Serotiny and seed germination in three threatened species of Mammillaria (Cactaceae)

Individuals of some species of Mammillaria (Cactaceae) store some seeds on the plant over periods exceeding 1 year (serotiny). We examined the phenomenon of serotiny and germination behaviour of three rare and endangered Mammillaria species that occur in central Mexico. The species with the highest seed retention was Mammillaria solisioides, whose individuals kept on average 24% of their total seed crop throughout their observable lifetime. Individuals of Mammillaria napina and Mammillaria hernandezii did not differ in their degree of seed retention (about 5%). In M. solisioides and M. hernandezii, seed germination declined significantly with seed age, whereas in M. napina germination increased slightly. In all three species, over 70% of retained seeds were still alive after 8 years. Increasing fractions of dormant seeds were observed with seed age in M. solisioides and M. hernandezii, whereas in M. napina this fraction followed the opposite trend. All three species showed strict light dependence for germination. Serotiny was positively correlated with the harshness of the environment when species and populations were assumed independent. However, these correlations were not significant at the 5% level when the degree of relatedness of species and populations was taken into account using phylogenetically independent constrasts. We hypothesise that serotiny in these species represents a mechanism by which they can cope with a harsh, unpredictable environment. To our knowledge, this is the first assessment of serotiny in cacti.     

Tissue culture in synthetic atmospheres: diffusion rate effects on cytokinin-induced callus growth and isoflavonoid production in soybean [Glycine max (L.) Merr. cv. Acme]

Concentration is one factor that is known to determine how metabolic gases influence the growth and secondary metabolism of plant tissues in culture. How actual gas bioavailability influences these processes has not been studied despite its potential importance in specialized applications. A simple model system, soybean [Glycine max (L.) Merr. cv. Acme] callus culture, was selected for experiments because exogenous cytokinin (6-benzylaminopurine; BAP) elicits two types of responses: (1) enhanced callus proliferation, and (2) rapid induction of the isoflavonoid daidzein (7,4′-dihydroxyisoflavone). Synthetic atmospheres supplying metabolic gases with higher or lower bioavailability than in air were created by replacing the nitrogen moiety in standard air with either helium or argon, respectively. Callus was cultured on agar or in liquid shake cultures according to standard procedures. At an optimal cytokinin concentration for stimulation of callus proliferation, 4.4 × 10⁻⁷ M BAP, increased diffusion rates for the metabolic gases resulted in greater weight gain in agar cultures. Weight gain was 11% higher for He-treated and 39% lower for Ar-treated cultures than for the nitrogen control. In contrast, there was no significant effect of metabolic gas diffusion rate on daidzein production in either agar or liquid cultures. Apart from the potential application of these synthetic atmospheres for enhancing plant tissue culture growth, they may have unique value for the space program as an effective way of replicating the gas exchange limitations posed for plants by microgravity (Ar atmosphere), and as a countermeasure for this limitation (He atmosphere).     

A modified Vibrio harveyi mutagenicity assay based on bioluminescence induction

AIMS: Mutagenic pollution of natural environment is currently one of the most serious ecological problems. Therefore, rapid detection of the presence of mutagens is a very important issue. Although many mutagenicity assays have already been described, only a few are suitable for testing samples from natural environment. One of such assays is a microbiological mutagenicity test based on genetically modified Vibrio harveyi strains. The aim of this work was to modify and improve the V. harveyi assay. METHODS AND RESULTS: A series of V. harveyi dark and dim mutants were tested for reversion of their phenotype towards efficient light emission in response to incubation with known mutagens. Luminescence of the A16 strain (luxE mutant) increased significantly after a few hours of such a treatment with various mutagenic agents, revealing a dose-response correlation. Sensitivity of the assay has been determined for different mutagens. CONCLUSIONS: The luminescence-based V. harveyi mutagenicity assay is rapid, sensitive and reveals a dose-response correlation for various mutagens. SIGNIFICANCE AND IMPACT OF THE STUDY: The assay developed in this study is a potentially useful tool in studies on mutagenic pollution of environment, especially marine water.     

