Sex

Outline What is sex? Cost/Benefits of Sex What defines the sexes? Sexual Origins Sexual Conflict Male-male Competition Female Choice Cryptic Female Choice *Sperm Competition Where is this leading?

What is Sex? Sex: Meiosis and Syngamy Meiosis - Reduction Syngamy - Fusion

Syngamy Fusion of gametes 2 kinds: Isogamy- protists, fungi, algae costs Anisogamy beneficial

Benefits of Having Sex Traditional: increase the rate of adaptive evolution --> decreases extinction risk Creates genetic variation spread of advantageous traits and elimination of deleterious genes Resistance to parasites (Red Queen hypothesis) Repair of damaged DNA via recombination

Costs of Sex Only one sex can bear young Asexual population: both “sexes” can bear young, so population increases more rapidly Males and females must find each other to mate Predation risk

What defines the sexes? Gamete size! This defines Anisogamy Larger gamete = Female Increase zygote size Zygote fitness Smaller gamete = Male Get more for less, just like Walmart! This defines Anisogamy There is variation in gamete size though…

Giant Sperm Drosophila bifurca

Sexual Origin Giardia lamblia Very primitive group

Sexual Conflict Male-Male Competition Female Choice Cryptic Female Choice Sperm Competition

Male-Male Competition Can lead to extravagant characters and sexual dimorphism Territory size and quality Ornaments vs. Armaments Mate Gaurding

Female Choice Females preferentially mate with males that have larger or more intense exaggerated characters Morphological characteristics, display behaviors, territory size, nuptial gifts Honest indicators, sensory bias

Indirect Benefits of Mate Choice Sexy sons: female preferences are inherited Runaway selection Good Genes Handicap Principle

Cryptic Female Choice Female chooses which sperm will fertilize her eggs after mating with several males Denial of deeper genetalic access Discharge or digestion of sperm Breaking copulation

Cryptic Female Choice If females do these things non-randomly then it is cryptic female choice

Sperm Competition Sperm from two or more males compete inside the female Calopteryx Number of Sperm Sperm Quality Mating Order

Sperm Competition Sperm Displacement Producing more sperm Copulatory organ modifications Humans Genital plugging and removal

Where is this leading us? Mating Systems Monogamy Polyandry Polygyny Promiscuity Life History Evolution