Male Choice and Male-male Competition in Idotea baitica (Crustacea,Isopoda)

Sexual selection in mate-guarding Crustacea may involve several processes: male choice, male-male competition, and female choice. To evaluate the relative importance of the different processes in mate choice of the aquatic isopod I. baitica we studied 1) the mate-choice criteria of males, 2) effects of sex ratio on the outcome of the mating contest, and 3) the role of size in male-male interactions. When given a choice between a small and a large female, males most often chose the one that matured earlier for parturial ecdysis. Maturity was a more important choice criterion than female size, but these also correlated positively. Large males had a mating advantage in both male- and female-biased sex ratios; pairing was size-assortative only in the male-biased ratio where guarding was also longer. If an extra male was placed with a precopulatory pair, 30 % take-overs occurred, large males surpassing. Present and earlier work suggests that male size is an asset in both intra- and intersexual interactions. There is little or no direct phenotypic sexual selection on female size: sexual selection for large males presumably contributes to the evolution of sexual size dimorphism in I. baitica.     

Biology and population dynamics of Porcellionides sexfasciatus (Crustacea,Isopoda, Oniscidea)

The biology and the population dynamics of Porcellionides sexfasciatus Budde-Lund (1879) were studied on a field and carried out at Garat Naam (Kasserine, Tunisia) from July 1996 to June 1998. The reproduction exhibited a seasonal pattern extending from February/March to October/November. The juveniles appeared in the population from April to November. Size frequency distributions were analysed and 14 cohorts were recognised during the sampling period. Six cohorts were identified at the first sampling and eight new ones on the other samplings. Among these latter cohorts, three were tracked till they disappeared. Minimum average length of new cohorts ranged from 3.07 +/- 0.35 mm to 3.47 +/- 0.2 mm. Maximum average length of cohorts was 10.42 mm. P. sexfasciatus is a semi-annual species (females producing two or three broods per year), with iteroparous and amphogenes females (females reproducing twice or more in their life and producing both males and females), and bivoltine life cycle (two generations per year). The females are able to produce two broods, in the laboratory, without new mating. Fecundity and fertility, corresponding to the number of eggs or embryos per brood, appeared positively correlated with females' size. Although oscillating throughout the year, the sex ratio was often in equilibrium.     

Energetics of a population of Asellus aquaticus (Crustacea, Isopoda): respiration and energy budgets

SUMMARY. Respiration of Asellus aquaticus was determined on tiine occasions throughout the year using a Gilson differential respirometer. On each occasion the determination was made at the lake temperature, which ranged from 2 to 18°C, Linear regressions were derived for log oxygen uptake against log dry weight. There was a significant difference between mean rates of oxygen uptake at the various temperatures but the slopes of the regression lines, which varied from 0,62 to O.85 with a mean of 0,76, were not significantly different.
The temperature of the lake was monitored throughout the year. Using the relationship of oxygen uptake against temperature, and estimates of population density obtained previously, the total annual respiration of the population was calculated as 4571 ml O₂ m^-2, equivalent to an energy loss of 92.3 kj m^-2 year^-1 from a mean biomassof 752 mg m^-2.
Consumption of decayed Alnus glutinosa leaves and faecal production rates, and thus assimilation efficiency, were determined by gravimetric methods in the laboratory at 10°C, close to the mean temperature of the lake (10.rC), In the four size classes investigated, larger animals consumed more food per individual, but less on a weight specific basis. However, it was shown that consumption was greater if the leaf material was more highly decomposed, Assimiliation efficiency was calculated as 23%.
Using data for respiration, population density and the assimilation efficiency, the annual population energy budget was estimated as (kJ m^-2year^-1): consumption, 568.9 (100%); production, 38.5 (6.8%); respiration, 92.3 (16.2%); faeces, 438.1 (77%). The significance of these energy values, and the ecological efficiencies calculated from them, are discussed in relation to other published work.     

Metapopulation structure of the marine isopod <Emphasis Type="Italic">Idotea metallica</Emphasis>, a species associated with drifting habitat patches

The neustonic isopod Idotea metallica inhabits objects drifting at the sea surface. Animals found on floating patches represent not just ephemeral assemblages but persistent local populations. Drift material collected in the Mediterranean, the North Atlantic, and the North Sea harboured populations of up to about 50 animals including all developmental stages. In laboratory experiments the species proved to be able to establish populations on spatially limited, isolated substrates. The capacity of 5-litre-microcosms for I. metallica was about 130 animals. In the presence of the coastally distributed congener Idotea baltica, however, laboratory populations of I. metallica went extinct within 12 weeks. Even though high colonisation rates can be expected in coastal waters because of high patch densities, metapopulation persistence is mostly restricted to the open sea. In coastal waters extinction rate of local populations increases because of patch destruction and the species' inferiority to coastally distributed competitors. Due to high uncertainties in estimating patch densities, it is difficult to determine the parameters underlying metapopulation dynamics such as the migration rate and the rate of patch occupancy. Electronic Publication     

