Isopod Survival Research Articles

Morphological traits - desiccation resistance - habitat characteristics: a possible key for distribution in woodlice (Isopoda, Oniscidea).

Terrestrial isopods, as successful colonizers of land habitats, show a great variety in species distribution patterns on a global, continental, or regional scale. On a local, within-habitat level these patterns reflect the species’ tolerance limits and the presence of suitable hiding places (shelter sites, refugia). Humidity preference reflects a species’ capability for water retention which, in turn, depends on the integumental barrier. Desiccation resistance is a key feature in isopod survival under different environmental conditions. The present study shows a correlation between cuticle thickness and desiccation resistance under three relative humidity (RH) ranges (about 30, 75 and 100% RH) in nine species, relating these to the species’ differences in meso- and microhabitat choices. Habitat preferences are also associated with differences in cuticle surface morphology. The results support our hypothesis that species distribution and desiccation resistance are associated with particular cuticular morphological traits. Phylogenetic relations seem to be less important in desiccation resistance than cuticle thickness and external morphology.

Effects of food salinization on terrestrial crustaceans Porcellio scaber

Salinization of soil as the main cause for soil degradation is a global issue. Despite this, the data concerning the effects of different salts on terrestrial organisms are still missing. Our aim was to address the effects of four different salts (NaCl, KCl, NaNO3, and KNO3) on terrestrial isopods Porcellio scaber. Two types of experiments were performed. In the first experiment, the isopods were exposed to 1, 2, and 5g salt/kg dry leaf for 14 days and afterwards animal mortality, feeding activity, moult and growth were monitored. In the second experiment, a 48-h soil selection tests was done to investigate their preference/avoidance to certain salts. The feeding rate and growth efficiency of isopods decreased in a dose-dependent manner after 14 days exposure to KNO3 and NaNO3. We suggest that nitrate (NO3−) may be the predominant reason for these effects, because (i) the effects were only observed in the case of NO3−-salts, and (ii) K+ and Na+ induced no effects in the case of Cl−-salts where the concentrations of these two cations were even higher as in the case of NO3− salts. 48-h soil selection test showed that isopods were able to choose between NaCl dosed and unamended soil: the isopods preferred to spend time on NaCl spiked soil (up to 5g salt/kg dry soil). In the case of KNO3 and NaNO3 no significant soil selection by isopods was found. In these two exposures isopods spent approximately 50% of their visits on both sides of the soil. The survival of isopods decreased in a dose independent manner when exposed to NaNO3, KNO3, and KCl. We conclude that NaNO3, KCl, and KNO3 affect the isopods, while no effects were caused by NaCl under the exposure conditions of this study. This study implies that also other salts besides commonly investigated NaCl should be tested when the potential hazard of soil salinization to terrestrial organisms is in question.

CeO2 nanoparticles induce no changes in phenanthrene toxicity to the soil organisms Porcellionides pruinosus and Folsomia candida

Cerium oxide nanoparticles (CeO2 NPs) are used as diesel fuel additives to catalyze oxidation. Phenanthrene is a major component of diesel exhaust particles and one of the most common pollutants in the environment. This study aimed at determining the effect of CeO2 NPs on the toxicity of phenanthrene in Lufa 2.2 standard soil for the isopod Porcellionides pruinosus and the springtail Folsomia candida. Toxicity tests were performed in the presence of CeO2 concentrations of 10, 100 or 1000mg Ce/kg dry soil and compared with results in the absence of CeO2 NPs. CeO2 NPs had no adverse effects on isopod survival and growth or springtail survival and reproduction. For the isopods, LC50s for the effect of phenanthrene ranged from 110 to 143mg/kg dry soil, and EC50s from 17.6 to 31.6mg/kg dry soil. For the springtails, LC50s ranged between 61.5 and 88.3mg/kg dry soil and EC50s from 52.2 to 76.7mg/kg dry soil. From this study it may be concluded that CeO2 NPs have a low toxicity and do not affect toxicity of phenanthrene to isopods and springtails.

