Do constructional constraints influence cyprinid (Cyprinidae: Leuciscinae) craniofacial coevolution? C. DARRIN HULSEY* and PHILLIP R. HOLLINGSWORTH JR Department of Ecology and Evolutionary Biology University of Tennessee, 569 Dabney Hall Knoxville, TN 37996, USA Received 19 August 2010; revised 8 December 2010; accepted for publication 8 December 2010 Constraints on form may determine how organisms diversify. As a result of competition for the limited space within the body, investment in adjacent structures could represent an evolutionary compromise. For example, evolutionary trade-offs resulting from limited space in the head could have influenced how the sizes of the jaw muscle, as well as the eyes, evolved in North American cyprinid fishes. To test the evolutionary independence of the size of these structures, we measured the mass of the three major adductor mandibulae muscles and determined the eye volume in 36 cyprinid species. Using a novel phylogeny, we tested the hypotheses that the sizes of these four structures were negatively correlated with each other during cyprinid evolution. We found that evolutionary change in the adductor mandibulae muscles was generally positively and/or not correlated, suggesting that competition for space among cyprinid jaw muscles has not influenced their evolution. However, there was a negative relationship between mass of adductor mandibulae 1 and eye volume, indicating that change in these physically adjacent structures is consistent with an evolutionary constructional constraint. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 136–146. ADDITIONAL KEYWORDS: ecomorphology – freshwater fish – integration – modularity – North America – phylogenetic comparative method. INTRODUCTION For many morphological phenotypes, allocation to one structure may compromise investment in another structure. These trade-offs operate at many levels of biological organization and among diverse com- ponents of organismal design (Garamszegi, Moller & Erritzoe, 2002; Striedter & Northcutt, 2006). From a developmental perspective, if extensive somatic investment is made in one structure, this could limit soma dedicated to the formation of another structure (Emlen, 2001; Moczek & Nijhout, 2004). It is also possible that constructional trade-offs constrain investment in phenotypes because the structural space in organisms is limiting (Barel, 1983; Herrel, Aerts & De Vree, 2000; Devaere et al., 2006). If one structure is enlarged, then it could limit the size of other structures, especially adjacent ones. For example, debate continues regarding the modular versus compensatory evolution of mammalian brains (Barton & Harvey, 2000; de Winter & Oxnard, 2001). Similarly, a recent study of the craniofacial morphol- ogy of cichlid fishes found little evidence to bolster the frequently cited idea that craniofacial constructional constraints were evolutionarily important in teleost fish (Hulsey, Mims & Streelman, 2007). However, the absence of constructional constraints in this unique cichlid lineage might not generally characterize diver- sification in other diverse groups such as cyprinid fishes. To examine a set of long postulated con- structional constraints, we quantified morphology, reconstructed a novel phylogeny, and then employed independent contrasts to examine whether there are any negative correlations among adductor mandibu- lae (AM) muscle masses and/or eye volume in North American cyprinid fishes. Cyprinid fishes represent one of the most species rich groups of teleosts (Strange & Mayden, 2009). In species-rich lineages, identifying what components of *Corresponding author. E-mail: chulsey@utk.edu Biological Journal of the Linnean Society, 2011, 103, 136–146. With 3 figures © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 136–146 136 Downloaded from https://academic.oup.com/biolinnean/article-abstract/103/1/136/2452416 by guest on 06 June 2020