Lindberg, D. R. and R. P. Guralnick.  Have developmental pathways become more conservative? A geometric morphometric analysis of early development in gastropod molluscs. (in review).



Abstract. We visualize and quantify changes in gastropod developmental pathways for each of the eight major gastropod subclades by treating representative cell lineage trees as two dimensional morphologies with homologous x, y coordinates; x specifying the relative timing of cell lineage origination and y a standardized distance based on branching order and cell cycle. The x, y landmark data were analyzed and compared using geometric morphological methods. Mapping these results as deformation grids on a hypothesis of gastropod relationships produces a visual representation of the changes in the early development of gastropod molluscs. The transformations of the grids between taxa are gradual and they appear as continuations of earlier, smaller changes although the rates of change vary among taxa. The fossil record corroborates the groupings delimited by principal component analysis of partial warp scores, and there appears to be little change in cell lineage staging for approximately 60 Myr of early gastropod history, however substantial changes occurred after this hiatus. While the possibility of greater developmental diversity in extinct lineages cannot be rejected, there appears to be no support for early developmental stages of extant gastropods becoming more conservative over the last 500 Myr. Like cis-regulatory diversification where gene products are co-opted to perform new functions in developmental pathways, changes in cell lineage timing may make possible new developmental outcomes, primarily by changing the spatial and temporal context of biochemical control, and may have contributed to the morphological diversification seen in the gastropod bauplan.



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