Marine worms fight for control of the territory before their host

Researchers from the Center for Advanced Studies in Blanes of the Higher Council for Scientific Research (CEAB-CSIC) and the Institute of Ecology and Evolution (IEE-RAS) in Moscow (Russia) have described for the first time the behavior of two marine organisms from the group of the polychaete annelids or marine worms: Ophthalmonoe pettibonae, in the role of the symbiote, and Chaetopterus cf. appendiculatus, acting as a host. The results of the study published in the journal Scientific Reports were obtained from observations and experiments carried out both in the field and in the laboratory.

The work, signed by the researchers Daniel martin, CEAB – CSIC and Temir A. Britayev IEE – RAS, reveals for the first time the existence of extremely aggressive behavior in symbiotes, which results in fierce struggles to control the territory, in this case a host or, even in some cases, several hosts, which explains the uniform distribution (one symbiote for each host) observed in natural populations.

They live together in the tube built by the host

Under natural conditions, both worms live together, buried about 20 cm deep in the marine sediment and inside the tube built by the Chaetopterus. Said tube, which is made up of a mucilaginous substance that solidifies on contact with water, acquiring the appearance of an aged parchment, can reach about 80 cm in length and 4 cm in diameter and has two openings (called siphons), which allow the communication with water and measuring 1 cm in diameter.

Reveals for the first time the existence of extremely aggressive behavior in symbiotes

For its part, the body of the Chaetopterus (the host) can reach 20 cm in length, while that of the Ophthalmonoe (the symbiote) barely reaches 4 cm. As the two scientists have observed, the symbiote locates one of the siphons thanks to the stream of water that the host continuously expels to breathe and eat. Thus, Ophthamonoe accesses the interior and is placed near the head of Chaetopterus, with the belly attached to the tube and the back facing the host’s body.

A component of territoriality between symbiotes

“The observations made in the populations of Vietnam led us to think that there must be a territorial behavior between the symbionts, that they could even fight among themselves to maintain control of their host, since this represents a vital resource for their survival”Say the study authors.

The two scientists experimentally studied the influence of the ratio of the number of available hosts on the behavior of the symbionts. To do this, they transferred the host worms from their natural (opaque) tube to an artificial one made of transparent plastic that allowed them to observe what was happening inside.

The experiments show the existence of an extremely aggressive behavior in the symbiotes, which results in fierce struggles to control the territory, in this case a host or, even in some cases, several hosts, which explains the uniform distribution (one symbiote per each host) observed in natural populations.

Symbiotes can move in and out of the host tube, and turf fights to ward off potential competitors also occur outside the tube

Furthermore, they show that symbiotes can enter and exit the host tube and that territorial fights to keep potential competitors away also occur outside the tube. This constitutes the first empirical demonstration that a symbiotic marine invertebrate can control a territory that extends beyond its own host, even including other neighboring hosts.

The fight can include one to three matches

The territorial attacks between specimens of Ophthalmonoe show a clear aggressive component, where the owner of the tube, after locating an intruder who intends to occupy his same tube and approach him protected by the body of the host, attacks him by means of a powerful evagible trunk equipped with a pair of jaws shaped like a parrot’s beak. Both contenders, united by the bite of the owner of the tube, they turn on themselves for a long time, until the aggressor manages to separate a piece of the victim’s body. In fact, each fight episode (which can include between one and three fights), ends up leading to bodily injury.

“Sometimes both contestants show injuries”, say the scientists “since, if the intruder is larger, he can respond to the attack of the owner with another attack and get to force him to leave his own host.” And it is that, apparently, Ophthalmonoe lacks the ritualized behavior that other symbiotic species (for example, crabs) have developed to reduce the risk of injury.

The study provides the first empirical evidence that symbiote bodily injuries were caused during turf fights. It also shows that the lesions found during the experiments were identical to those observed under natural conditions, so the scientists conclude that the presence of bodily injury allows predicting the existence of intraspecific confrontations in symbiotic polychaetes.


Britayev, TA & Martin, D. “Behavioral traits and territoriality in the symbiotic scaleworm Ophthalmonoe pettiboneae”. Scientific Reports


Superior Council of Scientific Investigations

Rights: Creative Commons.

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