Speciation

Summary

In this biology lesson, Mr. Anderson delves into the fascinating process of reproductive isolation and speciation—the journey from one species to two. Using examples such as fruit flies, elephants, and plants, the video explains how different barriers, whether prezygotic or postzygotic, prevent species from interbreeding. These barriers include geographical isolation, mechanical differences, and behavioral changes. Notably, speciation can occur rapidly or over millions of years, influenced by genetic mutations and environmental changes. Thus, speciation is a crucial aspect of evolutionary biology, showcasing nature's diversity and adaptability.

Highlights

• Reproductive isolation is key to forming new species from one species. 🔑
• Diane Dodd's fruit fly experiment demonstrated dietary-induced reproductive isolation. 🍏
• Barriers to gene flow include physical, genetic, and behavioral factors. 💔
• Geographic isolation can lead to allopatric speciation, as seen with ice ages and metalarks. ❄️
• Prezygotic barriers prevent species from mating, like time-based breeding in toads. 🐸
• Mechanical barriers, like differing shell spirals in snails, prevent interbreeding. 🐚
• Behavioral differences, such as varied bird songs, can prevent cross-species mating. 🎶

Key Takeaways

• Speciation is the process of forming new species through reproductive isolation. 🐞
• Barriers such as geographical, mechanical, and behavioral prevent interbreeding. 🌍
• Speciation can be rapid or gradual, highlighting nature's adaptability. 🌿
• Different types of isolation include prezygotic barriers like temporal and mechanical isolation. ⏳
• Postzygotic barriers occur after fertilization, preventing viable offspring. 🚫
• Environmental changes can accelerate speciation, exemplified in punctuated equilibrium. ⚡
• Polyploidy in plants is a common cause of rapid speciation. 🌱

Overview

Speciation is an incredible biological process that transforms one species into two through the mechanism of reproductive isolation. Mr. Anderson, in this insightful video, uses various examples, including fruit flies and elephants, to illustrate how different barriers contribute to this process. These barriers can be prezygotic, occurring before fertilization, or postzygotic, happening after the egg is fertilized, both effectively preventing gene flow between emerging species.

The video emphasizes geographical isolation as a significant factor in allopatric speciation, where physical borders like mountains or ice can divide populations for long periods, leading to evolutionary divergence. Alternatively, sympatric speciation occurs without physical separation, often through genetic mutations or ecological niches, as seen in certain plants and animals like the African forest elephants.

An exciting aspect of speciation is its variable pace. While it usually occurs over long evolutionary periods, certain conditions can trigger rapid speciation. Polyploidy in plants, where chromosome numbers multiply, is a prime example. Moreover, environmental changes, supporting the punctuated equilibrium model, can hasten this process, leading to quick adaptive shifts within species.

