SPECIATION UNIT 5 EVOLUTION

Speciation Speciation – the process of one species splitting into two or more species Creates a diversity in life Shows how organisms share a common ancestor Forms a bridge between microevolution and macroevolution Microevolution – changes over time within a population Macroevolution – changes over time above the species level

Species Commonly known as a biological species concept Species – a population whose members have the potential to produce offspring with each other but not with members of other groups. Humans belong to the SAME species Species genetically resemble each other due to gene flow Gene Flow – the transfer of alleles between populations Absence of gene flow results in the formation of new species

The Fish Species

Reproductive Isolation Species are often identified by their reproductive capability Reproductive Isolation – the existence of barriers to prevent members of two species from producing offspring together Limits the formation of hybrids Hybrids – offspring produced through mating

Barriers Prezygotic Barrier – a barrier that prevents fertilization from occurring “Before the zygote” Can act in three different ways By preventing members of different species from attempting to mate By preventing an attempted mating from successfully completing By preventing fertilization, if mating has already occurred Postzygotic Barrier – a barrier that occurs after the zygote is formed Contributes towards reproductive isolation Can create developmental errors and can affect a hybrid’s chance of survival

Prezygotic Barriers These barriers can disrupt mating or prevent fertilizations from completing

Habitat Isolation Occurs when two species living in different habitats within the same area stop interacting with each other These species are not isolated by physical barriers – mountain ranges, hills, valleys, etc.

Temporal Isolation Species often breed during different times of the day, different seasons, or even different years Occurs when these species are not able to mix their gametes with each other

Behavioral Isolation When species perform rituals as a method of mate recognition Mate Recognition – a way to identify potential mates of the same species These are very effective reproductive barriers

Mechanical Isolation When mating is attempted, but cannot be completed due to morphological differences

Gametic Isolation Occurs when the sperm of one species cannot fertilize with the eggs of another species A male species may not be able to survive within a females reproductive tract due to this

Postzygotic Barriers These barriers can prevent a hybrid zygote from developing into a completely viable and fertile adult

Reduced Hybrid Viability Genes of different parent species can interact with each other in different ways The interactions can affect the hybrid’s development or survival in an environment

Reduced Hybrid Fertility If the chromosomes of two species have even the slightest difference, meiosis can prevent the production of normal gametes If hybrids cannot produce offspring when they mate, genes cannot flow smoothly between species

Hybrid Breakdown Some hybrids can be completely viable and fertile However, when they mate, their offspring can be sterile and unable to reproduce.

Barrier Limitations Does not apply to organisms that reproduce asexually Example – Prokaryotes

Other Species Concepts Morphological Species Concept Example – body shape and structural features Ecological Species Concept Example – a species in relation to their ecological niche Phylogenetic Species Concept Example – the smallest group of individuals from a common ancestor

Allopatric Speciation Allopatric Speciation – when a population becomes SEPERATED by a physical barrier “Geographic Speciation” or “Other Country Speciation” Creates an interruption in gene flow Example: The overflowing of a lake resulting in two or more smaller lakes home to separate populations A river dividing a population of animals that cannot cross it Occurs without genetic remodeling

Sympatric Speciation Sympatric Speciation – when populations of the same species AND habitat become reproductively isolated from each other “Same Country Speciation” Less common than allopatric speciation Occurs when gene flow is reduced Can be caused by many factors Polyploidy Sexual Selection Habitat Differentiation

Polyploidy Polyploidy – when a new species is created due to accidents in cell division, resulting in an extra set of chromosomes Occurs more commonly in plants There are two types of polyploidy Autopolyploid Allopolyploid Polyploidy

Polyploidy Autopolyploid – when chromosomes come from the SAME species Allopolyploid – when chromosomes come from DIFFERENT species Creates a new biological species Hybrids are usually sterile Example – a mule produced from a male donkey and female horse

Sexual Selection Sexual Selection – a selection based off a preference by one sex for certain characteristics in individuals of the other sex. Examples – color, fur, horns, size, wings, tails

Habitat Differentiation When a subpopulation uses a habitat or resource not used by the parent population Mutations allow individuals to exploit different conditions of the same environment

Allopatric and Sympatric Speciation Recap Allopatric Speciation - when a population becomes SEPERATED by a physical barrier Can cause an interruption in gene flow Many barriers restricting reproduction Sympatric Speciation - when populations of the same species sharing the same habitat become reproductively isolated from each other Polyploidy Sexual Selection Habitat Differentiation