Abstract
Growth form , that is, the shape and mode of construction of an organism, together with size sets fundamental opportunities as well as limits on the biology of living things. We consider here the case that organisms can be viewed as either basically unitary or modular in construction. This division pertains broadly to whether or not the life cycle consists essentially of repeated ontogenies at multiple levels. Being designed according to one plan or the other carries numerous implications, the most important of which are evolutionary consequences pertaining to fecundity and the transfer and expression of genetic variation. Further, it is argued that at least some microorganisms, notably the bacteria and fungi , are inherently modular in construction and share with macroorganisms the ecological properties that emerge from this design. Thus, the ecology and evolutionary biology of modular macroorganisms should be instructive to microbial ecologists. Conversely, experiments with the relevant microorganisms into the theoretical predictions of modularity may inform plant and animal ecologists.
Geometry is the most obvious framework upon which nature works to keep her scale in ‘designing’. She relates things to each other and to the whole, while meantime she gives to your eye most subtle, mysterious and apparently spontaneous irregularities in effects.
Frank Lloyd Wright, 1953, p. 53.
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Notes
- 1.
The term ‘module’ as used by ecologists differs from the module of developmental biologists, which is usually taken to be a discrete subunit with respect to gene expression (see Raff 1996, pp. 326–334), though modularity has multiple connotations from the molecular through the organismal level of organization (Klingenberg 2008).
- 2.
Microsatellites are simple sequence tandem repeats, typically of 1–6 bp DNA. Dinucleotide repeats, which are often the focus of interest, are almost always in noncoding genes and, as such, the microsatellites are more likely to evolve neutrally than if changes in protein-coding genes are used. Because microsatellite loci usually have relatively high mutation rates, they have greater resolution for age determinations (Rahman et al. 2000; O’Connell and Ritland 2004; Ally et al. 2008).
- 3.
Plant and animal stem cells reside in ‘stem cell niches’ and respond to signals regulating the balance between renewal and generation of daughters that become differentiated into various tissues. In plants such niches are located within the meristems (Heidstra and Sabatini 2014). Plant stem cells have been largely overlooked, other than by botanists, in recent years by all notoriety surrounding stem cells of humans! The term ‘stem’ is perhaps best avoided in plants because of ambiguous usage; see Evert (2006, p. 143).
- 4.
‘Diplontic’ in this context alludes to competition among cell lineages within the (diploid) plant axis. In organisms that are exclusively diplonts (typically multicellular animals), the haploid products of meiosis behave directly as gametes. Plants are typically ‘diplohaplonts’, alternating between haploid and diploid individuals. See Chap. 6.
- 5.
Studies under laboratory conditions among strains of Neurospora crassa suggest that during mating the controls on heterokaryon compatibility are relaxed and the specialized hypha involved (trichogyne) evidently is able to accept nuclei from one or multiple hyphae of compatible mating type belonging to any het genotype. The generality of this finding remains to be seen. For synopsis and references, see Roper et al. (2011); Roche et al. (2014).
- 6.
In a remarkably prescient assessment, Pontecorvo (1946) stated (p. 199) … “we may be justified in considering a hypha as a mass of cytoplasm with a population of nuclei. Such a population is subject to: (1) variation in numbers; (2) drift—i.e., random variation in the proportions of different kinds of nucleus; (3) migration—i.e., influx and outflow of nuclei, following hyphal anastomoses; (4) mutation; and (5) selection. Selection may act either on the nuclei themselves as proposed here, or on the hyphae carrying them.”
Suggested Additional Reading
Campillo, F., and N. Champagnat. 2012. Simulation and analysis of an individual-based model for graph-structured plant dynamics. Ecol. Model. 234: 93-105. This paper typifies the advanced computational analyses and simulations being applied in particular to growth and spatial distribution of clonal, modular organisms.
de Kroon, H., and J. van Groenendael. 1997. The Ecology and Evolution of Clonal Plants. Backhuys Publishers, Leiden, The Netherlands. The perspectives of multiple authors on the ecology and evolutionary biology of clonal plants. In many ways, this is the counterpart of the book on clonal animals by Hughes (1989), cited below.
Harper, J.L. 1977. Population Biology of Plants. Academic Press, London. This beautifully written, comprehensive synthesis remains the classic treatise on plant population biology and its lessons apply to ecology in general. There is extensive discussion of many topics raised in this chapter, such as the concept of genets and ramets, clonality, and modularity.
Harper, J.L., B.R. Rosen, J. White (Eds). 1986. The growth and form of modular organisms. Phil. Trans. Roy. Soc. B 313: 1-250. Also, Proc. R. Soc. B 228: 109-224. Perspectives of various authors on modular growth and its implications.
Hughes, R.N. 1989. A Functional Biology of Clonal Animals. Chapman and Hall, London. A thorough treatment of animal clones and a chapter on modular animals.
Jackson, J.B.C., L.W. Buss, and R.E. Cook (eds). 1985. Population Biology and Evolution of Clonal Organisms. Yale Univ. Press, New Haven, Conn. Proceedings of a symposium. Interesting perspectives; inconsistent terminology; absence of microbes from the synthesis.
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Andrews, J.H. (2017).
Growth and Growth Form.
In: Comparative Ecology of Microorganisms and Macroorganisms. Springer, New York, NY. https://doi.org/10.1007/978-1-4939-6897-8_5
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DOI: https://doi.org/10.1007/978-1-4939-6897-8_5
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