Chapters

• 00:00 - 00:30: Introduction to Reproductive Isolation and Speciation Introduction to the concept of reproductive isolation and its role in speciation, explaining the transition from one species to two by reproductive separation.
• 00:30 - 01:00: Diane Dodd's Experiment with Fruit Flies In Diane Dodd's experiment, two groups of fruit flies were fed different diets: one on starch and the other on maltose. After eight generations, the two groups, which initially interbred, began to ignore each other and would not interbreed, even when placed in the same environment. This behavior demonstrated the creation of reproductive isolation, a crucial step in the speciation process. The experiment is analogous to imagining a group of humans who, due to different diets like eating hamburgers or being vegetarians, eventually stop interbreeding, highlighting how dietary factors can contribute to speciation.
• 01:00 - 01:30: Speciation and Barriers The chapter 'Speciation and Barriers' discusses the process of speciation, which is the formation of new and distinct species in the course of evolution. The transcript explains that speciation starts with a single species, a group of individuals that can interbreed and produce fertile offspring. To form new species, a barrier must be present, which could be geographical (physical separation) or changes within the population itself. These barriers prevent interbreeding between groups, eventually leading to different species. An example given highlights how fruit flies underwent speciation due to such barriers.
• 01:30 - 02:00: Types of Isolation The chapter 'Types of Isolation' delves into the concept of reproductive isolation in biological populations. It introduces the terms pre-zgotic and post-zygotic, where 'zygote' means fertilized egg, to explain barriers that can occur before or after fertilization. These barriers lead to reproductive isolation, which prevents gene flow within a population, eventually contributing to the formation of new species.
• 02:00 - 02:30: Geographic and Temporal Isolation Examples The chapter 'Geographic and Temporal Isolation Examples' discusses the concept of speciation, specifically focusing on isolation mechanisms that lead to the formation of new species. It highlights how speciation can occur rapidly or over extended periods. Geographic isolation is introduced as a key example where a population becomes segregated due to physical separation, preventing interbreeding between groups. The transcript emphasizes understanding these mechanisms using geographic and temporal contexts to explain how species evolve separately.
• 02:30 - 03:00: Mechanical and Behavioral Isolation The chapter 'Mechanical and Behavioral Isolation' introduces the concept of species differentiation based on geographic and non-geographic factors. Two key terms are introduced: allopatric and sympatric speciation. Allopatric speciation refers to species that develop in separate geographic locations ('different lands'), while sympatric speciation occurs when species evolve together in the same geographic area ('same land'). The chapter hints that these basic definitions can be further nuanced, suggesting upcoming examples such as the case of metalarks in North America.
• 03:00 - 03:30: Zygote Mortality and Hybrid Sterility The chapter discusses zygote mortality and hybrid sterility, with a focus on speciation. During the last ice age, ice sheets divided populations, leading to allopatric speciation where species evolve separately due to physical separation. After the ice melted, the populations were reunited but did not interbreed, indicating the formation of new species. Sympatric speciation occurs within a population without physical barriers, as illustrated in plants where changes in chromosome numbers can prevent interbreeding. This phenomenon contributes to biodiversity and demonstrates the mechanisms of speciation.
• 03:30 - 04:00: Great Wall of China Example The chapter discusses the concept of parapatric speciation using the example of elephants. It mentions that there are two major types of elephants, the African and the Indian elephants, which exhibit significant phenotypic differences. The African elephants further include a group known as forest or pygmy elephants, which live in a different area.
• 04:00 - 04:30: Polyploidy and Speciation This chapter discusses the concept of polyploidy and its role in speciation, using the example of different elephant species. It highlights how DNA differences can signify emerging new species, specifically mentioning the forest elephant, which some scientists consider a separate species due to its significant genetic divergence from other types like the African and Indian elephants. The chapter suggests that changes in habitat and exploitation of different areas can contribute to this speciation process.
• 04:30 - 05:00: Speciation Rates and Polyploidy in Animals The chapter discusses the concept of speciation rates and polyploidy in animals, focusing on how different niches, such as living environments and behaviors, contribute to reproductive isolation. It highlights prezygotic barriers, including temporal, mechanical, and behavioral isolation, which occur before a zygote (fertilized egg) is formed.
• 05:00 - 05:30: Punctuated Equilibrium In the chapter titled 'Punctuated Equilibrium,' the focus is on different types of isolation that prevent species from interbreeding in nature. An example given is the American toad and the Fowler's toad, which can produce fertile offspring in a laboratory setting. However, in their natural environment, their breeding periods are temporally isolated: American toads breed in the spring, while Fowler's toads breed in the fall. This temporal isolation serves as a natural barrier to interbreeding despite their coexistence in the same habitats.
• 05:30 - 06:00: Conclusion: Importance of Reproductive Isolation In the conclusion chapter titled 'Importance of Reproductive Isolation', the discussion focuses on the mechanisms of reproductive isolation, specifically temporal and mechanical isolation. Temporal isolation is illustrated with species that breed at different times of the year, preventing interbreeding even if they are capable of producing offspring. An example of mechanical isolation is demonstrated through a study on snails in Japan, where two species look remarkably similar but differ in the direction their shells spiral, preventing mating. These examples highlight the importance of reproductive isolation in maintaining species boundaries.

