Post by skyship on Feb 1, 2010 1:32:00 GMT -5
Evolutionary and Ecological Implications of Plastic Responses of Algae
"Ironically, the study of phenotypic plasticity within phycology seems to predate contributions dealing with any other group of organisms. For example, the green algal genus Scenedesmus has been recognized as plastic since the mid 1800's."..............
............Thus, the ecotypic adaptation theory disregards both the effect of environmental fluctuations on populations over short periods of time and the fact that plasticity can also be a mechanism for speciation (Pigliucci 1996, Schlichting and Pigliucci 1998)
......In the present review we attempt to place available information on algal plasticity in an evolutionary context and discuss the implications for other phycological fields. The merging of phenotypic plasticity data with current phycological thinking completely changes our view of algae as biological entities. It leads to an integrated species concept in which morphology, physiology, ecology, and evolution are intertwined. In addition, it helps us to understand the relationship between organisms and their immediate environment and how individuals can endure in constantly changing and even newly invaded habitats.........
........Coarse grained variation: plasticity across generations
Variation in habitat conditions at intervals greater than the life span of individuals has been termed “coarse grained” variation (MacArthur and Levins 1967). In this case, changes in the environment trigger a mitotic cell division and the new phenotype is expressed in the filial generation. Most of the cases of plasticity in the phycological literature deal with this coarse-grained responses to environmental cues, for example, Phaeodactylum tricornutum, a pennate diatom, produces oval, fusiform, and triradiate morphs following changes in culture media, light, and temperature. This diatom was recognized as plastic in 1935 by Barker, and since then, various papers have been published on the DNA content, ultrastructural features, and biochemical characterization of the morphs (e.g., Borowitzka and Volcani, 1978, Darley 1968, Gutenbrunner et al. 1994, Lewin et al. 1958, Reimann and Volcani 1968)."..................
...........A critical body of evidence concerning plasticity has been gathered for a variety of cyanobacteria, and through this evidence, taxonomic implications of plasticity have become very clear. The historical development of the classification of this group depicts very well a classic confrontation between “splitter” and “lumper” approaches. Early publications (Geitler 1932) presented extensive lists of organisms that were later complemented with additional descriptions of cyanophytes from other parts of the world (cocke 1967, Desikachary 1959). The number of “species” was staggering, but it was not clearly stated whether the names were designed to represent different genotypes or strikingly different phenotypes. Subsequent collection of laboratory data on the plasticity of individual blue green algal genotypes led different authors to reduce drastically the number of taxa to be accepted."..............
.......". For the genus Spirulina for example, Jeeji-Bai and Sheshadri (1980) concluded that the degree of coiling of the trichomes (used to separate this genus from Arthrospira) varies with light intensity and nutrient concentration in the culture medium. Additionally, other “species” showed a wide spectrum of morphologies depending on both nutrient availability and the age of the material. In some cases, a single clone produced morphologies that could be placed within four different genera! Such was the case of Calothrix fuellerbornii, a species able to produce its own typical morphology, as well as Plectonema-like, Lyngbya-like, and Anabaena-like trichomes (Jeeji-Bai 1977). Recent molecular studies confirm that different cyanobacterial morphologies can be found in a single clade (Baurain et al. 2002).
A classic study on cyanobacterial plasticity was presented by Lazaroff and Vishniac (1961, 1964) and Lazaroff (1966), illustrating plastic responses of a strain of Nostoc muscorum. Morphological changes in this cyanophyte were triggered by differences in light intensity. A culture maintained in dark conditions always produced “aseriate” colonies, probably due to either a lack of essential substances for the formation of filaments, or by accumulation of inhibitory material. Under dim light conditions (0.2-0.9 µmol m2s-1), a transition from aseriate to filamentous forms was observed. In the range 16-90 µmol m2s-1 (still considerably less than full sun) typical filamentous forms were yielded. Furthermore, a culture containing aseriate colonies could be induced to produce filaments by adding an extract of a light-grown culture (Lazaroff and Vishniac 1961). "........
filaments are plastic??
