Species-specific defense strategies of vegetative versus reproductive blades of the Pacific kelps <Emphasis Type="Italic">Lessonia nigrescens</Emphasis> and <Emphasis Type="Italic">Macrocystis integrifolia</Emphasis> |
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Authors: | Christian Pansch Ivan Gómez Eva Rothäusler Karina Veliz Martin Thiel |
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Institution: | 1.Institut für Biowissenschaften, Lehrstuhl für Meeresbiologie,Universit?t Rostock,Rostock,Germany;2.Instituto de Biología Marina, Facultad de Ciencias,Universidad Austral de Chile,Valdivia,Chile;3.Departamento de Biología Marina, Facultad de Ciencias del Mar,Universidad Católica del Norte,Coquimbo,Chile;4.Centro de Estudios Avancados en Zonas Aridas CEAZA,Coquimbo,Chile |
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Abstract: | 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. |
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