The effect of a single burn event on the aquatic invertebrates in artesian springs

Fire can often occur in aquatic ecosystems, which may affect aquatic invertebrates. Despite the importance of aquatic invertebrates to ecosystem function, the effect of fire on these environments has been little studied. We studied the effects of fire on aquatic invertebrates in artesian springs in the arid zone of South Australia. Artesian springs are a unique and threatened ecosystem, containing several rare and endemic species. Evidence suggests these wetlands were routinely burnt by indigenous Aboriginal people before European settlement over 100 years ago. Recently, burning has been suggested as a reinstated management tool to control the dominant reed Phragmites australis. A reduction in the cover of the reed may benefit the threatened flora and fauna through enhancement of water flow. Three artesian springs were burnt and aquatic invertebrates sampled from the burnt and three unburnt springs. A single fire in late winter completely burnt the dominant vegetation, followed by recovery of Phragmites over the following 2 years. A single fire event did not deplete populations of endemic aquatic invertebrates in artesian springs, but probably did not substantially benefit these populations either. Isopods, amphipods, ostracods and three species of hydrobiid snail survived the fire event, and most had increased in number 1 month post fire but then returned to pre‐burnt numbers by 1 year post fire. Morphospecies richness of all identified invertebrates increased over time in all springs, but did not differ appreciably between burnt and unburnt springs. If burning artesian springs is to be adopted as a management tool to suppress the growth of Phragmites australis, we conclude that the endemic aquatic invertebrates will survive a single burn event, without negative effect to their populations.     

Garotenoids and colouration of poplar hawkmoth caterpillars (Laothoe populi)

Carotcnoids and chlorophylls a and b were extracted from final instar caterpillars of the poplar hawkmoth ( Laothoe populi ) and the eyed hawkmoth ( Smerinthus ocellata ), as well as from their food plants. Both species of caterpillar absorb the two chlorophylls and the carotenoids lutein, cis -lutein and β-carotene in the gut and deposit lutein and cis -lutein in the integument. It is the lutein, together with pterobilin, that is largely responsible for the colour of the insect: yellow-green poplar hawkmoth caterpillars have more lutein in the integument than dull green ones which in turn have more than white ones. Yellow-green and dull green caterpillars both sequester lutein and cis -lutein in the gut wall, but the yellow-greens translocate more of these pigments to the integument than the dull greens. The white caterpillars absorb very little lutein and cis -lutein into the gut, and so they have much less also in the integument. The mechanism by which the reflected light perceived by the caterpillar is translated into differential absorption of pigment by the gut and deposition in the integument is not known.     

Modelling the effect of feeding-related mortality on the feeding strategy of tsetse (Diptera: Glossinidae)

Abstract. Free-living haematophagous insects risk death through host grooming responses or through increased susceptibility to predation whenever they take a bloodmeal. In this paper we investigate the effects of these risks on the feeding strategy of tsetse. A model is presented that allows for death of tsetse by starvation if they do not succeed in feeding within a fixed time (set at 6 days in the first instance) and for mortality specifically associated with feeding. In addition there is background mortality that applies to all flies at all times.
The model is used to compute the individual life-time fertility (number of female puparia per female) as a function of the probability of obtaining a meal (indicated by field data to be very high, usually > 0.85 per day) and the day on which flies start to search for a meal. We suggest that the feeding strategy that would be selected for is that which allows the maximum reproductive output. The model shows that this strategy involves making no attempts to feed for 3–4 days after the previous meal and then attempting to feed with the greatest possible probability until a meal is obtained. The predicted feeding interval, obtained independently of any trapping data, agrees closely with all previous estimates from field studies using a variety of methods. Preliminary results from a laboratory experiment reveal an increased risk of predation of recently fed as compared with hungry tsetse. The lower the actual feeding mortality the more frequently will flies be able to feed should conditions so demand. It is adaptive, however, for tsetse to delay attempting to feed for as long as they can, which is made possible by the near certainty of locating and feeding on a host within 1 day, using their sophisticated sensory systems.     

