Article

The molecular physiology of increased egg desiccation resistance during diapause in the invasive mosquito, Aedes albopictus

Department of Biology, Georgetown University, 37th and O Sts. NW, Washington, DC 20057, USA.
Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.29). 09/2010; 277(1694):2683-92. DOI: 10.1098/rspb.2010.0362
Source: PubMed

ABSTRACT Photoperiodic diapause is a crucial adaptation to seasonal environmental variation in a wide range of arthropods, but relatively little is known regarding the molecular basis of this important trait. In temperate populations of the mosquito Aedes albopictus, exposure to short-day (SD) lengths causes the female to produce diapause eggs. Tropical populations do not undergo a photoperiodic diapause. We identified a fatty acyl coA elongase transcript that is more abundant under SD versus long-day (LD) photoperiods in mature oocyte tissue of replicate temperate, but not tropical, A. albopictus populations. Fatty acyl CoA elongases are involved in the synthesis of long chain fatty acids (hydrocarbon precursors). Diapause eggs from a temperate population had one-third more surface hydrocarbons and one-half the water loss rates of non-diapause eggs. Eggs from a tropical population reared under SD and LD photoperiods did not differ in surface hydrocarbon abundance or water loss rates. In both a temperate and tropical population, composition of hydrocarbon chain lengths did not differ between eggs from SD versus LD conditions. These results implicate the expression of fatty acyl coA elongase and changes in quantity, but not composition, of egg surface hydrocarbons as important components of increased desiccation resistance during diapause in A. albopictus.

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    • "It is unclear how these interspecific observations could be verified inside a species. No modulation of desiccation resistance was observed in eggs of a tropical strain of Kuala Lumpur, Malaysia, reared under different photoperiodic conditions (Urbanski et al., 2010a). Photoperiodic rearing conditions don't modify maternal wing length; consequently we dismiss a possible indirect effect of maternal size on eggs volume. "
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    ABSTRACT: The diapause of Aedes albopictus is maternally induced by photoperiod and initiates at the pharate larvae stage in eggs. This pre-diapause results in enhanced survival eggs during the winter. This study aims to disentangle the effects of photoperiod and diapause on embryonic developmental time and egg size in A. albopictus. A temperate strain capable to perform diapause and a tropical strain unable of diapause were reared at 21 °C with long-(LD) and short-day (SD) lengths. Four distinct traits were studied on embryos and eggs were measured at the end of embryogenesis. The chronologies of embryo development for both strains were influenced by maternal photoperiod, especially in the temperate strain in which the development of SD eggs took longer than LD eggs. The delay increased gradually in the temperate strain, and reached up to 38 h at the end of embryogenesis. The kinetics of embryogenesis differed among the temperate and the tropical strains, each one of the 4 studied traits showing differences. For example the serosal cuticle was secreted precociously in the tropical strain. Egg width and volume are influenced by the maternal photoperiod and the strain × photoperiod interaction. For both strains, larger eggs were laid by female reared under SD when compared to LD. The influence of several maternal effects was demonstrated in this study. The diapause process modifies greatly the length of embryogenesis in the temperate strain, whereas the maternal photoperiod has a direct influence on egg size and embryogenesis regardless of the strain considered. These findings provide useful data on chronology of embryonic development for integrative biology studies of egg pre-diapause stages.
    Journal of Insect Physiology 10/2014; 71:87-96. DOI:10.1016/j.jinsphys.2014.10.008 · 2.50 Impact Factor
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    • "Both species lack inducible egg immunity and develop on ephemeral resources that favour rapid development times [15,17,45], and specifically rapid embryonic development. Embryonic development in Nicrophorus is approximately 3–6 times faster than Tribolium and Manduca [46,47], and about 20 hours faster than Aedes, which are known to go into diapause, meaning they have to survive for a long time until the conditions favour hatching [48]. By contrast, Nicrophorus develop in the presence of a highly valuable and decaying resource; individuals need to hatch, feed and disperse before the carcass is either claimed by another animal or becomes unsuitable for development. "
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    ABSTRACT: Background Nicrophorus vespilloides eggs are deposited into the soil in close proximity to the decomposing vertebrate carcasses that these insects use as an obligate resource to rear their offspring. Eggs in this environment potentially face significant risks from the bacteria that proliferate in the grave-soil environment following nutrient influx from the decomposing carcass. Our aims in this paper are twofold: first, to examine the fitness effects of grave-soil bacteria to eggs, and second, to quantify egg immunocompetence as a defence against these bacteria.ResultsOur results provide strong evidence that grave-soil microbes significantly reduce the survival of Nicrophorus eggs. Females provided with microbe rich carcasses to rear broods laid fewer eggs that were less likely to hatch than females given uncontaminated carcasses. Furthermore, we show that egg hatch success is significantly reduced by bacterial exposure. Using a split-brood design, which controlled for intrinsic differences in eggs produced by different females, we found that eggs washed free of surface-associated bacteria show increased survival compared to unwashed eggs. By contrast, eggs exposed to the entomopathogen Serratia marcescens show decreased survival compared to unexposed eggs. We next tested the immune competence of eggs under challenge from bacterial infection, and found that eggs lacked endogenous production of antimicrobial peptides, despite well-developed responses in larvae. Finally, we found that despite lacking immunity, N. vespilloides eggs produce an extraembryonic serosa, indicating that the serosa has lost its immune inducing capacity in this species.Conclusions The dependency on ephemeral resources might strongly select for fast developing animals. Our results suggest that Nicrophorus carrion beetles, and other species developing on ephemeral resources, face a fundamental trade-off between egg immunity and development time.
    BMC Evolutionary Biology 09/2014; 14(1):208. DOI:10.1186/s12862-014-0208-x · 3.41 Impact Factor
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    • "of a diapause trait may increase desiccation resistance (Urbanski et al. 2010). Also, there is a distinct possibility that Ae. albopictus may survive in such harsh climates within suitable microhabitats, as suggested for Ae. "
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    ABSTRACT: Aedes albopictus (Skuse) is one of the most invasive mosquito species in the world and has infested islands in the Torres Strait, off the northern coast of Australia since at least 2004. This has led to fears that it may establish on the Australian mainland, including highly populated cities in southern temperate regions. To supplement theoretical projections addressing the range expansion of Ae. albopictus into Australia, laboratory-based trials were conducted to assess the performance of a Torres Strait Ae. albopictus population under a range of Australian conditions. First-instar larvae were placed in individual microcosms and maintained on a natural food resource, under average climatic conditions representing different regions of Australia's east coast. Larvae could not survive winter conditions in southern Australia. As the population performance index was >1.0 for tropical winter and summer conditions, and temperate summer conditions, populations would likely increase during these times. To test whether Ae. albopictus could overwinter during adverse conditions as eggs, we exposed cohorts to four different temperature (7, 17, 27, and 33°C) and relative humidity (35, 55, and 80%) combinations for up to 3 mo. High temperatures and low humidity were most detrimental to egg survival. However, those eggs maintained under cooler climates remained viable after 3 mo, including 17% of eggs kept at 7°C. Overall, this study suggests that a Torres Strait Ae. albopictus strain could proliferate all year round under northern tropical conditions and could overwinter in the egg stage before proliferating in the summer in southern temperate regions.
    Journal of Medical Entomology 09/2014; 51(5). DOI:10.1603/ME14079 · 1.82 Impact Factor
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