Biology subjects

Koella, J. C.

Publications and source records attributed to Koella, J. C..

9 recordsLinked to original sources

bioRxiv2025

Effects of nectar and sugar on the longevity of the mosquito Anopheles gambiae s.l.

In addition to taking blood-meals, mosquitoes regularly feed on the nectar of plants. The nectar, in particular the sugar it contains, serves as a source of energy that underlies many life-history traits, including longevity. To understand better how different nectars and sugars influence the longevity of mosquitoes, we allowed adult Anopheles gambiae s.l. to feed on several plant species (the flowers of Thevetia nerifolia, Mandalium coromandelianum, Ixora coccinea, and Tabernanthe iboga, and the fruit of Carica papaya), measured the concentrations of sucrose, fructose and glucose in the nectar and fruit juice, estimated the size of their sugar meal and measured their longevity. The plant that the mosquitoes fed on affected their longevity (which ranged from an average of 8.2 days when they fed on C. papaya to 21.1 days when they fed on M. coromandelianum), and the mosquitoes took larger meals (in a separate experiment) from the plants that gave a longer life. However, longevity was only slightly affected by the concentrations of glucose, fructose, sucrose, or total sugar in the sugar meals. In contrast, when we let mosquitoes feed on experimental sugar solutions consisting of glucose, sucrose, fructose, or trehalose at concentrations of 1.97 or 19.97 kcal per 100 ml, both the type and the concentration of sugar affected longevity. The mosquitoes lived approximately one week longer when fed sugar at the higher concentration and they lived longest (14.1 days) when fed with sucrose and shortest (4.8 days) when fed with trehalose. Overall, our results show the importance of nectar and sugar on the longevity of mosquitoes but suggest also that non-sugar components of nectar may have a large impact.

ecology↗

bioRxiv2024

The role of prooxidants and antioxidants in shaping life-history and parasite tolerance in Anopheles mosquitoes

Oxidative homeostasis plays important roles in physiology, for reactive oxygen species not only lead to damaging oxidative stress, but also regulate important physiological processes like immunity and longevity. ROS are therefore expected to be a key factor underlying many host-parasite interactions. We evaluated the role of the hosts oxidative status on the outcome of infection with the mosquito Anopheles gambiae infected by the microsporidian Vavraia culicis. To do so, we manipulated the oxidative status of the mosquitoes by feeding them early (the first four days after emergence) or late (from five days after emergence onwards) either a standard sugar source or one supplemented with a prooxidant (hydrogen peroxide) or antioxidant (vitamin C), and then measured the longevity and fecundity of uninfected and infected mosquitoes and (for infected mosquitoes) the parasite load at a given day (13 days after emergence) or when the mosquitoes died. The prooxidant generally increased longevity, but if consumed early after emergence its impact was lessened by the infection by Vavraia. In contrast the antioxidant increased fecundity, and the impact was not affected by the status of infection or by the timing of consumption. Finally, early consumption of both supplements increased Vavraias spore load at 13 days after emergence and at death. In contrast, late consumption enhanced the parasites growth late in the mosquitos life. Thus, our experiment revealed complex effects of prooxidant and antioxidant consumption, emphasising the critical role of timing and context in shaping their influence on biological traits.

evolutionary biology↗

bioRxiv2024

Mosquitoes self-medicate according to the dynamics of a microsporidian infection

Immune responses protect against infectious diseases but often incur physiological costs, such as oxidative stress. In mosquitoes, these costs may shape behaviours that help regulate oxidative balance, potentially including the consumption of nectar containing bioactive substances like prooxidants and antioxidants. We investigated whether Anopheles gambiae adjust their preferences for diets with such substances when they are infected with the microsporidian parasite Vavraia culicis. Using sugar solutions supplemented with hydrogen peroxide (a prooxidant) or ascorbic acid (an antioxidant), we assessed the feeding preferences of uninfected and infected mosquitoes at different ages and measured the effects of these diets on oxidative homeostasis, parasite load, and lifespan. Infected mosquitoes initially preferred the prooxidant diet, which reduced parasite load and extended lifespan, before shifting their preference towards the antioxidant diet as infection progressed. In contrast, uninfected mosquitoes consistently preferred the unsupplemented sugar, likely to avoid oxidative stress induced by the supplemented diets, which, surprisingly, also increased their lifespan. These results suggest a form of self-medication, despite benefits in uninfected individuals, where mosquitoes dynamically adjust their dietary choices throughout infection. We propose that such dietary strategies may be widespread among mosquitoes, helping them manage oxidative stress, with potential implications for vector-pathogen interactions and the success of biological control programmes.

