Parasitism of the rhizocephalan <Emphasis Type="Italic">Briarosaccus callosus</Emphasis> on the crab <Emphasis Type="Italic">Paralomis verrilli</Emphasis> (Crustacea: Lithodidae) in the waters of southeast Sakhalin

The crab Paralomis verrilli in the waters of southeast Sakhalin is infected by the parasitic rhizocephalan barnacle Briarosaccus callosus. The prevalence of parasitic infection was on the average 4.36% (6.29% for females, 3.28% for males) and varied between samples from none up to 14.9%. The degree of prevalence was not related to the average carapace width and the sex ratio of crabs in samples. Sterilization of female P. verrilli was caused by the B. callosus infestation or its consequences. No more than two parasite externae per crab were found. Crabs with two externae made up 5.6% of all infected specimens. The infestation of crab hosts with two B. callosus externae negatively influenced the growth of the externae. A positive relationship was found between the width of the crab carapace and the length of the parasitic externae. The survival rate of P. verrilli with either one or two parasite B. callosus externae did not differ substantially. The proportion of crabs with externae and those with “scars” (12.2% in our case) can be taken as the index of survival of the parasitized crabs.     

Hyperparasitism of the cryptoniscid isopod Liriopsis pygmaea on the lithodid Paralomis granulosa from the Beagle Channel, Argentina

A total of 29,570 false king crab Paralomis granulosa were sampled from the Beagle Channel (54 degrees 51'S, 68 degrees 12'W), Tierra del Fuego, Argentina, between July 1996 and August 1998. Crab size varied from 6.8 to 111.2 mm carapace length (CL). A few crabs parasitized by the rhizocephalan Briarosaccus callosus were found; prevalences of externae (the rhizocephalan reproductive body) and scars (the mark left on the host after the death of the parasite) were 0.28 and 0.16%, respectively. Of 85 externae examined, 55 were non-ovigerous and 30 ovigerous. The cryptoniscid isopod Liriopsis pygmaea infested 36.5% of the B. callosus examined. The most abundant stage was the cryptonicus larva, accounting for 208 of the 238 L. pygmaea recovered. Cryptonisci showed a highly aggregated distribution. A total of 92.7% of cryptonicsci were recovered inside empty externae, suggesting that the latter were attractive to cryptonisci. Early subadult females of L. pygmaea were rare; only 3 individuals occurred inside 1 ovigerous externa. Eight late subadult and 18 adult females were found on 3 and 7 non-ovigerous externae, respectively; in addition, 1 aberrant late subadult was found on 1 ovigerous externa. In the Beagle Channel, the population of P. granulosa harbours 3 different parasites: the bopyrid isopod Pseudione tuberculata, which reaches highest prevalence at 10 to 20 mm CL, the rhizocephalan B. callosus, with highest prevalence at 20 to 40 mm CL, and the cryptoniscid isopod L. pygmaea, which mainly infests rhizocephalan on crabs >40 mm CL.     

The Parasitic Fauna of Common Species of Hermit Crabs of Vostok Bay (Sea of Japan)

The parasitic fauna of common species of hermit crabs was investigated in Vostok Bay (the northwestern Sea of Japan). Pagurus proximus and Areopaguristes hirsutimanus had no parasites. The average prevalence of rhizocephalan infestation in other five species of hermit crabs ranged from 5.67 to 20.83%. The prevalence of the isopod Parapseudione lata on hermit crabs did not exceed 1%, the prevalence of infestation with the isopod Athelges takanoshimensis was significantly higher, reaching 14.58% in Pagurus middendorffii. Parasitism by the isopod P. lata on the hermit crabs Pagurus minutus and P. ochotensis, as well as parasitism by the rhizocephalan Peltogaster reticulata on P. minutus were recorded for the first time. Several variants of simultaneous infestation with two parasitic species were found. The decline in the abundance of P. middendorffii accompanied by the high prevalence of parasites, primarily the colonial rhizocephalan Peltogasterella gracilis, suggests that parasite invasion may play a more significant role in regulating the abundance of hermit crabs than was previously assumed.     