Foraminiferan (Protozoa) epizoites on deep-water arcturids (Crustacea,Isopoda)

Foraminiferan (Protozoa) epizoites were examined on two deep-water isopods, Neastacilla sp. and Pleuroprion hystrix (Valvifera, Arcturidae), from the north Atlantic Ocean and the Nordic Seas. Most foraminiferans belonged to genus Cibicides and occurred on 27% of Neastacilla and 23% of Pleuroprion hystrix. The pattern of foraminiferan epibiosis was similar in both species, with a concentration on the dorsal body and on the posterior pereopods. The arcturids showed an increase in number of foraminiferans with increased body size, suggesting that available time span for settling on the younger stages (mancas) was relatively short. There was a trend towards larger numbers of foraminiferans occurring on larger arcturid species, suggesting that available space is the factor that determines the total number of foraminiferans for epibenthic arcturid isopod species.     

Mitochondrial DNA polymorphism and feminizing sex factors dynamics in a natural population of Armadillidium vulgare (Crustacea,Isopoda)

Sex determination in Armadillidium vulgare may be under the control of two parasitic sex factors that reverse genetic males into functional neo-females. The first feminizing factor (F) is a Wolbachia and the other (f) is probably a sequence of the F bacterial DNA unstably integrated into the host genome. Both of these feminizing factors are mainly maternally transmitted. Here we investigate the mitochondrial DNA polymorphism of wild iso-female lineages harbouring either F or f. Among the four haplotypes present in the population, two were the f-harbouring lineages, while two were common to the F- and f-harbouring lineages. This result suggests that there has been an introgression of the f factor into lineages infected by F Wolbachia. Based on previous data, we propose two different ways to account for such introgression. Given the particular dynamics of feminizing factors (f-harbouring lineages increase in populations at the expense of F-harbouring lineages), such an introgression should prevent the replacement of F-linked mitochondrial types by f-linked mitochondrial types in wild populations.     

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.     

Two genetic lineages of sea slaters, Ligia (Crustacea: Isopoda) in South Korea: a population genetic approach

In this study, the species composition and population genetic properties of the sea slater, Ligia, in South Korea were investigated using mitochondrial and nuclear gene sequences. Two groups of sea slaters, genetically isolated from each other, a Western Group (WG) and an Eastern Group (EG) were identified. These groups exhibited considerable genetic divergence from Ligia exotica, previously recorded as a species inhabiting this country. These results indicate that there may be two species of Ligia in South Korea, but there is a small probability that both groups are L. exotica. A comparison of their genetic properties indicates that WG has a higher effective population size than EG, and that EG may have experienced a recent expansion, implying that it has a shorter history in South Korea than WG. These findings suggest that the South Korean sea slater populations may have been established as a result of several colonization events that can be traced on a continental scale by phylogeographic studies of sea slaters.     

Relationships within the Munnopsidae (Crustacea, Isopoda, Asellota) based on three genes

The Munnopsidae are a diverse group of asellote isopods that are an important component of deep‐sea fauna. Morphologically‐based phylogenetic inference attempts have proven to be of limited use due to the ecological and morphological diversity within the clade. Monophyly of the family is well‐established but relationships within the group remain unresolved. This project is the first molecularly‐based effort focused specifically on resolving phylogenetic relationships within the Munnopsidae. Partial 28S and COI and complete 18S genes were sequenced for 28 asellotes, 15 additional taxa were included from which only one or two of the three target sequences could be obtained, and 18S sequences for five additional taxa were available from GenBank. Sequences were analysed both as individual genes and in combination using Bayesian and maximum parsimony approaches. Each gene provided a phylogenetic signal that could be identified in the combined analyses, with 18S analyses providing the most resolution of phylogenetic relationships. The available representatives of subfamilies Munnopsinae and Ilyarachninae were monophyletic, as was the genus Munneurycope. Relationships within the subfamily Munnopsinae were well‐resolved by thorough taxon sampling, several new species were placed, and the need for taxonomic revision of Munnopsis/Munnopsoides was supported. These analyses supported putative Eurycope paraphyly and emphasized the need for careful revision of this highly variable genus. Tytthocope was sister to Munnopsurus. Syneurycope was suggested as the sister group to the ilyarachnines. Combined analyses provided increased support for clades suggested in at least two individual gene analyses and for clades not strongly contradicted by individual analyses. Further work is required to fully resolve the munnopsid phylogeny and should consist of increased taxon sampling for the complete 18S sequence and possibly identification of at least one slowly evolving, nuclear protein‐coding gene to resolve the basal polytomy and enable placement of the root.     

