Life HistoriesConsider; The Super-OrganismSlide 3An Economic AnalogyReproductive ValueSlide 6Slide 7Slide 8Slide 9Some Tradeoffs in Life-History EvolutionSlide 11Clutch Size/Parental CareIs this true?The Lack OptimumSlide 15Slide 16Slide 17Clutch size vs. LatitudeSlide 19SexSlide 21Slide 22Slide 23Slide 24Reproduce Now? Or Do It Later?Slide 26Slide 27Question; If humans began fishing a population of shad, so that the chance of survival between 2 and three years were dramatically reduced, how would you expect the population to evolve?Slide 29Slide 30Slide 31Slide 32Check it out http://www.esof2004.org/pdf_ppt/session_material/reznick.pdfLife HistoriesReading; S & S Chapter 13Consider; The Super-Organism•Indestructible•Immortal•Can subsist on anything•Produces millions of young•Produces young all the time•Young are indestructible•Is an excellent parent•First reproduction is 15 sec after birth•This super-organism is impossible because of the metabolic, developmental, and ecological tradeoffs inherent to living things.–Growing quickly means that there is no energy for early reproduction•Extended parental care means having fewer offspring.•Producing a clutch with many offspring means that each one must be smaller because there is only so much metabolic energy set aside for reproduction.•Setting aside more energy means not reproducing for a year or more.–Ultimately, reproducing means not living as long, because the act of reproducing drains energy, and subjects the organism to risks.An Economic Analogy•Imagine you had 1000 dollars to spend on reproduction. –Large offspring cost more than small offspring, but large offspring are more likely to survive. –Parental care costs, but it means your offspring are more likely to survive. –If you don’t spend it now, you can put it away and earn interest on the money, but you might be eaten or killed before you can withdraw it…•How would you spend the 1000? •How do you get the most return from your investment?Reproductive Value•Organisms allocate their resources in such a way as to maximize their lifetime reproductive success.–Lifetime reproductive success is the total number of offspring an organism produces over the course of their lifetime, (accounting for the proportion of an individual’s genes its offspring shares)•Of course, that is only measurable after an organism’s life is OVER. At any given time during the life of an organism the expected amount of reproductive success in an organism’s future is called its reproductive value.•At any given time during an organism’s life, the amount of reproduction they have in front of them can be expressed as follows;•Vx={i=x to infinity}(ly/lx)my•Where Vx= the reproductive value of the organism•my =the expected reproduction at time interval y•ly/lx=the probability of the organism living to time interval y–Thus, to maximize its own fitness, an organism will be selected to have those life-history attributes that maximize its reproductive value. This may involve a comprimise between reproducing now and reproducing in the future:•Vx=mx+{I=x+1 to infinity} (ly/lx)my–Where mx is contemporary reproductive output, and the second term is future reproduction.–Depending upon the ecology of the organism: energy expended reproducing now, mx, might affect the ability to reproduce in the future (my), or survive to the future (ly).–Optimal fitness involves maximizing Vx.–Which attributes maximize Vx depend upon the ecology of the organism.This is an optimality modelit assumes that organismswill evolve to ultimatelymaximize their fitness,given the constraintsunder which they operate.In theory, it is a perfectmodel.In practice?It is difficult to test But qualitatively, itseems to hold uppretty well.Some Tradeoffs in Life-History Evolution•Life histories evolve. Traits that affect the life history of an organism have an enormous potential to affect fitness.•The intensity and type of selective pressure on a life history character depends upon the particular ecological circumstances of the organism•MacArthur and Wilson coined the terms “r selection” and “K selection” to describe two general, and opposite trends in life history evolution.–R strategists are selected for rapid population growth–K strategists are selected for rapid competitive ability•Though thought-provoking and useful, this description deals is stereotpyes. Most organisms have a mixture of R and K selected traits. –(Also, check out the R, C, S system in your textbook)•Some Life-History Tradeoffs •Some of these have been studied extensively, some are thought to represent evolutionary tradeoffs based on our current ideas of how their evolution works.•Early reproduction vs. amassing resources to reproduce later•A few, large eggs vs. many smaller ones•Parental care vs. reproducing more often or having more offspring•Sexual or asexual reproduction•Male or female offspring•Use all your energy in one bout of reproduction (semalparous) or hold back, and live to reproduce later (iteroparous).Clutch Size/Parental Care•One crucial life-history tradeoff concerns the balance between clutch size (animals) or seed set (plants) vs. the size of each offspring. –Assume that the organism has a set amount of resources that they are able to devote to a bout of reproduction.–Producing more offspring means producing smaller offspring.•For a wide variety of organisms, smaller offspring have reduced survivorship relative to larger ones.•It also limits options regarding parental care.•Lack of parental care also restricts survivorship.Is this true?•It depends upon how you frame the question.»The Australian plague locust, Chorotoicities terminifera provides no parental care. It produces about five clutches of fifty eggs each.»The European earwig, Forficulata auricularia provivides extensive parental care, it produces about seven clutches of fifty eggs each.»Just comparing species is not much of a test, however, the two species have different ecologies.•It is better to ask whether, in the context of a given species, a larger clutch size means reduced survivorship.The Lack Optimum•For a wide variety of birds, and a parasitoid wasp, it is fairly well established that having more offspring translates into reduced survivorship for the offspring, OR, reduced opportunities to reproduce later.•The idea of optimum clutch size was