Exploitation of the resistance to carrot fly in the wild carrot species Daucus capillifolius

Under field conditions a wild Daucus species from Libya, D. capillifolius, supported less than one tenth as many carrot flies (Psila rosae) as the susceptible carrot cultivar Danvers Half Long 126. Breeding lines developed from crosses between D. capillifolius and three different carrot types were grown in a series of field experiments at Wellesbourne between 1980 and 1989. Each year selections were made for agronomic quality and/or for increased resistance to carrot fly. The programme produced lines which for size, shape and colour represented most of the commercially-important carrot types. Some of these lines were also significantly more resistant to carrot fly than selections from the partially-resistant cv. Sytan. However, the best lines were not as resistant as the wild parent. The highest quality resistant lines were sold to seed companies for variety production.     

The Freezing Response of an Arctic Cushion Plant, Saxifraga caespitosa L.: Acclimation, Freezing Tolerance and Ice Nucleation

Cold hardiness in actively growing plants of Saxifraga caespitosaL., an arctic and subarctic cushion plant, was examined. Plantscollected from subarctic and arctic sites were cultivated ina phytotron at temperatures of 3, 9, 12 and 21 °C undera 24-h photoperiod, and examined for freezing tolerance usingcontrolled freezing at a cooling rate of 3–4 °C eitherin air or in moist sand. Post-freezing injury was assessed byvisual inspection and with chlorophyll fluorescence, which appearedto be well suited for the evaluation of injury in Saxifragaleaves. Freezing of excised leaves in moist sand distinguishedwell among the various treatments, but the differences werepartly masked by significant supercooling when the tissue wasfrozen in air. Excised leaves, meristems, stem tissue and flowerssupercooled to –9 to –15 °C, but in rosettesand in intact plants ice nucleation was initiated at –4to –7 °C. The arctic plants tended to be more coldhardy than the subarctic plants, but in plants from both locationscold hardiness increased significantly with decreasing growthtemperature. Plants grown at 12 °C or less developed resistanceto freezing, and excised leaves of arctic Saxifraga grown at3 °C survived temperatures down to about –20 °C.Exposure to –3 °C temperature for up to 5 d did notsignificantly enhance the hardiness obtained at 3 °C. Whenwhole plants of arctic Saxifraga were frozen, with roots protectedfrom freezing, they survived –15 °C and –25°C when cultivated at 12 and 3 °C, respectively, althougha high percentage of the leaves were killed. The basal levelof freezing tolerance maintained in these plants throughoutperiods of active growth may have adaptive significance in subarcticand arctic environments. Saxifraga caespitosa L., arctic, chlorophyll fluorescence, cold acclimation, cushion plant, freezing stress, freezing tolerance, ice nucleation, supercooling     

The origin and paleoecologic significance of the trace fossil Asteriacites in the Pennsylvanian of Kansas and Missouri

The trace fossil Asteriacites, recorded in Cambrian to Recent shallow- and deep-marine facies, is traditionally interpreted as the resting trace of asterozoans. Well-preserved specimens of A. lumbricalis are abundant in Pennsylvanian (Upper Carboniferous) shallow- and marginal-marine siliciclastic deposits of eastern Kansas and western Missouri. Detailed morphologic analysis of these specimens suggests that they record the activities of mobile epifaunal ophiuroids. Evidence of a brittle star (ophiuroid) producer rather than sea star (asteroid) is provided by (1) trace-fossil morphologic features reflecting the anatomy of the producer (e.g., well-differentiated central structure, slender vermiform arms) and ophiuroid burrowing technique (e.g., proximal arm expansion, arm branching), and (2) mode of occurrence (e.g., gregarious behavior, horizontal and vertical repetition). Vertical and horizontal repetition produces complex aggregates of A. lumbricalis that are interpreted either as escape structures (fugichnia) or as feeding structures, respectively. Ophiura texturata is proposed as a modern analogue for the A. lumbricalis producer, based on inferred life habit and feeding behavior. Asteriacites lumbricalis is present in two different intertidal trace-fossil assemblages. The first assemblage is characterized by high diversity and records tidal flats developed outside of embayments under normal marine conditions. The second assemblage consists of A. lumbricalis together with a few other ichnotaxa and represents a depauperate association that developed in restricted tidal flats within an embayment or estuarine setting. This challenges the conventional view of Asteriacites as a normal-marine salinity indicator. Some echinoderms, and particularly asterozoans, penetrate and inhabit modern environments of depressed salinity. The presence of Asteriacites in Pennsylvanian marginal-marine facies of Kansas and Missouri provides evidence that ophiuroids had adapted to brackish-water conditions by the late Paleozoic.     

