Topic 4. Evolution and Animal BehaviorIf you examine the proportions of alleles at gene loci in a population and they change over time, then by our definition, evolution has occurred.How can this happen? One of the ways is through Natural Selection which was covered in previous topics.Other ways that allele proportions can shift in a population over time include:1. Mutations2. Non-random mating (sexual selection)3. Gene flow4. Genetic Drift (bottleneck or founder effect)5. Selection (natural or otherwise)There are several types of “Selection”1. Natural (environmental forces operating on a population)2. Artificial (human decisions regarding which animals or plants reproduce. Wild, tame, domestic, and feral animals have distinctively different definitions in animal behavior.)3. Kin (concept of inclusive fitness which helps explain altruism, such as alarm calls, anddeferring reproductive opportunities. Darwin did NOT define because it requires a knowledge ofgenetics to understand)4. Sexual (non-random mating. Asymmetry in reproductive success between males and females. “Male competition, female choice” is generally the case, but not always. Whichever sex contributes more to reproductive success is the limiting factor and the other sex competes foraccess to the limiting factor.)There can be competing selection pressures, such as between natural and sexual selection.How do we measure allele proportion or frequency changes in a population (gene pool)? Hardy-Weinberg equilibrium equation. 1 or 100% = p2 + 2(pq) + q2If these numbers change from generation to generation, then evolution has occurred.What circumstances would have to exist for evolution NOT to occur?1. large populations2. no mutations3. no gene flow in or out of the population4. no sexual selection – all individuals are equally sexy and able to reproduce5. no natural selection – all individuals are equally fitTHIS CAN NEVER HAPPEN! Thus evolution is inevitable in populations!So, what are some of the additional causes of evolution? (We already acknowledged mutation, natural selection, and non-random mating or sexual selection)1. Gene flow – migration in or out of a population2. Genetic drift – small, isolated or surviving populations can show allele frequency changes. Population bottlenecks and founders effects are examples of genetic drift.Assuming we start with a measurable phenotypic trait that has a normal or Gaussian distribution, then we can categorize or graph changes in the trait over time in 3 ways. Remember that this way of categorizing phenotypic changes is NOT restricted to any particular type of selection. In other words, these changes can come about though natural, artificial, sexual, and/or kin selection.1. Directional – variability remains the same, mean shifts2. Stabilizing – mean remains the same, variability shifts3. Disruptive – previously most common phenotype is disfavored, can result in incipient species event.Allele frequency shifts are examples of microevolution and can be seen in examples of domestication and natural selection changes over time in population responses to environmental changes.Speciation, or the establishment of reproductive barriers, are the result of macroevolutionary change. Behavior doesn’t fossilize, but we can make hypotheses regarding extinct animal behavior from some evidence and comparing to modern species.Animal behavior researchers can use the Biological Species Concept to define species since most animals reproduce sexually. The biological species concept is the most widely accepted species concept. It defines species in terms of interbreeding. For instance, Ernst Mayr defined a species as follows: "species are groups of interbreeding natural populations that are reproductively isolated from other such groups."Reproductive isolation means that a male and female cannot produce viable, fertile offspring.So the major question in Macroevolution is “How do populations become reproductively isolatedfrom each other?” Answer: Isolation and Time. You can think of reproductive isolation as establishing and maintaining a “virtual wall” between populations regarding reproductive success.Two major modes of speciation (there are more, but these are the most extreme on a continuum) are:Allopatric – Speciation occurs in geographically separate rangesSympatric – Speciation in geographically overlapping populations.Even with a seemingly clear definition of species using the Biological Species Concept, in the natural world it is often more complex. For example, squirrel populations on opposite sides of the Grand Canyon might successfully interbreed under artificial conditions, but not in nature.Phylogenetic Trees or charts are hypotheses suggesting the relationship and evolution of different species. The X-axis is “change,” and the Y-axis is “time.”Gradualism and Punctuated Equilibrium are examples of phylogenetic trees. If the entire population changes over time it is anagenesis, but if speciation occurs it is cladogenesis.Adaptive Radiation is the term for (relatively) rapid speciation and 3 of the best examples are:Darwin’s finchesLake Malawi cichlidsMammalian radiation (approx. 65 mya)Reproductive isolation mechanisms can be pre-mating:Geographical – separated by a barrierEcological – occupying different ecosystems, environments, or habitatsTemporal – most animal species have specific times of the year they can breed.Behavioral – these mostly involve the courtship behaviors and coordination of male and female Mechanical – an inability to fertilize due to incompatibility of sex organsPost-mating isolation mechanisms:Gametic incompatibilityHybrid inviabilityHybrid infertilityGiven that populations can branch off to form new species under the right conditions, extinction can wipe out a species.There are many situations that can result in the extinction of a species, including some behavioral characteristics that render a species too specialized or able to hybridize with another species.Currently, anthropogenic habitat change and destruction are the leading causes of