GATA repeats in the genome of Asellus aquaticus (Crustacea,Isopoda)

A 500 bp fragment of Drosophila genomic DNA containing 37 copies of the tetranucleotide GATA was used to probe, by Southern DNA blotting and in situ hybridization, two natural populations of the isopod crustacean Asellus aquaticus collected from the Sarno and Tiber rivers. This species does not have a recognizable sex chromosome pair. In a number of males from the Sarno population chromomycin A₃ staining reveals a heteromorphic chromosome pair. The heterochromosome has two blocks of heterochromatin. After digestion of genomic DNA with six restriction endonucleases and hybridization with the GATA probe, the two populations exhibit different fragment length patterns. No sex-linked pattern was observed in either population. In situ hybridization to chromosomes of males and females from the Sarno population does not reveal any sex-specific pattern of labelling and indicates a scattered distribution of GATA sequences on most chromosomes with some areas of preferential concentration. The heterochromatic arcas of the male heterochromosome are not labelled.by E.R. Schmidt     

Reproduction, growth and bionomics of Dynamene bidentata (Crustacea: Isopoda)

Laboratory and field investigations show that there are five distinct marsupial stages and eight post-marsupial stages in the development of the isopod Dynamene bidentata (Adams). Extensive sexual dimorphism is apparent, beginning at stage 6, and females undergo extensive tissue reduction at the moult to the eighth stage. Young stages inhabit and feed on intertidal algae, and the non-feeding adults (stage 7 and 8 females, and stage 8 males) shelter in crevices or empty barnacle tests. Average brood numbers are fairly high (c. 90) and the average marsupial mortality rate is about 36%. Release of young takes place in May/June, after which the females die, and a resident population of males remains in the crevices to be joined by newly maturing females and males from August onwards each year. The occurrence of two breeding seasons in males, but not in females, explains how the sex ratio of males to females as they leave the algal habitat (1:9) is about half the ratio of males to females in the reproductive habitat (1:4).     

Histological studies on the marsupium of two terrestrial isopods (Crustacea,Isopoda, Oniscidea)

The marsupium, a brood pouch in peracarid crustaceans (Crustacea, Malacostraca) has evolved in terrestrial environment for providing nutrition and optimal conditions for embryogenesis. In the present study we give details on the histology and ultrastructure of its constituting elements such as oostegites and cotyledons. Marsupia of two different eco-morphological types of woodlice, namely the non-conglobating species Trachelipus rathkii Brandt, 1833 and the conglobating species Cylisticus convexus De Geer, 1778 were investigated. Light microscopic (LM) studies showed some differences in the main structure of the two species’ brood pouch: in Trachelipus rathkii, a ‘clinger’ type woodlice, the oostegites bend outwards during brood incubation as growing offspring require more space, while in Cylisticus convexus, a ‘roller’ type isopod, the sternites arch into the body cavity to ensure space for developing offspring and still allowing conglobation of the gravid females. The quantitative analysis of the oostegites’ cuticle proved that the outer part is about 2.5 - 3 times thicker compared to the inner part in both species. Electron microscopic (TEM) examinations show only small histological differences in the oostegites and cotyledon structure of the two species. Cellular elements and moderately electron dense fleecy precipitate are found in the hemolymph space between the two cuticles of oostegites. The cells contain PAS positive polysaccharide areas. TEM studies revealed some differences in the cotyledon ultrastructure of the two species. Cotyledons of Trachelipus rathkii consist of cells with cristate mitochondria and granular endoplasmic reticulum with cisterns. Cotyledons of Cylisticus convexus consist of cells with densely cristate mitochondria and ribosomes attached to vesicular membrane structures. In both species cells with electron dense bodies were observed. We conclude that - besides the differences in marsupial shapes - the fine structure of the oostegites and cotyledons is hardly affected by the eco-morphological type, specifically the conglobating or non-conglobating character of the studied species.     

Morphology and evolution of respiratory structures in the pleopod exopodites of terrestrial Isopoda (Crustacea, Isopoda, Oniscidea)

The morphology of the respiratory structures located in the pleopod exopodites of terrestrial Isopoda is described for representative species of different genera. Special emphasis is set on the evolution of these lungs in the context of phylogenetic relationships as revealed by other morphological characters. In the most primitive species of the Oniscidea, and still of subordinate taxa of the Crinocheta, respiration takes place in the thin ventral integument of the exopodites. The evolution of dorsal respiratory fields with a weakly wrinkled surface occurred at least six times within the Crinocheta. In five of these cases, a further development can be observed. The evolution of a partly covered respiratory field with strongly wrinkled surface may have taken place six times. It is assumed that completely internalized lungs with spiracles surrounded by a water‐repellent surface microsculpture, evolved at least six times independently within the Oniscidea: in the Tylidae, Actaecia, Aphiloscia, the Eubelidae, the Armadillidae and in a taxon probably comprising Porcellionidae plus Armadillidiidae.     

