Sexual Selection in Vertebrates

• Testis size increases as body mass increases, a morphological adaptation
• In birds and fish, relative testes mass increases as competition increases
• Most salmon males are anadromous, meaning they are late to mature but change into males and grow bigger in order to mate guard females
• Some salmon are parr, where relative to body size they invest more in sperm number to sneak matings with larger females
• Humans can suit sperm ejaculate to respond in time spent apart from their partner, as after this ejaculate there will be a reduction in fertility due to acrosome chemicals and he will not be able to ejaculate as much sperm the second time
• Seminal fluid (which contains sperm) in humans acts as an alkaline buffer to wash out previous sperm as it is spermicidal (kills other sperm)
• Human sperm has polymorphisms to help kill rival sperm - macrosperm is the classic, egg getters seek the ova, kamikaze sperm has blockers with a coiled tail to stop others and seek and destroy sperm to attack other sperm
• Females will benefit from an extra-pair copulation near ovulation, where males will benefit from guarding
• In humans, 10% of those that went without seeing their partner for a long period had an extra-pair copulation
• In humans, attraction to other males is highest near ovulation, followed by increased vigilance of their partner as ovulation is detected through pheromonal cues
• Tradeoff between guarding and sperm competition - sperm quality decreases as guarding time increases
• Women seek men with high education (resources) and larger height (fitness, survivorship)
• Men resource display by showing their status symbol with expensive tech, such as men being on their phone increasing with male:female ratio
• COVID-19 lowered sperm concentration post-infection and increased white blood cells associated with infection, those who got the vaccine had a higher sperm count perhaps due to abstinence
• Fitness can be shown through facial asymmetry as it reflects genetic and environmental pressures throughout development and the individual's ability to cope with the pressures
• Females that prefer symmetric males may get better parental care and genes for offspring development and sperm quality - human skeletons that lived longer were more symmetrical
• Disease is positively correlated with FA, whereas sperm number and speed negatively correlated with FA
• MHC genes encode proteins involved with immune defences, and females should prefer males heterozygous for MHC loci, and these males were found to be more facially attractive
• Testosterone levels at puberty grow male secondary sexual facial characteristics which are seen as attractive due to honestly advertising quality through immunocompetence handicap
• Women ovulating found masculine faces more attractive for extra-pair copulations, as their facial masculinity was negatively correlated with respiratory disease