RIKEN ECL Unit Leader
Mariko Kikuchi Ph.D.

Life on Earth exhibits an extraordinary diversity of reproductive strategies. In addition to species with separate sexes (gonochorism), there are species that change sex during development or in response to environmental conditions, as well as gynogenetic species that produce clonal offspring without incorporating the sperm genome. Such remarkable diversity indicates that reproductive systems have evolved with considerable flexibility. How, then, has evolution enabled such dramatic transitions in reproductive mode?

Using the medaka fish, Oryzias latipes(Fig. 1) as a model organism, we have investigated the molecular genetic mechanisms underlying oogenesis. Our studies revealed that the molecular pathway driving meiosis, which halves the genome, and the pathway promoting oocyte maturation operate as distinct and independent functional modules. These findings suggest that the complex process of gametogenesis is orchestrated through combinations of multiple functional modules. Evolutionary transitions in reproductive mode may therefore occur by bypassing specific modules or rearranging the combinations of these modules.

To test this hypothesis, our laboratory extends these findings from medaka to the gynogenetic Amazon molly, Poecilia formosa (Fig. 2), and its close relative, the gonochoristic Atlantic molly, Poecilia mexicana. Using multi-omics approaches to compare the functional modules operating in germ cells, we aim to identify the molecular mechanisms that regulate the activation and inactivation of these modules. Through this work, we seek to uncover the general principles underlying the remarkable evolutionary flexibility of reproductive strategies.