BIOL 152 Exam #2 - Chapters 24,25: Speciation and Phylogenies

speciation

the evolution of two or more distinct species from a single ancestral species, resulting from a two-step process involving genetic isolation and genetic divergence

genetic isolation

occurs when some sort of barrier to gene flow isolates two populations within a species

genetic divergence

when mutation, natural selection, and genetic drift occur in each of the isolated populations during speciation

species

an evolutionarily independent population or group of populations

biological species concept

the definition of a species is such that species can interbreed in nature to produce viable fertile offspring among themselves but not with other species (reproductive isolation)

prezygotic isolation

prevents individuals from differing species from mating successfully

postzygotic isolation

when the hybrid offspring of mating between members of different species cannot survive or reproduce

1. cannot be evaluated in fossils

2. cannot be evaluated in species with asexual forms of reproduction

3. difficult to apply in populations without geographical overlap

4. more difficult than other methods and takes a lot of time

disadvantages of the biospecies concept (3 points)

morphospecies concept

wherein researchers identify evolutionarily independent lineages by differences in morphology, as distinguishing features are most likely to arise if populations are independent/isolated from gene flow

polymorphic species

a species with 2 or more distinct phenotypes in the same breeding population at the same time

cryptic species

a species which cannot be distinguished from a similar species through easily identifiable morphological traits

1. more subjective than other methods

2. cannot identify cryptic species

3. may lead to the naming of many more species than what actually exist

disadvantages of the morphological species concept (3 points)

phylogenetic species concept

where species are classified as the smallest monophyletic group in a phylogenetic tree

monophyletic group

an evolutionary unit that includes an ancestral population and all of its descendants, but no others

synapomorphy

a characteristic present in an ancestral species and shared exclusively (in more or less modified form) by its evolutionary descendants.

• allows for recognition of phylogenetic groups

• monophyletic groups are assumed to be nested within one another

1. carefully estimated phylogenies are available for only a tiny subset of populations on the tree of life

2. tends to recognize more species than the other two concepts (some think this is more representative of the diversity of life on earth, however).

disadvantages of the phylogenetic species concept (2 points)

systematics

discipline of biology that characterizes and classifies the relationships of all organisms

taxonomy

the practice of describing/naming/classifying species

allopatry

condition in which 2+ populations live in different geographic areas

allopatric speciation

speciation occurring when populations of the same species become geographically isolated, often due to dispersal or vicariance

biogeography

study of how species and populations are distributed geographically

allopatric speciation by dispersal

migration of a population from one habitat to another and experiencing selection that causes speciationa

allopatric speciation by vicariance

where continental drift, climate fluctuations, etc. fuel speciation by splitting a population and allowing selection act separately on each part

reinforcement

natural selection for traits that prevent interbreeding for recently diverged species (prevents hybridization; AKA disruptive selection)

sympatry

when populations of species live in the same geographic area, close enough to breed/interbreed

sympatric speciation

speciation that occurs even through living in the same geographic area, affected by both extrinsic and intrinsic factors

niche

the range of ecological resources that a species can use and the range of conditions it can tolerate. sort of like an ecological “role”

polyploidy

the condition of possession two or more sets of complete chromosomes, caused by massive error in mitosis or meiosis

autopolyploid

individuals are produced when a mutation results in a doubling of chromosomes and the chromosomes are all from the same species

• duplication of the SAME genome (diploid parents, tetraploid offspring)

allopolyploid

individuals created when parents of different species mate and an error in mitosis occurs, resulting in viable non sterile offspring with 2 full sets of chromosomes

• combination of 2 genomes from differing species

• common in plants

• increases genetic variation and heterozygosity

hybrid zone

geographic area where interbreeding occurs between species, sometimes producing fertile hybrid offspring

phylogeny

branching evolutionary history of species/other groups of organisms

phylogenetic tree

simplified diagram of evolutionary history

tree of life

universal phylogenetic tree

taxa

any named group of organisms at any level of a classification system

sister groups

two lineages that are each other’s closest relatives, represented by two branches emerging from a node in a phylogenetic tree

character

any heritable genetic, morphological, physiological, developmental, or behavioral characteristic of an organism to be studied (AKA trait)

outgroup

a taxon that is not part of the taxonomic group studied but is closely related; added to establish the direction of change for each character

ancestral trait

a trait found in the ancestors of a particular group

derived trait

a trait that is a modified form of an ancestral trait, found in a descendant

1. assumes homology (assumes derived character states evolve only once, and that if two organisms share a trait, they must be evolved from a common ancestor, which happens but is not always true)

