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Caecidotea burkensis, a new species of subterranean asellid isopod, is described and illustrated from material collected from Lawson Cave, in Burke’s Garden, Tazewell County, Virginia. The type-locality in Burke’s Garden is located within the highest mountain basin in the southern Appalachians. Burke’s Garden is a unique, geologically isolated area encompassing one of the headwater streams of the New River basin. Phylogenetically, the isopod is a member of the forbesi Group, a clade comprised primarily of epigean species. The complex mountain valleys and coves of southwestern Virginia are an area of intense speciation among asellids that have produced a bizarre array of cavernicolous species belonging to groups of otherwise epigean isopods. In addition to a few subterranean species of the Caecidotea cannula and stygia Groups, the Lirceus hargeri Group possesses over a dozen species endemic to caves and springs in the region, mostly only now in the process of being discovered and described. With so much species richness, syntopy of two, or even three, asellid species is commonplace in caves and springs in southwestern Virginia.

Six new epigean freshwater species of the genus Caecidotea in Mexico are described. These species were collected in waterbodies located along the Trans-Mexican Volcanic Belt (TMVB) and the eastern slope of the country: Caecidotea buzwilsoni sp. nov., Caecidotea chicoensis sp. nov., Caecidotea alvarezi sp. nov., Caecidotea mintzita sp. nov., Caecidotea zacapuensis sp. nov., and one additional species Caecidotea villalobosi sp. nov. is described from the Papaloapan basin at the Atlantic Slope of Mexico. The taxonomic treatment for each species includes a detailed description, figures of characters of diagnostic importance and comments. We also provide an updated map of Caecidotea records in Mexico. This work substantially increases the number of epigean Caecidotea known to occur in Mexico to 11 species, a new total of 99 species described to North America.

In some environments, species may exhibit trophic plasticity, which allows them to extend beyond their assigned functional group. For Gammarus minus, a freshwater amphipod classified as a shredder or detritivore, cave populations have been observed consuming heterotrophs as well as shredding leaves, and therefore may be exhibiting trophic plasticity. To test this possibility, we examined the C and N stable isotope and C/N ratios for cave and spring populations of G. minus. A 15-day feeding experiment using leaves and G. minus from a spring population established that the diet-tissue discrimination factor was 3.2 ‰ for δ15N. Cave G. minus were 8 ‰ higher in δ15N relative to cave leaves, indicating they did not derive nitrogen from leaves, whereas field collected spring populations were 2–3 ‰ higher than spring leaves, indicating that they did. Cave G. minus were 2.6 ‰ higher in δ15N than the cave isopod, Caecidotea holsingeri. Relative to spring populations, Organ Cave G. minus were 15N enriched by 6 ‰, suggesting they occupied a different trophic level, or incorporated an isotopically distinct N source. While stable isotopes cannot tell what the cave G. minus are eating, the isotopes certainly show that G. minus are not eating leaves and are trophically distinct form the surface populations. Differences in C/N ratios were observed, but reflect the size of the G. minus examined and not feeding group or habitat. The isotope data strongly support the hypothesis that cave populations of G. minus have become generalist or omnivorous by including animal protein in their diet.

The acanthocephalan Acanthocephalus dirus is a trophically transmitted parasite that infects freshwater isopods as intermediate hosts and fish as definitive hosts. Using a laboratory-based experiment, we examined if parasite infection was associated with changes in mating behaviour, refuge use and neurochemical levels of infected isopods (Caecidotea intermedius). Infected isopods were less likely to engage in mating behaviour and more likely to be located in the open than uninfected isopods. Infected isopods also contained lower levels of serotonin (5-HT) and dopamine (DA) and had a greater mass of neural tissue (CNS) than uninfected isopods. We propose that the parasite-related changes in mating behaviour and refuge use may be modulated by the serotonergic and dopaminergic systems. We also suggest that the parasites could potentially be modulating these behavioural changes by exploiting the neural-immune system of the hosts through their neuroinflammatory responses.

