ancestral sex roles	Behavioural differences between males and females arising soon after the evolution of mobility, originally defined by [2] and [1] in terms of higher male competitiveness for matings as a result of sexual selection, and now more often described as a higher optimal mating rate for males than females.
anisogamy	Occurrence within a species of gametes of two different sizes, resulting in two sexes, males (producing smaller gametes) and females (producing larger gametes).
isogamy	Occurrence within a species of gametes of one size; typically fusion occurs between gametes of different mating types.
post-ejaculatory traits	Traits evolved by post-ejaculatory (sometimes termed post-copulatory) sexual selection that increase the probability of fertilization.
pre-ejaculatory traits	Traits evolved by pre-ejaculatory (sometimes termed pre-copulatory) sexual selection that increase the probability of successful ejaculation (or copulation).
raffle principle	Sperm competition mechanism in which sperm from different ejaculates compete for fertilizations numerically, as in a lottery.
fair raffle	A given male's fertilization probability is proportional to his number of sperm ejaculated as a proportion of the total sperm from all competing ejaculates.
loaded raffle	A given male's fertilization probability is disproportional to his number of sperm ejaculated as a proportion of the total sperm from all competing ejaculates, usually modelled by a loading factor, r, applied to each of his sperm's competitive success.
relative testes size	Typically expressed as total testes mass as a proportion of of total body mass; equivalent to male gonadosomatic index as used in marine and fish biology.
sexual cascade	The sequence of evolutionary transitions in sexual strategy through time: under appropriate conditions each transition gives rise to the selective forces that generate the next, though some taxa remain ‘frozen’ at a given stage without further change.
sperm competition games	Models that seek ESS sperm allocations under various sperm competition conditions.
risk models	Sperm competition games where sperm competition is relatively infrequent; e.g. females mate twice with probability q and once with probability (1 – q).
intensity models	Sperm competition games where sperm competition is frequent; e.g. N > 1 ejaculates compete simultaneously.
sperm (inter-ejaculate) competition	Competition between the ejaculates of two or more males over the fertilization of a given set of ova. This differs from intra-ejaculate competition, i.e. competition between sperm within the same ejaculate over the fertilization of a given set of ova..
sperm displacement	Sperm competition mechanism in which sperm from the last male to mate displaces, either directly or indirectly, sperm from previous males stored in the female's sperm stores. Indirect sperm displacement typically involves action by the female.
sperm limitation	Cases where sperm density is insufficient to fertilize all available ova. High sperm limitation refers to cases where few of the available ova are fertilized.
syngamy	Fusion of two compatible haploid gametes to form a diploid zygote.