Search

We are still largely reliant on pesticides for the suppression of arthropod pests which threaten human health and food production, but the recent rise of evolved resistance among important pest species has reduced pesticide efficacy. Despite this, our understanding of strategies that effectively limit the evolution of resistance remains weak. Male‐killing sex ratio distorting microbes (SRDMs), such as Wolbachia and Spiroplasma, are common among arthropod species. Previous theoretical work has suggested that they could limit adaptive potential in two ways: first, because by distorting sex ratios they reduce the effective population size, and second, because infected females produce no male offspring which restricts gene flow. Here we present the results of a novel experiment in which we test the extent by which these two mechanisms limit the adaptive response of arthropods to pesticide. Using a fully factorial design, we manipulated the adult sex ratio of laboratory populations of Drosophila melanogaster, both in the presence and absence of SRDMs, and exposed these populations to six generations of pesticide poisoning. This design allows the effects of SRDMs on sex ratio and their effects on gene flow to be estimated separately. After six generations, individuals from populations with even sex ratios displayed a higher resistance to pesticide relative to individuals from female‐biased populations. By contrast, we found no effect of the presence of SRDMs in host populations on pesticide resistance independent of sex ratio. In addition, males were more susceptible to pesticide than females—this was true of flies from both naïve and previously exposed populations. These findings provide the first empirical proof of concept that sex ratio distortion arising from SRDMs can limit adaptation to pesticides, but cast doubt on the theoretical effect of male‐killers limiting adaptation by disrupting gene flow. [ABSTRACT FROM AUTHOR]

Maternally‐inherited sex ratio distorting microbes (SRDMs) are common among arthropod species. Typically, these microbes cause female‐biased sex ratios in host broods, either by; killing male offspring, feminising male offspring, or inducing parthenogenesis. As a result, infected populations can experience drastic ecological and evolutionary change. The mechanism by which SRDMs operate is likely to alter their impact on host evolutionary ecology; despite this, the current literature is heavily biased towards a single mechanism of sex ratio distortion, male‐killing. Furthermore, amidst the growing concerns surrounding the loss of arthropod diversity, research into the impact of SRDMs on the viability of arthropod populations is generally lacking. In this study, using a theoretical approach, we model the epidemiology of an understudied mechanism of microbially‐induced sex ratio distortion—feminisation—to ask an understudied question—how do SRDMs impact extinction risk in a changing environment? We constructed an individual‐based model and measured host population extinction risk under various environmental and epidemiological scenarios. We also used our model to identify the precise mechanism modulating extinction. We find that the presence of feminisers increases host population extinction risk, an effect that is exacerbated in highly variable environments. We also identified transmission rate as the dominant epidemiological trait responsible for driving extinction. Finally, our model shows that sex ratio skew is the mechanism driving extinction. We highlight feminisers and, more broadly, SRDMs as important determinants of the resilience of arthropod populations to environmental change. [ABSTRACT FROM AUTHOR]

Maternally‐inherited sex ratio distorting microbes (SRDMs) are common among arthropod species. Typically, these microbes cause female‐biased sex ratios in host broods, either by; killing male offspring, feminising male offspring, or inducing parthenogenesis. As a result, infected populations can experience drastic ecological and evolutionary change. The mechanism by which SRDMs operate is likely to alter their impact on host evolutionary ecology; despite this, the current literature is heavily biased towards a single mechanism of sex ratio distortion, male‐killing. Furthermore, amidst the growing concerns surrounding the loss of arthropod diversity, research into the impact of SRDMs on the viability of arthropod populations is generally lacking. In this study, using a theoretical approach, we model the epidemiology of an understudied mechanism of microbially‐induced sex ratio distortion—feminisation—to ask an understudied question—how do SRDMs impact extinction risk in a changing environment? We constructed an individual‐based model and measured host population extinction risk under various environmental and epidemiological scenarios. We also used our model to identify the precise mechanism modulating extinction. We find that the presence of feminisers increases host population extinction risk, an effect that is exacerbated in highly variable environments. We also identified transmission rate as the dominant epidemiological trait responsible for driving extinction. Finally, our model shows that sex ratio skew is the mechanism driving extinction. We highlight feminisers and, more broadly, SRDMs as important determinants of the resilience of arthropod populations to environmental change. [ABSTRACT FROM AUTHOR]

