Expression Of Phenotypic Plasticity Research Articles

Phenotypic and genotypic divergence of plant-herbivore interactions along an urbanization gradient.

Urban environments provide challenging conditions for species survival, including increased temperatures, drought and pollution. Species can deal with these conditions through evolution across generations or the immediate expression of phenotypic plasticity. The resulting phenotypic changes are key to the performance of species and their interactions with other species in the community. We here document patterns of herbivory in Arabidopsis thaliana along a rural–urban gradient, and tested the genetic background and ecological consequences of traits related to herbivore resistance. Aphid densities increased with urbanization levels along the gradient while plant size did not change. Offspring of urban mothers, raised under common garden conditions, were larger and had a decreased trichome density and seed set but a higher caterpillar (Pieris brassicae) tolerance. In contrast, no urban evolution was detected for defences against aphids (Myzus persicae). Aphids reduced seed set more strongly in urban offspring, but this effect disappeared in second‐generation plants. In general, urban adaptations as expressed in size and caterpillar tolerance were found, but these adaptations were associated with smaller inflorescences. The maternal effect on the response of seed set to aphid feeding demonstrates the relevance of intergenerational plasticity as a direct ecological consequence of herbivory. Our study demonstrates that the urban environment interacts with the plant's genotype and the extended phenotype as determined by ecological interactions.

Phenotypic plasticity and community composition interactively shape trophic interactions

Trait variation defines and underpins biodiversity, yet we are only beginning to understand how processes acting across biological scales (individuals to whole communities) interact to produce trait differences and their consequences, particularly over short time scales. First, species often differ widely in their mean phenotype, meaning that changes in community composition can alter average trait values of a guild. Second, phenotypic plasticity alters the trait values of individuals, and the net effect of plasticity can also shift the average trait values of a specific species or of whole communities. However, community assembly, phenotypic plasticity, and their effects on biological patterns are not independent. The expression of phenotypic plasticity tends to be species‐specific, meaning that differences in species’ relative abundances will shape trait change and resulting ecological patterns and processes. I test this idea using mesocosms and simulations of communities of dragonfly larvae that differ in activity rate. Some but not all species reduced their activity rate in response to predation risk, causing larger trait‐mediated changes in trophic interactions in experimental communities dominated by plastic versus aplastic species. Using surveys and simulations of natural ponds, I demonstrate that community composition will shape patterns of phenotypic plasticity, with likely consequences for ecological dynamics in the wild. The interactive effects of trait differences across scales of biological organization necessitates an integrated view of diverse biological processes, including plasticity and community assembly, in order to understand ecological interactions.

Adaptive Alignment of Plasticity With Genetic Variation and Selection.

Theoretical research has outlined how selection may shape both genetic variation and the expression of phenotypic plasticity in multivariate trait space. Specifically, research regarding the evolution of patterns of additive genetic variances and covariances (summarized in matrix form as G) and complementary research into how selection may shape adaptive plasticity lead to the general prediction that G, plasticity, and selection surfaces are all expected to align with each other. However, less well discussed is how this prediction might be assessed and how the modeled theoretical processes are expected to manifest in actual populations. Here, we discuss the theoretical foundations of the overarching prediction of alignment, what alignment mathematically means, how researchers might test for alignment and important caveats to this testing. The most important caveat concerns the fact that, for plasticity, the prediction of alignment only applies to cases where plasticity is adaptive, whereas organisms express considerable plasticity that may be neutral or even maladaptive. We detail the ramifications of these alternative expressions of plasticity vis-à-vis predictions of alignment. Finally, we briefly highlight some important interpretations of deviations from the prediction of alignment and what alignment might mean for populations experiencing environmental and selective changes.

Beyond buying time: the role of plasticity in phenotypic adaptation to rapid environmental change.

