Temperature and prey capture: opposite relationships in two predator taxa

Abstract 1. All other things equal, predator capture rates are expected to depend on encounter rate with prey, prey escape capability (including prey defences), and on predator agility. Ectotherm predators and their prey both respond to increasing temperature by increased activity, i.e. predators increase their search area and prey may enhance their escape capability. This means that, as temperature changes, the ability of a predator to catch prey will decrease, increase, or remain unchanged depending on the relative effect of temperature on predator and prey. Their responses may further be differentially moulded by light conditions depending on whether the predator is diurnally or nocturnally active. It was hypothesised that flying Diptera are vulnerable to carabid beetles only at low temperatures and over the full temperature range for spiders because carabids, in contrast to spiders, are not built to catch swiftly moving prey. 2. The first experiment examined the spontaneous locomotor activity of the predators and of fruit flies at different temperatures (5, 10, 15, 20, 25, and 30 °C) and light conditions (light, dark). A second experiment examined the effect of temperature and light on the predation rate of two carabid beetles (Pterostichus versicolor and Calathus fuscipes) and two spiders (Clubiona phragmitis and Pardosa prativaga) using fruit flies (Drosophila melanogaster) as prey. 3. All four predators and the fruit fly increased their locomotory activity at higher temperatures. Activity of the carabid beetles peaked at intermediate temperatures; spiders and fruit flies were most active at the highest temperatures. Predation rate of the spiders increased with temperature whereas the beetles caught flies only at low temperatures (5 and 10 °C). 4. Diurnal variation in temperature may bring different prey groups within the set of potential prey at different times of the day or at different seasons. The ability of many carabid beetles to forage at low temperatures may have nutritional benefits and increases the diversity of interactions in terrestrial food webs.     

Evidence for mate‐encounter Allee effect in an invasive longhorn beetle (Coleoptera: Cerambycidae)

1. Limited empirical support is available for mate‐encounter Allee effects in invasive insects due to the logistical challenges of studying demographic trends in low‐density populations. 2. Traps baited with pheromone and spruce volatiles were used to monitor the abundance of female Tetropium fuscum F. (Coleoptera: Cerambycidae) at multiple sites in Nova Scotia in 2011 and 2012. Each female was dissected to determine the presence or absence of sperm in its spermatheca (mated or virgin female, respectively). 3. Both male and total T. fuscum abundance declined with increasing distance to the focal point of T. fuscum's invasion. Female mating probability declined with male abundance and with distance from the invasion focus, and mating probabilities were very low at the most peripheral sites. Difficulty in encountering mates may thus contribute to limiting the spread of T. fuscum. 4. The approach outlined here could be integrated into existing surveys of wood borers using traps baited with semiochemicals to improve our understanding of the role of the mate‐encounter Allee effect in invasion dynamics.     

A late Quaternary phylogeography for Metrosideros (Myrtaceae) in New Zealand inferred from chloroplast DNA haplotypes

Because of its remoteness and mid-latitude position, New Zealand lacks access to the tropical climates that might have ensured straightforward survival for frost-sensitive species during glacial times. Nevertheless, the New Zealand lowland flora retains a substantial complement of plants sourced in the tropics. While there have been extinction pulses for elements of the frost-sensitive flora under glacial/stadial regimes, the surviving remnants have been able to recolonize large areas of habitat during successive warm climate periods. Refugia for such species in stadial New Zealand are likely to have been localized and ecologically suboptimal. To examine these relationships we have applied chloroplast DNA sequence data to the investigation of phylogeographical pattern for five endemic species of Metrosideros subg. Metrosideros , a wide-ranging group of mostly frost-sensitive woody plants in New Zealand. The results of this research verify the location of two generally mooted stadial refugia for the country and provide support for the existence of a third. A simple pattern of chloroplast haplotype diversity was recorded in extra-refugial areas, compared with a greater complexity in the vicinity of the identified refugia. This pattern was independently repeated in both main islands. The proposed refugia correspond to contemporary localities of high average winter temperatures. The sharing of chloroplast haplotypes between the different species of Metrosideros examined suggests that there has been a history of repeated hybridization and introgression for these plants, possibly initiated by periods of refugial confinement.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 399–412.     

