Pyganodon Cataracta Research Articles

A proposed method for analyzing molecular signatures to detect hermaphroditism in freshwater mussels: a case study using the eastern floater (Pyganodon cataracta)

Many freshwater mussels (order Unionida) have an unusual system of doubly uniparental inheritance (DUI) of mitochondrial (mt) DNA. In species with DUI, males possess a female-transmitted (F-type) mt genome and a male-transmitted (M-type) mt genome. These genomes contain non-canonical open reading frame (orf) genes, referred to as f-orf and m-orf, present in F and M mt genomes, respectively. These genes have been implicated in sexual development in Unionida. When gonochoric species become hermaphroditic, which has happened several times in Unionida, they lose their M-type mt genome and f-orf genes evolve dramatically. Resulting F-ORF proteins are highly divergent in terms of primary nucleotide sequence, inferred amino acids, and hydrophobic properties; these genes (and proteins) are referred to as hermaphroditic orfs or h-orfs (and H-ORFs). We investigated patterns of hydrophobicity divergence for H-ORF proteins in hermaphrodites versus F-ORF proteins in closely related gonochoric species against cytochrome c oxidase subunit 1 (cox1) divergences. This approach was used to assess whether cryptic hermaphrodites can be detected. Although we did not detect evidence for the recent transition of any populations of eastern floaters (Pyganodon cataracta (Say, 1817)) to hermaphroditism, our analyses demonstrate that molecular signatures in mtDNA can be used to detect hermaphroditism in freshwater mussels.

Annual winter water level drawdowns limit shallow‐water mussel densities in small lakes

Abstract Regulated water level fluctuations alter the physical, chemical, and biological environments in lakes. However, few studies have measured the effects of repeated annual winter drawdowns on freshwater mussel populations (Bivalvia: Unionida), and it is unknown whether drawdowns permanently constrain mussel populations to deeper depths or are resilient to the annual disturbance. We quantified mussel densities during normal water levels and their mortality after the initiation of drawdown in lakes with annual winter (December–March) water level drawdown regimes that have existed for several decades. We used systematic quadrat sampling and visual snorkel surveys to estimate the number of live mussels at the surface and buried, and shell length in six drawdown and three control lakes at exposed (0.5‐m) and unexposed (1‐m) depths during winter drawdown. We also estimated mortality of mussels along the exposed lakebed for nine drawdown lakes. Study lakes were dominated by Elliptio complanata and Pyganodon cataracta. During normal water levels, mussel densities were much lower in drawdown lakes than control lakes at 0.5‐m depths. When mussels were present in drawdown lakes at 0.5‐m depths, they were often burrowed in the substrate and smaller than buried mussels in control lakes. At unexposed 1‐m depths, mussel densities were primarily explained by geographic region (western versus central Massachusetts), and found higher densities in drawdown lakes compared to control lakes. Mussel mortality after a single drawdown event in nine drawdown lakes was not correlated with drawdown magnitude or rate. Concordance of shell length‐frequency distributions between dead and buried living mussels in drawdown lakes suggests annual mortality of colonising individuals, which are typically small and presumably of young cohorts. Annual winter drawdowns still limit densities of E. complanata and P. cataracta in shallow‐water habitats in the following autumn (September–October) after 4–5 months of potential recovery, and hence constrain their distribution in lakes exposed to drawdowns. The development of sustainable water level management practices will be essential to minimise impacts to native mussel populations.

Escape Burrowing of Modern Freshwater Bivalves as a Paradigm for Escape Behavior in the Devonian Bivalve Archanodon catskillensis

