This question is subtly different than asking if organisms are distinct - a fact which made it hard for me to see how to approach it! This question arises from thinking about the variability associated with hybrid swarms, which we assume are morphologically variable as a result of genetic variability. The answer is "not neccessarily", as phenotypic plasticity also can be a source of non-genetic morphological variability.
The first set of abstracts on this page refer to recent papers on phenotypic plasticity. The second set of abstracts refer to hybrid swarms. Go directly to abstracts on hybrid swarms. Go back to Finding Order in Chaos
Alvinellid polychaetes are, to date, restricted to deep-sea hydrothermal vents of the eastern and the western ridges of the Pacific Ocean. These organisms Live in various sulfide-rich habitats, including the hottest part of the hydrothermal environment (i.e. chimneys). They experience transient anoxia, high levels of heavy metals and H2S, natural radioactivity and temperatures ranging from 5 to 80 degrees C which vary greatly with time. The Alvinellidae, as many vent organisms, have developed specific adaptations to cope with this harsh and unstable environment. Enzyme systems are good markers of the adaptation of ectotherms to temperature, which acts on both enzyme kinetics and protein denaturation. We estimated genetic distances between 11 alvinellid species using a data set of allozymes and studied in vitro allozyme thermostabilities of aspartate-amino transferase (AAT), glucose-6-phosphate isomerase (GPI) and phosphoglucomutase (PGM), which may play a role in orientating aerobic versus anaerobic metabolism pathways, for 8 species using the most common homozygous genotypes. Results show great genetic divergences between species living in distinct microhabitats as well as strong thermostability differences within and between species which also rely on different enzymatic strategies (phenotypic plasticity versus genetic variability). Allelic fitness to temperature in a highly fluctuating environment may explain the high level of polymorphism found in alvinellids and may have also provided sufficient genetic divergence between individuals living in distinct thermal regimes to produce speciation.
When measured directly, rather than inferred from pedigree analyses, the relationship between similarity in phenotype and similarity in DNA sequence was detectable at the level of members of a single population and strongly depended on the environmental context. Genetic divergence among 27 co-occurring genotypes of Abutilon theophrasti, a common annual plant, was less than 5 per cent as revealed by RAPD-PCR analysis based on over 400 bands per genotype. Nevertheless, within this narrow range, there was a positive correlation between genetic similarity and similarity in the performance of genotypes on temperature and moisture gradients, suggesting that plasticity itself has a genetic basis. No relationship was detected, however, when the phenotypic plasticity was expressed in response to gradients of light intensity or soil fertilization, indicating a weaker genetic basis, or suggesting possible involvement of a few genes of major effect.
We review recent studies in ecological genetics considering the way genes interact with the environment. Studies on morphological and allozyme polymorphisms continue to highlight problems in identifying selective factors. Selection on allozymes as well as quantitative traits may only occur under specific conditions. Responses to toxins illustrate how adaptive changes can be based on major genes with polygenic modifiers. Analyses of continuous variation in ecologically relevant traits suggest low levels of heritable variation in some natural situations and emphasize the importance of genetic interactions. It is still not clear if adaptive responses in quantitative traits tend to involve major or minor genes. There is some evidence for genetic tradeoffs among environments and life history traits. Low levels of genetic variation, tradeoffs, and gene flow may restrict distributions and habitats occupied by species, but their relative importance remains unclear.
Levels of genetic variation and phenotypic plasticity for two quantitative traits, biomass and fecundity, were investigated in two Swedish and one German population of the rare species Vicia pisiformis. Open pollinated progenies were cultivated under four different temperature conditions in growth chambers. One population, Borgehall, was represented by a sufficient number of families to allow an analysis of within-population variation. For the Borgehall population, large variance components and highly significant family effects for both dry matter production and number of flowers per plant were found. Two measures of phenotypic plasticity (coefficient of variation, CV, and the treatment effect in the analysis of variance), demonstrated a greater response to temperature for number of flowers, than for dry weight. At the population level, the treatment effect and the family within population effect were significant for both variables. Furthermore, the significant population x treatment interaction for flower number indicated genetic variation among populations in temperature response for this trait. The considerable amount of genetic variation in adaptive traits contrasts with the low variation previously detected at the DNA level. It is concluded that the technique chosen to describe genetic variation can have a major impact on the conservation strategy of threatened plant species. Knowledge about the generic variation in quantitative traits and their phenotypic plasticity for conservation of genetic diversity are discussed.
