K Kannabium BioDev · Evolutionary biology
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Chordata · Molecular evolution · Comparative genomics

Origin and diversification
of cannabinoid receptors.

A comparative synthesis of the CB1/CB2 receptor family in chordates. The page distinguishes sequence evidence, phylogenetic inference, and hypotheses about biological function.

Examine phylogenetic relationships ↘ Synthetic topology · branch lengths not to scale

01 · Interpretive principle

Phylogenetic relatedness does not establish a hierarchy of complexity.

Cephalochordata, Tunicata, and Vertebrata are extant lineages that share common ancestors. Their positions in the tree express relationships, not degrees of evolutionary progress; no living taxon should be interpreted as the direct ancestor of another.

Conceptual illustration of a marine environment with a lancelet, tunicates, and a transmembrane protein
Comparative contextChordate lineages document independent evolutionary trajectories.

02 · Phylogenetic synthesis

Distribution of co-orthologs and origin of vertebrate paralogs.

The visualization maps the occurrence of BfCBR and CiCBR and the proposed duplication that originated CNR1 and CNR2 in the vertebrate lineage onto the species tree.

Species tree · gene distribution overlay Selection · chordate common ancestor
Chordate topology with inferred events in the CB1/CB2 family Cephalochordata is sister to Olfactores. Olfactores comprises Tunicata and Vertebrata. BfCBR occurs in Branchiostoma, CiCBR in Ciona, and an inferred duplication in the vertebrate lineage originated CNR1 and CNR2, which encode the CB1 and CB2 receptors. CHORDATA CB1/CB2 RECEPTOR INFERRED IN THE ANCESTOR Cephalochordata Olfactores Tunicata Vertebrata BfCBR CiCBR CNR1 → CB1 receptor ↗ CNR2 → CB2 receptor divergence between Cephalochordata and Olfactores Tunicata + Vertebrata inferred gene duplication in the vertebrate lineage

Species topology with gene distribution overlay and an inferred duplication; branches do not represent time or genetic distance.

Chordate common ancestor

An ancestral CB1/CB2-type receptor is inferred

BfCBR and CiCBR are interpreted as co-orthologs of the vertebrate CB1 and CB2 receptors. The ancestral receptor was not observed directly; its occurrence is reconstructed from taxonomic distribution and phylogenetic relationships among extant genes.

Primary reference Elphick, 2007 ↗

03 · Evidence hierarchy

Interpretation should remain proportional to the available evidence.

Genomic identification, expression, and functional characterization address different questions and are not interchangeable levels of demonstration.

01

Homology relationship

Sequence comparison and phylogenetic inference support hypotheses about common ancestry, orthology, and paralogy.

phylogenetic evidence
02

Molecular expression

Detection of RNA or protein informs spatial and temporal distribution but does not, in isolation, demonstrate physiological activity.

occurrence evidence
03

Functional characterization

Assigning function requires appropriate assays, controls, biological context, and evaluation of alternative hypotheses.

experimental evidence
Conceptual illustration of three transmembrane receptors associated with a molecular branching event
Gene-history reconstructionCommon ancestry does not imply complete conservation of function.

04 · Inference and terminology

From gene history to inference of biological function.

Orthology and paralogy describe evolutionary relationships among genes; they do not, by themselves, demonstrate pharmacological equivalence. Robust functional inference requires integration of sequence, structure, expression, biochemical assays, and comparative physiology.

● observed datum ● evolutionary inference ● unresolved hypothesis
Ortholog Genes in different lineages derived from an ancestral gene through speciation events.
Paralog Genes derived from a duplication event within the same gene history.
Monophyly A group comprising a common ancestor and all of its descendants.
Biological function An activity or role supported by experimental evidence in a defined context.

05 · Bibliographic basis

Primary sources and selected syntheses.

  1. 01

    Elphick, M. R.; Satou, Y.; Satoh, N. 2003. The invertebrate ancestry of endocannabinoid signalling: an orthologue of vertebrate cannabinoid receptors in the urochordate Ciona intestinalis. Gene, 302(1–2), 95–101.

  2. 02

    Elphick, M. R. 2007. BfCBR: a cannabinoid receptor ortholog in the cephalochordate Branchiostoma floridae. Gene, 399(1), 65–71.

  3. 03

    Delsuc, F. et al. 2006. Tunicates and not cephalochordates are the closest living relatives of vertebrates. Nature, 439, 965–968.

  4. 04

    Putnam, N. H. et al. 2008. The amphioxus genome and the evolution of the chordate karyotype. Nature, 453, 1064–1071.

  5. 05

    Clarke, T. L. et al. 2021. The Endocannabinoid System and Invertebrate Neurodevelopment and Regeneration. International Journal of Molecular Sciences, 22(4), 2103.

  6. 06

    NCBI Taxonomy. Chordata: taxonomic reference record. Accessed 12 September 2026.