Many freshwater bivalves restore themselves to the sediment water interface after burial by upward escape burrowing. We studied the escape burrowing capacity of two modern unionoids, Elliptio complanata and Pyganodon cataracta and the invasive freshwater venerid Corbicula fluminea, in a controlled laboratory setting varying sediment grain size and burial depth. We found that the relatively streamlined E. complanata is a better escape burrower than the more obese P. cataracta. E. complanata is more likely to escape burial in both fine and coarse sand, and at faster rates than P. cataracta. However, successful escape from 10 cm burial, especially in fine sand, is unlikely for both unionoids. The comparatively small and obese C. fluminea outperforms both unionoids in terms of escape probability and escape time, especially when body size is taken into consideration. C. fluminea can escape burial depths many times its own size, while the two unionoids rarely escape from burial equivalent to the length of their shells. E. complanata, and particularly P. cataracta, are morphological paradigms for the extinct Devonian unionoid bivalve Archanodon catskillensis, common in riverine facies of the Devonian Catskill Delta Complex of the eastern United States. Our observations suggest that the escape burrowing capability of A. catskillensis was no better than that of P. cataracta. Archanodon catskillensis was likely unable to escape burial of more than a few centimeters of anastrophically deposited sediment. The long (up to 1 meter), vertical burrows that are associated with A. catskillensis, and interpreted to be its escape burrows, represent a response to episodic, small-scale sedimentation events due to patterns of repetitive hydrologic or weather-related phenomena. They are not a response to a single anastrophic event involving the influx of massive volumes of sediment.

Behavioral responses of freshwater mussels to experimental dewatering

Understanding the effects of flow alteration on freshwater ecosystems is critical for predicting species responses and restoring appropriate flow regimes. We experimentally evaluated the effects of 3 dewatering rates on behavior of 6 freshwater mussel species in the context of water-removal rates observed in 21 Atlantic Coast rivers. Horizontal movement differed significantly among species and dewatering rates, but a significant species × dewatering interaction suggested that these factors influence movement in complex ways. Species differences in movement were evident only in controls and under slow dewatering rates, but these differences disappeared at moderate and fast dewatering rates. Burrowing behavior did not differ with respect to species identity or dewatering rate. The proportion of individuals that became stranded did not differ among species, but most individuals became stranded under low and moderate dewatering, and all individuals became stranded under fast dewatering. Mortality after stranding differed strongly among species along a gradient from 25% in Pyganodon cataracta to 92% in Alasmidonta marginata. Together, these results suggest that species behavior may differ under gradual dewatering, but all species in our study are poorly adapted for rapid dewatering. Most of the 21 rivers we assessed experienced dewatering events comparable to our moderate rate, and several experienced events comparable to our fast rate. Dewatering events that exceed the movement or survival capability of most mussel species can be expected to result in assemblage-wide impacts. Consequently, the rate of water level change may be important in refining target flow conditions for restoration.

Non-target trials with Pseudomonas fluorescens strain CL145A, a lethal control agent of dreissenid mussels (Bivalvia: Dreissenidae)

In an effort to develop an efficacious and environmentally safe method for managing zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena rostriformis bugensis), we initiated a research project investigating the potential use of bacteria and their natural metabolic products as biocontrol agents. This project resulted in the discovery of an environmental isolate lethal to dreissenid mussels, Pseudomonas fluorescens strain CL145A (Pf-CL145A). In previous published reports we have demonstrated that: 1) Pf-CL145A’s mode of action is intoxication (not infection); 2) natural product within ingested bacterial cells lyse digestive tract epithelial cells leading to dreissenid death; and 3) high dreissenid kill rates (>90%) are achievable following treatment with Pf-CL145A cells, irrespective of whether the bacterial cells are dead or alive. Investigating the environmental safety of Pf-CL145A was also a key element in our research efforts, and herein, we report the results of non-target trials demonstrating Pf-CL145A’s high specificity to dreissenids. These acute toxicity trials were typically single-dose, short-term (24-72 h) exposures to Pf-CL145A cells under aerated conditions at concentrations highly lethal to dreissenids (100 or 200 mg/L). These trials produced no evidence of mortality among the ciliate Colpidium colpoda, the cladoceran Daphnia magna, three fish species (Pimephales promelas, Salmo trutta, and Lepomis macrochirus), and seven bivalve species (Mytilus edulis, Pyganodon grandis, Pyganodon cataracta, Lasmigona compressa, Strophitus undulatus, Lampsilis radiata, and Elliptio complanata). Low mortality (3-27%) was recorded in the amphipod Hyalella azteca, but additional trials suggested that most, if not all, of the mortality could be attributed to some other unidentified factor (e.g., possibly particle load or a water quality issue) rather than Pf-CL145A’s dreissenidkilling natural product. In terms of potential environmental safety, the results of these invertebrate and vertebrate non-target trials are encouraging, but it would be unrealistic to think that dreissenids are the only aquatic organisms sensitive to Pf-CL145A’s dreissenid-killing natural product. Additional testing is needed to better define Pf-CL145A’s margin of safety by identifying the sensitivity of other susceptible organisms. The results of these non-target safety trials – in combination with equally promising mussel control efficacy data – have now led to Pf-CL145A’s commercialization under the product name Zequanox ® , with dead cells as the product’s active ingredient. The commercial availability of only dead-cell Zequanox formulations will eliminate the risk of any possible non-target infection by Pf-CL145A, further reducing environmental concerns. During the non-target project reported herein, the limited quantities of Pf-CL145A cells that we were able to culture severely restricted the number and size of our trials. In contrast, the availability of Zequanox will now greatly expand the opportunities for non-target testing. The trials reported herein – exposing non-target organisms under aerated conditions to unformulated, laboratory-cultured cells – clearly point to Pf-CL145A’s potential for high host specificity, but non-target trials with Zequanox – using PfCL145A cells cultured, killed, and formulated using industrial-scale protocols – will be even more important as they will define the nontarget safety limits of the actual commercial products under a wide range of environmental conditions.

