Seasonal decline in plant defence is associated with relaxed offensive oviposition behaviour in the viburnum leaf beetle Pyrrhalta viburni

1. Plant defence of Viburnum shrubs against oviposition by its specialist herbivore, the viburnum leaf beetle [VLB Pyrrhalta viburni(Paykull)], involves an egg‐crushing wound response in twigs. Although the response is variable among Viburnum species, it can have a strong impact on egg survivorship. Beetles typically aggregate egg masses with conspecifics along infested twigs, forming clusters that can overwhelm the twig response. It was investigated whether twig responses and beetle oviposition behaviour vary seasonally. 2. In a field experiment, twig defences decreased towards the end of the VLB oviposition period: wound response of the North American Viburnum dentatum L. and the European V. opulus L. was reduced by 100% and 54%, respectively, in September compared with the July to August period. 3. Oviposition trials demonstrated a corresponding behavioural change: VLB females displayed aggregative oviposition in August, but not in September. 4. Further tests revealed that late‐season VLB females reverted to aggregative oviposition after being kept on uninfested twigs, whereas females kept on heavily infested twigs did not. This behavioural change suggests that relaxation of aggregative oviposition originates from cues associated with high densities of egg masses. 5. Relaxation of aggregative oviposition may be adaptive (and beneficial for invasion) on shrubs with low levels of defences by reducing intra‐specific competition.     

Evaluating Residual Tree Patches as Stepping Stones and Short-Term Refugia for Red-Legged Frogs

Abstract: Temperate pond-breeding amphibians are vulnerable to forest fragmentation because they must access upland terrestrial sites during the nonbreeding season but are prone to desiccation in hot, dry environments without canopy cover. Harvesting techniques that retain live trees in the cut block are advocated for sustaining forest biodiversity, but the effects of these practices on amphibians are unknown. We studied red-legged frogs (Rana aurora) in movement trials to assess: 1) how short-term use of residual trees was affected by tree patch size, streams, and neighborhood features; 2) whether residual tree patches were used as stepping stones in negotiating cut blocks; 3) the effects of patch size and patch proximity in altering movement paths; and 4) the effects of retention level and patch size on interpatch distance. Residual tree patches were potentially valuable short-term refugia but their value was size dependent. Virtually all frogs released at the base of single trees or inside small tree clusters left within 72 hours, but the proportion leaving decreased curvilinearly with increasing patch size. Frogs were less likely to leave tree patches with a running stream or where neighborhood stream density was high. Residual tree patches did not systematically alter movement paths. Frogs intercepted residual tree patches mostly at random and had to be within 5-20 m of a tree patch before moving to it in greater proportions than expected by chance. However, amphibian movements were biased toward large (0.8 ha) patches and away from small (0.3 ha) patches 50 m away. Our results indicated that residual trees should not be retained singly but should be aggregated in groups between 0.8 ha and 1.5 ha, preferably in stream locations.     

Ovine lymphocyte antigens: a comparison of Australian and European antisera

Lymphocyte alloantigens were determined in 183 Australian merino sheep, using antisera from Australian and European laboratories. The study had two aims: (1) to compare reagents characterized in the different laboratories and to correlate antigen definition; and (2) to define lymphocyte antigens for use as genetic markers in two flocks of sheep which had been selectively bred for resistance or susceptibility to the intestinal parasite Trichostrongylus colubriformis, in order to extend a previous study which had indicated linkage between resistance to the parasite and the sheep major histocompatibility system. Good or excellent correspondence was found between four Australian and four European specificities and it was concluded that continued international collaboration would allow definition of markers for future genetic or disease susceptibility studies.     

DISAPPEARANCE OF NITRATE REDUCTASE ACTIVITY FROM CHLAMYDOMONAS REINHARDI

Nitrate reductase activity was induced in Chlamydomonas reinhardi following addition of nitrate. Enzymic activity was assayed in cell-free supernatants and in whole cells whose permeability had been increased by freezing. Nitrate reductase activity in cells decreased rapidly when CO₂-fixation was prevented by (a) darkening cultures, (b) aerating cultures with CO₂-free air, or (c) addition of DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea). A smaller loss of nitrate reductase activity from darkened cells occurred when (a) acetate-adapted cells were supplied with acetate, or (b) cells were allowed to accumulate carbon reserves by nitrogen starvation before darkening. It was concluded that maintenance of nitrate reductase activity was dependent upon the availability of a suitable carbon source.     

Representation of Landcover Along Breeding Bird Survey Routes in the Northern Plains

ABSTRACT The North American Breeding Bird Survey (BBS) is used extensively to make inferences about populations of many North American bird species and is increasingly being used for avian conservation planning. How well BBS routes represent the landscape is poorly known, even though accuracy of representation could significantly affect inferences made from BBS data. We used digital landcover data to examine how well landcover within 400-m buffers around BBS routes represented the surrounding landscape (the route neighborhood) for 52 routes in the Prairie Pothole Region of North Dakota and South Dakota. Differences in composition between landcover along BBS routes and the route neighborhood were not statistically significant for upland cover classes. The area of temporary and seasonal wetland basins was accurately represented by BBS routes in our study area, but the area of semipermanent and permanent wetland basins was significantly underrepresented along BBS routes. Number of wetland basins and upland patches was higher along routes. Area of urban, forest, and hay landcover classes was higher along routes, although differences were not statistically significant. Amount of bias in landcover representation was negatively correlated with the proportion of each landcover type in the study area, but bias was not correlated with area of the route neighborhoods. Differences between landcover along BBS routes and the route neighborhood were primarily attributable to increased anthropogenic activity along roads and siting of roads away from relatively large, deep water bodies. Our results suggest that inferences made from BBS data in our study region are likely biased for species that are associated with deeper-water habitats or are strongly influenced by landscape fragmentation. Inferences made from BBS data for species associated with uplands or shallow wetlands are less likely to be biased because of differences in landcover composition.