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Beren W. Robinson - One of the best experts on this subject based on the ideXlab platform.
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Adult Snapping Turtle ( Chelydra serpentina ) Feeding on Goldeneye Embryos of Pumpkinseed ( Lepomis Gibbosus ) in Defended Nests
The Canadian Field-Naturalist, 2018Co-Authors: Alexanader J. Buse, Meghan A. Douglas, Thomas N. Giguere, Beren W. RobinsonAbstract:Rarely observed predatory behaviour of adult Snapping Turtles ( Chelydra serpentina ) was recorded using remote video technology. We observed turtles inspecting and, in one case, apparently feeding on goldeneye stage embryos (< 3 mm) from defended nests of Pumpkinseed ( Lepomis Gibbosus ). This novel behaviour was limited to nests in a secluded bay and was not observed at nests located along exposed shorelines or on shallow shoals in the deep open water habitat of an inland oligotrophic lake. The benefit of feeding on small prey is likely enhanced by embryos being clustered in nests and by an abundance of sunfish nests. Low-cost and low-intrusion video technology provides excellent opportunities, even in aquatic systems, to document novel predator and prey behaviours.
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Flexible mate choice may contribute to ecotype assortative mating in pumpkinseed sunfish (Lepomis Gibbosus).
Journal of evolutionary biology, 2017Co-Authors: Will M. C. Jarvis, Scott F. Colborne, S. M. Comeau, Beren W. RobinsonAbstract:Gene flow is expected to limit adaptive divergence, but the ecological and behavioural factors that govern gene flow are still poorly understood, particularly at the earliest stages of population divergence. Reduced gene flow through mate choice (sexual isolation) can evolve even under conditions of subtle population divergence if intermediate phenotypes have reduced fitness. We indirectly tested the hypothesis that mate choice has evolved between coexisting littoral and pelagic ecotypes of polyphenic pumpkinseed sunfish (Lepomis Gibbosus) that have diverged in morphology and resource use and where intermediate phenotypes have reduced performance. We assessed the ecotype of nesting males and females using stable isotope estimates of diet and a divergent male morphological trait, oral jaw width. We found positive assortative mating between ecotypes in a common spawning habitat along exposed lake shorelines, but contrary to expectations, assortative mating was variably expressed between two sampling years. Although the factors that influence variable assortative mating remain unclear, our results are consistent with mate choice being expressed by ecotypes. Despite being variably expressed, mate choice will reduce gene flow between ecotypes and could contribute to further adaptive divergence depending on its frequency and strength in the population. Our findings add to a growing body of evidence indicating mate choice behaviour can be a plastic trait, an idea that should be more explicitly considered in empirical studies of mate choice as well as conceptual frameworks of mate choice evolution and adaptive divergence.
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Divergent walleye (Sander vitreus)‐mediated inducible defenses in the centrarchid pumpkinseed sunfish (Lepomis Gibbosus)
Biological Journal of the Linnean Society, 2007Co-Authors: Andrzej J. Januszkiewicz, Beren W. RobinsonAbstract:Predation has important ecological and evolutionary consequences. Evolutionary responses to diversifying selection include genetic differentiation, the evolution of adaptive phenotypic plasticity, and the genetic differentiation of plastic responses between populations. We tested if pumpkinseed sunfish (Lepomis Gibbosus) respond to predation cues by changing their external body form in functionally sensible ways. We then asked whether predation has influenced the divergence of coexisting littoral and pelagic ecomorphs, by testing for divergent predator-induced responses. Juvenile L. Gibbosus of both ecomorphs were reared with and without predation cues supplied by walleye (Sander vitreus) feeding on L. Gibbosus. Predation cues stimulated increased body depth and dorsal spine length, but no increase in anal spine length or pectoral fin size. The dorsal spines of pelagic ecomorphs also grew longer than did those of littoral ecomorphs, while positive body depth responses were similar in both ecomorphs. This is the second fish taxa in which predator-induced morphological responses have been found, and the first in which divergent responses have been detected between ecomorphs. This suggests that the developmental systems of L. Gibbosus ecomorphs have diverged under selection related to predation. We propose that other 'resource polymorphisms' in fishes have evolved under selection arising from a variety of factors, including predation, and not just selection related to resource use.
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Foraging performance of diet-induced morphotypes in pumpkinseed sunfish (Lepomis Gibbosus) favours resource polymorphism.
