The genus Phymatolithon (Hapalidiaceae,Corallinales, Rhodophyta) in South Africa,including species previously ascribed to Leptophytum

Of the genera within the coralline algal subfamily Melobesioideae, the genera Leptophytum Adey and Phymatolithon Foslie have probably been the most contentious in recent years. In recent publications, the name Leptophytum was used in quotation marks because South African taxa ascribed to this genus had not been formally transferred to another genus or reduced to synonymy. The status and generic disposition of those species (L. acervatum, L. ferox, L. foveatum) have remained unresolved ever since Düwel and Wegeberg (1996) determined from a study of relevant types and other specimens that Leptophytum Adey was a heterotypic synonym of Phymatolithon Foslie. Based on our study of numerous recently collected specimens and of published data on the relevant types, we have concluded that each of the above species previously ascribed to Leptophytum represents a distinct species of Phymatolithon, and that four species (incl. P. repandum) of Phymatolithon are currently known to occur in South Africa.Here we present detailed illustrated accounts of each of the four species, including: new data on male and female/carposporangial conceptacles; ecological and morphological/anatomical comparisons; and a review of the information on the various features used previously to separate Leptophytum and Phymatolithon. Southern African species ascribed to the genus Phymatolithon may be separated from one another in the field by their growth forms, the substrata on which they are generally found, and the colour of living thalli. A key for identifying southern African specimens in the field is included. Our data support the conclusion that the characters upon which Leptophytum is based are unreliable for generic delimitation from Phymatolithon.     

Relationship between cover of Chondrus crispus (Gigartinales,Rhodophyta) and Phymatolithon (Corallinales,Rhodophyta) on friable rock substrata

Field observations in sublittoral Prince Edward Island, Canada, indicated that on a friable sandstone substratum Chondrus crispus was more commonly associated with Phymatolithon sp. than with bare rock. Thus, a substantial proportion of the population of Irish moss along the coast of Prince Edward Island occurs on this encrusting coralline. These observation may be explained on the basis of the relative stability of the substratum in contrast to other studies in which sloughing of epithallial cells by species of both Phymatolithon and Lithothamnium has been reported to limit epiphytism by fleshy macrophytes.Issued as NRCC 31426.     

The genera Lithothamnium,Leptophytum (nov. gen.) and Phymatolithon in the Gulf of Maine

Summary This paper is the fourth of a series covering the crustose corallines of the Gulf of Maine. Information on anatomy, cytology and the development of the reproductive structures is presented to show that Lithothamnium and Leptophytum (new genus) are distinct from Clathromorphum and Phymatolithon. An additional species, P. lenormandi, is placed in Phymatolithon. The reproductive patterns and geographic and bathymetric distributions of the five species involved are presented and discussed.The necessary field work for this study was made possible by the generous support of: The American Petroleum Institute, The Geological Society of America and the ONR (through the Department of Geology and Geophysics, Massachusetts Institute of Technology).     

Vertical distribution of chitons (Mollusca: Polyplacophora) in the rocky intertidal zone of central Chile

The patterns of vertical distribution of chitons in various exposed rocky shore habitats of central Chile are described. The density and size of the individuals were determined at different levels on intertidal rock walls, in pools and on boulders. A group of four species was found on rock walls while another group of four species was found in tidal pools and on boulders. The species showed vertical separation on rock walls and segregation according to a range of increasing frequency of water movement in pools and on boulders. Only the two species with largest adult individuals (Acanthopleura echinata (Barnes) and Chitonlatus Sowerby) showed vertical segregation in size. Small-sized species and small individuals of large-sized species were found higher on rock walls or in zones where water movement is less; large chitons occur in zones of greatest water impact. This suggests that water movement may be a significant factor in setting the lower limits of distribution of these herbivores. Some of the species examined were extremely abundant (600·m^-2) with densities of one to two orders of magnitude greater than for other chiton species elsewhere.     

