Effects of Microphallus turgidus (Trematoda: Microphallidae) on the predation, behavior, and swimming stamina of the grass shrimp Palaemonetes pugio

The effect of the trematode Microphallus turgidus on its second intermediate host, the grass shrimp, Palaemonetes pugio, was tested. To do so, we measured the susceptibility of infected and uninfected shrimp to predation by the mummichog, Fundulus heteroclitus. Shrimp behavior was compared in the presence and absence of a fish predator, and the swimming stamina and backthrust escape responses of infected and uninfected shrimp were measured. Infected shrimp were more likely to be eaten by a predator than uninfected shrimp, had lower swimming stamina, and spent more time swimming and less time motionless in the presence of a predator. There was no difference between backthrust distances traveled in response to a stimulus by either infected or uninfected shrimp. Thus, M. turgidus may increase the predation of P. pugio in the wild, possibly by affecting the swimming stamina and predator avoidance responses of the shrimp.     

Prevalence,geographic distribution,and fitness effects of Microphallus turgidus (trematoda: Microphallidae) in grass shrimp (Palaemonetes spp.) from coastal Georgia

Grass shrimp, Palaemonetes pugio Holthuis and P. vilgaris (Say), were collected at 11 localities along the coast of Georgia and surveyed for digenetic trematode metacercariae. The effect of trematode infection on grass shrimp fitness was also examined. Microphallus turgidas (Leigh) was the only trematode observed. The prevalence of metacercarial cysts of this parasite in P. pugio (75%) was higher than in P. vulgaris (24%), as were the mean intensity, abundance, and population density (no. cysts/cm host body length) of the parasite. Infected shrimp were found at every collection locality and parasite prevalence and density were greatest in P. pugio from higher salinity localities (> or = 20 parts per thousand [ppt]). There was no relation between host body size and parasite density in P. vulgaris, and parasite density increased with host body size in P. pugio, suggesting that the parasite does not affect host survival. There was no relation between parasite density and shrimp egg mass, but nonovigerous female P. pugio were more heavily infected than ovigerous ones. In addition, 1 metacercaria of M. turgidus in each of 2 specimens of P. vulgaris was parasitized by the haplosporidian Urosporidium crescens De Turk. This represents a new shrimp host record for this hyperparasite.     

Life cycle of Calyptospora funduli (Apicomplexa: Calyptosporidae)

The taxonomic status of the extraintestinal piscine coccidium Calyptospora funduli is based in part on its requirement of an intermediate host (the daggerblade grass shrimp Palaemonetes pugio). In the present study, grass shrimp fed livers of Gulf killifish (Fundulus grandis) infected with sporulated oocysts of C. funduli exhibited numerous sporozoites suspended in the intestinal contents when fresh squash preparations were examined by light microscopy. Using this method, sporozoites were not seen in intestinal epithelial cells of the grass shrimp or in any other cell types. Ultrastructural examination, however, revealed sporozoites in the cytoplasm of the gut basal cells. Cross-sections of 1-13 sporozoites were seen within a single cell, and those sporozoites each appeared to be situated in individual membrane-bound vesicles, rather than in a single parasitophorous vacuole. These ultrastructural observations indicate that in the grass shrimp intermediate host, sporozoites that develop into an infective stage probably undergo that development in gut mucosal basal cells. Prior studies revealed that these sporozoites modified their structure over 4-5 days and that before that time, they were not infective to the fish host. Following ingestion of an infected shrimp by a killifish, the infective sporozoites apparently reach the liver of their killifish definitive hosts through the bloodstream. Sporozoites were seen in blood smears from the longnose killifish, Fundulus similis, 4 hr after fish were fed experimentally infected grass shrimp. Additionally, coccidian trophozoites and early meronts were seen in hepatocytes from several longnose killifish at 48, 72, and 96 hr postinfection. This study, in conjunction with previous findings, clearly confirms that a true intermediate host is required in the life cycle of C. funduli, that a developmental period of about 5 days in grass shrimp is necessary for sporozoites to become infective to killifishes, and that sporozoites do occur intracellularly in gut basal cells of the grass shrimp.     

