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Beetle horns and gender differences edit

NSF Award:

Phenotypic Integration During Development and Evolution of Beetle Horns  (Indiana University)

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The mechanisms responsible for novel, complex traits and their diversification are critical to the study of evolutionary and developmental biology. Beetle horns, which are a recent evolutionary invention, have diversified dramatically and on a variety of scales.

Through an extensive study of horned beetles, Indiana University researchers have discovered that rapid evolutionary changes in a master regulatory gene cause equally rapid changes in horn development across closely related species. The research team also found that the same regulatory mechanism controls the evolution of nutrition-dependent alternative male features.

Biologists Teiya Kijimoto, Armin Moczek and Justen Andrews learned that horned beetles rely on a developmental genetic mechanism involving the master regulatory gene "doublesex" to promote horn development in large males, but to inhibit it in females. Experiments to weaken this mechanism resulted in large males lacking horns and females suddenly making them. The researchers also examined a second species with a recently evolved and rare reversed sexual dimorphism or obvious difference between the sexes. In this species, females have much longer horns and the doublesex gene carries out a mix of conserved, reversed and novel functions.

While there are differences in location, number and shape of horn development, in most species only large males develop horns, which they use as weapons against rival males to better access the normally hornless females. In naturally smaller males, known as "sneakers," limited nutrition during larval development contributes to a lack of horns. The researchers were also able to show that a modification of this mechanism--failure to promote horn development--is used to keep horns minimal in these naturally smaller males who compete for females using nonaggressive, sneaking behavior.

These findings illustrate that sex-specific development of beetle horns is regulated by doublesex. Additionally, the findings suggest that doublesex function has been recruited to facilitate the evolution of nutrition-dependent alternative morphs within the male sex, and that swift evolutionary changes in doublesex function underlie rapid divergences in horn development across closely related species.

Images (1 of )

  • horned (left) and hornless male beetle morphs
  • male (left) and female beetles with an unusual reversed sexual dimorphism
Horned (left) and hornless male morphs.
Teiya Kijimoto, Indiana University
Male (left) and female beetles known for their unusual reversed sexual differences.
Teiya Kijimoto, Indiana University

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