Immunomagnetic recovery of Mycobacterium bovis from naturally infected environmental samples

AIMS: To adapt an immunomagnetic capture (IMC) technique to concentrate and cultivate Mycobacterium bovis from environmental samples including soil, faeces and urine. METHODS AND RESULTS: Cells of Myco. bovis BCG and wild-type Myco. bovis were successfully isolated and cultured from seeded and naturally infected materials respectively. The IMC cell recovery estimated by colony forming units (CFUs) counts ranged from 0.10% to 0.16% for spiked media, and 0.15-0.36% for naturally infected soil and faeces. Recovery estimated by cell counts calculated using semi-quantitative PCR ranged from 80.3% to 88.6% for spiked and 84.1-88.2% for naturally infected material. The differences in the recovery rates estimated by CFUs compared with pixel intensity is likely to be due to clustering of cells on culture plates, thereby underestimating the true cell count. CONCLUSIONS: The IMC techniques can be applied to isolate viable wild type Myco. bovis from naturally contaminated environmental samples. SIGNIFICANCE AND IMPACT OF STUDY: Cultivation of Myco. bovis from environmental samples using traditional methods is extremely problematic. Here, we demonstrate a novel development of IMC techniques that will greatly facilitate the study of the organism in situ in order to assess its epidemiological importance in bovine tuberculosis persistence.     

Early angiosperm ecology: evidence from the Albian-Cenomanian of Europe

BACKGROUND AND AIMS: The mid-Cretaceous is a period of sudden turnover from gymnosperm to angiosperm-dominated floras. The aim was to investigate the fossil plant ecology in order to follow the spread of angiosperm taxa. METHODS: Floristic lists and localities from the latest Albian-Cenomanian of Europe are analysed with Wagner's Parsimony Method, a clustering method currently used in phylogeny (cladistics). KEY RESULTS: Wagner's Parsimony Method points out that (a) gymnosperms dominated brackish water-related environments while angiosperms dominated freshwater-related environments (e.g. swamps, floodplains, levees, channels), (b) angiosperms showed the highest diversity in stable, freshwater-related environments, (c) a single angiosperm, 'Diospyros' cretacea, is restricted to brackish water-related environments and (d) the families Lauraceae and Platanaceae were exclusive to disturbed, braided river environments, implying a opportunist strategy for early tree angiosperms. CONCLUSIONS: During the Mid-Cretaceous, European floras were characterized by (a) coastal gymnosperms, (b) highly diversified fluvial angiosperms and (c) the first European brackish water-related angiosperm.     

Modelling environmental variation in Young's modulus for Pinus radiata and implications for determination of critical buckling height

• Background and Aims Although density-specific stiffness,E/, (where E is Young's modulus and is wood density) is oftenassumed constant by the elastic similarity model, and in determinationof critical buckling height (H_crit), few studies have testedthis assumption within species. Here this assumption is testedfor Pinus radiata growing across an environmental gradient,and theory is combined with data to develop a model of Young'smodulus. • Methods Analyses use an extensive series of environmentalplots covering the range of climatic and edaphic conditionsover which P. radiata is grown in New Zealand. Reduced majoraxis regression was used to determine scaling exponents betweenlog–log plots of H_crit vs. groundline diameter (D), andE/ vs. D. Path analysis was used to identify significant directand indirect (through stem slenderness) edaphic and climaticinfluences on E. • Key Results Density-specific stiffness exhibited 3-foldvariation. As E/ scaled positively with D, the exponent of 0·95between H_crit and D exceeded the assumed value of 0·67under constant E/. The final path analysis model included meanair temperature in early autumn (T_aut) and slenderness as significant(P < 0·05) positive direct influences on E. Tree leafarea index and T_aut were indirectly associated with E throughtheir significant (P < 0·05) positive direct relationshipwith stem slenderness. Young's modulus was most sensitive toT_aut, followed by stem slenderness then leaf area index, andthe final model explained 76 % of the variance in E. • Conclusions The findings suggest that within speciesE/ variation may influence H_crit and the scaling exponent betweenD and H_crit so important in assumptions regarding allometricrelationships. The model presented may provide a useful meansof determining variation in E, E/ and H_crit across environmentalgradients.     

