Isopod Populations Research Articles

The energetic cost of parasitism in isopods

Assessment of the energetic costs of parasitism is central to understanding the role of parasites in their hosts' foodwebs, but few studies have directly measured these costs. This study demonstrates that infection with the acanthocephalan parasite Acanthocephalus tehlequahensis causes a significant and direct energetic cost to its freshwater isopod intermediate host Ceacidotea communis at both individual and population levels. Bomb calorimetry was used to measure energy (kj·m−2.y−1) allocated to host growth, reproduction, and respiration in infected and uninfected isopods and to parasite tissue in infected isopods. Infected isopod individuals allocated ~21% of their net production energy to parasite growth, and they were larger (length), consumed more leaf detritus, and lost significantly more energy to respiration than uninfected controls (P ≤ 0.05). They also allocated proportionally less energy to tissue growth, allocated zero energy to reproduction, and were less efficient at converting energy into isopod biomass when compared to uninfected controls (P ≤ 0.05). In the field, isopod populations were surveyed monthly for a year. The parasite had a mean infection prevalence in the stream of 30.19% ± 8.31 SE with a mean intensity of 1.12 ± 0.39 SE parasites/host in the population, and based on this infection rate, it is estimated that ∼6.7% of total production energy of the isopod population (infected and uninfected) is diverted towards the parasite.

Reproductive toxicity of the endocrine disrupters vinclozolin and bisphenol A in the terrestrial isopod Porcellio scaber (Latreille, 1804)

Endocrine Disruptor Compounds (EDCs) have been largely studied concerning their effects on vertebrates. Nevertheless, invertebrates as targets for these chemicals have been neglected and few studies are available. Specifically for edaphic invertebrates, data concerning the effects of EDCs is residual. Influences of EDCs on the reproduction systems of these organisms, with consequences at the population level, are expected but have not been confirmed. This work aimed to study the effects of bisphenol A (BPA) and vinclozolin (Vz) on the reproduction of the terrestrial isopod Porcellio scaber. Isopods were coupled and exposed to increasing concentrations of Vz and BPA and the females’ reproductive cycle followed for 56 d. Both compounds elicited reproductive toxicity. Vz and BPA decreased female reproductive allocation. Vz reduced pregnancy duration; increased the abortion percentage; decreased the number of pregnancies; and decreased the number of juveniles per female while BPA increased abortions at the lowest and highest test concentrations. The reproductive endpoints presented in here are indicative of the possible impact that this type of compounds might have on isopod population dynamics, which may eventually lead to population decline.

Urban areas as hot-spots for introduced and shelters for native isopod species

Isopod assemblages were studied in Budapest, capital of Hungary. The analyses of literary and field data revealed a high species richness (28 species), compared to the total species number (57) in Hungary. Habitats characteristics for the city were categorized as native forests, urban forests, gardens of Buda, gardens of Pest, public parks, densely built-up areas and botanical gardens. We hypothesized that isolated and diverse habitat patches in the city matrix of Budapest support the introduction and establishment of exotic species and the survival of native ones. The composition of assemblages varied among sampling sites, but were characteristic for the biotope categories. We concluded that forests, parks and gardens play an important role in the survival of native isopod populations. Species numbers were highest in the gardens of Buda and in the botanical gardens (both 17 species). The overall presence of cosmopolitan and disturbance-tolerant species indicates an ongoing homogenization process.

Differences in parasite susceptibility and costs of resistance between naturally exposed and unexposed host populations

It is generally assumed that resistance to parasitism entails costs. Consequently, hosts evolving in the absence of parasites are predicted to invest less in costly resistance mechanisms than hosts consistently exposed to parasites. This prediction has, however, rarely been tested in natural populations. We studied the susceptibility of three naïve, three parasitized and one recently isolated Asellus aquaticus isopod populations to an acanthocephalan parasite. We found that parasitized populations, with the exception of the isopod population sympatric with the parasite strain used, were less susceptible to the parasite than the naïve populations. Exposed but uninfected (resistant) isopods from naïve populations, but not from parasitized populations, exhibited greater mortality than controls, implying that resistance entails survival costs primarily for naïve isopods. These results suggest that parasites can drive the evolution of host resistance in the wild, and that co-existence with parasites may increase the cost-effectiveness of defence mechanisms.