Journal of evolutionary biology, 2007Co-Authors: Kevin J. Parsons, Beren W. RobinsonAbstract:Morphological plasticity can influence adaptive divergence when it affects fitness components such as foraging performance. We induced morphological variation in pumpkinseed sunfish (Lepomis Gibbosus) ecomorphs and tested for effects on foraging performance. Young-of-year pumpkinseed sunfish from littoral and pelagic lake habitats were reared each on a ‘specialist diet’ representing their native habitat-specific prey, or a ‘generalist diet’ reflecting a combination of native and non-native prey. Specialist and generalist diets, respectively, induced divergent and intermediate body forms. Specialists had the highest capture success on their native prey whereas generalist forms were inferior. Specialists faced trade-offs across prey types. However, pelagic specialists also had the highest intake rate on both prey types suggesting that foraging trade-offs are relaxed when prey are abundant. This increases the likelihood of a resource polymorphism because the specialized pelagic form can be favoured by directional selection when prey are abundant and by diversifying selection when prey resources are restricted.
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Natural selection and the evolution of replicated trophic polymorphisms in pumpkinseed sunfish (Lepomis Gibbosus)
Evolutionary Ecology Research, 2004Co-Authors: Christopher J. Jastrebski, Beren W. RobinsonAbstract:Diversifying selection is expected to operate through all phases of adaptive divergence. If selection is not shown to be diversifying at the earliest stages of divergence when phenotypes are minimally differentiated, then this theory can be challenged. We test for evidence of diversifying selection between lake environments in the nascent divergence of pumpkinseed sunfish (Lepomis Gibbosus), a divergence that is embedded in the apparent adaptive radiation of North American sunfishes. Pumpkinseed individuals primarily inhabit and appear partially adapted to either inshore littoral or offshore pelagic habitats and resources, the same environmental axes that differentiate various sunfish taxa. We first demonstrate associations between phenotype, lake habitat and diet between ecomorphs in three populations from the Mazinaw region of Ontario. This confirms that the range of pumpkinseed trophic polymorphism extends beyond the Adirondack region of New York State. Second, we show a replicated pattern of divergence between ecomorphs across 26 populations in Ontario and New York, for four of ten external body form traits predicted to influence habitat-specific swimming and foraging performance. Selection is implicated because replicated divergence among populations at this larger regional scale is unlikely to have arisen through random processes. Plastic responses to environmental conditions contribute to body form variation in sunfish, but preliminary evidence from other studies suggests that it is the plastic developmental system that has begun to diverge between ecomorphs.
Gordon H Copp - One of the best experts on this subject based on the ideXlab platform.
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Trophic consequences of non-native pumpkinseed Lepomis Gibbosus for native pond fishes
Biological Invasions, 2016Co-Authors: Gordon H Copp, J. Robert Britton, Zhiqiang Guo, V. Ronni Edmonds-brown, Josie Pegg, Lorenzo Vilizzi, Phillip I. DavisonAbstract:Introduced non-native fishes can cause considerable adverse impacts on freshwater ecosystems. The pumpkinseed Lepomis Gibbosus, a North American centrarchid, is one of the most widely distributed non-native fishes in Europe, having established self-sustaining populations in at least 28 countries, including the U.K. where it is predicted to become invasive under warmer climate conditions. To predict the consequences of increased invasiveness, a field experiment was completed over a summer period using a Control comprising of an assemblage of native fishes of known starting abundance and a Treatment using the same assemblage but with elevated L. Gibbosus densities. The trophic consequences of L. Gibbosus invasion were assessed with stable isotope analysis and associated metrics including the isotopic niche, measured as standard ellipse area. The isotopic niches of native gudgeon Gobio gobio and roach Rutilus rutilus overlapped substantially with that of non-native L. Gibbosus, and were also substantially reduced in size compared to ponds where L. Gibbosus were absent. This suggests these native fishes shifted to a more specialized diet in L. Gibbosus presence. Both of these native fishes also demonstrated a concomitant and significant reduction in their trophic position in L. Gibbosus presence, with a significant decrease also evident in the somatic growth rate and body condition of G. gobio. Thus, there were marked changes detected in the isotopic ecology and growth rates of the native fish in the presence of non-native L. Gibbosus. The implications of these results for present and future invaded pond communities are discussed.
