Interpecfic difeernces in the phenotypic plasticity

JOURNAL OF CRUSTACEAN BIOLOGY, 30(3): 357-365, 2010

INTERSPECIFIC DIFFERENCES IN THE PHENOTYPIC PLASTICITY OF INTERTIDAL BARNACLES IN RESPONSE TO HABITAT CHANGES ´ Boris A Lopez, Roxana P Ramırez, Sandra Y Guaito, and Daniel A Lopez ´ ´
(BAL, corresondence, borislop@ulagos.cl); (RPR, rramirez@ulagos.cl); (SYG, sguaitro@ulagos.cl); (DAL, dlopez@ulagos.cl); Departamento de Acuicultura yRecursos Acuaticos, Universidad de Los Lagos, Casilla 933, Osorno, Chile ´ ABSTRACT
We evaluate the morphological variation of cirri of two intertidal barnacles in response to different wave-exposure regimes and population densities during growth. Length, diameter and number of segments of the third and sixth cirri were determined in Jehlius cirratus and Notochthamalus scabrosus, two dominant sympatricspecies in the rocky intertidal zone of Chile. Aggregated and isolated individuals of both species were collected in two coastal localities. Reciprocal transplant experiments were undertaken between waveprotected and wave-exposed zones, in addition to experimental modification of density during growth. For both species, individuals inhabiting wave-protected zones had cirri that were longer,thinner, with a greater number of segments, than in those inhabiting waveexposed zones. The sixth cirri of J. cirratus were longer, thicker and had more segments in specimens growing at high densities, than in individuals growing in isolation. In N. scabrosus, no density dependent effects were observed in cirral structure. Thus, phenotypic responses differed between species, depending on themorphometric or meristic variable of the cirral pair evaluated. Forty-five days after J. cirratus density conditions and wave-exposure regime were modified in the transplant experiments, changes were observed in cirral length, diameter, and number of cirral segments. No modification was observed in the cirral characteristics over time in specimens whose density was artificially reduced during growth. Resultsindicate that morphological structures associated with filtration and respiration, vary according to density and degree of wave-exposure. We suggest that cirral phenotypic variability can serve as an adaptive mechanism associated with the changing availability and access to food and contributes to explaining the success of these organisms in environments with high spatial-temporal fluctuations inbiotic and abiotic factors.

KEY WORDS: barnacles, cirral morphology, density dependence, phenotypic plasticity, transplants, waveexposure DOI: 10.1651/09-3211.1

INTRODUCTION Phenotypic plasticity is the variation of morphological characteristics in individuals of the same species, in response to local environmental variables (Stearns, 1989). The capacity to present different phenotypes canimprove survival and reproduction in populations that inhabit heterogeneous environments (Lively, 1999). Phenotypic plasticity has been reported in different species of sessile or semi-sessile marine invertebrates that inhabit the intertidal zone, due to their exposure to high spatial-temporal fluctuations in physical, chemical and biological factors (Kaandorp, 1999; Okamura and Partridge, 1999;Arsenault et al., 2001; Zhang, 2006). In the particular case of barnacles, it has been reported that exposure to predators can stimulate the rotation or reduction of the opercular aperture area (Lively, 1986a, b; Jarrett, 2008, 2009). Waveexposure level also produces morphological changes in the calcareous structures and the chitinous exoskeleton of individuals (Pentcheff, 1991; Arsenault et al.,2001; Miller, 2007; Neufeld and Palmer, 2008; Hoch, 2008, 2009). The cirri of individuals in wave-exposed environments tend to be shorter and thicker than those inhabiting wave-protected zones (Arsenault et al., 2001; Marchinko and Palmer, 2003; Li and Denny, 2004; Miller, 2007). This has been interpreted as a mechanism to increase particle capture efficiency (Arsenault et al., 2001). Cirral...