Dr Jacques Deere

The fall armyworm, , is a long-distance migratory pest, which invaded the African continent in 2016, causing enormous losses to agricultural crops, especially maize. Synthetic insecticides are primarily used for managing , but they leave residues on human food and animal feed and also cause environmental hazards. We evaluated the crude ethanolic extract of fruits for contact toxicity on larvae and determined the lethal concentration (LC ) of the extract. Additionally, we conducted an electrophysiological (EAG) experiment to determine the responses of adult males and females to and determined whether the extract influenced mating, oviposition, and repellence to the adult female. We found that extract caused significantly higher mortality to larvae than an ethanol control. Electrophysiologically, we observed significantly higher responses to the extract than the control, with some variations in response between the sexes. A wind tunnel experiment revealed that females moved more towards the control than towards the extract. Taken together, our results confirm that extract is effective against larvae and adults. Future research should explore the responses of to extract on a field scale.

Potential immortality is observed in several species (e.g. prickly pear cactus, hydra and flatworms) and is indicative of their negligible or even negative senescence rates. Unlike in senescent species, which experience reduced individual performance with age due to physiological degradation, species with negligible or negative senescence display mortality rates that remain constant or decline with age, respectively. These rates vary across taxa and are correlated with life history traits. Yet, the extent to which variable resource availability, a key driver of variation in life history traits, impacts species that show negligible or negative senescence is currently unknown. Here, we examine whether and how variation in the quantity, quality and feeding interval of resources impact population structure, population performance and life history trait trade-offs in two long-lived planaria that do not senesce: Schmidtea mediterranea and Dugesia tahitiensis. In a full factorial design, different combinations of resource quantity (reduced intake, standard intake and high intake) and quality (high and low quality) were provided in two different feeding intervals (7-day and 14-day intervals) for 19 weeks. We show that variability in resource availability, via decreases in quantity, quality and frequency of resources, does not diminish population viability in either species but does result in suboptimal conditions of stress in S. mediterranea. The high population viability we report can be attributed to two different mechanisms: increased reproduction or increased investment into maintenance at the expense of reproduction. Moreover, which mechanism was responsible for said high population viability was context-dependent and modulated by the specific life history strategy of the two planaria species. We show that suboptimal conditions can cause stress responses that have significant impacts on non-senescent species. The context-dependent response we observe suggests that species that do not senesce but are subject to suboptimal conditions of stress may ultimately exhibit declines in performance and ultimately die. A clearer understanding of the impact of suboptimal conditions of resource availability on non-senescent species is needed to determine the extent of stress experienced and ultimately whether a species can truly be immortal. Our work offers an important contribution to understanding how species with negligible or negative senescence respond to variation in available resources that could result in suboptimal conditions of stress. Using potentially immortal planaria, with unique life histories, as our system we provide novel insight into this under-represented area of research.image

Life history traits play an important role in population dynamics and correlate, both positively and negatively, with dispersal in a wide range of taxa. Most invertebrate studies on trade-offs between life history traits and dispersal have focused on dispersal via flight, yet much less is known about how life history trade-offs influence species that disperse by other means. In this study, we identify effects of investing in dispersal morphology (dispersal expression) on life history traits in the male dimorphic bulb mite (Rhizoglyphus robini). This species has a facultative juvenile life stage (deutonymph) during which individuals can disperse by phoresy. Further, adult males are either fighters (which kill other mites) or benign scramblers. Here, in an experiment, we investigate the effects of investing in dispersal on size at maturity, sex and male morph ratio, and female lifetime reproductive success. We show that life history traits correlate negatively with the expression of the dispersal stage. Remarkably, all males that expressed the dispersal life stage developed into competitive fighters and none into scramblers. This suggests that alternative, male reproductive strategies and dispersal should not be viewed in isolation but considered concurrently.

