An assemblage of terrestrial isopods (Crustacea) in southern Brazil and its contribution to leaf litter processing

Terrestrial Isopods Generate Microplastics from Low-Density Polyethylene Without Effects on Survival

With concern growing regarding the impact of microplastics (MPs) on terrestrial ecosystems, it is important to assess the role invertebrates may play in the fate of MPs within these ecosystems. Commonly, MPs enter these environments through improperly discarded waste or the application of treated biosolids and/or wastewater on agricultural soils. The present study investigated whether three species of terrestrial isopod (Porcellio scaber, Porcellio laevis, and Porcellionides pruinosus) ingest plastic debris and generate MPs during exposures varying from 24 h to 14 days and whether this may have an adverse effect on their health. Test vessels were designed to expose isopods to plastic fragments in the form of polyethylene plastic foam. Isopods were exposed to plastic that was either (1) pristine, or (2) weathered in a soil and water solution prior to incorporation in test vessels. When exposed to weathered polyethylene, all three species generated MPs (minimum-maximum size values for all durations inclusive: P. laevis = 114-1673 µm, P. scaber = 99-1635 µm, P. pruinosus = 85-1113 µm) through the consumption of macroplastic fragments with no observed impact on their health. In the shorter-duration exposures, the number of MPs generated by the isopod species in the present study was highly variable between experimental vessels (minimum-maximum generated MPs for 14-day exposure: P. laevis = 25-420, P. scaber = 50-583, P. pruinosus = 48-311). However, as the exposure durations increased, there was a clear trend of increasing MP generation, indicating that the isopods continued to consume the plastic fragments as long as the surface was weathered. A significant difference in the size of generated MPs was observed as well, with smaller isopod species generating smaller MP fragments on average. The results of the present study confirm that certain species of isopod can contribute to the generation of MPs, which constitutes an additional pathway of MP exposure to soil ecosystems. Environ Toxicol Chem 2024;00:1-9. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Terrestrial crustaceans (Arthropoda, Crustacea): taxonomic diversity, terrestrial adaptations, and ecological functions

Terrestrial crustaceans are represented by approximately 4,900 species from six main lineages. The diversity of terrestrial taxa ranges from a few genera in Cladocera and Ostracoda to about a third of the known species in Isopoda. Crustaceans are among the smallest as well as the largest terrestrial arthropods. Tiny microcrustaceans (Branchiopoda, Ostracoda, Copepoda) are always associated with water films, while adult stages of macrocrustaceans (Isopoda, Amphipoda, Decapoda) spend most of their lives in terrestrial habitats, being independent of liquid water. Various adaptations in morphology, physiology, reproduction, and behavior allow them to thrive in virtually all geographic areas, including extremely arid habitats. The most derived terrestrial crustaceans have acquired highly developed visual and olfactory systems. The density of soil copepods is sometimes comparable to that of mites and springtails, while the total biomass of decapods on tropical islands can exceed that of mammals in tropical rainforests. During migrations, land crabs create record-breaking aggregations and biomass flows for terrestrial invertebrates. The ecological role of terrestrial microcrustaceans remains poorly studied, while omnivorous macrocrustaceans are important litter transformers and soil bioturbators, occasionally occupying the position of the top predators. Notably, crustaceans are the only group among terrestrial saprotrophic animals widely used by humans as food. Despite the great diversity and ecological impact, terrestrial crustaceans, except for woodlice, are often neglected by terrestrial ecologists. This review aims to narrow this gap discussing the diversity, abundance, adaptations to terrestrial lifestyle, trophic relationships and ecological functions, as well as the main methods used for sampling terrestrial crustaceans.