How populations and species respond to modified environmental conditions is critical to their persistence both now and into the future, particularly given the increasing pace of environmental change. The process of adaptation to novel environmental conditions can occur via two mechanisms: (1) the expression of phenotypic plasticity (the ability of one genotype to express varying phenotypes when exposed to different environmental conditions), and (2) evolution via selection for particular phenotypes, resulting in the modification of genetic variation in the population. Plasticity, because it acts at the level of the individual, is often hailed as a rapid-response mechanism that will enable organisms to adapt and survive in our rapidly changing world. But plasticity can also retard adaptation by shifting the distribution of phenotypes in the population, shielding it from natural selection. In addition to which, not all plastic responses are adaptive-now well-documented in cases of ecological traps. In this theme issue, we aim to present a considered view of plasticity and the role it could play in facilitating or hindering adaption to environmental change. This introduction provides a re-examination of our current understanding of the role of phenotypic plasticity in adaptation and sets the theme issue's contributions in their broader context. Four key themes emerge: the need to measure plasticity across both space and time; the importance of the past in predicting the future; the importance of the link between plasticity and sexual selection; and the need to understand more about the nature of selection on plasticity itself. We conclude by advocating the need for cross-disciplinary collaborations to settle the question of whether plasticity will promote or retard species' rates of adaptation to ever-more stressful environmental conditions. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.

Ontogenetic changes in genetic variances of age-dependent plasticity along a latitudinal gradient.

The expression of phenotypic plasticity may differ among life stages of the same organism. Age-dependent plasticity can be important for adaptation to heterogeneous environments, but this has only recently been recognized. Whether age-dependent plasticity is a common outcome of local adaptation and whether populations harbor genetic variation in this respect remains largely unknown. To answer these questions, we estimated levels of additive genetic variation in age-dependent plasticity in six species of damselflies sampled from 18 populations along a latitudinal gradient spanning 3600 km. We reared full sib larvae at three temperatures and estimated genetic variances in the height and slope of thermal reaction norms of body size at three points in time during ontogeny using random regression. Our data show that most populations harbor genetic variation in growth rate (reaction norm height) in all ontogenetic stages, but only some populations and ontogenetic stages were found to harbor genetic variation in thermal plasticity (reaction norm slope). Genetic variances in reaction norm height differed among species, while genetic variances in reaction norm slope differed among populations. The slope of the ontogenetic trend in genetic variances of both reaction norm height and slope increased with latitude. We propose that differences in genetic variances reflect temporal and spatial variation in the strength and direction of natural selection on growth trajectories and age-dependent plasticity. Selection on age-dependent plasticity may depend on the interaction between temperature seasonality and time constraints associated with variation in life history traits such as generation length.

Transgenerational effects alleviate severe fecundity loss during ocean acidification in a ubiquitous planktonic copepod.

Ocean acidification (OA) caused by anthropogenic CO2 emission is projected for thousands of years to come, and significant effects are predicted for many marine organisms. While significant evolutionary responses are expected during such persistent environmental change, most studies consider only short-term effects. Little is known about the transgenerational effects of parental environments or natural selection on the capacity of populations to counter detrimental OA effects. In this study, six laboratory populations of the calanoid copepod Pseudocalanus acuspes were established at three different CO2 partial pressures (pCO2 of 400, 900 and 1550μatm) and grown for two generations at these conditions. Our results show evidence of alleviation of OA effects as a result of transgenerational effects in P.acuspes. Second generation adults showed a 29% decrease in fecundity at 900μatm CO2 compared to 400μatm CO2 . This was accompanied by a 10% increase in metabolic rate indicative of metabolic stress. Reciprocal transplant tests demonstrated that this effect was reversible and the expression of phenotypic plasticity. Furthermore, these tests showed that at a pCO2 exceeding the natural range experienced by P.acuspes (1550μatm), fecundity would have decreased by as much as 67% compared to at 400μatm CO2 as a result of this plasticity. However, transgenerational effects partly reduced OA effects so that the loss of fecundity remained at a level comparable to that at 900μatm CO2 . This also relieved the copepods from metabolic stress, and respiration rates were lower than at 900μatm CO2 . These results highlight the importance of tests for transgenerational effects to avoid overestimation of the effects of OA.

Kinase domain-targeted isolation of defense-related receptor-like kinases (RLK/Pelle) in Platanus×acerifolia: phylogenetic and structural analysis.

