Salamander predation and vertical distributions of zooplankton

SUMMARY. 1. The impact of different predation regimes of zooplanktivorous larval tiger salamanders, Ambystoma tigrinum nebulosum , on the vertical temporal distributions of Daphnia pulex, Diaptomus nudus and larval Chaoborus flavicans was studied in limnetic enclosures in a pond in east-central Arizona. Zooplankton densities were monitored 1-2 h before sunset, at sunset, and 1-2 h after sunset at three depths (0-0.4, 1.0 and 2.0 m) in four salamander treatments (0, 20, 40 salamanders per enclosure, and unenclosed limnetic areas).
2. Densities and body size of Daphnia pulex were consistently greater in salamander-free enclosures than in other treatments. More Daphnia were generally nearer the surface (0-1.0 m) than along the bottom before and at sunset than after sunset in enclosures without salamanders. After sunset, Daphnia was by far most dense along the bottom. Densities were uniform among depths and sample times in treatments with salamanders. Salamanders moved throughout the water column. Frequencies of D. pulex spined morphs (with prominent dorsal crest) did not differ among salamander treatments.
3. Chaoborus densities were positively correlated with D. pulex distributions among depths and sample times in treatments. Spatio-temporal distributions of Chaoborus were influenced more by their daphnid prey than by risk of predation from larval salamanders.
4. Densities of Diaptomus nudus were highest in open water controls and lowest in enclosures without salamanders. Diaptomus was generally more dense between 0 and 1 m than at 2.0 m depths in all treatments, and vertical distributions were not dependent on salamander density.     

DETECTION OF TYPE A BOTULINAL TOXIN-PRODUCING ORGANISMS SUBCULTURED FROM CHEESE USING AN AMPLIFIED ELISA SYSTEM

Mascarpone cheese implicated in a botulism outbreak was examined for preformed and cultural botulinal toxins using the mouse bioassay. The cheese was also assayed for cultural toxins and for the most probable number (MPN) of toxin-producing organisms/g using an amplified ELISA. No preformed botulinal toxins were discovered in the cheese samples (pH range 5.84-5.86) using the mouse bioassay. However, after cheese subculture in tryptone-peptone-glucose-yeast extract broth, type A botulinal toxin-producing organisms that formed more than 10,000 MLD (mouse lethal dose)/mL in culture were detected. The ELISA results also revealed that type A toxin was present in the culture with a sensitivity of ∼ 10 MLD/mL. The MPN of type A toxin-producing organisms/g in 12 cheese samples examined ranged from < 0.3-9.33. No ELISA cross-reactivity was noted between the type A toxic cultures and other types (B, E, or F). The ELISA sensitivity was ∼5 MLD/mL casein buffer using purified type A neurotoxin. The advantages of the ELISA test are that the toxin type and approximate lethal dose can be determined within one day compared to the mouse bioassay which takes 3–5 days.     

Predator avoidance costs and habituation to fish chemicals by a stream isopod

1. We examined whether long-term exposure to chemical cues of predatory longear sunfish (Lepomis megalottis) affected growth and rates of leaf processing by the isopod, Lirceus fontinalis, an important facultative shredder in low-order streams in the eastern United States, and whether isopods habituated to sunfish chemicals. 2. Long-term (24 days) exposure to fish chemicals did not affect growth or the extent of leaf processing by isopods in the laboratory. Thus, chemical cues alone may not be important in triggering long-term predator avoidance behaviours that could potentially reduce fitness or affect community processes like Litter breakdown. 3. Isopods exposed to fish chemicals for 3, 9 and 15 days were significantly more active than individuals unexposed to fish chemicals, when transferred to another environment with fish chemicals. This result, coupled with results of the growth experiment, suggests that isopods habituate to fish chemical stimuli and that time to habituation is c. 3 days or less. Because fish chemicals can mislead prey about predator presence, and hence be a non-threatening stimulus, they are probably important in eliciting only short-term antipredatory behaviours by isopods.     

Introductory Remarks: Symposium on Differentiation of Trypanosomatids

ABSTRACT. Leishmania differentiation in the gut of phlebotomine sand flies was evaluated based on five light and electron microscopic studies of natural (Leishmania panamensis/Lutzomyia gomezi, Leishmania chagasi/Lutzomyia longipalpis) and unnatural (Leishmania mexicana/Lutzomyia abonnenci, Leishmania panamensis/Phlebotomus papatasi, Leishmania major/Lutzomyia longipalpis) life cycles. In the bloodmeal, transformation of amastigotes into stumpy promastigotes occurred before or during division. Further division in pairs or rosettes resulted in the development of spatulate and/or elongate nectomonad (free-swimming) promastigotes. Elongate, short, and metacyclic nectomonad promastigotes, and nectomonad paramastigotes were present in the midgut lumen. Dividing short promastigotes predominated in the cardia, and appeared to generate metacyclic forms which were observed in three life cycles. Haptomonad (attached) forms of Leishmania panamensis in the hindgut were primarily spatulate promastigotes (natural host) or pear-shaped promastigotes (unnatural host); paramastigotes and dividing forms were rare. At the stomodeal valve, short haptomonad promastigotes predominated in unnatural hosts, while both short and pear-shaped haptomonads were abundant, along with paramastigotes in natural hosts. Haptomonad paramastigotes and pear-shaped promastigotes colonized the esophagus, while paramastigotes predominated in the pharynx. Metacyclics were free-swimming in the lumen of the foregut.     