Speciation Transcription

• 00:00 - 00:30 hi it's Mr Anderson and welcome to biology Essentials video number eight this is on reproductive isolation and speciation in other words how we go from one species to two uh and we do that through reproductive isolation or isolating them reproductively um example of this a really good example of this this is Dian DOD in the 1980s she took a group of fruit flies and she just fed them different things so this group at
• 00:30 - 01:00 ate just starch and these ones ate just maltos and after eight Generations when they were done a group of individuals that originally would interbreed ignored each other in other words the group that had just eaten starch and the group that had eaten malos even though they in the same jar they wouldn't inbreed and so what she had done is she' created reproductive isolation that's the first component you need to create brand new species um it's weird imagine if we had a group of humans where some were eating hamburgers and the other ones were all veget iians and eventually they just
• 01:00 - 01:30 wouldn't need breed anymore um that's probably not going to happen but in fruit flies it did and so this is what I'm going to talk about uh we have to start with a group one species so this is a group of individuals that can interbreed and produce fertile offspring and we're eventually going to end up with two species or that process is called speciation so what's the first thing that we have to do we have to create a barrier and so that barrier could be physical so it could be Geographic barrier in other words one group or one population is isolated and we could also have changes just within
• 01:30 - 02:00 that population we'll talk about that in a second but it also those could be pre and post zygotic and this word zygo means fertilized egg and so it could be something before this before the egg is fertilized or after it's fertilized but these barriers eventually create reproductive isolation what does that do we had one species that can't have gene flow in other words you've eliminated gene flow so the genes aren't being mixed within that population and that eventually can create species that have
• 02:00 - 02:30 the inability to breed um sometimes that speciation happens really fast an example would be like in poly Ploy and in Plants uh and sometimes it can happen over millions and millions of years um but we know this once we have speciation we've created one group uh that can interbreed with the other um and so let's talk about how that might actually occur um first of all let me talk about geographic isolation geographic isolation is when there is an isolation in the population due to where they
• 02:30 - 03:00 exist so example I'll talk about in a second uh well first of all let me Define these up here mainly you hear these two terms allopatric and S Patric speciation allopatric Patrick means Homeland and so uh allopatric is when you have two groups that are are that have different different lands or or they live in different lands uh Sy Patrick is when they live in the same land uh but we can kind of tweak that and I'll talk about that in just a second example metalark so we had metal archs inth North America but during the
• 03:00 - 03:30 last ice age as ice moved down through the middle of the continent it broke those metars into two populations we call that allopatric speciation now the ice has melted they're back again and they're not interbreeding generally in that middle hybrid area and so that' be brand new species sympatric speciation occurs when you have something just within that population example in in in plants you can have a mistake in the number of chromosomes that they have so they can't interbreed anymore it's actually really really common I'll talk about in just a second that's s Patrick
• 03:30 - 04:00 we in the same land but we can also have a gradient parapatric parap Patrick uh let me give you an example of that um when I was growing up I thought there were just two different types of of elephants and and there really are there's the African elephant and the Indian elephant there's some huge differences phenotypically when you look at them so this would be the typical this is a big male uh Savannah African elephant but what you may not know is that there's a group of forest elephants sometimes they're referred to as the pygmy elephants that live in a different area
• 04:00 - 04:30 and if we compare the DNA of these two the forest uh elephant is uh some scientists consider it a subspecies and some might even say it's a it's a separate species itself in other words its DNA is 2/3 the difference between an African elephant and an Indian Elephant and so they may be well on their way to uh forming a brand new species how did they do that it's probably one population or one group where they moved into a different area they're exploiting
• 04:30 - 05:00 a different Niche they live in the forest and so then there's reproductive isolation within that so where you live can create isolation what you do can also create isolation as well and so these are all prezygotic barriers and so a zygote is a egg that's fertilized by a sperm so a fertilized egg is referred to as a zygo and so these three types of isolation temporal uh mechanical and behavior are all things that occur before the zy is actually formed so the
• 05:00 - 05:30 first type of of isolation is called temporal uh this right here is an American toad and this is a Fowler's toad if you put them in the lab and let them mix they'll inter breed um you can get them to produce fertile offspring that will that will survive unfortunately or that's just the way it is in nature they may live in the same area but the American toads generally will breed in the springtime and the Fowler's toads will breed in the fall and so that's a temporal and the way I always remember temporal is the word