................On the other hand, the fate of plastic invading genotypes is far more complex. If the new environment is unstable, but the invading genotypes are sufficiently plastic to cope with these changes, then natural selection will favor them without any alteration in their genetic material. However, if the new habitat is substantially different from the original one, some of the plastic potential of these genotypes may be lost over time through genetic drift and/or modification of the epigenetic system (Schlichting and Pigliucci 1998). If the latter two processes are coupled with reproductive isolation from the main population, they might lead to speciation.
The fact that algal genotypes are able to adapt to their habitat through plasticity has been under-explored in evolutionary and phycological research. It is not difficult to conceive, however, that plasticity may be an important factor imparting fitness under changing environmental circumstances, and thus, confer on organisms at least a temporary resistance to evolutionary change (Bradshaw 1965, Sultan 1987). Many authors propose that it is the reaction norm itself which is the subject of natural selection. Genotypes that are able to produce a wider range of phenotypes and to cope more rapidly with changes in habitat conditions will be more apt to survive (Baldwin 1896, Bradshaw 1965, de Jong 1995, Gause 1947, Pigliucci et al. 1996, Scheiner and Lyman 1989, Scheiner 1993, Schlichting 1986, Stearns 1982, Via and Lande 1985). ".............
...."And finally, there are costs related to linkage, epistatic, and pleiotropic interactions of plastic genes. That is, plastic responses of a gene may have the detrimental consequences of the genes linked to it.
Accumulation of these costs can affect both the ecological performance of plastic organisms and their evolution. At the ecological level, an exaggerated cost of an adaptive plastic response may affect the competitive ability of an organism, favoring less plastic individuals that allocate more resources directly to reproductive fitness. Thus, even though plasticity may lead to the production of the most adequate phenotype in a given environment, such plasticity may not be selectively advantageous (DeWitt et al. 1998). "..............
...................
Conclusions
1. Phenotypic plasticity is the process by which a single genotype is able to produce different phenotypes when environmental conditions change. It is not an isolated phenomenon, restricted to certain taxa, but a widespread process among all organisms (including the algae). Phenotypic plasticity may be viewed as a way of maintaining fitness during changes in habitat conditions, and thus, as a way of buffering evolutionary change, making species less vulnerable to erratic climatic shifts (natural selection). Unwittingly, we have been considering plasticity in biology for a long time. Leaf dimorphism in aquatic macrophytes, chromatic adaptation in cyanobacteria, even cell differentiation in animals and plants, are some very well known examples that fit within the plasticity concept.
2. At times algal evolutionary, taxonomic, and ecological thinking does not incorporate sufficiently the concept of phenotypic plasticity. Perhaps we should no longer continue to think of many algal species as morphologically stable entities, since all genotypes may potentially be plastic and/or polymorphic. Our task is to ascertain the degree of plasticity and polymorphism in each one of them.
3. The implications of plasticity in other branches of phycological research (e.g., taxonomy and systematics) are obvious. Classification and identification should be based on analyses of as many types of traits as possible - the traditional morphological aspects as well as information on physiology, life histories, and even ultrastructural features, could provide important clues regarding organismal affinities. Considerations of phenotypic plasticity and polymorphism may significantly affect our view of phylogenetic relationships and classification schemes. In a number of cases, the use of laboratory techniques (e.g., culturing) is of utmost importance in the elucidation of plasticity, since they provide the opportunity to work with genetically homogeneous populations and environmentally homogeneous conditions. However, field and laboratory approaches must not be divorced from each other, for both may contribute to the establishment of true links among organisms. The adoption of either of these approaches to the exclusion of the other may lead to serious error. The development of more natural classification systems should now incorporate multidisciplinary considerations, including phenotypic plasticity and polymorphism. .......................
ucjeps.berkeley.edu/constancea/83/morales_etal/plasticity.html
Herein lies the MORPHology, so plastic genes.............
well, mmmmmmmmmm
However, why was this introduced into the natural pond?
scenedesmus.......was just planted recently in the NL
Skyship
"Ironically, the study of phenotypic plasticity within phycology seems to predate contributions dealing with any other group of organisms. For example, the green algal genus Scenedesmus has been recognized as plastic since the mid 1800's."..............
