Combining FISH and model-based predictions to understand chromosome evolution in Typhonium (Araceae)

Area of Science:

• Plant evolutionary biology
• Cytogenetics
• Phylogenetic analysis

Background:

• Inferring chromosome number evolution from molecular phylogenetics is challenging.
• Cytogenetic data is crucial for validating phylogenetic inferences of chromosome number changes.
• The Araceae family genus Typhonium exhibits extreme variation in chromosome numbers.

Purpose of the Study:

• To model chromosome number evolution in Typhonium using phylogenetic methods.
• To validate phylogenetic inferences with cytogenetic data, specifically fluorescence in situ hybridization (FISH).
• To investigate the evolutionary trajectories of chromosome numbers in relation to phylogenetic relationships.

Main Methods:

• Constructed a phylogeny using nuclear and plastid DNA sequences from 96 taxa.
• Modeled chromosome number evolution, considering polyploidization and dysploidy.
• Performed FISH with rDNA and telomere probes on ten Typhonium species.

Main Results:

• Phylogenetic models indicated numerous past chromosome number reductions.
• FISH revealed interstitial telomeric signals in species with low chromosome numbers, supporting decreasing dysploidy.
• A model-inferred polyploidization event correlated with an increase in rDNA sites.

Conclusions:

• The combination of phylogenetic modeling and FISH elucidated chromosome number evolution in Typhonium.
• Species with n=4 are highly derived, with evidence of Robertsonian fusion-like rearrangements.
• Cytogenetic data strongly supports phylogenetic models of chromosome number change.