Search orientation of Musca domestica in patches of sucrose drops

ABSTRACT. The searching tactics of the housefly, Musca dormestica L. (Diptera: Muscidae), have been delineated from digitized pathways of flies walking in patches of sucrose drops arranged in linear (ROW) and hexagonal (HEX) arrays. The areas covered by flies in ROW and HEX patches are distinctly different, but flies seem not to employ different tactics for the two types of resource arrays. The number of drops located, if at least one drop is found, does not differ between ROW and HEX. Most quantitative measures of local search remain constant after the first interdrop interval, although feeding time decreases as flies sample successive drops. Local search intensifies after each drop is ingested, with locomotory rate decreasing and turning rate increasing, followed by decay of both measures toward ranging levels. Searching can be characterized by two movement tendencies resulting from specific, definable, locomotory functions: a forward-moving tendency is expressed by the fly as it leaves a resource in approximately the same direction as it arrives; and local search is characterized by looping, rather than straight walking, with a variable turning rate that generates a rough ‘zigzag’ superimposed on looping. The two movement tendencies, combined, allow flies to locate resources in a linear arrangement, because of the forward-moving tendency, and to locate resources not arranged in a linear array because of the ‘noisy’ loop. M. domestica does not appear to retain and use information gained from one patch of drops in another, so the search tactic of the fly seems therefore to be a compromise between straight movement and circular movement that may be adaptive for an environment subject to frequent changes in the spatial distribution of resources. Giving-up-time, the period between ingesting the last drop and leaving the patch, is a function of the rate of change in the transition from local search to ranging, which is constant in our experiments. If a fly does not encounter another drop while ranging, during which it walks relatively straight, the fly moves out of and away from the patch.     

Observations on the intensity of diapause and cold tolerance in larvae from twelve populations and two reciprocal crosses of the Indian meal moth, Plodia interpunctella

ABSTRACT. The duration of diapause in larvae of Plodia interpunctella (Hübner) (Lepidoptera, Pyralidae) was assessed at 20°C in LD 11:13. Mean times from hatch to pupation for diapausing larvae from different populations ranged from 88 to 236 days. Most non-diapausing larvae pupated within 70 days at this temperature. Transferring diapausing larvae to 25°C and LD 9:15, or to 20°C and LD 15:9, 70 days after hatch reduced the subsequent mean time to pupation by 18–82% and 9–63% respectively. Only two population samples terminated diapause faster under LD 15:9 at 20°C than under LD 9:15 at 25°C. The mortality of diapausing larvae caused by 6- or 10-week exposures at 5, 7.5 or 10°C was generally less than 25%. Hybrids produced from a reciprocal cross between a temperate and a tropical African stock survived well. For other stocks there was some correlation between survival and diapause intensity. The low temperature regime which resulted in the greatest shortening of pupation time after return to the conditions used to induce diapause, did not always coincide with the temperature permitting the best survival. Results, however, indicate that some individuals of all stocks but one from the tropics are likely to survive in the U.K.     

The Vascular Pattern of Italian Ryegrass (Lolium multiflorum Lam.): 3. The Leaf Trace System, and Tiller Insertion, in the Adult

The leaf trace system in the region of congested internodesat the base of Lolium multiflorum is described. A typical major trace in a leaf consists of a collateral bundlehaving a double bundle sheath and incorporating a certain amountof sclerenchyma. As such a leaf trace is followed down intothe stem it increases in diameter, loses the inner (mestome)bundle sheath, and the xylem becomes associated with xylem transfercells. Lower down, the bundle diameter is reduced although nowit has become amphivasal. The internal xylem only is still associatedwith transfer cells. The proximal portions of the bundle aremuch reduced, transfer cells, mestome sheath, and sclerenchymaare lacking and the now insignificant bundle merges with a lowerleaf trace or some other vascular tissue. Such a bundle in thestem may be in direct contact via bridges with other leaf traces,with the nodal plexus, and with the peripheral plexus that surroundsthe inner leaf trace system. In the base of a typical young plant, approximately one-halfof all leaf traces, including all the median veins, join bundlesfrom the next oldest leaf. Approximately one-third join thenodal plexus, and the remainder variously join bundles fromthe same or next but one oldest leaf to join the peripheralplexus. The differentiation of tiller insertions into the pre-existingmain stem system is highly variable. In a very young tillera number of traces were seen to terminate before the main systemwas reached suggesting basipetal differentiation. The actualconnections made by the tiller traces may occur with any nearbyleaf trace, the nodal plexus, or with the peripheral plexus.Later differentiating leaf traces in a tiller join leaf tracesof the tiller itself. Occasional bundles from secondary tillers by-pass the vasculartissue of the primary tiller to join directly with that of theparent plant. Vascular connections between parent and tiller,although very variable, appear to be totally comprehensive froma functional standpoint.     