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Interspecific Aggressive Behaviour of Invasive Pumpkinseed Lepomis Gibbosus in Iberian Fresh Waters
PloS one, 2014Co-Authors: David Almeida, Lorenzo Vilizzi, Raquel Merino-aguirre, Gordon H CoppAbstract:Pumpkinseed Lepomis Gibbosus (L.) are successful invaders in Europe, where this species exerts multiple ecological effects, mainly through trophic interactions. Behavioural interference represents a potential impact for native fauna and this is of particular conservation concern in the Iberian Peninsula because of the highly valuable endemic fauna inhabiting streams of this region. However, aggressive interactions have not previously been examined under natural conditions in Iberian fresh waters. To address this gap in knowledge, the aim of the present study was to assess the effect of pumpkinseed aggression on endemic fauna of an Iberian stream, the River Bullaque (central Spain). In September 2009, we analysed the aggression and environmental contexts of these behavioural interactions by snorkelling: aggressor size, aggression type, shoal size, previous activity to aggression, recipient species, response to aggression, microhabitat structure and prey availability. Small pumpkinseed displayed more threat and fewer pursuit behaviours relative to medium and large individuals, reflecting an ontogenetic behavioural shift from low to high aggression intensity. Small aggressors came from large shoals, with bottom feeding being the most frequently observed activity prior to an aggressive interaction; whereas large pumpkinseed were less gregarious and they were mostly ambulating within the water column prior to aggression. Recipient species of aggression included non-native crayfish and fishes, and more importantly, endemic fishes and frogs. Retreat was the most common response to aggression, irrespective of aggressor size. Small pumpkinseed displayed aggressive behaviours over coarse substrata containing elevated macrobenthos biomass; whereas aggression by large individuals was observed in deeper waters. These findings suggest that small and large pumpkinseed exert a high impact on other stream residents through aggression in competition for food and territory defence, respectively. This study highlights the usefulness of direct observations in the wild for assessing the effects of behavioural interference of invasive fishes on Iberian aquatic communities.
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Cuckoldry features of introduced pumpkinseed sunfish (Lepomis Gibbosus) in contrasting environmental conditions in southern Europe
Canadian Journal of Zoology, 2012Co-Authors: David Almeida, Ibon Tobes, Rafael Miranda, Gordon H CoppAbstract:Reproduction of pumpkinseed sunfish (Lepomis Gibbosus (L., 1758)) in the species’ native range often involves cuckoldry, consisting of dominant nest-guarding (parental) males and the participation by small “sneaker” males. However, it remains unknown whether this behaviour occurs in populations of non-native pumpkinseed. Thus, the present study describes the phenotypic features of cuckoldry under contrasting environmental conditions (lentic versus lotic) in southern Europe. Parental and sneaker pumpkinseeds were captured in the summer of 2011 from the River Bullaque (central Spain) and from the Encinarejo Reservoir (southern Spain). No differences in total length were observed in sneaker males, although individuals of ages 1+ and 2+ were significantly predominant in the river and the reservoir, respectively. Parental males were larger and older in the reservoir than in the river. Gonadosomatic and hepatosomatic indices were significantly higher in sneaker than in parental males at both sites. Body conditi...
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Heated competition: how climate change will affect non-native pumpkinseed Lepomis Gibbosus and native perch Perca fluviatilis interactions in the U.K.
Journal of fish biology, 2011Co-Authors: Emily K. Fobert, Michael G. Fox, M. Ridgway, Gordon H CoppAbstract:Heated and ambient temperature experimental ponds were used to examine competition between introduced pumpkinseed Lepomis Gibbosus and native perch Perca fluviatilis in England, U.K., and how these interactions are likely to change under climate warming conditions. Results from three sets of two-week experiments indicated that in both species and in all sets, growth was faster in heated than in ambient temperature ponds. Growth of both P. fluviatilis and L. Gibbosus in sympatry did not differ significantly from that observed in allopatric ponds. Diet analysis indicated that increased resource partitioning occurred when P. fluviatilis and L. Gibbosus were reared in sympatry, with P. fluviatilis shifting to a diet higher in microcrustaceans. The results do not support the previous claims of adverse effects of L. Gibbosus on P. fluviatilis populations. Under conditions of climate change, however, which have been demonstrated experimentally to enhance L. Gibbosus recruitment, this species is expected to become invasive in England, resulting in higher densities that may exert a stronger competitive effect than examined in this study.