Terrestrial Isopods Porcellio scaber and Oniscus asellus (Crustacea: Isopoda) Increase Bacterial Abundance and Modify Microbial Community Structure in Leaf Litter Microcosms: a Short-Term Decomposition Study

Invasive terrestrial isopods are likely to have altered leaf litter decomposition processes in North American forests, but the mechanisms underlying these alterations and the degree to which they differ among isopod species are poorly characterized. Using mixed-deciduous leaf litter microcosms, we quantified the effects of two common, invasive isopods (Oniscus asellus and Porcellio scaber) on short-term leaf litter decomposition and microbial community structure and function. Microcosms containing ground litter and a microbial inoculant were exposed to one of the two isopod species or no isopods for 21 days. Mass loss was then quantified as the change in litter dry mass after leaching, and microbial respiration was quantified as the mass of CO₂ absorbed by soda lime. Litter leachates were plated on agar to quantify culturable bacterial and fungal abundance, and denaturing gradient gel electrophoresis of amplified leachate microbial DNA was used to characterize shifts in microbial community structure. Isopod presence increased litter mass loss by a modest ~ 6%, but did not affect litter microbial respiration. Bacterial abundance increased significantly in the presence of isopods, while fungal abundance was either unchanged or reduced. Overall litter microbial species richness was reduced by isopods, with O. asellus specifically reducing fungal abundance and diversity. Isopods modified the microbial community structure by suppressing four bacterial and one fungal species, while promoting growth of four other bacterial species (two unique to each isopod species) and two fungal species (one which was unique to O. asellus).

Consumption Performance of Five Detritivore Species Feeding on Alnus glutinosa L. Leaf Litter in a Microcosm Experiment

The present study was performed to assess the feeding performance of five detritivore species in a microcosm design. The test animals were four millipede species, Telodeinopus aoutii (Demange), Epibolus pulchripes (Gerstäcker), Cylindroiulus caeruleocinctus (Wood), Glomeris hexasticha (Brandt), and one isopod species, Porcellio scaber (Latreille), all feeding on Alnus glutinosa L. leaf litter for five consecutive weeks. At the end of each one-week interval, litter consumption, animal fresh weight, and excrement production were measured. Then, the feeding activity parameters for each species were calculated. Between big-size animal species, higher leaf consumption rates of 12.3–30.9 mg dry weight day−1 individual−1 were calculated for T. aoutii compared to those of 3.72–8.25 mg dry weight day−1 individual−1 for E. pulchripes. However, there was no difference in the consumption rates among small-size animals ranging from 0.46 to 1.65 mg dry weight day−1 individual−1. Excrement production rates followed a similar trend, as the consumption rates and the animals’ body weight remained constant during the experiment. Time was an important factor influencing the feeding activity of the animals, especially for the big-size group. Overall, the average assimilation efficiency of these species varied from 13.7% to 53.3%. The results of the present work will be the first step for understanding the ecological needs of these decomposer species in soil ecosystems.

How coexistence may influence life history: the reproductive strategies of sympatric congeneric terrestrial isopods (Crustacea, Oniscidea)

Patterns of allocation between reproduction, survival, and maintenance are what we call life history. By investigating the life-history strategy of sympatric species, we may understand how they are able to coexist, as different strategies are expected to evolve in species that occupy similar niche space. Terrestrial isopods are a group in which multiple species frequently inhabit the same area. Notably, they are usually infected by Wolbachia Hertig, 1936, a notorious manipulator of the hosts’ reproductive processes. Thus, the aim of this study was to analyze the investment in reproduction in three sympatric and closely related species of terrestrial isopods: Atlantoscia floridana (Van Name, 1940), Atlantoscia inflata Campos-Filho and Araujo, 2015, and Atlantoscia petronioi Campos-Filho, Contreira and Lopes-Leitzke, 2012, only the latter being infected with Wolbachia. We showed that the presence of the bacteria seems not to affect the fitness of A. petronioi, because there was no clear difference in the reproductive output of infected and noninfected individuals. On the other hand, we observed that the three species possess alternative life-history strategies; that is, they differ in how much they invest in maintenance (body size) and reproductive effort. Such differences probably facilitate the species coexistence, reducing the competition among them.

Boric acid as a reference substance in avoidance behaviour tests with Porcellio dilatatus (Crustacea: Isopoda)

