TABLE OF CONTENTS
Preface
Introduction - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0001
[plant modularity, evolution, lineage, metapopulations, phenotypic variance, multiplicity]
The paleontological and phylogenetic evidence have shown that the main features ultimately responsible for plant modularity were already present at a very early stage in the evolution of land plants, and are a property shared by the whole lineage. The ecological and evolutionary implications of plant modularity have frequently been highlighted following White's pioneering treatment of plant individuals as metapopulations of repeated modules. One of the consequences of plant modularity is the appearance of a distinctive source of phenotypic variance, that is, the within-plant or subindividual component. Another consequence of the multiplicity of modules is variation in the characteristics of the copies of the same organ produced on different modules of the same plant. A thesis is developed that the multiplicity of homologous structures arising from plant modularity gives rise to a subindividual level of phenotypic differences among organs of the same plant. (pages 1 - 8)
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Which Traits Vary within Plants? Many different features vary across reiterated structures of the same plant. - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0002
[subindividual variation, within-plant heterogeneity, nutrient concentration, multiovulate ovaries, leaf features, within-crop variation]
This chapter presents a review of the variety of morphological and functional features of plant-reiterated structures that exhibit significant amounts of variation within individuals. The focus is to provide just a catalogue of features that exhibit subindividual variation, rather than quantification of such variation. Within-plant heterogeneity in subtle structural, chemical, or functional leaf features is by no means confined to heterophyllous plants exhibiting discrete variation in leaf features. Broad within-plant variation in the number of filled seeds contained in each ripe fruit seems to be the rule among species with multiovulate ovaries. Significant within-crop variation in the concentration of major mineral nutrients may be inferred from some investigations that have examined the relationship between nutrient concentration and seed size in tropical and temperate wild plants. (pages 9 - 35)
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Continuous Within-Plant Variation of Reiterated Structures: The extent of subindividual variation in continuously varying leaf, flower, fruit, and seed traits is assessed. - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0003
[within-plant variability, morphological traits, reiterated plant structures, paired comparison method, phylogenetic correlations, taxonomic composition]
This chapter presents an overview of the within-plant variability of continuous structural and morphological traits of reiterated plant structures. It is found that all types of reiterated structures may exhibit considerable levels of continuous within-plant variation, and that, for any given structure, variability varies greatly among species. Comparisons between different structures should ideally be performed on data obtained from the same species and individuals by means of some paired comparison method, in order to avoid possible artifacts due to some combination of phylogenetic correlations and differences in the taxonomic composition of species samples. The results of the comparison between structures differ depending on the metric used to measure variability. Information from cultivated plants reveals that within-plant variation in the chemical composition of seeds can also be extensive. (pages 36 - 65)
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Distribution of Subindividual Variability in Time and Space: How are variants of reiterated structures organized along temporal, spatial, and architectural axes? - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0004
[subindiviual variability, spatial locations, multiple variants, within-plant variation, spatial analysis]
This chapter focuses on the ways in which subindividual variability is distributed in time, and among different parts and spatial locations within a plant. A sequential component arises whenever individual plants produce variants of the same organ over the same season or, in the case or perennials, in different years. The simultaneous component is generally due to plants producing multiple variants of the same organ simultaneously or over a relatively short period of time, in such a way that organ variants are borne at the same time by individual plants. The relative importance of annual variation as a component of sequential within-plant variation can be most easily examined for leaf characteristics on deciduous plants. Spatial analyses of within-plant variation in organ features reveal that after the broad-scale variation disclosed by gradient-oriented analyses has been statistically accounted for, much intraplant variation remains, occurring over very restricted spatial scales. (pages 66 - 97)
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Causes of Subindividual Variability: Mutations within individuals and organ-level responses to environmental cues are the main classes of remote causes of within-plant variability in reiterated structures. - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0005
[subindividual variation, genetic heterogeneity, environmental cues, phenotypic plasticity, genetic mosaicism]
This chapter explains the remote causes of subindividual variation, that is, those cases where reiterated parts vary because the organism's genes vary or the parts experience varied environments. This variation falls into two classes of genetic heterogeneity within individual and semiautonomous programmed responses of organs within individual to environmental cues, that is, developmental phenotypic plasticity of individual organs as governed by more or less rigid organ-level reaction norms. It is shown that widespread occurrence of organ-level phenotypic plasticity indicates that there is no need to invoke subindividual genetic mosaicism to account for within-plant variation in the phenotypic characteristics of all kinds of reiterated organs. The organ-level phenotypic plasticity provides the conceptual basis as a general phenomenon, which implies that a number of the organismal mechanisms that account for within-plant variation stem from the joint effects of location in the plant. (pages 98 - 130)
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Organismal Mechanisms of Subindividual Variability: Ontogenetic contingency, the interplay between inherent architecture and environmental milieu, and developmental stochasticity are mechanisms responsible for within-plant variability of reiterated struct - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0006
