Bio 3400 1nd Edition Exam 3 Study Guide Lectures 11 14 Lecture 11 Female Choice Red collared widow birds Group had tails artificially shortened expensive to carry around a big long tail Control and short treatments did not differ in territory establishment size of territory quality of territory DID differ in number of active nests long tailed control group had more Frogs Females prefer frogs with longer calls Why do female preferences evolve 1 good genes hypothesis handicap hypothesis 2 direct benefits 3 preexisting sensory biases 4 runaway sexual selection Good Genes Hypothesis Displays indicate genetic quality more attractive males are genetically superior ex peacocks ex frogs in high and low food conditions larval growth survival etc Direct Benefits Resources avoiding parasites etc Ex hanging fly direct relationship with duration of copulation and sperm transferred Pipefish males invest more resources than females in offspring females can produce eggs faster than males can rear a brood female reproductive success is limit by access to male pouch space therefore males are the choosy sex Preexisting Sensory Biases sensory preference exists for some reason unrelated to mate discrimination the preference for certain cues causes sexual selection on males to display those cues ex finch taped white feathers to male heads females strongly preferred white crest feather why white one hypothesis nests are lined with white feathers for camouflage Discussion Forsgren et al 1996 1 What is producing intrasexual selection in sand gobies the availability of resources specifically the number of shells 2 What is producing interseuxal selection in sand gobies a large number of shells and male size 3 What predictions do the authors make regarding these two types of sexual selection they predict that an increase in the number of shells will decrease intrasexual selection and increase intersexual selection 4 How did the authors test their predictions Which aspects were carried out in the field and which were carried out in artificial conditions 5 Did their results support their prediction Did you agree with their conclusions 6 What possible limitations to their study do the authors discuss 7 Do you think it is a good strategy to use both field and lab studies What do you think the strengths and weaknesses of each are Do you think one type of study is better than the other Lecture 12 Sexual Selection Good gene hypothesis handicap hypothesis Direct benefits Preexisting sensory biases Runaway sexual selection Runaway Sexual Selection The evolution of female preference and male advertisement reinforce each other This can happen if there is a genetic correlation between the male trait and female preference for the trait ex finches offspring will have 1 genes for long tail and 2 genes preferring long tail Cryptic Female Choice 1 Females often mate multiple times 2 Many species have the ability to store sperm for long periods of time 3 Opportunity for females to choose which sperm to use to fertilize eggs Methods for Studying Selection and Adaptation How do we know if something is an adaptation Adaptation a trait that increases an individual s fitness relative to those without the trait Adaptation is expected to be common Phenotypic variation is nearly always present Most traits have non zero heritability Phenotypic variation often correlates with fitness We do not accept adaptive hypotheses just because they are plausible or appealing Methods The comparative method Biology of natural populations Selection experiments Comparison of real organism with predictions of theoretical models Biology of Natural Populations Experimental Study Tephritid flies and jumping spiders Tephritid flies wave their wings to ward off predators such as the jumping spider Scientists tested the effect of wing waving groups flies left untouched control flies with wings cut off and reglued houseflies with tephritid fly wings tephritid flies with housefly wings normal housefly tested to see if the jumping spider would attach each group or not Observational Study Garter Snakes 8 In ectotherms performance is tied to temperature 9 performance measured as endurance speed digestive efficiency and hearing efficiency 10 Hypothesis 1 Garter snakes choose habitats that keep them near an optimal temperature 2 Garter snakes do not behaviorally thermoregulate 11 SO makes should choose habitats that keep their temperature in a certain range 12 For the experiment scientists tagged and tracked snakes monitored snake temperatures and monitored environmental temperatures 13 Results Garter snakes do a great job of keeping their body temperature in a optimal range by hiding under rocks and laying in the sun Lecture 13 Selection Experiments Laboratory selection experiments artificial conditions experimenter decides who reproduces many examples Why conduct selection experiments the process of evolution can be directly observed how do interrelated traits evolve EXAMPLE MICE Experimental Design 4 starting population 112 male and 112 female mice of the outbred Hsd ICR strain 5 genetic variation similar to human populations 6 used for several other selection experiments 7 selected based on how many times they ran on a wheel Background and Rationale voluntary activity levels affect energy expenditure balance body composition fitness psychological well being individual differences in voluntary activity levels are large in humans and mice Results wheel running had significant narrow sense heritability in the base population What else changes morphological changes lower body mass and fat larger heart kidneys and lungs behavioral decreased parental care more intermittent locomotion physiological more efficient glucose uptake higher hematocrit higher endurance Other selection experiments 14 Lenski s E Coli experiment 15 fitness increased over 50 000 generations 16 measured by how much of the plate the strains took up 17 fox tameness belyaev 18 increased tameness shorter skulls whining barking 19 Late reproduction in drosophilia Rose 20 later reproduction increased lifespan decreased early reproduction increased size increased stress resistance Selection on guppies in new environments Endler s guppies Greenhouse selection experiment no predation L low predation R high predation C Field introductions transferred guppies from high predation sites to low predation sites why wanted them to survive long enough to be observed high predation low predation Results when