326-7 Assessing Ecological Effects of the Late Ordovician Richmondian Invasion Event on Brachiopods Using Three-Dimensional Geometric Morphometrics

Abstract:

Invasive species can dramatically affect ecological communities and are often detrimental to native species. Analyzing the effects of ancient invasion events preserved in the fossil record may help us assess long-term ecological impacts of modern invasion events. We focus on the Late Ordovician Richmondian Invasion event, when several new taxa invaded the Cincinnati area, to assess changes in brachiopod morphology.

Morphological diversity and phenotypic plasticity are important for the ability of organisms to cope and adapt to changing environments. This is particularly relevant in sessile brachiopods, which primarily interact with their environment through the shape of their shell. Here, we investigate changes in the three-dimensional morphological diversity of brachiopods across the Richmondian Invasion to understand ecological impacts of major changes in community composition. 

We collected Late Ordovician brachiopod fossils along an environmental depth gradient of deep to shallow subtidal in the Cincinnati Arch from before (C2 sequence) and after (C5 sequence) the Richmondian Invasion event. To quantify changes in shell shape, Structured Light Scanning is used to digitally construct the 3-dimensional shape of brachiopods using the Revopoint INSPIRE2 scanner. The software ‘Revo Metro’ is used to build 3D models of the dorsal valve of each brachiopod. Fixed landmarks and semi-landmarks are placed across the surface of the shells using the software ‘3D Slicer’. General Procrustes Analysis and Principal Components Analysis (PCA) are performed in ‘R’ using the package ‘geomorph’ to determine shape changes. 

Preliminary results on Rafinesquina show significant shape changes after the invasion event, with post-invasion specimens showing weaker convexity of the pedicle valve and stronger rounding of the distal ends of the hingeline. PCA shows pre-invasion specimens occupy a greater range of morphospace, contrasted with tight clustering and a decrease in morphological diversity exhibited by post-invasion specimens. There is little to no overlap between the two groups within the morphospace. Analyses for Cincinetina specimens are currently being conducted. We expect to see similar patterns of decreased morphological diversity after the invasion, alongside shape changes across the environmental gradient from deep to shallow subtidal.

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