Geographic variation in decoration selectivity of Micippa platipes and Tiarinia cornigera in Japan

Abstract

Relatively few studies have compared behavioral variation of more than one species among different locations; yet examining geographic variation in behavior in a comparative context is crucial to help elucidate the generality of geographic patterns. We studied geographic variation in decoration preferences for 2 spider crabs (Brachyura: Majoidea), Micippa platipes and Tiarinia cornigera, which co-occur in intertidal areas along the coast of Japan. Both M. platipes and T. cornigera primarily feed on algae and use them for 'decoration' (i.e. attach them to hooked setae on their carapace). We tested whether individuals from 3 locations along the east coast of Japan differed in their decoration and consumption selectivity for certain algae in the field, and also tested decoration and consumption preferences of M. platipes in laboratory assays. At the 2 more northern locations, both species showed little selectivity among algae, primarily using them for decoration in proportion to their abundance. Conversely, at the southern location, M. platipes exhibited strong preferences for the alga Hypnea pannosa in both field and laboratory assays, and both crab species strongly avoided the alga Corallina pilulifera. Using both an overall selectivity index (SE o ) and a proportional selectivity index (PSE) calculated for each alga, we compared algal use by the crabs vs. algal availability at the 3 locations. Both indices indicated that both species were more selective (had stronger preferences or avoidances of available algae) at the southern location than at the 2 more northern locations. Potential factors driving this latitudinal gradient in selectivity include seasonal and geographic variability in both decoration availability and crab decoration preferences.

The use of specialisation indices to predict vulnerability of coral‐feeding butterflyfishes to environmental change

“…It is possible that species classified as specialists based on studies in a single location may only be functioning as specialists on a local scale, and across their entire geographic range these species may in fact have generalised ecologies (Fox and Morrow 1981). For example, on the south coast of Japan two species of decorator crab ( Micippa platipes and Tiarinia cornigera ) were highly selective in their preferences for algae, but on the north coast both species showed no selectivity (Hultgren et al 2006). Consideration of temporal and spatial variation in specialisation is crucial in systems where resources can become depleted (Pratchett et al 2006) or where the availability of resources may vary seasonally (Varela et al 2008) in order to accurately determine specialisation and predict vulnerability.…”

Patterns of epibiont colonisation on the spider crabInachus communissimus(Decapoda, Inachidae) from the Northern Adriatic Sea (Mediterranean Sea)

“…Indeed, the crabs represent a suitable substrate for many epibionts that may reap advantages in terms of food supply and larval dispersion (Maldonado & Uriz 1992), and the crabs tolerate their presence as they increase their masking level (Dudgeon 1980). Several kinds of organisms, such as algae, sponges, hydroids, bryozoans, amphipods, cirripeds, polychaetes, etc., have been recorded on the crabs (Sato & Wada 2000), and their amount seems to differ in relation to the chemical/mechanical properties of the organism and to the sex and maturity stages of the host (Dudgeon 1980;Maldonado & Uriz 1992;Woods & McLay 1994;Woods & Page 1999;Sato & Wada 2000;Cruz-Rivera 2001;Hultgren et al 2006;Martinelli et al 2006;Berke & Woodin 2008;Hultgren & Stachowicz 2008). It is also known that juvenile crabs undergo frequent moults, each time losing their covering materials (Wirtz & Diesel 1983).…”