Micropropagation by tissue culture triggers differential expression of infectious endogenous Banana streak virus sequences (eBSV) present in the B genome of natural and synthetic interspecific banana plantains

The genome of Musa balbisiana spp. contains several infectious endogenous sequences of Banana streak virus (eBSV). We have shown previously that in vitro micropropagation triggers the activation of infectious eBSOLV (endogenous sequences of Banana streak Obino l'Ewai virus ) in the synthetic tetraploid interspecific hybrid FHIA21 (AAAB). In this work, we show that another synthetic tetraploid (AAAB) hybrid and two natural triploid (AAB) plantains are equally prone to the activation of infectious eBSOLV during tissue culture. These results are a strong indication that such activation is a general phenomenon in interspecific Musa cultivars, whether synthetic or natural. We also report the first in-depth study of the correlation between the duration of tissue culture and the level of activation of infectious eBSOLV, and show that specific and common activation patterns exist in these banana plants. We hypothesize that these patterns result from the concomitant activation of infectious eBSOLV and a decrease in the virus titre in neoformed plantlets, resulting from cell multiplication outcompeting virus replication. We provide experimental data supporting this hypothesis. No activation of infectious eBSGFV (endogenous sequences of Banana streak Goldfinger virus) by tissue culture was observed in the two natural AAB plantain cultivars studied here, whereas such activation occurred in the AAAB synthetic hybrid studied. We demonstrate that this differential activation does not result from differences in the structure of eBSGFV, as all banana genomes harbour eaBSGFV-7.     

Carbon accumulation in agricultural soils after afforestation: a meta-analysis

Deforestation usually results in significant losses of soil organic carbon (SOC). The rate and factors determining the recovery of this C pool with afforestation are still poorly understood. This paper provides a review of the influence of afforestation on SOC stocks based on a meta-analysis of 33 recent publications (totaling 120 sites and 189 observations), with the aim of determining the factors responsible for the restoration of SOC following afforestation. Based on a mixed linear model, the meta-analysis indicates that the main factors that contribute to restoring SOC stocks after afforestation are: previous land use, tree species planted, soil clay content, preplanting disturbance and, to a lesser extent, climatic zone. Specifically, this meta-analysis (1) indicates that the positive impact of afforestation on SOC stocks is more pronounced in cropland soils than in pastures or natural grasslands; (2) suggests that broadleaf tree species have a greater capacity to accumulate SOC than coniferous species; (3) underscores that afforestation using pine species does not result in a net loss of the whole soil-profile carbon stocks compared with initial values (agricultural soil) when the surface organic layer is included in the accounting; (4) demonstrates that clay-rich soils (> 33%) have a greater capacity to accumulate SOC than soils with a lower clay content (< 33%); (5) indicates that minimizing preplanting disturbances may increase the rate at which SOC stocks are replenished; and (6) suggests that afforestation carried out in the boreal climate zone results in small SOC losses compared with other climate zones, probably because trees grow more slowly under these conditions, although this does not rule out gains over time after the conversion. This study also highlights the importance of the methodological approach used when developing the sampling design, especially the inclusion of the organic layer in the accounting.     

Embryo development and ageing in birds and mammals

The rate of ageing is a genetically influenced feature of an individual's life history that responds to selection on lifespan. Various costs presumably constrain the evolution of prolonged life, but these have not been well characterized and their general nature is unclear. The analyses presented here demonstrate a correlation among birds and mammals between rates of embryonic growth and ageing-related mortality, which are quantified by the exponents of fitted power functions. This relationship suggests that rapid early development leads to accelerated ageing, presumably by influencing some aspect of the quality of the adult individual. Although the mechanisms linking embryo growth rate and ageing are not known, a simple model of life-history optimization shows that the benefits of longer life can be balanced by connected costs of extended development.     

No simple answers for ecological immunology: relationships among immune indices at the individual level break down at the species level in waterfowl

Understanding immune function in the context of other life-history traits is crucial to understand the evolution of life histories, at both the individual and species levels. As the interest in assessing immune function for these comparative purposes grows, an important question remains unanswered: can immune function be broadly characterized using one or two simple measures? Often, interpretation of individual assays is ambiguous and relationships among different measures of immune function remain poorly understood. Thus, we employed five protocols to measure 13 variables of immune function in ten species of waterfowl (Anseriformes). All assays were based on a single blood sample subdivided into leukocyte (blood smear) and plasma (frozen until analysis) components. All assays were run using samples from every individual, and a nested analysis was used to partition variation/covariation at the levels of species and individuals within species. We detected positive correlations between functionally related measures of immunity within species, but these were absent from comparisons between species. A canonical correlation analysis revealed no significant relationships between the plasma and leukocyte assays at the levels of both individual and species, suggesting that these measures of immunity are neither competitive nor synergistic. We conclude that one measure of each assay type may be required to maximally characterize immune function in studies of a single species, while the same is not true in studies among species.     