Effects of the Briarosaccus callosus infestation on the commercial golden king crab Lithodes aequispina

Commercial crab populations off the Kamchatka coasts are infested to a considerable degree by the rhizocephalan parasite Briarosaccus callosus: of 769 Lithodes aequispina males examined, 43 (5.7%) were parasitized. Infestations result in the feminization of the crabs, a significant decrease in the cheliped length, and a significant decrease in the carapace length and width. We suggest that commercial selection of healthy males, and the returning of unsuitable crabs, including infested ones, back into the sea, results in an increase of the proportion of infested crabs in the population, their elimination from reproduction, and, eventually, the gradual degradation of a whole population. To minimize as far as possible the negative effects of commercial crab harvesting, all infested crab specimens caught must be destroyed, either aboard or elsewhere, instead of throwing them back into the sea.     

Microbial communities are indicators of parasite infection status

Growing evidence suggests that microbiomes have been shaping the evolutionary pathways of macroorganisms for millennia and that these tiny symbionts can influence, and possibly even control, species interactions like host–parasite relationships. Yet, while studies have investigated host–parasites and microbiomes separately, little has been done to understand all three groups synergistically. Here, we collected infected and uninfected Eurypanopeus depressus crab hosts from a coastal North Carolina oyster reef three times over 4 months. Infected crabs demonstrated an external stage of the rhizocephalan parasite, Loxothylacus panopaei. Community analyses revealed that microbial richness and diversity were significantly different among tissue types (uninfected crab, infected crab, parasite externae and parasite larvae) and over time (summer and fall). Specifically, the microbial communities from parasite externae and larvae had similar microbiomes that were consistent through time. Infected crabs demonstrated microbial communities spanning those of their host and parasite, while uninfected crabs showed more distinctive communities with greater variability over time. Microbial communities were also found to be indicators of early-stage infections. Resolving the microbial community composition of a host and its parasite is an important step in understanding the microbiome's role in the host–parasite relationship and determining how this tripartite relationship impacts coevolutionary processes.     

Parasites of the shore crab Carcinus maenas (L.): implications for reproductive potential and invasion success

The European shore crab, Carcinus maenas, is one of the most successful marine invasive species. Its success has been in part attributed to the loss of parasites, rekindling an interest in host-parasite interactions and impacts on host fitness in this crab. In the present study, we investigated C. maenas populations from Europe, South Africa and Australia for parasites, and assessed their impact on the fitness of male crabs. For the shore crab, testes weight along with success in mating competition is traded off against other life-history traits. We therefore used this parameter as an indicator both for reproductive fitness and a possible resource trade-off in response to parasite infestation. In the native range, crabs infested with Sacculina carcini showed significantly lower testes weight than uninfected crabs. However, helminth parasites did not generally cause reduced testes weights. Crab populations from South Africa and Australia were either parasitized at very low prevalences, or were completely parasite free. However, no population level effect of this parasite release was reflected in testes weight. These findings do not support a severe fitness impact of helminth parasites on C. maenas, which questions the role of parasites on its population dynamics, both in the native area and for invasive success.     

Associations between shorebird abundance and parasites in the sand crab, Emerita analoga, along the California coast

I investigated spatial variation in the prevalence and abundance of 4 species of parasites in the sand crab, Emerita analoga, on 8 sandy beaches along 800 km of the California coast, to assess the importance of bird abundance for the distribution of parasites among sand crab populations. I collected sand crabs and counted shorebirds and gulls at each beach during June and November 1994. Sand crabs served as intermediate hosts for 4 species of parasites, including a trematode, Spelotrema nicolli (Cable and Hunnienen, 1938); an acanthocephalan, Polymorphus kenti (Van Cleave, 1947); a nematode, Proleptus sp., and an unidentified trypanorhynch tapeworm. Among sand crab populations, there was substantial spatial variation in the prevalence and abundance of each parasite species. No latitudinal pattern was apparent for any of the 4 species observed. Temporally, parasite prevalence and abundance was significantly different between dates for all 4 parasites. Specifically, sand crab populations experienced higher trematode, nematode, and trypanorhynch prevalence and abundance in November than in June. In contrast, prevalence and abundance of acanthocephalans were higher in June than in November. There were strong positive associations between bird abundance and prevalence of parasitic infection for trematodes and acanthocephalans for some dates but not for nematodes or trypanorhynchs, which use elasmobranchs as definitive hosts. The spatial variation in prevalence and abundance of trematodes and acanthocephalans observed among sand crab populations may be attributed to the distribution and abundance of shorebirds and gulls that serve as definitive hosts.     

