Geographic variation and the evolution of reproductive allocation in the pitcher-plant mosquito, Wyeomyia smithii

Diapause characterisation and seasonality of Aedes japonicus japonicus (Diptera, Culicidae) in the northeast of France

The invasive mosquito Aedes japonicus japonicus (Theobald, 1901) settled in 2013 in the Alsace region, in the northeast of France. In this temperate area, some mosquito species use diapause to survive cold winter temperatures and thereby foster settlement and dispersal. This study reports diapause and its seasonality in a field population of Ae. japonicus in the northeast of France. For two years, eggs were collected from May to the beginning of November. They were most abundant in summer and became sparse in late October. Diapause eggs were determined by the presence of a fully developed embryo in unhatched eggs after repeated immersions. Our study showed effective diapause of Ae. japonicus in this part of France. At the start of the egg-laying period (week 20), we found up to 10% of eggs under diapause, and this rate reached 100% in October. The 50% cut-off of diapause incidence was determined by the end of summer, leading to an average calculated maternal critical photoperiod of 13 h 23 min. Interestingly, diapause was shown to occur in part of the eggs even at the earliest period of the two seasons, i.e. in May of each year. Even though we observed that the size of eggs was positively correlated with diapause incidence, morphology cannot be used as the unique predictive indicator of diapause status due to overlapping measurements between diapausing and non-diapausing eggs. This study provides new knowledge on diapause characterisation and invasive traits of Ae. japonicus.

Divergence in life history and behaviour between hybridizing Phymata ambush bugs (Heteroptera: Reduviidae)

Life-history variation plays a central role in evolutionary and ecological processes and might be especially pertinent to divergence in closely related species. We investigated differences in life history in a pair of parapatric species of ambush bugs (Phymata) and a putative hybrid population. Despite the evidence of gene flow among these species, we found clear divergence between these parapatric populations for a suite of juvenile and adult life-history traits, including components of fitness. The higher latitude species was also less active, suggestive of potential divergence in dispersal. Increased melanism was correlated with longevity in one species, although it was unclear whether this relationship was causal. Observed differences in the life history between species were consistent with expectations of high-latitude species putting a premium on early or rapid development and increased reproductive rates. However, these results were not consistent with ‘pace-of-life syndromes’ at the species level. Individuals from the putative hybrid zone exhibited intermediate values for most traits, although they had slower development and reduced mobility, consistent with some previous work suggesting natural selection via hybrid breakdown.

Wing morphometrics of Aedes (Ochlerotatus) albifasciatus (Macquart, 1838) (Diptera: Culicidae) from different climatic regions of Argentina

BACKGROUND

Gene flow restrictions between populations of Aedes albifasciatus, the vector of Western equine encephalitis and Dirophilaria immitis, have been described in the central region of Argentina. Genetic and eco-physiological variations usually result in local forms reflecting the climatic regions. Mosquito wings and their different parts have ecological functions in flight and communication. Therefore, wing shape could be considered an aspect of sexual dimorphism, and its eco-physiological responses can be expressed as morphological changes induced by the environment.

METHODS

To compare the geographical and sexual variations with respect to wing shape and size in two Ae. albifasciatus populations from contrasting climates of Argentina (temperate: Buenos Aires, and the arid steppe of Patagonia: Sarmiento), the wings of adults reared in thermal trays at different constant temperatures (10-29 °C) were analyzed.

RESULTS

The wing size of Ae. albifasciatus showed inverse linear relationships with the rearing thermal condition and higher slope for Buenos Aires. In the cool range (10-17 °C), geographical size variations responded to the converse Bergmann's rule, where Buenos Aires individuals were larger than those from Sarmiento. Sexual shape dimorphism occurred in both populations while geographical variation in shape was observed in both sexes.

CONCLUSIONS

Buenos Aires individuals showed greater response sensitivity with respect to the size-temperature relation than those from Sarmiento. The converse Bergmann's rule in size variation could be due to a higher development rate in Sarmiento to produce more cohorts in the limited favorable season. The shape could be more relevant with respect to the size in the study of population structures due to the size being more liable to vary due to changes in the environment. The geographical variations with respect to morphology could be favored by the isolation between populations and adaptations to the environmental conditions. Our results demonstrate that the shape and size of wing provide useful phenotypic information for studies related to sexual and environmental adaptations.

Transcript profiling reveals mechanisms for lipid conservation during diapause in the mosquito, Aedes albopictus

The Asian tiger mosquito, Aedes albopictus, is a medically important invasive species whose geographic distribution has expanded dramatically during the past 20 years, and one of the key elements of its success is its capacity to survive long distance transport as a diapausing pharate first instar larva, encased within the chorion of the egg. We report that pharate larvae entering diapause are larger and contain 30% more lipid than their nondiapausing counterparts. To improve our understanding of the molecular regulation of lipid metabolism during diapause, we assessed the relative mRNA abundance of 21 genes using qRT-PCR. Elevated expression of lipid storage droplet protein 2 during embryonic development likely contributes to the higher amounts of lipid we noted in diapausing individuals. The conservation of lipids during diapause is reflected in downregulation of genes involved in lipid catabolism, including lipase 2, lipase 3, lipase 4, acyl-CoA dehydrogenase 4, and isovaleryl-CoA dehydrogenase. Two genes involved in fatty acid synthesis and modification, Δ(9)-desaturase, and fatty acyl-CoA elongase, were both upregulated in diapausing pharate larvae, suggesting roles for their gene products in generating unsaturated fatty acids to enhance membrane fluidity at low temperatures and generating precursors to the surface hydrocarbons needed to resist desiccation, respectively. Together, the results point to substantial distinctions in lipid metabolism within the embryo as a consequence of the diapause program, and these differences occur both before the actual onset of diapause as well as during the diapause state.

