Hybrid haplotype vigor in Florida (USA) populations of the invasive exotic Brazilian peppertree, Schinus terebinthifolius

Authors: Geiger, John; Pratt, Paul; Wheeler, Gregory

Submitted to: Botanical Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/27/2009
Publication Date: N/A
Citation: N/A

Interpretive Summary: The process of invasive species establishment allows ecologists and evolutionary biologists to study these occurrences as human induced experiments in contemporary evolution. The success of invasive species exposes a genetic paradox. How can successful invaders overcome the hurdle of reduced genetic variation via small founder population sizes to thrive, persist, and adapt to a new set environmental conditions? An expanding body of literature posits hybridization, both inter- and intraspecific, as a driver of the evolution of invasiveness. Brazilian peppertree Schinus terebinthifolius; is a tree species native to Paraguay, northeastern Argentina, and Brazil that is a successful invader throughout most of Florida. The tree was introduced separately to the east and west coasts of Florida over 100 years ago and recent genetic analyses confirm these introductions were from genetically distinct source populations in its native range. We considered the hypothesis that hybridization between the eastern and western haplotypes may have stimulated the invasive potential of Brazilian peppertree. The purpose of this study was to investigate differences in the early life stages among the three haplotypes (i.e. eastern, western, and intraspecific hybrid) presently found in Florida using a common garden experiment. Western haplotypes had greater seed predation rates than hybrids, while eastern haplotypes were intermediate. Hybrid seeds germinated at higher rates (18 %) than eastern haplotype seeds (15 %). Over the eight month experiment, a greater proportion of western haplotype seedlings died than hybrid haplotypes (47 % vs. 36 %). Not surprisingly, there was also a significant linear relationship between the total number of germinated seeds and total number of living seedlings at the end of the experiment. Hybrid seedlings obtained greater total dry weights than their western counterparts. For these early life stages, hybrids appear to have advantages over both eastern and western haplotypes.

Technical Abstract: The process of invasive species establishment allows ecologists and evolutionary biologists to study these occurrences as human induced experiments in contemporary evolution. The success of invasive species exposes a genetic paradox. How can successful invaders overcome the hurdle of reduced genetic variation via small founder population sizes to thrive, persist, and adapt to a new set environmental conditions? An expanding body of literature posits hybridization, both inter- and intraspecific, as a driver of the evolution of invasiveness. Brazilian peppertree Schinus terebinthifolius; is a tree species native to Paraguay, northeastern Argentina, and Brazil that is a successful invader throughout most of Florida. The tree was introduced separately to the east and west coasts of Florida over 100 years ago and recent genetic analyses confirm these introductions were from genetically distinct source populations in its native range. We considered the hypothesis that hybridization between the eastern and western haplotypes may have stimulated the invasive potential of Brazilian peppertree. The purpose of this study was to investigate differences in the early life stages among the three haplotypes (i.e. eastern, western, and intraspecific hybrid) presently found in Florida using a common garden experiment. Western haplotypes had greater seed predation rates than hybrids, while eastern haplotypes were intermediate. Hybrid seeds germinated at higher rates (18 %) than eastern haplotype seeds (15 %). Over the eight month experiment, a greater proportion of western haplotype seedlings died than hybrid haplotypes (47 % vs. 36 %). Not surprisingly, there was also a significant linear relationship between the total number of germinated seeds and total number of living seedlings at the end of the experiment. Hybrid seedlings obtained greater total dry weights than their western counterparts. For these early life stages, hybrids appear to have advantages over both eastern and western haplotypes.