Mitigating human impacts including climate change on proliferative kidney disease in salmonids of running waters.

Over the last two decades, an increasing number of reports have identified a decline in salmonid populations, possibly linked to infection with the parasite Tetracapsuloides bryosalmonae and the corresponding disease, that is, proliferative kidney disease (PKD). The life cycle of this myxozoan parasite includes sessile bryozoan species as invertebrate host, which facilitates the distribution of the parasite in running waters. As the disease outcome is temperature dependent, the impact of the disease on salmonid populations is increasing with global warming due to climate change. The goal of this review is to provide a detailed overview of measures to mitigate the effects of PKD on salmonid populations. It first summarizes the parasite life cycle, temperature-driven disease dynamics and new immunological and molecular research into disease resistance and, based on this, discusses management possibilities. Sophisticated management actions focusing on local adaptation of salmonid populations, restoration of the riverine ecosystem and keeping water temperatures cool are necessary to reduce the negative effects of PKD. Such actions include temporary stocking with PKD-resistant salmonids, as this may assist in conserving current populations that fail to reproduce.

The hunter and the hunted-A 3D analysis of predator-prey interactions between three-spined sticklebacks (Gasterosteus aculeatus) and larvae of different prey fishes.

Predator-prey interactions play a key life history role, as animals cope with changing predation risk and opportunities to hunt prey. It has recently been shown that the hunting success of sticklebacks (Gasterosteus aculeatus) targeting fish larvae is dependent on both the size of the prey and the prior exposure of its species to stickleback predation. The purpose of the current study was to identify the behavioural predator-prey interactions explaining the success or failure of sticklebacks hunting larvae of three potential prey species [roach (Rutilus rutilus), perch (Perca fluviatilis) and whitefish (Coregonus wartmannii)] in a 3D environment. Trials were carried out for each prey species at four different size classes in a standardised laboratory setup and were recorded using a slow motion, stereo camera setup. 75 predator-prey interactions including both failed and successful hunts were subject to the analysis. 3D track analysis indicated that sticklebacks applied different strategies. Prey with less complex predator escape responses, i.e. whitefish larvae, were hunted using a direct but stealthy approach ending in a lunge, while the behaviourally more complex roach and perch larvae were hunted with a faster approach. A multivariate logistic regression identified that slow average speed and acceleration of the prey in the initial stages of the hunt increased the probability of stickleback success. Furthermore, predators adjusted their swimming direction more often when hunting larger whitefish compared to smaller whitefish. The results suggest that appropriate and adequately timed avoidance behaviours, which vary between prey species and ontogenetic stages, significantly increase the chances of outmanoeuvring and escaping stickleback predation. Small whitefish larvae can reach similar levels of swimming performance compared to older conspecifics, but display ineffective anti-predator behaviours, resulting in higher hunting success for sticklebacks. Thus, the development of appropriate anti-predator behaviours depending on size appears to be the crucial factor to escaping predation.

It's a hard knock life for some: Heterogeneity in infection life history of salmonids influences parasite disease outcomes.

Heterogeneity in immunity occurs across numerous disease systems with individuals from the same population having diverse disease outcomes. Proliferative kidney disease (PKD) caused by Tetracapsuloides bryosalmonae, is a persistent parasitic disease negatively impacting both wild and farmed salmonids. Little is known of how PKD is spread or maintained within wild susceptible populations. We investigated an aspect of fish disease that has been largely overlooked, that is, the role of the host phenotypic heterogeneity in disease outcome. We examined how host susceptibility to T. bryosalmonae infection, and the disease PKD, varied across different infection life-history stages and how it differs between naïve, re-infected and persistently infected hosts. We investigated the response to parasite exposure in host phenotypes with (a) different ages and (b) heterogeneous infection life histories. Among (a) the age phenotypes were young-of-the-year (YOY) fish and juvenile 1+ fish (fish older than one) and, for (b) juvenile 1+ infection survivors were either re-exposed or not re- exposed to the parasite and response phenotypes were assigned post-hoc dependant on infection status. In fish not re-exposed this included fish that cleared infection (CI) or had a persistent infection (PI). In fish re-exposed these included fish that were re-infected (RI), or re-exposed and uninfected (RCI). We assessed both parasite-centric (infection prevalence, parasite burden, malacospore transmission) and host-centric parameters (growth rates, disease severity, infection tolerance and the immune response). In (a), YOY fish, parasite success and disease severity were greater and differences in the immune response occurred, demonstrating an ontogenetic decline of susceptibility in older fish. In (b), in PI and RI fish, parasite success and disease severity were comparable. However, expression of several adaptive immunity markers was greater in RI fish, indicating concomitant immunity, as re-exposure did not intensify infection. We demonstrate the relevance of heterogeneity in infection life history on disease outcome and describe several distinctive features of immune ontogeny and protective immunity in this model not previously reported. The relevance of such themes on a population level requires greater research in many aquatic disease systems to generate clearer framework for understanding the spread and maintenance of aquatic pathogens.

