A revision of coregonine fish distribution and abundance in eastern James-Hudson Bay

Synopsis Recent sampling programs conducted in the estuaries of the Eastmain and La Grande rivers (James Bay) and the Great Whale, Little Whale, Innuksuac and Povungnituk rivers (Hudson Bay) revealed patterns of coregonine fish distribution that differ from previous observations. The relative abundance of cisco, Coregonus artedii, and lake whitefish, C. clupeaformis, varied among rivers but did not reveal a latitudinal cline. Previous sampling programs underestimated the abundance of cisco in the Little Whale River. In addition, cisco was the third most abundant species captured in the Povungnituk River, situated 200 km to the north of the previously proposed northern limit at Innuksuac River. As such, the low abundances of cisco in the Great Whale and Innuksuac rivers cannot be attributed to a physiological inability to cope with a reduced growing season. Immature cisco were almost totally absent from the estuaries of the Hudson Bay rivers following spring breakup whereas immature lake whitefish made up 100% of the catch in the Innuksuac River at the same time of year. Species-specific migration patterns in Hudson Bay that differ from those observed in James Bay and the existence of unique juvenile overwintering rivers are 2 hypotheses proposed to explain the discontinuous age-class distribution of cisco and lake whitefish observed in Hudson Bay.Contribution to the program of GIROQ (Groupe Interuniversitaire de Recherche Océanographique du Québec).     

Subtleties and episodes in the early life of fishes

Fluctuations in the abundance of fishes may be caused by episodic mortalities or by more subtle variability in the daily growth and mortality rates of eggs and larvae. Survival response surfaces are used to illustrate the relative effects of episodic and subtle mortality during early life. It is the subtle variability associated with small changes in growth or mortality rates that may exert the greater effect on recruitment. Massive advective losses of eggs or larvae, failed egg production, and acute contaminant mortalities are examples of episodic events that may impact recruitment significantly but which need not be catastrophic. Stabilization of recruitments through density-dependent growth rate variability in early life is demonstrated to be potentially important. Whether this mechanism actually is important in the sea remains to be determined.     

A short history of nuclear activation analysis

The major developments in the field of nuclear activation analysis, from 1936 to 1989, are discussed. The developments are grouped into five consecutive time periods. The impact of various scientists on the development of the field in the first 35 years is also discussed.     

Modeling in the museum: On the role of remnant models in the work of Joseph Grinnell

Accounts of the relation between theories and models in biology concentrate on mathematical models. In this paper I consider the dual role of models as representations of natural systems and as a material basis for theorizing. In order to explicate the dual role, I develop the concept of a remnant model, a material entity made from parts of the natural system(s) under study. I present a case study of an important but neglected naturalist, Joseph Grinnell, to illustrate the extent to which mundane practices in a museum setting constitute theorizing. I speculate that historical and sociological analyses of institutions can play a specific role in the philosophical analysis of model-building strategies.     

Development of Amblyospora campbelli (Microsporida: Amblyosporidae) in the Mosquito Culiseta incidens (Thomson)

The complete life cycle of Amblyospora campbelli (Kellen and Wills, 1962) (Microsporida: Amblyosporidae) requires a two-host system involving the mosquito host, Culiseta incidens (Thomson), and an obligatory intermediate copepod host. The parasite has dimorphic spore development producing meiospores (haploid condition) and binucleated spores (diploid condition), either as an exclusive infection or simultaneously (within females only). This is the 1st known report of concurrent spore development within an adult mosquito host, and, therefore, shows the Amblyospora campbelli system to be uniquely different from other Amblyospora spp. cycles previously described. The significance of dimorphic spore development is discussed. In females, diplokaryotic meronts may invade oenocytes, causing a benign-type of infection. A blood-meal is required to initiate sporulation of the binucleate spore. The binucleate spore contains the sporoplasm involved in transovarial transmission. A 2nd sporulation sequence, primarily in adipose tissue, may involve both males and females. In this sequence, repeated merogonic division greatly increased the density of diplokaryotic meronts and generally involved most of the body of the host. Production of meiospores, unlike that for the binucleate spore, appeared to be spontaneous (i.e. no obligatory blood meal). Survivorship of male and female larval mosquitoes was nearly equal. Adult females spread the parasite in three ways: transovarial, transovum, and by meiospore deposition.     

A two thousand year history of a northern Swedish boreal forest stand

Abstract. Successional processes within northern Swedish boreal forest are investigated for the last 2000 years by analysis of pollen, charcoal fragments and insect remains preserved in a deep mor humus layer on a small island in a large lake. Frequent disturbances by fire, blow-down, insect attack and flood have been the chief influence on vegetation dynamics. The gradual climatically induced replacement of Betula pubescens by Picea abies is superimposed on the disturbance dynamics. Picea first became established during the Little Ice Age, which was the longest period without fire in the record. A thin layer of volcanic ash from Iceland confirms the chronology at the onset of the Little Ice Age. The present importance of Pinus sylvestris and Ericaceae on the island is a product of a recent increase in disturbance frequency. The disturbance regime ensures that the communities stay in equilibrium with prevailing climate.     

