Spillover of an alien parasite reduces expression of costly behaviour in native host species

Typology of the ecological impacts of biological invasions

Biological invasions alter ecosystems by disrupting ecological processes that can degrade biodiversity, harm human health, and cause massive economic burdens. Existing frameworks to classify the ecological impacts either miss many types of impact or conflate mechanisms (causes) with the impacts themselves (consequences). We propose a comprehensive typology of 19 types of ecological impact across six levels of ecological organisation. This allows more accurate diagnosis of the cause of impact and can help triage management options to tackle each impact-mechanism combination. We integrated the typology with broad ecological concepts such as energy, mass, and information flow and storage. By highlighting cascading effects across multiple levels, this typology provides a clearer framework for documenting, and communicating invasion impacts, thereby improving management and research.

The impact of invasive Sinanodonta woodiana (Bivalvia, Unionidae) and mussel macroparasites on the egg distribution of parasitic bitterling fish in host mussels

Facilitative and competitive interactions among coexisting parasite species, as well as among alternative host species, produce considerable ecological and evolutionary responses to host-parasite relationships. Such effects can be illuminated by impacts of non-native species on relationships in local communities. We used the association between parasitic European bitterling fish (Rhodeus amarus) and unionid mussels (which host bitterling eggs in their gills) to test the effects of the invasive Chinese pond mussel (Sinanodonta woodiana) and the presence of non-bitterling mussel macroparasites on the pattern of host mussel use by the bitterling across 12 unionid mussel communities with the absence or presence of S. woodiana (and variation in duration of coexistence with local species). While all six European mussel species were used by the bitterling (with the prevalence of > 30% in Unio spp.), no S. woodiana individual was infected by the bitterling. The presence of S. woodiana did not affect bitterling eggs distribution in native mussels. Large native mussels hosted more bitterling. Infection by non-bitterling parasites, mostly water mites (prevalence 47%) and trematodes (25%), did not affect rates of bitterling parasitism. We discuss our results in the context of the rapid evolution of non-native species in their new range and its implication on mussel conservation.

The RodentGPOmics Atlas: a comprehensive database of rodent biology for genomes and pathogens

Rodents represent the most abundant order of mammals, exhibiting remarkable diversity in morphology, habitats, behaviors, and hosted pathogens. Significant attention is currently focused on rodents as experimental animals for biomedical research. However, numerous aspects of rodents remain unexplored, such as their potential in unconventional biomedical models, molecular underpinnings of intriguing complex phenotypes, adaptations to environment or climate change, and host-pathogen interactions and arms race evolution. These challenges require a systematic framework to integrate the genomic variations among rodents with information on rodent-borne pathogens. To address this gap, we have established a comprehensive, freely accessible, and user-friendly atlas named Rodent Genome and Pathogen multi-Omics (RodentGPOmics), which provides comparative analysis of rodent genomes and information on zoonotic pathogen sequences in rodents. The RodentGPOmics Atlas provides: (i) basic information on 2706 rodent species; (ii) chromosome-level visualization of genomes, functional annotations, and genomic comparisons across 121 rodent species; (iii) epidemiological profiles based on 21 852 pathogen sequences reported in rodents and (iv) a few genomic tools for in-depth exploration of rodent multi-omics. This resource aims to advance the development of biomedical models for humans for promoting public health, as well as innovate the genetics, genomics, and molecular evolution in rodents, and offer valuable knowledge on rodent-borne emerging/re-emerging zoonotic infectious diseases. The resources are freely available and easy-to-use at http://RodentGPOmics.njau.edu.cn:8888/Rodent/index/homePage.

Use of infrared thermography to detect reactions to stressful events: does animal personality matter?

The study of the relationship between animal stress and personality for free-ranging animals is limited and provides contrasting results. The perception of stressors by an individual may vary due to its personality, and certain personality traits may help individuals to better cope with them. Using non-invasive infrared thermography (IRT), we investigated the link between physiological and behavioral components expressed during an acute stress event by free-ranging Fremont's squirrels (Tamiasciurus fremonti). We expected that, during the acute stress event of being approached by the researcher, individuals that showed a fast pace-of-life syndrome (bolder, more active, and less social/more aggressive) based on an arena test would exhibit stronger sympathetic-adrenal-medullary system reactivity showing a more intense stress-induced hyperthermia (high core body temperature and low peripheral temperature) than individuals with a slow pace of life (shy, less active, and more social). We successfully employed IRT technology to images of Fremont's squirrels with identification of the individuals' body parts (eye, nose, ear, hind foot). However, we found no support for our hypothesis. Squirrels' body surface temperatures told us more about a squirrel's external environment and less about the thermal state of the body in that environment following a stressful event. Further studies need to assess how to make IRT effective and efficient in the field and improve its performance in studying the relationships between physiology and personality in wildlife.

