Spatial mosaic evolution of snail defensive traits
Steven G Johnson1, C Darrin Hulsey2 and Francisco J García de León3
1Department of Biological Sciences, University of New Orleans, 2000 Lake Shore Drive, New Orleans, LA, 70148 USA
2Department of Biology, Georgia Tech, 310 Ferst Drive, Atlanta, Georgia, 30332, USA
3Centro de Investigaciones Biologicas del Noroeste, P.O. Box 128, La Paz, B.C.S. Mexico
Recent models suggest that escalating reciprocal selection among antagonistically interacting species is predicted to occur in areas of higher resource productivity. In a putatively coevolved interaction between a freshwater snail (Mexipyrgus churinceanus) and a molluscivorous cichlid (Herichthys minckleyi), we examined three components of this interaction: 1) spatial variation in two putative defensive traits, crushing resistance and shell pigmentation; 2) whether abiotic variables or frequency of molariform cichlids are associated with spatial patterns of crushing resistance and shell pigmentation and 3) whether variation in primary productivity accounted for small-scale variation in these defensive traits.
Using spatial autocorrelation to account for genetic and geographic divergence among populations, we found no autocorrelation among populations at small geographic and genetic distances for the two defensive traits. There was also no correlation between abiotic variables (temperature and conductivity) and snail defensive traits. However, crushing resistance and frequency of pigmented shells were negatively correlated with molariform frequency. Crushing resistance and levels of pigmentation were significantly higher in habitats dominated by aquatic macrophytes, and both traits are phenotypically correlated.
Crushing resistance and pigmentation of M. churinceanus exhibit striking variation at small spatial scales often associated with differences in primary productivity, substrate coloration and the frequency of molariform cichlids. These local geographic differences may result from among-habitat variation in how resource productivity interacts to promote escalation in prey defenses.
BMC Evolutionary Biology 2007, 7:50. This is an Open Access article distributed under the terms of the Creative Commons Attribution License.