Complex predator–prey interactions between the rusty crayfish (Orconectes rusticus) and invertebrate and vertebrate prey within their native range

Crayfish can have profound effects on native species where they are introduced, yet few studies have examined the role of crayfish predation on species within their native ranges. We examined interactions between predatory rusty crayfish (Orconectes rusticus) and invertebrate and vertebrate prey in Southeast Indiana, where the crayfish are a native species. We conducted multiple experiments, which included assessing the predation efficiency of rusty crayfish on salamander larvae (Eurycea cirrigea) and aquatic isopods (Lirceus fontinalis), the role of substrate in prey survival, prey responses to chemical stimuli from crayfish, and the distribution of each species in a natural stream setting. We found that crayfish almost completely eliminated isopods, but the addition of even a simple gravel substrate dramatically increased survival. Although the size of the crayfish had no effect on isopod survival, salamander larvae were more likely to survive in the presence of smaller crayfish. Neither prey species responded to chemical stimuli from crayfish, yet field observations indicated that crayfish and isopods inhabit different microhabitats within the stream. Finally, the interaction between crayfish and salamander larvae is complex with the crayfish size and the natural distribution of size classes in streams likely reducing the larval predation risk and permitting coexistence. These results indicate that although crayfish are major predators on both invertebrates and vertebrates, coexistence over evolutionary time has likely led to multiple behavioral adaptations to avoid these predators.

Influence of soil pH on the toxicity of zinc oxide nanoparticles to the terrestrial isopod Porcellionides pruinosus

The effects of soil pH on the toxicity of ZnO nanoparticles (NPs) to the terrestrial isopod Porcellionides pruinosus were evaluated. Isopods were exposed to a natural soil amended with CaCO3 to reach 3 different pH(CaCl2) levels (4.5, 6.2, and 7.3) and to standard LUFA 2.2 soil (pH 5.5) spiked with ZnO NPs (30 nm), non-nano ZnO (200 nm), and ionic Zn as ZnCl₂. Toxicity was expressed based on total Zn concentration in soil, as well as total Zn and free Zn²⁺ ion concentrations in porewater. Compared with ZnO-spiked soils, the ZnCl₂-spiked soils had lower pH and higher porewater Ca²⁺ and Zn levels. Isopod survival did not differ between Zn forms and soils, but survival was higher for isopods exposed to ZnO NPs at pH 4.5. Median effect concentrations (EC50s) for biomass change showed similar trends for all Zn forms in all soils, with higher values at intermediate pH. Median lethal concentration (LC50) and EC50 values based on porewater Zn or free Zn ion concentrations were much lower for ZnO than for ionic zinc. Zn body concentrations increased in a dose-related manner, but no effect of soil pH was found. It is suggested not only that dissolved or free Zn in porewater contributed to uptake and toxicity, but also that oral uptake (i.e., ingestion of soil particles) could be an important additional route of exposure.

SETTLING BEHAVIOR OF THE DESERT ISOPOD HEMILEPISTUS REAUMURI IN RESPONSE TO VARIATION IN SOIL MOISTURE AND OTHER ENVIRONMENTAL CUES

ABSTRACT We report the results of three studies, one observational and two manipulative, that examine the settling behavior of isopods in response to soil moisture and other cues. In a census of isopod settling patterns in twenty-five 5 × 10 m plots arranged on a 200 m2 grid, isopods settled more densely in plots with more successful old burrows from the previous season, and in plots with more shrubs. Isopod settling was not correlated with soil moisture at 10 and 30 cm depths. In a manipulative experiment carried out over two years, isopods settled more densely in 3 × 3 m outdoor pens that received 20 mm of supplemental water in February than in unwatered plots. In a second experiment, 50 mm of water was added to open plots, and two densities of artificial holes were added as well. Isopods settled more densely in plots with added water, and settled much more densely in plots with artificial holes. Water did not significantly affect isopod survival or offspring weight. Unmanipulated plots with higher dens...

Toxicity of the organophosphorous insecticide chlormephos to the earthworm Eisenia andrei and the terrestrial isopod Porcellio scaber

In the present study we determined the toxicity of chlormephos to two common soil organisms – earthworms (Eisenia andrei) and isopods(Porcellio scaber) using Lufa 2.2 soil. The LC50 values for the effects on earthworm and isopod survival were 58 and 76 mg/kg dry soil, respectively. Mass change of earthworms and behaviour of isopods were more sensitive end points as survival. Based on earthworm body mass changes, NOEC and LOEC values were 1 and 3 mg/kg dry soil, respectively. The earthworms did not reproduce even at the lowest chlormephos concentration (LOEC < 1 mg/kg dry soil). Isopods significantly avoided burrowing in soil treated with ≥40 mg/kg dry soil. Compared with some other organophosphate insecticides, chlormephos was highly toxic to beneficial terrestrial invertebrates.

