Defensive strategies of modular organisms

Abstract

Convergences concomitant with the occurrence of modular growth among systematically remote plant and invertebrate taxa not only reflect similar optimal ways of exploiting resources such as space, but also common defensive requirements among such organisms. This paper analyses the kinds of unfavourable interspecific interactions, principally predation, epibiosis, and endobiosis, which are found among the major aquatic invertebrate groups that may be considered to be modular (Porifera, Bryozoa, and some of the Coelenterata and Tunicata). Most of the organisms are also non-locomotory, and in extreme cases, virtually immotile. The defence mechanisms of organisms exhibiting the opposing traits of (i) modular and unitary organization, and (ii) motility and immotility, are compared and contrasted. There is a more widespread occurrence of defence (i) by means of consolidated and unconsolidated skeletal reinforcement, and (ii) by actively and passively dispensed secondary substances, in less motile than in more motile organisms. These defensive modes represent alternatives to ‘fight’ and ‘flight’ responses seen within the more motile invertebrates. Lack of motility is of greater significance in correlating defensive modes than is modularity. The balance between physical and chemical mechanisms used in defence can vary, even among closely related taxa. A more particular pattern of significance is the more widespread occurrence of defence by the use of passively dispensed chemical substances within modular, rather than unitary non-locomotory invertebrate groups. This may be a response to the increased risks of pathogenic infection which modular biota face through their susceptibility to frequent large scale wounding and partial mortality.

Polymorphism and variation in modular animals: morphometric and density analyses of bryozoan avicularia

“…The morphological diversity of avicularia suggests that many facets of a defensive/protective strategy may have evolved among avicularium-bearing colonies. Defensive mechanisms displayed by sedentary marine invertebrates may be structural or chemical (Dyrynda 1986, Peters et al 2003, Sharp et al 2007. Possible defensive mechanisms displayed by avicularia may therefore be of a mechanical (the physical entrapment of organisms) or chemical (secretion of bioactive compounds) nature, or even both.…”

Prudent sessile feeding by the corallivore snail, Coralliophila violacea on coral energy sinks

“…Convergence of form and function has accompanied the evolution of modular growth in terrestrial plants and colonial marine invertebrates (Dyrynda 1986). Part of this convergence is related to optimal exploitation of resources (space and light) and the ability to translocate energy products from sources to sinks.…”

“…Carbon transfer between sources (sites that export assimilates) and sinks (sites that import assimilates) and its regulation within colonial organisms are critical aspects in their biology (Dyrynda 1986). In hermatypic corals, photosynthetic products are continuously translocated from the symbiotic zooxanthellae to the host tissue, thereby contributing to a variety of energetic requirements such as maintenance, synthesis of new cells, formation of skeletal matrix, mucus production, deposition of calcium carbonate, and storage of energy-rich compounds for coral reproduction (Muscatine & Cernichiari 1969;Crossland et al 1980a,b;Muscatine et al 1981Muscatine et al , 1984Rinkevich & Loya 1983Kellogg & Patton 1983;Stimson 1987).…”

Photomorphogenesis in Dracaena draco

“…Modularity allows best use of light and space and provides for flexibility needed in ever changing environment. This idea is also a key to our view of plants growth (Dyrynda 1986 A module of a Dicot tree is usually a short internode with a node, leaf and bud (Wyk and Wyk 2007). A module of D. draco (i.e.…”