Cell-Cell Interactions and Distal Outgrowth in Amphibian Limbs

SYNOPSIS. A current model concerning the process of limb regenerationin vertebrates is examined. According to this model (Bryantet al, 1981), new positional values in the proximal-distal limbaxis are laid down as a result of local interactions betweencells in the limb circumference. Cells with disparate circumferentialpositional values come together at the site of future outgrowthand intercalation between them generates more distal levelsof the pattern. The results of a number of experiments on surgicallycreated symmetrical limb stumps are discussed in relation tothis model. In addition, an extension of this model to accountfor digit formation is presented, and the implications of thisformulation for limb evolution are discussed.     

The efficiency of pitfall trapping for polyphagous predatory Carabidae

ABSTRACT.

• 1 The efficiency of pitfall trapping was investigated for seven carabid species, using time-lapse video recording equipment, in the laboratory.
• 2 The effects of differing substrates, trap designs and seasons of collection on the capture rates of the carabids was also investigated.
• 3 Capture rate differed significantly between the species studied. The differences in capture rates between the species were unrelated to beetle size, speed of movement and diurnal behaviour.
• 4 Few differences arose in the capture rates when type of substrate or trap or season of capture were changed.

     

The effect of a foliar disease (rust) on the development of Gastrophysa viridula (Coleoptera: Chrysomelidae)

Abstract.

• 1 Gastrophysa viridula Degeer (Coleoptera: Chrysomelidae) and the pathogenic rust fungus Uromyces rumicis (Schum.) Wint. both occur on leaves of Rumex crispus L. and R.obtusifolius L. Individual stages of beetle development, and egg laying, were compared on healthy and infected leaves of each plant species in the laboratory. Oviposition choice was investigated in the field and laboratory.
• 2 Beetles reared on infected leaves of each species had greater larval mortality and slower development than those reared on healthy leaves. Although larvae feeding on infected leaves consumed up to 2.5 times more dry weight than those reared on healthy leaves, they had a lower relative growth rate and pupated at a lower weight. These changes were consistent with the reduced nutritive quality of rust-infected Rumex leaves.
• 3 Fecundity of beetles reared on infected leaves of both species was considerably reduced. Eggs laid by beetles feeding on infected R.crispus leaves also had a reduced viability.
• 4 The beetle developed consistently poorer on healthy R.crispus than on healthy R.obtusifolius throughout its life-cycle. Differences in larval performance were greater between host species than between infected and healthy leaves.
• 5 Oviposition was similar on infected and healthy R.crispus in both the laboratory and field. However, adults consumed less, and laid fewer eggs on infected than on healthy R.obtusifolius. The pattern of egg laying on different aged leaves was affected by rust infection: a greater proportion of eggs was laid on the older, infected leaves, than on the equivalent aged leaves on the healthy plants. Few larvae survived from eggs laid on rusted leaves in the field.

     

Ribulose-1,5-Diphosphate Carboxylase Protein during Flag Leaf Senescence

Ribulose-l,5-diphosphate (RuDP) carboxylase protein and activitywere determined in relation to net photosynthetic rate duringthe senescence of intact flag leaves of wheat on the plant.Initially the decrease in RuDP carboxylase activity was greaterthan the decline in net photosynthesis. The major decrease inRuDP carboxylase activity over this period resulted from a decreasein enzyme specific activity from 11 to 2 µmol CO₂ fixedh^–1 mg^–1 protein. Loss of RuDP carboxylase proteindid not occur until late in senescence by which time chlorophyllconcentration had decreased by more than 50%. Treatment of flagleaves at weekly intervals with either 1000 parts 10^–62-chloro-ethyltrimethylammonium chloride or 100 parts 10^–6gibberellic acid with 1 part 10^–6 kinetin did not significantlyaffect net photosynthetic rate, RuDP carboxylase protein oractivity during senescence.     

Ribulose 1, 5-Bisphosphate Carboxylase/Oxygenase Activity and Photorespiration during the Ageing of Flag Leaves of Wheat

Photosynthesis, photorespiration, and ribulose bisphosphatecarboxylase/oxygenase activities were measured in intact flagleaves of wheat during ageing. Photorespiration declined verylittle as the leaves aged, and much less than photosynthesis.These changes could not be explained by changes in the ribulosebisphosphate carboxylase to oxygenase ratio of fraction 1 protein.As the leaves grew older the enzyme activities in extracts ofleaves declined in parallel so the ratio remained constant.     

