Isolation of MTX-resistant Cell Line NP-19 of Nicotiana plumbaginifolia: Phenotypic, Genetic and Biochemical Study

Several cell lines of Nicotiana plumbaginifolia resistant tomethotrexate (MTX) were isolated upon gradual elevation of theMTX concentration in the growth medium. One of the MTX-resistantcell lines, NP-19, acquired resistance to 10 mmol m^–3MTX, that is, at least 50-fold higher than the lethal dose forthe wild-type cell suspension. Its resistance was stably maintainedupon prolonged withdrawal of the drug. The acquisition of resistancewas accompanied by severe deterioration of regeneration potential.Regenerated shoots still manifested resistance to 50 mmol m^–3.MTX-resistant colonies and tiny shoots were recovered followingasymmetric fusion between -irradiated NP-19 protoplasts andN. plumbaginifolia leaf mesophyll-derived protoplasts on a mediumcontaining 10 mmol m^–3 MTX. The development of the shootsderived both from NP-19 calli and following somatic fusion wasarrested at the stage of 6–8 leaves. No difference wasfound in uptake of ³H-MTX between cell suspension of NP-19 andthe parental cell line. A 30-fold increase in binding of ³H-MTXto protein extract was found in cell line NP-19, suggestingdifferential capacity of MTX binding as a mechanism involvedin the MTX resistance of this cell line. Since differentiatedorgans seem more sensitive to MTX than undifferentiated tissues,this cell line is a promising source for a gene(s) conferringenhanced MTX-tolerance both in non-differentiated and differentiatedtissues. Key words: Methotrexate resistance, MTX-binding capacity, MTX uptake, tobacco cell culture     

Field estimation of variation in host plant use between local populations of pea aphids from two crops

Abstract. 1. In a reciprocal transplant experiment on pea aphids (Acyrthosiphon pisum (Harris)), the relative performance of clones collected from nearby alfalfa and red clover fields was tested by allowing clonal replicates to develop on both crops under field conditions.
2. Populations from alfalfa and red clover differed in relative survivorship and probabilities of reproduction on the two crops. Clones had significantly higher performance on the crop from which they were collected (the 'home' crop) than they did on the other crop.
3. Evidence is presented that previous experience on these host plants cannot account for the increased probability of reproduction observed on the 'home' crop. Thus, the differences between these two populations in their relative performance on alfalfa and clover are likely to be genetically based.
4. These results illustrate that local adaptation to different host plants can occur within small geographical areas, despite the high probability that migrants are exchanged between nearby fields of the two crops.
5. Experimental designs of the type described here permit estimation of patterns of genetic variation within and between insect populations. When applied to pest species, such designs will facilitate the study of evolution in agricultural systems.     

Adaptive significance of food income in European snakes: body size is related to prey energetics

Feeding strategies and diet patterns have been extensively investigated in vertebrates and, more specifically, in snakes. Although it has been hypothesized that prey species may differ in terms of energy content, almost no theoretical or practical study has been carried out to determine actual nutritional values of the common prey types of wild snakes. Our model taxa were a selection of widely distributed and well known European snake species, which have all been studied in depth: approximately 76% of their diet is composed of mammals, reptiles, and insects. We therefore selected a single model species for each of these categories and proceeded with the analyses. Nutritional values were determined using a standard procedure: lizards and mice were richer in proteins than insects (crickets); insects and mice were richer in lipids than lizards, and mice and crickets have a higher energy content than lizards; lizards were rich in ashes. We then applied our experimental results to a selected sample of European terrestrial snakes (11 populations, ten species, seven genera, two families) characterized by different body size (50–160 cm total length) and reproductive strategies (oviparous versus viviparous), aiming to correlate these parameters with patterns of energy income. A direct relationship was found between body mass/body length ratio (BCI, body condition index) and meal energetics: the higher the BCI, the higher was the metabolic requirement, whereas BCI was independent of species or of reproductive system effect. Large‐sized snakes thus need a highly diversified and more energy‐rich diet than smaller snakes, supporting previous hypotheses. The simple applicability of this method could be of valuable support in further comparative research work, reducing experimental costs and stimulating further ecological, behavioural, and, possibly, phylogenetic comparisons. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 307–317.     

Variability of Wax Ester Fermentation in Natural and Bleached Euglena gracilis Strains in Response to Oxygen and the Elongase Inhibitor Flufenacet

ABSTRACT. Euglena gracilis is able to synthesize adenosine triphosphate under anaerobic conditions through a malonyl-independent fatty acid synthesis leading to wax ester fermentation. Mitochondrial fatty acid synthesis uses acetyl-CoA and propionyl-CoA as C2- and C3-donors for de novo synthesis of even- and odd-numbered fatty acids, respectively. Euglena' s wax ester fermentation has only been described in the E. gracilis strain 1224-5/25 Z. Here we investigate eight E. gracilis strains isolated in 1932–1958 from different localities in Europe and two bleached substrains of E. gracilis 1224-5/25, obtained by treatment with streptomycin and ofloxacin, and examine their anaerobic growth, wax ester fermentation, and wax ester composition. Under ambient oxygen levels, all strains accumulated wax esters in concentrations between 0.3% and 3.5% of the dry weight, but the strains revealed marked differences in wax ester accumulation with respect to anaerobic growth. Most fermenting strains tested showed increased wax ester synthesis under anaerobic conditions as well as the increased synthesis of odd-numbered fatty acids and alcohols suggesting an activation of the mitochondrial fatty acid biosynthesis pathway. Addition of the elongase inhibitor flufenacet to the growth medium specifically reduced the accumulation of odd-numbered fatty acids and alcohols and tended to increase the overall yield of anaerobic wax esters.     