The acanthocephalan parasite Acanthocephalus dirus infects the freshwater isopod Caecidotea intermedius as an intermediate host before completing its life cycle in a fish. Transmission to the definitive host occurs after the parasite has reached the cystacanth stage, and development into this stage is associated with changes in several behavioral and physiological traits of the host. Given the potential importance of host energy availability to trait modification, we examined the relationship between cystacanth-stage infection and energy storage of adult isopods. Six samples of infected and uninfected male C. intermedius were collected from a population in March, April, and May during which time cystacanth-stage A. dirus dominate infections and modification of behavior and physiology occurs in nature. Biochemical assays revealed that infected male C. intermedius contained more glycogen and more lipid than uninfected males and that this difference was present throughout the sampling period, which represents the entire adult phase of the host's life. Additional analysis revealed that infected and uninfected males differed in their pattern of allocation to each energy source and that host lipid levels were negatively correlated with parasite intensity. We propose that the typical pattern of allocation and storage of host energy appears to be disrupted by A. dirus infection and that the changes are more likely to favor the parasite than the host.

Alarm cues are produced by an organism when injury occurs, and serve to signal danger when detected by conspecifics or to attract other predators that may disrupt the predation event. We exposed aquatic isopods (Caecidotea intermedius) and amphipods (Crangonyx setodactylus) to chemical stimuli from macerated conspecifics to test for the presence of alarm cues in these taxa. Three variables were examined during this experiment: time spent moving, time in refuge, and time in open. Despite previous evidence for the presence of alarm cues in both taxa, we found that only amphipods responded to alarm cues by decreasing overall movement. Isopods did not display any differences in behavior following exposure to alarm cues, which may be due to degradation of the active compounds in the alarm cues due to preparation and not the absence of these cues in general.

Predator avoidance behaviours occur when prey detect a predator but the predator has not yet detected and identified prey. These defences are critical because they prevent predation at the earliest possible stages when prey have the best chance of escape. We tested for predator avoidance behaviours in an aquatic macroinvertebrate (Caecidotea intermedius; order Isopoda) in a series of three experiments. The first experiment attempted to determine if isopods possess alarm cues by exposing them to stimuli from macerated conspecifics. We then exposed isopods to kairomones from non-predatory tadpoles (Rana catesbiana) and predatory fish (Lepomis macrochirus) that had been fed a benign diet. Finally, we exposed isopods to kairomones of predatory fish that had been fed a diet exclusively of isopods. We found that isopods did not respond to any kairomone cues or dietary cues from any potential predator, but did reduce activity in response to alarm cues. These results suggest that isopods exhibit predator avoidance responses toward chemical cues in a limited setting (they do not respond unless the information suggests an attack has occurred in the immediate past) or that bluegill have the ability to modify or mask the alarm cues from their prey.

The acanthocephalan parasite Acanthocephalus dirus infects the freshwater isopod Caecidotea intermedius as an intermediate host before completing its life cycle in a fish. Transmission to the definitive host occurs after the parasite has reached the cystacanth stage and development into this stage is associated with changes in several behavioral and physiological traits of the host. Despite the numerous examples of trait modification in this system, little is known about the multidimensional nature of this modification. Here, we examined the relationships between cystacanth infection, and expression of multiple traits (body color, refuge use, activity, and body size) of both male and female C. intermedius. The pattern of multidimensional modification was determined for males and females and then measures of behavioral plasticity, individual consistency, and trait correlations were obtained for the modified traits. The results revealed that the overall pattern of host modification differed between males and females. Infected males and females showed similar decreases in body color but differed in changes to the other traits. Infected females were larger and less active than uninfected females, whereas infected males spent less time in refuge than uninfected males. A comparison between two situations revealed that refuge use exhibited high levels of plasticity and activity exhibited high levels of consistency and that these patterns differed based on both host sex and infection status. Analysis of the relationships among modified traits showed that traits appeared to be modified independently of each other and that correlations between traits that existed in one situation were absent in another. We suggest that the pattern of multidimensional modification is sex-specific and that the traits are modified independently. We also show that the patterns of multidimensional modification were not associated with variation in either parasite intensity of parasite size indicting that competitive interactions among parasites did not appear to act as a constraint on host modification.

Decomposition of senesced primary production starts processing chains in aquatic systems. Shredding macroinvertebrates convert coarse particulate organic matter (CPOM) to fine particulate organic matter (FPOM) that supports 2 other feeding groups, collecting and filtering macroinvertebrates. This linkage is often invoked by aquatic ecologists, but the effect of detritivore assemblage composition on production of FPOM is relatively understudied. I manipulated detritivore assemblage composition (Limnephilus sp., Caecidotea sp., and Hyalella azteca) in aquatic mesocosms stocked with green speckled alder leaves (Alnus incana rugosa). I measured production rate, size distribution, and stoichiometry of FPOM produced through time. Detritivore species richness had a positive effect on FPOM production resulting from inclusion of the functionally dominant shredder, Limnephilus sp., in mixed-species treatments (e.g., sampling effect). Mixed-species treatments had significantly faster particle production than...