Vaccinium macrocarpon Aiton (cranberry) exhibits phalanx and guerilla growth patterns. Phalanx modules (uprights) bear fruit, while guerilla modules (runners) are important in vegetative spread. Although cranberry is known to respond to edaphic variation through altered phenotypes (phenotypic plasticity), patterns in natural populations, especially southern marginal populations, are enigmatic. The objectives of this study were to characterize spatial clonal patterns and phenotypic plasticity patterns within two isolated V., macrocarpon populations in the Appalachian mountains. We used RAPD (random amplified polymorphic DNA) profiling to examine spatial clonal patterns and genetic heterogeneity. The Tennessee (TN) population was genetically homogeneous, as shown by nearly monomorphic RAPD profiles, where only five clones were detected. In contrast, there were over four times more clones discernible and higher molecular diversity in the West Virginia (WV) population. Clonal spatial patterns indicated that one clone was at least 350 years old. Nitrogen and phosphorus were manipulated at the two sites and reaction norms of predominant and infrequent clones within each population were compared to characterize plastic responses. Cranberries in TN were apparently more plastic than WV, although direct statistical comparisons could not be made. The TN population was plastic for more guerilla growth traits and the WV population for more phalanx traits in response to edaphic variation. Within WV, the predominant clone and infrequent clonal reaction norms of several traits to nutrients differed as revealed using a linear analysis of covariance/heterogeneous slopes model.
The ability of organisms to produce different phenotypes under different environmental conditions (phenotypic plasticity) has been an object of evolutionary and ecological studies since the neodarwinian synthesis. Yet, until lately, our knowledge in this field was limited to statistical approaches based on the classical tools of quantitative genetics. In recent years, however, a new dialog between organismal biologists and researchers interested in uncovering the mechanistic details of physiological and phenotypic responses has yielded several new insights. Some classic examples of phenotypic plasticity have now been traced to specific alterations in DNA transcription and RNA translation rates, and to changes in patterns of protein expression. Conversely, the explicit use of evolutionary and ecological theory is helping us to put a panoply of molecular data into a coherent historical and organismal perspective.
The study of natural plant populations has provided some of the strongest and most convincing cases of the operation of natural selection currently known, partly because of amenability to reciprocal transplant experiments, common garden work, and long-term in situ manipulation. Genetic differentiation among plant populations over small scales (a few cm to a few hundred cm) has been documented and is reviewed here, in herbaceous annuals and perennials, woody perennials, aquatics, terrestrials, narrow endemics, and widely distributed species. Character differentiation has been documented for most important features of plant structure and function. Examples are known for seed characters, leaf traits, phenology, physiological and biochemical activities, heavy metal tolerance, herbicide resistance, parasite resistance, competitive ability, organellar characters, breeding systems, and life history. Among the forces that have shaped these patterns of differentiation are toxic soils, fertilizers, mowing and grazing, soil moisture, temperature, light intensity, pollinating vectors, parasitism, gene flow, and natural dynamics. The breadth and depth of the evidence reviewed here strongly support the idea that natural selection is the principal force shaping genetic architecture in natural plant populations; that view needs to be more widely appreciated than it is at present.
