Morphological Convergence of Shell Shape in Distantly Related Scallop Species (Mollusca: Pectinidae)
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Whittier College Poet Commons Biology Faculty Publications & Research 2011 Morphological convergence of shell shape in distantly related scallop species (Mollusca: Pectinidae) Alvin Alejandrino [email protected] Jeanne M. Serb Erik Otárola-Castillo Dean C. Adams Follow this and additional works at: https://poetcommons.whittier.edu/bio Part of the Biology Commons Recommended Citation Serb, J. M., Alejandrino, A., Otarola-Castillo, E., & Adams, D. C. (2011). Morphological convergence of shell shape in distantly related scallop species (Mollusca: Pectinidae). Zoological Journal of the Linnean Society, 163(2), 571-584. https://doi.org/10.1111/j.1096-3642.2011.00707.x This Article is brought to you for free and open access by the Faculty Publications & Research at Poet Commons. It has been accepted for inclusion in Biology by an authorized administrator of Poet Commons. For more information, please contact [email protected]. Zoological Journal of the Linnean Society, 2011, 163, 571–584. With 3 figures Morphological convergence of shell shape in distantly related scallop species (Mollusca: Pectinidae) Downloaded from https://academic.oup.com/zoolinnean/article/163/2/571/2625596 by Whittier College user on 17 September 2020 JEANNE M. SERB1*, ALVIN ALEJANDRINO1, ERIK OTÁROLA-CASTILLO1 and DEAN C. ADAMS1,2 1Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA 2Department of Statistics, Iowa State University, Ames, IA 50011, USA Received 3 June 2010; revised 3 October 2010; accepted for publication 4 October 2010 Morphological convergence is a central concept in evolutionary biology, but convergent patterns remain under- studied in nonvertebrate organisms. Some scallop species exhibit long-distance swimming, a behaviour whose biomechanical requirements probably generate similar selective regimes. We tested the hypothesis that shell shape similarity in long-distance swimming species is a result of convergent evolution. Using landmark-based geometric morphometrics, we quantified shell shape in seven species representing major behavioural habits. All species displayed distinct shell shapes, with the exception of the two long-distance swimmers, whose shells were indistinguishable. These species also displayed reduced morphological variance relative to other taxa. Finally, a phylogenetic simulation revealed that these species were more similar in their shell shape than was expected under Brownian motion, the model of character evolution that best described changes in shell shape. Together, these findings reveal that convergent evolution of shell shape occurs in scallops, and suggest that selection for shell shape and behaviour may be important in the diversification of the group.zoj_707 571..584 © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 571–584. doi: 10.1111/j.1096-3642.2011.00707.x ADDITIONAL KEYWORDS: adaptation – convergent evolution – geometric morphometrics – mollusc. One of the most compelling patterns observed in convergent evolution provide strong evidence of a link evolutionary biology is that of morphological and between the selective forces shaping trait evolution behavioural convergence amongst species inhabiting and the evolutionary responses to those forces. As a similar environments at different geographical loca- consequence, convergent evolution has long been tions. Evolutionary convergence frequently occurs treated as evidence of adaptation (e.g. Pagel, 1994; when environmental factors exert strong selection Schluter, 2000; Blackledge & Gillespie, 2004; Harmon pressures on the taxa in those environments, gener- et al., 2005), and the instances of convergent ating similar phenotypic responses amongst them evolution seen in nature demonstrate that in at least (Losos, 1992; Losos et al., 1998; Rüber, Verheyen & some circumstances, common selective pressures can Meyer, 1999; Rüber & Adams, 2001; Melville, Harmon generate repeated and predictable evolutionary & Losos, 2006; Stayton, 2006). Convergence can also responses (Losos et al., 1998). occur from functional or biomechanical requirements, A conspicuous feature in bivalve evolution is the when species exploit a common trophic niche and broad diversity of behaviour and shell shape exhibited respond evolutionarily to those selective constraints throughout the group (Kauffman, 1969; Stanley, 1970, (Herrel et al., 2008; Vincent et al., 2009). Patterns of 1975, 1988; Seed, 1980; Savazzi, 1982). Bivalves are found in a wide range of freshwater and marine habitats and often display particular behaviours asso- *Corresponding author. E-mail: [email protected] ciated with their ecological niche (Stanley, 