BIOEE 1780 1st Edition Lecture 16Outline of previous lectureI. Finch populationsII. FitnessIII. Back to finchesIV. Artificial selectionV. Examples of natural selectionOutline of current lectureI. AnnouncementsII. Life history evolutionIII. FitnessIV. Tradeoffs and constraintsA) Senescence as a life history tradeoffCurrent lectureI. Announcements*Exam tomorrow, in the same room as lecture*It will cover up to Cissy’s lecture on fungi (first 12 lectures) II. Life history evolution*What is it? It is the timing and duration of key events during a lifetime (age and duration of reproduction, number and size of offspring, lifespan). Central theme is a trade-off of these key elements.III. Fitness*Fundamental “currency” of natural selection*An individual’s proportional representation in the gene pool of subsequent generations*Things to ponder:1) What makes an organism fit or unfit?2) Fitness can only be measured in relation to others, right?3) Can individuals have a fitness of >0 if they themselves never reproduce?*Mate of wait game: You can either (A) have 10 offspring now, or (B) 5 offspring now and five for every year after. -If you have 90% chance each year of dying, which would you choose? A-If you have a 50% chance each year of dying, which would you choose? A (only by a little)-If you have a 10% chance each year of dying, which would you choose? B*Extrinsic mortality: the rate at which external events lead to death in a population-animal attacks, etc*Intrinsic mortality: the rate at which internal events lead to death in a population-heart disease, cancer, diabetes, etc*With the opossums, mainland ones have more predators so they reproduce a lot earlier in life than the ones on the island with few predators*Survival vs. reproductionSurvivalReproduction*Senescence: the deterioration in the biological functions of an organism as it agesSurvivorsAge*There are tradeoffs between future benefits (cellular repair) and current repairIV. Tradeoffs and constraints*Example: Elephant seals choosing to fight with the chance of getting seriously injured (negative) for the chance of mating (positive)A) Senescence as a life history tradeoff-Antagonistic Pleiotrophy: a trait may be selected for if it is beneficial early in life, even though it may be very detrimental to fitness later in life-Why? 1) At older ages, most individuals are already dead2) Fitness depends on reproduction; positive selection on post-reproductive traits is absent or very weak-Example: guppies in Trinidad-Guppies somehow got up above a waterfall, but predators did not, so the life history allocations differ enormously-Females have fewer offspring per year above the waterfall than at the bottom-Both babies and adult males are larger at the top-Rapid selection in transplant experiments: when they switched the guppies up, they evolved to mimic the populations that were already there and
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