MtDNA and AFLP markers demonstrate limited genetic differentiation within thePyganodon cataracta–Pyganodon fragilisfreshwater mussel complex in Atlantic Canada

Two nominal species of freshwater mussels, Pyganodon cataracta (Say, 1817) (eastern floater) and Pyganodon fragilis (Lamarck, 1819) (Newfoundland floater), occur in Atlantic Canada, but their taxonomic status has been controversial. We analyzed the female-transmitted mitochondrial cytochrome c oxidase subunit I (i.e., FCOI) and nuclear internal transcribed spacer region (ITS-1) gene sequences, as well as multilocus amplified fragment length polymorphism (AFLP) markers, to evaluate genetic variation in Pyganodon specimens from Atlantic Canada. We found that Pyganodon samples from this region displayed no or extremely low (i.e., <0.5%) genetic divergence for ITS-1 and FCOI sequence data, respectively. Inferences from nested clade analysis of FCOI haplotypes suggest restricted gene flow with isolation by distance and contiguous range expansion. Analysis of molecular variance inferred from presence or absence of nuclear-encoded AFLP bands showed moderate geographic structuring among provinces but no correspondence between mtDNA haplotypes and AFLP profiles. Similarly, there was no correspondence between presence of a single or a double loop on the umbo and FCOI haplotype. These mtDNA and AFLP markers demonstrate limited genetic differentiation within the Pyganodon cataracta–Pyganodon fragilis freshwater mussel complex in Atlantic Canada and question the species-level distinctness of these putative taxa.

Allopatric distribution of generalist parasites: interplay between postglacial dispersal and host species

Dispersal of freshwater mussels occurs when the larvae parasitize fishes. In northeastern North America, distributions of floater mussels ( Pyganodon spp.) are allopatric and arranged in an east–west pattern that corresponds poorly with the biogeographic patterns of the regional fish fauna. This study aims at determining whether associations with distinct fish species can explain the distribution of floaters. Here, we devised a framework based on a series of novel distributional null models to elucidate dispersal of species that are dependent on host species. The distributional patterns of floaters were tested by controlling for associations with fishes, while host–parasite associations were assessed with null models based on co-occurrence patterns. The disjoint distribution of the giant floater ( Pyganodon grandis ) and the eastern floater ( Pyganodon cataracta ) could not be explained by their association with distinct host fish and is likely the result of associations with distinct host populations rather than distinct species. In contrast, the distribution of the Newfoundland floater ( Pyganodon fragilis ) could be explained by its association with euryhaline fishes. Such associations may have also promoted differentiation with its sister taxa, the eastern floater. This study demonstrated the effects of positive biological associations on distributional patterns and the utility of a null model framework to uncover them.

