SPECIES and EVOLUTION

1. SPECIES andEVOLUTION

2. Understanding biodiversity Naming organisms • Carolus Linnaeus (18th century) founded the classification system we use today • Linnaeus gave two Latin names to every organism – a genus name and a species name • Genus is a group of similar species • Two examples: Homo sapiens (human) Zea mays (maize)

3. What is a species? • Species is a group of closely related organisms that are all potentially capable of interbreeding to produce fertile offspring How does one decide which organisms belong in the same species? • Look at the morphology and note differences and similarities of organisms. This can be very easy with some organisms but difficult with others • Molecular phylogeny is a new science that shows differences in DNA, RNA and proteins

4. LIGER lion - tiger OPAKI zebra-giraffe Reproductive definition of species • Species can be defined in terms of gene flow between individuals • When two individuals from different populations mate and produce fertile offspring they belong to the same species • In this case, genes flow from parents to children • Some cases are not so clear. A lion can mate with a tiger and produce fertile offspring • Other cases are clearer. A donkey can mate with a horse but any offspring produced (mule) is always sterile MULE

5. Ecology and adaptation • Ecology is the study of the relation of living organisms with each other and their surroundings • Each species exists in a particular ecological niche. This describes the role (position or function) of an organism in a community of plants and animals. • Niche is a very informative term. It defines how an organism feeds where it lives and how it interacts with other organisms

6. Useful terms • Ecosystem: it is an environment that includes all living organisms interacting together, nutrients cycling through the system and the physical and chemical environment in which organisms live. • Habitat: It is the place where an organism lives, such as, a pond, a tree etc. • Community: all the populations of living organisms living in a habitat at any one time • Population: a group of organisms of the same species living and breeding in a particular niche in a habitat i.e. the skin mites in your mattress.

7. Adaptation to niches Successful species adapt well to their niches meaning that individuals have good chances of survival and reproduction • Anatomical adaptations: such the thick layer of blubber in whales • Physiological adaptations: differences in the way the body works, for example, diving animals can stay longer under water • Behavioural adaptations: as in migration of birds to avoid harsh conditions

8. Evolution Natural selection leads to adaptations which give organisms advantages in a particular niche (Normandy and Greenland cormorants-behavioural change) • If conditions change, these adaptations may not be useful any more and selection pressure changes • This can cause change in the species, that is, evolution. • Natural selection often acts on the level of genes.

9. Mutations and natural selection • Mutations cause small changes in genes and produce variations. Natural selection acts on these variations • Mutations increase the size of the gene pool. The relative frequency of each gene in a pool can be calculated and this shows the extend of biodiversity. Alleles are affected by natural selection • A mutation can produce change in the phenotype, in the physiology or the pattern of behaviour of an organism.

10. Advantageous/Disadvantageous changes • When changes are advantageous, the organism is more likely to survive and reproduce. The frequency of these genes will increase • If the change is disadvantageous, natural selection will act to remove the genes • Sometimes the mutation is neutral and the genes will remain in the gene pool. • Story of warfarin (prevents blood from clotting) and rats!

11. Effect of small populations • Large populations have large gene pool • Advantageous genes can easily be lost from small populations. If the gene for running fast in a population of 10 animals is carried by only 1 animal (10% frequency) and this animal breaks a leg and a predator kills it, the advantageous gene will be lost • In a population of 5000, 500 animals will carry the gene and it cannot be lost easily. • Thus, large, genetically diverse populations are needed to maintain biodiversity.

12. Founder effect • Sometimes a small number of individuals leave the population and set up a new population • Genetic diversity can be lost as a result of this. The alleles they carry will probably be in different frequencies than the original population • Unusual genes in the founder members of the new population may become amplified as the population grows. This is the founder effect. Example:Ellis-van Creveld syndrome in the Amish of America. A rare genetic disorder.

13. Ellis-van Creveld Syndrome A 5 year old sufferer: Notice the long narrow chest and shortness of the limbs

15. Evolution in action: Production of a new species • Natural selection removes individuals who are not well adapted to survive. If the environment changes, the niche changes too • Other characteristics may make an individual more successful. • Natural selection will now favour those individuals with the different characteristics. • Thus, the selection pressure has changed and changes (evolution) will be seen within a species. The new individuals may become a new species.

16. Malpeque Bay (Canada) oysters • For many years Canadian fishermen caught oysters in Malpeque Bay • In 1915 a disease wiped out most of the oysters • Some carried an allele that made them resistant to the disease. These very few oysters survived • By 1935 Malpeque Bay was full of oysters again but with a different gene pool

17. Types of selection 1. Directional selection: It occurs where there is environmental pressure on the population. • The Malpeque Bay oysters is an example of directional selection. • It is also observed with insects and plants which are sprayed with herbicides and insecticides. After an initial elimination of many individuals, resistant individuals appear. • The rabbit disease myxomatosis was introduced in Britain in 1953 to control the number of wild rabbits. Initially almost all the rabbits were wiped out but 10 years later their numbers increased again. • Directional Selection causes shifts toward a particular trait that is one of the extreme ends of the trait.