The impact of long-term reduced access to cleaner fish on health indicators of resident client fish.

In many mutualisms, benefits in the form of food are exchanged for services such as transport or protection. In the marine cleaning mutualism, a variety of 'client' reef fishes offer 'cleaner' fish Labroides dimidiatus access to food in the form of their ectoparasites, where parasite removal supposedly protects the clients. Yet, the health benefits individual clients obtain in the long term from repeated ectoparasite removal remain relatively unknown. Here, we tested whether long-term reduced access to cleaning services alters indicators of health status such as body condition, immunity and the steroids cortisol and testosterone in four client damselfish species Pomacentrus amboinensis, Amblyglyphidodon curacao, Acanthochromis polyacanthus and Dischistodus perspicillatus To do so, we took advantage of a long-term experimental project in which several small reefs around Lizard Island (Great Barrier Reef, Australia) have been maintained cleaner-free since the year 2000, while control reefs had their cleaner presence continuously monitored. We found that the four damselfish species from reef sites without cleaners for 13 years had lower body condition than fish from reefs with cleaners. However, immunity measurements and cortisol and testosterone levels did not differ between experimental groups. Our findings suggest that clients use the energetic benefits derived from long-term access to cleaning services to selectively increase body condition, rather than altering hormonal or immune system functions.

Morphological and molecular data show no evidence of the proposed replacement of endemic Pomphorhynchus tereticollis by invasive P. laevis in salmonids in southern Germany.

Changes in parasite communities might result in new host-parasite dynamics and may threaten local fish populations. This phenomenon has been suggested for acanthocephalan parasites in the river Rhine and Danube where the species Pomphorhynchus tereticollis is becoming replaced by the Ponto-Caspian P. laevis. Developing knowledge on morphologic, genetic and behavioural differences between such species is important to follow such changes. However, disagreements on the current phylogeny of these two acanthocephalan species are producing conflicts that is affecting their correct identification. This study is offering a clearer morphological and genetic distinction between these two species. As P. tereticollis is found in rhithral tributaries of the Rhine, it was questioned whether the local salmonid populations were hosts for this species and whether P. laevis was expanding into the Rhine watershed as well. In order to test for this, brown trout, Salmo trutta, and grayling, Thymallus thymallus from South-Western Germany watersheds have been samples and screened for the occurrence of acanthocephalan parasites. For the first time, both species were confirmed to be hosts for P. tereticollis in continental Europe. P. tereticollis was found to be common, whereas P. leavis was found only at a single location in the Danube. This pattern suggest either that the expansion of P. laevis through salmonid hosts into rhithral rivers has not yet occurred, or that not yet ascertained biotic or abiotic features of rhithral rivers hinder P. laevis to spread into these areas.

Effects of parasite concentrations on infection dynamics and proliferative kidney disease pathogenesis in brown trout (Salmo trutta).

