Vegetative Reproduction Is More Advantageous Than Sexual Reproduction in a Canopy-Forming Clonal Macroalga under Ocean Warming Accompanied by Oligotrophication and Intensive Herbivory

Abstract

Ocean warming and the associated changes in fish herbivory have caused polarward distributional shifts in the majority of canopy-forming macroalgae that are dominant in temperate Japan, but have little effect on the alga Sargassum fusiforme. The regeneration ability of new shoots from holdfasts in this species may be advantageous in highly grazed environments. However, little is known about the factors regulating this in Sargassum species. Moreover, holdfast tolerance to high-temperature and nutrient-poor conditions during summer has rarely been evaluated. In the present study, S. fusiforme holdfast responses to the combined effects of temperature and nutrient availability were compared to those of sexually reproduced propagules. The combined effects of holdfast fragmentation and irradiance on regeneration were also evaluated. Propagule growth rate values changed from positive to negative under the combination of elevated temperature (20 °C–30 °C) and reduced nutrient availability, whereas holdfasts exhibited a positive growth rate even at 32 °C in nutrient-poor conditions. The regeneration rate increased with holdfast fragmentation (1 mm segments), but was unaffected by decreased irradiance. These results suggest that S. fusiforme holdfasts have a higher tolerance to high-temperature and nutrient-poor conditions during summer than propagules, and regenerate new shoots even if 1-mm segments remain in shaded refuges for fish herbivory avoidance.

Effect of Grazing Treatments on Phenotypic and Reproductive Plasticity of Kobresia humilis in Alpine Meadows of the Qinghai-Tibet Plateau

“…This indicates that although yak grazing activated the K. humilis shoot pool and improved the grazing tolerance of K. humilis (Wang et al, 2017), it did not stimulate further development of shoots into nutrient branches. Many studies have shown that increase investment in sexual reproduction decreases investment in vegetative reproduction, suggesting that there is a significant trade-off between sexual and vegetative reproduction (Wang et al, 2018;Liu, 2020;Endo et al, 2021). Our results support this suggestion.…”

The effects of desiccation and salinity gradients on the PSII photochemical efficiency of an intertidal brown alga, Sargassum fusiforme from Kagoshima, Japan

“…Clearly, more studies are needed to examine if populations that have a different genetic history, environmental history, and acclimation methodology show a different response to stress (e.g. Macrocystis pyrifera (Linnaeus) C. Agardh; Laminariales;Fern andez et al 2020Fern andez et al , 2021. Furthermore, in the present study, we did not elucidate the mechanism that details how desiccation reduces photochemical efficiency; however, elucidating this mechanism is essential for this species in future studies for a better understanding of why this species can flourish in such an extreme environment.…”

“…holdfast and new shoots) to survive a summer‐time environment (Endo et al . 2021). Likewise, according to our past study that reported the effects of temperature and irradiance characteristics on photosynthesis, which includes the diurnal change of photochemical efficiency in the natural state by using optical dissolved oxygenic sensors and pulse amplitude modulation (PAM)‐chlorophyll fluorometry (Kokubu et al .…”

“…For instance, a pioneering study by Yokohama (1973) on the manometric measurement of photosynthesis of this species revealed that the optimum temperature for photosynthesis was higher in summer samples than in winter samples, suggesting the possibility of long-term acclimation to environmental temperature or adaptation by the perennial thallus (e.g. holdfast and new shoots) to survive a summertime environment (Endo et al 2021). Likewise, according to our past study that reported the effects of temperature and irradiance characteristics on photosynthesis, which includes the diurnal change of photochemical efficiency in the natural state by using optical dissolved oxygenic sensors and pulse amplitude modulation (PAM)-chlorophyll fluorometry (Kokubu et al 2015), this species is tolerant of high irradiances and a relatively broad range of temperatures, suggesting that the ability of this species to recover from exposure to high irradiance is one of the mechanisms that allow it to flourish in the intertidal environment (Zou & Gao 2010).…”

Research on the Regulatory Mechanism of Algae Reproduction under Abiotic Stress Conditions

“…Endo et al [26] demonstrate a high tolerance of holdfasts (the equivalent of roots in seaweeds, which anchor the organism to the sea floor) to heat stress in the brown alga Sargassum fusiforrme. Under high temperature and low nutrition conditions, holdfasts can grow and regenerate into new shoots by vegetative reproduction, i.e., asexual reproduction.…”