HOW CAN I GO WITHOUT YOU? THE EFFECTS OF GEOLOGICAL EVENTS ON THE DIVERGENCE OF Rhagoletis pomonella AND ITS HOST

Xie, X. and Feder, J.L.

Department of Biology, University of Notre Dame, Notre Dame, IN 46556

The “true” fruit fly Rhagoletis pomonella (Diptera: Tephritidae) has been a model system for the study of speciation, and its host affiliation has been indicated as the major factor in the divergence of this fly. The fly has traditionally been found only in temperate North America, particularly northeastern US, utilizing typically temperate hawthorns as hosts. However, our recent survey surprisingly discovered its distribution in both highland and lowland Mexico, with two endemic hawthorn species as their host plants. Phylogeographic analyses based on the DNA sequences of multiple loci distributed across the genome reveal that: (I) The lowland fly populations may have been introduced into Mexico along with their host hawthorns during a cooling period in history, which corresponds with the introduction of many temperate plants from eastern United States into Mexico; (II) The highland populations belong to a different lineage that has been recently derived, corresponding with a warming period in history during which the fly’s temperate host plants could have spread onto Mexican highland regions. This study has multiple implications to various fields. First, it confirms that ecological factors, in this case host plants, are very important for the evolution of species. Second, geological events could have a great impact on the biogeography and divergence of species and the evolutionary response could be very rapid. Third, ecological diversity could be an important contributor to species diversity. Finally, the historical relationships between ecology and species richness could be revealed by evolutionary examination, particularly phylogeographic analyses.

Keywords: speciation, host affiliation, phylogeography, historical climate

LONG DISTANCE SEED DISPERSAL IN A FRAGMENTED LANDSCAPE:
IMPLICATIONS FOR PLANT RESPONSES TO CLIMATE CHANGE

McEuen, A.B.

Biology Department, University of Illinois at Springfield, Springfield, IL 62703

Many species may be unable to shift their distributions in response to the expected rates of climate change. Movement of species may be particularly impeded in fragmented landscapes where large distances exist between natural areas. Information on long distance dispersal (LDD) may help in determining the types of species that will be capable of distributional responses but such data are extremely rare. I sampled woody plant seed rain throughout five forest fragments in Michigan over two years (forest fragment size 4 - 8 ha, n = 114 traps total, trap surface area = 28.5 m2). To quantify between-fragment dispersal, I took advantage of species absences from individual fragments. Species absences for fragments were determined by initial surveys and were then verified through resurveys for all successful immigrants. Of seventeen species, seed dispersal into fragments was detected for only four disturbance-adapted woody plants (Acer negundo, Betula papyrifera, Celastrus scandens, Elaeagnus umbellata). In contrast, species such as Acer rubrum and Tsuga canadensis showed no between-fragment seed exchange despite the ability to saturate individual fragments with seed. Multiple LDD events were recorded for Betula papyrifera allowing some exploration of the spatial and temporal patterns of long distance dispersal. Long distance seed exchange was greatest in November, directly after leaf litter fall, with immigrant seed randomly distributed throughout the receiving fragment. The temporal pattern of exchange suggests wind patterns rather than peak seed availability may increase the number of long distance dispersal events. It is perhaps not surprising that early-successional, disturbance-adapted plants appear to be better than others at moving through fragmented landscapes. Conservation of species with other life history characteristics may require more direct intervention as on-going global change occurs.

Keywords: Northern hardwood forest, Seed dispersal, Forest fragmentation