BackgroundPlant receptor-like kinase (RLK/Pelle) family regulates growth and developmental processes and interaction with pathogens and symbionts.Platanaceae is one of the earliest branches of Eudicots temporally located before the split which gave rise to Rosids and Asterids. Thus investigations into the RLK family in Platanus can provide information on the evolution of this gene family in the land plants.Moreover RLKs are good candidates for finding genes that are able to confer resistance to Platanus pathogens.ResultsDegenerate oligonucleotide primers targeting the kinase domain of stress-related RLKs were used to isolate for the first time 111 RLK gene fragments in Platanus × acerifolia. Sequences were classified as candidates of the following subfamilies: CrRLK1L, LRR XII, WAK-like, and LRR X-BRI1 group. All the structural features typical of the RLK kinase domain were identified, including the non-RD motif which marks potential pathogen recognition receptors (PRRs). The LRR XII candidates, whose counterpart in Arabidopsis and rice comprises non-RD PRRs, were mostly non-RD kinases, suggesting a group of PRRs. Region-specific signatures of a relaxed purifying selection in the LRR XII candidates were also found, which is novel for plant RLK kinase domain and further supports the role of LRR XII candidates as PRRs. As we obtained CrRLK1L candidates using primers designed on Pto of tomato, we analysed the phylogenetic relationship between CrRLK1L and Pto-like of plant species. We thus classified all non-solanaceous Pto-like genes as CrRLK1L and highlighted for the first time the close phylogenetic vicinity between CrRLK1L and Pto group. The origins of Pto from CrRLK1L is proposed as an evolutionary mechanism.ConclusionsThe signatures of relaxed purifying selection highlight that a group of RLKs might have been involved in the expression of phenotypic plasticity and is thus a good candidate for investigations into pathogen resistance.Search of Pto-like genes in Platanus highlighted the close relationship between CrRLK1L and Pto group. It will be exciting to verify if sensu strictu Pto are present in taxonomic groups other than Solanaceae, in order to further clarify the evolutionary link with CrRLK1L.We obtained a first valuable resource useful for an in-depth study on stress perception systems.Electronic supplementary materialThe online version of this article (doi:10.1186/1756-0500-7-884) contains supplementary material, which is available to authorized users.

Crecimiento y desempeño fotosintético de cinco plántulas de especies arbóreas en respuesta a regímenes lumínicos naturales del Pacífico Central de Costa Rica

Environmental heterogeneity mostly dominated by differing light regimes affects the expression of phenotypic plasticity, which is important for plant growth and survival, especially in the forest understory. The knowledge about these responses to this heterogeneity is a key factor for forest restoration initiatives. In this study, we determine several phenotypic responses to contrasting light conditions in five native tree seedling species of La Cangreja National Park, Central Pacific of Costa Rica, four of them with threatened or relict populations. After 14 weeks at a medium gap condition (24% of full sun), seedlings were transferred and acclimated for 11 weeks to three different natural light regimes: large gap (LG), medium gap (MG) and small gap (SG), corresponding to 52%, 24%, 9% of the mean direct and indirect radiation at each site from full sun. Growth, biomass allocation and leaf gas exchange were measured after the acclimation period. Four species strongly reduced relative growth rate (RGR) in the lower light condition. Total biomass (TB) and RGR were different in Hymenaea courbaril and Platymiscium curiense. H. courbaril and Astronium graveolens had significant changes in the maximum assimilation rate, with a mean value in the LG of 11.02 and 7.70 micromolCO2/m2s, respectively. P. curuense showed the same trend and significant changes in RGR and biomass allocation. Aspidosperma myristicifolium and Plinia puriscalensis showed no adjustments to the light regimes in any of the measured variables. This study remarks the importance of determining the growth and physiological performance of these tree native species. It also demonstrates that the most threatened species are those with the less plastic responses to the light regimes, which stresses the difficult situation of their natural populations. This study highlights an urgent definition of the conservation and restoration needs of the degraded forests of the Costa Rican Central Pacific area, where these species dwell.

