Virus particles in an internal parasite, Portunion conformis (Crustacea: Isopoda: Entoniscidae), and its marine crab host, Hemigrapsus oregonensis

Based on morphological evidence and preliminary physicochemical data, we report the first picornavirus from crustacean hosts. The viral particles are widespread in the tissues of an isopodan parasitic castrator, Portunion conformis, and its shore crab host, Hemigrapsus oregonensis, collected in San Francisco Bay, California. Less frequently, infected cells of the parasitic isopod also contain larger viral particles.     

Ommochrome Deficiency in an Albino Strain of a Terrestrial Isopod,Armadillidium vulgare

In order to clarify the cause of ommochrome deficiency in an albino strain of the terrestrial isopod, Armadillidium vulgare, levels of xanthom-matin, 3-hydroxykynurenine, 3-hydroxyanthranilic acid and tryptophan in whole body extracts of the albino and the wild type individuals were determined together with enzyme activities of kynurenine-3-hydroxylase, kynureninase and tryptophan-2,3-dioxygenase. Xanthommatin could not be detected in the albinos. The levels of 3-hydroxykynurenine and 3-hydroxyanthranilic acid were determined by high-performance liquid chro-matography (HPLC) with electrochemical detection and were markedly low in the albinos compared with the wild type individuals. In contrast to those, the tryptophan levels determined by HPLC with fluorescence detection did not differ significantly between the two phenotypes. In the albino A. vulgare, kynurenine-3-hydroxylase activity was lower and kynureninase activity was higher than in the wild type, although the differences were not statistically significant. Tryptophan-2,3-dioxygenase activity in the albinos was less than 10% that in the wild type. Thus, ommochrome deficiency in the albino A. vulgare is considered to be caused by the extremely low activity of tryptophan-2,3-dioxygenase.     

An intra-species demonstration of the independence of distance and time in turn alternation of the terrestrial isopod, Porcellio scaber

In a study of turn alternation in the terrestrial isopod Porcellio scaber (woodlouse), smaller individuals (<11 mm long) took significantly longer to traverse a 60-mm open-ended post-forced-turn runway following a 90 degrees forced turn, than larger subjects (>11 mm long). However, there were no significant differences between the two groups in their probability of alternating, or in the magnitude of alternating turns as reflected in the size of the free-turn angles they turned on emerging from the runway. Nor was there a significant relationship for either group between the time taken to traverse the runway and either the probability of alternating or the size of a free-turn angle. In a second experiment, significant alternation occurred after woodlice emerged from runways that were 30 and 60 mm long, but not when they were 100 or 145 mm long. Their free-turn angles also became smaller as the runway length increased. Overall, the results of the three experiments supported the long-held view that, for reasons not yet understood, distance and time cannot necessarily be equated in the determination of invertebrate turn alternation.     

Food, feeding and growth rates of peracarid macro-decomposers in a Ria Formosa salt marsh, southern Portugal

The diet, feeding rates and growth rates of three species of isopod and three species of amphipod from a Ria Formosa salt marsh in southern Portugal are compared to test the hypotheses that the relative success of amphipods as macro-decomposers in salt marshes worldwide can be a) attributed to their utilizing a distinctly different range of potentially available food resources and b) attributed to them using similar food resources but at different rates.The first hypothesis was tested using a combination of gut contents analysis, stable isotope analysis and multiple-choice food preference tests. The results of all three analyses showed that there was a very broad overlap in the resource utilization curves for these species for the most abundant potential foods available in the upper salt marsh. The first hypothesis was therefore rejected.The second hypothesis was tested with palatability experiments in which consumption rates of each of the test animals were compared for each potential food offered alone. The amphipods ate all five of the foods significantly faster, consuming from 3-73× more food per unit mass than the isopods.Analyses of their relative growth rates from when released from the marsupium until first breeding, showed that amphipods have a faster growth rate than isopods in the field which is consistent with other traits in their rapid development-high fecundity life-history strategy. We conclude that these data support the second hypothesis and that their morphological adaptations to a shredding, high ingestion-rate rapid gut turnover digestive strategy enable them to have a more efficient resource acquisition rate than the slower growing, lower fecundity and slower ingestion-rate longer gut throughput time strategy of most isopods.     

Effects of predation risk on population variation in adult size in a stream-dwelling isopod

I used a combination of laboratory experiments and field surveys to examine the role that population-specific predation risk may play in shaping the life history strategy of a stream-dwelling isopod Lirceus fontinalis. Two focal populations were identified that were exposed to different predator types. The first population was exposed to larvae of the streamside salamander (Ambystoma barbouri) and the second to banded sculpin (Cottus carolinae). A laboratory experiment, in which different size classes of prey were offered simultaneously to individual predators, revealed that L. fontinalis suffered greatest mortality risk at small sizes with A. barbouri. Alternatively, with C. carolinae the risk of mortality was independent of size. Life history theory predicts that L. fontinalis from populations exposed to the gape-limited salamander larvae should be larger at maturity relative to individuals from populations exposed to C. carolinae. Field surveys on the two focal populations both within 1 year and across 4 years supported this prediction. Four other populations, two exposed to streamside salamander larvae and two to fish, provided additional support for the prediction. I concluded that L. fontinalis exhibited an adaptive response in size at maturity in response to population-specific predation risk. I then used gut content assays of the major predators to assess whether the population-specific life history strategies adopted by L. fontinalis were successful in avoiding predation.     

