Allen W. Shostak

Bio: Allen W. Shostak is an academic researcher from University of Alberta. The author has contributed to research in topics: Hymenolepis diminuta & Fecundity. The author has an hindex of 14, co-authored 36 publications receiving 6361 citations. Previous affiliations of Allen W. Shostak include Wake Forest University & University of Manitoba.

Parasitology meets ecology on its own terms: Margolis et al. revisited.

Abstract: We consider 27 population and community terms used frequently by parasitologists when describing the ecology of parasites. We provide suggestions for various terms in an attempt to foster consistent use and to make terms used in parasite ecology easier to interpret for those who study free-living organisms. We suggest strongly that authors, whether they agree or disagree with us, provide complete and unambiguous definitions for all parameters of their studies.

Patterns and processes in helminth parasite communities: an overview

Abstract: The structure of helminth communities, their dynamic components and processes and their range of diversities, have long held fascination for parasitologists. Perhaps the earliest body of work in this area was generated by the great Russian academician, V. A. Dogiel and his colleagues in the 1930s (Dogiel, 1964). While it is generally agreed that Crofton (1971a, b) was largely responsible for introducing a quantitative approach to the study of helminth population dynamics, most agree that Holmes (1961, 1962) initiated a quantitative approach to the study of helminth community dynamics. Since these bench-mark publications, significant advances have been made in each area, both empirically and conceptually. Indeed, some of the terminology and ideas which will be highlighted throughout this book were not in the literature at the time the idea for this publication was conceived a little over two years ago.

A Mark-Recapture Study of Trematode Parasitism in Overwintered Helisoma anceps (Pulmonata), with Special Reference to Halipegus occidualis (Hemiuridae).

Abstract: Etude de la dynamique des interactions entre H. anceps et H. occidualis pendant les mois d'hiver en utilisant des escargots marques individuellement. Les caracteristiques du parasitisme par le trematode dans la cohorte d'escargots sont etudiees et une methode de marquage-lâcher-recapture est utilisee pour suivre le cours des infections

Photocycle-dependent emergence by cercariae of Halipegus occidualis from Helisoma anceps, with special reference to cercarial emergence patterns as adaptations for transmission.

Abstract: Emergence by cercariae of Halipegus occidualis (Hemiuridae) from naturally infected Helisoma anceps (Pulmonata) was evaluated with respect to change in temperature and light. Total cercarial emergence per snail per day increased with temperature in 2 experiments: at constant temperatures of 16, 22, and 28 C, and at temperatures varying within the range 15-30 C. The number of cercariae emerging per snail per day varied extensively among snails and from day to day for individual snails. The proportion of cercariae that emerged during darkness in each 24-hr period on a 12-hr light: 12-hr dark photocycle was consistent for each snail over 3 photocycles, but it varied among snails: a mean of 73% of cercariae emerged during darkness at 16 C, 84% at 22 C, and 89% at C. The ecological consequences of nocturnal emergence by sessile, long-lived cercariae, such as those of H. occidualis, are discussed with reference to 3 hypotheses: synchronization with activity of the next host, enhancement of dispersal, and reduction of mortality. Daily cycles of emergence by cercariae from molluscan hosts are reported widely (Rees, 1948; Macy et al., 1960; Asch, 1972; Betterton, 1979; Th6ron, 1985, 1989; Lewis et al., 1989). These cycles of emergence correspond to daily changes in ambient light or temperature and often correlate with activity cycles of the next host (Ginetsinskaya, 1968; Cable, 1972; Betterton, 1979; Th6ron, 1984, 1985; Lewis et al., 1989). An absence of daily cycles has been reported for cercariae that encyst in the external medium following emergence (Kendall and McCullough, 1951; Ginetsinskaya, 1968). Several authors (Ginetsinskaya, 1968; Cable, 1972; Th6ron, 1984) interpreted these types of contrasting observations as evidence that daily cycles of emergence evolved as adaptations for transmission, by enhancing the ability of active, short-lived cercariae to find hosts rapidly. However, not all digeneans produce such cercariae. Cercariae of Halipegus occidualis are nonmotile and long-lived (Shostak and Esch, 1990) and they are ingested by their microcrustacean second intermediate hosts. Macy et al. (1960), in a limited study, reported that cercariae of H. occidualis tend to emerge from Helisoma subcrenatum during late afternoon and night. This observation seems contrary to the usual hypothesis to explain periodicity of cercarial emergence Received 9 April 1990; revised 12 June 1990; accepted 14 June 1990. * Present address: Department of Zoology, University of Alberta, Edmonton, Alberta, Canada T6G 2E9. (i.e., a necessity to find hosts rapidly). The present study evaluated the emergence of cercariae ofH. occidualis from Helisoma anceps, primarily with respect to photocycle but also with respect to the modifying influence of temperature. Nocturnal emergence by cercariae was confirmed, and alternate hypotheses were developed to explain periodic emergence by cercariae. MATERIALS AND METHODS Helisoma anceps was collected from Charlie's Pond, an impoundment in the piedmont area of North Carolina (described in Crews and Esch [ 1986]), in October 1987 and maintained at 20-24 C under natural lighting in a 50-L aquarium containing pond water and vegetation. Lettuce was provided. After 1-2 mo snails were screened individually for infection with H. occidualis, following the methods of Goater et al. (1989). One experiment evaluated the effect of temperature. At 1030 hr on day 0, 7 naturally infected snails (shell diameter: 9.0-11.3 mm) in individual 55-mm-diameter dishes, containing 30 ml filtered pond water and a 1-cm2 piece of lettuce, were placed in a controlled environment chamber at 22 ? 1 C. A 12-hr light: 12hr dark photocycle (light commencing 0500 hr) was established in the chamber using a 25-watt incandescent light bulb suspended 25 cm above the dishes. Based on the study by Asch (1972), it was assumed that body temperatures of H. occidualis changed negligibly when illuminated. At 1030 hr daily until day 24, each snail was transferred to a new dish containing fresh water and lettuce and cercariae in the old dishes were counted (total counts if 500 cercariae). The temperature was changed by 5 C every 3-4 days (Fig. 1). Snails were killed on day 24, and sporocysts and rediae were counted. A second experiment evaluated the effect of light. At 0700 hr on day 0, 24 infected snails (shell diameter:

Detection of density-dependent growth and fecundity of helminths in natural infections.

Abstract: Density-dependent constraints on parasite growth, survival or reproduction are thought to be important in preventing the unchecked increase in parasite numbers within individual hosts or host populations. While it is important to know where, and with what severity, density dependence is acting within the parasite life-cycle, interpretation of data from natural infections is difficult. In this paper, we present a Monte Carlo simulation technique for examining such data for evidence of density dependence. We also describe how this technique may be used to distinguish among mechanisms hypothesized to generate density-dependent phenomena.

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Quantifying parasites in samples of hosts

Abstract: Whereas terminological recommendations require authors to use mean intensity or mean abundance to quantify parasites in a sample of hosts, awkward statistical limitations also force them to use either the median or the geometric mean of these measures when making comparisons across different samples. Here, we propose to reconsider this inconsistent practice by giving priority to biological realism in the interpretation of different statistical descriptors and choosing the statistical tools appropriate to our decisions. Prevalence, mean intensity, and indices of parasite distribution (such as median intensity) are suitable descriptors to quantify parasites in a sample of hosts. These measures have different biological interpretations and need different statistical methods to be compared between samples.

Ticks and tickborne bacterial diseases in humans: an emerging infectious threat

Abstract: Ticks are currently considered to be second only to mosquitoes as vectors of human infectious diseases in the world. Each tick species has preferred environmental conditions and biotopes that determine the geographic distribution of the ticks and, consequently, the risk areas for tickborne diseases. This is particularly the case when ticks are vectors and reservoirs of the pathogens. Since the identification of Borrelia burgdorferi as the agent of Lyme disease in 1982, 15 ixodid-borne bacterial pathogens have been described throughout the world, including 8 rickettsiae, 3 ehrlichiae, and 4 species of the Borrelia burgdorferi complex. This article reviews and illustrate various aspects of the biology of ticks and the tickborne bacterial diseases (rickettsioses, ehrlichioses, Lyme disease, relapsing fever borrelioses, tularemia, Q fever), particularly those regarded as emerging diseases. Methods are described for the detection and isolation of bacteria from ticks and advice is given on how tick bites may be prevented and how clinicians should deal with patients who have been bitten by ticks.

A Standardized Terminology for Describing Reproductive Development in Fishes

Abstract: As the number of fish reproduction studies has proliferated, so has the number of gonadal classification schemes and terms. This has made it difficult for both scientists and resource managers to communicate and for comparisons to be made among studies. We propose the adoption of a simple, universal terminology for the phases in the reproductive cycle, which can be applied to all male and female elasmobranch and teleost fishes. These phases were chosen because they define key milestones in the reproductive cycle; the phases include immature, developing, spawning capable, regressing, and regenerating. Although the temporal sequence of events during gamete development in each phase may vary among species, each phase has specific histological and physiological markers and is conceptually universal. The immature phase can occur only once. The developing phase signals entry into the gonadotropin-dependent stage of oogenesis and spermatogenesis and ultimately results in gonadal growth. The spawning cap...

Ecosystem energetic implications of parasite and free-living biomass in three estuaries

Abstract: Parasites can have strong impacts but are thought to contribute little biomass to ecosystems. We quantified the biomass of free-living and parasitic species in three estuaries on the Pacific coast of California and Baja California. Here we show that parasites have substantial biomass in these ecosystems. We found that parasite biomass exceeded that of top predators. The biomass of trematodes was particularly high, being comparable to that of the abundant birds, fishes, burrowing shrimps and polychaetes. Trophically transmitted parasites and parasitic castrators subsumed more biomass than did other parasitic functional groups. The extended phenotype biomass controlled by parasitic castrators sometimes exceeded that of their uninfected hosts. The annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass. This biomass and productivity of parasites implies a profound role for infectious processes in these estuaries.