Phenotypic plasticity in response to food source in Triatoma infestans (Klug, 1834) (Hemiptera, Reduviidae: Triatominae)

In the Gran Chaco region of Argentina, Bolivia, and Paraguay, vector transmission of Trypanosoma cruzi, the etiological agent of Chagas disease, is still a severe problem because, among other causes, houses are reinfested with Triatoma infestans, the main vector of T. cruzi in southern South America. A better understanding of adaptation and evolution of T. infestans populations may contribute to the selection of appropriate vector control strategies in this region. Phenotypic plasticity is essential to understand development and maintenance of morphological variation. An experimental phenotypic plasticity study was conducted to assess if blood meal source induced head shape and size variation during development in T. infestans. Eighteen full-sib families were assigned to one of two food sources (pigeon and guinea pig) to examine the effect of food source on head shape and size in all nymph instars and adults. Data were analyzed using geometric morphometric tools and phenotypic plasticity analyses. Significant differences in head shape and size were observed between adults fed on different food sources. Allometric effects at the adult stage were observed. Head size showed significant food source×family interaction for fifth-instar nymphs and adults. For head size, significant differences between food sources were observed at stages and in ontogenetic trajectory. Phenotypic plasticity expression was found for head shape and size in adults; indeed, bugs fed on guinea pigs exhibited greater changes in head shape and larger heads than those fed on pigeon. Full-sib families exhibited different patterns of phenotypic expression in response to food source. Food source×family interaction may indicate that the observed variation in phenotypic plasticity may contribute to changes in head morphometry. These results may contribute to the selection of an appropriate control strategy for T. infestans in the Gran Chaco region, since they provide evidences of morphological plasticity in this species.

Phenotypic plasticity of reproductive traits in response to food availability in invasive and native species of nematode

Invasive species cause severe ecological and economic damage; however, the mechanisms underlying their successful invasion often remain elusive. In the case of Bursaphelenchus xylophilus, a global quarantine pest which invaded Asia and Europe, it has been suggested that this species possesses highly competitive abilities, which promotes its establishment and rapid spread. To explore biological traits that may explain its highly competitive abilities, we focused on expression of phenotypic plasticity in response to the food conditions experienced by the females during their development as juveniles in the invasive species B. xylophilus and native species Bursaphelenchus mucronatus. We report an unexpected significant difference of phenotypic trade-off between egg number and egg size in the invasive species B. xylophilus and native species B. mucronatus. This leads to superior propagation ability of invasive species, under high and low food conditions in culture. These effects reflect adaptive optimal resource allocation where more eggs are produced in favorable environments to enhance population viability. Furthermore, we show that B. xylophilus eggs hatched earlier than B. mucronatus when their parents experienced high food availability. Thus, this study revealed, for the first time, phenotypic plasticity of reproductive traits in B. xylophilus which empowers the species a competitive advantage relative to their native counterpart B. mucronatus when they are under different range of food availability. These results are a step towards answering the vital question of how an exotic invasive species exclude a native species from its original niche.

Expressão da plasticidade fenotípica em filhotes do lagarto Calotes versicolor (Squamata: Agamidae): influência da umidade do ninho.

Expression of phenotypic plasticity in hatchlings of the lizard Calotes versicolor (Squamata: Agamidae): influence of nest moisture. Calotes versicolor breed from late May to early October. The breeding activity begins with the onset of the southwest monsoon. The eggs laid in early breeding season experience more wet conditions than those of the late breeding season. We studied the influence of nest moisture levels on the phenotypic traits of hatchlings by burying the eggs in 5‑cm‑deep sand nests with ~50% (wet nest) or ~20% (relatively dry nest) moisture to simulate nesting conditions of early and late breeding seasons. A group of eggs were subjected to standard laboratory incubation procedure in which eggs are half‑buried in the moist sand and the other half exposed to air. Hatching time and hatchling body size varied with the treatment. The eggs from dry nests hatched later and hatchlings were the biggest but possessed least amount of residual yolk compared to those of ''wet nest'' and also ''lab incubated'' groups. In these hatchlings head and limb sizes were significantly larger than that of the other two groups. The findings show: (1) a developmental plasticity in the lizard, (2) that under low moist conditions larger body size is preferred, and (3) that the trade‑off between somatic growth of embryos and future energy reserves (residual yolk) of hatchlings is influenced by the soil moisture in C. versicolor.

