Genetic variability in the diapause response of the burnet moth Zygaena trifolii (Lepidoptera: Zygaenidae)

Genetic regulation of diapause and associated traits in Chilo partellus (Swinhoe)

Diapause is an endocrine controlled arrested metabolic state to delay development or reproduction under unfavorable conditions. To gain an understanding of importance of diapause for ecological adaptation, it is important to study regulation of diapause in insects. We examined genetics of diapause in Chilo partellus by crossing the hibernating (HD), aestivating (AD), post-hibernating (PHD), post-aestivating (PAD), and nondiapause (ND) strains. Reciprocal crosses were also made to gain full understanding of diapause regulation and the maternal effects, if any. Data were recorded on fecundity, egg hatching, larval survival, diapause induction and termination, adult emergence, and morphometrics of larvae, pupae and adults in the parents (P₁, P₂), F₁ hybrids, and the reciprocal crosses. Genetic analysis showed that AD strain is general combiner, which also improved egg hatching, larval survival, diapause termination, adult emergence and proportion of females in the progenies. Incidence of diapause was highest in HD × AD, whereas termination was greatest in PHD × AD. However, ND strain and its reciprocal crosses with other strains did not exhibit any noticeable developmental response associated with diapause. Specific combining ability analysis suggested that where PHD and AD strains exist together there will be likely reduction in diapause incidence, increased survival with greater fitness and faster multiplication of their progenies resulting in outbreak of C. partellus. Degree of dominance estimates revealed that diapause, developmental and morphometric traits in C. partellus are governed by over dominance gene effects, and mainly depend on parental diapause history.

Trans-generational Immune Priming in Invertebrates: Current Knowledge and Future Prospects

Trans-generational immune priming (TGIP) refers to the transfer of the parental immunological experience to its progeny. This may result in offspring protection from repeated encounters with pathogens that persist across generations. Although extensively studied in vertebrates for over a century, this phenomenon has only been identified 20 years ago in invertebrates. Since then, invertebrate TGIP has been the focus of an increasing interest, with half of studies published during the last few years. TGIP has now been tested in several invertebrate systems using various experimental approaches and measures to study it at both functional and evolutionary levels. However, drawing an overall picture of TGIP from available studies still appears to be a difficult task. Here, we provide a comprehensive review of TGIP in invertebrates with the objective of confronting all the data generated to date to highlight the main features and mechanisms identified in the context of its ecology and evolution. To this purpose, we describe all the articles reporting experimental investigation of TGIP in invertebrates and propose a critical analysis of the experimental procedures performed to study this phenomenon. We then investigate the outcome of TGIP in the offspring and its ecological and evolutionary relevance before reviewing the potential molecular mechanisms identified to date. In the light of this review, we build hypothetical scenarios of the mechanisms through which TGIP might be achieved and propose guidelines for future investigations.

Direct and correlated responses to bi-directional selection on pre-adult development time in Drosophila montana

Selection experiments offer an efficient way to study the evolvability of traits that play an important role in insects' reproduction and/or survival and to trace correlations and trade-offs between them. We have exercised bi-directional selection on Drosophila montana flies' pre-adult development time under constant light and temperature conditions for 10 generations and traced the indirect effects of this selection on females' diapause induction under different day lengths, as well as on the body weight and cold tolerance of both sexes. Overall, selection was successful towards slow, but not towards fast development. However, all fast selection line replicates showed at the end of selection increased variance in females' photoperiodic diapause response and about one hour increase in the critical day (CDL), where more than 50% of emerging females enter diapause. Indirect effects of selection on flies' body weight and cold-tolerance were less clear, as the flies of the slow selection line were significantly heavier and less cold-tolerant than the control line flies after five generations of selection, but lighter and more cold-tolerant at the end of selection. Changes in females' diapause induction resulting from selection for fast development could be due to common metabolic pathways underlying these traits, collaboration of circadian clock and photoperiodic timer and/or by the interaction between the endocrine and circadian systems.

