Vol. 62-18, 2023
Understanding the Symbiotic Relationship between the Sea Urchin Loxechinus albus (Molina, 1782) and the Pea Crab Pinnaxodes chilensis (H. Milne Edwards, 1837): a Potential Parasitism
Hans N. Jaramillo
Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile.
Luis P. Salas-Yanquin
Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile.
Joseline A. Büchner-Miranda
Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile.
Víctor M. Cubillos
Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile.
Jaime A. Montory
Universidad de Los Lagos, Centro i~mar, Camino a Chinquihue km 6, Puerto Montt, Chile.
Jan A. Pechenik
Biology Department, Tufts University, Medford, MA 02155, USA.
Luis M. Pardo
Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile.
Oscar R. Chaparro
Universidad Austral de Chile, Instituto de Ciencias Marinas y Limnológicas, Valdivia, Chile.
Communicated by James D. Reimer
The echinoderm Loxechinus albus has a symbiotic relationship with the pinnotherid crustacean Pinnaxodes chilensis. Females of the crustacean develop in the terminal section of the sea urchin’s digestive system, remaining there for life. This relationship has been suggested as commensalism. However, a potential negative impact on gonadal development and on the morphology of the sea urchin’s digestive system suggest that it is instead parasitic. To study if there is a negative impact of the crustacean symbiont on the host, specimens of L. albus of all sizes were collected from a rocky shore in southern Chile. The gonadal and somatic tissues of sea urchins that were and were not harboring the pinnotherid were weighed and compared. Our results show that the presence of the pinnotherid was related to sea urchin gonads of lower biomass, decreased gonadosomatic index levels, and alterations in the morphology of the terminal portion of the host digestive system. The lower gonadal biomass suggests a negative impact on gamete production as well as a diversion of energy due to changes of the digestive system tissues and the potential consumption of algal food by the resident crustacean. These results suggest that the prolonged relationship between these two species is one of parasitism rather than one of commensalism.
Keywords
Parasitism, Symbiosis, Sea urchins, Pinnotherid, Crustacean.
Supplementary materials
A) Relationship between sea urchin test diameter and total wet weight for parasitized sea urchin males (red circles) and females (blue circles). B) Relationship between the total wet weight of male (red circles) and females (blue circles) host sea urchins and the carapace length of the pinnotherid. N = 62.
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A) Relationship between sea urchin test diameter and dry gonadal weight in males (red circles) and females (blue circles) of parasitized sea urchins. B) Relationship between the gonad dry weight of male (blue circles) and female (red circles) sea urchin and the carapace length of the hosted pinnotherid. N = 62.
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A) Relationship between sex (red circles: male, blue circles: female) of the sea urchin host on non- gonadal tissue weight. B) Influence of the size of the hosted pinnotherid on the dry non-gonadal tissue weight of the male (read circles) and females (blue circles) of sea urchin specimens collected in the Calfuco Becah. N = 62.
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