Precise Manipulation Through a Modeling Study

Organisms are characterized by a suite of characteristics that collectively constitute a phenotype. Interactions with the biotic and abiotic environment result in modifications of the phenotype, and consequently in modifications of the interactions of the individual with community members. Chemical ecologists have a keen interest in the information component of phenotypes. They unravel the mechanisms that underlie phenotypic changes in terms of the emission of information-conveying chemicals and the ecological consequences of such phenotypic changes. For instance, feeding by a pierid caterpillar on a brassicaceous plant results in the production of a complex bouquet of volatiles that include fatty-acid-derived compounds, terpenoids, and glucosinolate-derived compounds (Geervliet et al. 1997). The induced volatiles can evoke a range of behavioral responses. They result not only in the attraction of parasitic wasps that attack the caterpillars (Scascighini et al. 2005), but also in the attraction of Plutella xylostella moths for whom the Pieris-infested plant provides enemy-free space (Shiojiri et al. 2002). Induced phenotypic changes allow organisms to adjust to local conditions. However, this requires that an individual perceives environmental changes and responds to them at a speed that results in timely phenotypic change. The expression of phenotypic plasticity is usually thought to be an indication of costs related to the expressed characteristics, either in terms of energy or in terms of ecology (Agrawal 2001). The ecology of herbivore-induced plant volatiles (HIPV) has shown a rapid development since the late 1980s (Dicke and Sabelis 1988; Turlings et al. 1990). In the past decade, molecular genetic tools have been embraced by students in this field (Van Poecke and Dicke 2002; Kessler et al. 2004; Halitschke et al. 2008). In doing so, certain characteristics could be eliminated from or enhanced in plants with a chirurgic precision at the level of individual genes. This approach has allowed us to study individuals that had been modified in the expression of individual genes, usually in a digital method where the gene of interest was knocked out or silenced or where the expression of the gene of interest was enhanced. These methods have revolutionized the field of insect–plant ecology (Dicke et al. 2004; Kessler et al. 2004). They allow the investigation of the effects of individual characteristics on species interactions as well as community dynamics. Apart from molecular genetical tools, mathematical modeling is another powerful tool that allows researchers to investigate the effects of individual characteristics on species interactions. If sufficient knowledge about a system has been gathered to develop an adequate model, the model parameters may be modified to assess their effects on species interactions. Within the field of chemical ecology, modeling has not been a tool that has been exploited frequently (but see e.g., Vos et al. 2001; Kobayashi et al. 2006). Analytical tools have mainly dominated the field. The following two papers by Puente and colleagues have taken a detailed modeling approach to the study of herbivore-induced parasitoid attraction. They especially address the temporal and spatial aspects of plant–parasitoid interactions through HIPV. Timing of HIPV emission relative to herbivore presence is likely to be important, as it determines the reliability of the cues. The induction dynamics of volatile emission vary with the type of volatiles and their biosynthesis. However, after herbivores have been eliminated, continuation of the emission is no J Chem Ecol (2008) 34:943–944 DOI 10.1007/s10886-008-9470-y

Genetic differentiation between morphotypes in the Antarctic limpet Nacella concinna as revealed by inter-simple sequence repeat markers

The limpet Nacella concinna (Strebel 1908) was the focus of numerous studies dealing with Antarctic benthos. One of the main characteristics of the species is the presence of two distinguishable morphotypes, one inhabiting the intertidal (during summer) and the other inhabiting the subtidal. For a long time these forms were considered as an expression of phenotypic plasticity, since previous studies did not found genetic differences between them. In the present work, we performed both a morphometric and a genetic differentiation analysis (using ISSR-PCR markers) of these two forms in three stations sampled at Potter Cove, South Shetland Islands. The results confirmed the morphological differences between intertidal and subtidal forms reported in other Antarctic localities. The genetic differences detected indicate that the two forms can be considered as genetically distinct populations maintaining low levels of gene flow. The degree of reproductive isolation of the ecotypes is discussed, as well as the possible origin of the divergence. The genetic differentiation observed can also have behavioral and physiological correlates, pointing out the importance of taking into account the potential differences in the response of both populations to different conditions in future studies in this species.

