Elevated CO2 stimulates cells to divide in grass meristems: a differential effect in two natural populations of Dactylis glomerata

In this study, we tested the hypothesis that elevated [CO₂] shortens the cell cycle in meristems of Dactylis glomerata, more in a Portuguese population (38°53′N) than in a Swedish population (63°09′N). In the shoot meristem, the cell cycle shortened to about the same extent (～ 26%) in both populations exposed to the elevated [CO₂] treatment. In the root meristem, the cell cycle shortened by 17% in the Portuguese and by 8% in the Swedish population. However, the proportion of rapidly cycling cells increased in the Portuguese much more than in the Swedish population in both meristems. In the root meristem, there was a 1.86-fold increase in the Portuguese compared with a 1.31-fold increase in the Swedish. In the shoot meristem, the increases were 1.5–3-fold for the Portuguese and 1.2-fold for the Swedish. The data are consistent in showing that a major response to the elevated [CO₂] treatment was an increase in the proportion of cells that were cycling and that this was more marked for the Portuguese population. A more general response to the elevated [CO₂] treatment was a shortening of the cell cycle regardless of population.     

3种禾草圆锥花序小穗及小花分布格局的比较

分析草芦、鸭茅、苇状羊茅 3种圆锥花序禾草小穗及小花的分布格局 ,结果表明 ,3种禾草在各节位上的小穗、小花数量均适合于Weibull分布 ,随着节位序的增加均呈饱和型曲线增长 .通过赋予各统计参数生物学涵义 ,从宏观上分析与揭示了有关生命现象与发展规律及其生物生态学机理 .     

Phylogenetic relationships and gene flow between sympatric diploid and tetraploid plants ofDactylis glomerata (Gramineae)

Phylogenetic relationships between sympatric, morphologically indistinguishable diploid and tetraploid plants ofDactylis glomerata L. (Gramineae) in Galicia (Spain) were assessed using allozyme markers for 6 distinct systems. The study exploited recent introduction in Galicia and subsequent hybridization of an alien 4xDactylis subspecies possessing distinct allozymes from those of all the native plants. Opportunities for gene exchanges between the ploidies were estimated from in situ observations of flowering, examination of progenies in 2x/4x natural and experimental crosses, and enzyme analyses. Results show a high genetic similarity between the Galician diploids and tetraploids, which possess peculiar alleles in common. Although the ploidy levels usually have distinct flowering periods, interploidal crosses do occasionally occur. Gene flow is likely much more important from the diploid to the tetraploid level. A good genetic intermixing occurs between the Galician and the alien tetraploid entities which have simultaneous flowering. Autopolyploidization of the diploids followed by various rates of hybridization is proposed as one very probable origin of natural tetraploids inDactylis.     

Simulated heatwave conditions associated with global warming affect development and competition between hyperparasitoids

Anthropogenic global warming and attendant effects like heatwaves affect the biology and ecology of both individuals and species within and across different trophic levels. Here, we examined the effects of a simulated heatwave on development of and competition between two hyperparasitoid wasps, Lysibia nana and Acrolyta nens when attacking the same host, cocoons of the primary parasitoid, Cotesia glomerata. Parasitized hosts were exposed to three different day and night temperature regimes (low, medium and high) that reflect cool, normal and heatwave conditions in the Netherlands. We found that higher temperatures decreased survival to eclosion more strongly in the hyperparasitoids than in their host. Heatwave conditions also shortened development time and led to the production of smaller adult wasps of both hyperparasitoid species in singly parasitized hosts. In multiparasitized hosts, L. nana won most of the contests when it oviposited first, irrespective of the time interval between the first and second parasitism, whereas A. nens only dominated when it had a 24 h head start or longer. Most importantly, our results show that L. nana in particular benefited in competition at higher temperatures, perhaps due to an increase in the metabolic rate and more rapid egg and/or larval development. This may potentially reduce opportunities for coexistence following heat waves. Our results suggest that heatwaves associated with global warming will enhance the rate of development, but negatively affect survival and other fitness‐related traits in (hyper)parasitoids. Moreover, the outcome of larval competition may be determined via physiological responses that are species‐specific and thus influence phenology.     

Summer dormancy in perennial temperate grasses

BACKGROUND AND AIMS: Dormancy has been extensively studied in plants which experience severe winter conditions but much less so in perennial herbaceous plants that must survive summer drought. This paper reviews the current knowledge on summer dormancy in both native and cultivated perennial temperate grasses originating from the Mediterranean Basin, and presents a unified terminology to describe this trait. SCOPE: Under severe drought, it is difficult to separate the responses by which plants avoid and tolerate dehydration from those associated with the expression of summer dormancy. Consequently, this type of endogenous (endo-) dormancy can be tested only in plants that are not subjected to moisture deficit. Summer dormancy can be defined by four criteria, one of which is considered optional: (1) reduction or cessation of leaf production and expansion; (2) senescence of mature foliage; (3) dehydration of surviving organs; and (4, optional) formation of resting organs. The proposed terminology recognizes two levels of summer dormancy: (a) complete dormancy, when cessation of growth is associated with full senescence of foliage and induced dehydration of leaf bases; and (b) incomplete dormancy, when leaf growth is partially inhibited and is associated with moderate levels of foliage senescence. Summer dormancy is expressed under increasing photoperiod and temperature. It is under hormonal control and usually associated with flowering and a reduction in metabolic activity in meristematic tissues. Dehydration tolerance and dormancy are independent phenomena and differ from the adaptations of resurrection plants. CONCLUSIONS: Summer dormancy has been correlated with superior survival after severe and repeated summer drought in a large range of perennial grasses. In the face of increasing aridity, this trait could be used in the development of cultivars that are able to meet agronomic and environmental goals. It is therefore important to have a better understanding of the genetic and environmental control of summer dormancy.     

Life-history traits in closely related secondary parasitoids sharing the same primary parasitoid host: evolutionary opportunities and constraints

Thus far, few studies have compared life-history traits amongst secondary parasitoids attacking and developing in cocoons of their primary parasitoid hosts. This study examines development and reproduction in Lysibia nana Gravenhorst and Acrolyta nens Hartig (both Hymenoptera: Ichneumonidae), two related and morphologically similar secondary parasitoids that attack pupae of the gregarious endoparasitoid, Cotesia glomerata L. (Hymenoptera: Braconidae). On black mustard, Brassica nigra L. (Brassicaceae) plants in a field plot, adults of L. nana and A. nens frequently emerged from the same cocoon broods of C. glomerata . Based on similarities in their phylogeny and morphology, it was hypothesized that both species would exhibit considerable overlap in other life-history traits. In both L. nana and A. nens , adult wasp size increased with host cocoon mass at parasitism, although L. nana wasps were slightly larger than A. nens wasps, and completed their development earlier. Adult females of both species emerged with no eggs but matured eggs at similar rates over the following days. When provided with 20 host cocoons daily, fecundity in female L. nana was slightly more skewed towards early life than in A. nens , although lifetime fecundity did not differ between the two species. Longevity was significantly reduced in females of both species that were provided with hosts. Both parasitoids were found to exhibit strong similarities in life-history and development traits and in their ecological niche, thereby supporting our general hypothesis. Competition between L. nana and A. nens is presumably diffused because their preferred host ( C. glomerata ) is relatively abundant in open habitats.