Comparative brain morphology of cleaning and sponge-dwelling Elacatinus gobies.

Introduction Comparative studies of brain anatomy between closely related species have been very useful in demonstrating selective changes in brain structure. Within-species comparisons can be particularly useful for identifying changes in brain structure caused by contrasting environmental selection pressures. Here, we aimed to understand whether differences within and between species in habitat use and foraging behaviour influence brain morphology, on both ecological and evolutionary time scales. Methods We used as a study model three species of the Elacatinus genus that differ in their habitat-foraging mode. The obligatory cleaning goby Elacatinus evelynae inhabits mainly corals and feeds mostly on ectoparasites removed from larger fish during cleaning interactions. In contrast, the obligatory sponge-dwelling goby Elacatinus chancei inhabits tubular sponges and feeds on microinvertebrates buried in the sponges' tissues. Finally, in the facultatively cleaning goby Elacatinus prochilos, individuals can adopt either phenotype, the cleaning or the sponge-dwelling habitat-foraging mode. By comparing the brains of the facultative goby phenotypes to the brains of the obligatory species we can test whether brain morphology is better predicted by phylogenetic relatedness or the habitat-foraging modes (cleaning x sponge-dwelling). Results We found that E. prochilos brains from both types (cleaning and sponge-dwelling) were highly similar to each other. Their brains were in general more similar to the brains of the most closely related species, E. evelynae (obligatory cleaning species), than to the brains of E. chancei (sponge-dwelling species). In contrast, we found significant brain structure differences between the cleaning species (E. evelynae and E. prochilos) and the sponge-dwelling species (E. chancei). These differences revealed independent changes in functionally correlated brain areas that might be ecologically adaptive. E. evelynae and E. prochilos had a relatively larger visual input processing brain axis and a relatively smaller lateral line input processing brain axis than E. chancei. Conclusion The similar brain morphology of the two types of E. prochilos corroborates other studies showing that individuals of both types can be highly plastic in their social and foraging behaviours. Our results in the Elacatinus species suggest that morphological adaptations of the brain are likely to be found in specialists whereas species that are more flexible in their habitat may only show behavioral plasticity without showing anatomical differences.

First record of intraspecific cleaning behavior by the threatened Leuciscidae Squalius alburnoides (Steindachner, 1866) at the Guadiana River basin (Portugal).

Squalius alburnoides (Steindachner, 1866) is an endemic threatened species from the Iberian Peninsula. Here, we report the first observations of intraspecific cleaning behavior in isolated summer pools in the Guadiana River Basin (Portugal). We found that focal S. alburnoides solicited cleaning by adopting an immobile tail-stand position known as "posing," which immediately signaled a response to a few conspecifics that approached and inspect them. Our study expands the list of cleanerfish species in freshwaters, giving emphasis to the importance of mutual positive behavior within an endangered species, particularly when facing seasonal disturbance.

Reef Location and Client Diversity Influence the Skin Microbiome of the Caribbean Cleaner Goby Elacatinus evelynae.

Fish-associated microorganisms are known to be affected by the environment and other external factors, such as microbial transfer between interacting partners. One of the most iconic mutualistic interactions on coral reefs is the cleaning interactions between cleaner fishes and their clients, during which direct physical contact occurs. Here, we characterized the skin bacteria of the Caribbean cleaner sharknose goby, Elacatinus evelynae, in four coral reefs of the US Virgin Islands using sequencing of the V4 region of the 16S rRNA gene. We specifically tested the relationship between gobies' level of interaction with clients and skin microbiota diversity and composition. Our results showed differences in microbial alpha- and beta-diversity in the skin of gobies from different reef habitats and high inter-individual variation in microbiota diversity and structure. Overall, the results showed that fish-to-fish direct contact and specifically, access to a diverse clientele, influences the bacterial diversity and structure of cleaner gobies' skin. Because of their frequent contact with clients, and therefore, high potential for microbial exchange, cleaner fish may serve as models in future studies aiming to understand the role of social microbial transfer in reef fish communities.

Oestradiol reduces female bill colour in a mutually ornamented bird.

