Visual Acuity of the Goby-Associated Shrimp, Alpheus Rapax Fabricius, 1798 (Decapoda, Alpheidae)

Crustaceana 85 (12-13) 1487-1497

VISUAL ACUITY OF THE GOBY-ASSOCIATED SHRIMP, ALPHEUS RAPAX FABRICIUS, 1798 (DECAPODA, ALPHEIDAE)

BY

Z. JAAFAR1) and Y. ZENG Department of Biological Sciences, National University of Singapore, Singapore 117543

ABSTRACT

Species of alpheid shrimp that form symbiotic associations with gobiid fish are believed to possess poor visual capabilities. These shrimps are thought to heavily rely on their gobiid partners to detect threats and predators. The present study tested the visual capabilities of a goby-shrimp, Alpheus rapax Fabricius, 1798 to determine its visual reliance on the goby partner, Myersina macrostoma Herre, 1934. Alpheus rapax was found to possess the ability to perceive the colours green and blue, but not red. Although individuals tested did not respond to stationary figures, a statistically significant number of inviduals elicited a response when presented with a moving object. Results obtained from this study support the hypothesis that A. rapax does have limited visual acuity and is visually reliant on its goby partner while performing various activities outside its burrow. Key words. — Alpheus, Myersina, vision, goby-shrimp, symbiotic association

RÉSUMÉ

Les espèces de crevettes alphéides qui forment des associations symbiotiques avec des poissons gobidés sont supposées présenter de faibles capacités visuelles. On pense que ces crevettes se reposent fortement sur leurs partenaires gobidés pour détecter les dangers et les prédateurs. Cette étude a testé les capacités visuelles de la crevette Alpheus rapax Fabricius, 1798 pour déterminer sa dépendance visuelle à l’égard de son gobie partenaire Myersina macrostoma Herre, 1934. Il a été trouvé que Alpheus rapax possède la capacité de percevoir les couleurs vertes et bleues, mais pas le rouge. Bien que les individus testés n’aient pas répondu à des figures statiques, un nombre d’individus, statistiquement significatif, ont montré une réponse lorsqu’un objet mouvant leur est présenté. Les résultats obtenus dans cette étude confortent l’hypothèse que A. rapax a une acuité visuelle limitée et est visuellement dépendant de son partenaire gobie lorsqu’elle effectue diverses activités en dehors de son terrier.

1) Corresponding author; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2012 DOI:10.1163/15685403-00003128 1488 Z. JAAFAR & Y. ZENG

INTRODUCTION Snapping shrimps of the genus Alpheus Fabricius, 1798 often form symbiotic associations with a variety different organisms, including sponges (Banner & Banner, 1982; Anker et al., 2007), hermatypic corals (Glynn, 1980; Banner & Banner, 1982) and sea anemones (Knowlton, 1980). In some of these associations, the shrimps render protection to host organisms in exchange for shelter and food, such as in the case of Alpheus lottini Guérin Méneville, 1829, which defends its host coral, Pocillopora damicornis (L.), from the corallivorous seastar Acanthaster planci (L.) (Glynn, 1980). Alpheid shrimps are also known to live in association within burrows shared with other organisms such as echiuran worms (Anker et al., 2005, 2007), decapod and stomatopod crustaceans (Felder & Rodriguez, 1993; Froglia & Atkinson, 1998; Dworschak et al., 2000; Anker et al., 2001; Silliman et al., 2003), and gobiid fishes (Karplus, 1987 and references therein). Of these, perhaps the most-studied association is the one with gobiid fishes (e.g. Preston, 1978; Yanagisawa, 1978, 1982, 1984; Karplus, 1987; Randall et al., 2005; Kramer et al., 2009). The association between gobies and snapping shrimps (Alpheus spp.) was first observed by Longley & Hildebrad (1941). Further studies found 13 species of Alpheus associating with about 120 species of gobiid fishes (Karplus & Thompson, 2011). Host shrimps construct complex burrows (Yanagisawa, 1984), providing a refuge from predators both for themselves and for the gobies (Magnus, 1967). The gobies, with a considerably better sense of vision, act as sentinels and in some cases warn their shrimp partners via a tactile warning system (Magnus, 1967; Karplus, 1987). The reliance of these snapping shrimps on their partner gobies was attributed to the poor vision in the former (Karplus & Tuvia, 1972, 1979; Karplus et al., 1972a, b; Karplus, 1987). However, no studies have been performed on the visual capabilities of goby-associated alpheid shrimps. Physiological and behavioural studies have been conducted to determine the vi- sual abilities in several crustacean groups, including stomatopods and brachyuran crabs (Glantz, 1974a, b; Cronin & Jinks, 2001; Berón de Astrada & Tomsic, 2002; Johnson et al., 2002; Marshall et al., 2007). While there exist several studies on visual orientation of alpheid shrimps in host selection (Ache & Davenport, 1972; VandenSpiegel et al., 1998; Huang et al., 2005), the aspect of visual cues had been studied in only one species, Alpheus heterochaelis Say, 1818, which does not form associations with gobiid fishes. In A. heterochaelis visual cues are important in communication between con-specifics (Hughes, 1996a, b), indicating visual capa- bility superior to that expected for goby-associated species of Alpheus (Karplus & Tuvia, 1972; Karplus et al., 1972a, b). The present study thus aimed to determine the visual acuities of a model species of goby-associated shrimp, Alpheus rapax Fabricius, 1798 (fig. 1), with respect to (i) light colour and (ii) motion at close