Parasite modification of predator functional response

Parasite alteration of the host (predator) functional response provides a mechanism by which parasites can alter predator–prey population dynamics and stability. We tested the hypothesis that parasitic infection of a crab (Eurypanopeus depressus) by a rhizocephalan barnacle (Loxothylacus panopei) can modify the crab’s functional response to mussel (Brachidontes exustus) prey and investigated behavioral mechanisms behind a potential change in the response. Infection dramatically reduced mussel consumption by crabs across mussel densities, resulting in a decreased attack rate parameter and a nearly eightfold reduction in maximum consumption (i.e. the asymptote, or inverse of the handling time parameter) in a type II functional response model. To test whether increased handling time of infected crabs drove the decrease in maximum consumption rate, we independently measured handling time through observation. Infection had no effect on handling time and thus could not explain the reduction in consumption. Infection did, however, increase the time that it took crabs to begin handling prey after the start of the handling time experiment. Furthermore, crabs harboring relatively larger parasites remained inactive longer before making contact with prey. This behavioral modification likely contributed to the reduced mussel consumption of infected crabs. A field survey revealed that 20 % of crabs inhabiting oyster reefs at the study site (North Inlet estuary, Georgetown, South Carolina, USA) are infected by the barnacle parasite, indicating that parasite infection could have a substantial effect on the population level crab-mussel interaction.     

滨鹬马蹄吸虫(复殖目:微茎科)的尾蚴和囊蚴期的季节动态

对科威特湾微茎科滨鹬马蹄吸虫幼虫期的中间宿主双带盾桑椹螺(Clypeomorus bifasciata)及小相手蟹(Nanosesarma minutum)的季节动态进行了研究。调查期超过一年,在检查的1 600只螺和415只蟹中, 11.8 %的螺感染了8种马蹄属线虫中的一种,且以滨鹬马蹄吸虫的感染占优势(9.9 %螺感染) ; 80 %的蟹感染滨鹬马蹄吸虫囊蚴。虽然一年四季两种宿主都会感染,但吸虫的流行和尾蚴(指成熟期感染)在夏季呈现高蜂。从螺体排出的尾蚴具有明显季节性,在此海湾必须要超过最低温度20℃。总的感染率在较大(较老)的螺里有所下降,显示吸虫影响宿主生存并随之影响宿主群体结构。囊蚴的感染丰度与蟹的个体大小有明显相关性;较大的蟹感染较多的囊蚴,显示宿主能耐受更多的吸虫。调查显示,囊蚴的感染率与蟹的大小或性别无相关性。囊蚴体外脱囊以及产卵吸虫的释放证明,成熟虫体终年存在于所有大小和性别不同的蟹里,显示从蟹到鸟的持续感染是可能的。总的来说,滨鹬马蹄吸虫在海湾的传播动态是由这两种无脊椎动物宿主来协调,并似乎是被一系列依赖于温度的活动控制,这些活动影响易感宿主种群及感染性幼虫期尾蚴和囊蚴的存在。     

An experimental evaluation of host specificity: the role of encounter and compatibility filters for a rhizocephalan parasite of crabs

The encounter/compatibility paradigm of host specificity provides three qualitative pathways to the success or failure of a potential host-parasite interaction. It is usually impossible to distinguish between two of these (encounter and compatibility filters closed versus encounter filter open and compatibility filter closed) because unsuccessful infection attempts are difficult to observe in nature. We were able to open the encounter filter under experimental laboratory conditions. Our analytical system used the rhizocephalan barnacle, Sacculina carcini, a parasitic castrator of the European green crab, Carcinus maenas, and Pachygrapsus marmoratus, a native European crab that occurs with C. maenas but is not parasitized by S. carcini in nature. Penetration followed by unsuccessful infection of P. marmoratus crabs by parasitic barnacle larvae leaves a uniquely permanent record in the thoracic ganglion of the crabs. This provided us with a novel tool to quantify the encounter filter in a host-parasite system in nature. We demonstrated, in the laboratory, that the compatibility filter was closed and that, in nature, even where barnacle larvae were present, the encounter filter was also effectively closed. The closure of both filters in nature explains the failure of this potential host-parasite interaction, an outcome favored by selection in both host and parasite.     

