[Music] we have learned that speciation occurs when two populations are reproductively isolated and differential selection occurs speciation then results in one species splitting into two or more separate species we can use more specific terms Sy Patric and allopatric to describe how speciation occurs when popul in different geographical areas become separate species alop Patric speciation has occurred the prefix Alo means different or other while Patrick means Place alop Patrick means different place and therefore it makes sense that two populations of one species living in different places could diverge and become two separate species on the other hand a population of species living together in one geographical area could split into two populations that do not interbreed if they remain reproductively isolated the populations could diverge to form separate species this is called sympatric speciation the prefix Sim means same and again Patrick means Place s Patrick speciation means same place and therefore means that one population diverges into two separate species while living in the same place reproductive isolation in sympatric populations may result from behavioral differences in animals and temporal differences in animals or plants differences in Behavior are often behaviors related to attracting and mating with another individual of the same species if two individuals are not attracted to one another then their mating signals could prevent them from reproducing together these signals can include auditory cues like chirping humming or clicking visual signals like colorful physical features seen in this peacock or chemical signals like giving off pheromones and other smells when differences in Behavior prevent two individuals from mating it is known as behavioral isolation sympatric speciation can also occur due to temporal isolation or differences in the timing of critical reproductive events which prevent members of a single species from breeding with one another this phenomenon is often observed in Plants since populations May mate or flower in different seasons or at different times of day let's look at an example of orchids that live in the same rainforest some orchids have flowers that last only one day and must be pollinated on that day to produce seeds if individuals Bloom on different days they cannot pollinate each other and are therefore tempor ly isolated in animals differences in breeding schedules are a form of temporal isolation for example two species of frogs inhabit the same area but one reproduces from January to March whereas the other reproduces from March to May because these frogs reproduce at different times of year they are reproductively isolated adaptive radiation is a source of biodiversity adaptive radiation is an evolutionary process where a single ancestral species rapidly diversifies into many new species this diversification happens as the species adapt to different ecological niches as seen in section B 4.2 an ecological niche refers to the role and position a species has in its environment including all the interactions it has with the biotic and abiotic factors it encompasses how a species meets its needs for food and shelter how it survives and how it reproduces because no two species can occupy the same exact ecological niche populations can adapt to occupy different niches some key aspects of adap itive radiation include the following all of the new species originate from a single ancestor the formation of new species occurs relatively quickly in ecological terms and new species can exploit a variety of ecological roles or niches this leads the species to develop distinct physical or behavioral traits to adapt to their specific environments we've discussed the birds of the Galapagos Islands multiple times yet again they illustrate important concepts of evolution when the first population of birds arrived on the galpagos islands they were presented with a new environment and there was a new opportunity for diversification the population of birds rapidly adapted to the various niches available on the islands which led to the distinct physical and behavioral traits that we see in the galpagos finches today each Finch species of the Galapagos Islands has evolved distinct beak shapes allowing them to utilize different food sources another example of adaptive radiation can be seen among mammals following the extinction of the dinosaurs about 65 million years ago mammals rapidly Diversified to fill ecological niches that were left vacant when the dinosaurs went extinct adaptive radiation illustrates how life on Earth can diversify rapidly and respond to new challenges and opportunities leading to the rich biodiversity that we see today a hybrid is an offspring resulting from the mating of two different species a hybrid typically combines characteristics of both parent species the creation of hybrids can occur naturally or be facilitated by human intervention while hybrids do EX exist there are barriers to hybridization and stability of interspecific hybrids which prevents mixing of alals between species this mixing of alal is referred to as gene flow recall when gene flow increases two populations will become more and more similar however when gene flow decreases two populations can begin to diverge and become more and more different from one another natural barriers are divided into two categories prezygotic and postzygotic prezygotic refers to barriers that occur before ferti ation and prevent mating or successful fertilization temporal habitat and behavioral isolation are all prezygotic barriers if two species mate at different times live in different habitats or display different courtship behaviors reproduction will not occur in animals one of the functions of courtship behavior is for an individual to check whether a potential partner is a member of its