Martin, L.J. and M.B. Cruzan. 1998. Patterns of hybridization in the Piriqueta caroliniana complex in central Florida: Evidence for an expanding hybrid zone. (in review.)

Abstract.-- We have identified a broad zone of hybridization between P. caroliniana and P. viridis that extends more than 300 km across the central Florida peninsula. We examine the distribution of diagnostic morphological characters and nuclear genetic markers to assess the extent of introgression in this system. The results are consistent with the hypothesis that this hybrid zone has expanded north in recent history. Genetic markers diagnostic for P. caroliniana (the northern taxon) are consistently high across the hybrid zone, while markers for P. viridis display high levels of variation with frequency reversals in adjacent populations. The latter pattern is presumably the result of the northward introgression of P. viridis alleles and the combined effects of limited dispersal and drift in small populations. Additional evidence for the recent expansion of this hybrid zone comes from patterns of variation for both morphological and genetic markers. Populations at the southern end of the hybrid zone are morphologically intermediate to the parental taxa, but display low levels of phenotypic variability within populations. In the northern portion of the hybrid zone there are higher proportions of fixed alleles, higher levels of variation for the genotypic hybrid index, and higher levels of morphological variation within populations.

Keywords: Hybridization, introgression, morphological variation, RAPDs, hybrid zone.