Melanoderma boninense,a new species of Melanoderma (Polyporales,Agaricomycota) from the Bonin Islands in Japan

Melanoderma boninense is described and illustrated as a new species from the Bonin Islands, Japan, on the basis of morphological and phylogenetic investigations. This species is characterized by sessile basidiocarps with an ungulate pileus, a black crust on the pileus surface, pores 4–6/mm, a dimitic hyphal system comprising clamped generative hyphae and cyanophilous skeletal binding hyphae with or without a dextrinoid reaction, cylindrical basidiospores measuring 5.5–7.5 × 2–3 μm, and cystidioles on the sides of tubes and near the pore surface. Morphological examination of authentic specimens of other Melanoderma species revealed that the genus is variable in terms of the shape and size of cystidioles. A black crust on the pileus surface composed of palisade and highly agglutinated hyphae is a distinctive diagnostic morphological feature of Melanoderma that differentiates it from allied genera. Melanoderma boninense, which is currently known from a restricted area of the Bonin Islands, is potentially threatened by environmental reduction of the type locality due to the invasive tree Bischofia javanica.     

Fairy, tadpole, and clam shrimps (Branchiopoda) in seasonally inundated clay pans in the western Mojave Desert and effect on primary producers

Background

Fairy shrimps (Anostraca), tadpole shrimps (Notostraca), clam shrimps (Spinicaudata), algae (primarily filamentous blue-green algae [cyanobacteria]), and suspended organic particulates are dominant food web components of the seasonally inundated pans and playas of the western Mojave Desert in California. We examined the extent to which these branchiopods controlled algal abundance and species composition in clay pans between Rosamond and Rogers Dry Lakes. We surveyed branchiopods during the wet season to estimate abundances and then conducted a laboratory microcosm experiment, in which dried sediment containing cysts and the overlying algal crust were inundated and cultured. Microcosm trials were run with and without shrimps; each type of trial was run for two lengths of time: 30 and 60 days. We estimated the effect of shrimps on algae by measuring chlorophyll content and the relative abundance of algal species.

Results

We found two species of fairy shrimps (Branchinecta mackini and B. gigas), one tadpole shrimp (Lepidurus lemmoni), and a clam shrimp (Cyzicus setosa) in our wet-season field survey. We collected Branchinecta lindahli in a pilot study, but not subsequently. The dominant taxa were C. setosa and B. mackini, but abundances and species composition varied greatly among playas. The same species found in field surveys also occurred in the microcosm experiment. There were no significant differences as a function of experimental treatments for either chlorophyll content or algal species composition (Microcoleus vaginatus dominated all treatments).

Conclusions

The results suggest that there was no direct effect of shrimps on algae. Although the pans harbored an apparently high abundance of branchiopods, these animals had little role in regulating primary producers in this environment.     

Algal colonization and its ecophysiology on the fine sculptures of terracotta monuments of Bishnupur,West Bengal,India

The blackish brown crust on the fine carvings of seven terracotta monuments of Bishnupur were studied with regards to the presence of algal species. Forty five taxa of micro algae belonging to 36 species of cyanobacteria, 5 species of chlorophyta and 4 species of bacillariophyta were found in crusts of these monuments. Among the algal groups, cyanobacteria were the dominant population growing in all the monuments with maximum diversity of 30 species in Rasmancha. Lyngbya corticicola, Scytonema schmidtii and Nostoc microscopicum were the major taxa in all crust samples. The absorption ratio of chlorophyll: carotenoid: MAAs (mycosporine-like amino acid substances) and scytonemin showed scytonemin and MAAs were more abundant than the chlorophyll pigment in all the crust. The MAAs and scytonemin of the crusts were identified as Mycosporine glycine having absorption maxima at 310 nm with retention time (RT) 4.1 min and scytonine having absorption maxima 386 nm with RT 3.2 min respectively. Among the major crust cyanobacteria cellular carbohydrate of N. microscopicum was maximum and lowest in S. schmidtii. However, the extra polymeric substance released to the medium was more in L. corticicola and so intense that the medium become coloured. The slimes of the major crust cyanobacteria plug the fine carvings of the terracotta structures which led to disfiguration of fine architecture, act as a biofilm that facilitated growth of fungi, lichens and subsequently to mosses and small plants leading to create creaks in the monuments and deteriorate these archeologically important monuments.     

