Managing the tradeoff between reproduction and survival requires flexibility in behavior and gene regulation in three-spined stickleback

Predators exert a powerful selective force, however, predator avoidance
can conflict with other important activities such as attracting mates.
Decisions over whether to court mates versus avoid predators are vital to
fitness, yet the mechanistic underpinnings of how animals manage such
tradeoffs are poorly understood. Here, we investigate the flexibility of
behavior and gene regulation in response to a tradeoff between avoiding
predators (survival) and courting potential mates (reproduction) in
three-spined stickleback (Gasterosteus aculeatus). We compared behavioral
and transcriptomic responses of male sticklebacks faced with a courtship
opportunity and cues of a predator simultaneously to males faced with a
courtship opportunity or cues of a predator alone and found that males
behaviorally compromised courtship in favor of predator avoidance when
faced with a tradeoff between them. The need to manage this tradeoff
elicited dynamic changes in brain gene expression, and sets of
functionally connected genes were organized into discrete modules based on
co-expression. Additionally, we found that behavioral flexibility in
response to tradeoffs corresponded to flexibility in gene regulatory
network structure. Combined, these results uncover the coordinated
response by the brain to a fundamental ecological tradeoff, providing
insight into the structure and function of genetic networks underpinning
how animals make fitness-influencing decisions.