Observations with a different approach to morphological colour variation in an isopod population (Crustacea: Isopoda)

Morphological colour variation in Idotea baltica basteri Audouin, 1827 (Isopoda: Crustacea) is reported for the first time on populations from a brackish water lake (Kucukcekmece Lagoon) in Turkey. According to pigmentation characteristics, the isopods were described and sorted to ten different colour morphs which are named as maculata, maculata-lineata, uniformis, uniformis-lineata, immaculatum, immaculatum-lineata, nigrum, nigrum-lineata, albafusca, and albafusca-fasciatum. The similarity of the morphs was compared by defining digit codes to some of the visual pigmentation characteristics and calculating the Bray-Curtis similarity index of the colour morphs. The albafusca and albafusca-fasciatum forms were found to be the most similar to each other (similarity 96%), whereas immaculatum forms were considered the most different from maculata-lineata (similarity 50%). The morphs named maculata and maculata-lineata, having the highest abundance with 70%, belong to the most successful forms which may achieve crypsis by background matching in their living habitat in Kucukcekmece Lagoon which has sandy and rocky bottom surface area.

Subterranean archipelago: mitochondrial DNA phylogeography of stygobitic isopods (Oniscidea:Haloniscus) from the Yilgarn region of Western Australia

The arid Yilgarn region of Western Australia contains numerous isolated calcrete aquifers, within which a diverse subterranean fauna has been discovered. Genetic and morphological studies of subterranean dytiscid beetles and amphipods have suggested that individual calcretes are equivalent to closed island habitats, which have been isolated for millions of years. Here we test this ‘subterranean island’ hypothesis further by phylogeographic analyses of subterranean oniscidean isopods (Haloniscus), using mitochondrial DNA (mtDNA) sequence data derived from the cytochrome c oxidase subunit I gene. Phylogenetic and population genetic analyses provided evidence for significant phylogeographic structuring of isopod populations, with evidence for at least 24 divergent mtDNA lineages, each restricted in their distribution to a single calcrete aquifer. The high level of divergence among calcrete populations (generally >25%) and several mtDNA lineages within calcretes (>16%) suggests that each lineage is likely to represent a distinct species. These analyses, together with comparative phylogeographic data from dytiscid beetles and amphipods, provide strong support for the ‘subterranean island’ hypothesis, applying to both air-breathing and fully aquatic arthropod groups. The finding of several epigean lineages that grouped with stygobitic Haloniscus populations, and the overall phylogeographic structure of populations, suggests that the majority of stygobitic species evolved within individual calcretes following independent colonisation by epigean ancestors.

Long-term Hg pollution induced Hg tolerance in the terrestrial isopod Porcellio scaber (Isopoda, Crustacea)

The aim of our work was to assess the pollution-induced community tolerance (PICT) of isopod gut microbiota and pollution-induced isopod population tolerance (PIPT). Animals collected from a chronically Hg polluted and an unpolluted location were exposed for 14 days to 10 μg Hg/g dry food under laboratory conditions. The lysosomal membrane stability, hepatopancreas epithelium thickness, feeding activity and animal bacterial gut microbiota composition were determined. The results confirm the hypothesis that the response to short-term Hg exposure differs for animals from the Hg polluted and the unpolluted field locations. The animals and their gut microbiota from the Hg polluted location were less affected by Hg in a short-term feeding experiment than those from the unpolluted environment. We discuss the pollution-induced population tolerance of isopods and their gut microbiota as a measure of effects of long-term environmental pollution. The ecological consequences of such phenomena are also discussed.

