Multicellularity Drives the Evolution of Sexual Traits

From the male peacock’s tail plumage to the floral displays of flowering plants, traits related to sexual reproduction are often complex and exaggerated. Why has sexual reproduction become so complicated? Why have such exaggerated sexual traits evolved? Early work posited a connection between multic...

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Bibliographic Details
Published in:The American naturalist 2018-09, Vol.192 (3), p.E93-E105
Main Authors: Hanschen, Erik R., Herron, Matthew D., Wiens, John J., Nozaki, Hisayoshi, Michod, Richard E.
Format: Article
Language:English
Subjects:
Algae
Biological Evolution
Cells
Chlamydomonas reinhardtii - genetics
Complexity
E-Article
Eggs
Evolution
Fertilization
Flowering
Meiosis
Plants (botany)
Plumage
Reproduction
Reproduction (biology)
Sex Characteristics
Sexual dimorphism
Sexual reproduction
Species
Volvox - genetics
Zygotes
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Summary:From the male peacock’s tail plumage to the floral displays of flowering plants, traits related to sexual reproduction are often complex and exaggerated. Why has sexual reproduction become so complicated? Why have such exaggerated sexual traits evolved? Early work posited a connection between multicellularity and sexual traits such as anisogamy (i.e., the evolution of small sperm and large eggs). Anisogamy then drives the evolution of other forms of sexual dimorphism. Yet the relationship between multicellularity and the evolution of sexual traits has not been empirically tested. Given their extensive variation in both multicellular complexity and sexual systems, the volvocine green algae offer a tractable system for understanding the interrelationship of multicellular complexity and sex. Here we show that species with greater multicellular complexity have a significantly larger number of derived sexual traits, including anisogamy, internal fertilization, and secondary sexual dimorphism. Our results demonstrate that anisogamy repeatedly evolved from isogamous multicellular ancestors and that anisogamous species are larger and produce larger zygotes than isogamous species. In the volvocine algae, the evolution of multicellularity likely drives the evolution of anisogamy, and anisogamy subsequently drives secondary sexual dimorphism. Multicellularity may set the stage for the overall diversity of sexual complexity throughout the Tree of Life.
ISSN:0003-0147
1537-5323
DOI:10.1086/698301