Optimization of culture conditions for in vitro fertilization and reproduction of Microphallus turgidus (Trematoda: Microphallidae)

Most attempts to culture adult digeneans in vitro are unsuccessful. Even progenetic digeneans typically fail to produce infective eggs in axenic culture. However, metacercariae of Microphallus turgidus grown in vitro mature into adults and release eggs infective to the hydrobiid snail Spurwinkia salsa. The objectives of the present study were to verify the reproducibility of the M. turgidus culture protocol, to define optimal culture conditions for M. turgidus further, and to investigate why the parasite can be grown successfully in the absence of the definitive host. In the original cultivation protocol, excysted M. turgidus metacercariae from grass shrimp (Palaemonetes pugio) were incubated overnight in a conical-bottom centrifuge tube containing Hank's balanced salt solution and then cultivated in flat-bottom culture plate wells containing RPMI-1640 plus 20% horse serum. The gas phase was air. Worms cultured under this protocol consistently deposited eggs infective to snails. Worms grown in anaerobic conditions deposited few eggs, and those cultured in a gas phase of 5% CO(2) survived longer and produced more eggs than those cultured in air. However, snails were less likely to become infected when fed eggs deposited by worms cultured in 5% CO(2). Additionally, worms incubated with conspecifics in conical-bottom tubes prior to cultivation were more likely to be inseminated than worms incubated in flat-bottom culture wells; the highest percentages of inseminated worms occurred when metacercariae were incubated 24 hr in conical-bottom tubes at a density of 50 worms/tube and at a temperature of 37 C. Worms incubated in the absence of conspecifics were not fertilized and failed to produce infective eggs.     

Serological estimation of prey-protein gut-residence time and quantification of meal size for grass shrimp consuming meiofaunal copepods

A series of experiments using serological reagents was conducted to examine predation, ingestion and digestion in a model predator-prey system. The harpacticoid copepod Amphiascoides atopus, obtained from mass culture, was used as prey and the grass shrimp, Palaemonetes pugio, as predator. Bulk-gut passage time in P. pugio was measured by visualization of latex beads and ranged from 0.5 to 4 h in starved and continuously-fed grass shrimp. A polyclonal antibody was prepared from crude extracts of A. atopus; cross reactions with P. pugio and three other crustaceans were either negligible or not detected using slide agar-gel-double-immunodiffusion (AGID) and Western blot preparations. The presence of A. atopus antigens was detected with great sensitivity (e.g., seven copepods, 35 μg dry weight, gave positive results) in grass shrimp gut contents even when proteins of other crustacean prey were present. Prey-proteins could be detected for as long as 4 h with AGID and 8 h with Western blot techniques. Individual grass shrimp that were fed A. atopus and consumed from 0 to 98 copepods h(-1) were subjected to Western-blot preparation with chemiluminescence detection and densitometric evaluation. There was a significant curvilinear relationship between protein content and the number of copepod prey ingested. Results suggest that serological techniques can be modified to estimate the mass or abundance of standard-sized prey ingested by field-collected predators.     

True Intermediate Hosts for Eimeria funduli (Apicomplexa) from Estuarine Fishes1

Grass shrimp (Palaemonetes pugio) fed liver containing sporulated oocysts of Eimeria funduli permitted development of sporozoites that became infective to a variety of killifishes. The shrimp's gastric mill mechanically ruptured the oocysts. Sporozoites then excysted through an opening in the sporocyst, and by 12 and 13 h postinfection (p.i.) numerous empty sporocysts and free sporozoites occurred extracellularly in the intestine of the grass shrimp. Even at 5, 7, 8, 11, 46, 79, and 83 days p.i., and presumably for many months, numerous sporozoites still occurred free in the alimentary tract or between intestinal cells. The coccidium did not infect killifish at either 2 or 4 days p.i., but did at 5 days; after release from the sporocyst, it became more elongate with a distinct nucleus and two relatively large refractile bodies. Infections of E. funduli resulted in about one half of the fish that were fed either entire hepatopancreas or tips of hepatopancreas from experimentally infected shrimp. Feeding either the entire alimentary tract proximal to the first abdominal segment or any portion of that section from experimentally infected shrimp produced infections in nearly all tested fish. Feeding portions of the cephalothorax without any attached hepatopancreas or alimentary tract failed to produce an infection. Feeding killifish with wild grass shrimp from an enzootic area produced infections in only a fourth of the fish sample; however, feeding experimentally infected wild, laboratory-reared, and juvenile grass shrimp produced infections in nearly all fish. Palaemonid shrimps other than P. pugio also can serve as intermediate hosts for E. funduli, and these shrimps include Palaemonetes vulgaris, P. paludosus, P. kadiakensis, and Macrobrachium ohione. In contrast, a penaeid shrimp, mysidacean, amphipod, and crab fed liver with sporulated oocysts did not produce infections when fed to killifish.     