Mexistenasellus floridensis sp. n. is described from Hole in Wall Cave, Jackson County, Florida. The discovery of this unique isopod nearly doubles the range of the Family Stenasellidae in North America, which was previously known from Oaxaca, Mexico to southern Texas, USA. This is the first stenasellid reported swimming in the water column of a cave, a curious finding for an isopod that belongs to a group that is generally more adapted to inhabiting interstitial spaces. Mexistenasellus floridensis occurs syntopically with the subterranean asellid Caecidotea putea. Both species have been observed swimming in the water column, although neither has apparent anatomical adaptations for swimming as compared to the natatory pereopods of Remasellus parvus, an asellid that occurs in caves in Alachua, Madison and Wakulla counties, Florida.

A number of shallow groundwater habitats that occur in the Coastal Plain and Piedmont of the mid-Atlantic region are documented and described. These isolated tiny aquifers are underlain by clay (hypotelminorheic habitats) and exit at seepage springs, springs, tiled fields and tile drains, and shallow wells. These shallow groundwater habitats harbor species with reduced eyes and pigment that are limited to these habitats. The distribution of 23 such species—four planarians (Sphalloplana and Phagocata), one snail (Fontigens), 13 amphipods (Stygobromus), and five isopods (Caecidotea)—is documented, based on over 450 records. More species (16) were found in hypotelminorheic habitats than in other shallow groundwater habitats. Also, more species were found exclusively in either the Piedmont or Coastal Plain, but seven species were found along the boundary (Fall Line) between these physiographic provinces. Compared to surface waters in nearby habitats, hypotelminorheic water had higher conductivity, higher dissolved oxygen, and slightly lower pH.

Five species of subterranean asellid are known from Maryland: Caecidotea pricei, C. franzi, C. holsingeri, C. mausi and C. vandeli. Caecidotea nordeni, n. sp. is a subterranean species described from Washington Co., Maryland and assigned to the hobbsi Group. A new locality for C. franzi in Kentucky is presented. This species was previously known from two caves in Maryland and Pennsylvania. The newly discovered population represents a range extension of over 400 km. The male pleopod 2 morphology of specimens from a Maryland population of the subterranean asellid C. holsingeri is compared with populations from three caves in West Virginia. The range of C. holsingeri extends from eastern West Virginia and adjacent Virginia to Garrett Co., Maryland.

Two asellid isopods were described from Nickajack Cave, Tennessee: Caecidotea nickajackensis Packard (in Cope & Packard 1881) and Caecidotea richardsonae Hay (1901). It was long assumed that only one species was actually present in the cave, but Packard's type specimens were lost and the inundation of the cave by a Tennessee Valley Authority impoundment in 1967 eliminated the possibility of collecting additional specimens. Further confusion was created when specimens from Metcalf, Georgia were erroneously identified by Richardson as C. nickajackensis, then redescribed as that species by Steeves (1964). Examination of Hay's type specimens as well as a 1967 collection from Nickajack Cave now confirms the presence of two taxa. The name Caecidotea nickajackensis is applied to the Nickajack Cave asellid represented in the 1967 collection, whereas Caecidotea richardsonae is applied to the species represented in Hay's collection. Caecidotea catachaetus (Fleming & Steeves) is considered a junior synonym ...

The acanthocephalan parasite Acanthocephalus dirus develops from the egg to the cystacanth stage inside the freshwater isopod Caecidotea intermedius. We have shown previously that cystacanth-infected male C. intermedius are less likely to initiate mating attempts with females than uninfected males in competitive situations. Here, we used a field-based experiment to examine whether cystacanth-infected males were also less likely to initiate mating attempts with females in noncompetitive situations. We found that infected males were less responsive to females than uninfected males, and we propose that the cystacanth-related change in male mating behavior is mediated by a change in the mating response of males to females rather than male-male competition. We then examined whether cystacanth-related changes in reproductive function, i.e., sperm content and fertilization ability, could explain this variation in male mating behavior. We found that cystacanth-infected males contained both developing and mature sperm and fertilized as many eggs as uninfected males. Thus, we propose that changes in reproductive function are unlikely to explain cystacanth-related variation in male mating behavior in C. intermedius.