evolutionary biology↗

bioRxiv2024

Mechanisms of host exploitation by a microsporidian parasite

Parasites exploit their hosts to enhance their growth and reproduction, yet the mechanisms underlying host manipulation remain understudied for many taxa. The microsporidian Vavraia culicis, a potential biological control agent for mosquitoes, serves as an excellent model to explore such mechanisms. In this study, we investigate how infection by V. culicis lines that vary in virulence alters resource dynamics within the mosquito host Anopheles gambiae. Using metallomics and quantification of protein, carbohydrate, and lipid content, we show that infection alters host resource concentrations in ways that depend on parasite virulence. More virulent parasites led to increased protein levels and greater energy demands, evidenced by higher carbohydrate reserves. Additionally, infection with V. culicis impacted host metal content, particularly zinc and manganese, used by V. culicis independently of its evolutionary background. Iron availability, a key nutrient for parasite growth, enhanced spore production, with selected parasite lines better able to exploit host iron than unselected. These findings provide insight into the mechanisms by which V. culicis manipulates host resources, shedding light on the role of host exploitation in parasite virulence and the potential use of microsporidia as biological control agents in vector biology.

evolutionary biology↗

bioRxiv2024

Energetic shifts predict the mortality of Anopheles gambiae

Life history theory predicts that resource allocation adapts to ecological and evolutionary pressures. We investigated resource and energy in the malaria vector Anopheles gambiae following exposure to two stressors: blood meals and infection by the microsporidian Vavraia culicis. Our findings reveal the costs of blood feeding and parasitism on longevity, highlighting trade-offs in lifetime protein, carbohydrate, and lipid reserves. Notably, shifts in carbohydrate-to-lipid ratios were associated with survival likelihood, with survivors exhibiting higher resource reserves and uniquely transitioning from carbohydrate to lipid utilization, a pattern absent in non-survivors. This study emphasizes the coevolutionary dynamics between hosts and parasites, highlighting how intrinsic and extrinsic factors shape host physiology. More broadly, our results underscore the importance of integrating host metabolic responses into ecological and epidemiological frameworks to enhance understanding of parasite transmission and survival strategies. HighlightsO_LIHaving a blood meal did not affect mosquito longevity, resource content or V. culicis parasitemia. C_LIO_LIAlive mosquitoes harboured fewer spores than mosquitoes that had just died, independently of the stage of infection, supporting the parasite load upon death hypothesis. C_LIO_LIAlive mosquitoes exhibited a shift in their usage of the energetic reserves (i.e., carbohydrates to lipids) late in life, which mosquitoes at death did not. C_LIO_LIOur findings support the hypothesis that Plasmodium may have coevolved with its vectors dynamics of lipid release, a nutrient essential for its development. C_LI

evolutionary biology↗

bioRxiv2024

Sublethal insecticide exposure of larvae affects the blood-feeding behaviour of adult mosquitoes