Proliferative kidney disease (PKD) is an emerging disease of salmonids, which is exacerbating with increasing water temperature. Its causative agent, the myxozoan parasite Tetracapsuloides bryosalmonae, exploits freshwater bryozoans as primary hosts and salmonids as intermediate hosts. Our experiments showed that the manipulation of exposure concentrations of infective malacospores had relatively minor impacts for the disease outcomes in the fish host. In this study, brown trout (Salmo trutta) were exposed to three different exposure concentrations of T. bryosalmonae malacospores: (a) a single low parasite concentration (LC), (b) a single high parasite concentration (HC) and (c) three times a low concentration (repeat exposure, RE). Parasite dynamics in the fish host and release of fish malacospores were quantified and fish kidney histopathology was evaluated to determine PKD pathogenesis. Infection prevalence was always lower in the LC group than in the other groups over the course of the study. While the parasite proliferation phase was slower in the LC group, the maximum parasite burden did not differ significantly amongst treatments. The onset of fish malacospore release (day 45 post-exposure), indicated by detection of T. bryosalmonae DNA in the tank water, occurred at the same time point for all groups. Reduced intensity of kidney pathological development was observed in the LC treatment indicating lower disease severity. While the LC treatment resulted in reduced outcomes across several infection parameters (infection prevalence, parasite proliferation, total fish malacospores released), the overall differences were small. The RE and HC treatment outcomes were for most parameters comparable. Our results suggest that repeated exposure, as is likely to occur in the wild during the summer months, might play a more important role in the dynamics of PKD as an emerging infectious disease than the actual concentration of spores.

Scale-up manufacturing of gelatin-based microcarriers for cell therapy.

Microcarriers, including crosslinked porous gelatin beads (Cultispher G) are widely used as cell carriers for cell therapy applications. Microcarriers can support a range of adherent cell types in stirred tank bioreactor culture, which is scalable up to several thousands of liters. Cultispher G in particular is advantageous for cell therapy applications because it can be dissolved enzymatically, and thus cells can be harvested without the need to perform a large-scale cell-bead filtration step. This enzymatic dissolution, however, is challenged by the slow degradation of the carriers in the presence of enzymes as new extracellular matrix is being deposited by the proliferating cells. This extended dissolution timelimits the yield of cell recovery while compromising cellular viability. We report herein the development of crosslinked porous gelatin beads that afford rapid, stimuli-triggered dissolution for facile cell removal using human mesenchymal stem cells (hMSC) as a model system. We successfully fabricated redox-sensitive beads (RS beads) and studied their cell growth, dissolution time and cell yield, compared to regular gelatin-based beads (Reg beads). We have shown that RS beads allow for much faster dissolution compared to Reg beads, supporting better hMSC detachment and recovery following 8 days of culture in spinner flasks, or in 3L bioreactors. These newly synthesized RS beads show promise as cellular microcarriers and can be used for scale-up manufacturing of different cell types while providing on-demand degradation for facile cell retrieval.

Thyroid Hormone Disruptors Interfere with Molecular Pathways of Eye Development and Function in Zebrafish.

The effects of thyroid hormone disrupting chemicals (THDCs) on eye development of zebrafish were investigated. We expected THDC exposure to cause transcriptional changes of vision-related genes, which find their phenotypic anchoring in eye malformations and dysfunction, as observed in our previous studies. Zebrafish were exposed from 0 to 5 days post fertilization (dpf) to either propylthiouracil (PTU), a thyroid hormone synthesis inhibitor, or tetrabromobisphenol-A (TBBPA), which interacts with thyroid hormone receptors. Full genome microarray analyses of RNA isolated from eye tissue revealed that the number of affected transcripts was substantially higher in PTU- than in TBBPA-treated larvae. However, multiple components of phototransduction (e.g., phosphodiesterase, opsins) were responsive to both THDC exposures. Yet, the response pattern for the gene ontology (GO)-class "sensory perception" differed between treatments, with over 90% down-regulation in PTU-exposed fish, compared to over 80% up-regulation in TBBPA-exposed fish. Additionally, the reversibility of effects after recovery in clean water for three days was investigated. Transcriptional patterns in the eyes were still altered and partly overlapped between 5 and 8 dpf, showing that no full recovery occurred within the time period investigated. However, pathways involved in repair mechanisms were significantly upregulated, which indicates activation of regeneration processes.