Reintroduction of the endangered fern species <Emphasis Type="Italic">Woodsia ilvensis</Emphasis> to Estonia: a long-term pilot study

Woodsia ilvensis has become extinct from its last known natural localities in Estonia and has not been rediscovered since 1977. This fern grew in northern and north-western Estonia in areas of suitable habitat. Considering that habitat conditions may have changed in previous localities, an experimental project was started to test if it would be possible to reintroduce W. ilvensis into new localities where suitable habitat conditions exist. Two experiments were performed, one on an old stone wall, constructed of stones collected from the surrounding fields, and another on two granite boulders in two localities, one where the surrounding soil was acidic, and the other where the soil was basic. The plants were grown from spores of wild provenance received from Finland via the seed and spore exchange system of botanical gardens. Results confirmed that individual plants can establish and persist for at least 10 years on stone walls without maintenance. The experiment on boulders failed, as plants did not establish there. Young, 2-year old mature individuals proved to be the best stage for planting out onto the stone walls in this case study. The best indicators for selecting suitable habitat were characteristic plant species of the natural community. Here I discuss the experimental methods used and first results of the experiment.     

The natural exclusion of red deer from large boulder grazing refugia and the consequences for saxicolous bryophyte and lichen ecology

Large boulder grazing refugia permitted comparison of saxicolous bryophyte and lichen assemblages with those boulder tops accessible to red deer (Cervus elaphus) on a sporting estate in northwest Scotland. Plant succession was predicted to occur unchecked by grazing on the tops of these large boulders with cascading effects on bryophytes and lichens—assuming boulders had been in place over the same time period. Fifty pairs of boulders (one ≥2 m and the other accessible to red deer) were selected at random from various locations below north-facing crags. Percentage cover of each bryophyte and lichen species was estimated from three randomly placed quadrats on each boulder top. Due consideration was given to the influence of island biogeography theory in subsequent model simplification. Mean shrub cover and height, leaf-litter, bryophyte cover and bryophyte species richness were significantly higher within quadrats on large boulder tops that naturally excluded red deer. Lichen cover and lichen species richness were significantly higher on boulder tops accessible to red deer. Lichen cover was in a significant negative relationship with bryophyte cover, shrub cover and litter cover. Bryophyte cover showed a significant positive relationship with shrub height but there was an optimum shrub cover. Natural exclusion of red deer from the tops of large boulders has facilitated plant succession. The results suggest that grazing arrests the lithosere on boulder tops accessible to red deer at an early plagioclimax favouring saxicolous lichens. The results are relevant to situations where red deer might be excluded from boulder fields that hold lichen assemblages of conservation value.     

Multiple phases of mg‐calcite in crustose coralline algae suggest caution for temperature proxy and ocean acidification assessment: lessons from the ultrastructure and biomineralization in Phymatolithon (Rhodophyta,Corallinales)1

Magnesium content, strongly correlated with temperature, has been developed as a climate archive for the late Holocene without considering anatomical controls on Mg content. In this paper, we explore the ultrastructure and cellular scale Mg‐content variations within four species of North Atlantic crust‐forming Phymatolithon. The cell wall has radial grains of Mg‐calcite, whereas the interfilament (middle lamella) has grains aligned parallel to the filament axis. The proportion of interfilament and cell wall carbonate varies by tissue and species. Three distinct primary phases of Mg‐calcite were identified: interfilament Mg‐calcite (mean 8.9 mol% MgCO₃), perithallial cell walls Mg‐calcite (mean 13.4 mol% MgCO₃), and hypothallium Mg‐calcite (mean 17.1 mol% MgCO₃). Magnesium content for the bulk crust, an average of all phases present, showed a strongly correlated (R² = 0.975) increase of 0.31 mol% MgCO₃ per °C. Of concern for climate reconstructions is the potential for false warming signals from undetected postgrazing wound repair carbonate that is substantially enriched in Mg, unrelated to temperature. Within a single crust, Mg‐content of component carbonates ranged from 8 to 20 mol% MgCO₃, representing theoretical thermodynamic stabilities from aragonite‐equivalent to unstable higher‐Mg‐calcite. It is unlikely that existing current predictions of ocean acidification impact on coralline algae, based on saturation states calculated using average Mg contents, provide an environmentally relevant estimate.     

Ontogenetic Shifts in Patterns of Microhabitat Utilization in the Small-headed Clingfish, Apletodon Dentatus (Gobiesocidae)

The patterns of microhabitat utilization by the clingfish Apletodon dentatus were investigated, based on SCUBA diving surveys at the Arrábida Marine Park (Portugal). In all inspected microhabitats, this species was only found in algal turfs, sea urchins and boulders. The association of A. dentatus with sea urchins is here analysed for the first time. There was a differential utilization of the microhabitats, with small juveniles recruiting to algal turfs, intermediate individuals found in association with the sea urchins Paracentrotus lividus and Sphaerechinus granularis and larger fish occurring mainly in boulders. The depth distribution patterns are also analysed.     

