Diversification patterns in cosmopolitan earthworms: similar mode but different tempo

Area of Science:

• Evolutionary Biology
• Phylogeography
• Zoology

Background:

• Comparative phylogeography of widespread species aids understanding of biodiversity patterns and evolutionary processes.
• Soil-dwelling animals, due to low vagility and distinct population structures, are ideal models for studying palaeogeographical influences on distribution and diversification.

Purpose of the Study:

• To investigate the spatial lineage diversification and cladogenesis of two invasive earthworm species, Aporrectodea rosea and Aporrectodea trapezoides.
• To compare diversification patterns, genetic variability, and cladogenesis between these two species in their putative ancestral area (Western Palearctic) and North America.

Main Methods:

• Molecular analyses using mitochondrial and nuclear markers from 220 individuals of A. rosea and 198 individuals of A. trapezoides across 56 and 57 localities, respectively.
• Comparison of lineage diversification, genetic variability, and cladogenesis between the two species.

Main Results:

• Both species exhibited similar diversification from the Western Mediterranean to Northern Europe and the Iberian Peninsula, forming two main lineages.
• Diversification aligned with palaeogeographical events in the Iberian Peninsula and Western Mediterranean, with North American colonization originating from the Eurosiberian lineage.
• Cladogenesis was primarily influenced by Mediterranean plate shifts, not climatic oscillations like the Messinian salinity crisis, suggesting cryptic lineages and recurrent evolutionary events in invasive earthworms.

Conclusions:

• A. rosea and A. trapezoides show congruent diversification patterns driven by geological events, with distinct timing for A. rosea potentially being more ancient.
• The study identified distinct cryptic lineages within these invasive earthworms, suggesting recurrent evolutionary patterns in their ancestral Western Palearctic range.
• North American populations originated exclusively from the Eurosiberian lineage, underscoring the role of specific lineages in invasive species spread.