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Chemically mediated interactions have important ecological and evolutionary effects on populations and communities. Despite recognition that herbivory can significantly affect the biomass and composition of freshwater macrophyte communities, there are few investigations of chemical defenses among freshwater vascular plants and mosses and none of freshwater red algae. This study compares the palatability of five species of freshwater red algae (Batrachospermum helminthosum, Boldia erythrosiphon, Kumanoa sp., Paralemanea annulata, and Tuomeya americana) that occur in the southeastern United States relative to two co-occurring macrophytes (the chemically defended aquatic moss Fontinalis novae-angliae and the broadly palatable green alga Cladophora glomerata). We assessed the potential role of structural, nutritional, and chemical traits in reducing macrophyte susceptibility to generalist crayfish grazers. Both native and non-native crayfish significantly preferred the green alga C. glomerata over four of the five species of red algae. B. erythrosiphon was palatable, while the cartilaginous structure of P. annulata reduced its susceptibility to grazing, and chemical defenses of B. helminthosum, Kumanoa sp., and T. americana rendered these species as unpalatable as the moss F. novae-angliae. Extracts from these latter species reduced feeding by ~30-60% relative to solvent controls if tissues were crushed (simulating herbivore damage) prior to extraction in organic solvents. However, if algae were first soaked in organic solvents that inhibit enzymatic activity and then crushed, crude extracts stimulated or had no effect on herbivory. B. helminthosum, Kumanoa sp., and T. americana all exhibited "activated" chemical defenses in which anti-herbivore compounds are produced rapidly upon herbivore attack via enzymatic processes. In an additional accept/reject behavioral assay, B. helminthosum extracts reduced the number of crayfish willing to feed by >90%. Given that three of the five red algal taxa examined in this study yielded deterrent crude extracts, selection for defensive chemistry in freshwater rhodophytes appears to be substantial. Activated chemical defenses are thought to be an adaptation to reduce the resource allocation and ecological costs of defense. As such, activated chemical defenses may be favored in freshwater red algae, whose short-lived gametophytes must grow and reproduce rapidly. Roughly 20% of the known chemical defenses produced by marine algae are activated; further examination is needed to determine whether the frequency of activated chemistry is higher in freshwater red algae compared to their marine counterparts. Continued investigation of chemical defenses in freshwater red algae will contribute to among-system comparisons, providing new insights in the generality of plant-herbivore interactions and their evolution.

Philosophiae Doctor - PhD / Coralline red algae (Corallinales, Hapalidiales, Sporolithales: Corallinophycidae, Rhodophyta) are widespread and common in all the world’s oceans (Adey & McIntyre 1973; Johansen 1981; Littler et al. 1985; Björk et al. 1995; Aguirre et al. 2007; Harvey & Woelkerling 2007; Littler & Littler 2013). They achieve their highest diversity in the tropics and subtropics (Björk et al. 1995; Littler & Littler 2013; Riosmena-Rodríguez et al. 2017), and within the photic zone of rocky shores (Lee 1967; Littler 1973; Adey 1978; Adey et al. 1982; Steneck 1986; Kendrick 1991; Kaehler & Williams 1996; Gattuso et al. 2006; van der Heijden & Kamenos 2015; Riosmena-Rodríguez et al. 2017) where they serve as important carbonate structures (Adey et al. 1982; Littler & Littler 1994, 1997; Vermeij et al. 2011) and habitats for a host of marine species (Foster 2001; Amado-Filho et al. 2010; Foster et al. 2013; Littler & Littler 2013; Riosmena-Rodríguez et al. 2017). Coralline algae are resilient, inhabiting extreme conditions that include: low temperatures (Adey 1970, 1973; Freiwald & Hendrich 1994; Barnes et al. 1996; Freiwald 1996; Aguirre et al. 2000; Roberts et al. 2002; Björk et al. 2005; Martone et al. 2010); limited light exposures (Adey 1970; Littler & Littler 1985; Littler et al. 1985; Liddell & Ohlhorst 1988; Dullo et al. 1990; Littler & Littler 1994; Iryu et al. 1995; Stellar and Foster 1995; Gattuso et al. 2006; Aguirre et al. 2007; Littler & Littler 2013); severe wave action (Steneck 1989; Littler & Littler 2013); intense grazing pressures (Steneck 1989; Steneck & Dethier 1994; Maneveldt & Keats 2008; Littler & Littler 2013), highly fluctuating salinities (Harlin et al. 1985; Barry & Woelkerling 1995; Barnes et al. 1996; Wilson et al. 2004); including occurring in freshwater (Žuljevic et al. 2016), and constant sand scouring (Littler & Littler 1984; D’Antonio 1986; Kendrick 1991; Chamberlain 1993; Dethier 1994).