Amblyospora trinus N. Sp. (Microsporida: Amblyosporidae) in the Australian Mosquito Culex halifaxi (Diptera: Culicidae)

ABSTRACT. A new species of Amblyospora , a parasite found in wild populations of the predacious Australian mosquito Culex halifaxi , was investigated with light and electron microscopy. This species was found to be heterosporous with two concurrent sporulation sequences in the host larvae, both arising from diplokaryotic meronts and ending with haploid spores. One sequence was dominant and involved meiosis to produce eight thick-walled, broadly oval meiospores in a sporophorous vesicle (SV). The other sequence involved nuclear dissociation to produce lanceolate, thin-walled spores in a subpersistent SV. Horizontal transmission to the mosquito host, by one or both of two distinctly different pathways (one via an intermediate host, the other by cannibalism of infected individuals) and by vertical transmission, are postulated but have not been demonstrated. A new species, Amblyospora trinus , is proposed and its affinities to other heterosporous microsporidia in mosquitoes are discussed.     

Assessing the risk of invasive success in Pinus and Banksia in South African mountain fynbos

Abstract. South African mountain fynbos has been severely invaded by trees and shrubs introduced from other mediterranean-climate regions. Management of these invasions should involve controlling current invaders and screening future introductions. Invasion windows are described and functional groups are defined for pines based on life history attributes important for invasion in the fire-prone mountain fynbos. The most successful invasive pines here (Pinus halepensis, P. pinaster and P. radiata) are fire-resilient and have small seeds, low seed-wing loadings, short juvenile periods, moderate to high degrees of serotiny and relatively poor fire-tolerance as adults. Other species with these attributes, especially from mediterranean-climate regions, wouldbe high-risk introductions. Taxa in other functional groups have not become major weeds even with widespread man-aided dissemination. Experience with pine invaders was used to define functional groups in western Australian Banksia species (Proteaceae), shrubs and trees which include taxa with similar attributes to fynbos invaders (e.g. Hakea and Pinus spp.). Banksias have only recently been introduced to the Cape, and are likely to be increasingly cultivated for the cut flower market. Tall serotinous shrubs with many small seeds per plant, short juvenile periods and low fire tolerance were identified as high risk introductions. This group includes thicket-forming species which maintain very large viable seed banks, e.g. Banksia burdettii, B. hookeriana and B. leptophylla. Low sprouting shrubs with few large seeds per plant and long juvenile periods are unlikely to become invasive in mountain fynbos. The approach of defining functional groups based on life history attributes and invasion windows is valuable for predicting the probability of invasive success. Chance interactions suchas an opportunistic dispersal mutualism between Pinus pinea and an introduced squirrel sometimes confound these predictions and underscore the idiosyncracies inherent in biological invasions.     

THE EFFECTS OF PREDATION ON THE AGE AND SIZE OF MATURITY OF PREY

The effects of nonselective predation on the optimal age and size of maturity of their prey are investigated using mathematical models of a simple life history with juvenile and adult stages. Fitness is measured by the product of survival to the adult stage and expected adult reproduction, which is usually an increasing function of size at maturity. Size is determined by both age at maturity and the value of costly traits that increase mean growth rate (growth effort). The analysis includes cases with fixed size but flexible time to maturity, fixed time but flexible size, and adaptively flexible values of both variables. In these analyses, growth effort is flexible. For comparison with previous theory, models with a fixed growth effort are analyzed. In each case, there may be indirect effects of predation on the prey's food supply. The effect of increased predation depends on (1) which variables are flexible; (2) whether increased growth effort requires increased exposure to predators; and (3) how increased predator density affects the abundance of food for juvenile prey. If there is no indirect effect of predators on prey food supply, size at maturity will generally decrease in response to increased predation. However, the indirect effect from increased food has the opposite effect, and the net result of predation is often increased size. Age at maturity may either increase or decrease, depending on functional forms and parameter values; this is true regardless of the presence of indirect effects. The results are compared with those of previous theoretical analyses. Observed shifts in life history in response to predation are reviewed, and the role of size-selective predation is reassessed.     

Temperature influence on cohort parameters and demographic characteristics of the two cowpea coreids Clavigralla tomentosicollis and C. shadabi

Age-specific life tables of two important pests of cowpea, Vigna unguiculata (L.) Walp., the pod sucking bugs Clavigralla tomentosicollis Stål and C. shadabi Dolling (Heteroptera: Coreidae), were obtained from observations carried out at different temperatures. A biophysical model was found satisfactory to describe the temperature-response of developmental and mortality rates of egg and nymphal stages, with a peak developmental rate around 34°C in both species. The variability in development times was small and the experimental data did not permit any conclusion with regard to the Erlang probability density function. Survival of eggs and nymphs remained high between 20° and 30°C for both species. At temperatures above 34°C, C. tomentosicollis survivorship and fecundity was higher than that of C. shadabi, which in turn laid more eggs at temperatures between 20° and 30°C. Maximum fecundity is estimated to be at 29°C for C. tomentosicollis (99 eggs/female) and 26°C for C. shadabi (261 eggs/female). At 30°C, the intrinsic rate of increase reached a maximum in both species, 0.152 per day for C. tomentosicollis and 0.145 per day for C. shadabi, and remained high for C. tomentosicollis until 36°C. C. tomentosicollis performed significantly better on pigeonpea, Cajanus cajan Millsp., than on cowpea at higher temperatures.