Carotenoid-based colour signals can be costly to produce and maintain, and trade-offs between signalling and other fitness traits are expected. In mutually ornamented species, trade-offs with reproduction may be stronger for females than males, because females often dedicate more resources to offspring production, which may lead to plastic investment in colour signals and plastic sexual dichromatism. Oestradiol is a candidate mediator of this trade-off because it regulates reproductive physiology and may also influence the expression of coloration. We tested this hypothesis by giving female common waxbills (Estrilda astrild) either oestradiol (17ß-oestradiol) or empty implants during the early breeding season and measured spectral reflectance of carotenoid-based bill coloration weekly for two months. Using a model of avian vision, we found that bill colour in oestradiol-implanted females became less saturated, less red in hue and brighter, compared with control females and with unimplanted males. This resulted in a change in bill sexual dichromatism from imperceptible to perceptible. Results support the hypothesis that female reproductive physiology influences investment in coloration through changes in oestradiol and show a form of female-driven plastic sexual dichromatism. Greater sensitivity of female colour to physiological and/or environmental conditions helps explain why differences in sexual dichromatism among species differing in ecology often evolve owing to changes in female rather than male phenotype.

A test of context- and sex-dependent dopaminergic effects on the behavior of a gregarious bird, the common waxbill, Estrilda astrild.

The dopaminergic (DAergic) system has well-known influences on behavioral and cognitive functions. Previous work with common waxbills (Estrilda astrild) reported context-specific DAergic effects that could have been due to social environment. Manipulating the dopamine D2-like receptor family (D2R) pathways had opposing effects on behavior depending on whether waxbills were tested alone or in a small cage with a mirror as a social stimulus. As waxbills are highly gregarious, it was hypothesized that being alone or perceiving that they have a companion might explain this context dependence. To test context-dependent DAergic effects, we compared behavioral effects of D2R manipulation in waxbills in the same familiar environment, but either alone or with a familiar, same-sex companion. We found that D2R agonism decreased movement and feeding, similar to previous results when testing waxbills alone. However, contrary to the hypothesis of dependence on social context, we found that the behavioral effects of the D2R agonist were unchanged when waxbills were tested with a companion. The context dependence reported earlier might thus be due to other factors, such as the stress of being in a novel environment (small cage) or with an unfamiliar social stimulus (mirror image). In tests with a companion, we also found a sex-specific social effect of D2R manipulation: D2R blocking tended to decrease aggression in males but to increase it in females. Together with past work, our results suggest that DAergic effects on behavior involve different types of context or sex dependence.

Emotional behavior in aquatic organisms? Lessons from crayfish and zebrafish.

Experimental animal models are a valuable tool to study the neurobiology of emotional behavior and mechanisms underlying human affective disorders. Mounting evidence suggests that various aquatic organisms, including both vertebrate (e.g., zebrafish) and invertebrate (e.g., crayfish) species, may be relevant to study animal emotional response and its deficits. Ideally, model organisms of disease should possess considerable genetic and physiological homology to mammals, display robust behavioral and physiological responses to stress, and should be sensitive to a wide range of drugs known to modulate stress and affective behaviors. Here, we summarize recent findings in the field of zebrafish- and crayfish-based tests of stress, anxiety, aggressiveness and social preference, and discuss further perspectives of using these novel model organisms in translational biological psychiatry. Outlining the remaining questions in this field, we also emphasize the need in further development and a wider use of crayfish and zebrafish models to study the pathogenesis of affective disorders.

Dopamine and serotonin mediate the impact of stress on cleaner fish cooperative behavior.

Stress is known to modulate behavioral responses and rapid decision-making processes, especially under challenging contexts which often occur in social and cooperative interactions. Here, we evaluated the effects of acute stress on cooperative behavior of the Indo-Pacific cleaner wrasse (Labroides dimidiatus) and the implications of pre-treatment with monoaminergic compounds: the selective serotonin reuptake inhibitor - fluoxetine, the 5-HT1A receptor antagonist - WAY-100,635, the D1 receptor agonist - SKF-38393, and the D1 receptor antagonist - SCH-23390. We demonstrated that stress decreased the predisposal to interact and increased cortisol levels in cleaners, which are alleviated by fluoxetine and the dopaminergic D1 antagonist. Overall, our findings highlight the crucial influence of stress on cooperative behavior.

Experimental evidence for a role of dopamine in avian personality traits.

