Peter Wimberger

Updated: December 2012

I am an evolutionary and conservation biologist. The general goals of my research are to increase our understanding of the patterns and processes of evolution. I am interested in a broad array of questions that range from molecular phylogenetics, phylogeography and ecology to studies that utilize museum specimens to answer evolutionary, ecological and conservation questions. Currently I have projects on ice worms and Anna’s Hummingbirds.  I also help students with other projects that utilize museum specimens or just grab my interest.

Ice worm evolution
Ice worms are annelids that live only in glaciers. They probably feed on bacteria, algae and detritus that lands on the ice. They are small (20 mm x 1.5 mm), pigmented worms that are a bit like miniature earthworms. Ice worms can be found from central Oregon (Sisters volcanoes) to south central Alaska. Previous work identified two primary evolutionary lineages – one from Alaska and the other from the Cascades and southern British Columbia. A few years ago, a Biology student, Ben Lee, looking for a way to spend the summer in the mountains and still do thesis research, proposed doing some kind of population genetic study on ice worms. No one had looked at how worms in the Olympic Mountains and on Vancouver Island fit into the overall evolutionary picture. Our prediction was that the worms in the Olympics and on Vancouver Island would be most closely related to worms from the Cascades.

As often happens when one does science, the answer to the question was much more interesting than we expected. We used DNA sequence data from the mitochondrial gene cytochrome oxidase 1 and the nuclear gene 28s ribosomal RNA to estimate relationships. Worms from the Vancouver Island and majority of the Olympic populations were descendants of the Alaska evolutionary lineage. It was only when we looked at the highest glaciers in the Olympics that we found representatives of the Cascade lineage. However, these worms coexisted on the glaciers with worms from the Alaska evolutionary lineage!

How do we explain this surprising and intriguing pattern? Usually evolutionary biologists use geology to help make inferences about geographic population patterns. The primary mode of worm dispersal is likely glacial movement. Worms are transported from place to place on glaciers. The presence of worms in alpine glaciers is likely the result of continental glaciers moving the worms from farther north. The most recent incarnation of glaciers in the northern hemisphere was probably about 3 mya. There have been numerous “ice ages” over the past 2.5 mya, meaning that continental glaciers made their way south like the recent one that departed only ~11,000 years ago. The problem with each glacial event is that it wipes out records of previous ones. Most of the worms, based on amounts of DNA divergence clearly made it here prior to the last glacial event, some long before. I think that the phylogeography of ice worms actually allows us a window to earlier glacial events not accessible via traditional geology.

Our explanation of the pattern we see in the Olympics and Cascades is this… A continental glaciation perhaps 2 mya or older left worms in the Cascades and Olympics. In subsequent interglacials all of the alpine glaciers in the Cascades melted and all but the highest glaciers in the Olympics melted leaving Cascade lineage worms in refugia on those high Olympic peaks and somewhere in north-central British Columbia. A more recent glacial event recolonized the Cascades, with the source of the continental ice (and Cascade lineage ice worms) in the Cascades from that BC refuge. Continental ice from somewhere in north BC or Alaska (and Alaska lineage ice worms) made its way down the coast, through the Straits of Georgia, into the Strait of Juan de Fuca and Hood Canal carrying Alaska lineage worms that connected with the lower alpine glaciers of the Olympics. These glaciers from further north that travelled the coastal route are now the source of the worms we now find on Vancouver Island and the majority of Olympic Mountain glaciers. Data suggest that a subsequent interglacial melted most of the glaciers in the Cascade with the exception of a few high peaks like Rainier.  The alternative hypothesis is that worms or their cocoons were dispersed by birds during migration.

We are finishing up studies examining how Oregon and Mt. Rainier populations fit into the overall picture.  To extend the phylogeographic work I am hoping to do some next-generation sequencing so that we can mine single-nucleotide polymorphisms to examine the phylogeographic questions in more depth. 

Rapid Evolution in Anna’s Hummingbirds
Historically, Anna’s Hummingbirds were native to the southwestern US.  Anna’s were first observed in the Pacific Northwest in the 1960s and were first reported as year-round residents in the 1970s.  It appears that the increased use of hummingbird feeders allowed Anna’s to expand their range and become resident in areas that would not normally support resident populations because of cool winter conditions and lack of naturally occurring food. 

Rapid evolution has been reported in numerous species including Blackcaps, House Finches, House Sparrows, Sockeye Salmon and Three-Spined Sticklebacks.  We have examined morphological and dietary differences in Anna’s Hummingbirds from California and Washington to look for indications that rapid evolution may have occurred or is occurring.  We predicted that birds in the Northwest will be larger as the result of selection for decreasing surface:volume ratio to more efficiently thermoregulate.  We predict that bill sizes will be smaller as the result of there being fewer long corolla flowers in the Northwest and a greater reliance on feeders in the Northwest birds, combined with the decreased heat loss from shorter bills. Morphological measures from banders and museum specimens confirm these predictions.

Cane sugar used in hummingbird feeders is from sugar cane, a C4 plant.  Nectar-bearing flowers are mostly C3 plants.  Animals that include more carbon from C4 plants have higher carbon isotope ratios. We are interested in examining C and N isotopes to look at diet variation over space and also over time.  We predict that the Northwest Anna’s Hummingbirds will have C ratios indicating a greater reliance on feeders (cane sugar) than California birds.  In addition we want to compare Anna’s Hummingbirds from California prior to the 1930 (hummingbird feeders not used) to birds from after 1990 (hummingbird feeders common), again predicting that carbon ratios will indicate a greater reliance on hummingbird feeders in the more recent specimens.  We have stable isotope data that need to be analyzed.  This would make a great small student project for someone interested in dietary ecology and stable isotopes.

The next step of the project is to see whether the morphological differences are indicative of genetic differences between the populations.  This research will involve DNA extraction, PCR, and genotyping samples to generate genotype data to be used in population comparisons.

Other Museum Projects
If you are interested in using museum specimens to test ecological or evolutionary hypotheses, we have a number of ongoing projects that we are doing in collaboration with other researchers.  Peter Hodum, Gary Shugart and students have been working on plastic ingestion by seabirds.  They have been looking at what species are prone to ingest plastics, what kinds of plastics they are ingesting and the physiological impacts of plastic ingestion.  Another student is examining the chemical makeup of preen oil to see whether the makeup varies with hunger status, age or season.  Another student examined molt pattern in the Surf Scoter, a sea duck.  Other students have examined wing feather morphology that might be related to the whistling sounds made by some ducks and pigeons when they fly.  Come talk to me if you are interested in any of these projects.