Frida Ben-Ami

In temporary waterbodies such as ponds, pools and small lakes, the diversity of smaller invertebrates, such as rotifers, remains understudied, despite their ecological importance as prey and decomposers of organic matter. Especially in regions such as Israel, where natural lakes are scarce, temporary waterbodies become even more important as refuges for aquatic biodiversity. Our study aims to (1) update existing records of monogonont rotifer biodiversity across Israel, providing an updated checklist, and (2) identify potential environmental factors influencing species richness and the composition of monogonont rotifer communities. This study presents the first comprehensive analysis of (rehydrated) monogonont rotifer diversity in 30 temporary freshwater habitats in Israel, spanning different regions that vary in climate and topography. By rehydrating dry sediment, we stimulated the hatching of resting eggs to recover the monogonont rotifer species inhabiting these habitats. We then examined the environmental and spatial factors associated with their diversity and community composition. We identified 39 species of monogonont rotifers, with 26 species being reported for the first time in this area, increasing the previously known monogonont rotifer fauna by 41%. Altitude and high temperature negatively influenced rotifer species diversity. dbRDA ordination further showed that spatial components such as latitude, longitude, and altitude and the permanency contributed to community structure. Our findings demonstrate that temporary and semi‐perennial habitats across climatic gradients are important reservoirs of rotifer biodiversity, underscoring their relevance for regional freshwater biodiversity under ongoing environmental change. Broader habitat sampling, combined with surveys of active communities and molecular approaches to resolve cryptic taxa, is expected to substantially increase current estimates of rotifer diversity beyond those obtained from sediment rehydration alone.

Host–parasite interactions represent an evolutionary arms race, with parasites evolving strategies to exploit host resources, and hosts deploying mechanisms to resist or tolerate infection. Unlike vertebrates, which possess a sophisticated immune system, invertebrates rely entirely on innate immunity to combat pathogens. Yet, the molecular underpinnings and life‐history consequences of immune activation remain little understood in non‐insect invertebrates. Here, we combine life‐history trait analysis with transcriptomics to investigate immune responses in an aquatic invertebrate exposed to a natural yeast parasite. By comparing infected, exposed‐uninfected, and unexposed individuals, we identified candidate genes potentially involved in haemocyte recruitment and the reinforcement of the gut epithelium. These patterns highlight candidate mechanisms that may contribute to resistance following pathogen exposure. Exposed‐uninfected individuals also showed delayed reproductive maturation, though lifetime reproductive output was ultimately maintained. Therefore, this suggests that successful exposure and immunity changes may be associated with a transient shift in reproductive allocation rather than a persistent reduction in reproductive output. In contrast, infected hosts exhibited stronger changes in metabolic and protein biosynthesis processes, consistent with a resource depletion hypothesis. These metabolic shifts align with reduced investment in reproduction, as infection appears to affect the number of offspring produced in the first brood. Our findings provide novel insights into the molecular and life‐history responses associated with pathogen exposure and established infection and suggest candidate mechanisms through which host responses may shape life‐history strategies in non‐insect invertebrates, with broad implications for understanding host–parasite coevolution.

Heatwaves challenge our understanding of how environmental stressors reshape host–parasite interactions, particularly during the critical “off‐host” stages of endoparasites. These stages, often dismissed as inert and unaffected by environmental changes, remain a black box in ecological research despite their key role in parasites' life cycle. Here, we examined how heatwaves affect the infectivity and progression of infection of Pasteuria ramosa , a bacterial parasite of the planktonic crustacean Daphnia magna . In order to measure the respective influences of the bacterial genotype and the heatwaves, we exposed the off‐host stages (=spores) from four genetically distinct parasite clones to three temperature regimes (20°C, 30°C, 40°C) and tested their subsequent effects on host and parasite traits. Heatwaves reduced parasite infectivity, regardless of parasite genotype. Intriguingly, heat‐stressed spores induced genotype‐specific shifts in their host: One host clone increased castration rates at higher temperatures, while others experienced moderate to dramatic declines. Furthermore, individuals exposed to heat‐stressed spores that remained uninfected exhibited enhanced survival, suggesting reduced costs of resistance against damaged parasite spores. This study provides insights into how heatwaves, endured only by the parasite, can modulate various aspects of host–parasite interactions, underlying the importance of the parasite's environmental history in evolutionary ecology and epidemiology.

Survival of aquatic invertebrates relies on the resistance of dormant stages to environmental stress and the synchronization of dormancy with seasonal changes. We investigated hatching patterns in Daphnia magna from four Mediterranean populations that experience seasonal drying. Ephippial eggs were either transferred directly to hatching-stimulation conditions or first exposed to one of the following storage treatments: wet, dark storage at 20 °C or 1 °C; or dry, dark storage at 20, 40, or 60 °C. Surprisingly, the most successful and synchronous hatching occurred after 2-month dark, cold (1 °C) storage at the temperature that rarely, if ever, occurs in their natural habitats. Dry storage led to more gradual hatching. Early diapause termination was observed in two of the studied populations, with part of the eggs hatching prior to storage and within a few days of ephippium production. Across all populations, ephippial eggs demonstrated high heat resistance and dry storage temperature had no significant effect on hatching rates or egg mortality. Despite similar natural environmental pressures, populations differed significantly in their hatching timing, suggesting fine-scale local or temporal adaptation in dormancy regulation.