Climatic niche and range shifts of grey squirrels (Sciurus carolinensis Gmelin) in Europe: An invasive pest displacing native squirrels

BACKGROUND

As an invasive pest from North America, grey squirrels (GSs; Sciurus carolinensis Gmelin) are displacing native squirrels in Europe. However, the climatic niche and range dynamics of GSs in Europe remain largely unknown. Through niche and range dynamic models, we investigated climatic niche and range shifts between introduced GSs in Europe and native GSs in North America.

RESULTS

GSs in North America can survive in more variable climatic conditions and have much wider climatic niche breadth than do GSs in Europe. Based on climate, the potential range of GSs in Europe included primarily Britain, Ireland, and Italy, whereas the potential range of GSs in North America included vast regions of western and southern Europe. If GSs in Europe could occupy the same climatic niche space and potential range as GSs in North America, they would occupy an area ca. 2.45 times the size of their current range. The unfilling ranges of GSs in Europe relative to those of GSs in North America were primarily in France, Italy, Spain, Croatia, and Portugal.

CONCLUSION

Our observations implied that GSs in Europe have significant invasion potential, and that range projections based on their occurrence records in Europe may underestimate their invasion risk. Given that small niche shifts between GSs in Europe and in North America could lead to large range shifts, niche shifts could be a sensitive indicator in invasion risk assessment. The identified unfilling ranges of the GS in Europe should be prioritized in combating GS invasions in the future. © 2023 Society of Chemical Industry.

Interactions between native and invasive species: A systematic review of the red squirrel-gray squirrel paradigm

The eastern gray squirrel (Sciurus carolinensis) has been labeled as one of the 100 worst invasive alien species by the IUCN. In Europe, the species has been introduced to Britain, Ireland and Italy, and its subsequent spread has resulted in wide-scale extinction of native Eurasian red squirrels (Sciurus vulgaris) from the areas colonized by the gray squirrel. This replacement of a native by an alien competitor is one of the best documented cases of the devastating effects of biological invasions on native fauna. To understand how this replacement occurs, we present a systematic review of the literature on competition and interactions between red and gray squirrels. We describe the patterns of red and gray squirrel distribution in those parts of Europe where gray squirrels occur and summarize the evidence on the different processes and mechanisms determining the outcome of competition between the native and alien species including the influence of predators and pathogens. Some of the drivers behind the demise of the red squirrel have been intensively studied and documented in the past 30 years, but recent field studies and mathematical models revealed that the mechanisms underlying the red-gray paradigm are more complex than previously thought and affected by landscape-level processes. Therefore, we consider habitat type and multi-species interactions, including host-parasite and predator-prey relationships, to determine the outcome of the interaction between the two species and to better address gray squirrel control efforts.

Thinking "outside the box": The effect of nontarget snails in the aquatic community on mollusc-borne diseases

There is a great need to understand the impact of complex communities on the free-living parasite stages that are part of them. This task becomes more complex as nonnative species emerge, changing existing relationships and shaping new interactions in the community. A relevant question would be: Can the coexistence of nontarget snails with the target hosts contribute to trematodasis control? We used field and experimental approaches to investigate nonnative competitor-induced parasite dilution. During a three-year field study, we investigated digenean infection in Lymnaea stagnalis from eight Polish lakes inhabited or uninhabited by Potamopyrgus antipodarum. Additionally, we verified the presence of digenean infections in the populations of P. antipodarum. Moreover, we conducted an experimental infection of L. stagnalis with miracidia of Trichobilharzia szidati under increasing densities of P. antipodarum and aimed to infect P. antipodarum with them separately. The prevalence of avian schistosomes in lymnaeid snails was significantly higher in uninhabited lakes than in lakes inhabited by P. antipodarum. Our study indicates that waters with a higher density of invaders have a lower prevalence of avian schistosomes in lymnaeid hosts. The results of experimental studies confirmed that the presence of high densities of P. antipodarum reduces the probability of target host infection. Both field and experimental studies rule out the role of P. antipodarum as a source of avian schistosome cercariae. Here, a nonnative species was tested as a diluter, which in practice may be harmful to the local environment. This work is not a call for the introduction of nonnative species; it is intended to be a stimulus for researchers to continue searching for natural enemies of parasites because, as our results show, they exist. Finding natural enemies to the most dangerous species of human and animal parasites that will pose no threat to the local environment could be groundbreaking.

