Sex Life of Branching Worms

[Recusant]

Indeed, a more appropriate title would be "Reproduction of . . ." but I didn't resist the impulse to go for the obvious cliché clickbait. This particular species of branching marine worm, Ramisyllis kingghidorahi lives inside sponges.

These branching marine worms produce a sort of "bud" on the end of a branch, called a stolon. Some may have heard that term in relation to plants--the runners from strawberries are stolons, for instance. These worm stolons grow eyes and an independent nervous system and eventually detach from the main body--swimming off in search of a mate. That mate will be another stolon of the opposite sex. They have that single mission--the paper describes them as "autonomous reproductive units." The female stolons produce eggs, from which I assume larvae would emerge. As yet I've not found what form the larvae take, but it seems likely it would be a drifting/swimming planktonic organism.

I did some looking around and find that I managed to miss earlier items about other species of the Syllidae family that reproduce via stolons.

"A head and a hundred tails: How a branching worm manages reproductive complexity" | Phys.org

Scientists have uncovered the genetic underpinnings of one of the ocean's most bizarre animals: a branching marine worm named Ramisyllis kingghidorahi that lives inside sea sponges and reproduces in a truly extraordinary way. Living hidden in tropical waters, this worm grows multiple body branches within a host sponge, each tail capable of producing separate living reproductive units called stolons.

But how does a single animal coordinate sexual reproduction across so many branches? To find out, researchers led by the University of Göttingen analyzed gene expression across different body regions and between male, female and juvenile specimens. This provides the first complete "genetic activity map"—or transcriptome—of any branching worm, revealing how this creature manages to control reproduction across its branching body.

The researchers found clear patterns in their analyses: Differences in gene activity were more pronounced between different body regions in the same worm than between the sexes. The stolons—short-lived reproductive units that break off from the branches and swim away to mate—had the most distinctive genetic signatures when comparing males and females, probably reflecting their specialized role in gamete production and metamorphosis.

"We were surprised to find that the head of the worm, which was previously thought to house a sex-specific control system, didn't show the dramatic differences we expected between males and females," said Dr. Guillermo Ponz-Segrelles, former researcher at the Autonomous University of Madrid. "Instead, the stolons emerged as the true hotspots of gene activity during sexual development."

[Continues . . .]

The paper is open access:

"Sex-specific differential gene expression during stolonization in the branching syllid Ramisyllis kingghidorahi (Annelida, Syllidae)" | BMC Genomics

Abstract:

Background
Ramisyllis kingghidorahi (Annelida, Syllidae) is one of few annelid species with a ramified body, one anterior end and hundreds of posterior ends. R. kingghidorahi belongs to the family Syllidae, whose members reproduce by forming stolons, small autonomous reproductive units, at the posterior end. Molecular mechanisms controlling sexual reproduction are still poorly understood, but previous studies support an important role of the anterior end and stolons. The roles of different body regions during sexual reproduction in a complex branched body where there is only one head but multiple posterior ends, which develop hundreds of simultaneous stolons, have never been investigated. Consequently, we aimed to research the transcriptomic basis of sexual maturation and stolonization in R. kingghidorahi by performing differential gene expression analyses.

Results
Transcriptomes were assembled from different body regions (anterior end, midbody, and stolons) of male, female, and non-reproductive individuals. Comparative analyses revealed that body region had a greater impact on gene expression profiles than sex, with the anterior end and stolons showing extensive gene upregulation. Across-sex comparisons revealed sex-specific processes in all body regions, with stolons exhibiting the most differences in differential expression, likely related to gametogenesis and external sexual dimorphism. Fewer genes than expected were differentially expressed in the anterior region, a result for which different possible explanations are discussed. Surprisingly, key genes typically associated with segmentation and metamorphosis, such as Wnt and Hox, showed little differential expression, aligning with recent findings that stolon segments lack a specific segment identity.

Conclusions
This study presents the first transcriptomic data for a branched annelid species and offers new insights into the complex genetic regulation of reproduction in R. kingghidorahi. Additionally, it provides the first glimpse into the mechanisms of sexual maturation in branched syllids, which must coordinate stolonization across multiple posterior ends. These findings enhance our understanding of annelid reproductive biology and highlight the need for further research to uncover the physiological and molecular pathways regulating sexual maturation and stolonization in syllids and other annelids.

[Tank]

There has to be a horror/zombie film plot in there somewhere.

[Dark Lightning]

Somebody skin diving and that crap pops up in their face. Yeesh.

[Icarus]

Is there no end to the mysteries that abound on our pale blue dot?