The Diversity of Species Speciation A single species

The Diversity of Species

Speciation • A single species can diverge to produce several new species • Ancestral South American tortoise split to produce the giant Galapagos Island tortoise • Speciation is a key par of theory of evolution

Speciation • 3 broad processes that work together: – Natural selection - better adapted to environment. – Population changes over time as genes accumulate small changes in response to natural selection - microevolution – Accumulation of so many changes – new species formation and multiplication of species – Rapid series of speciation can lead to development of whole new collection of species, genera, families or higher classification groups - macroevolution

Extinction • Another important process in evolution that helps us to identify current species via the fossil record • Vast disappearance of species over time allows new species to evolve

The Biological Species Concept • The biological species model defines a species as a reproductively isolated group of organisms. • These organisms can be identified through consistent differences in morphological and physiological traits as well as genetic differences

Mechanisms of Speciation • Isolating mechanisms – – Pre-reproductive isolating mechanisms Post reproductive isolating mechanisms Allopatric speciation Sympatric speciation • Separation of groups, preventing them from producing fertile, viable offspring • Can occur before or after reproduction • After isolation, different phenotypes can occur

Pre-reproductive isolating mechanisms

Pre-reproductive isolating mechanisms • Summarise the following types of isolating mechanisms: – Geographic – Temporal (time) – Behavioural – Morphological

Post-reproductive isolating mechanisms • �two frogs from different species will be unab mate and produce fertile offspring • Chromosomes in gametes do not line up successfully at meiosis, so no zygotes formed • This is an example of post-reproductive isolation. Reproduction can occur, however no viable offspring produced

Post-reproductive isolating mechanisms • Summarise three types of postreproductive isolating mechanisms • Explain why hybrid sterility is not a barrier in plants as it is in animals.

Allopatric Speciation • Allopatric speciation is when new species arise due to isolation of a population by geographical barriers. • Features such as rivers or mountain ranges isolate populations of animals and plants. • Movement of land-masses by continental drift led to geographical isolation millions of years ago.

Sympatric Speciation • Sympatric speciation is when new species arise despite occupying the same geographical area. • Ecological barriers - although groups are not geographically isolated from each other they may be isolated by occupying different habitats or breeding areas, p. H and salinity. • Behavioural barriers – a population may carry out complex mating rituals that may create a barrier to reproduction. • Different timings, locations or mating dances may result in members of a population, who are not geographically separated, not being able to mate with each other.

Questions • Complete questions on page 200 of your textbook. • Make sure that you answer questions thoroughly and make notes on anything that you’re not sure about.

Useful slides • The following slides are from another source – I have added them in for some extra notes if you want to read them.

Isolating Mechanisms • Since members of the same species share a common gene pool, in order for a species to evolve into 2 new species, the gene pools must be separated into 2 • As new species evolve, populations become reproductively isolated from each other

Reproductive isolation • When the members of 2 populations cannot interbreed and produce fertile offspring

Behavioral Isolation • When two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies

Eastern & Western Meadowlark

Geographical Isolation • When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water

Albert & Kaibab Squirrels

Temporal Isolation • When 2 or more species reproduce at different times Rana aurora - breeds January March Rana boylii - breeds late March - May

Testing Natural Selection in Nature Q: Can evolution be observed in nature? A: YES

The Grants

Testing Natural Selection in Nature • Darwin hypothesized that finches had descended from a common ancestor and overtime, natural selection shaped the beaks of different bird populations as they adapted to eat different foods • The Grants, realized that Darwin’s hypothesis relied on two testable assumptions

1. There must be enough heritable variation in these traits to provide raw materials for natural selection 2. Differences in beak size and shape must produce differences in fitness that cause natural selection to occur

Variation • The Grants identified and measured every variable characteristic of the birds on the island • Their data indicated that there is a great variation of heritable traits among the Galapagos finches

Natural Selection • During the… • Rainy season – enough food for everyone, no competition • Dry season – some foods become scarce • At that time, differences in beak sizes can mean the difference between life and death • Birds become feeding specialists

Natural Selection • The Grants discovered that individual birds with different size beaks had different chances of survival during a drought

Speciation in Darwin’s Finches • Speciation in the Galapagos finches occurred by founding of a new population, geographical isolation, changes in the new population’s gene pool, reproductive isolation and ecological competition

Founders Arrive • Many years ago, a few finches from South American mainland • Species A, flew or were blown to one of the Galapagos Islands

Geographic Isolation • Later on, some birds from species A crossed to another island in the Galapagos group • The finches then became unable to fly from island to island become isolated from each other and no longer share a common gene pool

Changes in the Gene Pool • Overtime, populations on each island became adapted to their local environments

Reproductive Isolation • Now imagine that a few birds from the second island cross back to the first island • Q: Will the population A birds, breed with the population B birds? • A: Probably not

Ecological Competition • As these two new species live together in the same environment, they compete with each other for available seeds • The more different birds are, the higher fitness they have, due to less compitition

Continued Evolution • This process of isolation on different islands, genetic change, and reproductive isolation probably repeated itself time and time again across the entire Galapagos island chain • Over many generations, it produced the 13 different finch species found there today

Studying Evolution Since Darwin • It is useful to review and critique the strength and weakness of evolutionary theory • Darwin made bold assumptions about heritable variation, the age of the Earth, and the relationships among organisms • New data from genetics, physics, and biochemistry could have proved him wrong on many counts, and they did not • Scientific evidence supports theory that living species descended with modification from common ancestors that lived in the past

Limitations of Research • The Grants data shows how competition and climate change affects natural selection • However, they did not observe the formation of a new species

Unanswered Questions • Many new discoveries have led to new hypotheses that refine and expand Darwin’s original ideas • No scientist suggests that all evolutionary processes are fully understood. Many unanswered questions remain

Why Understanding Evolution is Important? • Evolution continues today Ex. ) • Drug resistance in bacteria and viruses • Pesticide resistance in insects • Evolutionary theory helps us understand respond to these changes in ways that improve human life