species to prevent interspecific hybridization courtship Behavior needs to be distinctive the birds of paradise provide a clear example of how courtship behaviors can influence mating the birds of paradise rely on feather displays intricate dance routines and songs and calls if any aspect of the courtship behavior is not desirable to the female then mating will not occur in addition differences in physical structures between two species can make mating impossible sperm and egg could be unable to fuse to form a zygote if the proteins on the surface of their gametes prevent successful fertilization these natural barriers to hybridization help prevent organisms from wasting energy on producing offspring that might not survive or be fertile however if two species do successfully produce Offspring additional barriers prevent further mixing of alals between species the stability of hybrids is a postzygotic barrier which occurs after fertilization let's take a look at a common example of the mule a mule is a cross between a donkey and a horse mules have been deliberately bred for 5,000 years or more mules are stronger and have more endurance than donkeys or horses in general they are healthier and more resistant to disease and require less maintenance in terms of food and Veterinary Care these are a few of the characteristics that make them a desirable hybrid however mules are sterile this means that mules cannot mate with other mules to produce more offspring reproductive problems arise because horses have 64 chromosomes and donkeys have 62 the result is that mules have 63 chromosomes but there are problems in meiosis and for that reason and other genetic incompatibilities mules are nearly always sterile because a mule hybrid is sterile it means that horses and donkeys remain distinct separate species on the other hand closely related species could continue to reproduce and have fertile hybrid Offspring The more gene flow that occurs between these two closely related species the less likely they are to remain two distinct species over time if the two species continue to mate and produce fertile hybrids the two species could converge and become one species abrupt speciation can occur in Plants by hybridization and polyploidy polyploidy is a condition where an organism has more than two compl sets of chromosomes it can occur in two main ways some terms to remember as we dive into this concept are haid and diploid recall diploid refers to a cell or organism that contains two complete sets of chromosomes one from each parent haid refers to a cell that contains half or just one set of chromosomes polyploid then refers to a cell that has more than the diploid number of chromosomes or more than two sets there are two ways polyploidy can occur autop poly involves chromosome duplication within a single species for example if a diploid plant under goes a myotic error and produces diploid gtes instead of haid ones these can self fertilize or fuse with another diploid gamt resulting in a tetrol Offspring recall the prefix Auto means self so autopolyploidy results when a plant self fertilizes speciation can then occur The tetrol Offspring is reproductively isolated from the diploid parent population because the tetrols and diploids typically can cannot produce viable Offspring together this is due to differences in chromosome number which leads to immediate reproductive isolation and speciation Alo polyploidy is another way polyploidy can occur when two different species hybridize and produce Offspring with combined sets of chromosomes from both parents it is called alop polyi recall the prefix Alo means other or different Alo polyploidy results when two different plant species produce Offspring with extra sets of chromosomes initially the hybrid might be sterile because the chromosomes from each parent cannot pair properly during meiosis however if a subsequent chromosome doubling event occurs either naturally or through human intervention the hybrid can become fertile with itself resulting in a new species with chromosomes from both parent species here is an example to help illustrate alop polyol knotweeds are a family of plants found in genus persicaria Japanese knotweed is octoploid with 88 chromosomes giant knotweed is tetrol with 44 chromosomes and many researchers have found varying chromosome numbers in the hybrids with the most common being hexaploid 66 chromosomes since the hybrid species is reproductively isolated from both of the parent species it is now a new species at least 15 species in the genus persicaria have originated by Alo poly since poly is fairly common it must provide some clear advantages polyploids tend to exhibit Vigor or enhanced biological traits compared to their parents these traits can give the poly po plate Offspring a competitive advantage in certain environments and help establish a new population hybrids might also be better able to exploit different ecological niches compared to their parent species strawberries provide an example of the advantages of polyploidy wild strawberry species are diploid but cultivated strawberries are octoploid octoploid strawberries have larger fruits compared to their diploid ancestors they can also adapt to a wider range of environmental conditions and the octopoid species has genetic material from multiple species of strawberries giving it a broader genetic base this can enhance disease resistance and other adaptive traits however polyploidy also has some disadvantages polyploids can have problems with gene expression since they contain multiple copies of the same gene they often experience reduced fertility or sterility due to problems with meiosis and gamet formation in addition having a larger amount of DNA means cell Siz is also larger this can lead to changes in cell function metabolism and overall resource demands of the organism [Music]