Native species exhibit physiological habituation to invaders: a reason for hope

Animals cope with environmental perturbations through the stress response, a set of behavioural and physiological responses aimed to maintain and/or return to homeostasis and enhance fitness. Vertebrate neuroendocrine axis activation in response to environmental stressors can result in the secretion of glucocorticoids (GCs), whose acute increases may be adaptive, while chronic elevation may be detrimental. Invasive grey squirrels (Sciurus carolinensis) act as a stressor eliciting elevation of GCs in native red squirrels (Sciurus vulgaris). Here we used 6-year data of variation in faecal glucocorticoid metabolite (FGM) concentrations following invasion by grey squirrels in three red squirrel populations, to identify if red squirrels showed physiological habituation to this stressor. The decrease in FGMs over time was more pronounced shortly after invasion and at high densities of grey squirrels while it decreased less strongly and was no longer influenced by the invader density as time since invasion elapsed. At the individual level, FGMs also decreased more markedly as each red squirrel experienced prolonged contact with the invader. Our study provides compelling new data suggesting that native species in the wild can habituate to prolonged contact with invasive species, showing that they may avoid the potentially harmful effects of chronic elevations in GCs.

Living on the edge: morphological and behavioral adaptations to a marginal high-elevation habitat in an arboreal mammal

Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species, which can result in habitat-dependent phenotypic differences among animals living in heterogeneous environments. We studied three alpine populations of Eurasian red squirrels (Sciurus vulgaris), one living in a marginal high-elevation habitat at the edge of the species' altitudinal distribution, and two occurring in higher-quality habitats. Here, we investigated whether squirrels living in the marginal area differed in two morphological parameters (body size and body mass) and/or in the expression of four personality traits estimated with an open field test and a mirror image stimulation test (activity, exploration, activity-exploration and social tendency). Furthermore, we tested whether within-individual variance of the traits (behavioral plasticity) was higher in the edge habitat. Male squirrels in the edge habitat were smaller and weighed less than in the other study areas, while among females size-habitat relationships were less marked. These sex-specific patterns were explained by a strong association between body mass and reproductive success in female squirrels. Squirrels in the marginal habitat were more active, explorative and had a more social personality than in the other habitats. However, in contrast to our predictions, behavioral plasticity was smaller in the marginal habitat, but only for the trait exploration. Our results suggest that animals choose the habitat that best fits their personality, and that habitat-related differences in selective pressures may shape animals' morphology. This article is protected by copyright. All rights reserved.

Invasive alien species as an environmental stressor and its effects on coping style in a native competitor, the Eurasian red squirrel

Free-living animals cope with environmental stressors through physiological and behavioural responses. According to the unidimensional model, these responses are integrated within a coping style: proactive individuals (bold, active-explorative and social) have a lower hypothalamic-pituitary-adrenal (HPA) axis reactivity than reactive ones (shy, less active-explorative, less social). These associations may change when individuals are exposed to human-induced rapid environmental change (HIREC), such as the introduction of invasive alien species (IAS). Here, we studied Eurasian red squirrels to investigate the relationship between personality traits and one integrated measure of HPA axis activity, both in areas uncolonized (natural populations) and colonized by an IAS, the Eastern grey squirrel (invaded populations). We expected an association between physiological and behavioural responses, and that activity, exploration and social tendency would covary, forming a behavioural syndrome in natural populations, while competition with the IAS was predicted to disrupt these associations. We used faecal glucocorticoid metabolites (FGMs) as an integrated measure of adrenocortical activity, and measured the levels of four personality traits (exploration, activity, activity-exploration and social tendency) with an open field test and a mirror image stimulation test. We found no correlation between FGMs and personality traits, neither in natural nor invaded populations. However, we found correlations among personality traits in areas without interspecific competition, indicating a behavioural syndrome, which was disrupted in invaded populations. This is one of the few studies showing that an IAS, acting as an environmental stressor, alters a native species' behavioural syndrome, but does not influence its coping style.

Restricted access to private properties limits management of invasive alien species: A literature review and case studies

