What trade-off creates evolutionary tension between sexual selection and viability selection concerning a trait like a bright orange beak?
The attractive trait might require significant metabolic investment that compromises immune function necessary for survival.
Evolutionary tension arises when two powerful selective forces—sexual selection (driven by mate choice) and viability selection (driven by survival)—pull traits in opposing directions. If a trait strongly favored by females, such as a notably bright orange beak, requires substantial metabolic resources to produce and maintain (perhaps derived from carotenoids), this investment may detract from other critical systems, like the immune system. This creates a direct conflict: displaying the trait necessary to attract a mate compromises the physical health required to survive long enough to reproduce successfully. Research suggests that sexual selection can sometimes operate independently of viability selection, meaning a highly attractive mate may not always be the fittest survivor when facing environmental adversity.