HIERARCHICAL RESPONSES OF TADPOLES TO MULTIPLE PREDATORS

The impact of multiple factors on the expression of phenotypic plasticity has been poorly studied. The simultaneous presence of factors inducing diverging responses may result either in a trade-off between the responses or in a hierarchy of responses. Inducible defenses offer a suitable model to investigate these alternatives. Inducible defenses evolve in response to variability in predation risk. Here, we investigated the impact of the nonlethal presence of both pursuing (fish, Gasterosteus aculeatus) and sit-and-wait (dragonfly larvae, Aeshna cyanea) predators on tadpole morphology in two frogs (Rana dalmatina and R. ridibunda). Predation tests showed that Aeshna were the more dangerous of the two predators for the tadpoles of both species. In both species, induced responses differed according to predator type. In the presence of fish, tadpoles invested in both tail muscle depth and tail length. In the presence of dragonfly larvae, the investment was made in tail fin depth. When faced with the two types of predators simultaneously, the response was similar to that expressed in the presence of Aeshna alone, suggesting a hierarchy of response according to predation risk. Such a hierarchy of response could result from selection against the phenotype induced by the other predator.

Size as indicator of origin of salmon lice Lepeophtheirus salmonis (Copepoda: Caligidae)

Salmon lice Lepeophtheirus salmonis (Krøyer, 1837)from farmed Atlantic salmon have been implicated in the drastic sea trout and salmon stock declines found in Ireland and Norway. Can salmon lice from farmed and wild fish be distinguished? The hypothesis has been advanced that the treatment of salmon infested with salmon lice with organophosphate pesticides has resulted in the evolution of early maturing, smaller female lice, which are favoured because they have the chance to reproduce before treatment. Salmon lice on wild fish have been reported to be larger and have more eggs in their egg strings (sacks) than lice on farmed fish. The question is whether the size differences between the lice are genetically fixed or an expression of phenotypic plasticity. In this study, lice from wild and farmed fish were collected and measured, and it was found that the former were significantly larger. When larvae from these two sources were raised on salmon at the same temperature, they bad the same growth rate and morphology. Larvae from the wild lice were raised at 8.7°C and 12.2°C, and attained a significantly larger size at the lower temperature. These results suggest that the salmon louse size is plastic and consequently a poor indicator of salmon louse origin.

The genetic component of copula duration in the yellow dung fly

The heritabilities of copula duration ( h 2=0.39, P<0.01), body size ( h 2=0.76, P<0.001) and development time ( h 2=0.23, P<0.05), plus their genetic covariances, in the yellow dung fly, Scathophaga stercoraria(L.), were assessed using full sibling analysis. The relative order of magnitude of the values agrees with that of other data: morphological>behavioural>life-history characters. Repeated measures of copula duration for each male revealed a general increase in copula duration with Julian date or age. The individual pattern of this change in copula duration (here termed ‘flexibility’), an expression of phenotypic plasticity, was itself marginally heritable ( h 2=0.19, P=0.065). Significant positive phenotypic and genetic covariance was evident only between flexibility of copula duration and body size. All other correlations were not different from zero, including those between development time and body size and between copula duration and body size. It is suggested that in S. stercoraria populations there is some averaging selection towards a mean optimal copula duration which can guide an individual's behaviour in a variety of environments. At the same time, there is selection for phenotypic plasticity which allows individuals to adapt their behaviour to their immediate environment. These effects together are consistent with both the assumptions of optimality models and the classic results on copula duration in yellow dung flies.