Rapid adaptive evolution of photoperiodic response during invasion and range expansion across a climatic gradient

Abstract Understanding the mechanisms of adaptation to spatiotemporal environmental variation is a fundamental goal of evolutionary biology. This issue also has important implications for anticipating biological responses to contemporary climate warming and determining the processes by which invasive species are able to spread rapidly across broad geographic ranges. Here, we compare data from a historical study of latitudinal variation in photoperiodic response among Japanese and U.S. populations of the invasive Asian tiger mosquito Aedes albopictus with contemporary data obtained using comparable methods. Our results demonstrated rapid adaptive evolution of the photoperiodic response during invasion and range expansion across ∼15° of latitude in the United States. In contrast to the photoperiodic response, size-based morphological traits implicated in climatic adaptation in a wide range of other insects did not show evidence of adaptive variation in Ae. albopictus across either the U.S. (invasive) or Japanese (native) range. These results show that photoperiodism has been an important adaptation to climatic variation across the U.S. range of Ae. albopictus and, in conjunction with previous studies, strongly implicate the photoperiodic control of seasonal development as a critical evolutionary response to ongoing contemporary climate change. These results also emphasize that photoperiodism warrants increased attention in studies of the evolution of invasive species.

Reproduction-longevity trade-off in Anopheles gambiae (Diptera: Culicidae)

Reduced survival and future reproduction due to of current reproduction is a trade-off known as the cost of reproduction. Surprisingly, only a few studies have assessed the cost of reproduction in arthropod disease vectors, despite its effect on longevity, and thus on vectorial capacity. We evaluated the cost of reproduction on survival of Anopheles gambiae Giles by comparing mosquitoes that were denied exposure to the other sex, hereafter named virgins, and those that were allowed exposure to the other sex and mating, hereafter named mated. Merely 6 d of exposure to females with mating activity reduced male survival from a median of 17 d in virgins to 15 d in mated, indicating that male mating cost is substantial. The increase in mortality of mated males began several days after the exposure to females ended, indicating that mating is not associated with immediate mortality risk. Notably, body size was negatively correlated with male mortality in mated males, but not in virgins. The rate of insemination declined after 4 d of exposure to females, indicating that male mating capacity is limited and further supporting the hypothesis that mating is costly for males. Consistent with previous studies, female survival on sugar alone (median=16 d) was shorter than on blood and sugar (median=19 d), regardless if she was mated or virgin. Overall, survival of mated females was lower than that of virgins on a diet of blood and sugar, but no difference was found on a diet of sugar only. However, the cost of reproduction in females remains ambiguous because the difference in survival between virgin and mated females was driven by the difference between virgin (median=19 d) and uninseminated females exposed to males (median=17 d), rather than between virgin and inseminated females (median=19 d). Accordingly, sperm and seminal fluid, egg development, and oviposition have negligible cost in terms of female survival. Only exposure to males without insemination decreased female survival. Nonetheless, if exposure to males under natural conditions is also associated with reduced survival, it might explain why females remain monogamous.

Reproductive output of female Anopheles gambiae (Diptera: Culicidae): comparison of molecular forms

Knowledge of ecological differences between the molecular forms of Anopheles gambiae Giles (Diptera: Culicidae) might lead to understanding of their unique contribution to disease transmission, to better vector control, and to identification of the forces that have separated them. We compared female fecundity measured as egg batch size in relation to body size between the molecular forms in Mali and contrasted them with their sibling species, Anopheles arabiensis Patton. To determine whether eggs of different egg batches are of similar "quality," we compared the total protein content of first-stage larvae (L1s), collected < 2 h after hatching in deionized water. Egg batch size significantly varied between An. gambiae and An. arabiensis and between the molecular forms of An. gambiae (mean batch size was 186.3, 182.5, and 162.0 eggs in An. arabiensis and the M and the S molecular form of An. gambiae, respectively). After accommodating female body size, however, the difference in batch size was not significant. In the S molecular form, egg protein content was not correlated with egg batch size (r = -0.08, P > 0.7) nor with female body size (r = -0.18, P > 0.4), suggesting that females with more resources invest in more eggs rather than in higher quality eggs. The mean total protein in eggs of the M form (0.407 microg per L1) was 6% higher than that of the S form (0.384 microg per L1), indicating that the M form invests a greater portion of her resources into current (rather than future) reproduction. A greater investment per offspring coupled with larger egg batch size may reflect an adaptation of the M form to low productivity larval sites as independent evidence suggests.