Are Museum Collections Adequate to Test the Escalation Hypothesis?: A Preliminary Case Study Using the Plio-Pleistocene Strombus Alatus Species Complex from Florida

Museum collections are often integral components of lineage-level tests of the escalation hypothesis, which evaluates whether biological hazards become more severe with time and whether adaptations to those hazards increase in expression. Use of museum collections confers many benefits, including increased sample size and greater stratigraphic and geographic coverage, including the potential to “sample” localities that may no longer be accessible. However, potential biases must be considered before using the unique information stored in museum collections, especially when the original collector and their sampling strategy are unknown. Collector biases may include selectivity with respect to fossil size, ornamentation, and evidence of attack and repair.

Here, we examine the utility of existing museum collections for addressing the escalation hypothesis using the Plio-Pleistocene history of interaction between members of the Strombus alatus species complex and their shell-crushing predators in Florida. Antipredatory traits of this gastropod group hypothesized to reduce the effectiveness of shell-crushing predators include: large body size and thick and ornamented (knobbed) shells. We quantified temporal trends of these morphological traits, as well as the frequency of repair scars resulting from unsuccessful predatory attacks, for 62 samples (25 new field samples and 37 existing museum samples). Sample sizes ranged between 26-364 and 20-199 for field and museum samples, respectively. Field samples were collected by intensive unselective sampling of outcrop surfaces. Preliminary comparisons between field and museum samples suggest that the latter faithfully captures the same temporal trends in Strombus antipredatory traits, as well as the frequency of shell repair, that new field samples yield. Future work will concentrate on the utility of museum samples in this system as reliable sources of information to estimate the range of spatial variability of morphological traits and predation indices in tests of the escalation hypothesis.