Isopods are macrodecomposers in terrestrial ecosystems, contributing to soil organic matter breakdown and nutrient cycling. They have been considered sensitive in laboratory tests designed to evaluate contaminants effects and are considered likely candidates to have a standardized protocol for ecotoxicity tests. For this purpose, a reference substance should be proposed as positive control in laboratory tests. This work aimed to evaluate the avoidance behaviour of the isopod species Porcellio dilatatus to boric acid (H₃BO₃; BA). Interlaboratory comparison tests were carried out based on the ISO guideline for earthworms, using tropical artificial soil as substrate, in the concentrations of 0, 125, 250, 500, 750, 1000, 1300 and 1800 mg BA kg^-1 soil. Avoidance behaviour was evaluated in group (six organisms per replicate) and in individual tests (one organism per replicate), in dual-section plastic boxes, which received control soil (not contaminated) in one side and tested soil (with BA) in another one. The percentage of organisms in each side was recorded after 48 h, and data were analysed using Fisher exact test (p < 0.05) and t-test. Results showed significant avoidance response in individual tests at 250 mg kg^-1 and in group tests at 500 mg kg^-1. Limited habitat function (< 20% of organisms) for both tests and laboratories were observed at the highest tested concentration of 1800 mg kg^-1, indicating the low sensitivity of this species to BA in avoidance tests, if compared to other substances in literature. Results showed that BA can be used as reference substance until a better option will be proposed.

New species and new records of terrestrial isopods (Crustacea, Isopoda, Oniscidea) from Brazil

ABSTRACT. A large collection of terrestrial isopods from different Brazilian regions was examined. Two new species of Amazoniscus Lemos de Castro, 1967 (Scleropactidae) are described: A. zimmeri Campos-Filho, Montesanto & Araujo sp. nov. from the state of Pará and A. schmidti Campos-Filho, Montesanto & Taiti sp. nov. from the state of Minas Gerais. Pseudotyphloscia alba (Dollfus, 1898) (Philosciidae) is firstly recorded from Brazil. The systematic position of Venezillo tuberosus (Budde-Lund, 1904) is discussed and transferred to Ctenorillo Verhoeff, 1942. Androdeloscia lejeunei (Lemos de Castro & Souza, 1986) and Diploexochus echinatus Brandt, 1833 from the state of Pará, are redescribed.

Does the Cave Environment Reduce Functional Diversity?

Caves are not colonised by all taxa present in the surface species pool, due to absence of light and the tendency to food limitation when compared to surface communities. Under strong species sorting during colonisation and later by the restrictive environmental filter, traits that are not adaptive in subterranean habitats may be filtered out. We tested whether cave communities were assembled by the restrictive regime propitiated by permanent darkness or by competitive exclusion due to resource scarcity. When compared to surface communities, the restrictive subterranean regime would lead to lower functional diversity and phenotypic clustering inside the caves, and the opposite should be expected in the case of competitive exclusion. Using isopods (Oniscidea) as model taxa, we measured several niche descriptors of taxa from surface and cave habitats, used a multivariate measure of functional diversity, and compared their widths. We found phenotypic overdispersion and higher functional diversity in cave taxa when compared to surface taxa. On the one hand, the dry climate outside of caves hampered the survival of several taxa and their ecological strategies, not viable under severe desiccation risk, culminating in the clustering of functional traits. In contrast, this restriction does not occur inside of caves, where isopods find favourable conditions under lower predation pressures and more amenable environmental parameters that allow occupation and subsequent diversification. Our results showed that, at least for some taxa, caves may not be such a harsh environment as previously thought. The high functional diversity we found inside caves adds an additional reason for the conservation of these sensitive environments.

Evidence of self-organization in a gregarious land-dwelling crustacean (Isopoda: Oniscidea)

How individuals modulate their behavior according to social context is a major issue in the understanding of group initiation, group stability and the distribution of individuals. Herein, we investigated the mechanisms of aggregation behavior in Porcellio scaber, a terrestrial isopod member of the Oniscidea, a unique and common group of terrestrial crustaceans. We performed binary choice tests using shelters with a wide range of population densities (from 10 to 150 individuals). First, the observed collective choices of shelters strengthen the demonstration of a social inter-attraction in terrestrial isopods; especially, in less than 10 min, the aggregation reaches its maximal value, and in less than 100 s, the collective choice is made, i.e., one shelter is selected. In addition, the distribution of individuals shows the existence of (1) quorum rules, by which an aggregate cannot emerge under a threshold value of individuals, and (2) a maximum population size, which leads to a splitting of the populations. These collective results are in agreement with the individual's probability of joining and leaving an aggregate attesting to a greater attractiveness of the group to migrants and greater retention of conspecifics with group size. In this respect, we show that the emergence of aggregation in terrestrial isopods is based on amplification mechanisms. And lastly, our results indicate how local cues about the spatial organization of individuals may favor this emergence and how individuals spatiotemporally reorganize toward a compact form reducing the exchange with the environment. This study provides the first evidence of self-organization in a gregarious crustacean, similar as has been widely emphasized in gregarious insects and eusocial insects.