Ontogenic increase of metabolic carbon in freshwater mussel shells (Pyganodon cataracta)

Incorporation of isotopically light metabolic carbon (CM) can obscure carbon isotope records of dissolved inorganic carbon from biogenic carbonates. Ontogenic increases of CM are common in marine bivalved mollusks, likely reflecting increasing absolute metabolism with increasing body size. Here we use shell aragonite from four specimens of Pyganodon cataracta to test if the same is true in freshwater bivalves. Annual δ18Oaragonite values were not different between individuals suggesting that the aragonite samples represent the same time interval. δ13Caragonite, however, showed an ontogenic decrease, with a strong linear relationship between shell height (H in mm) and %CM (R2 = 0.96; %CM = 0.23*H + 13.33), indicating that more CM is incorporated into larger shells. We estimate that between 15 and 35% of shell carbon is derived from metabolic CO2. Nevertheless, this vital effect does not exclude the use of δ13Caragonite records from freshwater shells as environmental proxies.

Cryptic lineages and hybridization in freshwater mussels of the genus Pyganodon (Unionidae) in northeastern North America

The distribution of freshwater mussels Pyganodon Crosse and P. Fischer, 1894 traditionally inferred from morphological characters was validated by a genetic characterization of the genus within the Quebec peninsula. Individuals were identified by comparing the sequences from the female mitochondrial genome (COI and 16S) with those of reference individuals, while hybridization was assessed with male mitochondrial (COI and COII) and nuclear genomes (ITS1 and ITS2). The results confirmed most of the previous morphological identifications but revealed unexpected results. Both male and female mitochondrial genomes support the distinction between Pyganodon fragilis (Lamarck, 1819) and Pyganodon cataracta (Say, 1817). However, only one lineage of Pyganodon grandis (Say, 1829), instead of the two expected, was detected in the sampled area. The genetic survey also revealed the presence of two unidentified Pyganodon lineages, previously unreported within the Quebec peninsula. These extremely rare lineages harbour the signature of ancestral hybridizations. Finally, recent divergence and hybridizations make shell characters only partially efficient in discriminating Pyganodon lineages.

The Status of Freshwater Mussels in Rhode Island

Abstract Between 1980 and present, we inventoried freshwater mussel populations at 129 aquatic sites throughout Rhode Island. We found 8 native mussel species and documented the presence of Corbicula sp. (Asiatic clam). The Rhode Island mussel fauna has been degraded by a long history of damming and discharges into rivers. Significant lake populations have also been eliminated by basin reconfigurations, pollution, and urban development. Elliptio complanata is currently the most widespread and common Rhode Island species. Pyganodon cataracta and Alasmidonta undulata are also widespread but less common. Anodonta implicata and Pyganodon cataracta may be expanding because of increased fish passage and stocking. Lampsilis radiata, Ligumia nasuta, Margaritifera margaritifera, and Strophitus undulatus are rare or localized and should be considered high conservation priorities in Rhode Island.

Freshwater Molluscs of the United States Military Academy Drainages (West Point, NY) and Comparative Regional Biodiversity of Gastropods

Thirty-four species of molluscs have been found in the drainage systems of the United States Military Academy at West Point, NY. A few rare species were found as well as a single specimen of a presumed new gastropod taxon. Only two species of unionids, Pyganodon cataracta and Elliptio complanata, were found within the drainages. The largest drainage system, Popolopen Brook, contained the highest diversity of molluscs. Species redundancy between drainages aligned well as a function of the extent of lentic and lotic habitats with brooks and streams having a Bray-Curtis similarity index of ≈ 64.0 when compared to lakes and ponds. On the other hand, a number of species collected were found in only a single drainage. Total drainage area did not correspond well with diversity unless determined as total predicted usable habitat. Thus the drainages with the greatest number of discernible lakes, ponds, streams, and creeks, also had the highest molluscan diversity. On the whole, molluscan diversity of these drainages compared favorably to those of other regional New York sites, but relative abundance or population densities varied, with variations reflecting survey effort, time or season of collections, and incorporation of historic museum collections.