The molecular basis of an avian plumage polymorphism in the wild: a melanocortin-1-receptor point mutation is perfectly associated with the melanic plumage morph of the bananaquit, Coereba flaveola

BACKGROUND: Evolution depends on natural selection acting on phenotypic variation, but the genes responsible for phenotypic variation in natural populations of vertebrates are rarely known. The molecular genetic basis for plumage color variation has not been described in any wild bird. Bananaquits (Coereba flaveola) are small passerine birds that occur as two main plumage variants, a widespread yellow morph with dark back and yellow breast and a virtually all black melanic morph. A candidate gene for this color difference is the melanocortin-1 receptor (MC1R), a key regulator of melanin synthesis in feather melanocytes. RESULTS: We sequenced the MC1R gene from four Caribbean populations of the bananaquit; two populations of the yellow morph and two populations containing both the yellow morph and the melanic morph. A point mutation resulting in the replacement of glutamate with lysine was present in at least one allele of the MC1R gene in all melanic birds and was absent in all yellow morph birds. This substitution probably causes the color variation, as the same substitution is responsible for melanism in domestic chickens and mice. The evolutionary relationships among the MC1R haplotypes show that the melanic alleles on Grenada and St. Vincent had a single origin. The low prevalence of nonsynonymous substitutions among yellow haplotypes suggests that they have been under stabilizing selection, whereas strong selective constraint on melanic haplotypes is absent. CONCLUSIONS: We conclude that a mutation in the MC1R is responsible for the plumage polymorphism in a wild bird population and that the melanic MC1R alleles in Grenada and St. Vincent bananaquit populations have a single evolutionary origin from a yellow allele.     

Zinc and cadmium hyperaccumulation by Thlaspi caerulescens from metalliferous and nonmetalliferous sites in the Mediterranean area: implications for phytoremediation

Growth, tolerance and zinc and cadmium hyperaccumulation of Thlaspi caerulescens populations from three metal contaminated soils and three normal soils were compared under controlled conditions. Individuals of six populations were cultivated on five soils with increasing concentrations of zinc (50–25000 μg g⁻¹) and cadmium (1–170 μg g⁻¹). There was no mortality of normal soil populations in the four metal-contaminated soils, but plant growth was reduced to half that of populations from metal-contaminated soils. However, in noncontaminated soil, the growth of individuals from normal soils was greater than that of individuals from metal-contaminated soils. Individuals from normal soils concentrated three times more zinc in the aboveground biomass than those from metal-contaminated soils, but the latter accumulated twice as much cadmium. We conclude that populations of T. caerulescens from both normal and metal-contaminated soils are interesting material for phytoextraction of zinc and cadmium, but to optimize the process of phytoextraction it is necessary to combine the extraction potentials of both type of populations.     

Growth,development, and life‐history strategies in an unpredictable environment: case study of a rare hoverfly Blera fallax (Diptera,Syrphidae)

1. Development in organisms can vary in response to fluctuating environments. In holometabolous insects, variation in adult phenotypic traits is strongly influenced by growth conditions experienced by larvae. The main aim of this study was to assess how much environmental insight can be gained from analysis of the phenotypic changes in an insect's life history parameters in response to realistic food limitations. 2. This investigation was motivated by a need for more information about the developmental requirements of the endangered pine hoverfly Blera fallax (Linnaeus) (Diptera, Syrphidae) in Scotland. Blera fallax depends on a scarce and often ephemeral habitat, rot holes of Scots pine Pinus sylvestris L. stumps. We studied how rearing conditions affected growth in captive larvae, and compared these responses with a wild population. 3. The growth curve observed in the field was similar to that in resource‐limited, lab conditions, suggesting that resources are limiting in nature. The effects of resource availability on development time and body size depended on sex. Adult females were larger but had more variable size at maturity compared with males. In contrast, males typically were not smaller in resource‐limited conditions, but rather continued to develop for another year. Between 2% and 20% of larvae extended development over 2 years regardless of growth conditions, perhaps indicating a semivoltine strategy to circumvent extinction during years with a low breeding success. 4. These results identify life history traits that may be important for other saproxylic Diptera in rot holes, and organisms that experience food restrictions during growth.     

The fine-scale population dynamics of spruce budworm: survival of early instars related to forest condition

Abstract.  1. A lagged, density-dependent relationship between survival of early instars and host-tree condition is revealed during outbreaks of spruce budworm, Choristoneura fumiferana Clem. Persistent damage to hosts leads to deterioration of the stand.
2. Resource limitation affects survival during early-instar dispersal of spruce budworm. Impediments to distinguishing these events with estimates of survival were overcome with a simple model that describes the dispersal and survival processes. The model was used to analyse a recent 15-year population series from Black Sturgeon Lake and two historical datasets from Green River, in Canada.
3. Defoliation-induced damage to the trees resulted in increased losses of spring-emerging larvae that are dispersing in search of feeding sites. Losses were further exacerbated by biotic factors such as maternal fecundity, rates of infection by the pathogen, Nosema fumiferanae , and by weather-related effects on the foraging period.
4. Survival of early-stage budworm larvae in persistent outbreaks declined and the likelihood of other density-related factors such as rate of mortality from natural enemies increased. These results may reconcile outstanding differences in interpretation of the role of the forest resource in spruce budworm population dynamics and point to a common process linking the dynamics of other well-known budworm species.