1970, © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 571–584 571 572 J. M. SERB ET AL. 1972). Species from phylogenetically disparate fami- where there is a tight correlation between shell shape lies frequently occupy common environments and and functional performance, the morphology of that display behavioural habits that are alike (e.g. Stanley, organism is predicted to be under strong selection, 1970: fig. 6). These similar phenotypes demonstrate resulting in a narrow area of morphospace being that distinct behaviours have evolved multiple times occupied by that behavioural group. Alternative mor- in bivalves, suggesting the possibility of adaptive phologies exhibited by members of that behavioural evolution (Stanley, 1970, 1975). In addition, species group that fall outside of the optimal region will have occupying similar niches sometimes exhibit similarity lower performance as compared to individuals exhib- Downloaded from https://academic.oup.com/zoolinnean/article/163/2/571/2625596 by Whittier College user on 17 September 2020 in particular morphological elements of their shells iting more ‘typical’ morphology. Based on such (e.g. Trueman, Brand & Davis, 1966; Stanley, 1981; functional considerations, we can predict that phylo- Watters, 1994; Checa & Jimènez-Jimènez, 2003), indi- genetically distant species with similar performance cating that shell shape may be convergent as well or functional needs will converge on the same region (Kauffman, 1969; Stanley, 1970). However, these ana- of morphospace (Vincent et al., 2009). For scallops, if tomical observations are largely qualitative and effective long-distance swimming requires a specific descriptive; a quantitative test of the hypothesis of shell shape, we predict that species exhibiting this morphological convergence has not been performed. behaviour will be morphologically constrained Bivalved scallops of the family Pectinidae because of the functional demands of this behaviour. Rafinesque, 1815 are a good system to examine con- In this study, we use three-dimensional (3D) vergent evolution, as several species exhibit long- landmark-based geometric morphometric methods to distance swimming via jet propulsion (Gould, 1971; quantify shell shape for the first time, and to compare Morton, 1980; Joll, 1989; Ansell, Cattaneo-Vietti & patterns of variation in shell shape within and Chiantore, 1998). Although all nonpermanently amongst taxa. We examined shells of seven species of attached scallop species have the ability to swim for scallops representing a wide shape range to address short distances (< 1 m) to escape predators or seek the following hypotheses: more favourable surroundings, few species can swim 1. If long-distance swimmers are convergent in shell greater than 5 m in a single swimming effort (Brand, shape, we predict that they will occupy the same 2006). Long-distance swimming (5–30 m/effort) is dis- area in morphospace. tinguished from a common swimming response by the 2. When phylogeny is taken into consideration, we presence of a level swimming phase, where the predict that long-distance swimmers will be more animal is able to maintain a near-horizontal trajec- similar in shell shape to each other than they are tory above the substrate (Morton, 1980; Joll, 1989; to species not displaying this behaviour, such as Ansell, Cattaneo-Vietti & Chiantore, 1998). This epifaunal free-living and byssal attaching species. swimming phase also contains a glide component, 3. We predict that morphological disparity (multi- where the animal is propelled forward while the variate variation) in long-distance swimmers will valves are held closed (Manuel & Dadswell, 1993; be less than the disparity observed in species not Chang, Davison & Demont, 1996; Ansell et al., 1998). exhibiting this behaviour. Neither a level swimming phase nor a glide compo- nent is present in short distance swimming (Marsh, We examined these hypotheses by first identifying Olson & Guzik, 1992; Ansell et al., 1998; Donovan multiple origins for the long-distance swimming et al., 2002), making this a unique behaviour in behaviour through the estimation of ancestral states scallops. Interestingly, long-distance swimming has on a molecular phylogeny. We then evaluated shell evolved multiple times in the Pectinidae (Puslednik & shape morphology for selected taxa that display a Serb, 2008 and below). In addition, long-distance range of behavioural habits, and assessed patterns of swimming scallops possess shells that are qualita- shell shape within and amongst species. Finally, we tively similar in overall shape (Stanley, 1970; determined whether long-distance swimmers exhib- Hayami, 1991; Millward & Whyte, 1992), suggesting ited patterns consistent with the hypothesis of mor- the possibility of repeated coevolution between