EFFECTS OF ACANTHOCEPHALUS LUCII (ACANTHOCEPHALA) ON INTERMEDIATE HOST SURVIVAL AND GROWTH: IMPLICATIONS FOR EXPLOITATION STRATEGIES

Intermediate host exploitation by parasites is presumably constrained by the need to maintain host viability until transmission occurs. The relationship between parasitism and host survival, though, likely varies as the energetic requirements of parasites change during ontogeny. An experimental infection of an acanthocephalan (Acanthocephalus lucii) in its isopod intermediate host (Asellus aquaticus) was conducted to investigate host survival and growth throughout the course of parasite development. Individual isopods were infected by exposure to fish feces containing parasite eggs. Isopods exposed to A. lucii had reduced survival, but only early in the infection. Mean infection intensity was high relative to natural levels, but host mortality was not intensity dependent. Similarly, a group of naturally infected isopods harboring multiple cystacanths did not have lower survival than singly infected isopods. Isopods that were not exposed to the parasite exhibited sexual differences in survival and molting, but these patterns were reversed or absent in exposed isopods, possibly as a consequence of castration. Further, exposed isopods seemed to have accelerated molting relative to unexposed controls. Infection had no apparent effect on isopod growth. The effects of A. lucii on isopod survival and growth undermine common assumptions concerning parasite-induced host mortality and the resource constraints experienced by developing parasites.

Impact of a microphallid trematode on the behaviour and survival of its isopod intermediate host: phylogenetic inheritance?

The extent to which the ability of parasites to alter host behaviour is phylogenetically inherited as opposed to independently evolved has received little attention. We investigated the impact of an undescribed species of Microphallus on the behaviour and survival of its host, the freshwater isopod Austridotea annectens, to determine if it produced effects comparable to those induced by other trematodes of this genus. There was no difference between the vertical distribution and responses to light of infected isopods and those of uninfected isopods. In contrast, we found that infected isopods were more active swimmers than uninfected isopods, and that they failed to show the evasive responses shown by uninfected isopods when exposed to a simulated predator. There was no detectable effect of Microphallus infection on isopod survival, however. Overall, our results provide no strong evidence that the behavioural manipulation shown by our Microphallus species and that displayed by the well-studied Microphallus papillorobustus are inherited from a common ancestor rather than independently derived.

Time-dependent toxicokinetics of [14C]lindane in the terrestrial isopod Porcellionides pruinosus.

Preliminary acute soil toxicity tests are a starting point for risk assessment. These tests are performed at one exposure time and are used to estimate the lethal concentration for 50% of the population (LC50). However, it is known that LC50 varies over time, following an exponential decay model. Here, we present the variation of LC50 over time in the isopod Porcellionides pruinosus exposed to [14C]lindane when considering the concentrations measured in bulk soil and in extracted water. Using a wide range of concentrations, the percent mortality was recorded over various time intervals. Higher concentrations strongly influenced isopod survival. The LC50 infinity value for P. pruinosus was 3.57 micrograms/g for bulk soil concentration, suggesting a great sensitivity of this species to lindane. Simultaneously, the values estimated for the lethal body concentration (LBC) were 2.36 micrograms/g animal for bulk soil concentrations and 2.79 micrograms/g animal when extracted water concentrations are considered. An alternative to the LC50 determination is the estimation of LBC, which is proposed as a better way to describe the acute toxicity of chemicals. Kinetic-based toxicity models were fitted to the data and revealed uptake rate constants of 1.1 g soil/g animal/week and 84.3 ml extracted water/g animal/week for bulk soil and extracted water concentrations, respectively. Elimination rate constants of 1.7 per week were found for both pathways of exposure.

Interactions of Intraspecific, Interspecific, and Apparent Competition with Host‐Pathogen Population Dynamics

I investigated the interactions of intra— and interspecific competition with parasitism for populations of two terrestrial isopods, Porcellio scaber and Porcellio laevis, infected with a lethal virus. In field experiments, I varied densities of one or both isopod species in enclosures in which food and virus presence were also manipulated. I estimated the effects of intra— and interspecific competition, additional food, and virus infection on both the survival of P. scaber and the prevalence of the virus. In uninfected populations, intraspecific and interspecific competition negatively affected isopod survival, although food resources had no effect. In infected treatments, interspecific competition produced higher levels of virus prevalence than did intraspecific competition. Virus infection and reduced food interacted to produce higher overall mortality in interspecific competition treatments than in intraspecific competition treatments. The lack of significant effect of food on competition suggests that interference interactions rather than resource competition predominated. This mechanism is supported by a laboratory study in which total food availability was controlled. These results indicate that competition and parasitism interacted to produce the observed mortality patterns, and that ignoring mortality due to the virus would produce apparent interspecific competition. The data suggest that the impact of P. laevis on P. scaber involves both direct and indirect effects.