Rising temperatures due to climate change are predicted to accelerate the life cycle of arthropod herbivores thereby exacerbating pest formation. Notorious pests like spider mites thrive in areas with high temperatures (32–35 °C), and it is predicted that the size and number of such areas will expand in the coming decades. Higher temperatures can directly accelerate population growth, but also indirectly affect them through changes in the plant's defensive mechanisms. Spider mites have been shown to adapt to plant defences, with natural selection favouring defence-suppressing traits. However, it is not known to what extent suppression is affected by rising temperatures and how this might tie into the rate of adaptation and pest damage. In this study, we investigated the effect of two temperatures (25 °C and 32 °C), on the spider mite–tomato interaction, predicting the influence of rising temperatures on favouring defence-adapted mites. We found that all mite strains caused more plant damage at 32 °C, but temperature did not affect the overall patterns of induction and suppression of defence genes. Although fecundity was higher for all strains at 32 °C, juvenile and adult survival was lower, especially for inducer mites. With these data, we parametrized population models for the two strains over three months, indicating that suppressor mites might displace inducers at the higher temperature, either when it is constant or in the form of heat waves. Our models predict that in areas with higher temperatures, defence-suppressing mites are favoured, which will accelerate and consequently spur pest formation.

•Individual costs associated with dispersal morph expression carry over to negatively impact the natal population.•Different dispersal scenarios and dispersal expression increase generation time but population growth rate declines.•Increasing generation time is due to the addition of a life stage and to other life-history effects of the dispersal stage.•We suggest that dispersing individuals that fail to disperse may affect the population dynamics of persistent natal populations. Individuals that disperse from one habitat to another has consequences for individual fitness, population dynamics and gene flow. The fitness benefits accrued in the new habitat are traded off against costs associated with dispersal. Most studies focus on costs at settlement and effects on settlement populations; the influence of dispersal to natal populations is assessed by monitoring change in numbers due to emigration. However, the extent to which natal populations are affected when individuals that invest in dispersal fail to disperse/emigrate is unclear. Here, we use an Integral Projection Model (IPM) to assess how developing into a disperser affects natal population structure and growth. We do so using the bulb mite (Rhizoglyphus robini) as a study system. Bulb mites, in unfavourable environments, develop into a dispersal (deutonymph) stage during ontogeny; these individuals are called dispersers with individuals not developing into this stage called non-dispersers. We varied disperser expression and parameterised IPMs to describe three simulations of successful and unsuccessful dispersal: (i) ‘no dispersal’ - dispersal stage is excluded and demographic data are from non-disperser individuals; (ii) ‘false dispersal’ - dispersal stage included and demographic data from non-disperser individuals are used; (iii) ‘true dispersal’ - dispersal stage included and demographic data are from individuals that go through the dispersal stage and from non-disperser individuals. We found that the type of dispersal simulation (no dispersal

Dispersal is an important form of movement influencing population dynamics, species distribution and gene flow between populations. In population models, dispersal is often included in a simplified manner by removing a random proportion of the population. Many ecologists now argue that models should be formulated at the level of individuals instead of the population level. To fully understand the effects of dispersal on natural systems, it is therefore necessary to incorporate individual-level differences in dispersal behavior in population models. Here, we parameterized an integral projection model, which allows for studying how individual life histories determine population-level processes, using bulb mites, Rhizoglyphus robini, to assess to what extent dispersal expression (frequency of individuals in the dispersal stage) and dispersal probability affect the proportion of successful dispersers and natal population growth rate. We find that allowing for life-history differences between resident phenotypes and disperser phenotypes shows that multiple combinations of dispersal probability and dispersal expression can produce the same proportion of leaving individuals. Additionally, a given proportion of successful dispersing individuals result in different natal population growth rates. The results highlight that dispersal life histories, and the frequency with which disperser phenotypes occur in the natal population, significantly affect population-level processes. Thus, biological realism of dispersal population models can be increased by incorporating the typically observed life-history differences between resident phenotypes and disperser phenotypes, and we here present a methodology to do so.