The Effects of Priming and Accelerated Ageing upon the Nucleic Acid Content of Leek Seeds and their Embryos

Using seed priming and accelerated ageing techniques, a singlelot of leek (Allium porrum) seeds was manipulated to producefour lots of seeds with different germination performance. Changesin content of the major nucleic acid species in whole seedsand embryos of two of these lots (primed and unprimed), weredetermined over the early stages of germination. The major effectof priming was an increased level of RNA species in the seedsand embryos, and this difference was maintained during germination.Comparison of nucleic acid levels in the dry seeds of thesetwo lots and two others (aged and aged then primed) indicatedthat there was no correlation with germination performance.Similar comparisons of the nucleic acid levels in the embryosof seeds imbibed for 1 d showed only a limited correlation betweenrRNA levels and germination performance. Analysis of these datasuggests that accelerated ageing has an adverse effect uponendosperm cells, which results in the degradation of their nucleicacids during priming. Furthermore, the viability of these agedseeds also falls during priming. The data also indicate thatratios of rRNA to DNA correlate with germination performanceof the four lots of seeds studied. It is proposed that sucha relationship is indicative of the efficiency of a primingtreatment, and may be useful in comparisons of naturally varyingseed lots. Key words: Leek, seed, germination, priming, nucleic acids     

Novel fungal disease in complex leaf‐cutting ant societies

Abstract 1. The leaf‐cutting ants practise an advanced system of mycophagy where they grow a fungus as a food source. As a consequence of parasite threats to their crops, they have evolved a system of morphological, behavioural, and chemical defences, particularly against fungal pathogens (mycopathogens). 2. Specific fungal diseases of the leaf‐cutting ants themselves have not been described, possibly because broad spectrum anti‐fungal defences against mycopathogens have reduced their susceptibility to entomopathogens. 3. Using morphological and molecular tools, the present study documents three rare infection events of Acromyrmex and Atta leaf‐cutting ants by Ophiocordyceps fungi, agenus of entomopathogens that is normally highly specific in its host choice. 4. As leaf‐cutting ants have been intensively studied, the absence of prior records of Ophiocordyceps suggests that these infections may be a novel event and that switching from one host to another is possible. To test the likelihood of this hypothesis, host switching was experimentally induced, and successfully achieved, among five distinct genera of ants, one of which was in a different sub‐family than the leaf‐cutter ants. 5. Given the substantial differences among the five host ants, the ability of Ophiocordyceps to shift between such distant hosts is remarkable; the results are discussed in the context of ant ecological immunology and fungal invasion strategies.     

Cladogenesis and endemism in Tanzanian mole‐rats,genus Fukomys: (Rodentia Bathyergidae): a role for tectonics?

African mole‐rats of the family Bathyergidae are subterranean hystricomorph rodents found throughout sub‐Saharan Africa, where the distributional ranges of the most speciose taxa are divided by the African Rift Valley. In particular, mole‐rats of the genera Heliophobius and Fukomys are distributed widely, and their adaptive radiation appears to have been strongly influenced by the geological process of rifting. As a result, virtually all members of the genus Fukomys occur in locations west of the Rift Valley. However, a small number of isolated populations occur east of the Rift Valley in Tanzania, where Heliophobius is widespread and is the predominant bathyergid rodent. Phylogenetic analysis of mitochondrial cytochrome b sequences of previously unstudied Tanzanian mole‐rats (genus Fukomys) and geographically adjacent populations strongly suggests that vicariance in the Western Rift Valley has subdivided populations of mole‐rats and, together with climatic changes, played a role in the isolation of extralimital populations of Fukomys in Tanzania. Together with molecular clock‐based estimates of divergence times, these results offer strong support for the hypothesis that the observed patterns of cladogenesis are consistent with tectonic activity in the ‘Mbeya triple junction’ and Rungwe volcanic province between Lakes Rukwa and Nyasa. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 337–352.     

Vertical stratification of feeding guilds and body size in beetle assemblages from an Australian tropical rainforest

Abstract The vertical stratification of insect species assemblages inhabiting tropical rainforests is well established but few have examined whether these patterns are reflected in vertical stratification of body size or feeding guilds. We used Malaise and Flight Interception Traps to sample beetle assemblages from five locations, at both canopy and ground zones of a tropical lowland rainforest site near Cape Tribulation, Australia. Beetles from 4 years of sampling were sorted to Family and morphospecies, and allocated to one of five feeding guilds. Within feeding guilds the number of species and individuals, from canopy‐ and ground‐caught traps were compared. The body lengths of species were measure and compared within feeding guilds and families. Herbivores was the dominant guild but was not the majority of all species or individuals. Most beetle species (69%) were less than 5 mm in length and the mean size of canopy‐caught species was greater than that for ground‐caught species. This was probably due to slightly more species of plant feeders (herbivores and xylophages) present in the canopy, which were significantly larger than saprophages, fungivores and predators. Among feeding guilds, there were few overall canopy–ground differences. These results contrast with species composition results presented elsewhere where strong differences between the canopy and the ground were evident. We suggest that our guild groupings may have been too coarse to detect fine‐scale differences and that resource partitioning may have also masked faunal stratification. We propose that fine‐scale differences in resources between the canopy and the ground, together with strong microclimate gradients, are likely to be important in structuring the vertical stratification of insect assemblages at the level of species, but not with respect to functional groups.