Inbreeding depression and mixed mating in Leptosiphon jepsonii: a comparison of three populations

BACKGROUND AND AIMS: Inbreeding depression is thought to play a central role in the evolution and maintenance of cross-fertilization. Theory indicates that inbreeding depression can be purged with self-fertilization, resulting in positive feedback for the selection of selfing. Variation among populations of Leptosiphon jepsonii in the timing and rate of self-fertilization provides an opportunity to study the evolution of inbreeding depression and mating systems. In addition, the hypothesis that differences in inbreeding depression for male and female fitness can stabilize mixed mating in L. jepsonii is tested. METHODS: In a growth room experiment, inbreeding depression was measured in three populations with mean outcrossing rates ranging from 0.06 to 0.69. The performance of selfed and outcrossed progeny is compared at five life history stages. To distinguish between self-incompatibility and early inbreeding depression, aborted seeds and unfertilized ovules were counted in selfed and outcrossed fruits. In one population, pollen and ovule production was quantified to estimate inbreeding depression for male and female fitness. KEY RESULTS: Both prezygotic barriers and inbreeding depression limited self seed set in the most outcrossing population. Cumulative inbreeding depression ranged from 0.297 to 0.501, with the lowest value found in the most selfing population. Significant inbreeding depression for early life stages was found only in the more outcrossing populations. Inbreeding depression was not significant for pollen or ovule production. CONCLUSIONS: The results provide modest support for the hypothesized relationship between inbreeding depression and mating systems. The absence of early inbreeding depression in the more selfing populations is consistent with theory on purging. Differences in male and female expression of inbreeding depression do not appear to stabilize mixed mating in L. jepsonii. The current estimates of inbreeding depression for L. jepsonii differ from those of previous studies, underscoring the effects of environmental variation on its expression.     

Mating behaviors of the proboscis monkey (Nasalis larvatus)

The mating behaviors of the proboscis monkey were observed in a riverine forest along a tributary of the Kinabatangan River, Sabah, Malaysia, for a period of 30 months. Solicitation for copulation was initiated frequently by males and occasionally by females. Most copulations involved only one mount; however, some multiple-mount copulations were observed and a maximum of six mounts per copulation were recorded. The mean duration of mounts was about 27 sec. Nonsexual mounts (female-female, female-juvenile/infant, juvenile-juvenile, and juvenile-infant) were also observed. Female-female mounts occurred shortly after failed solicitations toward males were observed. Harassment by juveniles and/or infants was observed during copulation; however, these harassments apparently did not interfere with copulation. Sexual swelling was evident in 77.4% of copulating females, with copulating subadult females showing the most distinct swelling.     

Characterization of photosynthetic pathway of plant species growing in the eastern Tibetan plateau using stable carbon isotope composition

The photosynthetic pathway of plant species collected at Menyuan, Henan, and Maduo sites, east of Tibetan Plateau, China, during the growing season were studied using stable carbon isotopes in leaves. The 232 samples leaves analyzed belonged to 161 species, 30 families, and 94 genera. The δ¹³C values (from −24.6 to − 29.2 ‰) indicated that all the considered species had a photosynthetic C₃ pathway. The absence of plant species with C₄ photosynthetic pathway might be due to the extremely low air temperature characterizing the Tibetan Plateau. The average δ¹³C value was significantly (p<0.05) different between annuals and perennials at the three considered study sites. Hence the longer-lived species had greater water-use efficiency (WUE) than shorter-lived species, that is, longer-lived species are better adapted to the extreme environmental conditions of the Tibetan Plateau.     

Diffusive transport in Stokeslet flow and its application to plankton ecology

In this paper we consider the advective/diffusive transport of a solute near a hovering zooplankter. We approximate the fluid flow with that of a Stokeslet, corresponding to the plankter exerting a point force on the water, and assume that the plankter acts as a point source for the transported solute, located at the same point as the force. We find an analytical expression in closed form for the steady-state concentration of the solute. We also discuss the situation where the plankter performs Brownian motion. Finally we apply the results to the courtship of the marine copepod Pseudocalanus elongatus, where the male performs a mating dance below the hovering female. For this situation, our model supports the hypothesis that the mating dance is guided by the plume of a signalling pheromone.