Developmental plasticity alters phenotypes and can in that way change the response to selection. When alternative phenotypes show different life history trajectories, developmental plasticity can also affect, and be affected by, population size-structure in an ecoevolutionary interaction. Developmental plasticity often functions to anticipate future conditions but it can also mitigate current stress conditions. Both types of developmental plasticity have evolved under different selections and this raises the question if they underlie different eco-evolutionary population dynamics. Here, we tested, in a long-term population experiment using the male polyphenic bulb mite ( Rhizoglyphus robini), if the selective harvesting of juveniles of different developmental stages concurrently alters population size (ecological response) and male adult phenotype expression (evolutionary response) in line with eco-evolutionary predictions that assume the male polyphenism is anticipatory or mitigating. We found that the frequency of adult males that expressed costly (fighter) morphology was lowest under the most severe juvenile harvesting conditions. This response cannot be explained if we assume that adult male phenotype expression is to anticipate adult (mating) conditions because, in that case, only the manipulation of adult performance would have an effect. Instead, we suggest that juveniles mitigate their increased mortality risk by expediating ontogeny to forego the development of costly morphology and mature quicker but as a defenceless scrambler. If, like in mammals and birds where early-life stress effects are extensively studied, we account for such pre-adult viability selection in coldblooded species, it would allow us to (i) better characterise natural selection on trait development like male polyphenisms, (ii) understand how it can affect the response to other selections in adulthood, and (iii) understand how such trait dynamics influence, and are influenced by, population dynamics.

The impacts of resource availability on senescence, the loss of vitality with age, are formalised under the Calorie Restriction (CR) theory, which predicts that the onset of senescence is delayed and life expectancy prolonged due to the ultimate effects of restricted resource intake without malnutrition. However, CR studies are largely implemented in unrealistic environments that do not consider how interacting, stochastic drivers impact longevity. Indeed, little is known about the impact of stochastic resource availability on senescence, even though environmental stochasticity is the norm rather than an exception in natural populations. Here, we examine whether and how stochasticity in the quantity, quality, and frequency of resources impact lifespan, life history trait trade-offs, and population structure in two long-lived planaria: Schmidtea mediterranea and Dugesia tahitiensis. For each species, we estimate weekly population size, survival, and a size distribution metric that quantifies population structure and skew. Over the 19-week study, survival in S. mediterranea is lower than D. tahitiensis across all feeding regimes. However, for both species, CR does not diminish survival. There are also no clear shifts in population structure over time across the different feeding regimes. For S. mediterranea, in most treatments, population structure changed to fewer smaller than larger individuals (right-skewed). In the case of D. tahitiensis, only treatments where resources are provided frequently cause right-skewed population structures. Population size also varied between species, with that of D. tahitiensis never declining across treatments, and always becoming larger than S. mediterranea; in the case of S. mediterranea, most treatments show a decline in population counts over the study period. As before, no clear pattern emerges in the changes in population counts under CR conditions for both species. As such, we did not find evidence of CR providing benefits in terms of lifespan nor trade-off between population counts, survival, and body size. We call for the careful re-evaluation of decades of CR work in short-lived species, by expanding and testing predictions in more realistic settings and across a wider range of life histories.Competing Interest StatementThe authors have declared no competing interest.

Despite exponential growth in ecological data availability, broader interoperability amongst datasets is needed to unlock the potential of open access. Our understanding of the interface of demography and functional traits is well-positioned to benefit from such interoperability. Here, we introduce MOSAIC, an open-access trait database that unlocks the demographic potential stored in the COMADRE, COMPADRE, and PADRINO open-access databases. MOSAIC data were digitised and curated through a combination of existing datasets and new trait records sourced from primary literature. In its first release, MOSAIC (v. 1.0.0) includes 14 trait fields for 300 animal and plant species: biomass, height, growth determination, regeneration, sexual dimorphism, mating system, hermaphrodism, sequential hermaphrodism, dispersal capacity, type of dispersal, mode of dispersal, dispersal classes, volancy, and aquatic habitat dependency. MOSAIC includes species-level phylogenies for 1,359 species and population-specific climate data. We identify how database integration can improve our understanding of traits well-quantified in existing repositories and those that are poorly quantified (e.g., growth determination, modularity). MOSAIC highlights emerging challenges associated with standardising databases and demographic measures.

The world’s human population is reaching record longevities. Consequently, our societies are experiencing the impacts of prolonged longevity, such as increased retirement age. A major hypothesized influence on aging patterns is resource limitation, formalized under calorie restriction (CR) theory. This theory predicts extended organismal longevity due to reduced calorie intake without malnutrition. However, several challenges face current CR research and, although several attempts have been made to overcome these challenges, there is still a lack of holistic understanding of how CR shapes organismal vitality. Here, we conduct a literature review of 224 CR peer-reviewed publications to summarize the state-of-the-art in the field. Using this summary, we highlight the challenges of CR research in our understanding of its impacts on longevity. We demonstrate that experimental research is biased toward short-lived species (98.2% of studies examine species with