Disease management in two sympatric Apterostigma fungus‐growing ants for controlling the parasitic fungus Escovopsis

Antagonistic interactions between host and parasites are often embedded in networks of interacting species, in which hosts may be attacked by competing parasites species, and parasites may infect more than one host species. To better understand the evolution of host defenses and parasite counterdefenses in the context of a multihost, multiparasite system, we studied two sympatric species, of congeneric fungus‐growing ants (Attini) species and their symbiotic fungal cultivars, which are attacked by multiple morphotypes of parasitic fungi in the genus, Escovopsis. To assess whether closely related ant species and their cultured fungi are evolving defenses against the same or different parasitic strains, we characterized Escovopsis that were isolated from colonies of sympatric Apterostigma dentigerum and A. pilosum. We assessed in vitro and in vivo interactions of these parasites with their hosts. While the ant cultivars are parasitized by similar Escovopsis spp., the frequency of infection by these pathogens differs between the two ant species. The ability of the host fungi to suppress Escovopsis growth, as well as ant defensive responses toward the parasites, differs depending on the parasite strain and on the host ant species.     

Short report on the effect of a parasitic isopod on the reproductive performance of a shrimp

The present work studied the degree of inhibition caused by the bopyrid isopod Eophryxus lysmatae (Caroli, 1930 [Caroli, E., 1930. Notizia di tre specie nuove ed una poco nota di Bopiridi addominali, parassiti di Caridei del golfo di Napoli. (Contributo alla conoscenza del genere Phrixus Rathke). Boll. Soc. Nat. Napoli 41, 258-269]), an abdominal parasite, on the reproductive performance of its host, the protandric simultaneous hermaphrodite shrimp Lysmata seticaudata (Risso, 1816). Parasitized shrimp (PS) was not able to produce embryos, although they could successfully fertilise the eggs of unparasitized shrimp (US). All US paired with PS were able to fertilise eggs when paired with other US. The average number of larvae (±S.D.) produced by US shrimp paired with US and PS (344±27 and 346±23, respectively) was not significantly different (p=0.73). The average intermolt period duration (±S.D.) for US and PS (10±1.2 and 11±0.8 days, respectively) was not significantly different (p=0.82), with bopyrid parasites molting synchronously with their host. No PS lost its parasite during ecdysis. Although only three parasitized shrimp were used in the present work, parasitic castration induced by E. lysmatae seems to only affect the female sexual system of the simultaneous hermaphrodite L. seticaudata, and therefore parasite-induced “reproductive death” does not occur in this species as in other gonochoric and sequencial hermaphroditic caridean shrimp. Nutritional drain and disruption of endocrine mechanisms possibly caused by the bopyrid parasite are discussed.     

Interaction of a host plant and its holoparasite: effects of previous selection by the parasite

If parasites decrease the fitness of their hosts one could expect selection for host traits (e.g. resistance and tolerance) that decrease the negative effects of parasitic infection. To study selection caused by parasitism, we used a novel study system: we grew host plants (Urtica dioica) that originated from previously parasitized and unparasitized natural populations (four of each) with or without a holoparasitic plant (Cuscuta europaea). Infectivity of the parasite (i.e. qualitative resistance of the host) did not differ between the two host types. Parasites grown with hosts from parasitized populations had lower performance than parasites grown with hosts from unparasitized populations, indicating host resistance in terms of parasite’s performance (i.e. quantitative resistance). However, our results suggest that the tolerance of parasitic infection was lower in hosts from parasitized populations compared with hosts from unparasitized populations as indicated by the lower above‐ground vegetative biomass of the infected host plants from previously parasitized populations.     

Effect of the endosymbiotic pea crab Calyptraeotheres garthi on the metabolic rate and oxidative status of the slipper limpet Crepidula cachimilla

Parasites may induce metabolic changes and imbalances in the redox status of hosts. This study tested the effect of parasites on the O₂ consumption rate (O₂‐CR) of hosts, and explored the link between O₂‐CR and oxidative stress in parasitized hosts. We used the symbiotic pea crab Calyptraeotheres garthi and its slipper limpet host Crepidula cachimilla as models. The O₂‐CR of long‐term (3 months) infested limpets was 2.5 times greater than that of long‐term uninfested limpets. Also, the O₂‐CR of limpets stripped of crabs 24 h before measurements was intermediate between that of long‐term infested and uninfested limpets. These results indicate a parasitic relationship between C. garthi and Cr. cachimilla, and suggest that the effect of the parasite on the metabolic rate of limpets is reversible. Lastly, the activity of two antioxidant enzymes (CAT and GST) as well as lipid peroxidation did not vary between infested and uninfested limpets. Thus, increased O₂‐CR is not necessarily coupled with oxidative stress in pea crab‐parasitized slipper limpets.     

