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Contingency Theory  -  A mathematical model to determine when an animal should eat a less profitable, but more abundant food and when the animal should pass this food up in search of a more profitable, but scarce food. Contingency Theory states that you should eat the less profitable food 2 if: E2/h2 > E1/(h1 + s1)
Degree of relatedness  -  The probability of two individuals sharing identical genes by descent.
Diploid  -  Having two copies of every chromosome, one from each parent.
Direct fitness  -  The number of offspring an individual produces.
Eusocial  -  A social strategy marked by a reproductive division of labor, cooperative rearing of young, and overlapping generations.
Evolutionarily Stable Strategy  -  A strategy such that if all members of a population follow the rules, no other strategy could invade the population through natural selection.
Fitness  -  A nonspecific term usually referring to direct fitness.
Frequency-dependent selection  -  A form of natural selection in which the fitness of an individual's genes is dependent upon the relative frequency of that gene in the population.
Games  -  An interaction between two players with a conflict of interest.
Haplodiploid  -  A reproductive system in which females are diploid and males result from unfertilized, haploid eggs.
Haploid  -  Having only one set of chromosomes, usually by meiosis, or resulting from an unfertilized eggs.
Inclusive fitness  -  The sum of direct fitness and indirect fitness.
Indirect fitness  -  The number of relatives produced multiplied by the degree of relatedness to those individuals.
Intersexual selection  -  A form of sexual selection in which members of one sex are differentially attracted to members of the opposite sex, and so competition is for the attention of the opposite sex.
Intrasexual selection  -  A form of sexual selection in which members of one sex compete with each other to mate with the opposite sex. Males will frequently fight each other for a female or for a desirable territory to attract a female.
Marginal value theory  -  A mathematical model to analyze when an animal should leave a food patch in search of another, fresher patch. Reminiscent of the economic principle of the law of diminishing returns.
Meiosis  -  Cell division from one cell into four cells during two separate divisions. The result are haploid cells.
Mitosis  -  Cell division from one cell into two. Resultant daughter cells have the same number of chromosomes as the parent cell.
Monogamy  -  A mating strategy in which two individuals from a permanent pair-bond. Most cases are actually behavioral monogamy where males contribute to parenting and protection, but both sexes may engage in extra-pair copulations.
Optimality  -  Behavior analyzed in terms analogous to economic decision making.
Operational Sex Ration (OSR)  -  The Operational sex ratio is the ratio of sexually available females to ready males.
Parthenogenesis  -  Asexual reproduction. Literally "virgin origin".
Polyandrous  -  A mating system in which females mate multiple males.
Polygamous  -  Describes individuals engaged in a mating system where individuals (of either sex) have multiple mates.
Polygyny  -  A mating system in which males mate several females.
Polymorphic  -  The coexistence of two or more traits within a species. For example, eye color and blood type are polymorphic.
Profitability  -  The amount of energy yielded by a food source divided by the amount of time spent handling it once it is found. P=E/h
Promiscuous  -  Promiscuity is a mating system in which individuals of both sexes mate with multiple individuals, a combination of polygyny and polyandry.
Resource defense polygyny  -  A mating strategy in which males arrive at breeding sites early to fight over desirable territories. Females arrive at the breeding site and choose males based on their occupied territories.
Sexual selection  -  A form of natural selection in which individuals have differential reproductive success based on competition for mates.
Spermatophore  -  A bundle of sperm and proteinaceous material presented to female insect as a nuptial gift.
Strategies  -  The rules describing the behavior an animal may engage in while engaged in games. The Proportion of the population employing two different strategies: p+q=1, or p(Q) + q(R) = p(S) + q(T).
Syngamy  -  The fusion of egg and sperm cells into a zygote.