Altered predator/prey behavior in polluted environments: implications for fish conservation

Predator/prey behavior has important consequences for individual survival and recruitment into fish populations, both of which can be affected by stressors such as environmental contaminants. The degree to which prey capture or predator avoidance abilities of a predator or prey species are affected will determine the direction in which the balance will be shifted. In a contaminated estuary we have studied, prey capure and predator avoidance of resident mummichogs, Fundulus heteroclitus, are impaired, which may account for individuals in that estuary having reduced growth and longevity compared with those from uncontaminated sites. Exposure to sediments, water, and grass shrimp from the contaminated site can impair the predatory abilities of mummichogs from a clean site. An important prey species, the grass shrimp, Palaemonetes pugio, has a greater population density and a greater proportion of large individuals at the polluted site, apparently because of reduced predation pressure. Mummichog larvae at the polluted site are initially more active and better at prey capture and predator avoidance than larvae from clean sites, but later they become poorer at both. Differences in predator vulnerability among larvae appear to be due to population differences in behavior, which may be due in part to both genetic and environmentally-caused factors. Conservation of fish populations should consider fish behavior and its interaction with contaminants.     

Avian cestodes affect the behaviour of their intermediate host Artemia parthenogenetica: an experimental study

The brine shrimp Artemia parthenogenetica (Crustacea, Branchiopoda) is intermediate host for several cestode species whose final hosts are waterbirds. Previous field studies have shown that brine shrimps infected with cestodes have a bright red colour and are spatially segregated in the water column. However, the ethological mechanisms explaining such field observations are unknown. Changes in appearance and behaviour induced by trophically transmitted parasites have been shown to increase the risk of predation by the final host. In this experimental study, we compared the behaviour of uninfected Artemia and those infected by avian cestodes. We found that parasitised individuals behave differently from unparasitised ones in several ways. In contrast to uninfected individuals, infected brine shrimps were photophilous and showed increased surface-swimming behaviour. These observations suggest that the modified behaviour (in addition to the bright red colour of the majority of the infected individuals) results in infected brine shrimps becoming more vulnerable to avian final hosts, which facilitates parasite transmission. We discuss our results in terms of the adaptive nature of behavioural changes and their potential implications for the hypersaline ecosystem.     

Infection of adult migratory river shrimps,Macrobrachium ohione,by the branchial bopyrid isopod Probopyrus pandalicola

Abstract. Macrobrachium ohione is a migratory (amphidromous) river shrimp (Decapoda, Caridea) that may be parasitized by the branchial parasite Probopyrus pandalicola (Isopoda, Bopyridae). The parasite disrupts gonadal maturation and spawning in female shrimps, resulting in the total loss of reproduction. Shrimps are usually infected by bopyrid parasites during the late zoeal or early postlarval stages; in this study, we investigated the apparent parasite infection of adult shrimps. We analyzed the relationships between parasite body size (total length) and host shrimp body size (carapace length) to test the hypothesis that parasite infection of adult shrimps occurs during the shrimps' reproductive migrations. The results presented here indicate that infection of adult shrimps is common in M. ohione in the Atchafalaya and Mississippi Rivers, Louisiana, USA. In the two upriver sites sampled, Butte La Rose (BLR) and River Bend (RB), parasite size was not associated with host body size. In these locations, many parasitized adult M. ohione were infected with immature P. pandalicola (40.3% in BLR and 51.2% in RB), indicating that the shrimps were adults at the time of infection. A possible explanation is that when female shrimps enter the estuary to hatch larvae, they molt and spawn another brood. The smaller male shrimps that accompany the females downstream are also assumed to molt and continue growth. The intermediate host of the parasite is an estuarine copepod, and thus the parasite cryptoniscus larva that infects the host shrimp is primarily estuarine as well. Newly molted shrimps have soft cuticles, which may facilitate their infection by parasite cryptonisci. Our conclusion is that most infections of adult shrimps occur during their migration into estuarine waters, the primary habitat of infective parasite larvae, and that host vulnerability is probably increased following host ecdysis.     

