Pioneering Betta splendens as a new vertebrate model for evolutionary and behavioral genetics

Project Summary
Ever since the development of Darwin’s evolutionary theory, domesticated animals such as dogs and pigeons
have provided key insights into the evolutionary process, the molecular bases of morphological and
physiological adaptations, as well as into the genetics of biomedical traits. Yet, the experimentation in
domesticated animals needed to obtain mechanistic insights is challenging because of difficulties with genetic
manipulation, relatively long generation times, and ethical concerns. To leverage the advantages of
domesticates while allowing for detailed dissection of the genes and pathways underlying important traits, we
propose to develop Siamese Fighting Fish, Betta splendens, as a powerful new vertebrate model for
evolutionary genetics. This model will allow us to learn about the molecular causes and phenotypic
consequences of morphological and behavioral adaptations.
Betta splendens were domesticated in Thailand beginning around 650 years ago for fighting in organized com-
petitions, providing a unique window into the evolution of extreme aggressive behavior. For the last 120 years,
Betta have also been bred for ornamental purposes and are now one of the most popular pet fish. Like in many
domesticates, artificial selection has led to a remarkable diversity of morphological phenotypes, including col-
ors and fin types, as well as to traits of potential biomedical interest, including vertebral column defects and
infertility. At the same time, Betta present a number of advantages as an experimental system: (i) they fertilize
externally, facilitating genetic manipulation; (ii) they develop quickly inside transparent eggs, allowing for effi-
cient analyses of development; (iii) they have generation times of nine weeks and clutch sizes of ~400, facilitat-
ing experimental genetic analyses; and (iv) the Betta genome is only 441 Mb, among the smallest in verte-
brates, making whole genome resequencing methods particularly affordable. To leverage these features, we
propose to combine population genetics of wild and domesticated animals with quantitative genetic mapping
and functional studies under controlled laboratory conditions. Specifically, we will:
Develop a genomic toolkit in a new vertebrate system for evolutionary genetics; unravel the domesti-
cation genetics of Betta splendens; discover molecular bases of morphological diversity; and study
the evolutionary genetics of aggression.
Impact: This project will establish B. splendens as a novel model organism in evolutionary genetics, help to
dissect the genetic and molecular bases of behavioral and morphological evolution, and provide the foundation
for studies that address how evolution can reshape neuronal circuits of aggression, vital for elucidating the mo-
lecular basis underlying this important trait.

Grant Number: 5R35GM143051-05
NIH Institute/Center: NIH
Principal Investigator: Andres Bendesky