Hooked on you: shape of attachment structures in cymothoid isopods reflects parasitic strategy.

BACKGROUND: Parasite attachment structures are critical traits that influence effective host exploitation and survival. Morphology of attachment structures can reinforce host specificity and niche specialisation, or even enable host switching. Therefore, it is important to understand the determinants of variation in attachment structures. Cymothoid isopods are striking ectoparasites of fishes that include the infamous 'tongue-biters.' They are known to parasitise hosts in one of four qualitatively distinct anatomical regions. Here, we quantify variation in cymothoid attachment structures - hook-like appendages called dactyli - and test whether differences in dactylus shape are correlated with parasite mode (where they attach), allometry, or both, using multivariate ordinary least squares regression. We also assess the influence of shared ancestry on shape using a molecular phylogeny to weight our models using phylogenetic generalised least squares regression. RESULTS: We find clear differences in shape between externally-attaching and internally-attaching cymothoids but also between anterior and posterior dactyli across various species with the same attachment mode. Allometric effects are significant for anterior but not posterior dactyli. Mouth-attaching species show greater shape variability than gill- and mouth-attaching species. We find no evidence that there are clade-specific patterns of association between parasite mode and dactylus shape. CONCLUSIONS: Parasite mode appears to be the main driver of attachment morphology. This likely reflects several components of parasite ecology including feeding and functional demands of attachment in different microhabitats. Geometric morphometric approaches to the quantification of shape variation of simple structures is an effective tool that provides new insights into the evolvability of parasite attachment

Unique co-occurrence of two genera of cymothoid ectoparasitic isopods on the same individual fish host

Parasitism of a host fish by a single species of cymothoid is regularly reported. For the first time on a temperatefish host and in South African waters, we  observed two species of cymothoids, the flesh-infesting Anilocra capensis and the tongue-infesting Ceratothoa africanae, simultaneously infesting the same individual hottentot seabream Pachymetopon blochii. Each P. blochii harboured an ovigerous and non-ovigerous A. capensis and an ovigerous and non-ovigerous C. africanae. Cymothoid co-occurrence is rarely reported, and this is the first report of two cymothoid species infesting a single fish host from Africa. Globally, it is the first record of flesh- and tongueinfesting cymothoids parasitising the same individual fish.Keywords: Anilocra, Ceratothoa, Cymothoidae, marine fish, parasite, South Africa, southeastern Atlantic Ocea

Host-dependent differences in measures of condition associated with Anilocra spp. parasitism in two coral reef fishes

Parasites account for over half of the biodiversity on coral reefs, yet their ecological impacts are poorly understood. Cymothoid isopods of the genus Anilocra are large, conspicuous ectoparasites of coral reef fishes. French grunt (Haemulon flavolineatum) and brown chromis (Chromis multilineata) are commonly infected by Anilocra spp. in the Caribbean. These fishes play a significant role in trophic connectivity through their foraging and activity patterns, and Anilocra spp. infection has been reported to influence the trophic interactions of some fishes. Yet, how these changes manifest physiologically has not been quantified. Thus to determine the energetic effects of Anilocra spp. on French grunt and brown chromis, the relationships between Anilocra spp. infection and condition factor, percent moisture in the muscle tissue, total muscle tissue calories, and gut content volume were examined. The results of these analyses revealed that A. haemuli-infected French grunt had greater percent moisture in the muscle tissue but similar condition scores, calorie values, and gut content volumes compared to uninfected conspecifics. By comparison, Anilocra chromis-infected brown chromis had reduced condition factor, but similar percent moisture in the muscle tissue and total muscle tissue calories, as compared to uninfected conspecifics. This study provides evidence that infection by parasites of the same genus and within the same localities can have differential effects on fish host species, such that generalizations about the effects of parasitism across and within genera should be made cautiously

Behavioural effects of the common brain-infecting parasite Pseudoloma neurophilia in laboratory zebrafish (Danio rerio)

Research conducted on model organisms may be biased due to undetected pathogen infections. Recently, screening studies discovered high prevalence of the microsporidium Pseudoloma neurophilia in zebrafish (Danio rerio) facilities. This spore-forming unicellular parasite aggregates in brain regions associated with motor function and anxiety, and despite its high occurrence little is known about how sub-clinical infection affects behaviour. Here, we assessed how P. neurophilia infection alters the zebrafish´s response to four commonly used neurobehavioral tests, namely: mirror biting, open field, light/dark preference and social preference, used to quantify aggression, exploration, anxiety, and sociability. Although sociability and aggression remained unaltered, infected hosts exhibited reduced activity, elevated rates of freezing behaviour, and sex-specific effects on exploration. These results indicate that caution is warranted in the interpretation of zebrafish behaviour, particularly since in most cases infection status is unknown. This highlights the importance of comprehensive monitoring procedures to detect sub-clinical infections in laboratory animals

Low Susceptibility of Invasive Red Lionfish (Pterois volitans) to a Generalist Ectoparasite in Both Its Introduced and Native Ranges

Escape from parasites in their native range is one of many mechanisms that can contribute to the success of an invasive species. Gnathiid isopods are blood-feeding ectoparasites that infest a wide range of fish hosts, mostly in coral reef habitats. They are ecologically similar to terrestrial ticks, with the ability to transmit blood-borne parasites and cause damage or even death to heavily infected hosts. Therefore, being highly resistant or highly susceptible to gnathiids can have significant fitness consequences for reef-associated fishes. Indo-Pacific red lionfish (Pterois volitans) have invaded coastal habitats of the western tropical and subtropical Atlantic and Caribbean regions. We assessed the susceptibility of red lionfish to parasitic gnathiid isopods in both their native Pacific and introduced Atlantic ranges via experimental field studies during which lionfish and other, ecologically-similar reef fishes were caged and exposed to gnathiid infestation on shallow coral reefs. Lionfish in both ranges had very few gnathiids when compared with other species, suggesting that lionfish are not highly susceptible to infestation by generalist ectoparasitic gnathiids. While this pattern implies that release from gnathiid infestation is unlikely to contribute to the success of lionfish as invaders, it does suggest that in environments with high gnathiid densities, lionfish may have an advantage over species that are more susceptible to gnathiids. Also, because lionfish are not completely resistant to gnathiids, our results suggest that lionfish could possibly have transported blood parasites between their native Pacific and invaded Atlantic ranges