Temperature-related parasite infection dynamics: the case of proliferative kidney disease of brown trout.

Climate change, in particular rising temperature, is suspected to be a major driver for the emergence of many wildlife diseases. Proliferative kidney disease of salmonids, caused by the myxozoan Tetracapsuloides bryosalmonae, was used to evaluate how temperature dependence of host-parasite interactions modulates disease emergence. Brown trout (Salmo trutta fario) kept at 12 and 15 °C, were experimentally infected with T. bryosalmonae. Parasite development in the fish host and release of spores were quantified simultaneously to unravel parasite transmission potential from the vertebrate to the invertebrate host. A change to a stable plateau in infection intensity of the kidney coincided with a threshold at which spore shedding commenced. This onset of parasite release was delayed at the low temperature in accordance with reaching this infection intensity threshold, but the amount of spores released was irrespective of temperature. The production of parasite transmission stages declined with time. In conclusion, elevated temperature modifies the parasite transmission opportunities by increasing the duration of transmission stage production, which may affect the spread and establishment of the parasite in a wider range of rivers.

The arginine-vasotocin and serotonergic systems affect interspecific social behaviour of client fish in marine cleaning mutualism.

Many species engage in mutualistic relationships with other species. The physiological mechanisms that affect the course of such social interactions are little understood. In the cleaning mutualism, cleaner fish Labroides dimidiatus do not always act cooperatively by eating ectoparasites, but sometimes cheat by taking bites of mucus from so-called "client" reef fish. The physiological mechanisms in these interspecific interactions, however, are little studied. Here, we focussed on three neuromodulator systems known to play important roles in intraspecific social behaviour of vertebrates to examine their role in clients' interspecific behaviour. We subjected the client fish Scolopsis bilineatus to ectoparasites and the exogenous manipulation of the vasotocin (AVT), isotocin (IT) and serotonin systems to test how this affects client willingness to seek cleaning and client aggression towards cleaners. We found that a single dose of AVT agonist and a selective antagonist caused clients to seek proximity to cleaners, independently of ectoparasite infection. In contrast, in a direct encounter task, the selective blocker of serotonin 5HT2A/2C receptors, Ketanserin (KET), made client reef fish more aggressive towards cleaners in the absence of cleaners' bites of mucus. IT did not yield any significant effects. Our results suggest that the AVT system plays a role in social affiliation towards an interspecific partner, while the serotonin system affects clients' acceptance of level of proximity to cleaner fish during interactions. These two systems, therefore, were apparently co-opted from intraspecific social interactions to affect the course of interspecific ones also.

Comparative study of proliferative kidney disease in grayling Thymallus thymallus and brown trout Salmo trutta fario: an exposure experiment.

Proliferative kidney disease (PKD) is an emerging disease threatening wild salmonid populations, with the myxozoan parasite Tetracapsuloides bryosalmonae as the causative agent. Species differences in parasite susceptibility and disease-induced mortality seem to exist. The aim of the present study was to compare incidence, pathology and mortality of PKD in grayling Thymallus thymallus and brown trout Salmo trutta under identical semi-natural conditions. Young-of-the-year grayling and brown trout, free of T. bryosalmonae, were jointly exposed in cage compartments in a river in the northeast of Switzerland during 3 summer months. Wild brown trout were caught by electrofishing near the cage, and PKD status was compared with that of caged animals. Cage-exposed grayling showed a PKD incidence of 1%, regardless of whether parasite infection was determined by means of real-time PCR or histopathology/immunohistochemistry. In contrast, PKD incidence of caged brown trout was 77%. This value was not significantly different to PKD prevalence of wild brown trout caught above and below the cage (60 and 91%, respectively). Mortality in grayling was significantly higher compared with that of brown trout (40 versus 23%); however, grayling mortality was not considered to be associated with PKD. Mortality of caged and infected brown trout was significantly higher than mortality of non-infected caged trout. Histopathology indicated an ongoing mostly acute or chronic active infection in brown trout, which survived until the end of exposure. The results suggest that grayling are less susceptible to infection with T. bryosalmonae compared with brown trout under the tested field conditions.