Experimental studies on direct and indirect interactions in a three trophic-level stream system.

We used a complete block design to experimentally study direct and indirect interactions in a three trophic-level freshwater system consisting of a top predator, the green sunfish, Lepomis cyanellus, an intermediate predator, small-mouthed salamander larvae, Ambystoma barbouri, and prey, hatchling isopods, Lirceus fontinalis. This system occurs naturally in small stream pools in central Kentucky; experiments were done in laboratory pools. Salamander larvae ate isopods and thus had a direct, negative effect on isopod survival. Accordingly, isopods responded to the presence of salamander larvae by increasing their tendency to bury themselves in the sand substrate. Fish ate salamanders and thus had a direct, negative effect on salamander survival. Salamanders responded to fish presence by increasing their time spent under plexiglass plates that simulate refuge rocks. The overall effect of fish on isopods depended on the presence of salamanders. In the absence of salamanders, fish predation on isopods had a direct, negative effect on isopod survival; isopods thus responded to the presence of fish by burying themselves in the sand. With salamanders present, fish had a positive overall effect on isopod survival; i.e., direct, negative effects of fish on isopods were outweighed by indirect, positive effects. Indirect positive effects of fish on isopods came through a reduction in salamander predation rates on isopods in the presence of fish. The mechanism involved both a decrease in the number of salamanders (a trophic-linkage indirect effect; cf. Miller and Kerfoot 1987) and a reduction in the feeding rate of individual salamanders on isopods (a behavioral indirect effect). The decrease in individual salamander feeding rates on isopods was due to reductions in both salamander activity and in spatial overlap between salamanders and isopods in the presence of fish. The latter effect reflected the fact that salamanders and isopods used different refuges from fish; salamanders went under refuge plates, whereas isopods primarily buried themselves in sand. Estimates of the relative importance of various direct and indirect effects of sunfish on isopods suggested that positive, behavioral indirect effects were of roughly the same magnitude as direct, negative effects, both of which were more important than were trophic-linkage indirect effects. Contrary to expectations, the presence of isopods did not affect the refuge use or survival of salamanders in the presence of fish.

Experimental Studies on Behaviorally Mediated, Indirect Interactions through a Shared Predator

We examined indirect interactions between two noncompeting prey species (small—mouthed salamander larvae, Ambystoma texanum, and freshwater isopods, Lirceus fontinalis) that were mediated by the prey's antipredator responses to a shared predator (green sunfish, Lepomis cyanellus). Lirceus fontinalis responded to sunfish by decreasing overall activity and by decreasing their time spent of refuges. Male isopods were more active than females; as a result, males suffered higher predation rates than did females. Salamander larvae tended to drive isopods out of refuges; as a result, female (but not male) isopods suffered higher predation rates with than without salamanders. Ambystoma texanum responded to sunfish by decreasing their time spent outside of refuges. Despite this shift into refuges. A. texanum suffered high predation rates. Isopods increased the behavioral response of salamander larvae to sunfish. A. texanum decreased their emergence rate from refuge in response to sunfish, only when isopods were present. The apparent behavioral mechanism was that with isopods present, sunfish were more active, which, in turn, elicited a stronger antipredator response from salamanders. As a result, the presence of isopods significantly increased the survival of salamanders when fish were also present. Salamander larvae negatively affected female isopod survival, whereas isopods positively affected salamander survival. These effects were caused by changes in antipredator behavior and thus in predation rate. The indirect interaction between salamander larvae and isopods can be termed @`apparent predation" or indirect antagonism."

The importance of geological formations and slope aspect to desert isopod survival

Hemilepistus reaumuri is one of the most plentiful macroscopic invertebrates in the Negev desert. Its distribution and abundance were studied in relation to geological formation, soil moisture and slope aspect. The results show that, although burrows are less dense on south facing slopes, survival is higher. Conversely survival is lower on north facing slopes but burrow density is higher. Choice of a suitable geological formation coupled with slope aspect, seems necessary to maximise survival on rocky hillsides in the Negev desert.