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Using Thin-plate Spline Grids in Modeling Sex Differences in the Shapes of the Apical Disc in the Sea Urchin Tripneustes gratilla

By: Alinasser Alfad Yusop, Nurullaji Aguil, Roldan Echem, Mark Anthony J. Torres

Key Words: Thin-plate spline grids, Tripneustes gratilla, Geometric Morphometrics, Sexual Dimorphism, Sea Urchin.

J. Bio. Env. Sci. 8(2), 320-326, February 2016.


Variations in the shapes of the apical discs between sexes in the sea urchin Tripneustes gratilla were modeled through the use of Thin-plate spline (TPS) deformation grids.The analysis was done in two levels. First, the consensus or average morphologies of each sex were established and compared. Second, patterns of shape variation were analyzed through a careful study of a series of TPS grids when data was subjected to the geometric morphometric method of Relative Warp Analysis (RWA). The results show that differences in the shapes of apical disc were almost impossible to detect when only the consensus shapes were compared. Variations were much more obvious when the TPS of the top seven relative warps were analyzed. Among the local variations observed was the presence of two shape classes among the females. The males on the other hand assumed a unimodal distribution which is suggestive of it belonging to a single shape class. An important recurrent theme is the apparent asymmetry in the shapes of the lateral margins of the apical disc in both sexes.


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