Parasite effects on isopod feeding rates can alter the host’s functional role in a natural stream ecosystem

Changes to host behaviour as a consequence of infection are common in many parasite–host associations, but their effects on the functional role hosts play within ecosystems are rarely quantified. This study reports that helminth parasites significantly decrease consumption of detritus by their isopod hosts in laboratory experiments. Natural host and parasite densities across eight contiguous seasons were used to estimate effects on the amount of stream detritus-energy processed. Extrapolations using mass-specific processing rates from laboratory results to field patterns suggest that the effects of the parasites occur year round but the greatest impact on the amount of detritus processed by isopods occurs in the autumn when the bulk of leaf detritus enters the stream, and when parasite prevalence in the isopod population is high. Parasites have a lesser impact on the amount of detritus processed in spring and summer when isopods are most abundant, when parasite prevalence is not high, and when fish predation on isopods is high. These results support the idea that parasites can affect the availability of resources critical to other species by altering behaviours related to the functional role hosts play in ecosystems, and suggest that seasonality may be an important factor to consider in the dynamics of these parasite–host interactions.

Mitochondrial Genome Haplotype Hypervariation Within the Isopod Parasitic Nematode Thaumamermis cosgrovei

Characterization of mitochondrial genomes from individual Thaumamermis cosgrovei nematodes, obligate parasites of the isopod Armadillidium vulgare, revealed that numerous mtDNA haplotypes, ranging in size from 19 to 34 kb, are maintained in several spatially separated isopod populations. The magnitude and frequency of conspecific mtDNA size variation is unprecedented among all studied size-polymorphic metazoan mitochondrial genomes. To understand the molecular basis of this hypervariation, complete nucleotide sequences of two T. cosgrovei mtDNA haplotypes were determined. A hypervariable segment, residing between the atp6 and rrnL genes, contributes exclusively to T. cosgrovei mtDNA size variation. Within this region, mtDNA coding genes and putative nonfunctional sequences have accumulated substitutions and are duplicated and rearranged to varying extents. Hypervariation at this level has enabled a first insight into the life history of T. cosgrovei. In five A. vulgare hosts infected with multiple nematodes, four carried nematodes with identical mtDNA haplotypes, suggesting that hosts may become infected by ingesting a recently hatched egg clutch or become parasitized by individuals from the same brood prior to dispersal of siblings within the soil.

Geographical divergence in host use ability of a marine herbivore in alga–grazer interaction

When the selective environment differs geographically, local herbivore populations may diverge in their host use ability and adapt locally to exploit the sympatric host population. We tested whether populations of the marine generalist herbivore Idotea baltica have diverged in host us ability and whether they locally adapted to exploit the sympatric population of their main host species, the bladderwrack Fucus vesiculosus. We fed isopods from three local populations reciprocally with the sympatric and two allopatric populations of the host. The bladderwrack populations varied in their quality as food for isopods suggesting variation in the selective environment. The ability to exploit the main host showed considerable divergence among the isopod populations. There was no significant interaction between host and isopod origin, indicating that the patterns observed in the reciprocal feeding experiment could be explained by differences in overall suitability of the hosts and differences in overall performance of the isopod populations. Isopod population that was sympatric to a bladderwrack population with low phlorotannin content showed high performance on the algae from the sympatric but low performance on the algae from the two allopatric populations. Performance of isopods, especially in this population, decreased quickly with the increasing phlorotannin content of food algae. We therefore hypothesize that the isopods adapted to a low phlorotannin content were unable to utilize high-phlorotannin algae efficiently. Isopod populations sympatric to the high-phlorotannin bladderwrack populations may be generally better adapted to deal with phlorotannins, being thereby able to utilize a range of bladderwrack populations.