Evolutionary processes in any population depend upon patterns of phenotypic variation available to selection and their underlying heritability. In this thesis, I used the filamentous red seaweed Asparagopsis armata, with particular focus on its modularity, to test several key questions underlying its growth-form evolution in heterogeneous environments. I established that experimental manipulations of light quantity and quality mimicking variation in underwater light due to shading or depth induce growthform plasticity in A. armata that may be evolutionarily significant given its variability among clones. Current patterns of plasticity displayed by A. armata appear adaptive, moreover, given that a reciprocal transplant of phenotypes between light environments found densely-branched (phalanx-like) phenotypes to have higher relative growth rates than sparsely-branched (guerrilla-like) phenotypes in well-lit patches, but lower relative growth rates than the latter in shaded patches. Using the capacity for rapid growth as a proxy for fitness, multivariate selection analyses identified environment-dependent patterns of directional selection on single traits coupled with linear and nonlinear selection on multi-trait combinations that shape growth-form variation within patches of differing light intensity, thereby reinforcing plasticity across light environments. Quantitative genetic analyses, however, suggest that the modular iteration of genes in morphogenesis may limit further growth-form evolution in A. armata populations exposed to spatial heterogeneity in light by constraining thallus responses to environment-dependent selection. Last, heritable responses to artificial selection on growth-form variation among clonal cell-lineages revealed the surprising capacity for A.armata to circumvent genetic constraints inherent to its development by adapting to environmental change in the absence of sexually-generated variance among clones.

Contains copies of 43 author's publications and introductory statement / Includes bibliographies / 44 pts : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (D. Sc.)--University of Adelaide, 1986

Thesis (Ph.D.)(Botany))--University of Pretoria, 2003. / Includes bibliographical references.

