Macro n megaevolution

Macroevolution And Megaevolution

Submitted to: Dr.Fakhar Un NisaClass: BS-IV

Roll no: 329Semester: 7th

Department of Zoology

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Microevolution

Definition:

Micro evolution is the change in alleles frequency that occur within time through evolution.thischange is due to four different processes:•Mutation•Selection(artificial or natural)•Gene flow •Genetic drift


Macroevolution

Definition:Macroevolutionary studies focus on change that occurs at or above the level of specie.•An example of macroevolution is the appearance of feathers during the evolution of birds from theropod dinosaurs.

An Example of Macroevolution


•genus of Equidae, Equus

http://en.wikipedia.org/wiki/Equus_(genus)

Pattern of Macroevolution


we can think of patterns as "what happened when" All of the changes,diversifications, and extinctions that happened over the course of

life's history are the patterns of macroevolution.General patterns that recur across the tree of life:

•Stasis•Character change•Lineage-splitting•extinction


Biological Species Concept

Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.

•Breeding behavior can be real or potential, if two species come together and breed then there was only one species.

•Breeding behavior in nature can be different than in captivity.


How do new species arise?How do new species arise?

Speciation is the development of a new species through evolution.Evolution within a species means a change in that population’s allele frequency.When two populations are separated their allele frequency changes. Since they no longer have migration between the populations, two separate species develop.There are many ways to separate two populations besides geographically.


Allopatric Speciation

•Allopatric means ‘of other countries’

When geographical barriers divide a population,followed by the development of mechanisms in the separated populations that prevent interbreeding.

•Geographical isolation is the most important factor in starting speciation.•Physical or behavioral changes develop that will keep the two species isolated from interbreeding.


Reproductive Isolation

Any factor in nature that prevents interbreeding between individuals of the same or closely related species.

Extrinsic isolating mechanism – outside of the organisms in question

Geographic isolation is extrinsicIntrinsic isolating mechanism – internal characteristics that prevent interbreeding

Differences in anatomy, physiology and behavior


Intrinsic Reproductive Isolating Mechanisms

•Ecological •Temporal •Behavioral •Mechanical •Gametic


Ecological Isolation

When two species have different habitats they will rarely have contact.

•Lions prefer open grassland, tigers prefer forest

Temporal Isolation

Two species that share the same habitat but do not mate within the same time frame.

•Two populations of the same species of plant release their pollen at different times of the year.


Behavioral Isolation

Even if populations are in contact and breeding can occur, they must choose to mate.Such a choice is based on specific courtship and mating displays.

Behavioral Isolation

These albatrosses are behaviorally isolated from other bird species by their elaborate, species-

specific courtship behavior.


Mechanical Isolation

Reproductive organs differ in size or shape or other feature.

•Different species of Alpine Butterfly look similar but have different reproductive organs.


Gametic Isolation

Even if mating occurs, offspring may not result if there are incompatibilities between sperm and egg, or between sperm and the female reproductive tract.


Any speciation that does not involvegeographic separation.e.g.Sympatric Speciation in fruit flies•Only 6% of flies interbreed•Conduct courting, mating, laying eggs in their specific type of tree•In transition to being two separate species•Mutation or combination of rare alleles •allowed flies to smell the apple trees

Sympatric speciation


Parapatric Speciation

•Populations in contact along a common border giant velvet

worm

blind velvet worm

early reptile

pterosaur

chicken

bat

porpoise

penguin

•Change from body form of a common ancestor

•Produces homologous structures


Morphological Divergence

human



body wall (exoskeleton)

strong membrane (extension of wall)

wing veins


Adaptive Radiations of Mammals


Megaevolution

Definition:The term "megaevolution" is used for great changes.A list was prepared by John Maynard Smith and which he calledThe Major Transitions in Evolution.On the 1999 edition of the list they included:•Replicating molecules: change to populations of molecules in protocells.•Independent replicators leading to chromosomes.•RNA as gene and enzyme change to DNA genes and protein enzymes.

Megaevolution

•Bacterial cells (prokaryotes) leading to cells (eukaryotes) with nuclei and organelles•Asexual clones leading to sexual populations•Single-celled organisms leading to fungi, plants and animals•Solitary individuals leading to colonies with non-reproducing castes (termites, ants & bees)•Primate societies leading to human societies with language

Megaevolution

The Cambrian radiation example

When it was first described, the Cambrian fossil Opabinia was thought tobe unrelated to any known phylum.Later discoveries have shown it to beclosely related to the ancestors of

arthropods.

The Cambrian organism Marrella,was clearly an arthropod, but

with features not seen inmodern organisms

Dickinsonia, an organism of theEdiacaran Period that precedesthe Cambrian, whose affinity is

still unknown.

Macro n megaevolution

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