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the effect of elevated temperature on spawning of introduced pumpkinseed Lepomis Gibbosus in europe
Journal of Fish Biology, 2010Co-Authors: G Ziȩba, Gordon H CoppAbstract:In an experimental comparison of pumpkinseed Lepomis Gibbosus reproduction under ambient and climate change water temperature regimes, spawning occurred earlier in the season, which is likely to lead to greater young-of-the-year survival with concomitant implications in the U.K. under warmer climatic conditions.
Michael G. Fox - One of the best experts on this subject based on the ideXlab platform.
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Impact of the cestode Triaenophorus nodulosus on the exotic Lepomis Gibbosus and the autochthonous Perca fluviatilis.
Parasitology, 2014Co-Authors: Gérard Masson, Michael G. Fox, M. Vanacker, Jean-nicolas BeiselAbstract:The effects of plerocercoids of the cestode Triaenophorus nodulosus infecting the livers of native Eurasian perch Perca fluviatilis and non-native pumpkinseed Lepomis Gibbosus was investigated in 17 sites along the Moselle watershed. With a single exception, infected individuals were not observed in the main channel whether or not northern pike Esox lucius , a final host, was present. In ponds where the pike was present, the prevalence of T. nodulosus averaged 86% in Eurasian perch and 15% in pumpkinseed. The parasite was not present at all in ponds when pike were absent. Parasite load, hepatosomatic index (HSI), gonadosomatic index (GSI) and body condition index (CI) were compared between hosts in one site where parasite prevalence and fish abundance was highest. HSI in infected perch was significantly higher than in uninfected perch, whereas no differences in HSI were detected between infected and uninfected pumpkinseed. While perch were more frequently infected and had a greater average parasite load than pumpkinseed, there were no significant differences in either indicator between the two species. Furthermore, no significant differences in GSI or CI were observed between infected and uninfected fish in either species, by either gender or maturity stage. We hypothesize that pumpkinseed is more resistant to the parasite or less likely to feed upon infected copepods than perch.
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Heated competition: how climate change will affect non-native pumpkinseed Lepomis Gibbosus and native perch Perca fluviatilis interactions in the U.K.
Journal of fish biology, 2011Co-Authors: Emily K. Fobert, Michael G. Fox, M. Ridgway, Gordon H CoppAbstract:Heated and ambient temperature experimental ponds were used to examine competition between introduced pumpkinseed Lepomis Gibbosus and native perch Perca fluviatilis in England, U.K., and how these interactions are likely to change under climate warming conditions. Results from three sets of two-week experiments indicated that in both species and in all sets, growth was faster in heated than in ambient temperature ponds. Growth of both P. fluviatilis and L. Gibbosus in sympatry did not differ significantly from that observed in allopatric ponds. Diet analysis indicated that increased resource partitioning occurred when P. fluviatilis and L. Gibbosus were reared in sympatry, with P. fluviatilis shifting to a diet higher in microcrustaceans. The results do not support the previous claims of adverse effects of L. Gibbosus on P. fluviatilis populations. Under conditions of climate change, however, which have been demonstrated experimentally to enhance L. Gibbosus recruitment, this species is expected to become invasive in England, resulting in higher densities that may exert a stronger competitive effect than examined in this study.
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Morphological diversification in introduced pumpkinseed (Lepomis Gibbosus): assessing truss-based and geometric morphometric approaches
Fundamental and Applied Limnology, 2011Co-Authors: Yakuta Bhagat, Michael G. Fox, Maria Teresa FerreiraAbstract:We examined morphological diversification in introduced pumpkinseed, Lepomis Gibbosus from Iberian reservoirs using traditional morphometric (TM) and geometric morphometric (GM) approaches to assess the degree of external differentiation among pumpkinseeds occupying four habitats separated along simultaneous dimensions of flow and trophic structure. Results from both approaches showed significant differentiation among pumpkinseeds occupying these habitats. Among functional characters deemed significant in differentiating among morphs, body depth and caudal dimensions were the most consistently significant under the TM approach, whereas differences in the caudal peduncle region were more evident under the GM approach. Recent comparative studies advocate the use of GM over TM; however, our results demonstrate that TM is beneficial for quantifying differences in specific morphological characters, which is the crux of studies in functional morphology.