Androgen responses to reproductive competition of males pursuing either fixed or plastic alternative reproductive tactics.

Alternative reproductive tactics (ARTs), which can be plastic or fixed for life, may be characterized by distinct hormonal profiles. The relative plasticity hypothesis predicts flexible androgen regulation for adult males pursuing plastic tactics, but a less flexible regulation for males using a fixed tactic throughout life. Furthermore, androgen profiles may respond to changes in the social environment, as predicted by the social reciprocity models of hormone/behaviour interactions. The cichlid fish Lamprologus callipterus provides a rare opportunity to study the roles of androgens for male ARTs within a single species, because fixed and plastic ARTs coexist. We experimentally exposed males to competitors pursuing either the same or different tactics to test predictions of the relative plasticity and the social reciprocity models. Androgen profiles of different male types partly comply with predictions derived from the relative plasticity hypothesis: males of the plastic bourgeois/sneaker male trajectory showed different 11-ketotestosterone (11-KT) levels when pursuing either bourgeois or parasitic sneaker male behaviours. Surprisingly, males pursuing the fixed dwarf male tactic showed the highest free and conjugated 11-KT and testosterone (T) levels. Our experimental social challenges significantly affected the free 11-KT levels of bourgeois males, but the androgen responses did not differ between challenges involving different types of competitors. Furthermore, the free T-responses of the bourgeois males correlated with their aggressive behaviour exhibited against competitors. Our results provide new insights into the endocrine responsiveness of fixed and plastic ARTs, confirming and refuting some predictions of both the relative plasticity and the social reciprocity models.

Thyroid disruption in zebrafish (Danio rerio) larvae: Different molecular response patterns lead to impaired eye development and visual functions.

The vertebrate thyroid system is important for multiple developmental processes, including eye development. Thus, its environmentally induced disruption may impact important fitness-related parameters like visual capacities and behaviour. The present study investigated the relation between molecular effects of thyroid disruption and morphological and physiological changes of eye development in zebrafish (Danio rerio). Two test compounds representing different molecular modes of thyroid disruption were used: propylthiouracil (PTU), which is an enzyme-inhibitor of thyroid hormone synthesis, and tetrabromobisphenol A (TBBPA), which interacts with the thyroid hormone receptors. Both chemicals significantly altered transcript levels of thyroid system-related genes (TRα, TRß, TPO, TSH, DIO1, DIO2 and DIO3) in a compound-specific way. Despite these different molecular response patterns, both treatments resulted in similar pathological alterations of the eyes such as reduced size, RPE cell diameter and pigmentation, which were concentration-dependent. The morphological changes translated into impaired visual performance of the larvae: the optokinetic response was significantly and concentration-dependently decreased in both treatments, together with a significant increase of light preference of PTU-treated larvae. In addition, swimming activity was impacted. This study provides first evidence that different modes of molecular action of the thyroid disruptors can be associated with uniform apical responses. Furthermore, this study is the first to show that pathological eye development, as it can be induced by exposure to thyroid disruptors, indeed translates into impaired visual capacities of zebrafish early life stages.

Dear Enemies Elicit Lower Androgen Responses to Territorial Challenges than Unfamiliar Intruders in a Cichlid Fish.

In many territorial species androgen hormones are known to increase in response to territorial intrusions as a way to adjust the expression of androgen-dependent behaviour to social challenges. The dear enemy effect has also been described in territorial species and posits that resident individuals show a more aggressive response to intrusions by strangers than by other territorial neighbours. Therefore, we hypothesized that the dear enemy effect may also modulate the androgen response to a territorial intrusion. Here we tested this hypothesis in male cichlid fish (Mozambique tilapia, Oreochromis mossambicus) using a paradigm of four repeated territorial intrusions, either by the same neighbour or by four different unfamiliar intruders. Neighbour intruders elicited lower aggression and a weaker androgen response than strangers on the first intrusion of the experiment. With repeated intrusions, the agonistic behaviour of the resident males against familiar intruders was similar to that displayed towards strangers. By the fourth intrusion the androgen response was significantly reduced and there was no longer a difference between the responses to the two types of intruders. These results suggest that the dear enemy effect modulates the androgen response to territorial intrusions and that repeated intrusions lead to a habituation of the androgen response.

