CP and AC: Adaptation and Speciation

Learn how adaptation and speciation drive evolution!

Passing down advantageous adaptations One organism may have a trait that is very advantageous, HOWEVER, if they do not reproduce their trait will not continue. Evolution ONLY happens to populations. Individuals do not evolve (sorry Lamarck).If a trait is advantageous and increases the organisms fitness, the trait may increase in relative frequency.On the other hand, if a trait is NOT advantageous and decreases the organisms fitness, the trait may decrease in relative frequency.If a trait doesn't affect fitness in any way the trait will not be under pressure from natural selection and shouldn't increase OR decrease in frequency. Speciation - How do we see new species? Organisms that cannot interbreed and produce viable offspring are are considered separate species. Behavioral, Geographic, and Temporal are three types of reproductive isolation.Behavioral Isolation:Two populations are capable of interbreeding but they have differences in courtship rituals or other reproductive strategies that involve behavior. For example: some birds sing specific songs to attract mates while some birds do complex dance routines. If they do it incorrectly they may never reproduce even though they are otherwise fit. Other organisms may danceor build nests or even dress up. If two populations diverge enough they may no longer recognize and mate with each other. This would leave them as technically two separate populations and perhaps even separate species if they can't make viable offspring together anymore.Geographic Isolation:Two populations separated by geographic rivers, mountains, or bodies of water. A great example of this is the Abert and Kaibab squirrels that were split on opposite sides of the Colorado river. The two geographically separated populations had to fend for themselves on either side of the river using their variations to survive in their environment and compete for limited resources. Over many generations of being separated they no longer recognize and mate with each other leaving them technically to separate populations and showing speciation.Temporal Isolation:Temporal Isolation refers to when two populations are in the same area and could technically interbreed but their tempo, their timing, is different. For example orchids of different species can live in the same area but if they release their pollen on different days they won't interbreed or create viable offspring.These types of isolation an lead to speciation. Watch this video to review types of reproductive isolation. Evolution... It's a thing. This whole unit we've talked about the Theory of Evolution which explains the observable change over time in a population.Darwin explained natural selection and proved how it works, Hardy-Weinberg lets us calculate it and Gould let us compare the speed at which it happens. BUT are those the only ways populations change over time?? Genetic Drift Genetic Driftis a type of evolution that occurs without natural selection... it's evolution just by chance.Sometimes, due to chance, a population frequency can change. Two examples of this are the Founder effect and the Bottleneck effect.Founder Effect is a situation where allele frequencies change as a result of the emigration of a small subgroup. Fruit flies, Cheetahs, and some of the Amish communities in Pennsylvania can show the effects of small populations relocating.In the founder effect the red bugs aren't more or less fit... by chance they are the only frequencies that wound up in a new area and therefore have a limited gene pool.Bottleneck Effect is similar in that a new population with a limited gene pool survives but is different in that a natural disaster is what causes the change. In this example only the orange and a few green survived... changing the population and causing evolution to occur. Natural Selection on Polygenic Traits When traits are controlled by more than one gene the effects of natural selection are more complex.There are three types of selection: Directional, Stabilizing, and Disruptive.Directional selection can be observed with bird beaks. If birds have variation - for example small, medium, and large beaks - but a drought causes all the seeds produced to be tiny, the large beaked birds may struggle to get food leading the variation of small beaks to be most fit.In directional selection one extreme version of the trait is favored and overtime all the individuals in the population will resemble that extreme.Stabilizing Selection can be observed in babies. Newborn babies can vary in weight from very petite (8.6 ounces is the record which is approximately the same as 98 pennies) to average (7.5 pounds average in US) to large (22 pounds is the record!).Unfortunately large and small babies don't survive as well as average babies. Since average is the most fit variation and both extremes are not as fit we see more and more babies at the average range. Disruptive Selection is when BOTH extremes are fit! A great example for this one is trout. A male trout will gather a school of females to protect and mate with. If another male intrudes the two males will fight. The largest males fight best and tend to win the ladies. But... small trout sometimes pretend they're ladies and sneak into the nest! They don't have to fight because they aren't recognized as a threat. So the large traits get passed down AND the small traits get passed down. Medium sized trout are the least fit.Take a look at the summary below and then complete the activity on google classroom. Knowledge Check Match the terms to their correct description Behavioral Isolation A type of reproductive isolation where organisms who behave in a certain way get to mate Geographic Isolation A type of reproductive isolation where two populations are separated physically and can't mate Temporal Isolation A type of reproductive isolation where two populations are in the same area but differ in their reproductive timing so they don't mate. Speciation The creation of a new species Mimicry An adaptation where two organisms resemble each other Camouflage An adaptation where an organism blends into its environment Knowledge Check Match the terms to their correct description Bottleneck effect The type of genetic drift evolution where a natural disaster disrupts the allele frequencies Founder Effect The type of genetic drift evolution where a small group of organisms finds a new place to live changing the allele frequencies. Directional Selection When ONE extreme is favored and the population shifts the average towards one extreme or the other. Stabilizing Selection When neither extreme is favored and the population shifts to the average Disruptive Selection When BOTH extremes are favored and the population splits to either extreme while the average decreases.