THE EVIDENCE OF REPRODUCTIVE MECHANISMS IN FOSSIL DASYCLADS (ALGAE: CHLOROPHYTA)

Dasyclads (members of Order Dasycladales: Algae, Chlorophyta) are reviewed for evidence of reproductive structures in the fossil state, and then compared with what is known of the reproductive processes in living examples. The effects of poor preservation in most of the fossils are shown to result in many uncertainties, and the resulting degree of interpretation required is emphasized. Selected genera of fossil dasyclads considered relevant to this problem are briefly analysed and discussed: Archaeobatophora (Ordovician), Kulikia (Carboniferous), Imperiella (Permian), Stichoporella (Jurassic) and Cympolia (Cretaceous to Recent). The pioneer views of J. Pia on dasyclad reproduction through geological time are seen to need much modification in the light of later work. The fundamental dasyclad nucleus-fragmentation-reproduction mechanism is believed to have operated within the great morphological variety of known dasyclads, giving rise to modification in genera where basic evolution was structural. In this way the variety of dasyclads can be seen to be the result of varied morphological evolution, often modified by the consistently simple basic reproductive mechanism.     

Enemy-free space and the feeding niche ofan aphid

1. The nymphs of the aphid Monaphis antennata occupy an unusual feeding niche, being restricted to the upper surfaces of leaves and petioles. The possibility that this is a predator-avoidance strategy was investigated.
2. Nymphs could be induced to feed on the under surfaces of petioles and the mortality of these nymphs was then compared with the mortality of nymphs feeding from the upper surfaces when exposed to coccinellid predators.
3. Coccinellid larvae spent less time foraging on the upper surfaces of leaves and petioles than on the under surfaces of leaves and petioles.
4. The nymphs occupying the upper surfaces of petioles, the normal feeding position, were encountered by the coccinellids later and less often, and fewer were attacked compared with those occupying the under surfaces.
5. It is concluded that the feeding niche of the nymphs of this aphid is adaptive in that it reduces exposure to foraging predators and is the result of selection to occupy enemy-free space.     

A Micro-electrode Fast Data Capture Technique: Its Use to Examine Plant Cell Electrophysiology in the Wheat Root

Perturbations in the local electric field sensed during thepassage of a micro-electrode through cellular tissue cannotbe recorded with a conventional chart recorder because the responsetime is far too slow. This was overcome by using a micro-computerto record the rapid changes in electrical potential difference(PD). Transient PDs were rapidly collected and digitized, storeddigitally, and replayed in analog at a slower speed afterwards.Some ‘control’ experiments to verify the speed ofthe data acquisition system and demonstrate the absence of quantitativeartefacts in this procedure were performed. We have used thissystem to investigate cell PDs in the roots of wheat seedlings.Certain abrupt transients clearly represented the boundariesof the cells; this enabled further interpretation of individualcell PDs. Cyanide addition resulted in a major change in thetransients within a minute, with a smaller component of thecell PD, interpreted as the diffusion potential, remaining.Ethanol treatment gave a predictable loss of membrane integrity,seen as discharging membrane PDs. The value of this new useof a digital data system is discussed. Key words: Boundary layers, trans-root potential, tonoplast PD, cyanide effects, ethanol effects     

Pharmacological observations on body fluids from the milkweed bug,Oncopeltus fasciatus (Dallas) (Heteroptera: Lygaeidae)

A report is given on the pharmacological activity of body fluids from milkweed bugs maintained on a diet of sunflower seeds, together with observations on the toxin accumulating system of the adult insect.     

Optimal Foraging in Hummingbirds: Testing the Marginal Value Theorem

To a hummingbird, clusters of flowers on inflorescences representpatches and provide an ideal situation to test prediction ofoptimal patch-use. The basic question is what decision ruleshould a hummingbird use to decide whether or not to leave aninflorescence? The hypothesis is that hummingbirds will adoptthe decision rule that maximizes their net rate of energy gainwhile foraging. This hypothesis leads to an analogue of Charnov'smarginal value theorem which determines an optimal decisionrule. The optimal decision ruleis then used to predict aspectsof the hummingbirds' foraging, and these predictions are comparedwith field data The optimal decision rule is a function of how much informationis used by the hummingbirds. Data indicate that a decision toleave an inflorescence is a function of the number of flowersvisited, the number of flowers available on the inflorescence,and the amount of nectar obtained at the last flower. The optimaldecision rule was calculated assuming no additional informationis used.     

Relationship between nectar production and seasonal patterns of density and nesting of resident honeyeaters in heathland near Sydney

Some individual honeyeaters were repeatedly seen near the same location over at least a 2 day period and were considered resident in the present study. Such resident honeyeaters (mostly New Holland and White-cheeked Honeyeaters) were present on the heathland study areas from about February until about October. Production of nectar energy is negligible prior to April and low after October. It is hypothesized that the density of residents is determined by their ability to obtain energy in nearby habitats while establishing nesting sites in the heathland in February and March. Nesting tended to occur between April and July when there was sufficient production of nectar-energy.     

Burrows, surface movement, and swimming of Tachyoryctes splendens (Rodentia: Rhizomyidae) during flood conditions in Kenya

The effect of flooding on the behaviour of most mammals has not been studied, even though in tropical areas there are well delineated wet and dry seasons which produce flood conditions on a regular basis. Fossorial mammals can be expected to be particularly vulnerable to flooding because of the absolute dependence on a sub-surface existence and poor climbing ability.
Behaviour of the East-African mole-rat, Tachyoryctes splendens , was studied under flood conditions and compared with published field work conducted under non-flood conditions. Four completely excavated burrow systems were obviously abbreviated (2–9 m in length), although the nest area did not appear to be affected. Live-trapped animals released on the surface travelled as far as 80 m before attempting to dig; surface speed was generally slow (7 m/min). Animals generally (83% of the trials) excavated towards the increase in slope on the study area; total digging time before closure of the tunnel ranged from 7–49 min. In swimming trials, animals were not hesitant to enter water but swimming endurance was short (range 115-550s).
Flooding may be a very disruptive but not an entirely negative aspect of the biology of Tachyoryctes. Dispersal may be instigated and even assisted by providing surface routes over edaphic barriers and moist soils which are readily workable.     

Pollination ecology of Christmas Bells (Blandfordia nobilis Sm.): Effects of adding artificial nectar on pollen removal and seed-set

Addition of artificial nectar to Blandfordia nobilis plants increased fruit set in plants treated in December but had no apparent effect on either fruit set for plants treated in January or the amount of pollen removed per plant for either the December or January plants. Increased nectar production would therefore have conferred no apparent reproductive advantage to a plant flowering in January and would have been advantageous to a December flowering plant only in terms of reproduction as a female, and not in terms of male reproduction.