Population dynamics of Excirolana armata (Isopoda: Cirolanidae) in Buenos Aires beaches, Argentina

The population dynamics and structure of the cirolanid isopod Excirolana armata were studied from January 2004 through March 2005 in three sandy beaches of Buenos Aires Province (Argentina). Beaches with different types of anthropogenic influences were selected. The von Bertalanffy's growth function parameters were determined for each population. There was a marked fluctuation in growth, with lowest rates in late autumn and winter. The isopod population of the beach exposed to the highest degree of anthropogenic erosion had the lowest and most stable values of abundance and biomass, the highest mortality rate and the shortest life span. Temporal fluctuations of the allometric coefficient of the length-dry weight relationship indicated a cycling pattern, with lowest values during the autumn-winter period and peak values in the summer. Females predominated in the populations due to the short duration of the reproductive season. Argentine and Uruguayan populations showed similar growth performance indices, but differed in their abundance and biomass values, probably as a response to variations in beach morphodynamics and biological interactions.

Spatial distribution of isopods in an oak–beech forest

Soil macroinvertebrates were studied in a Mediterranean-type forest on brown-pebble forest soils in southern Russia. At the site, 144 intact soil cores (76 cm 2 each) forming a grid of 24 × 6 units were taken in order to determine animal spatial distribution. Abundance of isopods was 166.3 ± 16.0 indiv. m –2 and they constituted about 12% of the total macrofaunal abundance. Biomass of isopods was 3.5 g m –2, or about 21% of the total biomass of macrofauna. Three woodlice genera ( Armadillidium, Cylisticus, and Trachelipus) were found at the site. The two latter genera formed almost all (93%) of the isopod population. We found that spatial distribution of woodlice was heterogeneous: areas with 4–5 individuals per sample were neighboring those without animals. In order to study soil factors influencing isopod distribution in the brown-pebble forest soil, the size of a sample was artificially increased by combining adjacent sample units. Litter mass (r = 0.41) and loss on ignition (LOI) (r = –0.55) significantly influenced isopod distribution. Soil pH was near neutral (6.79), LOI was 8.39, and the water holding capacity was 70.9%. Pebbles comprised up to 84% of the sample's mass. Ca. 40 samples are recommended for estimation of isopod abundance in brown forest soil.

Stress Proteins (hsp70, hsp60) Induced in Isopods and Nematodes by Field Exposure to Metals in a Gradient near Avonmouth, UK

Heat shock proteins (hsps) are potential biomarkers for monitoring environmental pollution. In this study, the use of hsps as biomarkers in field bioassays was evaluated in terrestrial invertebrates exposed to a metal gradient near Avonmouth, UK. We investigated the hsp70 response in resident and transplanted isopods of the species Oniscus asellus and Porcellio scaber and the hsp60 response in transplanted nematodes of the species Plectus acuminatus in six field sites along the metal gradient. Considerable differences were detected in the stress responses between nematodes and isopods (isopods responded in a gradient-specific manner, nematodes did not), the two isopod species and the transplanted and resident specimens of each isopod species: in the sites closest to the smelter, O. asellus residents showed high hsp70 levels while O. asellus transplanted from an unpolluted site displayed comparatively low hsp70 levels. For P. scaber, it was just the opposite. In resident isopod populations of both species, tolerant phenotypes were revealed in the most contaminated field sites. The hsp70 level in both isopod species was a suitable biomarker of effect (but of exposure only in non-tolerant individuals) even in long-term metal-contaminated field sites. The hsp60 response in the nematode alone was not a suitable biomarker for heavily contaminated soils. However, it had indicative value when related to the hsp70 response in the isopods and could be a suitable biomarker for less heavily contaminated soils.

Effects of temperature and precipitation on a flood plain isopod community: a field study

