Laura V. Ferguson

Parallel ionoregulatory adjustments underlie phenotypic plasticity and evolution of Drosophila cold tolerance

Low temperature tolerance is the main predictor of variation in the global distribution and performance of insects, yet the molecular mechanisms underlying cold tolerance variation are poorly known, and it is unclear whether the mechanisms that improve cold tolerance within the lifetime of an individual insect are similar to those that underlie evolved differences among species. The accumulation of cold-induced injuries by hemimetabolous insects is associated with loss of Na+ and K+ homeostasis. Here we show that this model holds true for Drosophila; cold exposure increases haemolymph [K+] in D. melanogaster, and cold-acclimated flies maintain low haemolymph [Na+] and [K+], both at rest and during a cold exposure. This pattern holds across 24 species of the Drosophila phylogeny, where improvements in cold tolerance have been consistently paired with reductions in haemolymph [Na+] and [K+]. Cold-acclimated D. melanogaster have low activity of Na+/K+-ATPase, which may contribute to the maintenance of low haemolymph [Na+] and underlie improvements in cold tolerance. Modifications to ion balance are associated with both phenotypic plasticity within D. melanogaster and evolutionary differences in cold tolerance across the Drosophila phylogeny, which suggests that adaptation and acclimation of cold tolerance in insects may occur through similar mechanisms. Cold-tolerant flies maintain haemolymph osmolality despite low haemolymph [Na+] and [K+], possibly through modest accumulations of organic osmolytes. We propose that this could have served as an evolutionary route by which chill-susceptible insects developed more extreme cold tolerance strategies.

Influence of Hepatozoon parasites on host-seeking and host-choice behaviour of the mosquitoes Culex territans and Culex pipiens.

Graphical abstract Highlights ► We observed behaviour of uninfected mosquitoes and those infected with Hepatozoon parasites. ► We observed mosquito choice of infected and uninfected frogs and snakes. ► Host-seeking behaviour of infected Culex pipiens differed from uninfected mosquitoes. ► We report the first parasite-induced changes in host behaviour in this system.

Insect Immunity Varies Idiosyncratically During Overwintering

ABSTRACT Overwintering insects face multiple stressors, including pathogen and parasite pressures that shift with seasons. However, we know little of how the insect immune system fluctuates with season, particularly in the overwintering period. To understand how immune activity changes across autumn, winter, and spring, we tracked immune activity of three temperate insects that overwinter as larvae: a weevil (Curculio sp., Coleoptera), gallfly (Eurosta solidaginis, Diptera), and larvae of the lepidopteran Pyrrharctia isabella. We measured baseline circulating hemocyte numbers, phenoloxidase activity, and humoral antimicrobial activity, as well as survival of fungal infection and melanization response at 12°C and 25°C to capture any potential plasticity in thermal performance. In Curculio sp. and E. solidaginis, hemocyte concentrations remained unchanged across seasons and antimicrobial activity against Gram‐positive bacteria was lowest in autumn; however, Curculio sp. were less likely to survive fungal infection in autumn, whereas E. solidaginis were less likely to survive infection during the winter. Furthermore, hemocyte concentrations and antimicrobial activity decreased in P. isabella overwintering beneath snow cover. Overall, seasonal changes in activity were largely species dependent, thus it may be difficult to create generalizable predictions about the effects of a changing climate on seasonal immune activity in insects. However, we suggest that the relationship between the response to multiple stressors (e.g., cold and pathogens) drives changes in immune activity, and that understanding the physiology underlying these relationships will inform our predictions of the effects of environmental change on insect overwintering success. GRAPHICAL ABSTRACT We compared immune responses during overwintering in three insect species. Immunity varies seasonally in a species‐dependent fashion. Warmer and less thermally variable microhabitats decrease spring immune activity. Species‐specific responses are likely a product of the response to different iterations of multiple overwintering stressors. Figure. No caption available.

Reciprocal Trophic Interactions and Transmission of Blood Parasites between Mosquitoes and Frogs

The relationship between mosquitoes and their amphibian hosts is a unique, reciprocal trophic interaction. Instead of a one-way, predator-prey relationship, there is a cyclical dance of avoidance and attraction. This has prompted spatial and temporal synchrony between organisms, reflected in emergence time of mosquitoes in the spring and choice of habitat for oviposition. Frog-feeding mosquitoes also possess different sensory apparatuses than do their mammal-feeding counterparts. The reciprocal nature of this relationship is exploited by various blood parasites that use mechanical, salivary or trophic transmission to pass from mosquitoes to frogs. It is important to investigate the involvement of mosquitoes, frogs and parasites in this interaction in order to understand the consequences of anthropogenic actions, such as implementing biocontrol efforts against mosquitoes, and to determine potential causes of the global decline of amphibian species.