Caecidotea williamsi Escobar-Briones & Alcocer (2002) is the first asellid described from a saline aquatic habitat in America, Alchichica crater-lake, Puebla, Central Mexico. No previous reports exist for asellid isopods from inland saline waters in America in spite of the extensive research undertaken so far on the continent. Differing from other asellids, C. williamsi inhabits saline waters (i.e. 8.5 g l−1) dominated by sodium, magnesium, chloride, and bicarbonate ions and markedly alkaline (pH 9.0 ± 0.1). Water temperature ranges from 14.5°C throughout the water column in winter and in the deep waters for the rest of the year, up to 20°C in the surface waters in summer. C. williamsi occurs in a depth range of surface to 30 m (lake’s maximum depth is 64 m), below which an anoxic layer is found during 9 months of the year. Generally it lives cryptically in tufa crevices and at shallower depths many inhabit empty trichopteran cases embedded within the tufa crevices. Some specimens are heavily covered by epizooic ciliates on the thoracic and abdominal segments of the exoskeleton and the pleopods. Data are presented on the diet, possible predators, saprobity and trophism, and regional distribution of C. williamsi. The continued survival of this unique isopod is threatened by anthropogenic desiccation of its habitat.

A survey of cave and spring fauna in Oklahoma resulted in the discovery of Caecidotea mackini, new species, which is described from specimens collected in Long's Cave, Delaware County. Within the hobbsi group of the genus Caecidotea, C. mackini belongs to a subset of nine species termed the tridentata assemblage. All nine are subterranean, but several retain vestigial eyes or pigmentation. Correlated with zoogeographic and climatic evidence, the invasion of groundwaters by an epigean progenitor during the middle to late Tertiary is suggested. Besides C. mackini, new records for C. macropropoda, C. acuticarpa, C. stiladactyla, C. steevesi, C. ancyla, C. antricola, C. adenta, and C. simulator expand the known ranges of these cryptic species. With the recognition of two patterns of fourth pleopod morphology in C. acuticarpa, the species specificity of this character has become questionable. Although previously used to differentiate C. simulator and C. steevesi, further splitting or synonymy based on...

Anecdotal observations of the Dougherty plain cave crayfish (Cambarus cryptodytes), the Georgia blind cave salamander (Haideotriton wallacei), and albinistic isopods (Caecidotea sp.) at great depths below the land surface and distant from river corridors suggest that obligate aquifer-dwelling (troglobitic) organisms are widely distributed throughout the limestone Upper Floridan aquifer (UFA). One mechanism by which subterranean life can proliferate in an environment void of plant productivity is through a microbial food web that includes chemosynthesis. We examined this possibility in the UFA by measuring the isotopic composition ((13)C, (14)C, and (15)N) of tissues from troglobitic macrofauna. Organisms that were captured by cave divers entering into spring conduits had delta(13)C values that suggested plant matter as a primary food resource (cave crayfish, -24.6 +/- 2.7 per thousand, n = 9). In contrast, delta(13)C values were significantly depleted in organisms retrieved from wells drilled into areas of the UFA remote from spring and sinkhole conduits (cave crayfish -34.7 +/- 9.8 per thousand, n = 10). Depleted (13)C values in crayfish were correlated with radiocarbon (Delta(14)C) depletion relative to modern values. The results suggest that methane-based microbial chemosynthetic pathways support organisms living in the remote interior of the aquifer, at least in part.

The acanthocephalan parasiteAcanthocephalus dirusinduces a colour change in the intermediate host, the aquatic isopodCaecidotea intermedius, which increases transmission to definitive hosts (creek chub, sunfish). We examined the potential for conflict to occur between infective (cystacanth) and non-infective (acanthor, acanthella) stages ofA. dirusover the level of colour modification that should be induced when these stages share a host. Using a field survey, we showed that host sharing by infective and non-infective stages was relatively common and that infective and non-infective stages differed in their effects on colour modification. Non-infective stages induced a colour change over 40% of the body, whereas infective stages induced a colour change over 80%. Thus, conflict could occur between stages over the level of modification that should be induced. We then showed that mixed-stage infections induced a colour change in the host that was consistent with the level of modification induced by the infective stage. We discuss the potential significance of these results to patterns of host modification and their effects on stage-related survival in nature.

