Biology subjects

Duncan, A. B.

Publications and source records attributed to Duncan, A. B..

6 recordsLinked to original sources

bioRxiv2026

Differing effects of parasite-parasite interaction types on the spatial epidemiology of co-circulating parasites

Interactions among co-circulating parasite species influence infection risk and disease progression. Interactions can occur within hosts, e.g. altering susceptibility, or indirectly through host demography or movement, potentially affecting landscape-scale transmission. Despite their ubiquity, the spatial implications of these interactions have received limited attention. We combine spatially-explicit modelling with laboratory experiments to investigate how parasite-parasite interactions influence disease spread. We model within-host, demographic, and dispersal-related interactions across a linear landscape, showing that within-host interactions modifying host susceptibility have the strongest effects on parasite prevalence, spatial heterogeneity, and rate of spread. These effects are amplified when parasites invade sequentially, generating pronounced patch-level priority effects. We tested these predictions experimentally using a protist host (Paramecium caudatum) and two bacterial parasites (Holospora undulata and H. obtusa). Consistent with model predictions, we found that H. obtusa reduces the overall prevalence and spread of H. undulata across a landscape of interconnected patches, likely through reductions in host susceptibility, and evidence of priority effects, observing reduced H. undulata prevalence when introduced after H. obtusa. Our results highlight that parasite-parasite interactions can have important implications for the landscape-scale epidemiology of co-circulating parasites, but the effect magnitude depends on the interaction type and the timing of invasion.

ecology↗

bioRxiv2025

Interactions between a spider mite and a virus revealed via effects on their host plant.

Coinfection, when hosts are infected with more than one parasite, can modify life-history traits of both parasites and their host. We investigated reciprocal interactions between tomato spotted wilt virus (TSWV) and a non-vector spider mite, Tetranychus urticae, in coinfections on tomato plants. We compared the number of T. urticae daughters and adults and the viral load for two TSWV isolates (France81, which is more virulent, and LYE1137vir) in single and coinfections, and measured host traits (height, fresh weight, chlorophyll content, and number of flowers). TSWV infection reduced plant height, weight, flowers and chlorophyll content, especially when infected with isolate France81. T. urticae only reduced plant height. The more virulent TSWV isolate facilitated spider mites by increasing the number of daughters per unit of plant height, thus potentially enabling equivalent levels of mite transmission as from virus-free plants. In contrast, there was no effect of T. urticae on the load of either TSWV isolate. Nevertheless, the additive reduction in plant height in coinfection may increase host mortality and reduce the time available for transmission of both parasites. This work highlights that it can be important to incorporate measures of host and parasite life-history traits across an entire infection when investigating the consequences of coinfection for parasite fitness.

evolutionary biology↗

bioRxiv2024

Tomato spotted wilt virus facilitates non-vector spider mite species (Tetranychus urticae and Tetranychus evansi) on whole tomato plants

Coinfections where hosts harbour more than one parasite species are common in nature. Facilitation among parasites enabling them to better exploit host resources is widespread with direct consequences on their life-history. Plant viruses can facilitate their vectors to increase their transmission, but equivalent studies in virus-non vectors are lacking. Here we study facilitation of two (non-vector) species of Tetranychus spider mites, Tetranychus urticae and T. evansi, by a plant virus, tomato spotted wilt virus (TSWV), in coinfections on a host tomato plant, Solanum lycopersicum. We compared the effect of different strains of TSWV on life-history traits of Tetranychus mites on cut leaves and whole plants of different tomato varieties. TSWV facilitated both species of spider mite on two different tomato varieties on whole plants, with more offspring of both species becoming adults. In contrast, on cut leaves, facilitation of T. urticae was much more variable depending on the experiment, viral strain and tomato variety. We attribute this to the non-homogeneous spread of virus throughout the host plant. Virus is first transported to the top leaves, and not middle leaves which we had used for the experiment. Indeed, if facilitation is indirect via the host immune system or resource based via the release of free-amino acids then this may be less efficient on cut plant parts. These results highlight that facilitation among parasites may increase parasite fitness and at the same time levels of virulence experienced by the host.

ecology↗

bioRxiv2023

Intraspecific density changes the impact of interspecific competitors on parasite infection traits in multiple infections

Co-infections are frequent, with consequences for parasite life-history traits expressed at within- and between-host levels. However, little is known about whether the effect of interspecific competitors on traits are correlated or independent or if they change with intraspecific competition. To address this, we investigated the occurrence of genetic correlations among within- and betweenhost traits at different intra-specific densities of inbred lines of the spider mite, Tetranychus urticae with its competitor T. evansi. First, we found T. evansi presence on a shared host leaf produced a negative (non-genetic) correlation between virulence (leaf damage) and number of daughters (transmitting stages) at intermediate intraspecific densities; this same relationship was not significant without competitors. Second, we show interspecific competitors increases transmission to adjacent leaf discs, measured as movement of adult T. urticae females, but only at low and intermediate intraspecific densities. Finally we tested whether within-host traits (virulence and transmitting stages) were correlated with between-host traits (movement to adjacent patches), with or without competitors, at different conspecific densities. We found traits were mostly independent; interspecific competitors may increase transmission across hosts without affecting virulence (or vice versa). These independent effects on within- and between-host traits indicate competition may impact epidemiology and parasite trait evolution.

evolutionary biology↗

bioRxiv2021

Virulence constrains transmission even in the absence of a genetic trade-off

The virulence-transmission trade-off predicts that parasite fitness peaks at intermediate virulence. However, whether this relationship is driven by the environment or genetically determined and if it depends on transmission opportunities remains unclear. We tackled these issues using inbred lines of the macro-parasitic spider-mite Tetranychus urticae. When transmission was not possible during the infection period, we observed a hump-shaped relationship between virulence and parasite fitness, as predicted by theory. This was environmentally driven, as no genetic correlation between traits was detected. However, when transmission to uninfected hosts occurred during the infection period, virulence was positively, environmentally and genetically correlated with parasite fitness. Therefore, the virulence-transmission trade-off depends on within-host dynamics and on the timing of transmission, rather than on a genetic correlation. This fundamental correlation may thus be easier to manipulate than previously thought.

evolutionary biology↗

bioRxiv2020

A sexual dimorphism in the spatial vision of band-winged grasshoppers

Visual acuity (VA) --- a measurement of the fineness or coarseness of vision --- correlates with the size of an animal, with larger species often possessing sharper vision. However, it is unknown whether the same relationship between visual acuity and size holds within a species when individuals differ consistently and substantially in size, such as through a sexual size dimorphism. Here we examine the visual acuity of three species of sexually dimorphic band-winged grasshoppers, in which females are the larger sex (Arphia pseudonietana, Dissosteira carolina, and Spharagemon equale; total n = 98). Using a radius of curvature estimation method, we find that females have [~]21% finer vision in the most acute region and axis of the eye than do males. Further explorations of the eyes of the species showing the greatest size dimorphism (D. carolina) suggest that this VA dimorphism is driven by females having larger eyes with more ommatidia. In contrast to many flying insects where males have finer vision to acquire mates, our study is one of the first to demonstrate a female-biased sexual dimorphism in acuity. Given the number of species in which females are larger than males, our results suggest that differences in VA between the sexes may be more common than currently appreciated.

physiology↗