IB Biology Option D D2 Species and Speciation All syllabus statements ©IBO 2007 All images CC or public domain or link to original material. Ms. Fargo Jason de Nys IB Biology Option D D2 Species and Speciation All syllabus statements ©IBO 2007 All images CC or public domain or link to original material. Ms. Fargo Jason de Nys “…if I really have as bad an expression, as my photograph gives me, how I can have one single friend is surprising."

D.2.1 Define allele frequency and gene pool al·lele fre·quen·cy Allele frequency is the proportion of all copies of a gene that is made up of a particular gene variant (allele). gene pool Noun: The total collection of different alleles in an interbreeding population. Example Say if a recessive allele h made up 2% of the total in a human population… …then the dominant allele H would make up 98%. The frequency for h would be expressed as 0.02 and for H 0.98 Recessive allele frequency + dominant allele frequency = 1 (for characteristics determined by two alleles)

D.2.2 State that evolution involves a change in allele frequency in a population’s gene pool over a number of generations New combinations of alleles lead to new phenotypes that can then be selected for or against by the environment. This leads to evolutionary change in the species

D.2.3 Discuss the definition of the term species What is a species?

D.2.3 Discuss the definition of the term species Ecological species A set of organisms adapted to a particular set of resources, called a niche, in the environment. Genetic species Based on similarity of DNA of individuals or populations. Having a common gene pool. Cladistic Species A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species. (This differs from the Evolutionary definition in that the parent species goes extinct when two new species are recognised). Evolutionary species A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, some members may diverge from the main population and evolve into a subspecies. Breeding Species Two organisms that are able to reproduce naturally to produce fertile offspring of both sexes. There are many definitions, here are five! Lots to discuss if you get a question about this!

The genetic definition is most widely used and works well for most multicellular organisms The following 4 slides outline the exceptions: …is anything ever simple in Biology?

It could be (ahem) physically impossible for members of the same species to mate. Therefore they are genetically isolated. Hors d’oeuvre?

1 : Lesser Black-backed Gull 2 : Siberian population Black-backed gull 3 : Heuglin's gull 4 : Birula's Gull 5 : East Siberian Herring Gull 6 : American Herring Gull 7 : Herring Gull 1 and 7 cannot produce offspring. Ring Species: Adjacent populations can interbreed but the populations at the “end of the line” cannot. So close… …and yet so far :’(

The liger is a hybrid cross between a male Panthera leo (lion), and a female Panthera tigris (tiger) and is denoted scientifically as: Panthera tigris × Panthera leo. The tiglon is a hybrid cross between a female Panthera leo (lion), and a male Panthera tigris (tiger) and is denoted scientifically as: Panthera leo × Panthera tigris. …conversely… Ligers and tiglons sometimes produce offspring when mated back with a parent species e.g. The hybrid of a male lion and a female tiglon is a li-tiglon! MADNESS!! Hybrids are usually infertile and can not produce offspring together, for example the mule (63 chromosomes): a cross between a Male horse (64 chromosomes) and a female donkey (62 chromosomes) Why are 63 chromosomes a problem when reproducing?

The genetic definition only applies to sexually reproducing organisms and doesn’t apply to single-celled organisms Rats!

Additionally: Fossil remains can’t tell us whether species were able to interbreed or produce viable offspring so palaeontologists tend to use the cladistic definition ?

D.2.4 Describe three examples of barriers between gene pools The circumstances preventing different species from interbreeding are known as reproductive isolating mechanisms

Temporal isolation JFMAMJJASOND MAX Pinus radiata (Monterey Pine) Pinus attenuata (Knobcone pine) Pollen Production Pinus radiata and Pinus attenuata are prevented from hybridising because they have separate pollination times. They can be made to hybridise by pollinating them manually. *Random fact: The Monterey pine is at risk in it’s native range but is one of the most common plantation trees in the world. If you see a pine forest in Australia or NZ, it is probably Pinus radiata Month

Ecological isolation The two species are in the same area, but live in different habitats I love me some CaCO 3 in my soil Blechhh! Acidic soils are more my thing Viola arvensisViola tricolor

Behavioural isolation Animals exhibit courting behaviour (song, dance etc.) or release pheremones to attract mates. Individuals are only attracted to, and will only mate with, members of the opposite sex who perform the appropriate ritual or release the correct chemical. Yo! I don’t like your music! Its like, totally mutual!