Selective feeding by three native North American freshwater mussels implies food competition with zebra mussels

We examined the ability of three species of native North American freshwater mussels (Margaritifera margaritifera, Amblema plicata, and Pyganodon cataracta) to preferentially ingest or reject various phytoplankton species and nonliving particles. Our objective was to: (1) determine the particle preferences of the native mussels, (2) determine whether native mussels are able to differentiate between nutritious and less nutritious particles, and (3) compare sorting abilities and particle preferences to those of the invasive zebra mussel (Dreissena polymorpha). Native mussels selected and preferentially ingested the unicellular cyanobacteria Microcystis over most other phytoplankton species. However, despite their ability to select between phytoplankton, they did not select against cattail (Typha) detritus. Our results suggest that native mussels (1) prefer particles (Microcystis) that may no longer be abundant in some systems, such as the Hudson River, (2) must compete with zebra mussels for the same preferred food types (Microcystis), and (3) are unable to differentiate between nutritious (phytoplankton) and less nutritious (Typha detritus) particles. We suggest that native mussels must compete with zebra mussels for many of the same food types and are less efficient than zebra mussels at differentiating between nutritious and less nutritious particles. This indicates that there is an additional mechanism, other than direct physical interference, contributing to native mussel mortalities following zebra mussel invasions.

Ultrastructural evidence for nutritional exchange between brooding unionid mussels and their glochidia larvae

Abstract. The life history of unionid bivalve molluscs includes retention of developing embryos within the gills of parental mussels. This brooding behavior may facilitate nutrient transfer to the glochidia larvae, i.e., matrotrophy. To address this possibility, morphological relationships between brood chambers and developing larvae of Pyganodon cataracta and Utterbackia imbecillis were examined with TEM, and larval shells were observed with SEM, for features that could be associated with the uptake of dissolved materials. Early in brooding, glochidia are enclosed in a vitelline membrane that physically contacts numerous cilia and microvilli of the epithelial cells lining the brood chamber (marsupium). The vitelline membrane subsequently disappears. Lamellar tissues of parental mussels initially have large deposits of glycogen that diminish during the course of brooding. Septa separating brood chambers from adjacent secondary water tubes have numerous mitochondria and microvilli, suggesting the potential for active transport of materials into or out of the marsupia. Since punctae (pores) in the larval shells become filled with an organic matrix early in brooding, they are unlikely to be involved in nutrient exchange. Ultrastructure of the brood chamber and physical contact between the parental mussel and larvae are consistent with a nutritive role for retention of glochidia in the marsupia.

Genetic Differentiation between Unionicola formosa and U. foili (Acari: Unionicolidae): Cryptic Species of Molluscan Symbionts

Genetic Differentiation between Unionicola formosa and U. foili (Acari: Unionicolidae): Cryptic Species of Molluscan Symbionts

Effects of temperature and pO 2 on the heart rate of juvenile and adult freshwater mussels (Bivalvia: Unionidae)

The heart rate of juvenile and adult Utterbackia imbecillis and Pyganodon cataracta was monitored during experimental manipulation of temperature and pO 2. Animals that had been acclimated to 15 and 25°C for 1 week were exposed to an ascending series of temperatures (10, 15, 20, 25 and 30°C). The effects of oxygen tension on heart rate were assessed by subjecting mussels to a descending series of oxygen tensions (100, 75, 50, 25, 5 and 0% air saturation). Results indicated that the heart rates of juvenile and adult mussels are markedly affected by experimental temperature, with Q 10's approaching 4.5. Acclimation had no effect on adult mussels. However, juvenile U. imbecillis exhibited inverse acclimation; whereas, juvenile P. cataracta fit a typical pattern of acclimation (Prosser's Type IVA). When exposed to a descending series of oxygen tensions, adult U. imbecillis maintained a constant heart rate until a significant increase occurred at 25% air saturation, followed by a significant decrease at 5 and 0%. Juvenile U. imbecillis maintained a constant rate until bradycardia occurred at pO 2's of 5 and 0% air saturation. Juvenile and adult P. cataracta exhibited similar patterns, with sustained rates until a significant decrease occurred at 0% air saturation. The differences in acclimation patterns exhibited by juvenile and adult mussels may reflect differences in the thermal conditions experienced by these two life-history stages; however, there are no data available that characterize the microhabitat of juvenile freshwater mussels. Utterbackia imbecillis appears to be more sensitive to low oxygen levels than P. cataracta, and the heart rate of juveniles of both species is more responsive to hypoxia than that of adults.