2. assumes reversals in a character state doesn’t occur, which creates the appearance that no change occurred.

issues with Henig’s method (2 points)

homoplasy

similarity among organisms of different species due to reasons other than common ancestry (like convergent evolution)

parsimony

the principle that the most likely explanation of a phenomenon is the most economical/simplest. For phylogenetic trees, this means that the most likely is the one requiring the fewest character changes.

bioinformatics

a discipline at the intersection of biology, compsci, and statistics concerned with the storage, analysis, and presentation of biological data

convergent evolution

common cause of homoplasy; the independent evolution of similar traits in different organisms due to similar habitats/lifestyles

paleontologist

scientist who studies the fossil record/history of life

fossils

any physical trace of an organism that existed in the past. Includes tracks, burrows, bones, casts, and so on

intact fossil

forms when decomposition does not occur/the organic remains are preserved intact

compression fossil

forms when sediments accumulate on top of an organism and become cemented into rocks

cast fossil

forms when a buried organism decomposes, leaving an empty cavity in the sediments that fills with dissolved minerals and hardens into an accurate cast of the remains

permineralized fossil

forms when organisms decompose extremely slowly and dissolved minerals gradually infiltrate the interior of cells/harden into stone

trace fossil

forms when sedimentation and mineralization preserve indirect evidence of an organism in the environment, including footprints, tracks, burrows, feeding marks, and feces

habitat bias

organisms living in environments where sediment is actively deposited are more likely to form (beaches/wetlads/mudflats)

taxonomic and tissue bias

where organisms with hard parts like bones/shells are more likely to fossilize because of their slower rates of decomposition

temporal bias

wherein recent fossils are much more common because the older a fossil is, the longer it has been exposed to potentially destructive forces in deep layers of rock

abundance bias

when the fossil record is weighted toward common species, as abundant organisms are much more likely to leave more traces than others

precambrian

interval between the formation of earth and the appearance of animals

• mostly unicellular organisms (like, exclusively)

• divided into Hadean, Archaean, and Protozoan eons

• oxygen was virtually absent from the oceans and atmosphere. eventually, cyanobacteria released enough O2 to change this

phanerozoic eon

interval between 541 million years ago and the present. divided into 3 eras:

• paleozoic era - appearance of most major animal lineages/ends with obliteration of almost all unicellular life

• mesozoic era - ends with extinction of dinosaurs (except birds) and other groups. Gymnosperms are dominant plants, dinosaurs are dominant animal.

• cenozoic era - angiosperms are dominant plants, birds and mammals are dominant vertebrates

anthropocene

proposed new, current epoch in the geologic time scale to reflect the dramatic physical, chemical, and biological changes that humans are causing on earth

adaptive radiation

rapid evolutionary diversification in one lineage, producing many descendant species that have adapted to a wide variety of habitats

1. ecological opportunity - there are many vacant niches in a given environment and few competitors

2. innovation - new morphological, physiological, or behavioral traits that allow for new habitat colonization, new food sources, etc. that may trigger adaptive radiation

reasons/conditions for adaptive radiation (2 points)

ecomorphs

groups of organisms that have similar behavioral/physical traits and are adapted to specific ecological niches

cambrian explosion

rapid diversification of animal body types/lineages occuring in a 50 million year period

• documented by fossil assemblages with distinctive fauna

fauna

all the animal species characteristic of a particular region/period/environment

• in the cambrian period - sponges, jellies, comb jellies, mollusks, echinoderms, etc.

mass extinction

rapid extinction of a large number of diverse species around the world (specifically when 60%+ of species are wiped out within 1 million years)

background extinction

the lower, average rate of extinction observed when a mass extinction is not occurring

• occurs with normal environmental change, disease, predation pressure, or when competition reduces populations to zero

end-permian extinction

“Mother of mass extinctions” wherein flood basalts belched heat, CO₂, and SO₂ into the atmosphere. Resulted in:

• severe acid rain

• widespread coal fires pumping toxic ash into atmosphere

• severe depletion of O₂ in the atmosphere

• dramatic reduction in sea level

End-cretaceous extinction

mass extinction event involving the impact hypothesis stating that a collision between earth and asteroid caused the mass extinction ending the cretaceous period.

• fireball of hot gas spreading from impact site let to massive wildfires

• largest tsunami in the last 3.5 billion years disrupted ocean sediments/circulation patterns

• sulfate-containing rock disrupted which reacted w/ water to form acid rain

• sun was blocked by large quantities of dust and ash, causing a crash in plant productivity

sixth mass extinction

extinction due to human impacts (habitat loss, pollution, overexploitation, climate change, invasive species, etc.)