Territoriality and Conflict Avoidance Explain Asociality (Solitariness) of the Endosymbiotic Pea Crab Tunicotheres moseri

Abstract

Host monopolization theory predicts symbiotic organisms inhabiting morphologically simple, relatively small and scarce hosts to live solitarily as a result of territorial behaviors. We tested this prediction with Tunicotheres moseri, an endosymbiotic crab dwelling in the atrial chamber of the morphologically simple, small, and relatively scarce ascidian Styela plicata. As predicted, natural populations of T. moseri inhabit ascidian hosts solitarily with greater frequency than expected by chance alone. Furthermore, laboratory experiments demonstrated that intruder crabs take significantly longer to colonize previously infected compared to uninfected hosts, indicating as expected, that resident crabs exhibit monopolization behaviors. While territoriality does occur, agonistic behaviors employed by T. moseri do not mirror the overt behaviors commonly reported for other territorial crustaceans. Documented double and triple cohabitations in the field coupled with laboratory observations demonstrating the almost invariable success of intruder crabs colonizing occupied hosts, suggest that territoriality is ineffective in completely explaining the solitary social habit of this species. Additional experiments showed that T. moseri juveniles and adults, when searching for ascidians use chemical cues to avoid hosts occupied by conspecifics. This conspecific avoidance behavior reported herein is a novel strategy most likely employed to preemptively resolve costly territorial conflicts. In general, this study supports predictions central to host monopolization theory, but also implies that alternative behavioral strategies (i.e., conflict avoidance) may be more important than originally thought in explaining the host use pattern of symbiotic organisms.

Host-use pattern of the shrimp Periclimenes paivai on the scyphozoan jellyfish Lychnorhiza lucerna: probing for territoriality and inferring its mating system

“…Our observations also agree with previous studies conducted in other localities that have reported P. paivai living gregariously on the surface of the same or a different host species (e.g., [33,34]). By contrast to that observed in P. paivai, territorial species display a uniform population distribution and live solitarily (or in male-female pairs) in/on their respective host species with a frequency greater than expected by chance alone [25,27,55].…”

“…Also in agreement with theory, other symbiotic species live in large non-territorial aggregations in naturally abundant, relatively large and morphologically complex host species [18,27]. Although our understanding about the environmental conditions driving the host-use pattern of symbiotic crustaceans has improved considerably during the last decade (e.g., [12,25]), more studies are needed before major generalizations regarding the mechanisms explaining the social behavior of symbiotic crustacean can be formulated.…”

“…We compared the observed distribution (i.e., frequency of occurrence of hosts with zero, one, two, three or four shrimps) with the Poisson random distribution [45]. If P. paivai exhibits territoriality, then the number of symbiotic guest per host individual should be one (on average) and P. paivai is expected to exhibit a uniform distribution on its host species (see, [25]). By contrast, if P. paivai is not territorial, this shrimp should exhibit a random and/or aggregate (contagious) distribution [27].…”

“…Even other symbiotic crustaceans form complex societies i.e., the sponge-dwelling eusocial shrimp Synalpheus regalis Duffy, 1996 [19]. The variety of host-use patterns exhibited by symbiotic crustaceans coupled with disparity in host ecology [20] makes these species excellent models to study the effects of environmental conditions on the social behavior of marine organisms [21][22][23][24][25][26].…”

Population distribution, host-switching, and chemical sensing in the symbiotic shrimp Lysmata pederseni: implications for its mating system in a changing reef seascape

“…These strategies often involve sensing of water-borne sound (Schwartz et al 2004), visual signals (Díaz and Thiel 2004), chemical cues (Ginzel and Hanks 2005), or a combination of two or more of the above (Uetz et al 2009). Cues might originate either from members of the opposite sex (Díaz and Thiel 2004) or from the refuges (i.e., host species in symbiotic organisms) harboring them (Ginzel and Hanks 2005;Ambrosio and Baeza 2016), and the efficiency with which individuals transmit and/or perceive cues depends on environmental conditions. In shallow marine environments, for instance, sound and light propagation can be erratic (e.g., due to sudden shifts in water turbidity and/or density; Astoreca et al 2006), in turn impacting the ability to perceive the direction and/or distance of the signal's origin (Meager et al 2005).…”