Comparative allometric variation in intertidal chitons (Polyplacophora: Chitonidae)
Allometry involves the study of the relationship between size and shape of an individual, and in particular, the manner in which shape depends on size. Animals with multi-element skeletons may have differing growth allometries in different parts of the body. Chitons, for example, have eight overlapping shell plates or valves of three distinct types: head (one plate), intermediate (six plates), and tail (one plate). The overall chiton body is ellipsoidal and different species differ in their eccentricity. The aim of this study was to examine overall allometry in size and shape over adult ontogeny, and how these patterns vary among four closely related species of intertidal chitons from Southeastern Pacific Ocean. For each specimen (n = 407), measurements were taken of total body length and the exposed anterio-posterior lengths of the eight shell plates. Multivariate allometry was evaluated by means of a principal component analysis for each species separately, and for the total. The results showed differential allometric growth of specific skeletal elements, which varied among species; however, there was no clear evidence for specific differentiable growth stages. The overall trend among the combined species was for weakly positive allometry of shell plate widths, but isometric growth of total length and width; thus, the lateral proportion of the animal occupied by shell increases over growth and conversely “thinner looking” girdles may be generally indicative of older animals.
KeywordsAllometry Shell shape Growth Polyplacophorans Morphometry Southeastern Pacific
This study was financially supported by FONDECYT #1130266 Grant “Evolutionary biogeography of the Southeastern Pacific polyplacophorans” to C.M. Ibáñez. We are grateful to F. Alfonso, A. Cifuentes, S. Curaz, A. Fabres, A. Navarrete, M.C. Pardo-Gandarillas, V. Sanhueza, J. Salazar, C. Tobar and G. Torretti for their assistance in field and laboratory work.
Compliance with ethical standards
This research was approved by the Universidad Andres Bello ethical committee and the Chilean government through FONDECYT. The manuscript has not been submitted to more than one journal for simultaneous consideration nor has it been published previously.
Conflict of interest
The authors declare that they have no conflict of interest with any other projects, researchers or organizations, commercial or otherwise.
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