Life history plasticity of Nemoura trispinosa (Plecoptera: Nemouridae) along a permanent‐temporary water habitat gradient

SUMMARY1. The life history of the small herbivorous stonefly Nemoura trispinosa Claassen was studied in a variety of small springs in southern Ontario, Canada. Nymphs generally were able to tolerate a wide range of environmental conditions and were found in 78% of habitats sampled, although population densities differed markedly.2. Life‐cycle patterns varied from a univoltine, slow seasonal type to a univoltine, fast seasonal type with extended egg development. In one, highly stable, spring the life cycle was semivoltine. Inter‐year variation was studied for 5 years in one spring and was found to be low relative to among‐spring variation.3. Differences in the life history traits of N. trispinosa populations from our spring series were most probably an expression of phenotypic plasticity rather than of genetic differentiation.4. Maximum annual water temperature was the factor most influential on nymphal growth rate (non‐linear relationship), whereas range in generation time was related to the degree of habitat permanence.

The choice of genetic material for mechanistic studies of adaptation in forest trees.

There is considerable urgency to study the mechanisms by which forest trees track environmental change, given the prospect of possible rapid climatic changes. Environmental tracking is achieved through three basic processes: (1) expression of phenotypic plasticity at the level of the individual; and (2) evolutionary change and (3) migration, both expressed at the level of the population over generations. The current distribution and genetic architecture of a species reflect how these processes interacted in response to past climatic changes during and after the last glaciation. Part of that record is encoded in the DNA of the current generation of trees and, as a result of existing field tests, is accessible for study. These field tests include, in ascending order of genetic resolution, (1) provenance tests, (2) progeny tests, and (3) three-generation clonal tests; as well as (4) clone tests, with or without genetic structure. The suitability and limitations of these tests for mechanistic studies of environmental tracking are described, both as field installations and as sources of material for parallel in-depth studies. We conclude that they represent an important information resource, which deserves to be more effectively used by the scientific community.

Cell wall alterations in staphylococci growing in situ in experimental osteomyelitis.

When cells of both Staphylococcus aureus and Staphylococcus epidermidis are grown in batch culture in nutrient-rich media, their cell walls are regular in thickness, their cell size is within the normal range for each species, and their septation patterns are orderly. When cells of each of these species are examined directly in infected tissue in the rabbit tibia model infection, their cell wall thickness is often much increased and very irregular around the circumference of the cell, their cell size is often increased, and their septation patterns are often severely deranged. All of these alterations in cell wall structure occur in the absence of antibiotics, and we suggest that they may be an expression of phenotypic plasticity in response to altered environmental conditions such as specific nutrient limitations, the presence of antibacterial factors, and growth of the cells on hard surfaces such as rabbit bone or plastic catheters. Some of these specific cell wall alterations are also seen when staphylococcal cells are exposed, in vitro or in vivo, to antibiotics such as clindamycin, but we emphasize that growth in tissue alone is sufficient for their induction.

Genetic variation and phenotypic plasticity of roots in two cultivated species of jute (Corchorus olitorus L. andC. capsularis L.)

1. A number of varieties of cultivated juteGorchorus oHtorius L. andG. capsularis L. were tested in artificially created drought, waterlogging and control conditions. 2. The number of lateral roots with secondary growth was reduced to the minimum inC. capsularis under waterlogged conditions, but the weight of the roots was increased to the maximum, due to the production of numerous spongy and fibrous roots.C. olitorius suffered in both the characters under similar environment and failed to produce fibrous and spongy root. This species gained in root weight and lateral root number in drought under whichC. capsularis suffered in these two characters. These were the main features of adaptation of these two species. 3. Within species among varieties the variations regarding these two characters have been found to be controlled by genotypes. Lateral root number within both the species has been found to be a more strongly heritable character than root weight. Expected genetic advance has revealed the scope of selection for lateral root number. 4. While variations among thé varieties within species have been interpreted as an expression of phenotypic flexibility, the variation between species is an expression of phenotypic plasticity, which is an outcome of basically physiological mechanisms.Corchorus capsularis L. andC. olitorius L. are two cultivated jute species. The most striking distinction between these two species hitherto known is that whileG. capsularis can withstand waterlogging successfully,C. olitorius cannot. This general view formed the basis of testing these species under artificially created environmental stresses to find out the general components contributing to this specific difference.