LS15 - Week 8 notes
LS15 - Week 8 notes Life Science 15
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This 5 page Class Notes was uploaded by AK315 on Thursday March 10, 2016. The Class Notes belongs to Life Science 15 at University of California - Los Angeles taught by Professor Phelan in Winter 2016. Since its upload, it has received 17 views. For similar materials see Life: Concepts and Issues in Biology at University of California - Los Angeles.
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Date Created: 03/10/16
Week 8 Sex behavior predictions • More investment > More determining ◦ Demand honest signals or health ◦ Value ﬁghting ability ◦ Elicit a commitment to invest ▪ Females make male do courtship dances ▪ Asking males to get her nuptial gifts (insects do this) ◦ Because female reproductive investment is initially higher, they are vulnerable early on. We expect the evolution of choosiness and demands for investment ◦ Example: Bush cricket lose 1/3 of their weight when they mate! Therefore they are highly constrained on their mating ability and thus making a bad decision about who to mate with can drastically aﬀect their ﬁtness, which is why they are gonna be extremely choosy and demanding when it comes to ﬁnding the right mate! • Lower reproduction investment > more competition and need for paternity certainty ◦ Competition for access ◦ Mate guarding/extended mating (in humans - wedding ring for example is a signal that the person is married. Hickey/Facebook status/holding hands/chastity belt) ◦ Sperm competition/anti-sperm ▪ Observation: Lots of cuckoldry ▪ Evolutionary response: produce more sperm ▪ They measured testes size of gorilla (it was found to be small) ▪ Physical manifestation: Gorillas (all females choose to mate mate with 1 male) ▪ Chimps? (females have sex w/dozens of partners) - chimps had large testes and produced a lot more sperm!] ▪ Why do males exhibit more mate guarding than females? Paternity uncertainty ▪ Initial low reproductive investment and paternity uncertainty lead to male-to-male competition for access to females, indiscriminate male mating, mate guarding and sperm wars. ▪ Extreme nature examples - black widow spider males break their sex organ oﬀ into females preventing the male and the female from mating with anyone else. ▪ Think about why many females aren’t partners at law ﬁrms - they realize that 7 years of work for the ﬁnal payout may not be worth as much! Could be due to ﬁnal outcome and weighing that outcome • Mating system deﬁnitions ◦ Polygyny: (high variance in Male Rs/ low variance in female Rs) so one male bonds with multiple females. Most mammals are polygynous ◦ Polyandry: (low variance in Male Rs/ high variance in female Rs) so one female bonds with multiple males. Very rare but example is mouse lemur, bush cricket example etc. ◦ Monogamy: low variance in both, low number of mates each so one female bonds with one male. Most birds are monogamous. • Sexual dimorphism is considered a very good predictor of mating systems. Why? ◦ Biological constraints make reproductive investment asymmetric ◦ The more asymmetric the investment: • Why would we see more monogamy in birds than mammals? ◦ They are sexually dimorphic - there is no need to be so choosy when they look similar. ◦ Birds feed their babies food, they cannot lactate like mammals. Both MALE AND FEMALE can feed their kids so reproductive investment is SHARED. It’s divided up better! which explains why monogamy works. ◦ Mating systems - monogamy, polygyny and polyandry describe the variance in mate number of males and females in a population. • Normal development requires: ◦ Stable environment ◦ Good genes ◦ Heterozygotes can develop normally even in a turbulent and variable environment. ◦ Homozygotes don’t develop that normally…. ◦ How can we spot abnormal development? ▪ as deviations from bilateral symmetry ▪ this is called asymmetry ▪ Measured as for example :(diﬀerence between size of right index ﬁnger - left index ﬁnger)/average size of index ﬁnger ◦ Another study was done with scorpion ﬂies (symmetric scorpion ﬂies produce sexier pheromones) - where pheromones from male ﬂies were given and females chose the more symmetric males. This was done with human males too. ◦ Study 2: Women smelled shirts worn by diﬀerent men and rated ‘most attractive’ - found to be for more symmetric guys ◦ Study 3: Relation between increased orgasms and increased symmetry ◦ Study 4: Who are the most symmetrical people? ▪ Bi-racial individuals tend to be much more symmetrical ▪ people who are symmetric (grow quicker, produce better orders, have more sexual partners, are better lovers, produce more babies) ▪ symmetric horses are faster runners ▪ symmetric ﬂowers produce more nectar About the nervous system • Your body has 2 systems for responding to stimuli and co-ordinating info within the body; Hormones and Neurons • Central nervous system CNS and the peripheral nervous system PNS • Neurons are the cells that transmit nerve impulses. ◦ When we do something injurious or dangerous, we feel pain. Pain is crucial because those nerve impulses that transmit the pain, tells our body that whatever we are doing is going to be harmful to us. It’s an adaptive behavior, which is why it is important for the body to be able to feel pain. ◦ Plants do NOT have neurons and they don’t feel pain ◦ Cool stuﬀ: Surgery to correct tremors = planting electrodes within certain parts of brain. ◦ A vertebrate neuron - dendrites (receive signals) > through the axon > conducts information out of the terminal buttons ◦ Neurons release neurotransmitters (chemicals that basically carry the signal across a synapse from one neuron to another neuron, muscle cell or gland cell) ◦ 10-15x gleal cells compared to neurons ◦ How neurons work: ▪ Signal - initiated somewhere else in body in response to external stimuli. Travels from dendrite through cell body and down the AXON ▪ Axon - electrical signal (Na+ in, K+ out) travels down until (also Axons are extremely long - the cell can stretch from spinal cord to ﬁngertips) ▪ Synapses with: ▪ A muscle: causing contraction ▪ Another neuron: causing ﬁring/no ﬁring ▪ Neurons, in some cases (rare), have been found to grow and regenerate. However, for the most part, neurons do die ▪ London cab drivers - had larger hippocampus (used for spatial memory). • Action potential - is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. • Myelin sheath = insulator • What do babies and individuals with multiple sclerosis have in common? • An action potential is a self propagating, all-or-none change in the membrane potential that travels down an Axon. • We detect the MAGNITUDE of stimulation based on the number of neurons that were activated/involved. However, the process and action potential returns the exact same. • What are sensory cells? ◦ They are all the same thing ▪ modiﬁed dendrites ▪ interacting with the outside word ▪ and sending info to our brain ◦ The senses: ▪ smell - chemoreceptors ▪ taste - chemoreceptors ▪ vision - photoreceptors ▪ hearing - mechanoreceptors ▪ touch - mechanoreceptors + thermo-receptors ▪ others - electricity, magnetism etc.