• 05:30 - 06:00 time they breed at different times of the year and so even though they could produce for L ring they don't uh because of the timing example of mechanical isolation this is a study that was done on in uh snails in Japan you can see species that live right next to each other so this one right here looks almost exactly like this snail right here you'd think same species but if you look look a little bit more carefully you'll find that this one right here it spirals in One Direction so we could call that left-handed and this one is going to spir F in the other direction
• 06:00 - 06:30 so we call that right-handed and so even though these are very similar their DNA is almost identical and they're very uh closely related they don't interbreed because their sex Parts can't get next to each other so that's mechanical isolation you couldn't even transfer the sperm to the egg because they're isolated mechanically and lastly we could have behavioral isolation so I talked about these these are two types of metal arcs the Western and the Eastern metalarc they were separated during the last ice age where ice started to come down through the middle of North America so we now we had the
• 06:30 - 07:00 Western Metal Arch which is our state bird in Montana Eastern metal Arch and so now that we've eliminated that isolation and they live in this hybrid zone They Don't inter breed and the reason why is that they attract mates through their songs and a lot of birds do that and so the males are able to attract a mate by singing a song and the more songs that they can sing the more likely they are to attract a mate but during this period of time those songs have separated and so now we have um a behavior avior that's different and so
• 07:00 - 07:30 there's no uh sperm meeting egg it's a prezygotic barrier sometimes we'll actually have organisms living in the same area and the sperm and the Egg will get together but that zygote may die and so in reefs what we'll find is that sperm is transferred from one Coral to another it'll fertilize the egg making a zygote but that zygote immediately dies and so that's an example of zygote mortality sometimes you'll you'll have different species living in the same area so for example horses and donkeys you can actually uh fertilize the egg
• 07:30 - 08:00 you can create a brand new Offspring that's called a mule but it's sterile so it can't produce more offspring and so these are all postzygotic barriers they're in the same area they are able to fertilize the egg but The Offspring are sterile and so it's not able to move any farther than that and so what does that produce well that produce eventually um a reduction in the gene flow and so if you ever have reproductive isolation the genes can't flow from one area to another a great
• 08:00 - 08:30 study was done on the the Great China Wall so the this wall was built you have plants on either side um but some plants are being impacted by that just that production of the the wall and so alus pomila is a type of plant that's grown on either type either side of the wall but it is fertilized by wind in other words uh pollen must be transferred by the wind and that wall serves as a block to that wind and so what's happening is
• 08:30 - 09:00 you're creating populations on either side that are reproductive reproductively isolated in other words we're seeing a decrease in the DNA decrease in the genetic variability now there are other plants that live on either side of the wall that aren't uh pollinated by wind they're actually pollinated by insects and insects have no problem getting over the wall and so we're seeing that there's actually genetic diversity that's uh that's remaining there and so reproductive isolation cons essentially break your species down into two
• 09:00 - 09:30 different uh populations that can't inter breed eventually you can create brand new species through that now the speciation rate is going to vary in other words how fast this occurs uh it can happen very quickly or it can happen slowly over time so polyi is an example of very fast speciation and so essentially what you have is a mistake in the uh chromosome number so we're going from a a diploid organism to a tetraploid organism uh but it can even get crazier than that now what
• 09:30 - 10:00 eventually happens eventually this organism can't interbreed with the normally diploid organism and so you eventually have brand new species forming now we find in Plants that's incredibly common something like 30% of brand new Fern species form through this mistake and 15% of angiosperms which is all the plants that you're looking at came to be through a polyploidy or a mistake in the chromosomes wheat for example has been formed through multiple polyploid uh events it's rare in in uh
• 10:00 - 10:30 animals that you can have this this is an example of a the Vish vaka rat um hopefully I'm pronouncing that right was formed through polyploid in general if you have uh any kind of mistake in the chromosome numbers in animals they die and the reason why is that you get a duplication of the sex chromosomes and so what we think happened in this rat is they actually um shed that extra x uh XY chromosome or those sex chromosomes and they're able to reproduce
• 10:30 - 11:00 uh as a as a tetrol animal um now if we put that aside there's been a debate going on over um the actual rate of speciation and so this is the the philogenetic tree that was drawn by uh Darwin or it's the the belief that through time so if we put T in this direction speciation occurs gradually over time now there's been a tweak to that it's just a different form of gradualism called punctuated equilibrium uh it's most famous proponent is this
• 11:00 - 11:30 man Steph J Gould who is an incredible writer if you're interested in evolution you could read uh Panda thumb is a great place to start but his idea is that it doesn't occur gradually over time it actually occurs very quickly in other words there's some kind of a change in the environment which forces speciation to occur and that would account for why we don't see a lot of these transitional fossils and also when we actually study evolution in the lab we're finding that it can occur very very quickly um and so that's just another idea on how how fast speciation can occur um and that's kind
• 11:30 - 12:00 of Up For Debate now but what do we do know about uh speciation is it starts with uh reproductive isolation so I hope that's helpful