Inbreeding and Sexual Selection

by Jason Amores Sumpter
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hi. In this video, we're going to talk about genetic variation and populations and different types of natural selection Now, even though the goal is usually to increase genetic variation because that tends to help populations, sometimes there are circumstances that actually decrease the genetic variation in a population and in breeding is a great example of this. Inbreeding is mating between relatives, and it tends to increase homocide gossett e in the population. And this can also lead to something called inbreeding depression, which is a decline in the average fitness. As homocide, gossipy increases and headers, I gossipy decreases No home, ozai gossipy. Increasing would mean that there is less genetic variation, right, because that's going to mean that one Lille in particular is going to be pretty dominant in the population, dominant not necessarily in terms of whether it's dominant or recessive, but dominant in the sense of it's going to be prevalent. It's going to be wide spread in our population. So here we have a nice model of a pedigree for Shetland ponies, and you will see that there is the capital, a dominant Lille, this lower case, a recess of Lille and over generations when you have inbreeding that tends to result in more Hamas egas individuals were as out breeding tends to result in more hetero zegas individuals. Now it is advantageous generally to have more hetero six individuals and to increase the genetic variation in a population home is I gossipy tends to decrease fitness in the long run. Now there are exceptions to this. I'm just talking about general trends here and in breeding is why it's so difficult to bring back species that are on the brink of extinction because their populations air so small. It's really difficult to avoid inbreeding so generally when trying to revive those species those endangered species. Inbreeding happens, and the overall fitness of those organisms in that population tends to decrease. Its just one of the many challenges that conservationists have to face Now sexual selection is a type of natural selection. That's where some individuals out compete, others because they're better at securing mates. And often this can pertain to you sexual dime, or if is, um, which is a fiend tip IQ difference between the males and females of a species, and you're probably very familiar with this in terms of bird mating, which is a great example of inter sexual selection, which is selection between the sexes. Usually when a female chooses a male and many birds display a great degree of sexual dime or if ism or a great degree of variation between the appearance of the males and females. And usually this comes in the form of males having very decorative perhaps so kind of lavish or grandiose appearance that they use to attract mates. So here you see an example of the peacock, with its very large, impressive tail feathers and the well, no offenses rather unimpressive Pea hen, the female of the species peacocks and pea hens have a use, a form of inter sexual selection. Females display their impressive feathers, and the females decide whether or not they're impressed. Now you can also have in trust sexual selection and in trust. Sexual selection is selection within a sex, and this is usually in the form of males competing with one another for mating rates. Like you see, these two elephants seals right here that are squaring off for a fight, they're competing for mating rates. Now, the interesting thing about inter sexual selection not backtrack, too much is that inter sexual selection can actually result in some kind of funny appearances for organisms. So you might think peacocks feathers are kind of lavish and grandiose and guess what they are. They're a little ridiculous, right? Why does a bird needs such crazy tail feathers? Well, the reason is that the females tend to pick males who have the most impressive display of plumage, meaning that over generations the males of the species that are going to be producing the most offspring because they're going to be securing the most mates are those with the most impressive tail feathers, meaning that over generations the males of the species are going thio. Because of this inter sexual selection, they're going Thio Thea Leal's In the Population are Going Thio three Wheels form or impressive tail feathers air going to increase. So over generations you're going to have a larger and larger percentage of males who have crazier and crazier tail feathers, and this can actually go awry. This can actually go awry for organisms. There is an example of a particular type of extinct dear who scientists think mating waas, a type of inter sexual selection For this organism and these deer. Their antlers grew so big they grew bigger and bigger and bigger because the females they picked the males with big antlers. So over generations, the males evolved to have bigger and bigger antlers to try to compete for those female mates. And it got to the point where their antlers got so ridiculously big that it was actually very hard for these organisms to even lift their necks. It basically the inter sexual selection pressures made drove this species to extinction because the males of the species eventually ended up with antlers that were so big they couldn't even function properly. They couldn't live normal lives. So it just goes to show that sexual selection isn't always driving organisms to be more fit. Sometimes it actually hurts the fitness of those organisms, whereas intra sexual selection tends to favor males. You know, again, we're just speaking generally Now it tends to favor males who are more fit, who are bigger, stronger mawr Oh, are bad Skerry, right? The guys who are gonna win the fight. Now let's flip the page and talk about some other types of natural selection