Reference values for feeding parameters of isopods (Porcellio scaber,Isopoda, Crustacea)

The advantage of using terrestrial isopods in toxicity studies is that a battery of parameters can be tested at different levels of biological complexity. Feeding parameters for example link organism level response to potential ecological consequences but a problem with using feeding parameters in toxicity tests with terrestrial isopods is their high variability. The aim of our study was to set benchmark values for feeding parameters for isopod Porcellioscaber (Isopoda, Crustacea) in laboratory-controlled experiments. In the work presented here, the daily feeding rate of the central 50% of the control population of Porcellioscaber and a correlation between feeding rate and isopod weight were set. Values outside these ranges need additional evaluation to increase the relevance of test outcomes. We suggest using benchmark values for feeding parameters as well as the coefficient of variation (a) to identify animals with altered feeding parameters with respect to controls, and (b) to assess the data quality in each experiment.     

Demography of some non-native isopods (Crustacea,Isopoda, Oniscidea) in a Mid-Atlantic forest,USA

Introduced species dominate the terrestrial isopod fauna in most inland habitats of North America, including urban landscapes. These non-native species are often very abundant and thus potentially play a significant role in detritus processing. We monitored isopod assemblages in an urban forest for a year to examine the relationship between surface activity and abiotic environmental factors, and to analyze reproductive characteristics that might contribute to their successful establishment. Using pitfall trap samples we recorded five species, two of which, Trachelipus rathkii and Cylisticus convexus, were highly abundant. We determined size, sex and reproductive state of each individual. Surface activity of both species reflected variability in abiotic stress factors for isopods, such as soil moisture and soil temperature. Early spring the main trigger was soil temperature while later in the season increasing temperature and decreasing soil moisture jointly affected population dynamics. Activity significantly correlated with soil moisture. The temporal pattern of sex ratios supported the secondary sex ratio hypothesis. Males dominated the samples on the onset of the mating season in search of females. The pattern was reversed as females searched for suitable microsites for their offspring. Size independent fecundity decreased as conditions became more stressful late in the season.     

Phenetic analysis of populations of Porcellionides pruinosus (Brandt, 1833) (Crustacea, Isopoda, Oniscidea)

The cosmopolitan species, Porcellionides pruinosus (Brandt, 1833), exhibited a geographical variation of its morphological features and its reproduction pattern. In fact, some Tunisian populations had a seasonal reproductive period and other ones showed a reproductive activity. A phenetic analysis has been performed to compare populations belonging to P. pruinosus from different geographical localities. For this, nineteen quantitative characters in 800 specimens of P. pruinosus issued from nine populations located in the North, the Centre, and the South of Tunisia, and one population from Athens (Greece) were studied. These populations were characterized by different reproductive behaviours. The populations of Tabarka, Korba, and Tamerza showed reproductive activity, whereas those of Garat Naam, Raccada, Sahline, Gafsa, Rdayef, Gabès, and Athens exhibited a seasonal reproductive period. The variability of the first three axes of the principal components analysis (PCA) and their significance showed an intraspecific variability structure. The graphical representation of the population's dispersion generated by the two first axes (63.55% of the total variability) revealed a great heterogeneity among females of the different populations of P. pruinosus. The Garat Naam population was set apart from the other ones by its cephalic width and length and also by its apophysis length. Furthermore, cephalic and uropod length separated the Garat Naam and Tabarka populations. The dendrogram, based on Euclidean coordinates, confirms an isolation of the populations of Tabarka and Garat Naam, exhibiting respectively reproductive activity and seasonal reproduction. However, the other populations do not show any relationship with the reproduction behaviour. They were clustered in two groups. The first one is represented by the populations of the Southeast and the West of Tunisia. The second pooled the populations of the Northeast and the Centre of Tunisia with the population of Athens (Greece). Phenetic analysis of Tunisian populations exhibits an important heterogeneity, which is worth noting. Thus, we need to complete and deepen this study by genetic analysis and crossbreeding tests in order to define the taxonomic status of these populations.     

Toxicity of heavy metals to Asellus aquaticus (L.) (Crustacea,Isopoda)

Effects of heavy metals on the isopod Asellus aquaticus (L.) are studied by static toxicity tests. Results demonstrate that the species is sensitive to Cd⁺², Cr⁺⁶, Cu⁺², Fe⁺³, Hg⁺², Ni⁺² Pb⁺² and Zn⁺², but the toxicity of each metal is different. Differences are also found between adults and between adults and juveniles. The comparative analysis of all data on the toxicity has been performed on the concentrations of metal ions and not on metal compound concentrations.Criteria for establishing water quality in order to guarantee protection of the environment are discussed.