[subindividual variation, organ traits, causal agents, proximate mechanism, within-plant variation]
This chapter describes the organization of the response of the organism to its changing environment as well as the organization that it generates in and of itself. The author finds that the subindividual variation in reiterated organ traits is widespread, extensive, and spatially organized; affects almost every conceivable trait; and is the visible outcome of a complex underlying web of remote causal agents and proximate mechanisms. This description of the mechanism of subindividual variability has laid the biological foundations for the analysis of the ecological and evolutionary implications of subindividual variation. For a given organ trait, plant species differ widely in levels of within-plant variability and in the relative contributions to this variability of differences among and within branches or stems. The comparative analyses testing hypotheses ascertain the importance of sectoriality as a cause of within-plant variation and examine whether its importance remains consistent across species or environments. (pages 131 - 185)
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Subindividual Variability as an Individual Property: The Haldane-Roy conjecture is verified and extended: individual plants have not only their characteristic means, but also their characteristic standard deviations and characteristic spatial patterns of - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0007
[subindividual variability, individual property, Haldane-Roy conjecture, within-plant variation, plant phenotypes, within-individual variability]
This chapter articulates subindividual variability as an individual property in the format of the Haldane-Roy conjecture that describes within-plant variability in organ characteristics denoting a significant shift of opinion about the importance of a phenomenon. The verification of the Haldane-Roy conjecture, and its reinforcement by indications of a genetic basis of within-plant variation, should impel us to change the ways in which the individual plant phenotypes are characterized. Within-plant variance should be granted a descriptive value of the phenotype similar to the value traditionally conferred on the within-plant mean of organ trait values. Hence, acceptance of the Haldane-Roy conjecture opens the way to examining variation among characters, among species, and among populations of the same species, also from the perspective of their levels of within-individual variability. (pages 186 - 210)
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Consequences of Within-Plant Variation for Interacting Animals: Phytophagous animals' discrimination among organs of the same plant can lead to the most profitable choice but has attendant costs that may influence their overall performance and promote amo - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0008
[within-plant variation, reiterated organs, among-plant selection, variance behaviors, short-term performance, empirical studies]
This chapter reviews the consequences for animals of within-plant variation in characteristics of reiterated organs. The vast experimental evidence on variance-sensitive animals supports the hypothesis that within-plant variation in organ traits may lead to among-plant selection by consumers. Most theoretical models and experimental results for variance behaviors are specifically concerned with responses to variability in energetic rewards, to a large extent because such models initially arose as an outgrowth of optimal foraging theory. These models suggest that as far as nonlinearities, the law of diminishing returns, and Jensen's effects are involved, variance-sensitive behaviors will also develop in response to variability in plant organ traits which, although not directly affecting the energetic rewards of animals, may affect other components of their fitness or short-term performance. Thus, empirical studies are required that explicitly look for animal responses to naturally occurring variation in the field. (pages 211 - 264)
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Fitness Consequences of Subindividual Variability in Organ Traits for Plants: Subindividual variation in the characteristics of reiterated organs may influence the fecundity or vegetative performance of plants, and through this mechanism, individual fitne - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0009
[subindividual variability, within-plant variation, division of labor, phenotypic characteristics, discontinuous variation, organ traits]
This chapter elaborates myriad mechanisms in subindividual variability in organ traits that might in the long run have some nontrivial evolutionary consequences for the plants. It is seen that the fitness effects of within-plant variation in organ traits are not much better established to date for discrete than for continuous variation. It is shown that “division of labor” exploitation of environmental patchiness or partitioning of environmental gradients need not be restricted either to discontinuous variation or to the partitioning of the physical, abiotic environment. The biotic environment represented by pollinators or seed dispersers is also susceptible to partitioning, or “division of labor,” by structures borne on the same plant performing the same function but differing slightly in their phenotypic characteristics. (pages 265 - 310)
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Evolutionary Implications of Within-Plant Variability in Organ Traits: Subindividual multiplicity of organs can affect the evolutionary trajectory of organ traits by setting upper limits on responses to selection, opening the possibility of selection by a - Carlos M. Herrera
DOI: 10.7208/chicago/9780226327952.003.0010
[evolutionary implications, within-plant variation, organ traits, ecological phenomena, phenotypic variance, subindividual variability]
This chapter focuses on evolutionary implications that can be inferred from the existence of within-plant variation in organ traits and the associated ecological phenomena mediated by interactions with animals. The adaptive levels of environmental phenotypic variance in organ traits can be maintained by selection, regardless of the mechanisms producing it. Subindividual variability often accounts for nontrivial proportions of total environmental phenotypic variance of organ traits; selection by animals on variability has the potential to modify the magnitude of environmental variance and, in so doing, shift the balance between the genetic and environmental components. It is suggested that the environmental and genetic factors may be envisaged as “competing” to produce a given level of phenotypic variance. Thus, the spatial and temporal dynamics of such competition has manifold evolutionary implications, and animals can play a driving role by shifting the balance toward one side or the other. (pages 311 - 338)
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Epilogue
Literature Cited
Index