Pteroceramium, a descriptive name given to an undescribed winged species closely related to Ceramium, has uniaxial filamentous thallus construction with pseudodichotomous branching. Alternate branches become dominant. This pattern of growth is referred to as cellulosympodial growth. All growth is from an apical cell which cuts off subapical cells. The subapical cells develop into axial cells. Each axial cell cuts off six pericentral cells in a ring around its apical pole. The pericentral cells divide further to form the cortical band. Pc1 always forms on the outer face of the thallus as determined by the preceding pseudodichotomy and gives rise to the larger outer wing which is a lateral expansion of the cortical band. The smaller inner wing forms from Pc6 on the inner face. The other pericentral cells give rise apically to uniseriate spines. The pericentral cells also give rise to rhizoids and adventitious lateral branches. Each axial cell has a large central vacuole with a few peripheral chloroplasts, mitochondria and floridean starch granules. The smaller wing cells have a much denser cytoplasm with fewer small vacuoles, many chloroplasts which are more closely packed together and more floridean starch granules than axial cells. Chloroplasts have a typical Rhodophyta ultrastructure with single, evenly spaced thylakoids with phycobilisomes. Pit connections have a plug core but no plug cap. Pteroceramium has a typical Polysiphonia-type triphasic life history. The carposporophyte is naked and tetraspores are produced in a characteristic decussate cruciate arrangement. The effect of a number of physical and chemical factors on growth and morphogenesis was investigated. Pteroceramium grew best at irradiance levels between 79 μmol m⁻² S¯¹ and 129 μmol m⁻² S¯¹ with growth being limited at 30 μmol m⁻² S-I. The largest axial cells and wings were obtained from the material grown at 79 μmol m⁻² S¯¹ and the smallest measurements for material grown at 129 μmol m⁻² S¯¹. Monochromatic light fields of red, green and blue caused reduced growth rates compared to the control replicates grown in a white light from both incandescent and fluorescent lights. Light quality had no effect on morphogenesis. The critical daylength for maximum rates of cell elongation was 10 hours or longer, although 16 hours light caused a decrease in final axial cell volume. Optimum temperatures for growth of Pteroceramium were between 20°C and 25°C with growth decreasing at 15°C and 30°C. Axial cell volume was reduced and wing size was stunted at these two extreme temperatures tested. Scouring by sand caused axial cells to decrease in volume although the wings were unaffected. Smothering by sand did not prevent growth although axial cells and wings were greatly decreased in size, with the wings consisting of only one or two other cells. Tumbling to disrupt gravity did not affect the angle of each pseudodichotomy. Decreased levels of nitrogen and phosphorus limited growth but had little effect on axial cell volume and wing development. Pteroceramium was stenohaline with maximum growth at 34°/[00] and reduced growth at 300/[00] and 40°/[00]. Pteroceramium grew best at pH 7.5 and pH 8.5 with decreased growth at pH 6.5 and pH 5.5. The various pHs tested had little effect on morphogenesis. The best photosynthetic responses were obtained from material preconditioned at 80 μmol m⁻² S¯¹ compared with that at 30 μmol m⁻² S¯¹ and 150 μmol m⁻² S¯¹. There was a decrease in pigment content with increasing irradiance at which the alga was grown. Phycoerythrin was the dominant pigment. Exposure to a high irradiance (3000 μmol m⁻² S¯¹) for 30 minutes or longer inhibited photosynthesis. Plants did not fully recover even 24 hours later, indicating that this damage was permanent. Pteroceramium was able to acclimatize slowly over a week to temperature changes within the range of 15°C to 25°C. Rapid increases of 5°C within this temperature range increased photosynthetic performance and a rapid drop of 5°C decreased photosynthetic performance. However, a 10°C increase or drop reduced Pteroceramium's photosynthetic performance. Photosynthetic rates were decreased in alkaline conditions and increased in acidic conditions. Pteroceramium has well defined developmental patterns with basal band growth of axial cells and tip growth in the rhizoids. The pericentral cells are formed in a set sequence similar to Ceramium species with Pcl forming on the outer face, Pc2 and Pc3 forming on the lower and upper surface nearest to Pel respectively, Pc4 and PcS forming on the lower and upper surface respectively farthest from Pel, and Pc6 forming on the inner face. This sequence is unaffected by the direction of illumination or gravity. Exogenous application of plant hormones (IAA, GA3 and kinetin) in the concentration range of 10[-9] M to 10[-5] M had no effect on growth and morphogenesis in Pteroceramium. Application of polyamines and their precursors caused a decrease in growth and a reduction in cell size at concentrations higher than 10[-4] M. Polyamine inhibitors caused a reduction in growth and cell size at concentrations higher than 10[-5] M. Arginine increased growth at concentrations 10[-5] M and 10[-6] M. High power liquid chromatography (HPLC) separation of Pteroceramium extracts indicated that spermidine was present in Pteroceramium at approximately 38 μg spermidine g¯¹ fresh weight. The apical tip exerts an apical dominance effect on the subordinate branches, suppressing their elongation. Removal of the dominant apical tip increased adventitious branch formation. This effect was not reversed by application of exogenous IAA at concentrations of 10[-9] M to 10[-4] M. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1993.

Evolutionary processes in any population depend upon patterns of phenotypic variation available to selection and their underlying heritability. In this thesis, I used the filamentous red seaweed Asparagopsis armata, with particular focus on its modularity, to test several key questions underlying its growth-form evolution in heterogeneous environments. I established that experimental manipulations of light quantity and quality mimicking variation in underwater light due to shading or depth induce growthform plasticity in A. armata that may be evolutionarily significant given its variability among clones. Current patterns of plasticity displayed by A. armata appear adaptive, moreover, given that a reciprocal transplant of phenotypes between light environments found densely-branched (phalanx-like) phenotypes to have higher relative growth rates than sparsely-branched (guerrilla-like) phenotypes in well-lit patches, but lower relative growth rates than the latter in shaded patches. Using the capacity for rapid growth as a proxy for fitness, multivariate selection analyses identified environment-dependent patterns of directional selection on single traits coupled with linear and nonlinear selection on multi-trait combinations that shape growth-form variation within patches of differing light intensity, thereby reinforcing plasticity across light environments. Quantitative genetic analyses, however, suggest that the modular iteration of genes in morphogenesis may limit further growth-form evolution in A. armata populations exposed to spatial heterogeneity in light by constraining thallus responses to environment-dependent selection. Last, heritable responses to artificial selection on growth-form variation among clonal cell-lineages revealed the surprising capacity for A.armata to circumvent genetic constraints inherent to its development by adapting to environmental change in the absence of sexually-generated variance among clones.

Thesis (D. Sc.)--University of Adelaide, 1986. / Contains copies of 43 author's publications and introductory statement. Includes bibliographical references.

Thesis (M.Sc. (Zoology & Entomology)) - Rhodes University, 2009