Effects of a changing climate at individual, population and community levels on biocoenoses will cause profound changes in ecosystem functioning. Considering detritivore communities, we expect severe impacts on the balance of nutrient input through annual leaf fall and nutrient cycling through leaf litter decomposition. Thus, fluctuations of detritivore populations under changing climatic conditions will affect the degradation of detritus. Monitoring populations of four isopod species, that represent the most abundant detritivores in a floodplain forest near Cologne, Germany, revealed three distinct patterns of breeding phenology. Porcellio scaber and Philoscia muscorum breed early in the season (late spring to summer), while Oniscus asellus breeds during summer and early fall. Hyloniscus riparius appears to have a prolonged breeding season, ranging from spring to fall. Over 5 years, I observed effects of annual variations in temperature and precipitation on isopod populations and the composition of the community of these detritivores. With respect to the onset of breeding and to overall population size, as estimated from the number of captured individuals, summer and winter temperature proved to be particularly important, while temperature during fall and spring had little influence on isopod number or phenology. Considering precipitation, mostly summer and spring were of importance, whereas fall and winter precipitation only played a role in determining phenology but did not influence population densities. Predominant effects of climatic factors were low population densities of P. scaber, P. muscorum and O. asellus after warm winters and moist springs and during dry summers, while moist springs increased numbers of H. riparius. After moist springs, in turn, P. scaber and O. asellus started breeding earlier than after dry springs. According to the present field data, isopods (and maybe other detritivores) will be affected by regional climate change in that numbers will be reduced in response to increasing winter temperature, more intense precipitation during spring and dry summers as predicted by current climate models. Thus, climate change will result in reduced faunal contributions to decomposition processes that, in turn, will lead to slowed-down microbial degradation of detritus and nutrient cycling.

First Report of the Acanthocephalan Plagiorhynchus cylindraceus in the Terrestrial Isopod Porcellio scaber

Terrestrial isopod populations were examined from 5 different sites on the Penn State–Altoona campus in Altoona, Pennsylvania, U.S.A. Length and sex of each isopod were recorded before it was examined for acanthocephalan parasites. Three isopod species were found: Armadillidium vulgare, Porcellio scaber, and Oniscus asellus. The acanthocephalan parasite Plagiorhynchus cylindraceus was found in P. scaber from a single site (site prevalence, 2.5%). This is the first report of natural infection of P. scaber by P. cylindraceus.

Postembryonic ontogenetic development in Porcellio scaber (Isopoda: Oniscidea): the significance of food

Summary Postembryonic ontogenetic development in Porcellio scaber was observed on an individual basis over 90 weeks. Under optimal nutritive conditions, the duration of development to maturity showed high inter-individual variability and ranged from 60 to 90 weeks. Both growth rates and mortality of juvenile woodlice depended on the available food source, the alder litter being of highest, the oak litter of lowest, and the birch litter of intermediate quality. The experimentally manipulated pH level of the litter that, in turn, affected some leaf litter traits and the density and activity of litter-colonizing microbiota was of minor significance. Previous results and the present study suggest that food sources of low nutritive value affect isopod populations by (1) increasing the mortality and (2) reducing the reproductive success of adult females, and by (3) increasing mortality and reducing growth rates of juveniles, and therefore by (4) delayed maturity.

Species‐specific patterns of litter processing by terrestrial isopods (Isopoda: Oniscidea) in high intertidal salt marshes and coastal forests

Summary The species‐specificity of litter processing by three species of isopods at the interface between salt marsh and coastal forest habitats in the south‐eastern United States was examined. To quantify isopod performance, measurements were taken of feeding, digestion and growth of isopods fed on three litter types (Juncus roemerianus, Quercus virginiana and Pinus palustris) and on artificial diets containing one of three classes of model phenolic compounds (simple phenolics and hydrolysable and condensed tannins). To quantify the ecosystem impact of isopods, promotion of microbial respiration, changes in detritus chemistry, and the quantity of litter processed by isopod populations were measured. The results support three hypotheses concerning isopod–litter interactions. (i) Isopod performance on different litter types can be predicted based on chemical litter traits, e.g. phenolic concentrations and C : N ratios. (ii) Fully terrestrial isopods are better adapted to the range of phenolics found in angiosperm litter than are semiterrestrial species inhabiting the supralittoral. (iii) Isopod species differ with respect to their impact on decomposition processes due to species‐specific digestive capabilities, different effects on microbial decomposition and different rates of net litter processing. Because isopods are transitional between semiterrestrial and terrestrial habitats, unlike most other salt marsh detritivores, they are likely to play a unique role in decomposition processes and in the flux of materials between salt marsh and terrestrial habitats.

