BIO 172 Ch. 23: Systematics, Phylogenies, and Comparative Biology

Systematics

study of the diversity of life and the evolutionary relationships between organisms

Phylogeny

hypothesis of evolutionary relationships between species

Why might basing evolutionary relationships off of phenotypic similarity not be reliable?

more time between evolutionary divergence does not equal more changed characteristics; two species can look similar without being recently related

Convergent Evolution

process by which unrelated organisms independently evolve similarities

Cladistics

reconstruction of evolutionary relationships on the basis of shared derived characteristics

Shared Derived Characteristics

characteristic or trait that the common ancestor of a group had and passed on to its descendants

Ancestral Character

a character that evolved in the most common ancestor of both groups

Primitive Character

a feature that is not new to a species and was present earlier in its lineage

Plesiomorphy

ancestral trait shared by a lineage or clade that is inherited from a common ancestor but is not unique to that group

Derived Character

trait that appears in recent parts of a lineage only by a subset, not the shared ancestor

Changed Character

a feature that is new to a species and was not present earlier in its lineage

Apomorphy

derived character unique to a particular species or evolutionary lineage, distinguishing it from its ancestral form

Character

a heritable feature that varies among individuals

Character State

one of the variant conditions of a character

Taxon

group or level of organization into which organisms are classified

Cladogram

phylogenetic tree constructed with clades

Clade

evolutionary branch of a cladogram or taxa that includes a single ancestor and all its descendants

Synapomorphy

shared derived trait that originated in the most recent common ancestor of a group of organisms and is inherited by all its descendants

Node

a common ancestor where a single lineage splits into two or more descendant lineages, marking a point of evolutionary divergence

Symplesiomorphy

shared ancestral trait present in multiple species that reflects common ancestry but does not uniquely define a specific evolutionary group

How can you determine if a characteristic is ancestral or derived?

establish state characters had in common ancestors of an entire group (polarize); select an outgroup

Outgroup

taxon closely related to main group but not a part of it that retains the more primitive forms

Parsimony

a hypothesis of relationships that requires the smallest number of character changes is most likely to be correct

Homoplasy

a character shared by a set of species but not present in their common ancestor

Evolutionary Reversal

the reappearance of an ancestral trait in a group that had previously acquired a derived trait

Taxonomy

science of classifying organisms

Binomial Name

scientific name of an organism that remains the same in all languages

The term Tenebrio molitor is an example of a __________.

Binomial Name

What are traditional taxonomic hierarchies based on?

shared traits

Monophyletic

a group of taxa that consists of a common ancestor and all of its descendants; clade

Paraphyletic

group that includes most recent common ancestor of the group, but not all its descendants

Polyphyletic

pertaining to a group of taxa that includes distantly related organisms but does not include their most recent common ancestor

Biological Species Concept (BSC)

species are interbreeding populations, reproductively isolated

What are the problems with the Biological Species Concept?

it is difficult to know if allopatric species would interbreed; there is no way to include asexual species

Phylogenetic Species Concept (PSC)

species is a population or set of populations characterized by one or more shared derived characters

What is a problem with the Phylogenetic Species Concept?

the degree of change necessary to identify as a different species is subjective