Influence of fire severity on the regeneration,recruitment and distribution of eucalypts in the Cotter River Catchment,Australian Capital Territory

Abstract Plant responses to fire are variable between and within species and are influenced by numerous factors including fire severity. This study investigated the effects of fire severity on the regeneration and recruitment of forest eucalypts in the Cotter River Catchment, Australian Capital Territory (ACT). This study also examined the potential for the obligate seeder Eucalyptus delegatensis R.T. Baker (Myrtaceae) to expand into adjacent stands dominated by the facultative resprouter Eucalyptus fastigata H. Deane & Maiden (Myrtaceae) by seed shed and seedling establishment beyond the pre‐fire boundary. Sites were located in areas of either higher or lower fire severity, and transects were placed across the boundary of stands of E. delegatensis and E. fastigata. Species distributions, tree survival and seedling densities and heights were recorded, and the location of each boundary was determined as the region of maximum change in species composition along the transects. Eucalyptus delegatensis was the only eucalypt killed by higher severity fire. However, E. delegatensis seedling density was greater at higher severity sites than lower severity sites. Eucalyptus fastigata seedling density was low across all sites, with other eucalypts producing few, if any, seedlings. There was no evidence that E. delegatensis had increased its range into downslope stands dominated by E. fastigata. Patterns of vegetative recovery and seedling recruitment may be related to a number of factors, including differences in allocation patterns between seeders and sprouters, and the effects of overstory and understory competition. It is unclear what processes impede E. delegatensis seedling establishment beyond the stand boundary, but may involve an inability of E. delegatensis to shed seed sufficiently far downslope; unsuitable conditions for germination beyond the boundary; or, competition from a retained or resprouting overstory, despite the potential for increased dispersal distance soon after fire.     

Factors affecting aphid acquisition and transmission of soybean mosaic virus

Myzus persicae transmitted soybean mosaic virus (SMV) most efficiently following 30 or 60 s acquisition probes on infected plants. There were no differences in susceptibility to SMV infection of soybean plants 1 to 12 wk old, but symptoms were more severe in plants inoculated when young than when old. Soybeans inoculated between developmental stages R3 and R6 only showed yellowish-brown blotching on one or more leaves. There were no observable differences in the time of appearance or type of symptoms shown by soybean seedlings inoculated either by sap or by aphids; infected plants became acquisition hosts for aphids 5–6 days after inoculation. There was no change in the efficiency with which M. persicae transmitted SMV from source plants up to 18 wk after inoculation. M. persicae transmitted SMV from leaves of field-grown soybeans when plants were inoculated at developmental stages V6, R2, and R3 and tested as sources 57–74 days after inoculation but not from plants inoculated at R5 and tested as sources 14 to 32 days after inoculation. M. persicae acquired SMV from soybean buds, flowers, green bean pods, and unifoliolate, trifoliolate, and senescent leaves. Middle-aged and deformed leaves were better sources of the virus than buds, unfolding and old symptomless leaves. The results are being incorporated into a computer model of SMV epidemiology.     

Observations on the ephippia of certain maerothricid cladocerans

Ephippia of four maerothricid cladocerans are described, that of Opbryoxus gracilis (perhaps the most primitive anomopod ephippium) for the first time. All are attached to substrata, but each in a different way, in a manner that must inhibit rather than encourage dispersal. Notwithstanding the drought-resistant properties of the eggs of at least two of these species, it has evidently been a more successful evolutionary stratagem to ensure continuity of an already established colony than to face the hazards of dispersal in the dried condition. Although proven only for Streblocerus serricaudatus it is almost certain that drying of the resting eggs is not obligatory before hatching for any of these species. Hatching of the resting eggs of S. serricaudatus and Acantholeberis curvirostris is described.     