Peracáridos associados aos bancos de Phragmatopoma caudata (Kröyer) (Polychaeta, Sabellariidae) na Praia de Caiobá, Matinhos, Paraná

A study about composition, relative abundance and densities of peracarid populations associated to worm reefs of P. caudata (Kroyer, 1856) from Caioba Beach, Matinhos, State of Parana (25o51'S and 48o 32'W) was carried out. Monthly samples were obtained from August/1997 to July/1998. The density was calculated as the number of individuais per liter of worm reef. Three amphipod and three isopod species were obtained. The total density of the amphipod populations varied from 3.85 ind./l (July) to 70.56 ind./l (December) and that of the isopod from 0.25 ind./l (May) to 11.73 ind./l (March), The annual fluctuation of the amphipod densities was closely related to the weight fluctuation of the associated algae. The most numerous amphipod species was Elasmopus pectenicrus (Bate, 1862) followed by Hyale media (Dana, 1853) and Ericthonius brasiliensis (Dana, 1853). The isopod Paradynoides brasiliensis Loyola e Silva, 1960 was the most numerous followed by Excirolana armata (Dana, 1852) and Dynoides castroi Loyola e Silva, 1960. All amphipods and two isopod species were considered as constant species and they showed continuous breeding all year round. The occurrence of males, females (including ovigerous ones) and juveniles in the most amphipod and isopod populations in the present study indicates that these peracarids perform a complete life cycle within the Phragmatopoma caudata reefs. These constitute an alternative substrate to peracarids living on phytal and sandy habitats.

Genetic diversity and metal tolerance of two marine species: a comparison between populations from contaminated and reference sites

Long-term contamination of the marine environment surrounding a lead smelter offered a unique opportunity to examine how pollutants might have acted to alter genetic characteristics of populations of organisms in the receiving system. This study used random amplified polymorphic DNA analysis to compare the genetic diversity of populations of the prawn, Leander intermedius, and the isopod, Platynympha longicaudata from the smelter discharge site with reference populations. The genetic diversity of the prawn population from the smelter discharge site (Port Pirie) was lower than that found in one reference population, and not significantly different from the other two reference populations. Genetic diversity of the Port Pirie population of isopods was found to be significantly lower than that of all reference populations. Prawns and isopods were also exposed to metal mixtures in the laboratory in a similar ratio to that found in seston near the smelter effluent discharge site. Both pre-exposed and reference populations of prawns tolerated elevated levels of metals and exhibited no significant difference in response. This contrasted with the isopods, with the pre-exposed isopod population showing greater tolerance to elevated metal levels compared with the reference population. These results highlight the need to include a number of reference populations for comparative purposes in genetic diversity studies, and the need to assess the influence of pollution on the genetic diversity of more than one species if genetic diversity analyses are to be used to gauge remediation success.

Sex ratio alterations in terrestrial woodlice populations (Isopoda: Oniscidea) from agroecosystems subjected to different agricultural practices in Italy

The influence of different agricultural practices on the sex ratio shown by Trachelipus rathkei (Isopoda: Oniscidea) populations was investigated by pitfall trapping in three nearby sites from an agricultural landscape in northern Italy, a conventional, high chemical input apple orchard, a biological, no chemical input apple orchard, and an uncultivated deciduous forest. In the forest site, the sex ratio changed from a significant male-bias during the first part of the annual activity period to a female-bias during the last part of the activity season. In the conventional orchard, however, the sex ratios showed a female-bias during the whole activity period. The biological orchard population showed a temporal pattern rather similar to that found in the forest population. These results are congruent with the hypothesis that distorted sex ratios, and especially female-biased ones, are likely to arise within populations subjected to one higher environmental disturbance. Accordingly, biological agriculture, at least in this case, could be considered as a gentler, less disturbing anthropogenic disturbance for isopod populations, so allowing the maintenance of more natural ecological features relatively to modern conventional, high chemical input agriculture. The adaptive, environmental and bioindicative significance of these results are discussed.