Biological invasions are one of the major drivers of global environmental change and there is a need to develop integrated strategies to counteract this phenomenon. Eradication is an effective management option to mitigate the deleterious impacts of invasive alien species (IAS). Eradication can be achieved if all reproductive individuals are removed and population recovery is prevented. However, individuals may survive removal operations in private areas if interventions are not allowed. Here, we present 1) three case studies in which restricted private property access prevented the local eradication of invasive alien populations, and 2) a list of reasons for denying access to private properties and a list of actions implemented or suggested by managers to facilitate access and reported in 29 reviewed papers. The restricted access affected the local eradication of three Eastern grey squirrel (Sciurus carolinensis) populations in Italy. In Lombardy region, in one area a planned eradication did not start and in another area the implemented eradication failed due to the refusal from the owner of a large private property to grant access to managers. In Umbria region, the lack of collaboration from an Italian financial institution produced a delay of 15 months in the removal. In our case studies, therefore, a single person or institution denied access for a personal gain or presumed internal security. The reasons behind landowner opposition may be diverse and individual attitudes towards IAS management will depend on interactions with owners. According to our review, in many cases the denial of access takes place in a general perception of mistrust or opposition to the project as the results of a limited engagement of local people. Such opposition often jeopardizes control activities, with profound negative consequences on eradication, expecially at landscape scale. Bottom-up approaches aiming at involving stakeholders can increase the possibility to achieve IAS eradication, however appropriate legislation remains pivotal to enforce eradication in case of non-cooperative behaviour.

Invading parasites: spillover of an alien nematode reduces survival in a native species

It is widely assumed that spillover of alien parasites to native host species severely impacts naïve populations, ultimately conferring a competitive advantage to invading hosts that introduced them. Despite such host-switching events occurring in biological invasions, studies demonstrating the impact of alien macroparasites on native animal hosts are surprisingly few. In Europe, native red squirrels (Sciurus vulgaris) are replaced by introduced North American grey squirrels (S. carolinensis) mainly through resource competition, and, only in the United Kingdom and Ireland, by competition mediated by a viral disease. In Italy such disease is absent, but spillover of an introduced North American nematode (Strongyloides robustus) from grey to red squirrels is known to occur. Here, we used long-term (9 years) capture-mark-recapture and parasitological data of red squirrels in areas co-inhabited by grey squirrels in Northern Italy to investigate the impact of this alien helminth on naïve native squirrels’ body mass, local survival, and reproduction of females. We found no negative effect of the alien parasite on body mass or reproductive success, but intensity of infection by S. robustus reduced survival of both male and female squirrels. Significantly, survival of squirrels co-infected by their native nematode, Trypanoxyuris sciuri, was less affected by S. robustus, suggesting a protective effect of the native helminth against the new infection. Hence, we demonstrate that alien S. robustus spillover adds to the detrimental effects of resource competition and stress induced by grey squirrels, further reducing the fitness of the native species in the presence of the invasive competitor.

Corticosterone response by Peromyscus mice to parasites, reproductive season, and age

A common response to parasite infestations is increased production of glucocorticoid hormones that regulate immune function. We examined relationships between ectoparasite infestations and fecal corticosterone metabolites (FCM) in deer mice (Peromyscus maniculatus). Furthermore, we experimentally removed fleas to determine if reductions in ectoparasites affected FCM production. Individuals were assigned to control (no flea removal) or treatment (anti-flea application, physical combing) groups and individuals were recaptured to assess changes in FCM concentrations. There was a significant and negative effect of number of anti-flea treatment applications on FCM concentrations of deer mice. However, models including host biology traits and environmental predictors had a better model fit compared to models containing ectoparasite predictors. In particular, there was a significant relationship of deer mouse FCM with date and host age, where glucocorticoid production decreased towards the end of the breeding season and increased with age. Overall, adverse events associated with reproduction and age class, rather than ectoparasites, may be more important to variation in glucocorticoids of deer mice.

Complex relationships between physiological stress and endoparasite infections in natural populations

Short-term elevation of glucocorticoids (GCs) is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors (stressors). However, when exposure to stressors occurs repeatedly or over a prolonged period of time, animals may experience chronic elevation of GCs, which reduces the immune response efficiency and can lead to higher intensity of parasitic infection. Here, we used invasive gray squirrels Sciurus carolinensis introduced in Northern Italy and their 2 most prevalent gastrointestinal parasites, the nematode Strongyloides robustus and coccidia of the genus Eimeria, as a model to investigate relationships among macroparasite infection and concentrations of fecal glucocorticoid metabolites (FGMs), an integrated measure of circulating GCs. Our results revealed an association of FGMs with infection by St. robustus, but not with coccidia. Individuals with higher FGMs appear to be responsible for the greatest St. robustus egg shedding within gray squirrel populations, thus possibly acting as superspreaders. However, FGMs were negatively associated with adult St. robustus, suggesting that the abundance of adults of this nematode species does not induce elevation in FGMs, but is only affected by it through immune-mediated effects on its fecundity. Finally, the relationship between St. robustus (both eggs and adult parasites) and FGMs was not linear, suggesting that only high levels of physiological stress influence parasite infection. Our findings highlight that the direction and magnitude of the stress-infection relationship may depend not only on the specific host-parasite system, but also on the different life stages of the same parasite.