Biological Diversity & SpeciationHow it evolves

There are about 1.8 million formerly classified (named) species

1,000,000 of these observations are insects.

300,000 of those are beetles (class Coleoptera)

There are about 300,000 recorded plant species

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There are about 1.8 million formerly classified (named) species

1,000,000 of these observations are insects.

300,000 of those are beetles (class Coleoptera)

There are 4,500 mammals and around 10,000 recorded bird species

There are about 4,000 recognized virus species

Extrapolations by biologists based on the rate at which new species are being discovered, suggest an exhaustive inventory of species would number somewhere between 10-100 million species.

What is biodiversity?The diversity of plant and animal life in a particular habitat (or in the world as a whole : Biodiversity is often used as a measure of the health of biological systems.

High biodiversity GoodLow Biodiversity Bad - Why?

What Is a Species?The Biological Species Concept defines a species as:A population or group of populations whose members have the potential to interbreed and produce fertile offspring.

The biological species concept cannot be applied in all situations, for example, with fossils and asexual organisms

Used for animals that reproduce sexually: Mammals, Birds, Reptiles, Fish etc.

The Morphological Species Concept Organisms are classified in the same species if they appear identical by morphological (anatomical) criteria. This is used when species do not reproduce sexually, some are known only from fossils. -Used for large microbes and phytoplankton

The Phylogenetic Species Concept: Based on gene sequences to for phylogenetic relationships - Based on rDNA or mtDNA sequences

Reproductive Barriers between SpeciesPrezygotic barriers prevent mating between species.Prezygotic barriers includeTemporal isolation.Habitat isolation.Mechanical isolation.Gametic isolation.Behavioral Isolation

Postzygotic barriersAre mechanisms that operate should interspecies mating actually occur and form hybrid zygotes.Postzygotic barriers includeHybrid inviability.Hybrid sterility.

Mechanisms of SpeciationA key event in the potential origin of a species occurs when a population is somehow severed from other populations of the parent species.

Two modes of speciationAllopatric speciation>Isolation of populations geographically allows populations to evolve independently

Sympatric speciation (meaning in the same space)>Genetic changes divide a population

Allopatric vs Sympatric

Allopatric Speciation barriers to dispersal are keyGeologic processesCan fragment a population into two or more isolated populations.Can contribute to allopatric speciation.

Biodiversity patterns are also reflect major changes in land masses, and extinctions.

About 250 million years agoPlate movements formed the supercontinent Pangaea

Mass extinctions (five major episodes recognized in the geological record) allow surviving lineages to diversify.

About 180 million years agoPangaea began to break up, causing geographic isolation & new species

Carl LinnaeusSwedish, 1707-1778 Established the naming conventionstill used in Biology (e.g. Homo sapiens)

Linnaeus grouping of invetebrate animals differed somewhat from Aristotles, and is also quite different (and is considered illogical)when compared to the grouping used today.

The goal of classification is to reflect phylogeny, the evolutionary history of a species.

Hierarchical ClassificationThe taxonomic hierarchy

since the late 20th century,Molecular studies (using usually DNA diversity) and cladistics (=statistical methods for building trees representing evolutionary relationships) have been around, widening the scope for understanding species diversity

Taxonomy based on genetic analysisBased on rRNA sequencesWhat are the three domains?ArchaeaEubacteriaEukaryota

Bacteria

Figure 14.26Four or more Kingdoms of eukaryotes are generally recognized in modern taxonomy

http://mindblog.dericbownds.net/2007_11_01_archive.html A tree based onDNA sequenceof a conservedgene for ribosomalRNA. Genetic analysisshows that the majorityof life on earth isin the Eubacteria and Archaea. The portion of diversityrepresented by recognizedEukaryote kingdoms ofFungi, Animals and Plantsis small!

Classification underestimates diversity

(a no-brainer?)

Phylogenetic trees can reveal genetic divisions within a species.

Figure 9.6, Zimmer 2010In this case a tree based on DNA sequences similarity, suggests the giraffe taxon, Giraffa camelopardalis, is 3 to 5 distinct genetic groups.

Should this type of information influence conservation strategies? HOW?

African Cichlid SpeciationSympatric

Allopatric

Lake Tanganyikian Cichlid Speciation Based on physical and behavioral adaptations Scale bitersGrazersSnail shell brooders

Lake Malawi Cichlid phylogenyBased on nuptial coloration/ mate selection* Mouth Brooding

African cichlid allopatric speciationTiger FishEmperor CichlidMid-water predator fish (Biological Barrier)