A review of bopyrid isopods infesting crabs from China

Isopod parasites of the subfamilies Ioninae and Pseudioninae infest the branchial chambers of brachyuran crabs. In total, 19 species of parasitic isopods infest crabs from China; they belong to 6 genera from the Ioninae and 1 genus from the Pseudioninae. Specifically, the following genera are represented: Allokepon Markham, 1982 (three species), Apocepon Nierstrasz and Brender à Brandis, 1930 (three species), Cancricepon Giard and Bonnier, 1887 (one species), Dactylokepon Stebbing, 1910 (four species), Gigantione Kossmann, 1881 (four species), Onkokepon, An et al. 2006 (two species) and Tylokepon Stebbing, 1906 (two species). The new species Tylokepon biturus from Menaethius monoceros (Latreille) collected in China is distinguished from other members of the genus by the striking shape of the head, two mid-dorsal projections on Pereomere 6, and entire pleopods and uropods without any tubercules on their surface. A list of all bopyrid species (19 species in seven families) along with their hosts and localities, is presented.     

Chemical host detection and differential attraction in a parasitic pea crab infecting two echinoids

Mechanisms of host detection and host choice are important for mobile parasites or symbionts that frequently move among host individuals. The parasitic pea crab Dissodactylus primitivus is an ectoparasite exploiting asymmetrically two spatangoid echinoid hosts, Meoma ventricosa and Plagiobrissus grandis. The entire life cycle takes place on M. ventricosa, while only adults colonize P. grandis, the host where female's fecundity is the greatest. Dissodactylus primitivus frequently exhibits host-switching, a behaviour that raises the question of host detection. To test if adult crabs are able to detect potential hosts and are attracted to the host where their fitness is greater, crab olfactory responses were investigated using a Y-tube. We first showed that D. primitivus are attracted by olfactory cues of M. ventricosa, versus those of a non-host echinoid species, Clypeaster rosaceus sharing the same habitat. This attractiveness was not due to a yellowish water-soluble substance secreted by the host. We then showed that the chemical attraction to the two hosts was different according to the origin of the crabs. Crabs coming from M. ventricosa were more attracted to this host than to P. grandis, a pattern compatible with an imprinting phenomenon. However, crabs collected from P. grandis were equally attracted to both host species, as if imprinting was lost after host change. We propose that the pattern of D. primitivus host detection could be intermediate between the behaviour of specialist and generalist symbionts.     

A Minchinia-like haplosporidan parasitizing blue crabs,Callinectes sapidus

A haplosporidan parasite was found infecting two moribund blue crabs, Callinectes sapidus, from Virginia and North Carolina. Spore stages were not found in either crab. Because of the presence of haplosporosomes in the cytoplasm, the parasites are thought to be a species of Minchinia or Urosporidium.     

A trematode infection with no effect on reproductive success of a sand-bubbler crab

The infection effects of the parasitic digenean trematode on the body weight and reproductive success of the sand-bubbler crab were examined. Gynaecotyla squatarolae (Trematoda: Microphallidae) infects the body cavity of Scopimera globosa (Decapoda: Scopimeridae) and uses the crab as its second intermediate host. The parasites infected all reproductive crabs examined to varying degrees. Larger crabs of both sexes had more parasites than smaller ones, probably because body size reflects age, and older crabs had a longer period of exposure to infection. Males had more parasites than females, probably because of sexual difference in acting time on the surface. Ovigerous females stay in closed burrows and do not act on the surface during incubation, and so have less chance of infection than males. The quantity of infecting parasites did not explain variations in either body weight or reproductive success of individual crabs in a field experiment. The life history of this parasite, relative body size of the crabs, and cost and the possible benefit of manipulation for the parasite may explain these results.     

Coastal crab Hemigrapsus longitarsis (Decapoda: Varunidae)—A new host for the rhizocephalan barnacle Polyascus polygenea (Cirripedia: Sacculinidae)

In Vostok Bay (Sea of Japan), the parasitic rhizocephalan barnacle Polyascus polygenea (Cirripedia: Sacculinidae) was found for the first time on a coastal crab Hemigrapsus longitarsis (Decapoda: Grapsidae). P. polygenea is a common parasite of H. sanguineus, a species very close to H. longitarsis in taxonomic position and biology.