Sandpipers Select Red Brine Shrimps Rich in Both Carotenoids and Parasites

Cestode parasites using brine shrimps Artemia as intermediate hosts and waterbirds as final hosts are known to change the colour of shrimps from pale pink to bright red owing to an increase in carotenoid pigments. In order to assess whether this coloration increases the chances of shrimp predation by the final host, we conducted an experiment in which 10 Calidris sandpipers were given a choice of 20 bright red and 20 pale pink shrimps. A strong preference for red, infected shrimps was recorded, suggesting that red colour is a manipulation by cestodes to increase transmission to its final hosts. The factors regulating access and functions of carotenoids in birds are under intense debate. For the first time, we show that access to carotenoid-rich foods in birds can have a cost derived from an increased exposure to parasites. To our knowledge, this is the first time that avian hosts have been shown to exert a colour-based preference for parasitized prey.     

Prevalence of the bopyrid isopod Probopyrus pandalicola in the grass shrimp, Palaemonetes pugio, in four tidal creeks on the South Carolina-Georgia coast

The grass shrimp, Palaemonetes pugio, is an important food source for many invertebrate and fish species, including several of commercial importance. The bopyrid Probopyrus pandalicola prevents reproduction in P. pugio by sexual sterilization. The purpose of our research was to determine bopyrid prevalence in grass shrimp over the course of a year. Shrimp were collected from 2 estuarine systems in South Carolina and 2 estuarine systems in Georgia and examined for parasite presence, sex, and gravidity. Site-specific monthly prevalence ranged from 0 to 6.3%. Country Club Creek had the maximum mean +/- SE prevalence of 3.1 +/- 0.3%, and Harbour Town had the minimum of 1.3 +/- 0.3%. Maximum prevalence was concurrent with peak gravidity for Moon River; thus, at this site the negative effect of this parasite on reproductive output may be greater. Reduced egg production may affect grass shrimp abundance and ultimately the recruitment success of its predators.     

A laboratory study of the behavior of two species of grass shrimp (Palaemonetes pugio Holthuis and Palaemonetes vulgaris Holthuis) and the killifish (Fundulus heteroclitus Linneaus)

In this laboratory study, the frequency of locomotor behaviors for two grass shrimp species, Palaemonetes pugio and Palaemonetes vulgaris, and the killifish Fundulus heteroclitus were determined. Additional behaviors, such as grouping of grass shrimp, and pursuit by killifish, the grass shrimp's common predator, were also analyzed. The results show that mean behavioral frequencies for the two shrimp species were rarely significantly different statistically. Each shrimp species altered its behavior differently in the presence of the other shrimp species, but responded similarly to the presence of the predator. The results indicate that the response of each shrimp species to the predator was dependent upon the predator's size and health. In situations involving the large health predator, both grass shrimp species significantly reduced swimming, but did not show a significant difference in walking. Behavioral frequencies of large and small healthy killifish were not significantly different from each other when alone, but were significantly different in the presence of prey, while the large unhealthy killifish's behavior was significantly decreased in all situations compared to both the large and small health killifish.     

On predatory tendencies in the feeding ecology of the fairy shrimp Streptocephalus proboscideus (Frauenfeld, 1873) (Crustacea: Anostraca)

The feeding habits of the filter-feeding fairy shrimp Streptocephalus proboscideus are documented experimentally by offering them ciliates, Volvox, rotifers, nematodes and small crustaceans as prey. Escape capabilities (e.g. swimming speed) rather than size or shape were found to determine these animals' vulnerability to predation by the fairy shrimp. Ingestion rates for Volvox increased hyperbolically with size and, at the high temperatures in which they live, fairy shrimps may daily remove the equivalent of their body weight from the environment.     