There is increasing interest in the genetic and physiological bases of behavioural differences among individuals, namely animal personality. One particular dopamine (DA) receptor gene (the dopamine receptor D4 gene) has been used as candidate gene to explain personality differences, but with mixed results. Here, we used an alternative approach, exogenously manipulating the dopaminergic system and testing for effects on personality assays in a social bird species, the common waxbill (Estrilda astrild). We treated birds with agonists and antagonists for DA receptors of both D1 and D2 receptor pathways (the latter includes the D4 receptor) and found that short-term manipulation of DA signalling had an immediate effect on personality-related behaviours. In an assay of social responses (mirror test), manipulation of D2 receptor pathways reduced time spent looking at the social stimulus (mirror image). Blocking D2 receptors reduced motor activity in this social assay, while treatment with a D2 receptor agonist augmented activity in this social assay but reduced activity in a non-social behavioural assay. Also, in the non-social assay, treatment with the D1 receptor antagonist markedly increased time spent at the feeder. These results show distinct and context-specific effects of the dopaminergic pathways on waxbill personality traits. Our results also suggest that experimental manipulation of DA signalling can disrupt a behavioural correlation (more active individuals being less attentive to mirror image) that is habitually observed as part of a behavioural syndrome in waxbills. We discuss our results in the context of animal personality, and the role of the DA system in reward and social behaviour.

Ecological differences in the facultative Caribbean cleaning goby Elacatinus prochilos do not predict learning performance in discriminatory two-choice tasks.

The ecological approach to comparative cognition emphasizes that the ecological and social environment are important predictors of cognitive performance. We used this approach to test whether differences in habitat use and social behavior in the facultative Caribbean cleaning goby Elacatinus prochilos predict differences in learning performance in two discriminatory two-choice tasks. This species has two behavioral ecotypes: one that frequently engages in cleaning interactions and inhabits corals in male-female pairs (cleaning gobies) and another that rarely engages in cleaning interactions and inhabits barrel sponges in large groups (sponge-dwellers). We predicted that cleaning gobies would outperform sponge-dwellers in a pattern-cued task, which consisted of identifying the pattern on a plate that consistently provided food, while sponge-dwellers would outperform cleaning gobies in a spatial task, which consisted of identifying the location of the plate. Contrary to our predictions, there was no difference in performance between the two ecotypes. Most of the gobies performed poorly in the pattern-cued task and well in the spatial task. A possible explanation for these results is that the association of a pattern with positive and negative reinforcement may not be a pre-requisite for engaging in cleaning interactions, while spatial skills might be equally required in both ecotypes. Alternatively, the two ecotypes can flexibly adjust to new feeding conditions, which would explain their similar performance in the spatial task. Further research should investigate which aspects of E. prochilos' social and ecological environment might impose challenges that require spatial cognition and whether individuals can flexibly adjust to new habitats and feeding conditions.

Estradiol shapes mutualistic behaviour of female cleaner fish (Labroides dimidiatus - Valenciennes, 1839): Potential implications of environmental disturbance.

The presence of endocrine-derived compounds in the environment occurs due to a myriad of human or industrial activity and can disrupt the endocrine system of animals, including fish. One important group of endocrine disruptors are the estrogens, such as 17-ß estradiol (E2, estradiol). Estrogens are gonadal steroid hormones, able to be influential even in small concentrations. Here, we demonstrate that E2 is linked to female' decisions made by an important coral reef species, the cleaner fish Labroides dimidiatus, during interactions with other reef fishes (known as clients). E2 treatment in natural conditions interfered directly in the cooperative relationships, by increasing cleaners' willingness to interact with clients, providing greater amounts of physical contact to their fish partners. We discuss the meaning of the observed behavioural disruption produced by E2, which by affecting a key species (cleaners) may produce a cascade impact in the aquatic ecosystem.

The integration of sociality, monoamines and stress neuroendocrinology in fish models: applications in the neurosciences.