............Thus, the ecotypic adaptation theory disregards both the effect of environmental fluctuations on populations over short periods of time and the fact that plasticity can also be a mechanism for speciation (Pigliucci 1996, Schlichting and Pigliucci 1998)
......In the present review we attempt to place available information on algal plasticity in an evolutionary context and discuss the implications for other phycological fields. The merging of phenotypic plasticity data with current phycological thinking completely changes our view of algae as biological entities. It leads to an integrated species concept in which morphology, physiology, ecology, and evolution are intertwined. In addition, it helps us to understand the relationship between organisms and their immediate environment and how individuals can endure in constantly changing and even newly invaded habitats.........
........Coarse grained variation: plasticity across generations
Variation in habitat conditions at intervals greater than the life span of individuals has been termed “coarse grained” variation (MacArthur and Levins 1967). In this case, changes in the environment trigger a mitotic cell division and the new phenotype is expressed in the filial generation. Most of the cases of plasticity in the phycological literature deal with this coarse-grained responses to environmental cues, for example, Phaeodactylum tricornutum, a pennate diatom, produces oval, fusiform, and triradiate morphs following changes in culture media, light, and temperature. This diatom was recognized as plastic in 1935 by Barker, and since then, various papers have been published on the DNA content, ultrastructural features, and biochemical characterization of the morphs (e.g., Borowitzka and Volcani, 1978, Darley 1968, Gutenbrunner et al. 1994, Lewin et al. 1958, Reimann and Volcani 1968)."..................
...........A critical body of evidence concerning plasticity has been gathered for a variety of cyanobacteria, and through this evidence, taxonomic implications of plasticity have become very clear. The historical development of the classification of this group depicts very well a classic confrontation between “splitter” and “lumper” approaches. Early publications (Geitler 1932) presented extensive lists of organisms that were later complemented with additional descriptions of cyanophytes from other parts of the world (cocke 1967, Desikachary 1959). The number of “species” was staggering, but it was not clearly stated whether the names were designed to represent different genotypes or strikingly different phenotypes. Subsequent collection of laboratory data on the plasticity of individual blue green algal genotypes led different authors to reduce drastically the number of taxa to be accepted."..............
.......". For the genus Spirulina for example, Jeeji-Bai and Sheshadri (1980) concluded that the degree of coiling of the trichomes (used to separate this genus from Arthrospira) varies with light intensity and nutrient concentration in the culture medium. Additionally, other “species” showed a wide spectrum of morphologies depending on both nutrient availability and the age of the material. In some cases, a single clone produced morphologies that could be placed within four different genera! Such was the case of Calothrix fuellerbornii, a species able to produce its own typical morphology, as well as Plectonema-like, Lyngbya-like, and Anabaena-like trichomes (Jeeji-Bai 1977). Recent molecular studies confirm that different cyanobacterial morphologies can be found in a single clade (Baurain et al. 2002).
A classic study on cyanobacterial plasticity was presented by Lazaroff and Vishniac (1961, 1964) and Lazaroff (1966), illustrating plastic responses of a strain of Nostoc muscorum. Morphological changes in this cyanophyte were triggered by differences in light intensity. A culture maintained in dark conditions always produced “aseriate” colonies, probably due to either a lack of essential substances for the formation of filaments, or by accumulation of inhibitory material. Under dim light conditions (0.2-0.9 µmol m2s-1), a transition from aseriate to filamentous forms was observed. In the range 16-90 µmol m2s-1 (still considerably less than full sun) typical filamentous forms were yielded. Furthermore, a culture containing aseriate colonies could be induced to produce filaments by adding an extract of a light-grown culture (Lazaroff and Vishniac 1961). "........
filaments are plastic??