Many arthropod species are vulnerable to infection by bacteria that kill the male offspring of their female hosts. These male‐killing bacteria (MKB) can greatly impact the ecology and evolution of their hosts, particularly when MKB prevalence is high and persistent through time. However, we still do not have a holistic understanding of the key determinants of MKB ecological epidemiology, particularly regarding the interplay between host‐MKB traits and environmental conditions. Here, we derived a mathematical model to analyse the role that several intrinsic and extrinsic factors play in determining MKB epidemiology, and how these factors interact with one another. We found that the invasion threshold and prevalence of MKB is determined by transmission rate and the rate at which female hosts recover from MKB infections. The invasion and prevalence of MKB is also highly sensitive to the extent that MKB can reduce intra‐brood competition by killing male offspring. Environmentally‐induced periodic changes to the epidemiological characteristics of MKB caused a sharp decline and a slow recovery of MKB prevalence and, in some cases, environmental disturbance can drive MKB extinct. Furthermore, the magnitude of the impact that environmental disturbance had on the dynamics of MKB prevalence was heavily modulated by intrinsic factors, particularly intra‐brood competition. This is the first study to explore how both intrinsic and extrinsic factors interact to influence the dynamics of MKB infections over large timescales; our findings are central to predicting the current and future impacts of MKB on host populations. [ABSTRACT FROM AUTHOR]

Cannibalism is taxonomically widespread and can have large impacts on individual fitness and population-level processes. As such, identifying how cannibalism rates vary in response to ecological cues is important for predicting species evolution and population dynamics. 2. In this study, we aimed to identify several eco-evolutionary factors that affect cannibalism rate and measure how they interacted with one another. 3. To do this, we conducted two experiments using complimentary methods to measure how cannibalism rates varied among larval Drosophila melanogaster and Drosophila simulans in response to changes in conspecific relatedness, social familiarity and density. 4. We found that larvae were more likely to cannibalise non-related larval victims in both species, and that this effect increased at high densities in D. simulans. We found no evidence that Drosophila larvae use social familiarity to assess relatedness. Finally, in D. melanogaster, cannibalistic larvae prefer to cannibalise larvae that are being attacked by a greater number of conspecifics, implying that cues linked to conspecific abundance encourage cooperative cannibalism. 5. By showing that cannibalism frequency in Drosophila spp. is sensitive to relatedness and several other factors, we reveal the complex relationship between cannibalism frequency and species ecology. Also, by showing that the effect of relatedness on cannibalism frequency is density dependent, we advance the current understanding of how ecological variables interact to affect kin selection. [ABSTRACT FROM AUTHOR]

Allee effects occur when individual or population survival decreases due to populations being small or sparse. A key mechanism underlying Allee effects is difficulty in finding mates at low densities. Species may be particularly vulnerable to mate‐finding Allee effects if females rely on an abundance of males to reproduce successfully. In sexually cannibalistic species, females may consume males before or after copulation, potentially reducing the supply of males to the point where a mate‐finding Allee effect occurs.In this study, we investigate the extent to which sexual cannibalism can modulate mate‐finding Allee effects, and the conditions under which sexual cannibalism is likely to be particularly detrimental to population viability.We created an individual‐based model that tracked specific females throughout the breeding season and used extinction risk and per capita growth rate to measure the strength of the Allee effects. We varied both founder population size and mate encounter rate independently of each other to expose the mechanism driving the Allee effects. We also analysed how cannibalism‐derived female fecundity benefits affected extinction risk.We found that sexual cannibalism could lead to high extinction risk, particularly when cannibalism occurred before copulation, founder population size was small and mate encounter rates were low. However, post‐copulatory cannibalism reduced extinction risk, if cannibalism increased female fecundity enough. We found that there were strong threshold effects, in which small changes in encounter rate could strongly alter population extinction risk.We find that sexual cannibalism is likely to negatively impact population survival as population size and mate encounter rate decrease. This may be exacerbated if male quality declines and female hunger increases in declining populations. As many top invertebrate predators, such as spiders and mantises, are sexually cannibalistic, this may have ecosystem‐wide impacts. We also suggest that other reproductive behaviours, such as rejecting all but high‐quality mates or requiring multiple mates to ensure fertility, are also likely to cause mate‐finding Allee effects when habitat quality degrades. [ABSTRACT FROM AUTHOR]

