THE PREDICTIVE POWER OF MORPHOLOGY: CAN WE USE MODERN EXPERIMENTAL STUDIES TO INFER PAST ECOLOGY?

Spatial variation in morphology within species is often presumed to be the result of different levels of selective forces present in the environment, such as predation pressure. Where morphological features can be constrained as resulting from precise selective pressures, recurrence of morphotypes in both fossil and modern populations can be used to predict specific aspects of current and past ecology.

This study used modern experimental work to test how the differential development of morphological features that presumably have anti-predatory function (e.g., the development of long spines and a bulge across the siphonal canal, the “tumid ridge”) affected performance of a prey species, a gastropod, against a durophagous predator, a crab. Busycon carica, the knobbed whelk (Massachusetts to Florida), was offered to the durophagous predator Menippe mercenaria, the stone crab (North Carolina to Florida), which overlaps with the prey’s modern range from North Carolina to Florida. Prey that possessed anti-predatory features (located today mostly along the southeastern U.S. coast) consistently performed better than the alternative morphology, and the presence of a tumid ridge in particular was found to be essential to ensuring prey survival during attacks.

Many of these morphological features occur repeatedly in different Plio-Pleistocene fossil assemblages of the U.S. Atlantic coastal plain (e.g. Busycon tritonis Conrad, Yorktown Formation; Sinistrofulgur grabaui Petuch, Duplin Formation; B. filosum Conrad, Yorktown Formation & Duplin Formation; S. perversum okeechobeensis, Fort Thompson Formation), with occurrences concentrated in the Pliocene. The recurrence of the tumid ridge, in both spinose and non-spinose populations, suggests that durophagous predation may be driving its repeated re-evolution. Ongoing work includes examination of various predation metrics within and between assemblages to determine whether populations possessing a tumid ridge face heightened predation pressures.