Evaluation of early generations for iron chlorosis in relation to productivity in groundnut (Arachis hypogaea L.)

Five popular but iron-inefficient cultivars were crossed with three efficient genotypes and both parents and F₁s were evaluated for iron-efficiency in potted calcareous and noncalcareous soil. The iron-efficient genotypes were dark green or green in both noncalcareous and calcareous soils whereas inefficient types were light green to yellow in calcareous soil. The chlorophyll and active iron (Fe²⁺) concentration of leaves was less in iron-efficient genotypes compared to efficient types in calcareous soil and reduction of both the parameters from noncalcareous to calcareous soil was considerably high in iron-inefficient lines. There was significant correlation between visual scores, chlorophyll and active iron content. There were no differences among F₁s for iron chlorosis and they were all iron-inefficient. The frequency of iron-inefficient plants was higher than the efficient plants in all F₂ populations. But most of the productive plants came from iron-efficient segregants indicating strong association between iron-efficiency and productivity. Based on the results selection for iron-efficiency in early generations and extensive evaluation for productivity in advanced generations is suggested for developing varieties for cultivation in calcareous soils.     

The lifetime of molecular (Davydov) solitons

The lifetime of Davydov solitons in a one-dimensional system is studied theoretically. The process of thermalization and the properties of solitons at finite temperature are investigated and the processes of soliton creation and disintegration are discussed.     

Effects of calcium input/output on the stability of a system for calcium-regulated viscoelastic strain fields

The Goodwin and Trainor model of pattern generation in calcium-regulated strain fields is studied in the case where calcium input and calcium output processes are involved. It is shown that the properties of the original model may still remain provided that the input-output processes are not unstable. In this last case, despite the eventual stabilizing effect of the calcium exchange term, perturbations of the generalized system can grow and lead to inhomogeneous solutions. Applications to cell differentiation and cell growth are discussed.     

The intrinsic rates of increase of insects of different sizes

ABSTRACT.

• 1 A negative relationship between intrinsic rate of increase, r, and body size has only clearly been shown using data for species drawn from a number of phyla and covering several orders of magnitude in size. Analyses for more closely related species are equivocal.
• 2 Data for ninety-one species of insects, from nine orders, were used to examine the correlation between intrinsic rate of increase and size.
• 3 Intrinsic rate of increase was negatively correlated with both length and weight across orders, but no relationship could be shown within orders.
• 4 Generation times were positively related to body size, but there was no relationship between net reproductive rate (R_Q) and size.
• 5 These results support the hypothesis that documented relationships between species size and colonization success in insects could be a consequence of the scaling of intrinsic rate of increase with size.

     

Efficient selection intensity in early generation index selection in groundnut (Arachis hypogaea L.)

Summary The F₂ potential of single and three-way crosses was evaluated using a set of physiological and yield components. Results were based on an index of selection using (a) only yield components and (b) both physiological and yield components. The indices were constructed using the percentage improvement of F₂ over the better parent of the corresponding F₁ cross for every character. The performance of F₂ plants assessed by the expected value of the regression index was ranked in descending order to provide a ranked F₂ distribution (FRD). The FRD was divided into four equal parts, T₂₅ (top 25%), T₅₀ (26–50%), T₇₅ (51–75%) and T₁₀₀ (76–100%). F₃ families derived from F₂ plants in T₂₅ were found to provide a higher frequency of selections for pod number than T₅₀, T₇₅ and T₁₀₀. The frequency of selections was higher in three-way than single crosses. Selection index based on physiological and yield components was more efficient in trapping F₂ plants providing selections in F₃ than the index based on yield components only. The results brought out the importance of bunch x bunch crosses as a complement to the usually advocated bunch x runner ones.     

Accumulated effect of elevated ultraviolet-B radiation over multiple generations of the arid-environment annual Dimorphotheca sinuata DC. (Asteraceae)

Two D. sinuata populations, established from the same seed batch, were cultured concurrently under ambient (2.5–8.9 kj m^?2 d^?1) and enhanced (4.7–11.4 kj m^?2 d^?1) ultraviolet-B radiation for two consecutive generations. The two populations, designated low- and high-UV-B cultivars, were each grown for an additional generation under both UV-B fluences at different alignments. Differences in plant performance were examined between UV-B treatments (immediate UV-B effects), cultivars (accumulated UV-B effects), alignments and their interactions. Accumulated UV-B had a greater effect on plant performance than immediate UV-B. The former induced earlier reproductive effort, substantial (up to 35%) reductions in dry mass (stems, leaves and reproductive organs), decreased stem and inflorescence production, and diminished steady-state fluorescence yields, chlorophyll a concentrations, pollen tube growth and germination of seeds set. The latter caused only diminished non-photochemical quenching, reduced chlorophyll a, soluble sugar and starch concentrations, decreased pollen germination, and increased carotenoid contents. Interactions between UV-B fluence level and alignment occurred for all measured dry mass parameters, leaf area, photosynthetic pigment and soluble sugar concentrations, and germination success of seeds set. These results indicate altered DNA integrity rather than an indirect UV-B effect of photomorphogenic origin.     

Variable generation times and Darwinian fitness measures

Summary Reproductive value (RV) and net reproductive output (R _o) are frequently used fitness measures. We argue that they are only appropriate when intervals between reproductive events are fixed, as they are dimensionless generation-to-generation scalings with units offspring per parent. A fitness measure should account for two different effects of a decrease in generation time: (1) increased survival due to shorter exposure to mortality agents and (2) increased frequency of reproduction.R _o andRV deal with the first of these two effects, while a measure with a physical dimensionper time [T^–1] is needed to account for the second. The Malthusian growth parameter,r, meets this requirement and in situations where time to reproduction is variable, we propose, the instantaneous rate of spread of descendants (from an individual) be used instead ofR _o. As an alternative toRV, we suggest using the instantaneous difference = –r, wherer is the population rate of increase. WhileRV andR _o are dimensionless ratios, , and areper time rates which are appropriate in accounting for alterations in generation time.     

Population density and genetic diversity are positively correlated in wild felids globally

Aim

Insights into the biological and evolutionary traits of species, and their ability to cope with global changes, can be gained by studying genetic diversity within species. A cornerstone hypothesis in evolutionary and conservation biology suggests that genetic diversity decreases with decreasing population size, however, population size is difficult to estimate in threatened species with large distribution ranges, and evidence for this is limited to few species. To address this gap, we tested this hypothesis across multiple closely related species at a global scale using population density which is a more accessible measure.

Location

Global.

Time Period

Contemporary.

Major Taxa Studied

Wild felids in their natural habitats.

Methods

We obtained data from published estimates of population density assessed via camera trap and within-population genetic diversity generated from microsatellite markers on 18 felid species across 41 countries from 354 studies. We propose a novel method to standardize population density estimates and to spatially join data using K-means clustering. Linear mixed-effect modelling was applied to account for confounding factors such as body mass, generation length and sample size used for the genetic estimates.

Results

We found a significant positive correlation between population density and genetic diversity, particularly observed heterozygosity and allelic richness. While the confounding factors did not affect the main results, long generation length and large sample size were significantly associated with high genetic diversity. Body mass had no effect on genetic diversity, likely because large-bodied species were over-represented in our data sets.

Main Conclusions

Our study emphasizes how recent demographic processes shape neutral genetic diversity in threatened and small populations where extinction vortex is a risk. Although caution is needed when interpreting the small population density effect in our findings, our methodological framework shows promising potential to identify which populations require actions to conserve maximal genetic variation.