Module 46 & 47

phylogeny

The evolutionary history and relationships among organisms, often depicted in a phylogenetic tree showing their common ancestry and divergence over time.

Root

the base of the tree (common ancestor of all)

Node

the branching point

branch

the branch where a species is split

taxon

the identified group

common ancestors on phylogenetic trees

common ancestors of two taxa are at the node where they meet (the more recent the common ancestor, the more closely related two groups are)

sister groups

more closely related groups

rotating nodes

any node can be rotated without changing the meaning of a phylogenetic tree

hypothesis of a phylogenetic tree

phylogenetic trees are hypothesis about the evolutionary history of a species

cladograms

Diagrams used in biology to show evolutionary relationships between species based on shared characteristics. Branches represent common ancestors.

Evolutionary tree based on clades

monophyletic group (clade)

a group that contains a common ancestor and all of its descendents

paraphyletic group

includes some, but not all, of the descendents of a common ancestor

characters

anatomical, physiological, or molecular features that make up an organism

shared character

found in two or more goups

homoogous traits

shared characters are present in common ancestor and maintained over time

analogous traits (due to convergent evolution)

shared characters that may have evolved more than once

derived characteristic

an evolutionary innovation

synapomorphy

a shared characters is found in the common ancestor of two or more taxa

outgroup

a taxon whose common ancestor with the group of interest

ingroup

older than the common ancestor of the ingroup

biological species concept

species are a group of actually or potentially interbreeding populations that are reproductively isolated from other species (closed gene pool)

shortcomings of the BSC

difficult to test in the field

cannot be applied to asexually reproducing organisms

interbreeding may occur in some areas of overlap

morphological species

members of the same species usually look alike

ecological niche

identifies species on their role in the community

phylogenetic species

members of a species all share a common ancestor

reproductive isolation barriers

facors that cause a reproductive isolation (and speciation)

prezygotic isolation barriers

act before the fertilization of an egg and prevent fertilization

postzygotic isolation barriers

occur after fertilization and prevent the zygote from developing into a fertile adult

habitat isolation (prezygotic)

2 species live in different habitats and don’t see each other

temporal isolation (prezygotic)

2 species breed at different times of the day or year

behavioral isolation (prezygotic)

courtship rituals are species specific and don’t attract other species

mechanical isolation (prezygotic)

the sexual pieces don’t fit together

gametic isolation (prezygotic)

even if sex occurs, the egg and the sperm can’t meet

hybrid inviability (postzygotic)

embryo forms but does not develop

hybrid sterility (postzygotic)

offspring are produces but are sterile)

speciation

the development of new species

divergent evolution

two populations of organisms become genetically and physically different

allopatric speciation

populations develop differences due to being geographically isolated from each other

dispersal allopatric speciation

organisms relocate

vicariance allopatric speciation

geographic barrier arises

sympatric speciation

populations develop differences between populations in the same location

speciation rates

gradual process

can occur more rapidly (islands)

adaptive radiation

a period of unusually rapid evolutionary diversification in which natural selection accelerates rates of speciation and adaptation

gradualism

model to explain periods when species change characteristics slowly over time

typically occurs in a slowly changing environment

punctuated equilibrium

model to explain periods of relatively little change followed by periods of rapid diversification

rapid diversification occurs when environment changes suddenly