Fleas (Siphonaptera) are Cretaceous, and evolved with Theria

Area of Science:

• Zoology
• Evolutionary Biology
• Molecular Phylogenetics

Background:

• Fleas (order Siphonaptera) are diverse, blood-feeding ectoparasites with an unclear evolutionary past.
• Understanding flea origins and diversification is crucial for comprehending host-parasite co-evolution.

Purpose of the Study:

• To reconstruct the molecular phylogeny of fleas (Siphonaptera).
• To estimate divergence times and ancestral host associations.
• To investigate the biogeographical origins of fleas.

Main Methods:

• Conducted a molecular phylogenetic study using a comprehensive taxon sampling of 259 flea taxa.
• Employed Bayesian phylogenetic analysis to infer evolutionary relationships.
• Estimated divergence times using fossil records and host associations (e.g., bats).
• Reconstructed ancestral states for host association and biogeography.

Main Results:

• A well-supported Bayesian phylogenetic tree revealed seven sequentially derived lineages, with Macropsyllidae and Stephanocircidae as early divergences.
• The common ancestor of extant Siphonaptera diversified in the Cretaceous, with most intraordinal divergence post-K-Pg boundary.
• Fleas likely originated in Gondwana and rapidly dispersed from South America.
• Theria (placental mammals and marsupials) are the most probable ancestral hosts, with marsupials playing a significant role.
• Major flea families evolved alongside placental mammal diversification; associations with monotremes and birds are likely secondary.

Conclusions:

• The study clarifies the evolutionary history and biogeographical origins of fleas (Siphonaptera).
• Fleas diversified significantly after the K-Pg extinction event, primarily associated with mammalian hosts.
• Recent interpretations of Mesozoic fossil "dinosaur fleas" should be approached with caution regarding their placement within extant Siphonaptera.