Animal-focused research has been crucial for scientific advancement, but rodents are still taking a starring role. Starting as merely supporting evidence found in rodents, the use of fish models has slowly taken a more central role and expanded its overall contributions in areas such as social sciences, evolution, physiology and recently in translational medical research. In the neurosciences, zebrafish Danio rerio have been widely adopted, contributing to our understanding of the genetic control of brain processes and the effects of pharmacological manipulations. However, discussion continues regarding the paradox of function versus structure, when fishes and mammals are compared and on the potentially evolutionarily conserved nature of behaviour across fish species. From a behavioural standpoint, we explore aversive-stress and social behaviour in selected fish models and refer to the extensive contributions of stress and monoaminergic systems. We suggest that, in spite of marked neuroanatomical differences between fishes and mammals, stress and sociality are conserved at the behavioural and molecular levels. We also suggest that stress and sociality are mediated by monoamines in predictable and non-trivial ways and that monoamines could bridge the relationship between stress and social behaviour. To reconcile the level of divergence with the level of similarity, we need neuroanatomical, pharmacological, behavioural and ecological studies conducted in the laboratory and in nature. These areas need to add to each other to enhance our understanding of fish behaviour and ultimately how this all may lead to better model systems for translational studies.

Stimulation of dopamine D1 receptor improves learning capacity in cooperating cleaner fish.

Accurate contextual decision-making strategies are important in social environments. Specific areas in the brain are tasked to process these complex interactions and generate correct follow-up responses. The dorsolateral and dorsomedial parts of the telencephalon in the teleost fish brain are neural substrates modulated by the neurotransmitter dopamine (DA), and are part of an important neural circuitry that drives animal behaviour from the most basic actions such as learning to search for food, to properly choosing partners and managing decisions based on context. The Indo-Pacific cleaner wrasse Labroides dimidiatus is a highly social teleost fish species with a complex network of interactions with its 'client' reef fish. We asked if changes in DA signalling would affect individual learning ability by presenting cleaner fish two ecologically different tasks that simulated a natural situation requiring accurate decision-making. We demonstrate that there is an involvement of the DA system and D1 receptor pathways on cleaners' natural abilities to learn both tasks. Our results add significantly to the growing literature on the physiological mechanisms that underlie and facilitate the expression of cooperative abilities.

Serotonin blockade delays learning performance in a cooperative fish.

Animals use learning and memorizing to gather information that will help them to make ecologically relevant decisions. Neuro-modulatory adjustments enable them to make associations between stimuli and appropriate behavior. A key candidate for the modulation of cooperative behavior is serotonin. Previous research has shown that modulation of the serotonergic system spontaneously affects the behavior of the cleaner wrasse Labroides dimidiatus during interactions with so-called 'client' reef fish. Here, we asked whether shifts in serotonin function affect the cleaners' associative learning abilities when faced with the task to distinguish two artificial clients that differ in their value as a food source. We found that the administration of serotonin 1A receptor antagonist significantly slowed learning speed in comparison with saline treated fish. As reduced serotonergic signaling typically enhances fear, we discuss the possibility that serotonin may affect how cleaners appraise, acquire information and respond to client-derived stimuli via manipulation of the perception of danger.

Brain levels of nonapeptides in four labrid fish species with different levels of mutualistic behavior.

There is strong evidence that brain nonapeptides are implicated as modulators of a wide array of social and reproductive behaviors in fishes. However, the question remains, as to whether there is a link between the distribution of active nonapeptides across brain regions and fishes specific behavioral phenotypes. To explore this link we compared the nonapeptides' profile across the brains of fishes representing different degrees of mutualistic behavior (here: cleaning behavior). Herein we studied the quantitative distribution of both nonapeptides, arginine vasotocin (AVT) and isotocin (IT), in the brains of four species of fish belonging to the family Labridae: two are obligatory cleaners throughout their entire life (Labroides dimidiatus and Labroides bicolor), one species is a facultative cleaner (Labropsis australis; juveniles are cleaners and adults are corallivorous), and one is a non-cleaner species, corallivorous throughout its entire life (Labrichthys unilineatus). The biologically available AVT and IT concentrations were measured simultaneously in distinct brain macro-areas: forebrain, optic tectum, cerebellum and brain stem, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We showed that the levels of both AVT and IT varied significantly across species, as measured in the whole brain or in the specific macro-areas. Significantly higher AVT concentrations in the cerebellum which were found in the obligate cleaners seemed to be related to expression of mutualistic behavior. On the other hand, the higher levels of brain IT in the non-cleaner L. unilineatus suggested that these might be linked to the development of sexual dimorphism, which occurs only in this non-cleaner species.

Cortisol mediates cleaner wrasse switch from cooperation to cheating and tactical deception.