Sexual differences in larval life history traits of acanthocephalan cystacanths

Sexual differences in life history traits, such as size dimorphism, presumably arise via sexual selection and are most readily observed in adults. For complex life-cycle parasites, however, sexual selection may also have consequences for larval traits, e.g., growth in intermediate hosts. Two acanthocephalan species (Acanthocephalus lucii and Echinorhynchus borealis) were studied to determine, whether larval life histories differ between males and females. The size of female A. lucii cystacanths had a much stronger relationship with intermediate host size than males, suggesting females invest more in growth and are consequently more limited by resources. No relationship between host size and cystacanth size was observed for E. borealis. For both species, female cystacanths survived longer in a culture medium composed entirely of salts, which could suggest that females have greater energy reserves than males. A comparative analysis across acanthocephalan species indicated that sexual size dimorphism at the adult stage correlates with cystacanth dimorphism. However, the relationship was not isometric; cystacanths do not reach the same level of sexual dimorphism as adults, possibly due to resource constraints. Our results suggest that larval life histories diverge between males and females in some acanthocephalans, and this is seemingly a consequence of sexual selection acting on adults.     

Phylogeographic patterns of a lower intertidal isopod in the Gulf of California and the Caribbean and comparison with other intertidal isopods

A growing body of knowledge on the diversity and evolution of intertidal isopods across different regions worldwide has enhanced our understanding on biological diversification at the poorly studied, yet vast, sea–land interface. High genetic divergences among numerous allopatric lineages have been identified within presumed single broadly distributed species. Excirolana mayana is an intertidal isopod that is commonly found in sandy beaches throughout the Gulf of California. Its distribution in the Pacific extends from this basin to Colombia and in the Atlantic from Florida to Venezuela. Despite its broad distribution and ecological importance, its evolutionary history has been largely neglected. Herein, we examined phylogeographic patterns of E. mayana in the Gulf of California and the Caribbean, based on maximum‐likelihood and Bayesian phylogenetic analyses of DNA sequences from four mitochondrial genes (16S rDNA, 12S rDNA, cytochrome oxidase I gene, and cytochrome b gene). We compared the phylogeographic patterns of E. mayana with those of the coastal isopods Ligia and Excirolana braziliensis (Gulf of California and Caribbean) and Tylos (Gulf of California). We found highly divergent lineages in both, the Gulf of California and Caribbean, suggesting the presence of multiple species. We identified two instances of Atlantic–Pacific divergences. Some geographical structuring among the major clades found in the Caribbean is observed. Haplotypes from the Gulf of California form a monophyletic group sister to a lineage found in Venezuela. Phylogeographic patterns of E. mayana in the Gulf of California differ from those observed in Ligia and Tylos in this region. Nonetheless, several clades of E. mayana have similar distributions to clades of these two other isopod taxa. The high levels of cryptic diversity detected in E. mayana also pose challenges for the conservation of this isopod and its fragile environment, the sandy shores.     

Central neuronal pathways of the cardioinhibitory reflex in the isopod crustacean Bathynomus doederleini

We have already identified central neurons for cardioinhibition and cardioacceleration in Bathynomus, an isopod crustacean. The 1st thoracic ganglion (TG1) has cardioinhibitory neurons, which we call CIs, while the 2nd and 3rd thoracic ganglia (TG2 and TG3) have cardioacceleratory neurons, which we call CA1s and CA2s. We examined neuronal pathways for cardioinhibitory reflexes in whole animal preparations, using intracellular and extracellular recording methods. Cardiac inhibition in response to a variety of external stimuli was mediated by activation of CIs and inhibition of both CAs. When preparations had the ventral nerve cord intact, CIs were activated by excitatory postsynaptic potentials and CAs were inhibited by inhibitory postsynaptic potentials in response to tactile stimuli applied to sensilla setae on appendages and afferent stimuli applied to ganglionic roots of the thoracic ganglia. However, stimulation of ganglionic nerve roots of TG2 and TG3, or tactile stimulation of the body surface, failed to evoke inhibition of CAs in preparations in which both the cerebral ganglion and TG1 had been excised. These results suggest that TG1 is an indispensable central region for the excitation of CI and for inhibition of CA neurons, induced by tactile stimuli and by stimuli applied to nerve roots of TG2 and TG3.     

Cold adaptation of the terrestrial isopod,Porcellio scaber,to subnivean environments

The terrestrial isopod, Porcellio scaber, was susceptible to subzero temperature: both freezing and chilling were injurious. The level of cold hardiness against chilling and freezing showed different patterns in their seasonal variation. The lower lethal temperature causing 50% mortality, an indicator of the tolerance to chilling, ranged from-1.37°C in August to-4.58°C in December. The whole body supercooling point, the absolute limit of freeze avoidance, was kept at about-7°C throughout the year. The winter decrease in lower lethal temperature was concomitant with an accumulation of low molecular weight carbohydrates which are possible protective reagents against chilling injury, whereas the less seasonally variable supercooling point seemed to be associated with the year-round presence of gut content. Food derivatives may act as efficient ice nucleators. The different trend in seasonal changes between lower lethal temperature and supercooling point may be related to the microclimate of the hibernacula in subnivean environments, where the winter temperature became lower than the lower lethal temperature in the summer active phase, but remained higher than the summer supercooling point.Abbreviations LLT₅₀ lower lethal temperature inducing 50% mortality - SCP supercooling point - T _a ambient air temperature - T _s soil surface temperature