Organisms are often coinfected by more than one parasite species. These coinfections can alter the fitness of both host and its coinfecting parasites. Changes in host fitness are usually estimated by comparing parasite virulence under coinfection to the virulence of each parasite under single infection. While many studies focus on host survival as proxies of virulence, virulence can be expressed via reduced host fecundity. Here, we studied the outcome of coinfection of water fleas (Daphnia magna) by two microparasitic species, the fungus Metschnikowia bicuspidata and the microsporidium Hamiltosporidium tvaerminnensis. We found that Metschnikowia expressed its virulence mainly via host mortality and Hamiltosporidium expressed it mainly via host reproduction. Despite their competitive interaction, indicated by their reduced spore production, both parasites were able to fully express their virulence during coinfection. Host survival was dominated by Metschnikowia while clutch-size was dominated by Hamiltosporidium. Furthermore, coinfected hosts experienced increased virulence that was manifested only by additional reduction in reproduction (less clutches were released). Our results demonstrate that focusing only on the survival component of host fitness can miss important outcomes of coinfections. Since reduced host fecundity is a common outcome of parasitism, the influence of coinfection on host reproduction deserves more attention.

Organisms are often coinfected by more than one parasite species. These coinfections can alter the fitness of both host and its coinfecting parasites. Changes in host fitness are usually estimated by comparing parasite virulence under coinfection to the virulence of each parasite under single infection. While many studies focus on host survival as proxies of virulence, virulence can be expressed via reduced host fecundity. Here, we studied the outcome of coinfection of water fleas ( Daphnia magna ) by two microparasitic species, the fungus Metschnikowia bicuspidata and the microsporidium Hamiltosporidium tvaerminnensis . We found that Metschnikowia expressed its virulence mainly via host mortality and Hamiltosporidium expressed it mainly via host reproduction. Despite their competitive interaction, indicated by their reduced spore production, both parasites were able to fully express their virulence during coinfection. Host survival was dominated by Metschnikowia while clutch-size was dominated by Hamiltosporidium . Furthermore, coinfected hosts experienced increased virulence that was manifested only by additional reduction in reproduction (less clutches were released). Our results demonstrate that focusing only on the survival component of host fitness can miss important outcomes of coinfections. Since reduced host fecundity is a common outcome of parasitism, the influence of coinfection on host reproduction deserves more attention.

Circadian rhythms regulate essential biological processes, including behavior, reproduction and survival, across diverse organisms. Disruptions to this cycle, whether through artificial light at night (ALAN) or reduced exposure to full-spectrum daylight, can interfere with biological processes and ultimately threaten biodiversity. This concern is growing as ALAN spreads beyond urban areas through streetlights and skyglow. Aquatic ecosystems, in which zooplankton play a key role as primary consumers as well as prey for higher trophic levels, are particularly vulnerable. Despite growing research on the impact of ALAN on some zooplankton, rotifers remain largely understudied. Here, we conducted two experiments to assess the effects of light on Brachionus species. The first experiment examined how different ALAN wavelengths influenced life history traits in three Brachionus species, while the second one investigated the attachment behavior of B. rubens on a Daphnia host under four light conditions. Our findings reveal that ALAN has strong but species-specific effects on rotifers. Green light enhanced survival and reproductive output in B. calyciflorus sensu stricto, while suppressed reproduction in B. fernandoi . In B. rubens , white light particularly altered reproductive patterns and attachment behavior. These results highlight the complex and species-specific impacts that ALAN has on rotifers, emphasizing the need for further research to fully understand its broader ecological consequences.

Understanding disease emergence and spread is a key challenge of evolutionary ecology, and there is growing evidence that host age at exposure is pivotal for improving our understanding. Previous studies of the Daphnia‐Pasteuria system found that younger hosts were more susceptible and produced more transmission stages than older ones, with the effects of earlier infection being more virulent. However, it is unknown whether these host age effects are general or specific to a particular host–parasite system, and if they are general, whether they exhibit the same pattern in magnitude and direction. Using three species of Daphnia (D. magna, D. similis and D. curvirostris) and two isolates of the pathogenic yeast Metschnikowia bicuspidata, we investigated the impact of host age at exposure on host susceptibility, parasite transmission and parasite‐induced host mortality (virulence). We found that host age at exposure affected the probability of becoming infected; although the three Daphnia species differed in the pattern and strength of infection. We also found that in all Daphnia species, older hosts produced more transmission stages than younger ones. Our results further show that host and parasite genetics, coupled with a mechanistic interaction between host body size and parasite spore length, strongly influence host and parasite traits. These results highlight the generality and diversity of host age effects and reinforce the need to incorporate them into epidemiological modelling in order to improve our response to an epidemic.

Did you choose to pursue PhD studies to make a difference, yet feel that you have achieved little? This letter encourages you to slow down, reflect and collaborate, with the goal of making a lasting contribution through a long and fruitful career.