Diversity and population characteristics of terrestrial isopods (Crustacea, Oniscidea) across three forest environments in southern Brazil

Terrestrial isopods are important and dominant component of meso and macrodecomposer soil communities. The present study investigates the diversity and species composition of terrestrial isopods on three forests on the Serra Geral of the state of Rio Grande do Sul, Brazil. The area has two natural formations (Primary Woodland and Secondary Woodland) and one plantation of introduced Pinus. The pitfall traps operated from March 2001 to May 2002, with two summer periods and one winter. There were 14 sampling dates overall. Of the five species found: Alboscia silveirensis Araujo, 1999, Atlantoscia floridana (van Name, 1940), Benthana araucariana Araujo & Lopes, 2003 (Philoscidae), Balloniscus glaber Araujo & Zardo, 1995 (Balloniscidae) and Styloniscus otakensis (Chilton, 1901) (Styloniscidae); only A. floridana is abundant on all environments and B. glaber is nearly exclusive for the native forests. The obtained data made it possible to infer about population characteristics of this species. The Similarity Analysis showed a quantitative difference among the Secondary forest and Pinus plantation, but not a qualitative one. The operational sex ratio (OSR) analysis for A. floridana does not reveal significant differences in male and female proportions among environments. The reproductive period identified in the present study for A. floridana was from spring to autumn in the primary forest and Pinus plantation and during all year for the secondary forest. The OSR analysis for B. glaber reveals no significant differences in abundance between males and females for secondary forest, but the primary forest was a significant difference. The reproductive period for B. glaber extended from summer to autumn (for primary and secondary forest). This is the first record for Brazil of an established terrestrial isopod population in a Pinus sp. plantation area, evidenced by the presence of young, adults and ovigerous females, balanced sex ratio, expected fecundity and reproduction pattern, as compared to populations from native vegetation areas.

Feeding rates of Balloniscus sellowii (Crustacea, Isopoda, Oniscidea): the effect of leaf litter decomposition and its relation to the phenolic and flavonoid content

The goal of this study was to compare the feeding rates of Balloniscus sellowii on leaves of different decomposition stages according to their phenolic and flavonoid content. Leaves from the visually most abundant plants were offered to isopods collected from the same source site. Schinus terebinthifolius,the plant species consumed at the highest rate, was used to verify feeding rates at different decomposition stages. Green leaves were left to decompose for one, two, or three months, and then were offered to isopods. The total phenolic and flavonoid contents were determined for all decomposition stages. Consumption and egestion rates increased throughout decomposition, were highest for two-month-old leaves, and decreased again in the third month. The assimilation rate was highest for green leaves. The mode time of passage through the gut was two hours for all treatments. Ingestion of leaves occurred after two or three days for green leaves, and on the same day for one-, two- and three-month-old leaves. The speed of passage of leaves with different decomposition stages through the gut does not differ significantly when animals are fed continuously. However, it is possible that the amount retained in the gut during starvation differs depending on food quality. The digestibility value was corrected using a second food source to empty the gut of previously ingested food, so that all of the food from the experiment was egested. The digestibility value was highest for green leaves, whereas it was approximately 20% for all other stages. This was expected given that digestibility declines during decomposition as the metabolite content of the leaves decreases. The phenolic content was highest in the green leaves and lowest in three-month-old leaves. The flavonoid content was highest in green leaves and lowest after two months of decomposition. Animals ingested more phenolics when consumption was highest. The estimated amount of ingested flavonoids followed the same trend as assimilation rate. Flavonoids accounted for a large portion of total phenolics, and the estimated amount of flavonoids consumed was similar for one-, two- and three-month-old leaves. Our results suggest that the high phenolic and flavonoid concentrations in green leaves are feeding deterrents. Isopods may discriminate among concentrations of flavonoids and modify their consumption rates to maintain their intake of flavonoids when ingesting leaves with lower flavonoid content.