Host recognition behaviour and its specificity in pontoniine shrimp Zenopontonia soror (Nobili, 1904) (Decapoda: Caridea: Palaemonidae) associated with shallow-water sea stars

Abstract

Host recognition is characteristic of many symbiotic invertebrates, including decapods. It was previously shown that, as a rule, the wider the range of hosts the less specific is the symbiont's recognition reaction. To test this hypothesis, we investigated pattern of host use, host recognition behavior and its specificity in an obligate generalist symbiont, pontoniine shrimp Zenopontonia soror. Worldwide this symbiont inhabits at least 23 species of shallow-water tropical sea stars, 10 species of which are in the studied area, the Bay of Nhatrang, Vietnam. The main part of the Z. soror population in the Bay is unevenly distributed between 4 abundant sea star species, Acanthaster planci, Culcita novaeguineae, Choriaster granulatus and Linckia laevigata. However, the prevalence of infestation of the latter species was very low despite its abundance. Such distribution across the hosts may be related to their relative size and morphological complexity. It seems that the distribution and the number of Z. soror shrimp in the Bay are controlled not only by the number, but also by species composition of the hosts. Host selection experiment in aquaria showed that Z. soror is able to recognize and distinguish the host species with which they were associated in the sea (C. novaeguineae or A. planci) among other sea stars including species recorded as possible hosts (L. laevigata, A. planci, and C. novaeguineae). Experimental results demonstrated that the symbiont-host relationship is based on host chemical and visual cues, however, symbionts' reaction to visual cues and their ability to recognize objects visually was low. Our data show that even generalists symbionts have specificity, which is probably supported by the habit forming to a specific species of host (host-imprinting).