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Genetic relationships among pumpkinseed (Lepomis Gibbosus) ecomorphs in freshwater reservoirs of Portugal
Ecology of Freshwater Fish, 2011Co-Authors: Yakuta Bhagat, Michael G. Fox, Chris C. Wilson, M. Teresa FerreiraAbstract:High levels of morphological differentiation have been found among pumpkinseeds (Lepomis Gibbosus) occupying four habitat types in Portuguese reservoirs. To investigate the underlying mechanism behind the phenotypic differentiation among ecomorphs, we used six microsatellite markers to assess patterns of genetic differentiation among and within eight naturalised reservoir populations. Greater genetic differentiation was seen among reservoir populations than within reservoirs (FST > 0.041, P < 0.002). structure analysis revealed the presence of two distinct genetic groups among the set of eight reservoir populations. However, an analysis of co- occurring forms that were identified a priori by their respective habitats was consistent with a single panmictic group, suggesting that morphological differentiation has arisen in sympatry (i.e., within a reservoir, postintroduction). The observed relationships within and among reservoir populations, combined with the timeframe of ecomorph divergence, suggest the strong likelihood of phenotypic plasticity as the underlying mechanism of diversification in the introduced pumpkinseed.
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Life-history traits and potential invasiveness of introduced pumpkinseed Lepomis Gibbosus populations in northwestern Europe
Biological Invasions, 2009Co-Authors: Julien Cucherousset, Gordon H Copp, Michael G. Fox, E Sterud, H.h. Van Kleef, Hugo Verreycken, Eva ZáhorskáAbstract:To evaluate the potential invasiveness of pumpkinseed Lepomis Gibbosus introduced to northwestern European inland waters, growth and reproduction traits were examined in ten populations along a trajectory spanning northwestern Europe (Norway, England, Holland, Belgium and France) and evaluated in light of published dataset from Europe. In the 848 pumpkinseed captured, maximum age was 3–4 years, with a sex ratio near unity in all but one population. Significant variations with increasing latitude were observed in adult growth (age 2–3 increment in total length, TL) and mean age at maturity (AM), with non-significant variations observed in juvenile growth (TL at age 2), sex ratio and gonado-somatic index. As observed elsewhere in Europe, mean AM decreased significantly with increasing TL at age 2. Using this relationship, which has been proposed elsewhere as a potential predictive model of pumpkinseed invasiveness, eight of the ten populations could be provisionally categorized as ‘non-invasive’ (five populations), ‘transitional’ (one population) and ‘potentially invasive’ (two populations), with two populations not categorized due to insufficient data. Based on the available knowledge on each population, the relationship between juvenile growth and age at maturity appeared to predict reasonably the status of pumpkinseed in northwestern Europe and its applicability to other species should be tested.
Peter C. Wainwright - One of the best experts on this subject based on the ideXlab platform.
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Variation in resource abundance affects diet and feeding morphology in the pumpkinseed sunfish (Lepomis Gibbosus)
Oecologia, 1992Co-Authors: Gary G. Mittelbach, Craig W. Osenberg, Peter C. WainwrightAbstract:The pumpkinseed sunfish ( Lepomis Gibbosus Linnaeus; Centrarchidae) feeds extensively on molluscs, crushing them between its pharyngeal jaws. To address whether differences in mollusc availability might affect pumpkinseed diet and jaw morphology, we collected pumpkinseed from six Wisconsin lakes that varied in mollusc abundance and diversity. The percentage of molluscs in the diet increased directly with mollusc abundance. Moreover, there was a positive correlation between the mass of the pumpkinseed's main crushing muscle, the levator posterior, and the percentage of molluscs in the diet. These data support our previous work in two Michigan lakes showing that pumpkinseed pharyngeal jaws were more robust, and mollusc crushing performance improved, in a lake with higher mollusc densities. The combined Wisconsin and Michigan data exhibit a single relationship between levator posterior mass and percentage of molluscs eaten. Taken together, these studies demonstrate strong, functional relationships between prey availability, diet, morphology, and feeding performance, and suggest how morphology and feeding efficiency may evolve in response to variation in resource density.
