In a study published in American Naturalist, Konuma & Chiba publish demonstrated an interesting evolutionary trade-off between “force” and “fit” in carabid beetles (such as Damaster blaptoides to the left) that feed on land snails. Force means the beetles are stout, large-headed and able to crush snail shells with powerful jaws. Alternatively, they can be slender, small-headed and are able to fit into the aperature of snail shells (as in the above photo).

Large-headed beetles were most successful with thin-shelled snails, whereas small-headed beetles were more successful on snails with larger aperatures. It has been demonstrated that the same trade-off diversifies shell morphology in studies of freshwater snails, where elongate shells are adaptive in protecting against entry attacks and rounded shells are adaptive in protecting against crushing attacks.

Functional trade-offs are likely to affect coevolution between the prey’s defensive characters and the predator’s attack characters. Thus, the trade-offs between force and fit could play a significant role in character diversification through coevolution between snails and their predators. (You can read more at Science Daily: The Beetle’s Dilemma)