18. Types of selection 2. Diversifying or disruptive selection: Here, the outcome is an increase in the diversity of a population. It occurs when conditions are very diverse and small subpopulations evolve different phenotypes suited to their very particular surroundings. The case of the long horned beetles illustrates well this type of selection

19. Types of selection 3. Balancing selection: In this case, an allele is kept within a population even though it might seem to be disadvantageous. An example of this is the thalassaemia allele that affects human haemoglobin. In its heterozygous form it gives protection against malaria. This is known as heterozygote advantage or hybrid vigour.

21. More on population genetics • Directional selection is a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction. Under directional selection, the advantageous allele increases in frequency independently of its dominance relative to other alleles; that is, even if the advantageous allele is recessive, it will eventually become fixed. • Directional selection occurs most often under environmental changes and when populations migrate to new areas with different environmental pressures. An example of directional selection is fossil records that show that the size of the black bears in Europe decreased during interglacial periods of the ice ages, but increased during each glacial period. Another example is the beak size in a population of finches. Throughout the wet years, small seeds were more common and there was such a large supply of the small seeds that the finches rarely ate large seeds. During the dry years, none of the seeds were in great abundance, but the birds usually ate more large seeds. The change in diet of the finches affected the depth of the birds’ beaks in the future generations.Their beaks range from large and tough to small and smooth.

22. Stabilizingselection is a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. This thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time. Stabilizing selection commonly uses negative selection (a.k.a. purifying selection) to select against extreme values of the character. • Stabilizing selection is the opposite of disruptive selection. Instead of favoring individuals with extreme phenotypes, it favors the intermediate variants. It reduces phenotypic variation and maintains the status quo. Natural selection tends to remove the more severe phenotypes, resulting in the reproductive success of the norm or average phenotypes. • A classic example of this is human birth weight. Babies of low weight lose heat more quickly and get ill from infectious disease more easily, whereas babies of large body weight are more difficult to deliver through the pelvis. Infants of a more medium weight survive much more often. For the larger or smaller babies, the baby mortality rate is much higher. • Because most traits change little over time, stabilizing selection is thought to be the most common type of selection in most populations. However, a meta-analysis of studies that measured selection in the wild found that stabilizing selection and disruptive selection were equally common.  • Methods for detecting stabilizing selection are complex. In general, detecting stabilizing selection requires measuring the fitness of the range of different phenotypes under natural conditions and comparing examining the relationship between these fitness measurements and the trait value.

23. Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups. • This evolutionary process is believed to be one of the main driving forces behind sympatric speciation.

24. GALAPAGOS ISLANDS

25. DARWIN’S JOURNEY

26. When one species evolves into more than one other species • Darwin finches provide the classic example where different niches produce different selection pressures and result in the evolution of several species. • The original finches that arrived on the Galapagos islands were of a single species but because the finches occupied different niches and were exposed to different pressures (i.e. finding food) gradually new species (14) evolved.

28. Evolution in action • The original finches that arrived possessed a variation in alleles and characteristics • Different niches on the islands favoured birds with different characteristics • A bird with a slightly smaller and stronger beak would feed on seeds and these birds would do very well in an area which had seeds. Over many generations, natural selection removed all individuals with different beaks and now all finches in this area have beaks adapted for eating seeds.

29. Evolution in action • A finch with a longer, thinner beak may be more adapted to finding and eating worms. • Thus, different variations of finches occupied different niches and avoided competing for the same food • Because of this, 14 different species of finches evolved on the Galapagos islands over seven million years, from the same ancestor. • DNA analysis has shown that all the species are remarkably similar!

30. Sexual selection • Selection of features that give reproductive success is known as sexual selection • In many animals there are clear anatomical adaptations to help in attracting a mate, such as: • The tail of the peacock • The mane of a lion • The antlers of a stag

31. Isolating mechanisms • How do different species evolve from one original species? • Normally, a population of the species has to become isolated so that mating and thus gene flow between members of different populations will not be possible • This can happen in a number of ways

32. Geographical isolation: a physical barrier (river, mountain) separates individuals from the original population • Ecological isolation: two populations inhabit the same region but develop preferences for different parts of the habitat • Seasonal isolation: the timing of sexual receptiveness of some members of a population changes from the norm of the group • Behavioural isolation: changes occur in the courtship ritual and some animals do not recognise others s potential mates. • Mechanical isolation: due to a mutation the genitalia can change and animals can only made with only some animals of the group

33. Speciation Speciation refers to the appearance of a new species. • Allopatric speciation: this happens when populations are physically separated • Sympatric speciation: this happens when two populations are geographically still close to each other

34. Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area. This can bring about sympatric speciation

35. Isolated islands (Cyprus?) They contain species found nowhere else. How did the new species appear? • The availability of niches • The different selection pressures in the new niches • The founder effect of limited gene pool All the above combine to form a new species. This is endemism.

36. Examples of endemism • Madagascar provides a good example. There are many endemic species there • Hawaii also is a good example. These islands are very isolated and many endemic species are found there • Australian marsupials and monotremes are very good examples of endemic species. Australia was joined to the rest of the world till 5.5 million years ago. At that time there were only marsupials and monotremes mammals. • When Australia separated there were only these mammals present. Placental mammals evolved everywhere else but only came to Australia when they were introduced by settlers

37. Vulnerable resource? • Isolated islands have endemic plants and animals • Island ecosystems are rather small and they are very vulnerable to human interference and damage. • 75% of all animals extinct over the last 400 years are island species