Mechanical isolation Animal example: Different species of bush baby (Galago) have particular shapes for their genitalia and they are physically incapable of copulation*. It is like a lock and key. In plants, mechanical isolation occurs when different species have different pollinators that are not able to service the flowers of other species *Take care when Googling “Bush baby genitalia”! She says “We’re not a good fit”. What is that supposed to mean?

Hybrid Inviability Remember: Male Horse + Female Donkey = Mule Horse 2n = 64 ∴ spermn = 32 Donkey 2n = 62 ∴ ovum n = 31 Sperm + Ovum = Mule zygote = 63 Mule 2n = 63 ∴ gamete n = ? Note: Sad eyes

D.2.5 Explain how polyploidy can contribute to speciation So far you’ve learnt that cells contain two homologous sets of chromosomes. Well….. that isn’t always the case. It goes on: Pentaploid Hexaploid Septaploid Octaploid Etc. up to: 84-ploid and 1260 chromosomes Ophioglossum reticulatum A small fern. The incredible thing is that this plant is able to carry out meiosis accurately with 1260 chromosomes to divvy up

How it happens: Remember: When non-disjunction occurs during meiosis in humans, an individual can end up with an extra chromosome or missing chromosomes. E.g. An extra chromosome 21 means Downs syndrome (see 4.2.4) Total non-disjunction, is when one of the two cells produced during Meiosis I gets all of the chromosomes. The other cell is not viable and is reabsorbed. This results in two (2n) daughter cells from meiosis instead of the usual four (n) daughter cells.  See animation Self fertilisation

Few polyploid organisms exist in the animal kingdom. Can you think of the reasons why not? Animal polyploid species include salamanders, goldfish and salmon. Polyploidy often leads to increased size, resistance to disease and overall vigour. Many plants used by humans are polyploid. Including cereal crops like wheat. Polyploid crops generally have bigger fruits, seeds and storage organs However, polyploidy is a great source of speciation amongst plants.

Two versions of Polyploidy: Autopolyploidy* Allopolyploidy *This is not autopolyploidy

Autopolyploidy (Auto = “self”) Autopolyploids are polyploids with multiple chromosome sets derived from a single species as described a couple of slides ago. Autopolyploids form following fusion of 2n gametes Autopolyploidy can be induced in plants using colchicine, a chemical extracted from the autumn crocus. Autopolyploids with odd ploidys eg triploid or pentaploid have trouble reproducing sexually WHY? That does not stop them from being good crops if they can be propagated asexually

Allopolyploidy (Allo = “different”) Allopolyploids come about when a sterile F 1 hybrid doubles all of its chromosomes and becomes fertile. For example, Triticale is the hybrid of wheat (Triticum turgidum) and rye (Secale cereale). It combines sought- after characteristics of the parents, but the initial hybrids were sterile until doubling of the number of chromosomes occurred Remember the poor sterile mule with 63 chromosomes? Imagine if we could somehow induce sperm and ova with 126 chromosomes Voila! The mule born would be fertile. Of course, it would need to be done a couple of times to get a few mules to breed together += Wheat Rye Triticale

D.2.6 Compare allopatric and sympatric speciation Allopatric speciation (Allo = “different”, patric = “fatherland”) This arises when a species is subject to geographic isolation. This can occur when a population is split by: A river A mountain range A desert A road The sea etc. Gene flow is cut off between the two split populations and they can evolve in different directions (See animations below) Remember Darwin’s finches?

Once the populations have been separated into two gene pools they can diverge through natural selection or through random genetic drift

Allopatric speciation of Drosophila in the lab Even when the “geographic barrier” is removed, the populations are still genetically isolated

Sympatric speciation (Sym = “same”, patric = “fatherland”) The formation of two or more descendant species from a single ancestral species all occupying the same geographic location. Whether it actually happens is still contested. Find a pair of species that are thought to have diverged by sympatric speciation

Diagrammatic comparison

D.2.7 Outline the process of adaptive radiation Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits with which they can exploit a range of divergent environments. Wikipedia Think Darwin’s finches (AGAIN!) They originated from a population of an ancestral species that flew or were blown to the Galapagos islands from mainland South America. They colonised the islands and (while geographically isolated) evolved via natural selection to have beaks that suited the types of food available on their islands. Their beaks are homologous structures in that they have evolved from a common structure to have different functions.