Sex and Life‐history Stage Alter Herbivore Responses to a Chemically Defended Red Alga

Abstract

Intraspecific variation in resistance to herbivory among genders and life-history phases of primary producers can significantly alter the ecological and evolutionary consequences of plant-herbivore interactions. Seaweeds (macroalgae) with complex life histories have multiple distinct phases with associated variation in traits that can potentially lead to differences in resistance to consumers and provide a unique system in which to simultaneously test the effects of sex and life-history stage on herbivory. We tested the susceptibility to grazing of the three life-history stages and separate sexes of the chemically defended red alga Asparagopsis armata against the sea hare Aplysia parvula, and we related this to the plant quality traits of different stages and genders. Differences in nutrient content and halogenated secondary metabolites between life-history phases were highly sex dependent. Male gametophytes had a low concentration of secondary metabolites and the highest nutrient content. The highest secondary metabolite content was found within the female gametophyte, in the wall of the reproductive structures (cystocarps) that contain the microscopic carposporophyte phase. Feeding choices by A. parvula were consistent with differences in algal quality and defense and resulted in the haploid male gametophytes being the most preferred food type. The diploid carposporophyte found inside the chemically rich cystocarps was the least consumed life-history stage. Selective herbivory of male gametophytes by A. parvula is consistent with an observed shift in gametophyte sex ratio in the field from unity at the beginning of the reproductive season to female bias at the end. The variation in susceptibility to herbivory found between sex and life-history stages of A. armata represents the first example of sex-biased consumption in seaweeds and may contribute to the maintenance of complex life histories such as those found in red algae.

Ecophysiological studies of the non-indigenous speciesGracilaria vermiculophylla(Rhodophyta) and its abundance patterns in Ria de Aveiro lagoon, Portugal

“…Gametophytes (Thornber et al, 2006;Verge´s et al, 2008). The deviations from the typical Polysiphoniatype cycle (mixed cystocarpic and tetrasporic ramets) that we observed are similar to many others found in literature for Gracilaria (see reviews by Kain & Destombe, 1995;Polifrone et al, 2006) and other red algae (Vera et al, 2008).…”

Responses of the haploid-to-diploid ratio of isomorphic biphasic life cycles to time instability

“…These could be seasonal, herbivory dependent and could possibly be due to their different cytological processes of gamete/spore production. Dissimilarities between ploidy phases were also found for spore performance by Destombe et al [4], Garza-Sanchez et al [9], Gonzalez and Meneses [10], Pacheco-Ruíz et al [16], Roleda et al [19] and Scrosati et al [24] and for ramet growth and survival rates by Destombe et al [4], Gonzalez and Meneses [10], Pacheco-Ruíz et al [16], Thornber et al [30] and Vergés et al [32], which are possibly due to conditional differentiation. A perturbation in the population structure may occur following environmentally extreme events, extreme grazing or competition events, provided that they affect ploidy phases differently.…”

No sex-related dispersal limitation in a dioecious, oceanic long-distance traveller: the bull kelp Durvillaea antarctica

“…Furthermore, in dioecious seaweeds, one sex may be more susceptible to environmental factors than the other (Delph 1999), and thus lose its reproductive potential during long-distance voyages. For example, male individuals of the red seaweed Asparagopsis armata Harvey 1855 are more susceptible to herbivory than females because they do not invest as much energy in anti-herbivore defences (Vergés et al 2008). Also, in dioecious plants, males and females can present substantial physiological differences ( Cornelissen and Stiling 2005).…”

“…This could indicate important chemical differences between the sexes that could impact their dispersal potential. Male and female individuals usually have differential energy allocation, where females invest a lot more energy into reproduction and protection of the gametes (Delph 1999, Cornelissen and Stiling 2005, Vergés et al 2008. This variation has a direct impact on the chemical composition of each individual.…”