Association of mandible shape and nesting material in Osmia Panzer (Hymenoptera : Megachilidae): A morphometric analysis

We combined methods of geometric morphometrics and phylogenetically control led comparisons to examine the relationship between the shape of mandibles and material used to construct the nest for 5 Osmia Panzer species. We meas ured leaf- and mud-using species from 2 subgenera: in the subgenus Osmin, O , lignaria Cresson (mud-user), O. cornuta Latreille (mud-user) and O, ribif loris Cockerell (leaf-user), and in the subgenus Centrosmia, O. tanneri San dhouse (mud-user), and O. bucephela Cresson (leaf-user). Landmark-based geo metric morphometrics and multivariate statistics provided a way to compare mandible shapes, distill major shape differences and visualize mandible reg ions that differed most among Lee species. Mandible shape differed signific antly among all species based on paired comparisons of Mahalanobis distance s. Principal component analysis of the shape variables (relative warps anal ysis) revealed greater similarity between the 2 leaf-using bees, than among the mud-users. There were however, no consistent differences between these mud- and leaf-using species. Testing with two-way multivariate analysis of variance showed that the differences in shape between the leaf- and mud-us ing species depended on the subgenus. A broad proximate bite surface charac terized leaf-using species. No such trait was common to mud-using species. Mandibles of leaf-using species may vary less because of selection on shape , or because of functional constraints for shearing and macerating leaf mat erial; both constraints are absent in mud-using species. Mandibles of mud-u sing bees may respond more to selection imposed by other aspects of bee bio logy.