The Effects of Cyclophosphamide on Alkaline Phosphatase Activity and on in vitro Post-Implantation Murine Blastocyst Development†

Cyclophosphamide, administered in doses of 20 and 40 mg/kg body weight to pregnant inbred CBA mice on the third day of gestation (60 h after the estimated time of ovulation) reduced the activity of non-specific alkaline phosphatase (E.C. 3.1.3.1.) in 84 h-old blastocysts in a dose-related fashion compared with controls (p < 0.02 in each case; comparison of groups by Kruskal Wallis analysis of variance). This effect was not demonstrated with 4 mg/kg body weight (p < 0.1). Forty mg/kg body weight, but not the lower doses of cyclophosphamide, significantly retarded the hatching of embryos from the zona pellucida, attachment to the culture dish, and the formation of trophoblast outgrowths when the blastocysts were subsequently cultured in vitro for 120 h. The growth of an expanded inner cell mass was impaired in the 20 and 40 mg/kg groups. The differentiation of the inner cell mass into endoderm and ectoderm was significantly affected in the 4 mg, 20 mg and 40 mg/kg groups (p < 0.05, p < 0.01 and p < 0.001 respectively). The possible relationships of these various findings are discussed in the text. These results suggest that alkaline phosphatase may be a useful indicator of impaired growth and differentiation of the inner cell mass after exposure of preimplantation embryos to teratogens.     

Panicle Differentiation and Spikelet Number Related to Size of Panicle in Pennisetum americanum

The size of the developing panicle of pearl millet (Pennisetumamericanum (L.) Leeke) was studied during panicle differentiation(from panicle initiation to the completion of spikelet production)in plants grown in pots or in the field and supplied with varyinglevels of nitrogen. The duration of panicle differentiationrequired a constant thermal time (day degrees) under all nitrogensupplies. However, the rate of growth of the developing panicleduring this phase was retarded by low nitrogen supply. Duringpanicle differentiation, it appeared that the developing paniclehad to reach a critical size before developmental events suchas the initiation of spikelet primordia commenced; timing ofdevelopmental events was related to the size of the developingpanicle. The number of spikelets produced depended on the rate of growthof the differentiating panicle and the duration of the phaseof spikelet initiation (from appearance of the first spikeletprimordium to completion of spikelet differentiation). Low nitrogensupply reduced the number of spikelets produced, by retardingthe rate of growth of the differentiating panicle; this delayedthe time to initiation of spikelets and thereby reduced theduration of spikelet initiation. All spikelets (irrespectiveof nitrogen supply on the mainstem and on tillers) occupiedthe same area of panicle surface at the completion of differentiationof the panicle and at anthesis. Key words: Millet, Panicle differentiation, Spikelet number     

Mitochondrial Interaction with Helminthosporium maydis Race T Toxin: Blocking by Dicyclohexylcarbodiimide

Treatment of mitochondria isolated from Texas male sterile cytoplasmcorn (T mitochondria) with high concentrations of dicyclohexylcarbodiimide(DCCD) (140 nmol DCCD mg^–1 mitochondrial protein) completelyand immediately inhibited T mitochondrial swelling by Helminthosporiummaydis Race T toxin (HmT toxin). In order to obtain a specificinteraction between DCCD and the ATPase complex T mitochondriawere incubated with lower DCCD concentrations (1–5 nmolDCCD mg^–1 mitochondrial protein) for up to 8 h at 4 °C.After 8 h incubation in the presence of 3.75 nmol DCCD mg^–1mitochondrial protein, toxin-induced swelling was decreasedby 69%. Specificity of DCCD action upon the ATPase complex wasconfirmed by (1) SDS gel electrophoresis and fluorographic analysesof proteins from [¹⁴C]-DCCD-treated T mitochondria and immunoprecipitatesand (2) physiological experiments showing that DCCD exertednone of its other documented effects. These data suggest thatHmT toxin interacts with the ATPase complex of T mitochondriaeither at or near the DCCD-binding protein within the membranesector of the complex. Key words: Zea mays L., Helminthosporium maydis, Mitochondria     

Gonidiogenesis in Padixonia bispora Subram. (Hyphomycetes)

(Hyphomycetes). Padixonia bispora produces two kinds of conidium arranged as acropetal tandem pairs. The pair consists of a distal enteroblastic conidium connected via a narrow neck to a proximal broad-based holoblastic conidium. The proximal blastospore is derived from a branched conidiphore axis and initially forms as a distal conidiogenous cell from which arises the distal blastospore. The wall between the two conidia is formed from the narrow neck occluded by a layered plug. Conidial maturation is concurrent with conidiogenesis. Secession of the proximal spore is by a rounding-off mechanism with circumscissile rupture of the outer layer of the continuous wall between the conidiogenous cell and the conidium and concurrent schizolysis of the duplex septum. The distal blastospore is released by mechanical transverse tearing of the plug through an undulate abscission zone. The abscission zone has two major concentric rings of thickening. The outer ring is derived from the outer layer of proximal spore cell wall.