The Flatwoods Salamander (Ambystoma cingulatum) was listed as a federally threatened species because loss and alteration of adult and larval habitats caused population declines. Current management plans for this species must include maintenance of appropriate larval habitat. However, much of the natural history of this species is poorly known. Our objective was to evaluate the diet of A. cingulatum larvae. We examined stomach contents of 122 larvae collected from Florida and South Carolina. We identified and measured invertebrate prey and estimated biomass using length-mass relationships. Crustaceans, mostly isopods (Caecidotea), amphipods (Crangonyx), cyclopoid copepods, and cladocerans (primarily Simocephalus and other daphnids) were the most abundant prey. Isopods and amphipods also dominated stomach content biomass because of their relatively large size. Stomachs of small A. cingulatum larvae had significantly higher numbers and proportions of cladocerans and smaller numbers and proportions of isopods compared to larger larvae (P < 0.05). Smaller larvae also had significantly lower amounts and proportions of isopod biomass in their guts compared to large larvae (P < 0.05). We found Hedruris siredonis, a parasitic nematode, in ∼11% of stomachs examined; this is a new host record for this parasite. Our results indicate that larvae feed primarily on freshwater crustaceans, particularly isopods, copepods, cladocerans, and amphipods. Management activities that adversely impact freshwater crustacean communities in breeding habitats, such as pesticide use or introductions of predatory fish, could adversely impact remaining populations of this salamander.

The amphipod Crangonyx floridanus and the isopods Caecidotea racovitzai and Asellus hilgendorfii were discovered in the Sacramento/San Joaquin Delta, California, U.S.A. We applied Chapman and Carlton's (1994) criteria for determining introduced species to test whether these species are non-indigenous to the delta. The majority of the attributes scored positive, indicating that these species are non-indigenous. These populations appear to be firmly established, as they occurred at a variety of freshwater wetland habitats throughout a one-year study. The species are briefly described, and distinguished from similar native and non-indigenous species known to exist in the surrounding area.

A new species of Caecidotea, an aquatic isopod crustacean is described from Alchichica crater-lake in the state of Puebla, Oriental Basin, central Mexico. This is the first report of an epigean asellid isopod, with cryptic behavior inhabiting inland saline waters in America. Comparisons made with other co-occurring asellid species in the region show that the species Caecidotea pasquinii differs from the new species in lacking eyes, having different features on the male endopod of pleopod 2, a shorter pereiopod 6, and having elongated uropods. The epigean species Caecidotea communis differs from the new species in having pleopod 4 of the A type pattern of Lewis & Bowman (1981) and 5–8 retinacula on pleopod 1 sympod.

The acanthocephalan parasite Acanthocephalus dirus infects the freshwater isopod Caecidotea intermedius as an intermediate host before completing its life cycle in a fish. Male C. intermedius infected by A. dirus parasites are less likely to engage in mating behavior than uninfected males but there is a significant intra-population variation in the occurrence of this behavioral change. Previous studies on uninfected isopods have shown that glycogen content is a predictor of male mating behavior and we examined whether the intra-population variation in the mating behavior of infected male C. intermedius could be explained by this relationship. A field-based behavioral experiment was used to quantify intra-population variation in male mating behavior, which showed that 50 % of infected males were responsive to females and 50 % were not responsive. Biochemical analysis of responsive and non-responsive males revealed that glycogen content was a predictor of the mating behavior for uninfected males but was not a predictor of mating behavior for infected males. For infected males, parasite intensity was a predictor of mating behavior. Males that contained more A. dirus parasites were less likely to undergo modification of mating behavior. We propose that the intra-population variation in the mating behavior of infected C. intermedius identified in nature was not mediated by host condition.

Effects of a botanical pesticide, azadirachtin, were evaluated on nontarget aquatic macroinvertebrates found in SW Montana. A neem product formulated for commercial use and its petroleum-based, inert carrier alone were used to test the hypothesis that a commercial, U.S. Environmental Protection Agency-approved formulation of the pesticide, azadirachtin-A, derived fromextractsofneemtreeseeds, Azadirachtaindica A.Juss.(Family:Meliaceae),istoxictonontarget aquatic macroinvertebrates in Montana river systems. LC50s (24 h) for 5 insect species, Drunella grandis (McDunnough), Drunella doddsi (Needham), Skwala parallela (Frison), Brachycentrus occidentalis Banks, and Brachycentrus americanus (Banks), and 1 isopod species, Caecidotea inter- media (Forbes) varied from 1.8 to 9.2 ppm of the full formulation. The full formulation consisted of: azadirachtin (3% wt:wt); other neem-extracted material (32% wt:wt); petroleum solvents (65% wt:wt). LT50s for 4 ppm of this formulation were 9.4 to 748 hours for these field-collected macro- invertebrates. Without azadirachtin, but with the petroleum-based carrier, LT50s were 13.6-46.7 h. These bioassays conducted late in winter and early spring of 1994 and 1995 and late summer and early fall of 1994 indicated mortality from the neem formulation was similar to herbicides 2,4-D and picloram, but mortality could be accounted for by action of petroleum solvents in the inert materials. This suggests the registration process of new pesticides should also include documented potential toxicity of inert components in the formulation to non-target aquatic insects.

