Attachment strength differs amongst life‐history stages of an intertidal, isomorphic red alga

Abstract

SUMMARY Complex haploid‐diploid life cycles amongst marine organisms may be maintained by ecological differences in life‐history phases. For red algal species within the Gigartinaceae, such differences may be driven, in part, by different cell wall composition and resultant biomechanical strengths of haploid and diploid phases. A field experiment tested the attachment strengths of gametophytes and tetrasporophytes of the isomorphic red alga, Chondrus verrucosus (with comparisons of fertile and vegetative fronds, with and without natural tissue damage across three wave‐exposed sites). Seventy‐nine percent of all fronds broke at the stipe‐holdfast junction. There were significant differences in attachment strength (break force and break stress), but not gross morphology (frond length, number of branch axes, wet weight and cross‐sectional area of fronds that dislodged at the stipe‐holdfast junction) of life‐history phases, with tetrasporophytes exhibiting weaker tissue strength and attachment, and therefore greater susceptibility to dislodgement by waves. However, fertility and tissue damage did not consistently influence dislodgement in pull‐to‐break tests simulating the effects of single waves. The ecological and evolutionary consequences of greater susceptibility to dislodgement of tetrasporophytes (relative to gametophytes) warrant further investigation.

Maintenance of Complex Life Cycles Via Cryptic Differences In The Ecophysiology Of Haploid And Diploid Spores Of An Isomorphic Red Alga1

“…, Zuccarello et al. , Bellgrove and Aoki , in press, Araujo et al. ), this study and others (Destombe et al.…”

“…) provide evidence of disproportionate provisioning of carpospores and tetraspores of an isomorphic red alga, Chondrus verrucosus . Moreover, we have shown previously (Bellgrove and Aoki ) that tetrasporophytic fronds of C. verrucosus are biomechanically weaker than those of fertile carposporophytic, potentially resulting in differential rates of dislodgement between phases; and that proportions of gametophytes and tetrasporophytes in populations differ (Bellgrove and Aoki ). These provisioning and experiential legacies may interact to differentially affect the relative dispersal potential of tetraspores and carpospores.…”

“…; Fig. ) with the diploid carpospores and haploid tetraspores being the prime agents of dispersal, although dislodged floating fronds may facilitate long‐distance dispersal (Bellgrove and Aoki ). There are no obvious differences in the sizes of carpospores and tetraspores (Bellgrove et al.…”

“…There is indeed growing evidence of ecological differences among isomorphic haploid and diploid phases of macroalgae, including differences in thallus (e.g., Mathieson and Burns , Hannach and Santelices , Lindgren and Åberg , Scrosati and Mudge , Bellgrove and Aoki ) and spore (Bhattacharya ) abundances, growth (Bhattacharya , Hannach and Santelices , Luxoro and Santelices ), biomechanics (Carrington et al. , Bellgrove and Aoki ), susceptibility to grazing (Hannach and Santelices , Luxoro and Santelices , Buschmann ), and desiccation (Luxoro and Santelices ). However, we find few accounts of phase differences in the ecology and/or physiology of dispersive propagules (Destombe et al.…”

Differential Frond Growth in the Isomorphic Haploid–diploid Red Seaweed Agarophyton chilense by Long‐term In Situ Monitoring

“…2013, Vieira et al. 2018a,b, Bellgrove and Aoki 2020). Besides direct observations, indirect evidence supporting conditional differentiation has also emerged.…”