Species-speciWc defense strategies of vegetative versus reproductive blades of the PaciWc kelps Lessonia nigrescens and Macrocystis integrifolia

Chemical defense is assumed to be costly and therefore algae should allocate defense investments in a way to reduce costs and optimize their overall fitness. Thus, lifetime expectation of particular tissues and their contribution to the fitness of the alga may affect defense allocation. Two brown algae common to the SE Pacific coasts, Lessonia nigrescens Bory and Macrocystis integrifolia Bory, feature important ontogenetic differences in the development of reproductive structures; in L. nigrescens blade tissues pass from a vegetative stage to a reproductive stage, while in M. integrifolia reproductive and vegetative functions are spatially separated on different blades. We hypothesized that vegetative blades of L. nigrescens with important future functions are more (or equally) defended than reproductive blades, whereas in M. integrifolia defense should be mainly allocated to reproductive blades (sporophylls), which are considered to make a higher contribution to fitness. Herein, within-plant variation in susceptibility of reproductive and vegetative tissues to herbivory and in allocation of phlorotannins (phenolics) and N-compounds was compared. The results show that phlorotannin and N-concentrations were higher in reproductive blade tissues for both investigated algae. However, preferences by amphipod grazers (Parhyalella penai) for either tissue type differed between the two algal species. Fresh reproductive tissue of L. nigrescens was more consumed than vegetative tissue, while the reverse was found in M. integrifolia, thus confirming the original hypothesis. This suggests that future fitness function might indeed be a useful predictor of anti-herbivore defense in large, perennial kelps. Results from feeding assays with artificial pellets that were made with air-dried material and extract-treated Ulva powder indicated that defenses in live algae are probably not based on chemicals that can be extracted or remain intact after air-drying and grinding up algal tissues. Instead, anti-herbivore defense against amphipod mesograzers seems to depend on structural traits of living algae

The taxonomic implications of genetic and environmentally induced variations in seaweed morphology

Morphological characters are the most widely used criteria for the discrimination of seaweed taxa. Even so, many examples of extreme phenotypic plasticity are known. Thus, several phycologists have recently initiated studies to evaluate the phenotypic range of taxa under varied conditions as well as to explore the degree of genetic control of individual characters. Several experimental techniques have been employed to enumerate the significance and basis of phenotypic plasticity in seaweeds, including culture studies, detailed seasonal observations of in situ populations, reciprocal transplantation of plants to diverse habitats, statistical analysis of character variations, and evaluation of genetic affinities. Obviously, the taxonomic status of seaweeds should reflect their genetic relationships. Three primary approaches are outlined including electrophoretic studies, quantitative genetic evaluations, and hybridization studies. A detailed summary of these genetic studies, as well as the other experimental field and laboratory techniques, is given in order to critically assess traditional taxonomic criteria and to aid in the search for new ones. An evaluation of the relative merits of morphological and biochemical characters in species delimitations is also outlined. It is suggested that there should be no tacit assumption that biochemical features are in some way more fundamental than morphological ones. Thus, even seemingly trivial morphological features may be of great adaptive value, even though not apparent to the taxonomist. A good taxonomic character is constant, readily observable, and the plant should survive identification. If obscure characters are used to delimit species, strenuous efforts should be made to correlate these characters with more readily observable ones