Wolbachia infections that reduce immature insect survival: Predicted impacts on population replacement

Abstract

BackgroundThe evolutionary success of Wolbachia bacteria, infections of which are widespread in invertebrates, is largely attributed to an ability to manipulate host reproduction without imposing substantial fitness costs. Here, we describe a stage-structured model with deterministic immature lifestages and a stochastic adult female lifestage. Simulations were conducted to better understand Wolbachia invasions into uninfected host populations. The model includes conventional Wolbachia parameters (the level of cytoplasmic incompatibility, maternal inheritance, the relative fecundity of infected females, and the initial Wolbachia infection frequency) and a new parameter termed relative larval viability (RLV), which is the survival of infected larvae relative to uninfected larvae.ResultsThe results predict the RLV parameter to be the most important determinant for Wolbachia invasion and establishment. Specifically, the fitness of infected immature hosts must be close to equal to that of uninfected hosts before population replacement can occur. Furthermore, minute decreases in RLV inhibit the invasion of Wolbachia despite high levels of cytoplasmic incompatibility, maternal inheritance, and low adult fitness costs.ConclusionsThe model described here takes a novel approach to understanding the spread of Wolbachia through a population with explicit dynamics. By combining a stochastic female adult lifestage and deterministic immature/adult male lifestages, the model predicts that even those Wolbachia infections that cause minor decreases in immature survival are unlikely to invade and spread within the host population. The results are discussed in relation to recent theoretical and empirical studies of natural population replacement events and proposed applied research, which would use Wolbachia as a tool to manipulate insect populations.

Larval Competition Extends Developmental Time and Decreases Adult Size of wMelPop Wolbachia-Infected Aedes aegypti

“…However, even a 5% relative viability cost of Wolbachia infection can make invasion difficult. 31 The wMelPop-infected adults tended to be slightly underrepresented in mixed and pure cohorts, although whether this minor cost of infection to larval viability is sufficient to affect wMelPop invasion requires further investigation. In contrast, wMel was significantly overrepresented in screened adults; wMel infection appears to provide a viability benefit relative to uninfected larvae in mixed cohorts.…”

“…13 An important component of this is relative larval viability. 31 However, the competitive ability of Wolbachia-infected larvae relative to uninfected larvae under stress is poorly understood. Recent studies suggest Wolbachia infection may have deleterious effects on immature host survival and development, 16,17,32 and studies on the naturally infected Ae.…”

“…33 A minor cost to survival of Wolbachia-infected larvae relative to uninfected larvae could render invasion difficult. 31 Therefore, it is important to assess the effect of wMelPop infection on competition for resources with uninfected larvae under stress.…”

Two-sex mosquito model for the persistence ofWolbachia

“…A continuous time non-spatial model and a reaction-diffusion model incorporating lifespan shortening and CI were developed to study factors that determine the spatial spread of Wolbachia through a population of female Aedes aegypti mosquitoes assuming constant population size and perfect maternal transmission of Wolbachia [46]. A two-sex deterministic model with deterministic immature life stages and stochastic female adult life stage was developed to understand Wolbachia invasion into uninfected host population [6].…”

Interaction ofWolbachiaand Bloodmeal Type in Artificially InfectedAedes albopictus(Diptera: Culicidae)

“…The wMelPop Wolbachia infection has been shown to impose fitness costs on multiple life history traits of host individuals (Moreira et al 2009a;Turley et al 2009;McMeniman and O'Neill 2010;Yeap et al 2011Yeap et al , 2014Suh and Dobson 2013;Ross et al 2014), and theoretical studies suggest the invasion of the Wolbachia infection can be hindered by fitness costs (Hoffmann et al 1990, Crain et al 2011, Yeap et al 2011. Particularly, introduction of wMelPop into aposymbiotic Ae.…”