Speciation and Macroevolution

Microevolution

changes in gene frequency over generations

• changes within a gene pool/population

macroevolution

level of change in organisms that is evident in the fossil record (requires a long period of time)

• changes above the species level

• creates new species / groups of species

________ bridges microevolution and macroevolution

speciation

species

a group of organisms that maintains a distinctive set of attributes in nature AND can produce FERTILE offspring

______ occurs by accumulation of microevolutionary changes or changes in the genes

macroevolution

biological species concept

groups where the members have the potential to interbreed in nature to produce viable, fertile offspring but their offspring cannot successfully interbreed with members of OTHER species

ring species

members of geographically neighboring populations are related closely that they interbreed (same species) but the members of the populations near the “end” of the spread are incapable of interbreeding (different species)

phylogenetic concept 

species are identified by having a unique combination of traits

• in the past, physical traits were used - now we identify unique traits by DNA sequences 

Evolutionary Concept

a species is derived from a single lineage that is distinct from other lineages and has its own evolutionary tendencies & historical fate 

Ecological concepts

each species occupies a unique set of habitat resources that it requires, as well as its influence on the environment and other species

• this results in competition, and such competing individuals are likely to be of the same species 

reproductive isolating mechanisms

process which keeps two groups separate

• prevents gene flow / interbreeding and thus the development of one single species 

temporal isolation

prezygotic (before egg fertilized) mechanism

breed at different times 

• nocturnal v day time

• fall v spring

behavioral isolation

PRE-ZYGOTIC

two individuals have different hobbies / behaviors

• decorating their nest in two different colors (blue v white bower birds) 

Mechanical Isolation

PRE-ZYGOTIC

reproductive parts fit perfectly with corresponding reproductive partner

Gametic Isolation

Pre-Zygotic

gametes of same species are very chemically similar to its own species and will not be fertilized by a different species

Ecological / Habitat Isolation

PRE-ZYGOTIC

two individuals living in different areas

• LA v NYC

Describe how Species can be isolated Post-zygotic

a. zygotic (fertilized egg) dies

b. the individual is a hybrid and is sterile

c. the individual is a hybrid and is weak, low fitness (ability to survive) and has a high mortality rate among their offspring ex: liger

How does speciation emerge?

the accumulation of genetic changes that ultimately results in enough differences so that we can determine that the population constitutes a unique species 

patterns of speciation

how microevolution (changes within species) results in macroevolution (changes in TYPES of species)

Anagenesis

small, progressive changes in a single species over long period

• NO INCREASE IN SPECIES NUMBER - the single species is just changing into another

• most common in bacteria 

anagenesis

cladogenesis

speciation pattern

cluster of species all derived from one single common ancestor (most common)

Allopatric Speciation

mode of speciation

• geographical isolation resulting in an new species - the gene flow between populations slows or stops (most common mode)

two species on different sides of the grand canyon would experience what mode of speciation?

allopatric - separated geographically

geographic separation leads to…

adaptive radiation: one group spreads out into new areas and undergoes new adaptations 

allopatric separation (geographically separated & hold different characteristics)

adaptive radiation (spreading out into new areas and undergoes new adaptations 

parapatric speciation

reproductive isolation (they don’t reproduce together) evolves in neighboring populations that share small zones of contact (but still have different habitats) and exhibit modest gene exchange (from living near each other) 

parapatric speciation

different patterned / colored giraffes is a result of parapatric speciation & how they evolve differently living in neighboring areas

sympatric speciation

new species evolves in same area as parental species (common in plants)

what causes sympatric speciation?

change in chromosome number due to abrupt genetic changes and leads to reproductive isolation

change in ecology - different eating habits, results in different size and in turn effects mating preferences & leads to reproductive isolation 

allopatric: 

same species

barrier formed

reproductive isolation lead to different species

same species 

an environmental niche / habitat change emerged

the niche / change lead to natural selection & reproductive isolation leading to a new species 

sympatric speciation

parent population

change in genetic appears and leads to reproductive isolation

reproductive isolation leads to emergence of new species 

gradualism

early division produces two lines and undergoes gradual transitions with new species emerging from the same common ancestor 

punctuated equilibrium

long periods of time with little changes are interrupted by widely spread episodes of speciation and each time results in a new species

gradualism 

punctuated equilibrium 

• a major change occurs and results in a new species