New Culture Medium for Maintenance of Tsetse Tissues and Growth of Trypanosomatids*

SYNOPSIS. A new culture medium (SM), based on the amino-acid composition of tsetse hemolymph and containing fetal bovine serum, was designed for the maintenance of tsetse organs and the cultivation of various trypanosomatids. For optimum growth 20% (v/v) serum was required. The medium supported prolonged peristalsis of the alimentary tract and salivary glands of pre-emerged Glossina morsitans morsitans. In established cultures, derived from bloodstream forms of pleomorphic Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense strains, inocula of ～ 10⁶ procyclics/ml yielded 4–5 × 10⁷ organisms/ml after 4 or 5 days of incubation at 28 C. Bloodstream forms of a cloned monomorphic T. b. brucei strain were also able to transform into procyclics, which, however, multiplied at a lower rate, with maximum yields of ～ 2 × 10⁷ after 5 days. Cultures of Trypanosoma congolense and of a nearly monomorphic Trypanosoma brucei gambiense strains could be established in SM medium only in the presence of tsetse alimentary tract. The procyclic trypomastigotes of these species, adapted to SM medium and able to grow in it without Glossina organs, gave maximum populations of ～ 4.5 × 10⁷ cells/ml. Promastigotes of Leishmania donovani, cultivated routinely in a diphasic Table's medium, multiplied actively upon being transferred into SM medium, producing yields of ～ 4 × 10⁷ cells/ml.     

Analysis of the Antigenic Composition of Trypanosoma brucei brucei Bloodstream and Culture Forms by the Quantitative Direct Fluorescent Antibody Methods*

SYNOPSIS The quantitative direct fluorescent antibody (QDFA) methods were employed for the antigenic analysis of bloodstream forms and culture procyclics of 2 variants, TRUM (Trypanosome Research University of Massachusetts) 106 and TRUM 107, of Trypanosoma brucei brucei. Intact and trypsinized trypanosomes were studied. It was demonstrated that: (A) The specific variant antigens are localized in the surface coat of bloodstream trypomastigotes. (B) In addition to the common antigens shared by bloodstream forms and culture procyclics, there are also certain antigens unique to these latter stages. (C) Still another group of antigens. not found in the culture procyclics, appears to be shared by the bloodstream forms, irrespective of their variant-specific antigens. These antigens may be present in part in the coat or on the cell membrane and in part within the cytoplasm. (D) Irrespective of the bloodstream-form variant from which they are derived, the procyclics are antigenically the same. The QDFA results are analyzed statistically and discussed in the light of the available literature.     

Altitudinal distribution of several eucalypt species in relation to other environmental factors in southern New South Wales

Four problems associated with studying the altitudinal distribution of eucalypt species are examined: the lack of specific physiological relationship between altitude and plant growth, the influence of other environmental factors, the availability of suitable data and the need for statistical analysis. Presence/absence data for eucalypt species were obtained from several sources. Probability of occurrence in 100 m zones is determined for E. maculata, E. muellerana, E. fastigata, E. sieberi, E. dalrympleana and E. pauciflora. The influence of other factors is demonstrated for several species using direct gradient analysis. Aspect is important for E. fastigata and E. rossii in addition to altitude and rainfall. The statisical model used was the logit-linear model: log (p/I– p) = linear function of environmental variables where p is the expected probability of being present for a given combination of environmental variables. Two examples are presented. E. dalrympleana can be predicted from altitude, rainfall, radiation index (measure of aspect) and an interaction term between altitude and aspect. E. rossii presence is predicted by altitude, rainfall, radiation index and geology. Altitude is transformed into an estimate of mean annual temperature which is shown to clarify some overlaps of species distribution. It is concluded that use of data collected for other purposes can be used in a generalized linear model for presence data to show the complex correlations which exist between the altitudinal distribution of some eucalypts and other environmental factors.     

Studies on Physiology of Nodule Formation: VI. The influence of Bacterial Numbers in the Rhizosphere on Nodle Initiation

The direct examination of the relation between inoculum sizeand infection rate for the nodulation of a legume is difficultbecause of the rapid multiplication of the nodule bacteria inthe rhizosphere. This has been overcome by (i) using mixturesof normal (virulent) and mutant avirulent strains of clovernodule bacteria, the avirulent acting as a diluent of the virulent,and (2) by employing large original inocula to reduce multiplication.By these means the numbers of virulent clover bacteria weremaintained during an experiment at approximately predeterminedlevels. When a strain of lucerne nodule bacteria was used asdiluent the multiplication of clover nodule bacteria was notsuppressed. Nodule number was found to approach the maximum asymptoticallywith bacterial density; very few bacteria (of the order of 10)were required to give rise to a single nodule only on a plantduring an experiment, under conditions where the full nodulatingcapacity of a root is saturated by a total rhizosphere populationof the order of 10⁴ bacteria. This relationship supports theview that infection only takes place at discrete foci on theroot. A good fit of the experimental data was given by a compoundMitscherlich curve and by a combination of a normal and a modifiedMitscherlich equation. This latter model takes into accountthe multiplication of sites of infection which occurs in theearly seedling stage from foci not occupied at high dilutionof virulent bacteria. Multiplication of this kind has also beendemonstrated by delayed inoculation experiments. In the preliminary experiments it was found that comparablerhizosphere stimulation of bacterial growth took place in sandculture, water culture and agar culture and with plants of diversenodulating habit.