Sexual cannibalism is common in spiders and can be advantageous for female fitness by increasing egg production. However, it is possible that, under low mate density, females will be at risk of consuming all of the males they encounter prior to copulation. Cannibalistic females may be able to mitigate the risk of virgin death if they reduce cannibalism rates in response to low mate availability. Here, we attempted to manipulate perceived mate density and observe whether it affected female aggression towards males in the fen raft spider (Dolomedes fimbriatus). We predicted that female attack rate would increase in response to an increasing number of male encounters. We also recorded male courtship effort. Despite previous literature finding that D. fimbriatus females were highly aggressive towards conspecific males, we found that females only attacked courting males in 14% of encounters. None of these attacks resulted in cannibalism. Moreover, attacks were not associated with how many males the female had previously been exposed to. Male courtship effort decreased in response to repeated exposure to females. Some of the virgin females laid and guarded unfertilized egg cases; this made them unattractive to males, potentially reducing their reproductive lifespan prematurely. [ABSTRACT FROM AUTHOR]

Abstract: Some behaviours that typically increase fitness at the individual level may reduce population persistence, particularly in the face of environmental changes. Sexual cannibalism is an extreme mating behaviour which typically involves a male being devoured by the female immediately before, during or after copulation, and is widespread amongst predatory invertebrates. Although the individual‐level effects of sexual cannibalism are reasonably well understood, very little is known about the population‐level effects. We constructed both a mathematical model and an individual‐based model to predict how sexual cannibalism might affect population growth rate and extinction risk. We found that in the absence of any cannibalism‐derived fecundity benefit, sexual cannibalism is always detrimental to population growth rate and leads to a higher population extinction risk. Increasing the fecundity benefits of sexual cannibalism leads to a consistently higher population growth rate and likely a lower extinction risk. However, even if cannibalism‐derived fecundity benefits are large, very high rates of sexual cannibalism (>70%) can still drive the population to negative growth and potential extinction. Pre‐copulatory cannibalism was particularly damaging for population growth rates and was the main predictor of growth declining below the replacement rate. Surprisingly, post‐copulatory cannibalism had a largely positive effect on population growth rate when fecundity benefits were present. This study is the first to formally estimate the population‐level effects of sexual cannibalism. We highlight the detrimental effect sexual cannibalism may have on population viability if (1) cannibalism rates become high, and/or (2) cannibalism‐derived fecundity benefits become low. Decreased food availability could plausibly both increase the frequency of cannibalism, and reduce the fecundity benefit of cannibalism, suggesting that sexual cannibalism may increase the risk of population collapse in the face of environmental change. [ABSTRACT FROM AUTHOR]