Limesink wetlands are a common aquatic habitat in southwest Georgia, USA. These wetlands are non-alluvial, occupying shallow depressions formed from dissolution of limestone bedrock and collapse of surface sands. They are seasonally inundated, with a typical hydroperiod extending from late February to early July. Little is known about factors influencing invertebrate community structure in limesink wetlands. Recently, it has been suggested that regular inundation and drying are important influences on community structure in some seasonal wetlands. We had an opportunity to examine this hypothesis in 3 forested limesink wetlands. Quantitative samples of invertebrates were taken monthly on benthic and wood surfaces from March 1994 through July 1995. This included a period of unusually heavy precipitation, summer and autumn of 1994, when the wetlands would normally be dry. Immediately following inundation, benthic samples were dominated by amphipods (Crangonyx sp.), isopods (Caecidotea sp.), cladocerans, and copepods. Maximum total densities (1000–4000 individuals per m2) were observed within 3 months of inundation. During summer and autumn, densities decreased (< 500 individuals per m2), and the benthos was dominated by larval chironomids. Wood surfaces were dominated by chironomids, with greatest densities (1000–3000 individuals per m2) observed in summer and autumn. Although not quantified, freshwater sponge became very abundant on wood surfaces during autumn. During the following spring (1995), invertebrate densities on sediments remained low, and few amphipods, isopods, cladocerans, or copepods were collected. Chironomids remained very abundant on wood. Our results suggest that extended inundation is a disturbance to some elements of wetland invertebrate communities. Extended inundation may cause short-term reductions in populations by eliminating summer refugia (amphipoda, isopoda) or by altering environmental cues necessary for the completion of life cycles (cladocerans, copepods).

1. The blind isopod Caecidotea tridentata is the dominant invertebrate in a simple community of subterranean organisms inhabiting the local, shallow aquifer under Konza Prairie, Kansas, U.S.A. 2. The ecology of this karst aquifer was explored by sieving water from a spring, collecting water samples for analysis, and manipulating sediments and invertebrates in the laboratory. The size frequency distribution was stable and gravid females were present throughout the year, suggesting continuous reproduction. 3. The number of isopods collected per litre was negatively correlated with discharge and the abundance of bacteria, but positively related to the numbers of an amphipod (Bactrurus hubrichti). This may be explained if both the isopods and the amphipods track the saturated zone below the top of the water table; at lower discharge, the top of the water table is closer to the spring outlet. The suspended bacteria wash out in greater numbers with high discharge. 4. When isopods and carbon were added in a pairwise experimental design to sediments collected from the aquifer, the isopods significantly stimulated numbers and activity of planktonic and sedimentary bacteria, while carbon had no effect. This suggests that invertebrates can affect the microbes locally in an aquifer.

The mechanisms of leaf decay, leaf-associated macroinvertebrate community structure, leaf-associated microbial activity and physicochemical stream characteristics were investigated on a mid-Michigan headwater stream in summer. An undisturbed wooded site was compared with two agriculturally perturbed sites. Discharge, total suspended particulates, and nutrients were all higher and more variable throughout the season within the agricultural reaches. Leaf decay rates were higher at the agricultural sites and results suggest discharge abrasion was the major leaf processing mechanism at these sites while microbial decay and macroinvertebrate shredding appear to be the primary mediators of leaf weight loss at the wooded site. Total macroinvertebrate densities on leaf packs at the agricultural sites were 1.9 times the densities at the wooded site. It is suggested that experimentally introduced leaf packs acted as a lure for net-spinning invertebrates limited by stable substratum at the agricultural sites. Species shifts were observed from wooded reaches where Pychnopsyche spp., Gammarus, Ephemeroptera, Bezzia, and Nigronia serricornis were important, to downstream agricultural reaches which were dominated by Cheumatopsyche, Chironomidae, Elmidae, Hydracarina, Hemerodromia, and Caecidotea.

