Session 12: Mate Choice
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Primate attraction, sexual selection, female versus male mate choice.
1. Key Concepts:
Reproduction is core to evolutionary patterns, to the ongoing success of the species, and to the reproductive success of individual organisms.
2. Terms & Definitions:
- Histocompatability
- From immunology, cells reject or not reject other cells based on their histocompatobility. This is directly due to the amount of similar cellular components.
- Cryptic behavior
- Behaviors that have a "hidden" meaning or behaviors that could signal multiple responses.
3. Choosing a Mate:
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- Limbic and neurological stimuli
- Experience
- Taste/preference
- Malleable choice
- “Good genes”
- Good health
- Good social skills
- Good parenting
Sexual selection:
Two main types of sexual selection exist. Each results in different displays, different major players, and different results. Often, both can be at work in the same system.
- Inter-sexual selection: Competition between males and females.
- Intra-sexual selection: Competition between individuals of the same sex, often male-male.
4. Mate Choice Evolution:
Hypotheses for Mate Choice for “Genes”:
- Zahavi’s (1975) handicap principle. This is a hypothesis based on honest signaling. If females are choosing males because of advertisements or displays which are difficult to maintain, then an honest signal is best. In other words, if the male can survive with the burden of a quality secondary sexual character, he must be a male with good genes.
- Hamilton and Zuk: Parasites and good genes. This is a hypothesis also based on honest signaling. If females are choosing males because of advertisements or displays, then an honest signal is best. Although this is close to the Zahavi's handicap principle, it differs in that if focuses on the energetic burden of maintaining a quality display despite the constant burden of parasite infection. In other words, if the male can survive with the burden of the display and maintain it despite a parasitic infection, he must be a male with good genes and a variable MHC region. The Major Histocompatability Complex, or MHC, region of the genome is instrumental in eliciting an immune response. This is especially important in responding to parasitic infections.
Coerced Mate Choice:
Competition between males and females can result in coerced mate choice. Males exerting behavioral and social threats can coerce females into copulation. Pan troglodytes are the poster child for coercion by males. Orangutans don’t actually use coercion, although it can appear as coercion. Only adult males are accepted and only during POP, or the peri-ovulatory period. No evidence of females being physically injured with orangutans.
Additionally, it has been hypothesized that the threat of infanticide is so great that females will mate with offspring to prevent infanticide. However, only scant evidence supports this hypothesis. However, the argument counters that females fight against infanticide so successfully that it is challenging to find evidence for these actions playing out. The data is still out as the hypothesis remains largely untestable.
Female Mate Choice:
Female choice is assumed for many mammals. However, the complex social structure of most primate species warrants further investigation. Because there may be a disconnect between mating and the pre-ovulatory period, or POP, mate choice behaviors are not easily teased out of the normal social context. Extra pair copulations (EPCs) are an obvious example of female mate choice. Additional factors to consider, in the realm of female mate choice, include:
- Female aversion to mating with high ranking males in some species.
- Attraction to migrant males, or preferentially mating with "new" males.
- Disconnect between mating choice and paternity.
- Costs to females of choice; this can be expressed in aggression or coercion.
- Choice for social status.
- Access to resources.
- Protection for self or infants.
- Inbreeding avoidance.
- Good genes signals.
- Friendship, or identifying the high frequency of affiliative behaviors between males and females as mate choice behaviors.
Male mate choice:
Male mate choice occurs, although it is less prevalent, especially among mammals. In primates, males choose mates based on several factors, including:
- Female rank or status.
- Female age.
- Sexual swellings.
Note, males do not choose females as mates for "good genes." Consider the evolutionary value of this trend.
5. Additional Material:
Required Reading:Primates in Perspective. 2007. C.J. Campbell. A. Fuentes. K.C. MacKinnon. M. Panger. S.K. Bearder. Oxford University Press.
Chapter 27: Mate Choice - Manson
