Genetic variation in the brooding brittle-star: a global hybrid polyploid complex?

Area of Science:

• Marine Biology
• Genomics
• Evolutionary Biology

Background:

• Amphipholis squamata is a widespread brittle-star species.
• It displays simultaneous hermaphroditism, complex mitochondrial phylogeography, and unusual sperm morphology.
• Previous studies indicated high levels of inbreeding or clonality.

Purpose of the Study:

• To investigate the nuclear genome composition of Amphipholis squamata.
• To understand the genetic basis of its reproductive complexity.
• To determine if it represents a hybrid polyploid asexual complex.

Main Methods:

• Exon-capture and transcriptome sequencing were employed.
• Single nucleotide polymorphism (SNP) analysis was used to assess ploidy.
• Comparative genomics with related genera were performed.

Main Results:

• The nuclear genome contains multiple (>3) divergent expressed components (π > 6%).
• Highly divergent mitochondrial lineages (>20%) were observed across samples.
• A massive sperm genome size, an order of magnitude larger than related species, was reported, consistent with elevated ploidy.

Conclusions:

• Amphipholis squamata likely represents a hybrid polyploid asexual complex with variable subgenome origins, ploidy, and reproductive modes.
• This finding provides a new perspective on the evolutionary biology of echinoderms.
• It may be the first reported allopolyploid complex within the phylum Echinodermata.