The Challenge of Pneumocystis carinii Culture1

ABSTRACT. Published and unpublished data on the cultivation of P. carinii were reviewed by a panel of investigators convened by the National Institutes of Health. Although several cell culture systems allow propagation of P. carinii for a limited time with modest rates of replication, these have not proved adequate for isolation of P. carinii in sufficient quantity to explore important basic biological investigation. Attempts at cell-free culture have yielded only transient proliferation. Because much of the unsuccessful work on cultivation of the organism has been unpublished, the panel agreed that these data may be useful to other investigators in designing experimental strategies for cultivation. Therefore, the purpose of this report is to make available this information to researchers, lest others unknowingly repeat unsuccessful methods. It is hoped that by documenting the history and the complexities of Pneumocystis culture, renewed interest and efforts will be directed toward this fundamental scientific challenge.     

Marine faunal assemblages in the Silurian-Devonian Keyser Limestone of the central Appalachians

Sedimentological analysis of the Keyser Limestone (Upper Silurian - Lower Devonian of the central Appalachians) indicates that its sediments were deposited in a range of marginal and shallow marine environments. Major depositional environments include: tidal flat, lagoon, barrier bar and island, and open marine shelf. Each major environment is represented by a lithofacies which is lithologically and faunally distinct. Tidal flat lithofacies are characterized by eurytopic organisms, including ostracodes, gastropods, stromatoporoids and blue-green algae. Lagoon lithofacies are dominated by bryozoans, brachiopods, ostracodes and stromatoporoids. Barrier lithofacies are characterized by rooted crinoids, encrusting bryozoans and robust brachiopods. Open shelf lithofacies contain a diverse fauna of cystoids, crinoids, bryozoans and brachiopods.
The distributions of faunal assemblages in the Keyser show no simple relationship to either water depth or distance from shore. They are, in general, related to the distributions of depositional environments.
Recurring associations of brachiopod genera were not found in the Keyser. With few exceptions, any genus may be found in any subtidal environment. Abundance of brachiopods is related to the abundance of local hard substrates (usually bryozoans).     

Growth of Leishmania donovani Amastigotes in a Continuous Macrophage-Like Cell Culture*

SYNOPSIS. The feasibility of using a macrophage-like murine tumor cell as a host for Leishmania donovani was investigated. This cell line, designated P388D₁, rapidly phagocytized amastigotes and supported their intracellular replication. It can serve as a model "host" without the inherent limitations of primary macrophage cultures.     

Occurrence of Amoebae In and Around the Mushroom Laccaria trullisata

ABSTRACT. Studies performed with the basidiomycete Laccaria trullisata collected from the sandy beach at the Hempstead Lake State Park, Long Island, New York, during the growing seasons of 1979 and 1980, have demonstrated a carposphere (equivalent to rhizosphere) effect. This region exerts a positive influence on the population density of amoebae when numbers are compared with those obtained in the bare sand 5 cm away. Moreover, amoebae have been shown to exist in, and have been recovered from, internal tissue of the cap (72%) and stalk (91%) of these mushrooms. A partial characterization of three strains of amoebae isolated from the internal tissue of L. trullisata and established in clonal culture is presented.     

Kinetics of Potassium and Magnesium Uptake by Intact Soybean Roots

The kinetics of uptake of K⁺ and Mg²⁺ were studied by using intact soybean [Glycine max (L.) Merr. cv. Amsoy] roots. Uptake of K⁺ in the concentration range 1.29 × 10^?5 to 1.82 × 10^?3 M can be represented by two phases of a single, multiphasic mechanism. Similarly, uptake of Mg²⁺ in the concentration range 4.10 × 10^?6 to 2.49 × 10^?4M was biphasic.     

Non-annual external annuli in the freshwater mussels Anodonta grandis grandis and Lampsilis radiata siliquoidea*

1. Two species of freshwater mussels, Lampsilis radiata siliquoidea and Anodonta grandis grandis were measured and permanently marked with pointed, plastic tape positioned at the postero-lateral edge of the shell. Mussels were returned to original conditions at two sites in an oligotrophic lake, retrieved at yearly intervals, re-measured, and external annuli that had been added since marking were counted. 2. External annuli were formed much less frequently than annually; the overall median number of annuli formed each year was 0.5. In one of the four populations studied, the rate of annulus formation was >1 in small animals and <1 in large ones. Many mussels showed no new external annuli at all, even several years after marking. 3. Ford-Walford plots of shell annuli did not yield consistent indices of shell growth. Repeated measurement of mussels in successive years showed that estimates of growth based on shell annuli consistently overestimated real shell growth.