Recent empirical research, mostly done on humans, recognizes that individuals' physiological state affects levels of cooperation. An individual's internal state may affect the payoffs of behavioural alternatives, which in turn could influence the decision to either cooperate or to defect. However, little is known about the physiology underlying condition dependent cooperation. Here, we demonstrate that shifts in cortisol levels affect levels of cooperation in wild cleaner wrasse Labroides dimidiatus. These cleaners cooperate by removing ectoparasites from visiting 'client' reef fishes but prefer to eat client mucus, which constitutes cheating. We exogenously administrated one of three different compounds to adults, that is, (a) cortisol, (b) glucocorticoid receptor antagonist mifepristone RU486 or (c) sham (saline), and observed their cleaning behaviour during the following 45min. The effects of cortisol match an earlier observational study that first described the existence of "cheating" cleaners: such cleaners provide small clients with more tactile stimulation with their pectoral and pelvic fins, a behaviour that attracts larger clients that are then bitten to obtain mucus. Blocking glucocorticoid receptors led to more tactile stimulation to large clients. As energy demands and associated cortisol concentration level shifts affect cleaner wrasse behavioural patterns, cortisol potentially offers a general mechanism for condition dependent cooperation in vertebrates.

Arginine vasotocin neuronal phenotype and interspecific cooperative behaviour.

The nonapeptide arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin are well known for their role in the modulation of several intraspecific social behaviours, such as social approach/withdrawal and aggression. Recently, we suggested that AVT might also be important in the regulation of interspecific social behaviours as it modulates interspecific cooperative behaviours in the Indo-Pacific bluestreak cleaner wrasse Labroides dimidiatus. AVT injections decreased cleaners' propensity to engage in cleaning interactions with their clients, suggesting that high levels of this peptide compromise the cleaners' cooperative motivation. Therefore, we hypothesise that low endogenous levels of AVT are a prerequisite for the expression of interspecific cleaning behaviour in cleaner wrasses, since it allows them to approach and interact with interspecific individuals, and that this should be reflected in their AVT neuronal phenotype. Here we test this hypothesis by comparing the AVT neuronal phenotypes of two phylogenetically closely related species that live in similar environments but diverge in the expression of interspecific cooperative behaviour: an obligate cleaner wrasse (L. dimidiatus) and a non-cleaner corallivore wrasse (Labrichthys unilineatus). The two species are predicted to differ in their AVT neuronal phenotypes as a reflection of their ability/inability to approach and interact with interspecific individuals, with cleaners presenting smaller and/or less numerous AVT-immunoreactive (ir) neurons. A sex difference in AVT neuronal phenotypes was also predicted because males of both species appear to be more aggressive than females. As described for most of the other teleost species, AVT-ir neurons were restricted to the preoptic area, and in agreement with our first prediction cleaners presented smaller and less numerous AVT-ir neurons in the gigantocellular preoptic area (gPOA) compared to non-cleaners. Contrary to our second prediction, AVT neuronal phenotypes did not differ between sexes in either species, but differences in other features of the AVT system cannot be ruled out. In summary, the results presented here suggest a putative role for AVT gPOA neurons in the ability of a cleaner wrasse to approach and interact with a client, through their projections to extrahypothalamic brain areas.

Effects of mesotocin manipulation on the behavior of male and female common waxbills.

The oxytocin family of neuropeptides is implicated in the regulation of sociality across vertebrates. Non-mammalian homologs of oxytocin, such as isotocin in fish and mesotocin in amphibians, reptiles and birds, all play crucial roles modulating social and reproductive behavior. In this study, we exogenously manipulated the mesotocinergic system in a highly social bird, the common waxbill Estrild astrild, and tested the effects on affiliative and aggressive behavior by performing tests of competition over food. Birds treated with mesotocin decreased almost all the behaviors we studied (movement, feeding, allopreening), while birds treated with an oxytocin antagonist showed a reduction only in social behaviors (aggressions and allopreening). We also found two sex-specific effects: mesotocin reduced allopreening more in males than females, and the oxytocin antagonist reduced aggressiveness only in females. Our results suggest sex-specific effects in the modulation of affiliative and aggressive behaviors via mesotocinergic pathways.

Effect of Tryptophan Dietary Content on Meagre, Argyrosomus regius, Juveniles Stress and Behavioral Response.