Studies of the Phoront of Hyalophysa chattoni (Ciliophora,Apostomatida) Encysted on Grass Shrimp1

ABSTRACT. The apostomatous ciliate Hyalophysa chattoni, an ectosymbiont of the grass shrimp Palaemonetes pugio, encysts and dedifferentiates within 48 h from the migratory tomite to a phoretic stage devoid of complex ciliary fields. The presettlement crawling and pivoting of the tomite may play a role in its initial attachment to the shrimp. Metamorphosis of exuviotrophic apostomes has been previously observed to take place immediately prior to host ecdysis. The study has found that Hyalophysa's metamorphosis to the feeding stage on grass shrimp is initiated by a cue from the premolt host and begins during earlier stages of the molt cycle (D₀ and D₁). Due to the long premolt stage of the host's diecdysic molt cycle, metamorphosis is initiated well before ecdysis (over six days). Hyalophysa was able to encyst and metamorphose within 41/4 h when exposed to shrimp in a late premolt stage, indicating that the control of apostome metamorphosis is solely host-dependent.     

Male Mating Tactics in the Shrimp Palaemonetes pugio (Decapoda, Caridea): Precopulatory Mate Guarding vs. Pure Searching

The guarding of females approaching a limited period of sexual receptivity is a common mating tactic of males. In many decapod crustaceans, such as the shrimp Palaemonetes pugio , females can only copulate during a short period after a reproductive molt. It has been predicted that mate guarding by males (pre-copula) evolves in such species if sex ratios are not highly female-biased and if males can detect the molt stage of the female. The mating tactics of males were investigated in P. pugio . Time-lapse video observations were made on interactions among two males, a pre-molt female, and an inter-molt female (20 replicates). There was no evidence that males recognized a pre-molt female until 24 h before its molt. Significant numbers of male contacts with pre-molt females occurred 1 h before and after the female molt. Copulation took place within 1–3 min of the molt. No behavior commonly associated with mate guarding in decapods was observed – no clasping, agonistic behavior, or close association. It is concluded that the male's mating tactic is pure searching, wherein males haphazardly contact many females in order to find a receptive one. The high encounter rate in nature of these very mobile, aggregated shrimps is proposed as the factor responsible for the evolution of pure searching. It is hypothesized that pure searching is the male tactic of the many species of decapod shrimps with small males, sexually monomorphic cheliped weapons, and aggregated populations.     

Vulnerability of cladoceran species to predation by the copepod Mesocyclops leuckarti: laboratory observations on the behavioural interactions between predator and prey

SUMMARY 1. We analysed the vulnerability of a number of cladoceran species ( Bosmina longirostris , B. fatalis , Diaphanosoma brachyurum , Ceriodaphnia reticulata , Daphnia ambigua and D. pulex ) to predation by Mesocyclops leuckarti in the laboratory.
2. The prey species represented a wide range of body size, morphology, and swimming behaviour. To compare vulnerability, we measured the efficiency of capture and ingestion of each prey species by Mesocyclops . We also measured the rate at which prey were damaged in attacks by Mesocyclops .
3. Mesocyclops preyed effectively on Diaphanosoma and small juvenile Ceriodaphnia but not on Bosmina or Daphnia . Observations suggested that various defence mechanisms, including protruding structures and swimming behaviour and speed, are important in determining prey vulnerability.
4. The body size of Daphnia and Ceriodaphnia seems to be important, because larger animals were better able to escape Mesocyclops attacks. Attacks by Mesocyclops often caused fatal damage, however, even to large Daphnia .     