The genus phymatolithon in the Gulf of Maine

Summary New information on anatomy, cytology and the development of reproductive structures is presented to show that Phymatolithon is a genus distinct from both Clathromorphum and the branching members of Lithothamnium. Also, a new species of Phymatolithon, Ph. rugulosum, is described. The reproductive cycles and geographic and bathymetric distributions of Ph. laevigatum and Ph. rugulosum in the Gulf of Maine are presented and discussed. There is strong indication that the geographic distribution of crustose corallines in the region is controlled primarily by maximum summer temperatures. The depth distributions are apparently controlled primarily by decrease of light with depth, though temperatures and substrate are also factors.Now at Colorado School of Mines, Golden, Colorado, U.S.A. The necessary field work for this study was made possible through the generous support of: The American Petroleum Institute, The Geological Society of America, the ONR (through the Department of Geology and Geophysics, Massachusetts Institute of Technology) and the Woods Hole Oceanographie Institution (Contr. No. 1500).     

Coralline algae as depth indicators in the Sommières Basin (early Miocene,Southern France)

The aim of this work is to demonstrate the benefits of digital surface-quantification and species identification in the study of coralline algae. Within the well-constrained context of the Miocene Sommières Basin (Southern France), whose sedimentological and paleontological setting has been reconstructed by previous researches, the abundance of coralline algae is estimated through quantification of the area occupied by the different species, which are thoroughly described in order to make future taxonomic-revisions as easy as possible. Coralline distribution patterns are studied along a bathymetric gradient to assess the response of the major groups and of the different species to variations in water depth. Surface quantification highlights clear trends both at the species level and higher taxonomic ranks, showing that coralline algae can be a quite accurate instrument in paleoenvironmental reconstructions. Among the clearly identified species, Lithophyllum sp. A, Sporolithon sp. A, and Spongites fruticulosus prefer shallow-water; Mesophyllum roveretoi dominates at intermediate depth together with Lithothamnion ponzonense, while Phymatolithon sp. A occurs at the lower limit of the photic zone. The approach presented here can be applied to a variety of different contexts, providing a powerful instrument for the interpretation of coralline-algal associations.     

Selective feeding by the echinoid,Evechinus chloroticus,and the removal of plants from subtidal algal stands in Northern New Zealand

Summary Feeding choice of the echinoid Evechinus chloroticus was examined for six fucoid and one laminarian species of algae. Three experiments were conducted to determine the algal choice by echinoids under controlled conditions. In the first experiment, the seven algal species were presented to echinoids in laboratory conditions. The second experiment had replicates of the algal species placed randomly on a subtidal rocky reef where echinoids were abundant and randomly dispersed. For the third experiment, which was also field-based, replicates of one highly-ranked species, Ecklonia radiata, were presented to naturally dispersed Evechinus. In addition, a series of controlled observations was used to examine the order in which echinoids removed algae from mixed species stands on subtidal boulders and to determine if this was related to the experimentally demonstrated choices of algal species.The results of the first two experiments showed that there were differences between algal species in the amount of material grazed by echinoids. Rankings of algal species from the field experiment were not correlated with rankings from the laboratory experiment. The order of removal of algal species from natural stands was correlated with the laboratory-based experimental rankings of algal species, but not with the rankings from the field-based experiment or with algal species availability. There were differences between algal species in their vulnerability to grazing by echinoids, as measured by regression analyses on the amount of material grazed from algal replicates vs. the number of attached echinoids. Within each species, echinoid numbers exerted a non-linear effect on the removal of algal material. In the third experiment, where only one species of algae was presented, the echinoids still distributed themselves non-randomly amongst replicates, aggregating on some samples.Data on the finer scale distribution of algal species over the entire subtidal reef on which these experiments and observations were conducted indicate that Evechinus are not often presented with a choice of adult plants of several different species in natural stands.The evidence from this study supports the conclusion that feeding preferences by echinoids are labile and do not clearly exert the major influence on the removal of plants from natural stands. Preference, as determined from experimental rankings of algal species, is only one of a number of factors which may affect the removal of algae by echinoids. Other important factors are the density of echinoids present, algal susceptibility to removal, and the distribution and abundances of the various algal species and echinoids relative to each other. It is suggested that algal life history characteristics may be unaffected by echinoids and that coevolutionary arguments are not appropriate for describing echinoid-algal interactions.     