Intra- and interspecific social challenges modulate the levels of an androgen precursor in a seasonally territorial tropical damselfish.

Studies on different vertebrate groups have provided evidence that androgen levels in males increase after competitive social interactions during the breeding season, as postulated by the Challenge Hypothesis. However, social modulation of androgen levels may vary with latitude and may differ between species holding seasonal versus year-round territories. Here, we tested the Challenge Hypothesis on a seasonal tropical damselfish, Abudefduf sexfasciatus, where males temporarily defend territory and eggs against both intra- and interspecific individuals. Carrying out simulated territorial intrusions (STIs) in the laboratory, we document for the first time a consistent increase in the plasma level of the androgen precursor 11-ketoandrostenedione (11KA) in fish confronted to either intra- or interspecific challenges. Collecting samples in the field also revealed higher 11KA levels in fish facing frequent territorial interactions than in non-territorial individuals. Levels of 11-ketotestosterone (11KT) were high in territorial males in the field, but were not incremented after simulated territorial intrusions in the laboratory. Plasma levels of cortisol and testosterone were not affected by challenges but were different in wild and captive specimens. Although the endocrine responses to STIs did not differ between intra- and interspecific challenges, agonistic displays expressed by resident fish were more intense towards intraspecific intruders. Taken together, our study emphasizes the need to incorporate androgen precursor concentrations to advance our understanding on the physiology of territorial interactions.

Physiological plasticity to water flow habitat in the damselfish, Acanthochromis polyacanthus: linking phenotype to performance.

The relationships among animal form, function and performance are complex, and vary across environments. Therefore, it can be difficult to identify morphological and/or physiological traits responsible for enhancing performance in a given habitat. In fishes, differences in swimming performance across water flow gradients are related to morphological variation among and within species. However, physiological traits related to performance have been less well studied. We experimentally reared juvenile damselfish, Acanthochromis polyacanthus, under different water flow regimes to test 1) whether aspects of swimming physiology and morphology show plastic responses to water flow, 2) whether trait divergence correlates with swimming performance and 3) whether flow environment relates to performance differences observed in wild fish. We found that maximum metabolic rate, aerobic scope and blood haematocrit were higher in wave-reared fish compared to fish reared in low water flow. However, pectoral fin shape, which tends to correlate with sustained swimming performance, did not differ between rearing treatments or collection sites. Maximum metabolic rate was the best overall predictor of individual swimming performance; fin shape and fish total length were 3.3 and 3.7 times less likely than maximum metabolic rate to explain differences in critical swimming speed. Performance differences induced in fish reared in different flow environments were less pronounced than in wild fish but similar in direction. Our results suggest that exposure to water motion induces plastic physiological changes which enhance swimming performance in A. polyacanthus. Thus, functional relationships between fish morphology and performance across flow habitats should also consider differences in physiology.

No scope for social modulation of steroid levels in a year-round territorial damselfish.

Both latitude and mating system have been proposed to shape relationships between steroid hormone levels and social behavior. Recently it has been postulated that species with long lasting non-seasonal territorial behavior have low androgen responsiveness. Tropical damselfishes are an ideal family to test this proposition because they show a large variety in mating systems. Here we contribute to the comparative dataset by measuring the response in steroid levels after social modulation in the banded sergeant, Abudefduf septemfasciatus, a species with non-seasonal territoriality. In highly territorial and brooding males, we found low androgen and cortisol levels that did not increase after experimental intraspecific simulated territorial intrusions (STI tests). No relationship was found between the variation in steroid hormone levels and territorial responses to naturally occurring territorial intrusions. Although steroid levels were low, male A. septemfasciatus were highly territorial both to STI challenges and to fishes that passed the territory. They often chased intruders for several meters away from the territory. This indicates that during nest defence in a non-seasonal territorial damselfish species, territorial behaviors are shown independent of variation in androgen and cortisol levels.

