Molecular Systematics
Molecular systematics uses DNA, RNA, and protein sequences to infer evolutionary relationships, identify organisms, and delimit species.
Definition
Molecular systematics is the branch of systematics that reconstructs evolutionary relationships and identifies and delimits taxa using the sequences of nucleic acids and proteins as characters.
Scope
This area covers the inference of phylogenies from molecular data, the use of standardized gene regions for identification through DNA barcoding, the choice of molecular markers for different evolutionary timescales, and the use of sequence data to delimit species boundaries. It complements morphology-based systematics with abundant, comparable molecular characters.
Sub-topics
Core questions
- How are phylogenies inferred from molecular sequence data?
- Which molecular markers suit which taxonomic and temporal questions?
- How can short standardized sequences be used to identify organisms?
- How can molecular data be used to delimit species?
Key theories
- Model-based phylogenetic inference
- Likelihood and Bayesian methods estimate phylogenies under explicit models of nucleotide or amino-acid substitution, accounting for unequal rates and multiple changes per site.
- DNA barcoding for identification
- Short, standardized gene regions such as the mitochondrial COI gene can identify specimens to species by comparison against reference libraries.
Clinical relevance
Molecular systematics underpins the identification and tracking of pathogens and disease vectors, the authentication of biological materials and foods, and the rapid characterization of biodiversity from environmental samples.
History
The use of molecules in systematics grew from early protein and ribosomal RNA comparisons to genome-scale phylogenomics, propelled by sequencing technology and by the maturation of likelihood and Bayesian inference; DNA barcoding in the 2000s extended molecular methods to large-scale identification.
Debates
- Gene trees versus species trees
- Individual gene genealogies can differ from the underlying species tree because of incomplete lineage sorting and introgression, raising the question of how best to estimate species relationships from many genes.
Key figures
- Joseph Felsenstein
- Ziheng Yang
- Paul Hebert
Related topics
Seminal works
- yang2012
- felsenstein2004
- hebert2003
- wiley2011
Frequently asked questions
- How is molecular systematics different from morphological systematics?
- It uses sequence characters from DNA, RNA, or proteins rather than anatomical features, providing large numbers of comparable characters but requiring explicit models of molecular evolution.
- Why might a gene tree disagree with the species tree?
- Processes such as incomplete lineage sorting, hybridization, and gene duplication can cause the history of an individual gene to differ from the history of the species carrying it.