Multipurpose Gills: Effect of Larval Brooding on the Feeding Physiology of Freshwater Unionid Mussels

During reproduction, the lateral (outer) demibranchs of the unionid mussel Pyganodon cataracta function in brooding females as marsupia in addition to serving in gas exchange, feeding, and ion transport. Recent studies indicate that glochidial brooding reduces clearance rates and particle retention efficiencies, but the opaque shell prevents direct observations of suspension feeding structures and makes it difficult to identify the underlying causes of the changes in feeding dynamics. In this study, video endoscopic techniques were used to describe and compare, in vivo, the feeding structures and dynamics of brooding and non-brooding females. Although circulation within the mantle cavity was slightly altered by the enlarged lateral (gravid) gills of brooding females, both medial and lateral gills continued to retain and process particles. During brooding, circulation through medial gills was maintained by the construction of secondary water tubes near the medial and lateral ends of the brood chambers. In vivo monitoring of particles retained by the frontal surface of the gill indicated that transport rates for particles processed by gravid gills of brooders were significantly slower than on lateral gills of non-brooders or on medial gills. Similarly, gravid gills were less efficient at retaining small particles (<6 ptm) than medial or non-gravid lateral gills. These findings are consistent with the hypothesis that observed reductions in particle clearance rates and retention efficiencies in brooding female mussels are the result of functional changes in the ciliature and flow dynamics of the marsupial gills. Moreover, similar mechanisms mediating particle capture and processing on medial demibranchs appear to be unaffected by the presence of developing glochidia in the water tubes of the lateral gills. Additional key words: glochidia, endoscopy, suspension feeding, filtration Though the gills of suspension feeding bivalves are typically identified as structures for feeding, gas exchange, and ion transport, the ctenidia of many marine and freshwater species also incubate larvae during reproductive periods. Brooding mechanisms vary considerably among species. Most freshwater bivalves, including members of the Corbiculidae and Unionidae, lack planktonic larval stages and incubate developing embryos within internal spaces between gill lamellae (Ortmann 1911; Britton & Morton 1982; Kat 1984; Mackie 1984). In other freshwater and marine bivalve molluscs, developing young are attached to pallial structures or restricted to specialized brood masses, papillae, or sacs (Heard 1977; Bartlett 1979; Richardson 1979; Mackie 1984; Kabat 1985). Conversely, some species, including oysters of the genus Ostrea, brood within the infrabranchial cavity but the young are not confined or physically attached to the mother and move about freely in the inter-demibranchial spaces (Chaparro et al. 1993). Although numerous studies have examined the mechanics of the bivalve pump and filter (for review see J0rgensen 1990), the effect of larval incubation on the gills' customary roles as feeding and respiratory structures has been ignored, except for the observation of Walne (1972) that clearance rates of the oyster Ostrea edulis are lower during brooding periods. In the Unionidae, modifications of ctenidia for brooding, including the location and arrangement of larvae (glochidia) within brood chambers, the degree of swelling of the lamellae, and the duration of larval incubation, vary among species and often serve as important taxonomic characters (Ortmann 1911; Heard & Guckert 1971). In most species, the water tubes of either the lateral (outer) demibranchs or all four demibranchs serve as ovisacs. In others, the marsupium is restricted to a portion of the lateral gills, often forming bulges or sulci along the ventral aspect of the demiThis content downloaded from 207.46.13.21 on Tue, 27 Sep 2016 04:23:58 UTC All use subject to http://about.jstor.org/terms

Life history characteristics of larvalUnionicola(Acari: Unionicolidae) parasitic onChironomus tentans(Diptera: Chironomidae)

Parasitic associations between larval Unionicola formosa and U. foili obtained from the freshwater unionid mussels Pyganodon cataracta and Utterbackia imbecillis, respectively, and the chironomid dipteran Chironomus tentans were established in the laboratory. Several life history characteristics of larvae of both species of water mites were examined during these associations. Larval water mites occurred exclusively on the ventral surface of C. tentans, attached to the articular membranes of the thorax and abdomen. There was no significant difference in the number of larvae parasitizing male and female chironomids, with a mean of approximately 2–3 larvae per host and a maximum of 9 larvae per host. Larval mites remained attached to an insect for an average of 3 days, during which time they increased significantly in size and weight. In the absence of an insect host, the larvae lived approximately 14 days. Larvae that had completed their parasitic phase and had detached from a chironomid lived an average of...

