Complex life cycles of multicellular eukaryotes: New approaches based on the use of model organisms

Abstract

A wide variety of life cycles can be found in the different groups of multicellular eukaryotes. Here we provide an overview of this variety, and review some of the theoretical arguments that have been put forward to explain the evolutionary stability of different life cycle strategies. We also describe recent progress in the analysis of the haploid-diploid life cycle of the model angiosperm Arabidopsis thaliana and show how new molecular data are providing a means to test some of the theoretical predictions. Finally, we describe an emerging model organism from the brown algae, Ectocarpus siliculosus, and highlight the potential of this system for the investigation of the mechanisms that regulate complex life cycles.

The Ectocarpus genome and the independent evolution of multicellularity in brown algae

“…1). We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae [2][3][4][5] , closely related to the kelps 6,7 (Fig. 1).…”

“…Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic 2 approaches to explore these and other 4,5 aspects of brown algal biology further.…”

OUROBOROS is a master regulator of the gametophyte to sporophyte life cycle transition in the brown alga Ectocarpus

“…brown algae | development | phaeophyceae | stramenopiles M any organisms have life histories that involve alternation between two multicellular generations, a sporophyte and a gametophyte (1). A considerable amount of theoretical work has been carried out to understand the evolutionary and ecological significance of such complex life cycles (1).…”

“…A considerable amount of theoretical work has been carried out to understand the evolutionary and ecological significance of such complex life cycles (1). Haploid-diploid life cycles (i.e., cycles in which there is an alternation between a diploid sporophyte and a haploid gametophyte generation) pose a particular problem because it is necessary to explain why they do not evolve towards either haploid or diploid life cycles, both of which have theoretical advantages under some conditions.…”

“…Possible advantages specific to haploid-diploid life cycles include the potential of the two generations to exploit alternative ecological niches, avoidance of biotic aggressors (because of differential susceptibility of the two generations), and a reduced cost of sex (one meiosis/fertilization every two generations). However, very little experimental work has been carried out to test these various hypotheses (1,2). One of the limiting factors in this regard is that the mechanisms that regulate life cycle progression at the molecular level remain poorly understood.…”