Adaptation and Speciation in Biology: Forms and Mechanisms Explained

1. Adaptation and Speciation SBI 3U

2. Adaptation • Any trait that increases an organism’s chance of survival and probability of successful reproduction • A product of natural selection • Organisms become adapted to their environment over a period of time through natural selection • Variations within a species are the raw material upon which natural selection acts

3. Types of Adaptations • 1. Structural Adaptation - physical features on an organism • Anatomical - shape and arrangement of features • Ex. Teeth in carnivores, vascular tissue in plants • Mimicry • Enables one species to resemble another species or part of another species • Ex. Fly that resembles a yellow-jacket wasp • Cryptic Colouration • Makes potential prey difficult to spot • Ex. Camouflage

4. (b) Green parrot snake (a) Hawkmoth larva Mimicry • A palatable • or harmless • species • mimics an unpalatable • or harmful • model

5. Cryptic Colouration

6. Types of Adaptations cont… • 2. Physiological Adaptations • Associated with functions in organisms • Ex. Enzymes for blood clotting • Ex. Proteins in spiders’ silk • Ex. Chemical defense in plants • Ex. Ability of bacteria to withstand heat

7. Types of Adaptations cont… • 3. Behavioural Adaptations • How organisms respond to their environment • Ex. Migration • Ex. Courtship displays • Ex. Foraging behaviour • Ex. Response of plants to light

8. How Species Form • Scientist must consider the following when distinguishing one species from another: • Physiology • Biochemistry • Behaviour • Genetics

9. Biological Species • Most common definition of species: • - a species consists of a reproductively compatible population • - a population that can interbreed and produce viable and fertile offspring Note: Not always possible to apply this definition

10. Forming New Species • Speciation • formation of a new species from an existing species • Macroevolution

11. Two general pathways: • Transformation - results from accumulated changes over long periods of time such that one species is transformed into another - also called Phyletic Speciation

13. 2. Divergent Speciation • One or more species arise from a parent species that continues to exist • Promotes biological diversity • increases number of species

15. *Support for both concepts suggests that a compromise or a combination of the two models works to produce new species

16. Barriers to Reproduction • Geographical Barriers • Keeps populations physically separated • Ex. Rivers • Biological Barriers • Keeps species reproductively isolated when their habitats overlap

17. Biological Barriers • Pre-zygotic Barriers - prevent mating or fertilization • Post-zygotic Barriers - prevent hybrid zygote from developing into a healthy fertile adult

18. Prezygotic Barriers • 1. Habitat Isolation • 2. Behavioural Isolation • 3. Temporal Isolation • 4. Mechanical Isolation • 5. Gametic Isolation

19. Habitat Isolation • Populations live in different habitats or ecological niches. • Ex – mountains vs lowlands.

20. Behavioral Isolation • Mating or courtship behaviors different. • Different sexual attractions operating. • Ex – songs and dances in birds.

21. Temporal Isolation • Breeding seasons or time of day different. • Ex – flowers open in morning or evening.

22. Mechanical Isolation • Structural differences that prevent gamete transfer. • Ex – anthers not positioned to put pollen on a bee, but will put pollen on a bird.

23. Gametic Isolation • Gametes fail to attract each other and fuse. • Ex – chemical markers on egg and sperm fail to match. • Separates certain closely related species of aquatic snails

24. Post-Zygotic Barriers • 1. Hybrid Inviability • Hybrid offspring are unlikely to live long • Ex. Hybrid from sheep and goat die in early development • 2. Hybrid Sterility • Offspring of genetically dissimilar parents are likely to be strong but sterile • Ex. Horse + Donkey = Mule

25. 3. Hybrid Breakdown • First generation of hybrids are viable and fertile • When hybrids mate the offspring of the next generation are sterile or weak • Ex. Cotton

26. Types of Speciation • I. Allopatric Speciation - When a population is split into two or more isolated groups by a geographical barrier - Sometimes called geographical speciation - Eventually the groups will become so distinct that interbreeding will be impossible - Isolation does not need to be indefinite, but it does need to be long enough for population to become reproductively incompatible Ex. Glacier, lava flow, ocean levels

28. Adaptive Radiation • This is a form of allopatric speciation where a common ancestral species diversifies into a variety of differently adapted species • Ex. Darwin’s Finches

29. Darwin’s Finches

30. II. Sympatric Speciation -When populations live in the same geographical area become reproductively isolated -More common in plants than animals -Speciation can occur in 1 generation if genetic change results from parent to offspring Ex. Extra chromosome (called polyploidy) usually in plants which can self pollinate

32. Convergent vs. Divergent Evolution • Divergent Evolution - a pattern of evolution in which species that were once similar to an ancestral species diverge, or become increasingly distinct (finches) • Convergent Evolution - similar traits arise because each species has independently adapted to similar environmental conditions, not because they share a common ancestor (ex. birds and bats)

33. The Pace of Evolution - 2 Hypotheses • Gradualism • Changes occur slowly and steadily before and after a divergence • Big changes = accumulation of many small changes • Fossil record doesn’t support this hypothesis well • Fossil record shows species appearing suddenly

34. Punctuated Equilibrium (Gould and Eldredge – 1972) • History consist of long periods stasis (no change) interrupted by periods of divergence • Most species undergo major change when they first diverge from parent species • Fossil records support this theory