Lecture Notes: Sexual Selection and Altruism

Recap from Last Lecture

Discussed independent assortment, recombination, and genetic variability.
Introduction to parthenogenic species (e.g., whiptail lizards) and asexual species (e.g., Daphnia).

Sexual Dimorphism: Differences in appearance between males and females of a species, e.g., birds of paradise with elaborate traits in males.
Maladaptive Traits: Traits that might hinder survival but aid in reproduction, e.g., bright plumage, long tail feathers.
Theory of Sexual Selection: Proposed by Charles Darwin and Alfred Russell Wallace; focuses on competition not just for survival but for reproduction.
- Males often develop secondary characteristics to gain access to females.
- Examples: Irish elk antlers, bighorn sheep, beetles, elephants, lions.

Male-Male Competition
- Within-Group Dominance: Establishing hierarchy to gain mating access (e.g., dogs, wolves).
- Female Defense Polygyny: Defending a group of females (e.g., elephant seals).
- Territorial Defense: Defending a territory attractive to females (e.g., impalas).
- Post-Copulatory Competition: Sperm from different males competing within a female’s reproductive tract.
Mate Choice (Female Choice)
- Females choose mates based on resources or genetic benefits.
- Anisogamy: Differences in gamete size between males and females drive female choosiness.
- Good Genes Hypothesis: Females select males with traits indicating superior genetic quality.
- Examples: Bright plumage in birds, long calls in frogs.

Lekking: Males aggregate to attract females, who choose mates based on displays.
- Hotshot Model: Males gather around a particularly attractive male.
Sensory Bias Hypothesis: Females have inherent preferences that males exploit.
- Examples: Chuck calls in frogs, swordtail fish preferences.

Altruistic Behavior: Acts that benefit others at a cost to oneself.
Mutualism: Both parties benefit (e.g., lion hunting groups).
Reciprocal Altruism: One party benefits now, with expectation of future reciprocation (e.g., grooming in primates).
Kin Selection: Favoring the reproductive success of relatives, even at a cost to oneself.
- Hamilton’s Rule: Altruism can evolve if the genetic gain from aiding relatives outweighs the cost.
- Inclusive Fitness: Total effect an individual has on proliferating its genes through direct and indirect means.

Calculating Relatedness: Probability of genes shared due to common ancestry (e.g., siblings share 50%).
Applications: Explains cooperation among relatives in species such as meerkats and vampire bats.

Next lecture will continue with kin selection and introduce biogenetics.