Examination of parental effect on the progeny diapause by reciprocal cross test in the cabbage beetle, Colaphellus bowringi

The cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), a serious pest of crucifers in China, undergoes summer or winter diapause in the soil as an adult. In the present study, the incidence of diapause were measured in reciprocal crosses between a high-diapause strain (HD strain) and a laboratory-selected nondiapausing strain (ND strain) under different photoperiods and temperatures, to explore parental influences on the progeny diapause. Sensitivity to photoperiod in the selected nondiapausing strain was nearly eliminated at 25 °C, whereas sensitivity to temperature of the selected nondiapausing strain was retained under continuous darkness at 20 and 22 °C. Reciprocal crosses between the HD strain and the ND strain showed that the incidence of diapause in the progeny was always intermediate to that of the parents under different photoperiods and temperatures, suggesting that diapause induction was determined by both female and male parents. There was a significant effect of temperature; temperature interacted with reciprocal cross on diapause induction, whereas no significant effect of reciprocal cross was demonstrated. The incidence of diapause in ♀(ND) × ♂(HD) was the same as in ♀(HD) × ♂(ND) under continuous darkness at 18 °C (100%) and 26 °C (0%), but the former was higher than that in ♀(HD) × ♂(ND) under continuous darkness at 22 °C, suggesting that female parent does not exhibit strong influence on the diapause response to temperature. There was a significant effect of photoperiod and reciprocal cross on diapause induction, whereas no significant interactive effect on diapause induction was demonstrated. Incidence of diapause in ♀(HD) × ♂(ND) was always higher than in ♀(ND) × ♂(HD) at 25 °C and 12:12 L:D, 14:10 L:D, and 16:8 L:D, suggesting a strong maternal influence on the diapause response to photoperiod, though a significant difference was observed only at 14:10 L:D. Our results support the idea that diapause induction is determined by both female and male parents. However, results also indicated that a strong maternal influence on diapause was exhibited only in response to photoperiod.

Dominant and recessive inheritance patterns of diapause in the two-spotted spider mite Tetranychus urticae

In this study, we investigated the diapause incidence in 3 geographic strains of the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae). Under diapause-inducing conditions of 12:12 light:dark at 15 degrees C, the diapause incidence was nearly 100% in a strain from northern Japan (Sapporo), whereas it was nearly 0% in 2 strains from southern Japan (Itoman and Takanabe). Reciprocal crosses clearly showed that the nondiapause phenotype is inherited in a completely dominant manner, and no maternal effect was detected. Backcrosses to the Itoman and Takanabe strains suggested that dominant nondiapause alleles control the nondiapause phenotype. To clarify the genetic basis of nondiapause in the northern population, we also established a nondiapausing variant ("selected nondiapause" abbreviated as snd) from the Sapporo strain. Crossing experiments revealed that a single recessive allele is responsible for the nondiapause phenotype. Thus, both dominant and recessive inheritance patterns of diapause were detected in the T. urticae populations studied here.

Development times under long- and short-day conditions in the Kanzawa spider mite Tetranychus kanzawai (Acari: Tetranychidae)

In a theoretical framework, the development time of arthropods is closely associated with population growth, so that strong selection pressure may be imposed on development patterns. In this context, selection towards shorter development times may act on female mites in the season when population size is growing. In contrast, such selective pressure may be weaker just before hibernation, because the stage adjustment may be more important than population growth in such seasons. Thus, selection to shorten development times may act more strongly in long daylength conditions, so that different developmental responses among the seasons (reaction norm) may evolve. I predicted that the development time is shorter under the long-day conditions of population-growing seasons than under the short-day conditions of hibernating seasons, and that genetic variation at the long-day is smaller than that at the short-day. In order to test this prediction, the egg-to-adult development time of a population of Tetranychus kanzawai (Acari: Tetranychidae) was investigated under short (9L:15D) and long (15L:9D) daylength conditions at 18 degrees C. In addition, genetic variation in female development times under these conditions was estimated by using half-sib design. The development time of females at short day was 1 day longer than at long day under the experimental conditions. Male development times follow the pattern of females with <1 day delay. However, heritabilities under these two treatments were quite low and neither was significant. Thus, only the first prediction was supported by the results. In addition, maternal and/or non-additive effects in the female development time were highly significant under both daylength conditions examined.