Fecal case -associated maternal effects promote postmating isolation between Neochlamisus bebbianae host forms

Neochlamisus leaf beetles belong to a chrysomelid lineage known as the “casebearers”. This name reflects the unusual life cycle of these beetles, whereby the mother covers each egg in a case constructed of her own fecal material. After emerging from this egg case, the larva continues to live within it throughout development. Neochlamisus bebbianae is comprised of host-specific populations (“host forms”) associated with particular tree species in eastern North America. Past work demonstrates partial reproductive isolation between these host forms. This study evaluates the possibility that the size of the egg case constructed by host forms that themselves differ in size may contribute to hybrid inviability by affecting the ‘fit’ of the larva to its case. To this end we have measured case size and hatchling larval size in the (larger) maple host form and the (smaller) willow host form, as well as in their F1 hybrids. Finally, we derive a means of evaluating case ‘fit’ to evaluate possible contributions to postmating isolation.