Morphological and molecular approach uncovers hidden cryptic diversity within Polysiphonia sertularioides species...

Area of Science:

• Marine Biology
• Algology
• Biodiversity Science

Background:

• Turf-forming seaweeds, like Polysiphonia sertularioides, are increasingly studied using combined molecular and morphological data.
• Previous molecular data suggest P. sertularioides is a species complex, challenging its presumed global distribution based on morphology.

Purpose of the Study:

• To investigate the extent of the Polysiphonia sertularioides species complex and its global distribution.
• To delimit species within the complex using molecular phylogenetics and morphometrics.

Main Methods:

• Phylogenetic inference and species delimitation using rbcL gene sequences and Generalized Mixed Yule Coalescent, Poisson Tree Processes, and Assemble Species by Automatic Partitioning.
• Morphometric analysis of nine characters from 75 specimens collected globally.

Main Results:

• The P. sertularioides complex comprises 14-21 species, with 10 consistently recovered across analyses.
• Two main clades were identified: one European and one encompassing Australia, Brazil, Europe, Panama, and South Africa.
• Morphological analysis revealed a continuum, with regional species being indistinguishable, but distinct from those in other regions.

Conclusions:

• True cryptic diversity exists within the Polysiphonia sertularioides complex, with most species being biogeographically restricted and 10 endemic.
• Highlights the necessity of molecular and morphological studies for small algae (<5 cm) to accurately assess biodiversity.