................On the other hand, the fate of plastic invading genotypes is far more complex. If the new environment is unstable, but the invading genotypes are sufficiently plastic to cope with these changes, then natural selection will favor them without any alteration in their genetic material. However, if the new habitat is substantially different from the original one, some of the plastic potential of these genotypes may be lost over time through genetic drift and/or modification of the epigenetic system (Schlichting and Pigliucci 1998). If the latter two processes are coupled with reproductive isolation from the main population, they might lead to speciation.
The fact that algal genotypes are able to adapt to their habitat through plasticity has been under-explored in evolutionary and phycological research. It is not difficult to conceive, however, that plasticity may be an important factor imparting fitness under changing environmental circumstances, and thus, confer on organisms at least a temporary resistance to evolutionary change (Bradshaw 1965, Sultan 1987). Many authors propose that it is the reaction norm itself which is the subject of natural selection. Genotypes that are able to produce a wider range of phenotypes and to cope more rapidly with changes in habitat conditions will be more apt to survive (Baldwin 1896, Bradshaw 1965, de Jong 1995, Gause 1947, Pigliucci et al. 1996, Scheiner and Lyman 1989, Scheiner 1993, Schlichting 1986, Stearns 1982, Via and Lande 1985). ".............
...."And finally, there are costs related to linkage, epistatic, and pleiotropic interactions of plastic genes. That is, plastic responses of a gene may have the detrimental consequences of the genes linked to it.
Accumulation of these costs can affect both the ecological performance of plastic organisms and their evolution. At the ecological level, an exaggerated cost of an adaptive plastic response may affect the competitive ability of an organism, favoring less plastic individuals that allocate more resources directly to reproductive fitness. Thus, even though plasticity may lead to the production of the most adequate phenotype in a given environment, such plasticity may not be selectively advantageous (DeWitt et al. 1998). "..............
...................
Conclusions
1. Phenotypic plasticity is the process by which a single genotype is able to produce different phenotypes when environmental conditions change. It is not an isolated phenomenon, restricted to certain taxa, but a widespread process among all organisms (including the algae). Phenotypic plasticity may be viewed as a way of maintaining fitness during changes in habitat conditions, and thus, as a way of buffering evolutionary change, making species less vulnerable to erratic climatic shifts (natural selection). Unwittingly, we have been considering plasticity in biology for a long time. Leaf dimorphism in aquatic macrophytes, chromatic adaptation in cyanobacteria, even cell differentiation in animals and plants, are some very well known examples that fit within the plasticity concept.
2. At times algal evolutionary, taxonomic, and ecological thinking does not incorporate sufficiently the concept of phenotypic plasticity. Perhaps we should no longer continue to think of many algal species as morphologically stable entities, since all genotypes may potentially be plastic and/or polymorphic. Our task is to ascertain the degree of plasticity and polymorphism in each one of them.
3. The implications of plasticity in other branches of phycological research (e.g., taxonomy and systematics) are obvious. Classification and identification should be based on analyses of as many types of traits as possible - the traditional morphological aspects as well as information on physiology, life histories, and even ultrastructural features, could provide important clues regarding organismal affinities. Considerations of phenotypic plasticity and polymorphism may significantly affect our view of phylogenetic relationships and classification schemes. In a number of cases, the use of laboratory techniques (e.g., culturing) is of utmost importance in the elucidation of plasticity, since they provide the opportunity to work with genetically homogeneous populations and environmentally homogeneous conditions. However, field and laboratory approaches must not be divorced from each other, for both may contribute to the establishment of true links among organisms. The adoption of either of these approaches to the exclusion of the other may lead to serious error. The development of more natural classification systems should now incorporate multidisciplinary considerations, including phenotypic plasticity and polymorphism. .......................
ucjeps.berkeley.edu/constancea/83/morales_etal/plasticity.html
Herein lies the MORPHology, so plastic genes.............
well, mmmmmmmmmm
However, why was this introduced into the natural pond?
scenedesmus.......was just planted recently in the NL
Skyship