Seasonality of the red algal crust 'Petrocelis franciscana'(Gigartinales, Rhodophyta) on boulder-strewn shores of southern British Columbia, Canada

The red algal crust,‘Petrocelis franciscana’ Setchell et Gardner [= tetrasporophytic phase of Mastocarpus papillatus (Agardh) Kützing] exists as discrete patches on boulders throughout the intertidal zone at Burrard Inlet in Vancouver (mainland British Columbia) and at Sooke, Vancouver Island (British Columbia). This study photographically quantifies monthly surface area of 60 individual crusts over 12‐ and 18‐month periods, respectively, at the two sites. Conspicuous seasonal fluctuations in ‘Petrocelis’ abundance and relatively low survivorship of crusts sampled suggest that not all crusts are as static and as long‐lived (> 25 years) as previously suggested. Herbivory, sloughing of senescing tissue and abiotic factors visibly reduce ‘Petrocelis’ abundance in fall and winter; regeneration of lost crust tissue and relatively rapid crust growth occur from spring to early fall.     

Phenotypic Plasticity of the Introduced New Zealand Mud Snail,Potamopyrgus antipodarum,Compared to Sympatric Native Snails

Phenotypic plasticity is likely to be important in determining the invasive potential of a species, especially if invasive species show greater plasticity or tolerance compared to sympatric native species. Here in two separate experiments we compare reaction norms in response to two environmental variables of two clones of the New Zealand mud snail, Potamopyrgus antipodarum, isolated from the United States, (one invasive and one not yet invasive) with those of two species of native snails that are sympatric with the invader, Fossaria bulimoides group and Physella gyrina group. We placed juvenile snails in environments with high and low conductivity (300 and 800 mS) in one experiment, and raised them at two different temperatures (16°C and 22°C) in a second experiment. Growth rate and mortality were measured over the course of 8 weeks. Mortality rates were higher in the native snails compared to P. antipodarum across all treatments, and variation in conductivity influenced mortality. In both experiments, reaction norms did not vary significantly between species. There was little evidence that the success of the introduced species is a result of greater phenotypic plasticity to these variables compared to the sympatric native species.     

Demography, competitive interactions and grazing effects of intertidal limpets in southern New Zealand

Population dynamics and the effects of intraspecific competition on limpet growth and maintenance of bare patches were investigated for the intertidal limpet Cellana ornata (Dillwyn) at a boulder-dominated site and on a rocky platform near Kaikoura (South Island), New Zealand. Distribution and abundance patterns of C. ornata were described in relation to other biota and tidal height. C. ornata occurred almost exclusively in patches devoid of macroalgae, particularly in the mid-tidal zone. Both adult and juvenile limpets were most abundant on the tops of boulders, where their numbers were positively correlated with barnacle cover, which averaged 77%. The size structure and growth patterns of C. ornata were different between populations. Mark-recapture studies showed that the slopes of annual growth increments regressed on initial sizes were similar at both sites but that the annual increments on the platform were about 6 mm greater than on boulders. Growth virtually ceased at 27 mm for limpets at the barnacle-dominated boulder site and at 40 mm at the platform site. Recruiting cohorts had 20% survival on boulders and 37% on the platform during their first year. The largest size classes at both sites had around 57% annual survival. To test the effects of varying limpet densities on the growth and mortality of limpets and the maintenance of bare patches, densities of C. ornata were experimentally increased at both sites. Beyond a density of 4 per 0.25 m², sizes and survival of limpets were reduced at both sites, but the effect was more pronounced at the boulder site. Limpets at the boulder site were more effective at maintaining bare space than those on the reef platform. Enclosing limpets in plots with and without barnacles showed that C. ornata and a co-occurring species (Cellana denticulata (Martyn)) grazed more effectively and had greater growth in cleared plots. Overall, there was considerable variation in the demographics of C. ornata between populations driven by site-specific characteristics.     