Intra- and interspecific challenges modulate cortisol but not androgen levels in a year-round territorial damselfish.

Interactions between individuals of different species are commonplace in animal communities. Some behaviors displayed during these interspecific social interactions may be very similar to those displayed during intraspecific social interactions. However, whether functional analogies between intra- and interspecific behaviors translate at the proximate level into an overlap in their underlying endocrine mechanisms remains largely unknown. Because steroids both mediate social behaviors and respond to them, we approached this question by comparing the behavioral and steroid response of free-living dusky gregories (Stegastes nigricans) to standardized territorial intrusions (sTI) of either conspecific or heterospecific food competitors. Stegastes nigricans is a year-round territorial fish that 'cultivates' the algae on which it feeds and is highly aggressive to both intra- and interspecific intruders. Behavioral differences between intra- and interspecific aggressive responses to sTI were marginal, and sTI tests caused an increase in cortisol levels that was positively related with the levels of aggression. In contrast, androgen levels did not increase in response to sTI, yet they showed a positive relationship with agonistic behavior. These results parallel a pattern that was first described for year-round territorial bird species. Furthermore, they suggest that changes in endocrine-hormone levels during territoriality might be independent of the species that induces the territorial response.

Morphometrical and genetic comparison of two nematode species: H. spumosa and H. dahomensis (Nematoda, Heterakidae).

Heterakis is a genus of parasitic nematodes, the majority of which are found in ground-feeding birds and only rarely in mammals. The best-known species is Heterakis spumosa, a parasite associated with the cosmopolitan invasive rodent Rattus rattus of Asiatic origin. Heterakis dahomensis was described in 1911 as a parasite of the Gambian giant rat (Cricetomys gambianus) from Benin (Africa), subsequently synonymized to H. spumosa by Hall (1916). The study of helminths in African rodents is scarce and patchy. Since the original description of H. dahomensis, there have been only a few reports from Africa of species belonging to the genus Heterakis and the validity of this species has never in fact been confirmed or rejected. In the present study individual Heterakis spp. were collected from C. gambianus from Senegal. The morphological data taken point to differences between Heterakis dahomensis and H. spumosa, specifically in the number of tail papillae in males and in the vulva cuticular processes of females. In addition, molecular data revealed differences between these taxa and so H. dahomensis should be considered as a valid species. Moreover, recent changes in the systematics of the genus Cricetomys mean that it is now necessary to study the morphology and genetics of the Heterakis specimens collected from Cricetomys spp. (previously assigned to C. gambianus) in order to determine their taxonomic status as either H. dahomensis o H. spumosa.

Intra- and interspecific aggression do not modulate androgen levels in dusky gregories, yet male aggression is reduced by an androgen blocker.

Discussions about social behavior are generally limited to fitness effects of interactions occurring between conspecifics. However, many fitness relevant interactions take place between individuals belonging to different species. Our detailed knowledge about the role of hormones in intraspecific interactions provides a starting point to investigate how far interspecific interactions are governed by the same physiological mechanisms. Here, we carried out standardized resident-intruder (sRI) tests in the laboratory to investigate the relationship between androgens and both intra- and interspecific aggression in a year-round territorial coral reef fish, the dusky gregory, Stegastes nigricans. This damselfish species fiercely defend cultivated algal crops, used as a food source, against a broad array of species, mainly food competitors, and thus represent an ideal model system for comparisons of intra-and interspecific territorial aggression. In a first experiment, resident S. nigricans showed elevated territorial aggression against intra- and interspecific intruders, yet neither elicited a significant increase in androgen levels. However, in a second experiment where we treated residents with flutamide, an androgen receptor blocker, males but not females showed decreased aggression, both towards intra- and interspecific intruders. Thus androgens appear to affect aggression in a broader territorial context where species identity of the intruder appears to play no role. This supports the idea that the same hormonal mechanism may be relevant in intra- and interspecific interactions. We further propose that in such a case, where physiological mechanisms of behavioral responses are found to be context dependent, interspecific territorial aggression should be considered a social behavior.