Outcrossing has been documented in a natural population of the self-fertilizing hermaphroditic killifish, Rivulus marmoratus. All of the 24 hermaphrodites collected in 1991 on Twin Gays, a small island adjacent to the Belize barrier reef, proved, by direct assay of their progeny, to be multiply heterozygous for mini- and microsatellite loci detected by DNA fingerprinting. The results are strikingly different from those obtained previously with this species, for ail other populations studied have consisted of arrays of homozygous clones. The outcrossing in the population presumably stems from male x hermaphrodite matings. Males of the species are usually rare in nature, but were relatively common on Twin Gays, possibly produced by temperature extremes on the island. Outcrossing in the Twin Gays populations may therefore be the direct result of the environmental induction of males. If true, this would be an example of phenotypic plasticity of almost unprecedented impact. However, there is evidence that social factors, as yet unresolved, may also be important in both the requisites of outcrossing: the induction of males and the reduction of internal self-fertilization in hermaphrodites.
The ovoviviparous Littorina saxatilis (Olivi) can be found in many intertidal habitats. Winkles From different habitats have different morphologies and behaviours, which are usually argued to reflect adaptations. Whether the different forms are caused by genetic differentiation or due to phenotypic plasticity is, however, less discussed. Our aim was to document morphological and behavioural differences among one exposed rock population, one sheltered boulder population, and one mud flat population, and we reared offspring in a common laboratory environment to see if the differences persisted. We used principal component analysis (PCA), based on 19 measurements, to compare size and shape differences. We also used PCA and linear regression to study allometry and compare growth trajectories. Behavioural differences were studied in three laboratory trials. Littorina saxatilis From the rock were relatively small, had small aperture lips, thin shells, blunt spires, and wide columellae. They preferred to stay in cracks and to be above the water surface, and they quickly emerged out of their shells after disturbance. L. saxatilis from the boulder shore were relatively large, had large lips, thick shells, pointed spires, and narrow columellae. They preferred open surfaces, submergence, and after disturbance they slowly emerged out of the shell. L. saxatilis from the mud flat were relatively small, had small lips, thin shells, pointed spires, and narrow columellae and most behaved similarly to the boulder shore snails. Although less pronounced, most of these morphological and behavioural differences persisted in the snails that we reared in the common environment. This indicates some genetic differentiation. All groups grew allometrically, and most groups differed in growth trajectories. Despite similar ages, the reared females were generally larger than the reared males, indicating higher growth rate in females. Sexual maturation seemed to be reached at a certain size rather than at a certain age. Theories predict genetic differentiation in intertidal snail species with low dispersal, but some investigations show results that contradict the theories, while others agree with them. Our study confirms the prediction that L. saxatilis should be genetically differentiated.
Genetic adaptation implies the shaping of population and species gene pools In response to environmental challenges. The two components of the abiotic land environment are climate and soil, both of which determine much of the evolutionary adaptedness of plants as, besides representing a set of surrounding physical, chemical and sometimes limiting traits, they determine the availability of nutrients and energy, of which they are the immediate source. Ecogeographical distribution of species and ecotypes and different physiological mechanisms and developmental patterns are good evidence of plant adaptedness to soil and climate. However, it is not always easy to determine the underlying genetics of adaptive processes, because 1) environmental factors to which the plants are responding are not always evident and are sometimes too complex, 2) several genes may be involved in the response to a given environmental factor, and 3) the same gene/s may be involved in different adaptive responses. In particular, data on Avena species and temperature as a key environmental factor will be used to illustrate some examples of climatic and edaphic adaptedness. Temperature affects the genetic evolution and geographical distribution of all organisms, and a great deal of evidence indicates that species and populations are genetically adapted to different temperature regimes. Isozymes and other molecular markers have helped in the understanding of the genetic basis of adaptedness. There are many examples of correlation between isozyme and DNA-marker variation and environmental differences. For many population geneticists, isozyme markers are just genetic markers with little or no direct involvement in adaptation. However, metabolic processes are controlled by enzymes, influenced by the environment and used to react in response to it. Evidence that isozymes, and perhaps other molecular polymorphisms, are directly involved in adaptedness will be also presented. Molecular genetic analyses at gene and population levels are opening the ways to a better understanding of plant genetic adaptation.