Laboratory study of the grass shrimp feeding preferences

Grass shrimps are very common in various aquatic habitats, and are generally considered omnivorous. But, despite the numerous studies on interspecific trophic interactions, few studies have evaluated their feeding strategy, especially by experimental approaches.In this study, we determined, in the absence of both intra and interspecific competitive interactions, the feeding preferences of the freshwater grass shrimp Palaemonetes antennarius for the most common potential resources in its habitat. Plant and animal items were offered as food to each adult shrimp in multiple-choice laboratory experiments. Resource selection was determined under conditions of low and high food availability and related to the shrimp body size. The role of microbial colonisation in favouring detritivory was also investigated.Results of these experiments showed that P. antennarius consumed only animal items, mostly preferring the isopod Proasellus coxalis. In addition, palatability of the unselected plant remains and non-living prey was not improved by the microbial enrichment. Shrimps also resorted to cannibalism at low ration. By contrast, at high ration they specialised on a narrower range of resources, directing more their feeding efforts towards isopods. The preference ranking of the selected food types was inversely related to the average mass of the prey and varied with the shrimp body size. In particular, the number of live isopods in the diet increased exponentially with the shrimp mass at food high ration, which resulted not to be limiting. In conclusion, food availability influences the food niche of P. antennarius whose feeding strategy in the laboratory is facultative specialisation on dead and live animals rather than omnivory. Ease of handling and/or capture seems to play a role in the food preference ranking.     

An acanthocephalan parasite boosts the escape performance of its intermediate host facing non-host predators

Among the potential effects of parasitism on host condition, the 'increased host abilities' hypothesis is a counterintuitive pattern which might be predicted in complex-life-cycle parasites. In the case of trophic transmission, a parasite increasing its intermediate host's performance facing non-host predators improves its probability of transmission to an adequate, definitive host. In the present study, we investigated the cost of infection with the acanthocephalan Polymorphus minutus on the locomotor/escape performance of its intermediate host, the crustacean Gammarus roeseli. This parasite alters the behaviour of its intermediate host making it more vulnerable to predation by avian definitive hosts. We assessed the swimming speeds of gammarids using a stressful treatment and their escape abilities under predation pressure. Despite the encystment of P. minutus in the abdomen of its intermediate host, infected amphipods had significantly higher swimming speeds than uninfected ones (increases of up to 35%). Furthermore, when interacting with the non-host crustacean predator Dikerogammarus villosus, the highest escape speeds and greatest distances covered by invertebrates were observed for parasitized animals. The altered behaviour observed among the manipulated invertebrates supported the 'increased host abilities' hypothesis, which has until now remained untested experimentally. The tactic of increasing the ability of infected intermediate hosts to evade potential predation attempts by non-host species is discussed.     

Endocrine-mediated effects of UV-A irradiation on grass shrimp (Palaemonetes pugio) reproduction

Although much is known regarding photoperiodic effects on crustacean egg production, the effects of ultraviolet (UV) light on reproduction has not been investigated. Likewise, little is known concerning the interaction between UV and xenobiotic exposure on crustacean reproductive cycles. In this study, male and female grass shrimp, Palaemonetes pugio, were exposed to sublethal concentrations of endosulfan (200 ng/l and 400 ng/l ES) under both white fluorescent (WF) and UV-A (315-400 nm) light conditions for 50 days in laboratory bioassays. Female endocrine (vitellogenin, ecdysteroids, and cholesterol), reproductive (percent gravid, clutch size), and embryo (days to hatch, hatching success, and hatching survival) responses were assessed. UV-exposure alone caused a significant (>4-fold) increase in total Palaemonetes pugio female egg production over the course of 50 days. Exposure to ES and UV significantly lowered the percentage of gravid females relative to UV controls, whereas ES-exposed shrimp under WF lighting did not exhibit these trends. Although higher vitellogenin concentrations and lower ecdysteroid titers were correlated with increased female egg production, cholesterol titers only exhibited a dose-dependent change when exposed to ES. Embryos from females exposed to UV had significantly lower ecdysteroid titers and shorter hatching times but there were no differences in embryo vitellogenin concentrations, hatching success, or hatching survival. These results indicate that UV-A exposure has a pronounced effect on grass shrimp (Palaemonetes pugio) reproduction and is likely mediated through 5-hydroxytrptamine (5-HT)-related neuroendocrine pathways. The implications for decapod aquaculture and evaluating chronic contaminant effects are discussed.