Systematics

Systematics

• the study of the units of biodiversity, dealing with diversification of lineages through time

  • inferring phylogeny (relatedness) of extinct and extant (still living) species

    • using organismal features — morphological, chromosomal, molecular

    • finding common characters between species

Taxonomy

• classificaiton of animals

Phylogeny

• evolutionary relationships

Carolus Linnaeus

• created the current scheme that we still use today

Taxonomic Categories

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• species

*some groups are incredibly diverse and need to include extra ranks (suborder and subfamily)

Binomial Nomenclature

• Genus name, species name

  • latin names, in italics

• Genus is always capitalized, species is lower case

What defines a species

• common descent

  • always need a common ancestor

• smallest distinct grouping

  • molecular and chromosomal characters

• reproductive community

  • interbreeding

  • mule = male donkey x female horse; cannot reproduce — technically not a true species

Species Concepts

• most common: biological species concept

  • reproductive community of populations

  • occupy a specific niche

• zoologists agree that a species should constitute a lineage with a unique history of evolutionary descent

DNA Barcoding

• using a DNA sequence common to all animals

  • cytochrome C oxidase: protein complex

  • variation of this gene sequence is smaller within species than between

  • need blood or tissue sample

Issues with DNA barcoding

• sometimes you don’t have blood or tissue to work with so you can’t use this

  • ex; working with bones or fossils

Homology

• character similarity from a common ancestor

  • ex; endothermy (warm-bloodedness) in humans and bears — feature comes from common ancestor

Convergent Evolution

• independent evolution of the same characteristic

  • ex; endothermy evolved in birds and mammals separately (arose twice in evolutionary history)

Phylogenetic Trees

• similar to a cladogram but includes more information, usually genetic

  • e.g., base substitutions in a specific gene

Cladograms

• nested hierarchy of branches with similar derived characters

Phylogeny

• evolutionary relationships can take 1 of 3 forms:

  • monophyly

  • paraphyly

  • polyphyly

Monophyly

• single common ancestor + all descendants

Paraphyly

• common ancestor and some of its descents

Polyphyly

• grouping with no recent common ancestor

LUCA

• last universal common ancestor (we don’t actually know what it is)

The Future of Taxonomy?

• taxonomy is constantly changing and is not perfect!

  • we don’t know everything about everything!

  • e.g., Euspira lewisii is now Neverita lewisii

• New taxonomic system in development: Phylocode

  • based on phylogeny

  • not hierarchical rankings

  • could someday replace binomial nomenclature