The isopod Caecidotea intermedius serves as the intermediate host for the acanthocephalan Acanthocephalus dirus. C. intermedius is preyed upon by the northern creek chub, Semotilus atromaculatus, which also serves as the definitive host for A. dirus. The effects of the parasite on the antipredator behavior of C. intermedius were examined. We tested the hypothesis that behavioral changes induced in C. intermedius by the parasite are by-products of increased energy demands induced by the parasite (i.e., increased hunger). Infected and uninfected C. intermedius were placed in a divided aquarium with 0, 1, or 2 creek chubs. Leaf discs provided both a food source and a refuge from the predator. In the presence of the creek chubs, uninfected C. intermedius avoided the predator, and were found more frequently in refugia as the number of creek chubs increased. However, infected C. intermedius were associated with the side of the aquarium containing the predator, and spent significantly more time out in the open away from the refuge regardless of the number of creek chubs. These data show that the antipredator behavior exhibited by C. intermedius is altered by A. dirus, and that such alterations are unlikely to be simply products of increased energy demands. Parasite-induced behavioral changes appear to increase C. intermedius' vulnerability to predation, thereby increasing the likelihood of A. dirus completing its life cycle. We find little evidence for greater foraging need as the mechanism indicating changes in antipredator behavior.

"El presente trabajo reconoce la composición, estructura y distribución espacial del ensamble de crustáceos bentónicos de Alchichica, un lago salino tropical ubicado en el extremo oriental del altiplano mexicano. El lago presenta una riqueza taxonómica de crustáceos bentónicos compuesta por 1 anfípodo (Hyalella azteca), 1 isópodo (Caecidotea williamsi) y 2 ostrácodos (Limnocythere inopinata y Candona sp.). Comparada con otros lagos tropicales, la riqueza de especies es reducida. A pesar de lo anterior, es importante mencionar el grado elevado de endemismo representado por C. williamsi, recientemente descrita para el lago Alchichica; adicionalmente, es factible que tanto Candona como H. azteca sean especies nuevas y endémicas del lago. Los crustáceos bentónicos se distribuyen desde la zona litoral hasta la zona más profunda del lago (62 m) con abundancias y riqueza taxonómica variables. Los ostrácodos fueron los crustáceos que con mayor frecuencia se recolectaron en el lago, en la zona litoral, en el talud, y en la zona profunda de la que son habitantesexclusivos. Los anfípodos constituyeron el segundo grupo en abundancia de la zona litoral y talud y estuvieron ausentes en la zona profunda. Los isópodos sólo se encuentran asociados a los depósitos de tufa, hábitat característico del lago que se extiende a lo largo del talud, por lo que con las técnicas de muestreo tradicional empleadas en el presente estudio no fueron capturados. En este ensamble de crustáceos predominan las especies de desarrollo directo y con posiciones tróficas que incluyen componentes herbívoros (H. azteca), omnívoros (C. williamsi) y bacterívoros (L. inopinata y Candona sp.)."

SUMMARY. 1 Spatial and temporal distribution, abundance and production of the floodplain macroinvertebrate communities of two low-gradient headwater streams in Virginia, U.S.A., were studied over 1 year. 2 Spatial and temporal distribution patterns of invertebrates were affected by inundation patterns. Numbers, biomass and production were higher in low than high floodplain areas and on a floodplain continuously inundated over 9 months compared with a floodplain completely flooded only occasionally during storms. 3 The predominant species in terms of numbers and production on both floodplains was the harpacticoid copepod Attheyella illinoisensis Forbes. Other species with relatively high production were the sphaeriid clam Pisidium sp., the leptophlebiid mayfly Leptophlebia sp., the isopod Caecidotea racovitzai (Williams), and the chironomids Paratendipes sp. and Polypedilum spp. 4 Annual invertebrate production (dry weight) on the floodplain continuously inundated over 9 months was 6.1 g m−2; production on the periodically inundated floodplain was 1.7 g m−2. Collector-gatherers accounted for 58–61%, and predators 19–25%, of the production. 5 Annual invertebrate production on the floodplains, calculated on the basis of a linear metre of channel length, was 84–490 gm−1, or about one to two orders of magnitude greater than probable production in the channels, suggesting the significance of floodplain invertebrates to stream system trophic dynamics.

