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Lecture 5

BIOLOGY 321 Lecture Notes - Lecture 5: Scrotum, Muscular Development, MinoxidilPremium

5 pages63 viewsSpring 2017

Department
Biology
Course Code
BIOLOGY 321
Professor
Dr.Drea
Lecture
5

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Primate Sexuality 1/26/17
I. Multi-male Multi-Female
a. In many species (see slides)
b. All ages and all sexes
c. “promiscuous” breeding, in that females may mate with multiple partners in one
cycle
d. Age graded meaning group sizes vary a lot
e. Organized by kinship with interlaced with dominance hierarchies, so may be vary
complicated structures
f. Ususally female dispersal is philopatry and males dispersal (not so for chimps)
II. Dispersed
a. Prosimian primates mostly, and orangutan
i. Generally small-bodied, nocturnal insectivores in tropical rainforest;
except orangutan
b. Females can mate with more than one male (so they are “promiscuous”)
c. Most simple social unit is mother plus offspring
i. Units often widly dispersed with intersecting ranges with males
d. Solitary =/ asocial
i. Aka, alarm calls may draw nearby groups to help out the “solitary” unit
e. Usually have twins or more, which they leave in nests (aka they “park” them)
f. Both sexes disperse (avoiding inbreeding)
g. Orangutan are unusual in that it is unusual for diurnal species to be solitary
Considerations
1. Certain characteristics are confined to one sex, making it likely they are connected with
reproduction
2. These are often only developed at maturity and often during the breeding season
a. Aka these are secondary sexual characteristics
3. There is evidence that individuals of one sex may show strong antipathy or preference for
certain individuals of the other sex
a. This is attraction and particularly choosing of a mate
- These three considerations developed Darwin to develop the theory of sexual selection
Sexual Selection & Dimorphisms
- Sexual selection: component in natural selection that tends to perpetuate the
characteristics that attract one sex to the other
o Hen mate chose is based on 2dary sex characteristics leading to enhancement of
sexual dimorphism
- Sexual dimorphism: any consistent different between male and female beyond the basic
functional portions of the sex organs
- The types of sexual selection could be
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I. Intrasexual selection (e.g. male-male competition)
a. Generally male-male competiton where they try to drive off the other, where the
female remains passive throughout the process
b. Prime example is when males are much heavier/more muscularsuch as in
elephant seals; the idea is that the heavier one can be dominant and “win” the
woman
II. Intersexual Selection (e.g. female choice) (Example is the peacock)
a. Coevolved with trait exaggerationselection is of indirect benefits
b. Gain direct benefits (‘good genes’/ ‘good fit’ theories)
c. Sensory bias or passive attraction
III. Fisher’s Process (coevolved ith trait exaggeration)
a. Phase 1: female process evolves because the trait is favored by natural selection
=> the offspring are more likely to carry the beneficial trait
i. For example, the peacock plumage may have originally acted as some sort
of camoflague, allowing it to get passed on
b. Phase 2: after F preferences, males with trait are extra fit (natural selelction
advantage PLUS sexual selection advantage)
c. Fisher’s runaway process: ever increasing selective force favoring stronger and
more extreme traitstraits may become so extreme they have a negative natural
selection
i. Handicap Ho / sexy son: if they have these “expensive” and detrimental
traits but are yet able to survive, then that means they must be very “good”
IV. Benefits to Choosiness
a. Choosiness is directly beneficial, female preferences will evolve and male trait
follow
b. Types of advantages of the traits:
i. Lower risk of mating with wrong species: species recognition
ii. Good genes hypothesis: mate actually has genetic material that is directly
beneficial to the kids of the female, signaling paternal care, territorial
defense, food
iii. Good fit hypothesis: there is not necessarily one male that is the best for
every female, but each female has a male that is more or less fit for her
personallyaka compatibility and fecundity
1. Maj histocompatibility complex: mom and dad have two different
set of immune traits, mating with each other provides the kids with
a wider variety of immune genes
V. Sensory Bias
a. Female preferences are a “side effect” (aka pleiotropism) of sensory evolution
i. Pleiotropism: when one gene codes for something that has many different
phenotypes
ii. A gene codes for x, y and z; x may be the beneficial trait, and when x is
increased, y and z come along too
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