Mismatch between shape changes and ecological shifts during the post-settlement growth of the surgeonfish, Acanthurus triostegus

Abstract

BackgroundMany coral reef fishes undergo habitat and diet shifts during ontogeny. However, studies focusing on the physiological and morphological adaptations that may prepare them for these transitions are relatively scarce. Here, we explored the body shape variation related to ontogenetic shifts in the ecology of the surgeonfish Acanthurus triostegus (Acanthuridae) from new settler to adult stages at Moorea Island (French Polynesia). Specifically, we tested the relationship between diet and habitat shifts and changes in overall body shape during the ontogeny of A. triostegus using a combination of geometric morphometric methods, stomach contents and stable isotope analysis.ResultsAfter reef settlement, stable isotope composition of carbon and nitrogen revealed a change from a zooplanktivorous to a benthic algae diet. The large amount of algae (> 75% of stomach contents) found in the digestive tract of small juveniles (25–30 mm SL) suggested the diet shift is rapid. The post-settlement growth of A. triostegus is highly allometric. The allometric shape changes mainly concern cephalic and pectoral regions. The head becomes shorter and more ventrally oriented during growth. Morphological changes are directly related to the diet shift given that a small mouth ventrally oriented is particularly suited for grazing activities at the adult stage. The pectoral fin is more anteriorely and vertically positioned and its basis is larger in adults than in juveniles. This shape variation had implications for swimming performance, manoeuvrability, turning ability and is related to habitat shift. Acanthurus triostegus achieves its main transformation of body shape to an adult-like form at size of 35–40 mm SL.ConclusionMost of the shape changes occurred after the reef colonization but before the transition between juvenile habitat (fringing reef) and adult habitat (barrier reef). A large amount of allometric variation was observed after diet shift from zooplankton to benthic algae. Diet shift could act as an environmental factor favouring or inducing morphological changes. On the other hand, the main shape changes have to be achieved before the recruitment to adult populations and start negotiating the biophysical challenges of locomotion and feeding in wave- and current-swept outer reef habitat.

Ecological characteristics and morphological-genetic differentiation in populations of European mudminnoow (Umbra krameri Walbaum, 1792) from Ba?ka, Ma?va and Semberija

“…Tako, od "Revolucije u morfometriji" (Rohlf & Marcus, 1993), pa do očekivanja da postane nova "tradicionalna" morfometrija (Adams et al, 2004), geometrijska morfometrija nalazi primenu u najrazličitijim taksonomskim, ekološkim i evolucionim studijama varijabilnosti veličine i oblika tela (Corti & Croseti, 1996;Loy et al, 1996Loy et al, , 1998Loy et al, , 1999aLoy et al, , 2000aWalker, 1997;Cavalcanti et al, 1999;Sará et al, 1999;Douglas et al, 2001;Rüber & Adams, 2001;Trapani, 2003;Klingenberg et al, 2003;Winans et al, 2003;Kassam et al, 2004;Gray et al, 2005;Nolte & Sheets, 2005;Johansson et al, 2006;Lopes et al, 2006;Collyer et al, 2007;Costa & Cataudella, 2007;Rincón et al, 2007;Maderbacher et al, 2008;Elmer et al, 2010;Hayden et al, 2010;Dornburg et al, 2011), pojedinih telesnih regiona (Loy et al, 1999b;Cavalcanti, 2004;Johansson et al, 2006;Krabbenhoft et al, 2009;Aguilar-Medrano et al, 2011;Dornburg et al, 2011;García-Rodríguez et al, 2011;Parsons et al, 2011;Frédérich et al, 2012), kao i glavenog skeleta riba (Frédérich et al, 2008a,b;…”

Comparison of isotopic turnover dynamics in two different muscles of a coral reef fish during the settlement phase

“…When sexual maturity is reached (standard length, SL=95 mm), adults move towards the barrier reef community, where they usually form large feeding schools (Randall 1961). Larvae feed on zooplankton while juveniles and adults graze on algae (Frédérich et al 2012). …”

“…These studies have provided reliable data about isotopic turnovers and allow comparisons among species. However few studies have focused on changes in isotope compositions during the growth of coral reef fishes correlated with diet shifts (but see Frédérich et al 2010Frédérich et al , 2012 and information about the dynamics of isotopic turnover during the settlement phase of tropical reef fishes is unavailable.…”

“…In grazing reef fishes (e.g. acanthurids and scarids), there is a drastic ontogenetic shift correlated with a change in prey consumed between settling larvae and adults that corresponds to a diet change from zooplanktivory to benthivory (Frédérich et al 2012). …”

“…We hypothesized that the turnover of both isotopes in the adductor mandibulae would be more rapid than in epaxial musculature, especially for the algal treatment. Indeed, the juvenile oral morphology should become shaped for grazing and algal treatment would stimulate morphological adaptations for biting (Frédérich et al 2012). According to the metamorphosis hypothesis, when reef fishes undergo morphological and physiological changes in a short period of time, we expected carbon and nitrogen composition in each tissue to approximate the equilibrium with the isotopic composition of their diets at the end of the experiments (i.e.…”