WFSC 448, Fish Ecophysiology Introduction to Evolutionary Adaptation (18 Sep 2015) Biological Diversity: From where comes the diversity of nature? Everywhere you look in nature you see a complex array of life, each form more intricate and fascinating than the next, all woven into a tapestry that is at once fierce, unforgiving and cold, and yet economical, complimentary, and nurturing. You can see it even in a jar of pond water. From where does it come? Ecology, science of: study of the distribution and abundance of organisms (Adrewartha & Birch) Evolution, science of: study of the distribution and abundance of organismal form (DeWitt & Langerhans) Physiology, science of: study of a group of internal traits of organisms, largely encompassed by organ system functions and their interactions with each other, and their response to the external environment (DeWitt, just now) Evolution—distr. & abundance of organismal form Evolution by natural selection can be axiomatized into three necessary and sufficient steps: 1) organisms exhibit variations variation 2) variations are heritable heredity 3) variations perform differently fitness Evolution by nat. selxn. creates adaptation… harmony from tragedy Charles E. Darwin The tragedy is that beings less suited to the conditions of life perish, or fail to reproduce. What arises however are subsequent generations of better fit organisms that can live in relative harmony with their environment. Premises 1&2—Phenotypic variation and heredity Components of phenotypic variation, including heredity… recall from intro bio or genetics, VP = VG + VE VG is genetic influence on phenotypic variation VE is environmental influence on phenotypic variation (Note, for the genetically erudite that VP actually = VG + VE + VG×E + 2 COVG,E + ε, and VG = VA + VI + VD + VM ) What we get then, from the confluence of all genetic and environmental effects is a distribution of phenotypes, z, for a given population: Frequency(z) z Evolution is driven by genetically based fitness differences: Δz = h2 s Δz – change in population mean of a trait h2 – degree of trait similarity among relatives s – trait difference between reproducers and population at large Consider a population (pop “A”) with a distribution of trait values… Frequency Fitness trait value (z) The blue distribution is before selection; the red distributiion is the population after (i.e. resulting from) selection Now consider a second population (pop “B”)… Frequency Fitness The cyan distribution is before selection; green is after (due to) selection trait value (z) And the outcome… Pop B Pop A Frequency trait value (z) Divergence is reinforced by selection against hybrids. This favors the evolution of mate choice not to hybridize. This process, termed reinforcement, further seals the process of divergence into speciation! As Darwin said, “…[T]here is grandeur in this view of life!” Summary of info/expectations from Dr. DeWitt’s material (not in book)… 1. Heritability is the magnitude of resemblance between relatives 2. Be able to draw a trait distribution for a population 3. Circle a tail and imagine only those breed 4.Draw the shifted trait distribution for this pop in the next generation 5.Understand the degree of shift, dz, is determined by the product of selection and heritability: Δz = h² s 6. Divergent natural selection drives population differentiation 7. Reinforcement (evolution of reproductive isolation stemming from DNS) creates speciation 8. Ecology and evolutionary biology are intimately entwined. Understanding one requires understanding the other. 9. Biological diversity deserves protection for aesthetic and utilitarian reasons. Protection requires understanding natural systems.