RECENT ADVANCES IN FERTILIZATION ECOLOGY OF MACROALGAE¹

Abstract

Our understanding of natural patterns of fertilization in seaweeds has increased substantially over the last 10 years due to new approaches and methods to characterize the nature and frequency of fertilization processes in situ , to recognize the conditions and mechanisms enhancing fertilization success, and to anticipate population and community consequences of the patterns of natural fertilization. Successful reproduction in many species depends on a delicate juxtaposition of abiotic and biotic conditions. Important abiotic factors are those triggering gamete release (e.g. single or interacting effects of light quality and water movement) and those affecting gamete viability or concentrations (e.g. salinity effects on polyspermy blocks; gamete dilution due to water movement). Examples of important biotic components are synchronous gamete release, efficiency of polyspermy-blocking mechanisms, population density of sexually fertile thalli, interparent distances, and male-to-female ratios. Field data indicate fertilization frequencies of 70%-100% in broadcasting-type seaweeds (e.g. fucoids) and 30%-80% in brooding-type (red) algae. Red algal values are higher than previously thought and challenge presently accepted explanations for their complex life histories. Important population and community questions raised by the recent findings relate to the magnitude of gene flow and exchange occurring in many micropopulations that seemingly breed during periods of isolation, the physiological basis and population effects of male-to-male competition and sexual selection during fertilization of brooding seaweeds, and the effects of massive gamete release, especially in holocarpic seaweeds, on benthic and planktonic communities. Comparative studies in other algal groups are now needed to test the generality of the above patterns, to provide critical pieces of information still missing in our understanding of natural fertilization processes, and to elucidate the evolutionary consequences of the different modes of reproduction (e.g. brooders vs. broadcasters).

Fertilization Strategies

“…Some authors have used this term to describe the release of sperm independently of whether the eggs are released or retained (e.g. Levitan 1998 ;Yund 2000 ;Santelices 2002) , and others to describe the release of both sperm and eggs, i.e. identical to broadcasting (e.g.…”

Understanding the Mechanism of Gamete Release in <i>Sargassum vulgare</i> C. Agardh

“…Great emphasis has been laid down on gamete release and post fertilization recruitment stages [2,26,27]. Reproductive events are governed by a number of environmental cues which evolve as a mechanism for populations to increase the probability of fertilization by releasing gametes at the same time.…”

Investigations on Reproductive Affinities in Red Algae

“…Gamete interaction requires a certain minimal gamete concentration (Nečas, 1981;Togashi and Cox, 2004), and a certain similar proportion of the two gamete types may be necessary for successful zygote formation (Richards and Sommerfeld, 1974). Synchronous gamete release is also crucial for successful fertilization of flagellated male and female gametes (see Santelices, 2002). In contrast, red algal gametogenesis is relatively frequent and successive at least in laboratory cultures, and hence, artificial hybridization can be carried out by putting fertile male and female thalli together, without any induction for gametogenesis and mating (e.g., Kamiya et al, 1997).…”