Population dynamics of two species of hyraxes in the Matobo National Park, Zimbabwe

Populations of the syntopic rock hyrax, Procavia capensis (Pallas), and yellow-spotted rock hyrax, Heterohyrax brucei (Gray), in the 42,400-ha Matobo National Park (MNP), Zimbabwe, were characterized from 1992 to 1996. The Procavia:Heterohyrax species ratio varied significantly ( P < 0.01) across years from 1.43:1.00 to 0.74:1.00. Estimates of abundance (31,114–39,869 Procavia and 21,833–46,619 Heterohyrax ) and densities (0.73–0.94 Procavia ha⁻¹ and 0.51–1.10 Heterohyrax ha⁻¹) indicated that populations had experienced a considerable decline since 1978, with drought suspected as the principal cause. The Heterohyrax population fluctuated more than the Procavia population. Although sex ratios of individuals trapped and collected in 1991–92 did not differ from 1:1 for either species, female Procavia nearly outnumbered males ( P < 0.10) among the prey of black eagles ( Aquila verreauxii Lesson), suggesting the possibility of divergence in the social organization and vigilance of the two species. In each year of the study, pups comprised < 30% of individuals in the two populations after the interspecifically synchronous annual birth event in March–April, and evidence exists for an effect by drought on fecundity. Females appear to breed, on average, no more than every other year. We estimated juvenile (0–1 year of age) mortality at 52.4–61.3% for Heterohyrax and 59.6–75.6% for Procavia . Mean mass (±1 SE) of Procavia adults was 3.4±0.2 kg and of Heterohyrax adults, 2.4±0.1 kg. Procavia had a significantly ( P < 0.01) greater condition index (body mass/total length) than Heterohyrax . Adults are especially important reservoirs of biomass for the diverse and numerous predators of the MNP, accounting for > 84% of hyrax biomass intraspecifically.     

Patterns of hydrological exchange and nutrient transformation in the hyporheic zone of a gravel-bottom stream: examining terrestrial—aquatic linkages

• 1 The terrestrial-aquatic interface beneath a riparian corridor was investigated as a region of hydrological and biological control of nutrient flux. Subsurface flow paths were defined from the channel toward the riparian zone and also from the riparian zone toward the channel using tracer-injection studies. Solute transport had a rapid channel component (m min^?1) and a slow hyporheic flow component (mh^?1, m day^?1). Subsurface flow beneath the riparian zone approximated a straight path entering at meanders but could also cross beneath the stream, possibly using relic channels.
• 2 Dissolved oxygen (DO) concentration in the hyporheic zone ranged from <1.0 to 9.5mgl^?1 due to permeability variations in bankside sediments. DO concentration was related to the proportion of stream water in the lateral hyporheic zone, indicating that the channel water was the DO source.
• 3 The magnitude and riming of lateral water exchange was linked to previously published studies of nitrification and denitrificarion. Both nitrification potential and channel exchange decreased with distance from the channel and were absent at sites lacking effective exchange, due to low DO. Field amendment of ammonium to an aerobic flow path indicated nitrification potential under natural hydrological conditions. Denitrification potential was inversely related to channel exchange and was insignificant in channel sediments. Field amendment of acetylene plus nitrate to a flow path with low DO and minimal channel exchange indicated denitrificarion of amended nitrate.
• 4 Comparison of hydraulic head to distribution of the biologically important solutes DO, ammonium, and nitrate was useful for interpreting previous findings and conceptualizing the riparian zone as a functioning ecotone between terrestrial and aquatic systems.