The effect of larval brooding on the filtration rate and particle-retention efficiency of Pyganodon cataracta (Bivalvia: Unionidae)

Following fertilization, the outer demibranchs of the unionid mussel Pyganodon cataracta undergo extensive morphological changes to accommodate approximately a million shelled glochidia larvae within the ctenidial water tubes which serve as brood chambers. The effect of larval incubation on particle filtration and quantitative selection was determined by comparing clearance rates and particle retention efficiencies of adult mussels during brooding and nonbrooding periods. Particle clearance rates for gravid females were significantly lower than those for nongravid females and were as much as 54% lower than those of males collected simultaneously. Females brooding larvae were less efficient at retaining particles &lt;5 μm than were males or nonbrooding females. Both particle clearance and retention spectra were nearly identical for males and females collected during nonbrooding periods. The effect of larval brooding on the activity of gill cilia on excised gill tissue was assessed by determining the beat frequency of the laterofrontal cirri and the pattern of transport of fluorescently labeled latex microspheres by frontal cilia. The metachronal beat of cirri on marsupial gills was significantly lower than on nonmarsupial gills of both males and females but did not differ between reproductive seasons. Particles were transported faster by frontal cilia on nonmarsupial and nongravid gills vs. gravid marsupial gills, suggesting that the reduction in particle clearance and retention by brooding females resulted from functional changes in the ciliature of the marsupial demibranchs.

The Effect of Larval Brooding on the Respiratory Physiology of the Freshwater Unionid Mussel Pyganodon cataracta

-The influence of glochidial incubation on the ventilation rate, valve activity and oxygen consumption (N02) of the unionid mussel Pyganodon cataracta was investigated using bivalves collected during brooding and prebrooding periods. Pumping rates of mussels ranged between 1.7 and 2.5 liters h-1 but were not significantly influenced by season or the presence of developing larvae in the lateral gills of females. The valve activity of adults held under constant conditions varied seasonally, but there was no apparent difference in the amount of time that the valves of gravid females were open and presumably engaged in suspension feeding and aerobic metabolism compared to males collected at the same time. Oxygen uptake by all mussels decreased under declining oxygen tensions suggesting that P. cataracta is an oxyconformer from 100% to 40% air saturation. Oxygen consumption of females was significantly lower than that of males during brooding periods, but did not differ between sexes during nongravid periods. Aerobic respiration was proportionally larger in isolated lateral demibranchs of gravid females than in males, and estimates of the contribution of developing larvae to the 0o2 of adults approached 10%. Under hypoxia, the presence of larvae in the gills of females had no effect on the dependence of N02 on oxygen tension for intact adults or their excised outer ctenidia.

Endoscopic visualization of the functional morphology of the ctenidia of the unionid mussel Pyganodon cataracta

During reproduction, the outer demibranchs of the unionid mussel Pyganodon cataracta serve as marsupia, with incubation of the developing shelled glochidia larvae occurring within the water tubes. In this study, recently developed endoscopic video analysis techniques were employed to examine in vivo the dynamics of filter feeding and water transport in mussels during gravid and postgravid periods. Particles entering the mantle cavity and retained by the gills were transported to the palps in a complex mucus-bound cord by the ventral food groove of the medial ctenidia. Larval incubation and ctenidial swelling impeded flow around the lateral demibranchs, although marsupial ctenidia were still actively involved in suspension feeding. Cilia on the distended ventral edges of marsupial demibranchs were often observed transporting filtered particles to the frontal surface of the medial gills. Larvae within the brood chambers were morphologically isolated from the surrounding medium by dorsal brood caps on the primary water tubes. Direct observations of the secondary water tubes of marsupial gills constructed during periods of larval incubation confirmed their role as temporary lumina for water transport during gravid periods. Time-lapse video recordings revealed that mature larvae are released from the brood chambers via the suprabranchial cavity and exhalant siphon by rapid adductions of the valves and contractions of the brooding demibranchs.