DOES COSMOPOLITANISM RESULT FROM OVERCONSERVATIVE SYSTEMATICS? A CASE STUDY USING THE MARINE SPONGE CHONDRILLA NUCULA

Area of Science:

• Marine Biology
• Systematics
• Genetics

Background:

• The sponge species Chondrilla nucula exhibits a simple morphology and a broad geographical distribution.
• This wide distribution raises questions about whether it represents a single, widely dispersed species or multiple cryptic species.

Purpose of the Study:

• To investigate the population structure of Chondrilla nucula across its extensive range.
• To compare classical (spicule morphology) and molecular (allozymes) methods for species delimitation.
• To identify potential cryptic species within the Chondrilla nucula complex.

Main Methods:

• Sampling of Chondrilla nucula across 10,000 km in the Mediterranean, Caribbean, and Southwest Atlantic.
• Analysis of spicule morphology for taxonomic comparison.
• Allozyme electrophoresis to assess genetic variation and population structure.

Main Results:

• Five distinct genetic forms of Chondrilla nucula were identified, with varying morphological characteristics.
• Spicule size differences did not correlate with genetic divergence, questioning its systematic value.
• The Brazilian population showed significant genetic structuring (FST = 0.21, Ne m = 0.96).

Conclusions:

• The cosmopolitan distribution of Chondrilla nucula is rejected; it comprises multiple distinct genetic lineages.
• Simple morphology can lead to conservative systematics, potentially masking cryptic species in marine invertebrates.
• Reappraisal of spicule size as a primary systematic character is suggested.