Sperm Competition as Post-Copulatory Selection
Males across animal species engage in microscopic warfare inside female reproductive tracts after mating, competing for fertilization success through physical and chemical weaponry in a high-speed evolutionary arms race.
Sneak Mating as Alternative Reproductive Tactic
Non-dominant males including subordinate elephant seals, brown trout, and small “sneaker” fish evolved alternative reproductive tactics emphasizing stealth and speed over size and strength to circumvent dominant male monopolies.
Mate Guarding and Physical Barriers
Males across mammals, birds, insects, and fish employ mate guarding behaviors and physical barriers to prevent rival sperm from accessing females and ensure paternity.
Female Cryptic Choice and Control
Females across many species actively control paternity through cryptic choice mechanisms, seeking additional mates, removing mating plugs, and biasing fertilization toward preferred males despite mate guarding attempts.
Sperm Morphology Evolutionary Adaptations
Males evolve diverse sperm morphologies optimized for competitive success, from fruit fly sperm 20 times longer than body length to helically-twisted passerine bird sperm resembling drills.
Ejaculate Economics and Strategic Allocation
Males across species including Norway rats adjust semen production quantities based on perceived sperm competition intensity, optimizing reproductive investment through prudent sperm allocation strategies.