from ejaculate consumption, if males suffer a fitness cost from supplying females with ejaculates, and if females prefer to mate and/or are more likely to store sperm from well fed than nutritionally stressed presumably inferior males. Experiments revealed that protein deprived E. eluta females derive nutrients for ovarian development through consumption of ejaculates of protein fed males. No seminal products affecting survival appear to be transferred in the consumed ejaculate. However, ovarian development, in contrast to testes growth, occurs in detriment of longevity. Females preferred to mate with protein fed males, yet sperm retention in spermathecae was extremely rare after a single mating. This finding suggests that females could be exerting post copulatory control. A key question that remained to be addressed for the understanding of this puzzling and promiscuous mating system is what ecological factors or male traits drive females to retain sperm from one or several males in order to achieve and/or maximize fertilization potential.

摘要: The geomagnetic field (GMF) is an environmental cue that provides directional information for animals. The intensity of GMF is varied over space and time. Variations in the GMF intensity affect the navigation of animals and their physiology. In this study, the phototaxis of the migratory insect rice planthopper Nilaparvata lugens (N. lugens) and frataxin in N. lugens (Nl-fh), which is a mitochondrial protein required for cellular iron homeostasis and iron-sulfur cluster assembly, were investigated by using different intensities of magnetic field. From the results, individuals of N. lugens showed decreased phototaxis when reared and tested in a behavioral arena under a strong magnetic field. Besides the reduction in performance, an accompanying effect of the strong magnetic field condition was a reduced level of Nl-fh-messenger RNA, and a Nl-fh knockdown indeed impaired the phototactic behavior in a tested sample of insects. This leads to the conclusion that the expression of frataxin is dependent on the strength of the surrounding magnetic field and that functional frataxin facilitates phototactic behavior in N. lugens.

摘要: The majority of adult parasitoid wasps are unable to synthesize lipids and therefore face a trade-off between the investment of lipids in eggs or in the maintenance of soma. It has been shown that resource allocation should depend on body size in parasitoids. Given that smaller females have shorter expected life times, they should concentrate their reproductive effort into early life. To test this prediction, we investigated the relationship between body size and the timing of egg production in parasitoids. We measured body size, lipid reserves, and reproductive investment (number of eggs, ovigeny index equivalent [OIE] and egg size) at eclosion in five species of Asobara (Hymenoptera: Braconidae) originating from different geographic and climatic environments. Our results show significant interspecific variation in all these traits. A diagnostic test for phylogenetic independence revealed that closely related species did not resemble each other more closely than expected by chance for all traits measured. Lipid reserves scaled positively with body size both between and within species. In agreement with theory, OI correlated negatively with body size both between and within species. Total egg area at eclosion correlated negatively with lipid reserves both between and within species. This indicates the existence of a trade-off between allocation of lipids to current reproduction and survival/future reproduction. With the exception of the most extreme pro-ovigenic species, A. persimilis, we found that pro-ovigeny was compensated for by small egg size. Our results indicate the role of habitats in shaping interspecific variation in resource allocation strategies.