The observation of pigmentation alteration in isopod crustaceans induced by acanthocephalans, known as pigmentation dystrophy, has been documented in North America in species of the aquatic genera Asellus Geoffroy, 1764, Lirceus Rafinesque-Schmaltz, 1820, and Caecidotea Packard, 1871, and in Europe, in Asellus. Recently, three depigmented specimens of Atlantoscia floridana (van Name, 1940), a terrestrial isopod, occurring from >Florida, USA to northern Argentina were found showing pigmentation dystrophy and harboring larval acanthocephalans. Photographic documentation of live and preserved, infected isopods is presented. Morphometric data and photomicrographs of the male, unencysted cystacanth specimen which allowed its placement in the genus Centrorhynchus Lühe, 1911 are presented. This is the first record of the phenomenon of pigmentation dystrophy in terrestrial isopod crustaceans, the first record of A. floridana infected by an acanthocephalan and the first record of a species of Centrorhynchus in a terrestrial isopod.

Nine species of asellid isopods are reported from groundwater habitats in Maryland. Three of these species are habitually found in springs: Lirceus brachyurus, Caecidotea kenki, and C. alleghenyensis, n. sp. The latter, described herein, is a member of the hobbsi group known only from the Allegheny Mountains in Garrett Co. Six species are obligate inhabitants of subterranean waters and are found primarily in Appalachian caves, although some have broad ranges that span noncavernous areas. The obligate subterranean species are Caecidotea pricei, C. franzi, C. holsingeri, C. mausi, C. vandeli and C. nordeni.

Density of troglobitic crustaceans and levels of potential food sources were compared in reference pools and pools polluted by septic system effluent in Banners Corner Cave, Virginia. Data from four physicochemical variables indicated slight to high pollution in five pools compared with two unpolluted pools. Polluted pools had high levels of conductivity, nutrients and fecal coliforms. Highly polluted pools also had decreased dissolved oxygen levels. Isopods (Caecidotea recurvata) were absent from highly polluted pools. Highest isopod density (up to 74.6/M2) occurred in slightly and moderately polluted pools. Amphipods (Stygobromus mackini) were absent from all polluted pools. Fungal biomass was negligible in all pools. Bacterial biomass accounted for a greater proportion of sediment total organic matter (TOM) in polluted pools, but there was little overall increase in TOM in polluted pools. Results of a laboratory growth experiment suggest that isopods can use bacteria from septic effluent as a food. However, presence of coarse particulate matter, not organic enrichment by septic system effluent, was the most likely cause of high isopod density in some pools. Septic system effluent may provide additional food to the aquatic community in Banners Corner Cave, but generally was damaging to the system.

The interspecific interactions of three pairs of cave isopods and amphipods, previously thought to be competitors, were examined by analyzing washouts and losses from laboratory streams and from manipulation experiments in streams of Organ Cave, West Virginia. None of the pairs were in fact competitors. The isopod Caecidotea holsingeri was an amensalist of the amphipod Stygobromus spinatus in the laboratory, but the two did not interact in the field. The amphipod Gammarus minus was a predator on C. holsingeri both in laboratory streams and in the field, and C. holsingeri was a competitor of G. minus, at least in laboratory streams. Stygobromus emarginatus was an amensalist of G. minus in laboratory streams and in the field; but in the field G. minus was a commensalist of S. emarginatus. This combination of commensalism and amensalism produces the dynamics of a predator-prey system. Interactions in both laboratory streams and cave streams were asymmetric and often had characteristics of several kinds of interspecific interactions. Negative interactions dominated in laboratory streams while positive interactions were more common in the field experiments. Negative interactions had an effect on microdistribution only at the level of individual stones in a riffle. Positive interactions may contribute to the positive association of some species at larger scales.

(1944). LXVIII.—On the freshwater Isopod genus Caecidotea Packard. Annals and Magazine of Natural History: Vol. 11, No. 84, pp. 815-817.

TWO species of crayfish are common in the caves of southern Indiana, often coexisting in the same cave (Eberly, 1954, 1955). Orconectes pellucidus (a somewhat variable species with several subspecies already designated by various workers) is the famous blind white cave crayfish found originally in Mammoth Cave. The other species is a form of Cambarus bartoni which,has up to the present been identified as C. bartoni laevis. Both of these species are ecological equivalents, and when they occur in the same cave come into direct competition with each other. The main environmental factor involved in this competition is food which is naturally scarce in caves. The chief food seems to be slow-moving isopods of the genus Caecidotea. However, C. bartoni, being much larger and more powerful, can and occasionally does kill and eat the other crayfish and is even cannibalistic at times. In this intense but slow-moving drama of the survival of the fittest, only one species seems destined to survive. Food is too scarce to permit both species to maintain very large populations side by side. The outcome will depend on the degree of specialization or adaptation to the cave environment. The usual cave adaptations are well known. The characters most relevant to this discussion are the following