Because of their widespread use for the control of disease vectors and agricultural pests, insecticides have become ubiquitous in the environment, including in water bodies harbouring mosquito larvae. These are therefore continuously exposed to sublethal doses. Since this has long-lasting effects on the mosquitoes physiology and life-history, we expected that it may also affect behaviours that underlie the mosquitoes population dynamics and disease epidemiology, such as egg-laying preference, blood-feeding motivation, and host-seeking behaviour. Using an insecticide-sensitive and a resistant strain of Anopheles gambiae, an important malaria vector, we evaluated the effects of sublethal exposure to permethrin throughout larval development on the resistance to the insecticide in adults, on host-seeking behaviour, on the motivation to blood-feed, and on egg-laying behaviour. Resistance, assessed by rates of knock-down and mortality, were similar between exposed and unexposed mosquitoes. However, exposure to sublethal doses of insecticide caused female mosquitoes to split their egg clutches into two parts and increased the motivation of mosquitoes to seek blood meals through permethrin-treated nets, regardless of their sensitivity to the insecticide. Furthermore, it enhanced the natural preference of resistant strains for permethrin-treated nets and increased their blood-meal size. Our results thus suggest that sublethal insecticide concentrations in larval breeding sites have important epidemiological implications.

evolutionary biology↗

bioRxiv2024

Virulence evolution: thinking outside of the host

The main theory of the evolution of virulence relies on a trade-off between virulence and transmission rate. However, it has been difficult to measure the required trade-off. A recent transmission decomposition framework explains that this might be partly due to a lack of information about the parasites survival in the environment outside its hosts, where the parasite finds itself during transmission to its next host. In this study, we used parasite lines of the microsporidian Vavraia culicis with varying levels of virulence upon infecting their host, the mosquito Anopheles gambiae, to explore the interaction between parasite-driven virulence within its host and its survival outside of the host. The parasite lines with greater virulence and growth within their hosts had a cost in their intrinsic ability to withstand the environment, irrespective of temperature. These results underscore the importance of considering the full context of transmission and other parasite fitness traits in studying and predicting the evolution and spread of infectious diseases.

evolutionary biology↗

bioRxiv2024

Complex interactions in the life cycle of a simple parasite shape the evolution of virulence

Evolutionary expectations about the virulence of parasites (i.e., the parasite-induced mortality rate of the host) often focus solely on the within-host transmission stage, overlooking the time spent between hosts and variations in transmission cycles. Moreover, the parasite growth rate within the host is closely linked to virulence. We here suggest that a simplified view of transmission and parasite evolution makes predicting how virulence will evolve difficult. We illustrate our ideas with a parasite with a simple life cycle, the microsporidian Vavraia culicis, which infects the mosquito Anopheles gambiae. We selected the parasite over six host generations for early or late host transmission, corresponding to shorter or longer time within the host. Selecting for late transmission increased their exploitation of the host, resulting in higher host mortality and a shorter life cycle with rapid infective spore production, comparatively to selection for early transmission. In response, hosts infected with late-selected spores shortened their life cycle and shifted to earlier reproduction. Using different host harm metrics, we demonstrate and discuss the pros and cons of using different it as measures of virulence. These and other findings emphasize the importance of considering the entire transmission cycle in studies of parasite evolution and raise concerns about how host density and social settings might influence virulence evolution.

evolutionary biology↗

bioRxiv2023

Exposure to Pseudomonas spp. increases Anopheles gambiae insecticide resistance in a population-dependent manner

The microbiota of mosquitoes influences many aspects of their biology, including developmental processes, mating and sexual reproduction, immune functions, and refractoriness to pathogens. Here, we considered their role in resistance against insecticides. In particular, we assessed how larval infection of a permethrin-resistant and a sensitive colony of Anopheles gambiae by four strains belonging to three different Pseudomonas species affects several life history traits and the impact of the insecticide on adult mortality. Our data showed that all four Pseudomonas strains persisted in adults until death. The bacteria increased the likelihood that mosquitoes survived 24 hours after exposure to permethrin by up to two-fold. The impact of the bacteria depended on the bacterial strains and the mosquito colony: in the resistant colony, all bacteria increased survival by about 2-fold, while in the sensitive colony, only two of the four strains increased survival. The benefit concerning insecticide resistance came with little to no impact on the other traits (i.e., larval mortality, developmental time and adult longevity). Altogether, our results highlight the importance of considering environmental microbial exposure and mosquito microbial communities in epidemiological and vector-control studies, while also suggesting a possible role for Pseudomonas spp. as a symbiont in A. gambiae.

evolutionary biology↗