The potential role of waterbirds in dispersing invertebrates and plants in arid Australia

1. The role of waterbirds as vectors of plants and invertebrates within and between arid‐zone wetlands is poorly understood. We present the first detailed study of passive dispersal by nomadic birds in Australasia. We investigated the numbers and types of invertebrate and plant propagules within freshly collected faecal samples as well as their viability. We compared dispersal among Grey Teal (Anas gracilis), Eurasian Coot (Fulica atra) and Black Swan (Cygnus atratus) in the Macquarie Marshes, a complex of temporary to semi‐permanent wetlands in New South Wales. 2. When faecal samples (n = 60) were inundated in the laboratory and monitored over 3 weeks, ciliates (75% of samples), nematodes (22%), ostracods (13%) and rotifers (5%) were recorded, with higher taxon richness in coot samples. Faecal samples (n = 71) were also sieved to quantify intact propagules, and ostracod eggs (70% of samples), large branchiopod eggs (31%) and bryozoan statoblasts (31%) were the most abundant invertebrates. Diaspores of 19 plant taxa were recorded, 14 of which were germinated in the laboratory or shown to be viable at the end of germination trials. The abundance and diversity of invertebrate propagules was highest in coot samples, whereas the abundance and diversity of diaspores was highest in teal samples. 3. One Australian Pelican (Pelecanus conspicillatus) sample was obtained and found to contain more taxa and far more propagules than any sample from other waterbirds, suggesting that piscivorous birds might have an important role in the indirect dispersal of propagules ingested by fish. 4. Our results support a role for birds in explaining the distributions of cosmopolitan plant genera such as Lemna, Typha, Myriophyllum and Nitella. The alien plants Ranunculus sceleratus, Medicago polymorpha and Polygonum arenastrum were recorded, demonstrating the potential role of waterfowl in the spread of exotic species. As the frequency and duration of flooding of arid‐zone wetlands decreases owing to human activities, the importance of waterbirds in facilitating recolonisation of temporary wetlands is likely to increase.     

Frequencies of plasma protease inhibitor alleles in Australian horse breeds and the recognition of two new alleles

Investigation of the plasma protease inhibitor system (Pi) in the Arabian and quarter horse breeds and re-examination of the standardbred breed resulted in the recognition of two new Pi alleles, designated E and L2. PiE is rare and has been found in only three quarter horses. In contrast, PiL2 is relatively common in the standardbred (0.107) and allowed subdivision of PiL into PiL and PiL2. Splitting of PiL resulted in an exclusion probability (PE) of 0.649 for the standardbred Pi system. Frequencies of the Pi genes have now been determined for four breeds (thoroughbred, standardbred, quarter horse and Arabian) of horses in Australia.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.     

Ultrastructural Aspects of Sporogenesis in a Fern, Pteridium aquilinum (L.) Kuhn

The meiotic process of sporogenesis in Pteridium is accompaniedby a regular cycle of ultrastructural events. These includethe dedifferentiation and redifferentiation of organelles, andthe elimination and restoration of ribosomes. Although similarin nature to corresponding stages in other land plants, sporogenesisin Pteridium provides several unique features. During prophase the plastids pass through a stage during whichno envelope can be resolved at the periphery of the stroma.They appear to survive this period and there is no evidencethat plastid lineage is broken from primary archesporium tospore. The plastid cycle is accompanied by the presence of theiron-protein complex phytoferritin. The repopulation of the spore cytoplasm with ribosomes, followingthe prophase elimination, is achieved through the agency ofnucleoloid-like bodies. These bodies, however, are not synthesizedwithin the nucleus, but form within membrane-bound regions ofthe early prophase cytoplasm. Prophase is also characterized by the development of nuclearvacuoles, expansions of the perinuclear space, which progressivelyramify through the karyoplasm prior to the dissolution of thenuclear envelope at metaphase I. The significance of these events, their similarities with, anddifferences from, comparable stages of meiosis in other plantsare discussed. Pteridium aquilinum (L.) Kuhn, bracken, meiosis, sporogenesis