Speciation The Evolution of new Species

Speciation The formation of new species from existing species Macroevolution Species = population/group in nature whose individual members can interbreed to produce viable, fertile offspring When some members of a sexually reproducing population change so much that they are no longer able to produce viable, fertile offspring with members of the original population, speciation has occurred.

Speciation

REPRODUCTIVE BARRIERS mechanismimpedes fertile and/or viable hybrid offspringAny mechanism that impedes two species from producing fertile and/or viable hybrid offspring. Two barriers:Two barriers: 1.Pre-zygotic barriers 2.Post-zygotic barriers

Pre-fertilization barriers Impede mating between species or prevent fertilization of the eggs 5 types of isolating mechanisms –Behavioural –Habitat –Temporal –Mechanical –Gemetic 1.PRE-ZYGOTIC BARRIERS

Behavioural Isolating Mechanisms Any special signals or behavious that are species specific prevent interbreeding with closely related species

Habitat Isolating Mechanisms Two species may live in the same general region but in different habitats, so they will probably never encounter each other

Temporal Isolating Mechanisms Species kept separate by timing barriers Two species may occupy the same habitat but mate or flower at different times of day, in different seasons, or in different years.

Mechanical Isolating Mechanisms Species that are closely related may attempt to mate but fail to achieve fertilization because they are anatomically incompatible

Gametic Isolating Mechanisms Gametes = egg and sperm Gametes of different species will rarely fuse to form a zygote

POST-ZYGOTIC BARRIERS A barrier that prevents hybrid zygotes from developing into viable, fertile individuals; also called post-fertilization barrier –Hybrid inviability –Hybrid sterility –Hybrid breakdown

Hybrid inviability Development of the hybrid zygote may stop E.g. embryos between sheep and goats die in early development before birth Due to genetic incompatibility

Hybrid Sterility Hybrid fails to produce functional gametes Example: A mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes. All male mules and most female mules are infertile.

Hybrid breakdown Offspring of hybrids are weak or infertile E.g. different species of cotton plants can produce fertile hybrids, but the offspring of the hybrids die as seeds or early in development

Types of Speciation The process of speciation requires populations of organisms to become, and largely remain, genetically isolated from one another. Two types of speciation based on how gene flow is disrupted within a population: –Sympatric - Allopatric helifewire/content/chp24/ html

Sympatric Speciation Enables populations that live in the same habitat to diverge genetically Result of a radical change in the genome that produces a reproductively isolated sub-population within the parent population (very rare)

SYMPATRIC SPECIATION the ancestors of apple maggot flies laid their eggs only on hawthorns—but today, these flies lay eggs on hawthorns (which are native to America) and domestic apples (which were introduced to America by immigrants and bred). Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in.

ALLOPATRIC SPECIATION ancestral separated geographical barrier/isolation.happens when the ancestral population becomes separated by a geographical barrier/isolation. Isolation might occur because of great distance or a physical barrier, such as a desert or river, as shown below

Speciation Tutorial en&biw=804&bih=871&q=types+of+spe ciation+tutorial+animation&ie=UTF- 8&sa=N&tab=iw#sclient=psy&hl=en&bi w=804&bih=871&source=hp&q=speciati on+animation&aq=f&aqi=&aql=&oq=&g s_rfai=&pbx=1&fp=6f32b8af52b7e0b8

ADAPTIVE RADIATION Emergence of numerous species common ancestorEmergence of numerous species from a common ancestor introduced to new and diverse environments. Example:Example: Darwin’s Finches m/thelifewire/content/ch p24/ html

INTERPRETATIONS OF SPECIATION Two theories:Two theories: 1.Gradualism (Neo-Darwinian): Slow changes in species overtime. 2.Punctuated Equilibrium: Evolution occurs in spurts of relatively rapid change.

CONVERGENT EVOLUTION Speciesevolutionary branches very similar environments.Species from different evolutionary branches may come to resemble one another if they live in very similar environments. Example:Example: 1.Sidewinder (Mojave Desert) and Horned Viper (Middle East Desert)

CONVERGENT EVOLUTION - EXAMPLE 1.Ostrich (Africa) and Emu (Australia).1.Ostrich (Africa) and Emu (Australia).

COEVOLUTION Evolutionary change selective force second firstEvolutionary change, in which one species act as a selective force on a second species, inducing adaptations that in turn act as selective force on the first species. Example:Example: 1.Acacia ants and acacia trees Video

COEVOLUTION - EXAMPLE 2.Humming birds and plants with flowers with long tubes he.com/biosci/ esp/2001_gbi o/folder_struct ure/ev/m3/s2/ evm3s2_4.ht m

Consequences of Human Activities Human-made barriers may prevent gene flow between the split populations Isolated populations may undergo adaptive radiation Severely fragmented populations may eventually die out if there is insufficient genetic diversity E.g. giant panda in China

Speciation and Mass Extinctions Five major mass extinctions have been identified