Evolutionary genetics of ruminant lysozymes

Comparative studies of mammalian lysozymes and their genes have contributed to knowledge of how new functions arise during evolution. The recruitment of lysozymes for functioning in the stomach fluid of ruminants has occurred in response to selection pressures that are partly known and on a time-scale that is known. A semiquantitative analysis of adaptive evolution is thus made possible by the ruminant lysozyme system. Large-scale production of lysozyme by the stomach lining entailed gene duplication as well as a change in gene expression. Remoulding of the lysozyme for working and lasting in the stomach fluid involved accelerated amino acid replacements, which may have been facilitated by intergenic recombination. The possibility that multigene families can accelerate adaptive evolution, by virtue of their capacity for bringing together functionally coupled substitutions, receives emphasis in this review.     

Discussion of the Reptilian Ear

Evidence presented at this symposium lends support to the conceptthat the reptilian auditory apparatus shows major modificationswhich correlate with large taxonomic groups, and that lesseranatomical differences suggestive of adaptive change can beseen at subfamilial levels. Structures concerned with transmission,reception, and dampening of sonic vibratory energy are mostfrequently involved in modifications noted; thus, anatomicaldifferences may account for diverse results of acoustic testingin reptiles. Preliminary investigation of the histology andcytology of certain features of the reptilian cochlear ductindicates considerable specialization at the cellular leveland the need for continuing anatomical and physiological study.     

FURTHER STUDIES ON QUANTITATIVE METHODS WITH TWO PLANT VIRUSES

The arrangement of experiments for intercomparison of a number of virus samples is discussed and the use of randomised blocks or Latin squares, combined in certain cases with half-leaf comparisons between all samples or against a standard, is recommended.
Improvements in the ground-glass spatula method of inoculation have been suggested.
Provided there is sufficient inoculum to cover the leaf when the spatula is rubbed over it, the amount, of inoculum makes no difference to the number of lesions produced.
The conditions to which test plants are subjected shortly before inoculation were found to influence the number of lesions produced by a given inoculum.
The number of lesions produced by otherwise similar inocula is influenced by their pH value and electrolyte content. The optimum pH . range for the virus of tomato spotted wilt is very limited (roughly pH 6.0–8.5). Tobacco mosaic virus in a potassium phosphate buffer at a pH value about 7 produced the maximum number of lesions in the concentration range 0.05-0.2 M . It is recommended that for most quantitative work viruses should be buffered at a definite pH value.
When effects due to varying pH value and electrolyte content were excluded, the virus of tomato spotted wilt was still found to be inactivated by certain oxidising agents and preserved by certain reducing agents.     

The anatomical basis of sexual dichromatism in non-iridescent ultraviolet-blue structural coloration of feathers

Despite extensive research on the evolution of avian dichromatism, the anatomical bases for differences between the sexes in species with structurally coloured plumage remain largely unknown. Using full‐spectrum spectrometry and transmission electron microscopy, we compared the colour and morphology of rump feathers of male and female eastern bluebirds (Sialia sialis). The ultraviolet (UV)‐blue feather colour in this species is caused by coherent scattering of light within the medullary ‘spongy layer’ of feather barbs. This spongy layer lies beneath a keratin cortex and on top of a layer of melanin granules that surround a hollow central vacuole. Irregularly shaped electron‐dense regions are present within the cortex. Male and female S. sialis differed substantially in their plumage colour and feather structure. A backwards logistic regression predicted sex with 100% accuracy using the colour variables brightness, UV‐violet (UV‐V) chroma and spectral saturation. A second backwards logistical regression predicted sex with 100% accuracy using relative cortex area and size of air spaces. Thus, S. sialis are dimorphic both in colour and in the structures causing this colour. Multiple regression analyses using data pooled from both sexes indicated that multiple features of feather barb structure contributed to colour variation in complex ways. Brightness was negatively related to the relative surface area of cortex in barb cross‐sections. Hue was positively related and UV‐V chroma was negatively related to the distance between scattering elements (i.e. keratin rods and air spaces) in the spongy layer. In contrast, hue was negatively related and UV‐V chroma was positively related to the thickness of the spongy layer. UV‐V chroma was also negatively related to the relative area of electron‐dense regions in the cortex. Spectral saturation was negatively related to the distance between scatterers and the standard error of the size of air spaces. These results suggest that the dimensions of spongy‐layer elements are critical to colour production, but that UV‐blue coloration can also be modified by the cortex and the thickness of the spongy layer. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 259–271.