Does cold activate the Drosophila melanogaster immune system

Cold exposure appears to activate aspects of the insect immune system; however, the functional significance of the relationship between cold and immunity is unclear. Insect success at low temperatures is shaped in part by interactions with biotic stressors, such as pathogens, thus it is important to understand how and why immunity might be activated by cold. Here we explore which components of the immune system are activated, and whether those components differ among different kinds of cold exposure. We exposed Drosophila melanogaster to both acute (2h, -2°C) and sustained (10h, -0.5°C) cold, and measured potential (antimicrobial peptide expression, phenoloxidase activity, haemocyte counts) and realised (survival of fungal infection, wound-induced melanisation, bacterial clearance) immunity following recovery. Acute cold increased circulating haemocyte concentration and the expression of Turandot-A and diptericin, but elicited a short-term decrease in the clearance of gram-positive bacteria. Sustained cold increased the expression of Turandot-A, with no effect on other measures of potential or realised immunity. We show that measures of potential immunity were up-regulated by cold, whereas realised immunity was either unaffected or down-regulated. Thus, we hypothesize that cold-activation of potential immunity in Drosophila may be a compensatory mechanism to maintain stable immune function during or after low temperature exposure.

Eco-immunology in the cold: the role of immunity in shaping the overwintering survival of ectotherms

ABSTRACT The effect of temperature on physiology mediates many of the challenges that ectotherms face under climate change. Ectotherm immunity is thermally sensitive and, as such, environmental change is likely to have complex effects on survival, disease resistance and transmission. The effects of temperature on immunity will be particularly profound in winter because cold and overwintering are important triggers and regulators of ectotherm immune activity. Low temperatures can both suppress and activate immune responses independent of parasites, which suggests that temperature not only affects the rate of immune responses but also provides information that allows overwintering ectotherms to balance investment in immunity and other physiological processes that underlie winter survival. Changing winter temperatures are now shifting ectotherm immunity, as well as the demand for energy conservation and protection against parasites. Whether an ectotherm can survive the winter will thus depend on whether new immune phenotypes will shift to match the conditions of the new environment, or leave ectotherms vulnerable to infection or energy depletion. Here, we synthesise patterns of overwintering immunity in ectotherms and examine how new winter conditions might affect ectotherm immunity. We then explore whether it is possible to predict the effects of changing winter conditions on ectotherm vulnerability to the direct and indirect effects of parasites. Summary: Immune investment shapes energy budgeting and survival upon infection in overwintering ectotherms, but can we predict how changing winters will modify immunity and its role in winter survival?

FECUNDITY REDUCTION IN THE SECOND GONOTROPHIC CYCLE OF CULEX PIPIENS INFECTED WITH THE APICOMPLEXAN BLOOD PARASITE, HEPATOZOON SIPEDON

Abstract: Fecundity reduction is a well-recognized phenomenon of parasite infection in insects. Reduced production of eggs might increase longevity of a host and release nutrients to both host and parasite that would otherwise be used for oogenesis. The objective of this study was to assess effects on fecundity caused by Hepatozoon sipedon, an apicomplexan blood parasite of snakes, in its invertebrate host, the mosquito Culex pipiens. In the first gonotrophic cycle, the mean number of eggs laid by mosquitoes infected with H. sipedon did not differ significantly from those laid by uninfected mosquitoes. However, in the second gonotrophic cycle infected mosquitoes laid significantly fewer eggs than did uninfected mosquitoes, and fecundity was reduced by 100% in mosquitoes with parasite burdens of more than 60 oocysts. There was a significant negative correlation between parasite burden, or the number of oocysts, and the number of eggs produced in the second gonotrophic cycle. Significantly fewer viable larvae hatched from eggs laid by infected compared to uninfected mosquitoes in the second gonotrophic cycle. These data indicate that fecundity reduction occurs in this system, although the physiological mechanisms driving this phenotype are not yet known.