Functional redundancy, the potential for the functional role of one species to be fulfilled by another, is a key determinant of ecosystem viability. Scavenging transfers huge amount of energy through ecosystems and is, therefore, crucial for ecosystem viability and healthy ecosystem functioning. Despite this, relatively few studies have examined functional redundancy in scavenger communities. Moreover, the results of these studies are mixed and confined to a very limited range of habitat types and taxonomic groups.This study attempts to address this knowledge gap by conducting a field experiment in an undisturbed natural environment assessing functional roles and redundancy in vertebrate and invertebrate scavenging communities in a South African savanna.We used a large‐scale field experiment to suppress ants in four 1 ha plots in a South African savanna and paired each with a control plot. We distributed three types of small food bait: carbohydrate, protein and seed, across the plots and excluded vertebrates from half the baits using cages. Using this combination of ant suppression and vertebrate exclusion, allowed us explore the contribution of non‐ant invertebrates, ants and vertebrates in scavenging and also to determine whether either ants or vertebrates were able to compensate for the loss of one another.In this study, we found the invertebrate community carried out a larger proportion of overall scavenging services than vertebrates. Moreover, although scavenging was reduced when either invertebrates or vertebrates were absent, the presence of invertebrates better mitigated the functional loss of vertebrates than did the presence of vertebrates against the functional loss of invertebrates. There is a commonly held assumption that the functional role of vertebrate scavengers exceeds that of invertebrate scavengers; our results suggest that this is not true for small scavenging resources.Our study highlights the importance of invertebrates for securing healthy ecosystem functioning both now and into the future. We also build upon many previous studies which show that ants can have particularly large effects on ecosystem functioning. Importantly, our study suggests that scavenging in some ecosystems may be partly resilient to changes in the scavenging community, due to the potential for functional compensation by vertebrates and ants. [ABSTRACT FROM AUTHOR]

Understanding the factors that control decomposition is critical for predicting how the carbon cycle will alter with global change. Until recently, the accepted paradigm was that climate primarily drives decomposition rates, and interactions among decomposers only control variation at finer scales. Although it is now understood that biotic agents can play an important role, we know less about the importance of species interactions with a lack of field experiments at a large scale. Predation is a key ecological interaction that could influence decomposition by directly or indirectly regulating the abundances of decomposer organisms, but a comprehensive understanding of the cascading effects that predation can have on decomposition, particularly at large scales, is missing.Here we report on an experiment where we suppressed the abundance of ants, which are major predators of termites, at a hectare scale in a natural African savanna and examined how this affected the decomposition of three common substrates (wood, grass and dung).Our study revealed that ants exert considerable top‐down control on decomposition via their predation of termites: decomposition of wood, grass and dung increased by 98%, 74% and 84% with ant suppression, respectively. Suppression of ants increased termite activity and consequently resulted in increased termite‐mediated decomposition. Remarkably, for all substrates, the suppression of ants nearly doubled decomposition by termites. Additionally, for grass and dung substrates, the dominant agent of decomposition switched from microbes to termites with ant suppression.Our study highlights the critical importance of considering species interactions in decomposition studies, particularly given declines in predatory species in the Anthropocene. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

We currently face significant, anthropogenic, global environmental challenges and the role of ecologists in mitigating these challenges is arguably more important than ever. Consequently there is an urgent need to recruit and train future generations of ecologists, both those whose main area is ecology, but also those involved in the geological, biological and environmental sciences. Here we present the results of a horizon scanning exercise that identified current and future challenges facing the teaching of ecology, through surveys of teachers, students and employers of ecologists. Key challenges identified were grouped in terms of the perspectives of three groups: students, for example the increasing disconnect between people and nature; teachers, for example the challenges associated with teaching the quantitative skills that are inherent to the study of ecology; and society, for example poor societal perceptions of the field of ecology. In addition to the challenges identified, we propose a number of solutions developed at a workshop by a team of ecology teaching experts, with supporting evidence of their potential to address many of the problems raised. These proposed solutions include developing living labs, teaching students to be ecological entrepreneurs and influencers, embedding skills‐based learning and coding in the curriculum, an increased role for learned societies in teaching and learning, and using new technology to enhance fieldwork studies including virtual reality, artificial intelligence and real‐time spoken language translation. Our findings are focused towards UK higher education, but they should be informative for students and teachers of a wide range of educational levels, policy makers and professional ecologists worldwide. [ABSTRACT FROM AUTHOR]