Evaluation of physical fish habitat quality enhancement designs in urban streams using a 2D hydrodynamic model

Creating a habitat for a variety of forms of life, such as riparian plants and various fish, is a necessity for stressed river ecosystems. In this study, the hydraulic characteristics of a fish habitat in an urban channel were analyzed using River2D, which is a two-dimensional (2D) depth-averaged finite element hydrodynamic model, to improve the habitat of two target fish in the Daejeon Stream, Korea. These species are Pseudopungtungia nigra, which is an endangered species in the Daejeon Stream, and Zacco platypus, which is a dominant species. In addition, changes in the weighted usable area (WUA) were compared and reviewed as boulders were placed in the stream. The best method for improving the P. nigra's habitat is proposed. A simulation analysis was performed on urban rivers for fish habitats. As a result, a straight and monotonous urban river flow was found to be an appropriate habitat environment for Z. platypus. The WUA for Z. platypus was about 20 times greater than that for P. nigra. Three different fish habitat enhancement methods were evaluated by calculating the WUA for the target fish in the study channel. By calculating the WUA to create fish habitats, the V-type riffle method was found to increase the usable area of the habitat environment for P. nigra by 360%, and the step stone method and single boulder method did so by 60% and 8%, respectively. For the single boulder method, boulders were placed in the channel bed at 3.5-m intervals, which significantly increased habitat availability. Moreover, centralizing the flow pattern in the channel among several types of boulder placements greatly expanded the habitat for P. nigra. Thus, an appropriate placement interval and boulder location that considers the characteristics of the riverbed and target fish species should be researched and implemented.     

Taxonomic and ecological implications of leaf cuticular morphology in Castanopsis, Castanea, and Chrysolepis

Leaves of 41 species of Castanopsis, six species of Castanea, and Chrysolepis chrysophyllum Hjelmq. were examined. In Castanopsis, all species possessed cyclocytic stomata with thickened subsidiary cells; thin-walled peltate trichomes are the most frequent type on the abaxial surface of the leaves of this genus. In Castanea, stomata are transitional between cyclocytic and anomocytic; thin-walled peltate trichomes were recorded for the first time on the abaxial surface of Castanea leaves. In Chrysolepis, cyclocytic stomata with non-thickened subsidiary cells and thick-walled peltate trichomes were observed. The thickened subsidiary cells support the placement of the “fissa-group” in Castanopsis. The results of this study support the idea that Castanopsis and Castanea are sister groups. Thick-walled peltate trichomes were only recorded in Chrysolepis, thus supporting its taxonomic separation from Castanopsis. The phylogenetic distribution of trichome types among genera of Fagaceae is summarized. The evolutionary trends of trichome types in Castanopsis are discussed, as are the implications of stomatal and trichome features on fossil identification and ecology.     

Some Biochemical Evidence on the Selective Insecticide Toxicity between the Two Aphids,Aphis citricola and Myzus malisuctus (Homoptera: Phididae), and Their Predator,Harmonia axyridis (Coleoptera: Coccinellidae)

This experiment was carried out to compare the differences in biochemical enzyme activity on the selective insecticide toxicity between the two species of aphid, Aphis citricola van der Goot and Myzus malisuctus Matsumura, and their predator, Harmonia axyridis Pallas. Esterase activities between the two species of aphids and between the two stages of H. axyridis were significant different. Glutathione S-traasferase (GST) activity toward 1-chloro-2, 4-dinitrobenzene (CDNB) was much higher than 1, 2-dichloro-4-nirobenzene (DCNB) in all species tested. No DCNB conjugation was detected in A. citricola and M. malisuctus. The predator, H. axyridis, had much higher GST activity than the preys, A. citricola and M. malisuctus. GST activity toward CDNB in H. axyridis adult was highest, even 6.2-fold higher activity than H. axyridis larva. M. malisuctus had much higher GST activity than A. citricola. The degree of acetylcholinesterase (AChE) inhibition by phosphamidon among all three species tested was significantly varied. The concentration of phosphamidon required for 50% AChE inhibition was lowest in H. axyridis larva, while highest in M. malisuctus. There fore, elevated GST activity and target-site insensitivity may be largely associated with the differential susceptibility between larva and adult of H. axyridis. However, differential susceptibility between A. citricola and M. malisuctus may be due to other various biochemical mechanisms responsible for the multiple selective toxicity, including elevated GST activity and target-site insensitivity.