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Transcript
A Simple Life • Bacteria cells reproduce by simple division. • A cell is either developing toward reproduction or, reproducing • The meaning of life is clear – fitness is in terms of reproduction Life History of Bacteria • LAG PHASE: slow growth as the bacteria acclimate to the food and nutrients • LOG PHASE: metabolic machinery is running, exponentially multiplication of population density, doubling in number every few minutes. • STATIONARY PHASE: competition for food and nutrients causes number of bacteria to stabilizes. • DEATH PHASE: Toxic waste products build up, food is depleted and the bugs begin to die. How many “Broods” per year? • Univoltine - organisms having one brood per year • Bivoltine - organisms having two brood per year • Multivoltine organisms having more than two brood per year , • How many times in its’ life does a bacterium divide? Semalparous – reproduce once Many plants live for one year – we plan them each spring Salmon grow for 3-6 years, first in the river of their birth and then in the sea. They then return to spawn in the headwaters of the river, and die. Link – reproduction in Salmon Fitness of a semelparous organism • The product of viability and fecundity w = vf We know when they are reproducing! Univoltine fitness • The reproductive “Burst” must be synchronized to environmental factors – The organism must start development early enough to allow for growth and eventual reproduction by the progeny – Instead of “hibernating – the univoltine organism can just die no loss to the species – Many insect species have Univoltine and Bivoltine representative Iteroparous • Breeding many time in the lifetime – Trees – Most vertebrates – Many marsupials – Many arthropods – Many flowers Semelparous vs Iteroparous • Energy for production & support of gonads • Energy for reproduction • Energy for locomotion • Energy for metabolism to support life • Energy for future reproduction Iteroparous fitness • How do you tell if the species is fit? • Long term “fitness” does not necessarily mean an exponential burst of growth • However – over evolutionary time, species that do not “go forth and multiply”, and been replaced by those that do Age structured life histories • Each age group has a unique probability of survival and an age specific fertility • When all age classes are growing at the same exponential rate – the population is in a stable age- distribution Age structure in Human Populations Why are these two age structures different? What can we predict about the future population growth of these countries? Offspring Size and Offspring Survival Reproductive Restraint (fecundity = number of offspring) More Eggs = Smaller Offspring An intermediate number of eggs is best for fitness Why? Ageless organisms Organisms that reproduce by fission or budding do not age – there is no such thing as “an adult” Organisms that reproduce only by eggs or ovules do not follow conventional aging. They are “ambiguous” coral Evolution of Aging • Really long lived trees can live thousands of years. • We are incapable of studying aging effectively • These trees are from very harsh environments Link to trees of the Methuselah trail Semelparous mortality • In annual plants– when reproduction is over – mortality increase • There is no evolutionary advantage to longevity Interesting fact: Salmon that are castrated live a lot longer than those that are allowed to breed? Why to you think this is so? Iteroparous Survival & Fertility organisms • Studied in cohorts • Measured by mortality and fecundity per age group • At 2 weeks the plateau= low mortality high fecundity Iteroparous aging • Long-lived Animals with "Negligible Senescence" • Turtles (video) Sexual maturity at 30 years Lifespan of 80-100 years What should a lifespan be? • Human aging – Between 30 and 50 – Gray hair & Hair loss – Reduced sexual performance – Loss of muscle tone – Unreliable memory Aging is based on a decline in the force of natural selection • If natural selection eliminates an immature organisms – the effect is complete (no viable offspring • If natural selection eliminates a young, but reproducing organism the effect is to reduce the reproductive potential of that organism • If natural selection eliminates an organism that is some producing – there is not biological effect. Iteroparous aging and evoloution • For some species, there is an evolutionary advantage to longer lifespan beyond the time of fecundity • Where does this evolutionary advantage end? An experiment in changing in aging patterns • Forced selection for deferred breeding • All eggs laid before the preferred age of reproduction are discarded – 100 generation major physiological changes – Resist stress better – Fly longer – Longer fecundity Evolution and Aging Food for thought • There are no “ageless vertebrates” – just longer lived ones • The life expectancies of longlived vertebrates seem to be remarkably constant zardoz