There are a high number of stressors present in aquaculture that can affect fish welfare and quality. One way of mitigating stress response is by increasing dietary tryptophan. In this study, three diets containing 0.5% (Tript1), 0.6% (Tript2), and 0.8% (Tript3) of tryptophan were tested in 32 g juvenile meagre for 56 days. At the end of the trial, survival, growth, and proximate composition were similar between treatments. Significant differences were found in the plasma parameters before and after a stress test consisting of 30 s of air exposure. Blood glucose levels were higher in the post-stress for all treatments (e.g., 63.9 and 76.7 mg/dL for Tript1 before and after the stress test), and the hemoglobin values were lower in the post-stress of Tript1 (1.9 g/dL compared to 3.0 and 2.4 g/dL for Tript2 and Tript3, respectively). In terms of behavior, three tests were carried out (novel tank diving and shoaling assays, and lateralization test), but no significant differences were found, except for the number of freezing episodes during the anxiety test (1.4 for Tript3 compared to 3.5 and 4.2 for the other treatments). This study suggests that supplementation with dietary tryptophan, particularly in higher dosage (0.8%), can reduce anxiety-like behavior in meagre exposure to acute stress (novel tank). Although the remaining results showed mild effects, they provide some clues as to the potential of this amino acid as a stress mitigator in aquaculture.

Dopamine modulates social behaviour in cooperatively breeding fish.

Dopamine is part of the reward system triggering the social decision-making network in the brain. It has hence great potential importance in the regulation of social behaviour, but its significance in the control of behaviour in highly social animals is currently limited. We studied the role of the dopaminergic system in social decision-making in the cooperatively breeding cichlid fish, Neolamprologus pulcher, by blocking or stimulating the dopaminergic D1-like and D2-like receptors. We first tested the effects of different dosages and timing of administration on subordinate group members' social behaviour within the group in an unchallenging environment. In a second experiment we pharmacologically manipulated D1-like and D2-like receptors while experimentally challenging N. pulcher groups by presenting an egg predator, and by increasing the need for territory maintenance through digging out sand from the shelter. Our results show that the D1-like and D2-like receptor pathways are differently involved in the modulation of aggressive, submissive and affiliative behaviours. Interestingly, the environmental context seems particularly crucial regarding the role of the D2-like receptors in behavioural regulation of social encounters among group members, indicating a potential pathway in agonistic and cooperative interactions in a pay-to-stay scenario. We discuss the importance of environmental information in mediating the role of dopamine for the modulation of social behaviour.

Hemolymph Glycemia as an Environmental Stress Biomarker in the Invasive Red Swamp Crayfish (Procambarus clarkii).

AbstractSeveral freshwater crayfish species, including Procambarus clarkii, are both ecologically important and commercially important benthic macroinvertebrates, remarkable for their potential to adapt and reproduce but also for their unique abilities to face distinct abiotic and biotic environments and become successful invaders. While much work has been done to study crayfish introductions, less focus has been given to how crayfish cope with pollution and other environmental stressors, in terms of physiological responses, and whether crayfish responses can be used to assess the effective state of their living environment. Here, we used a mixed approach combining laboratory experiments with field data to validate the use of hemolymph glucose as a relevant biomarker of red swamp crayfish (Procambarus clarkii) stress response. Three meaningful sampling locations were chosen across southern Portugal that are representative of different environments where crayfish live and are frequently captured for human consumption but also correspond to different pollution levels. To reference field measurements of glucose levels, we performed two lab-based experiments: (a) crayfish were exposed to different levels of stress (stress challenge) and (b) crawfish were exposed to a maze dispersal test, with or without water. Crayfish glucose levels were responsive to induced stress but were not correlated with dispersal efforts. Wild crayfish's body condition and stress levels responded differently to environmental conditions, with more challenged individuals showing higher glycemia levels but similar body condition. The glucose levels of the more stressed wild crayfish were visually similar to lab-based crayfish subjected to the higher stress levels (electric shocks), while the levels of glucose of crayfish at the less polluted site corresponded to those measured before the start of the challenge (baseline). The maintenance of high levels of glycemia in crayfish inhabiting more challenging habitats is revealing of their higher energetic demand state. Since P. clarkii ia globally distributed and easily sampled invasive species, quantifying its hemolymph glucose levels can be a particularly useful proxy for assessing environmental quality.