Global biogeographic patterns in bipolar moss species

Area of Science:

• Biogeography
• Evolutionary Biology
• Plant Science

Background:

• Bipolar disjunctions, common in non-vascular plants, involve species found in both Arctic and Antarctic regions.
• The mechanisms, origins, and timing of these disjunctions are poorly understood, with debates on vicariance versus long-distance dispersal.

Purpose of the Study:

• To investigate the biogeographic patterns of four bipolar Polytrichales moss species.
• To determine the driving mechanisms (vicariance or dispersal) behind their distribution.
• To understand the origin and timing of bipolar disjunctions in these mosses.

Main Methods:

• Analysis of a large-scale population dataset.
• Application of multiple molecular dating analyses.
• Phylogenetic and phylogeographic reconstructions.

Main Results:

• Three of the studied Polytrichales species originated in the Holarctic and dispersed to the Southern Hemisphere (SH).
• Polytrichum juniperinum diversified in the Antarctic region and subsequently colonized the Holarctic and other SH regions.
• Long-distance dispersal, occurring on multi-million-year timescales, was identified as the primary driver of bipolar disjunctions.

Conclusions:

• Bipolar disjunctions in these mosses are primarily driven by rare, long-distance dispersal events.
• High-altitude tropical populations did not serve as dispersal stepping stones.
• Plant presence in the Antarctic region predates previous glaciations, indicating a longer history than previously assumed.