Predator-inducible defences and local intrapopulation variability of the intertidal mussel Semimytilus algosus in central Chile

Abstract

Predator-inducible defences have a strong influence on the expression of morphological traits of intertidal invertebrates. For instance, mussels exposed to predators often have thicker shells than non-exposed. On the intertidal rocky shores of Chile, the mussel Semimytilus algosus is a preferred prey of many carnivorous invertebrates, including the snails Nucella crassilabrum and Concholepas concholepas, and the crab Acanthocyclus gayi. Preliminary observations indicated that S. algosus exists as 2 morphotypes: a thick, smooth shell and a thinner, ringed shell. The thick-shell morphotype was found mostly on compact, rocky platforms, whereas the thin one was found on emergent rocks. We examined the role of invertebrate predators in determining the morphological differences observed in S. algosus as a process of defence induction. The density and size of mussel predators showed significant differences between habitats: A. gayi dominating the platforms and N. crassilabrum emergent rocks. C. concholepas did not show differences between habitats. Waterborne cue experiments demonstrated that the mussel shell thickness is increased by the presence of predators, especially A. gayi. Furthermore, in contrast to the other predators, A. gayi preferentially selects mussels of the thin-shell morphotype. We demonstrate the cause and effect connection between variation in mussel shell morphology in the laboratory and their associated spatial distribution in the field, as well as the ecological role played by predators. We propose that, at local scales, the distribution and abundance of predators in the field explain the inter-population morphological differences of the mussel S. algosus.

Eastern oysters Crassostrea virginica deter crab predators by altering their morphology in response to crab cues

“…Bivalves readily utilize chemical exudates that emanate from predators and from injured conspecifics to evaluate predation risk (Caro & Castilla 2004, Cheung et al 2004, Smee & Weissburg 2006b. They respond to risk by increasing their burrowing depth (Griffiths & Richardson 2006, Flynn & Smee 2010, reducing their feeding behavior (Smee & Weissburg 2006a,b, Naddafi et al 2007, and increasing their shell thickness (Trussell & Smith 2000, Caro & Castilla 2004, Freeman & Byers 2006.…”

“…They respond to risk by increasing their burrowing depth (Griffiths & Richardson 2006, Flynn & Smee 2010, reducing their feeding behavior (Smee & Weissburg 2006a,b, Naddafi et al 2007, and increasing their shell thickness (Trussell & Smith 2000, Caro & Castilla 2004, Freeman & Byers 2006. Additionally, mussels produce additional byssal threads to in crease the force needed to dislodge them from substrates (Coté 1995, Leonard et al 1999, Shin et al 2009) and increase abductor muscle mass to deter prying predators (Freeman & Byers 2006).…”

Risk recognition and variability in escape responses among intertidal molluskan grazers to the sun star Heliaster helianthus

“…Predators not only have direct effects on prey populations and their communities by causing mortality of prey individuals, but they can also induce non-consumptive effects in the form of reversible or non-reversible phenotypical changes in prey traits, such as morphology (e.g. Lively 1986, Appleton & Palmer 1988, Caro & Castilla 2004, Caro et al 2008, growth (Peckarsky et al 1993, Yamada et al 1998, and behavior (Harrold 1982, Côté & Jelnikar 1999, Espoz & Castilla 2000, Trussell et al 2006, and see Havel 1987, Stearns 1989, Harvell 1990, Lima 1998and Miner et al 2005 for reviews). Indeed, several authors have argued that non-consumptive effects of predation might be equally or even more important than consumptive effects on prey distribution, prey growth rates and even on population abundance and community dynamics (Werner et al ABSTRACT: Escape responses are a common form of inducible defense in the presence of a predator, which can be species-specific and adaptive.…”

Phylogenetically mediated anti-predator responses in bivalve molluscs

“…While treatment-exposed mussels had thicker and heavier shells, this might have been a direct result of reduced feeding time and feeding potential, resulting in lower ingestion rates and diminished but dense shell growth. The results from this study, however, also suggest that reduction in shell and tissue growth may reflect the actual fitness costs of morphological defences, as proposed by Reimer & Tedengren (1996) and Caro & Castilla (2004). Enhanced allocation of resources to shell material resulting in a thicker shell might consequently be compensated for by reduced tissue and shell dimension growth.…”

“…Moreover, increased attachment strength decreases the probability of successful dislodgement by crabs (Hughes & Seed 1995). Induction of specific morphological defences increases survival and fitness in mussels by reducing attractiveness to their predators and predator attack success (Reimer & Tedengren 1996, Smith & Jennings 2000, Caro & Castilla 2004. The ability of Mytilus edulis to develop defences when they are needed rather than those being permanently expressed, i.e.…”