Nutritional versus genetic correlates of caste differentiation in a desert ant

1. In many ant species, caste differentiation stems from trophic differences at the larval stage. Adult workers that feed larvae have great control over the allocation of colony resources to growth (production of workers) versus reproduction (production of queens). However, larval caste fate may also be constrained very early on through direct genetic effects or non‐genetic maternal effects. 2. Here, we combined isotopic and genetic analyses to study the developmental origin of queens and workers in a desert‐dwelling ant, Cataglyphis tartessica (Amor & Ortega, 2014). Queens do not found new colonies alone but rather disperse with workers. As the latter are always wingless, selection pressures on specific queen traits such as flight ability have become relaxed. Though the phylogenetically related species, C. emmae (Forel, 1909) only produces winged queens much larger than workers, C. tartessica produces two types of small queens relative to workers: brachypterous (short‐winged) queens and permanently apterous ergatoid (wingless and worker‐like) queens. 3. Upon emergence, workers and ergatoids have similar δ15N isotopic values, which were lower than those of brachypters, suggesting the latter are fed more protein as larvae. Microsatellite analyses indicated that: (i) colonies are mostly monogynous and monandrous; (ii) both ergatoids and brachypters are equally related to workers; and (iii) in the few polyandrous colonies, patrilines were evenly represented across workers, brachypters and ergatoids. 4. Overall, there was no evidence of genetic caste determination. We suggest that, in contrast to brachypters, ergatoids are selfish individuals that escape the nutritional castration carried out by workers and develop into queens in spite of the colony's collective interests.     

Genetic and morphological divergence reveals local subdivision of perch (Perca fluviatilis L.)

The level of gene flow is an important factor influencing genetic differentiation between populations. Typically, geographic distance is considered to be the major factor limiting dispersal and should thus only influence the degree of genetic divergence at larger spatial scales. However, recent studies have revealed the possibility for small-scale genetic differentiation, suggesting that the spatial scale considered is pivotal for finding patterns of isolation by distance. To address this question, genetic and morphological differentiation were studied at two spatial scales (range 2–13 km and range 300 m to 2 km) in the perch ( Perca fluviatilis L.) from the east coast archipelago of Sweden, using seven microsatellite loci and geometric morphometrics. We found highly significant genetic differentiation between sampled locations at both scales. At the larger spatial scale, the distance per se was not affecting the level of divergence. At the small scale, however, we found subtle patterns of isolation by distance. In addition, we also found morphological divergence between locations, congruent with a spatial separation at a microgeographic scale, most likely due to phenotypic plasticity. The present study highlights the importance of geographical scale and indicates that there might be a disparity between the dispersal capacity of a species and the actual movement of genes. Thus, how we view the environment and possible barriers to dispersal might have great implications for our ability to fully understand the evolution of genetic differentiation, local adaptation, and, in the end, speciation.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 746–758.     

Patterns of life-history traits in open-nesting palearctic passerines as a function of the climatic variation of their ranges

Latitude, a surrogate of climatic conditions, is commonly used in the examination of life-history variation. However, the climatic mechanisms underlying latitudinal life-history variation have only rarely been tested. Here, we test whether the number of climates to which species are subjected in their ranges predicts geographical life-history variation. In particular, we examine whether eurytopic species, the range of which covers more climates, show different reproductive effort to stenotopic species, which are distributed over climatically more homogeneous environments. We examined female body mass, egg mass controlled for female body mass, clutch size and the number of breeding attempts per season for 34 sedentary and short-distance migratory passerine species of the Western Palearctic. For each species, we assessed how many climate zones extend over the species' wintering and breeding ranges. We found that avian body mass, and also clutch size, significantly increases with the number of climatic zones extended over the species' wintering range. In turn, species whose breeding ranges span more climates show more breeding attempts per season. Whereas the mass of a single egg declines, clutch size increases with increasing climatic variation in breeding ranges. Our study suggests that the level of climatic variation over species' ranges during and outside the breeding season might be responsible for variation in life-history traits in open-nesting Western Palearctic passerines.     

To be an intra‐guild predator or a cannibal: is prey quality decisive?

Abstract.  1. Many cannibalistic species are also intra-guild predators. Such predators will often face the decision whether to consume a conspecific or a heterospecific prey from the same guild. This decision may depend on the relative quality and abundance of the prey but also on other factors such as relatedness by descent, prey-specific defence and the probability of the victim harbouring shared diseases.
2. Here, intra-guild interactions among two cannibalistic species of predatory mites, Iphiseius degenerans and Neoseiulus cucumeris (Acari: Phytoseiidae) that belong to closely related genera were studied.
3. Individuals of I. degenerans were offered a diet of conspecifics or heterospecifics. Because I. degenerans is capable of recognising kin individuals from non-kin, and they were exclusively offered conspecifics that were either distantly related or non-kin, it was expected that it would not refrain from cannibalising for reasons of possible relatedness.
4. When corrected for numbers of victims eaten, survival, and juvenile development of predators fed with intra-guild prey was higher than that of cannibals. This was probably caused by a higher quality of heterospecific victims, even though conspecific victims were larger and therefore potentially contained more food. This led to the prediction that the predators should strongly prefer heterospecific prey. This was indeed borne out in independent choice experiments. Thus, the choice of predators between heterospecific and conspecific prey is not only affected by avoidance of consuming conspecifics, but also by relative prey quality.     

Temperature effects on forest herbs assessed by warming and transplant experiments along a latitudinal gradient

Slow‐colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large‐scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short‐ and long‐term persistence. We combined transplant experiments along a latitudinal gradient with open‐top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow‐colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e.g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open‐top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.