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Trophic polymorphism in the pumpkinseed sunfish (Lepomis Gibbosus Linnaeus) : effects of environment on ontogeny
Functional Ecology, 1991Co-Authors: Peter C. Wainwright, Craig W. Osenberg, G. G. MittelbachAbstract:The effects of diet on morphology of the feeding apparatus were explored in the pumpkinseed sunfish, Lepomis Gibbosus Linnaeus. Adult pumpkinseeds feed primarily on gastropod molluscs that they crush between their pharyngeal jaws. Development of the muscles and bones of the pharyngeal jaws was contrasted in two Michigan (USA) lakes that differed both in snail density and in the numbers of snails in pumpkinseed diets. In least squares regressions of muscle masses, bone masses and bone shape variables on body mass, all structures examined showed isometry or positive allometry, with those structures most directly involved in snail crushing tending to scale with positive allometry. Of nine pharyngeal jaw muscles that were examined, analyses of covariance found six to be significantly larger in fish from snail-rich Three Lakes. The primary crushing muscle, the levator posterior, was more than twice as massive in Three Lakes fish than it was in fish from snail-poor Wintergreen lake. All three of the pharyngeal jaw bones used to exert crushing forces on snails were found to be significantly larger and of different shape in fish from Three Lakes. The masses of one muscle and two bones that do not function in prey crushing showed no differences between lakes. Teeth on the crushing surfaces of the jaw bones were worn down, and thus, shorter :tPresent address: P. C. Wainwright, Department of Biological Sciences, Florida International University, Miami, Florida 33199, USA. in Three Lakes fish. Ontogenetic variation in growth rates of two muscles, the levator posterior and the retractor dorsalis, occurred in fish from Three Lakes. These muscles exhibited strong positive allometry between 40 and 80mm standard length (SL), the size range over which fish diets shift from soft-bodied invertebrates to snails, but growth slowed to strong negative allometry in fish larger than 80 mm. These differences between lakes in muscle and bone growth appear to be a direct consequence of the physical regime created by repeatedly crushing snails during ontogeny. This plasticity indicates that transformations in the feeding mechanism may originate as specific responses to the demands of novel diets. Key-words: Allometry, Lepomis Gibbosus, ontogeny, phenotypic plasticity
G. G. Mittelbach - One of the best experts on this subject based on the ideXlab platform.
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Trophic polymorphism in the pumpkinseed sunfish (Lepomis Gibbosus Linnaeus) : effects of environment on ontogeny
Functional Ecology, 1991Co-Authors: Peter C. Wainwright, Craig W. Osenberg, G. G. MittelbachAbstract:The effects of diet on morphology of the feeding apparatus were explored in the pumpkinseed sunfish, Lepomis Gibbosus Linnaeus. Adult pumpkinseeds feed primarily on gastropod molluscs that they crush between their pharyngeal jaws. Development of the muscles and bones of the pharyngeal jaws was contrasted in two Michigan (USA) lakes that differed both in snail density and in the numbers of snails in pumpkinseed diets. In least squares regressions of muscle masses, bone masses and bone shape variables on body mass, all structures examined showed isometry or positive allometry, with those structures most directly involved in snail crushing tending to scale with positive allometry. Of nine pharyngeal jaw muscles that were examined, analyses of covariance found six to be significantly larger in fish from snail-rich Three Lakes. The primary crushing muscle, the levator posterior, was more than twice as massive in Three Lakes fish than it was in fish from snail-poor Wintergreen lake. All three of the pharyngeal jaw bones used to exert crushing forces on snails were found to be significantly larger and of different shape in fish from Three Lakes. The masses of one muscle and two bones that do not function in prey crushing showed no differences between lakes. Teeth on the crushing surfaces of the jaw bones were worn down, and thus, shorter :tPresent address: P. C. Wainwright, Department of Biological Sciences, Florida International University, Miami, Florida 33199, USA. in Three Lakes fish. Ontogenetic variation in growth rates of two muscles, the levator posterior and the retractor dorsalis, occurred in fish from Three Lakes. These muscles exhibited strong positive allometry between 40 and 80mm standard length (SL), the size range over which fish diets shift from soft-bodied invertebrates to snails, but growth slowed to strong negative allometry in fish larger than 80 mm. These differences between lakes in muscle and bone growth appear to be a direct consequence of the physical regime created by repeatedly crushing snails during ontogeny. This plasticity indicates that transformations in the feeding mechanism may originate as specific responses to the demands of novel diets. Key-words: Allometry, Lepomis Gibbosus, ontogeny, phenotypic plasticity