Sex Brian O’Meara EEB464 Fall 2015 © BBC 2001, distributed under license from BBC Worldwide Limited |, downloaded from

Learning objectives Why is sex weird? Why has it evolved? How does sex ratio evolve? How does sexual selection evolve?

SexNo Sex Two-fold cost

SexNo Sex Half mother’s genes All mother’s genes

Stick insects Many plants Aphids Lizards Bees etc... Groups with parthenogenetic species Alistair J. Cullum Cnemidophorus inornatus, C. neomexicanus, C. tigris

No sex Sex Wikimedia commons

Muller’s ratchet

Muller’s ratchet

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Jokela et al. The maintenance of sex, clonal dynamics, and host-parasite coevolution in a mixed population of sexual and asexual snails. The American Naturalist (2009) vol. 174 (S1) pp

Mean (±SE) proportion of sexual snails (male %) in the shallow-habitat zone of Lake Alexandrina (black) and mean (±SE) prevalence of infection by Microphallus sp. (gray) between 1994 and Proportion of males corresponds closely to proportion of asexual females and can be used as a surrogate of frequency of sexuals in the population (Jokela et al. 2003).

Even sex ratio What is expected fitness of each of these?

Jordal et al. Extraordinary sex ratios and the evolution of male neoteny in sib-mating Ozopemon beetles. Biol J Linn Soc (2002) vol. 75 (3) pp

Sexual selection

Male-male competition

Female choice

Ryan 1990

Andersson and Iwasa. Sexual selection. Trends Ecol Evol (1996) vol. 11 (2) pp