So starts the next chapter...beginning my research for my PhD thesis. I've always wanted to do something that combines my varying interests (from archaeology to physical science, biology and earth system science) with a project that would allow me to travel to remote parts of the world while practicing cutting edge science. My adviser at UC Merced, Dr. Marilyn Fogel, told me about the potential of a large pile of seal and sea lion bones, un-analyzed and fresh for the picking (If you can consider several hundred or thousand year old bones fresh.) I jumped at the opportunity. As it turns out, funding such an endeavor is not necessarily the easiest task so I applied to the highly competitive NSF Graduate Fellowship. I didn't get it, but that hasn't stopped me from taking the first step, as you will soon see. Marilyn generously provided some of her lab start-up funds to help me pay for the multiple flights to the southern hemisphere and I also received a grant from the UC Merced School of Natural Sciences, for which I am exceedingly grateful. Below is my proposal for the NSF grant which will give you an idea of my "grand" goals for my thesis, if you, the casual reader, are unfamiliar with my project.
Understanding how pinniped (seal and sea
lion) populations were affected by the introduction of humans can elucidate how
ecological communities react to human disturbances. At the intersection between
the Atlantic, Pacific and Southern oceans, Tierra del Fuego and the Beagle
Channel are physical and biological nexus points that are poised to be highly
influenced by climate change given their locations at ~55⁰
South. This location is an ideal space for exchange between diverse marine and
terrestrial communities, as noted by Darwin himself. With the help of the NSF
GFRP, the Blois and Fogel labs, and my colleagues in Argentina, I plan to
identify human effects on the Beagle Channel by comparing pre-human and post-human
pinniped populations through measuring changes in food web dynamics and changes
in the population genetics. As top level predators of the Beagle
Channel, pinnipeds regulate community composition. However the evolution of
these species interactions over the past 10 Ka are unknown. I aim to disentangle
the interactions between pinnipeds, humans, and other important actors in this
system using three types of analyses: (a) stable isotope geochemistry (dietary
and trophic information), (b) ancient DNA phylogenetics (population demography),
and (c) radiometric dating (timing of these potential changes). I hypothesize
that when humans reach the Beagle Channel, they significantly alter pinniped
habitats and diets. Pinnipeds likely experienced a genetic bottleneck as marine
mammal hunting was a significant source of food for early human populations in
Tierra del Fuego, Argentina.
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Fig. 1 – A map of southern South America showing archaeological
sites with collections of seal samples (from Zagrando, et al. 2014)
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Modern populations of seals and sea lions are
largely limited to the fringes of Tierra del Fuego6. Top level
predators that forage closer to the coast near Tierra del Fuego have been shown
to have a higher trophic level than those that forage in deeper oceanic waters given
that a larger food web exists near the coast due to higher nutrient and energy
availability4. In this region, pinnipeds are top level predators
that regulate various lower level marine predators, such as fish. Coastal and
offshore diets are recorded in the stable isotopic signature of marine animals.
I predict a shift in stable isotopic values from a higher trophic level to a
lower trophic level as pinniped habitat shifted due to human impacts.
Concurrently with this isotopic shift, pinniped populations should decline as a
result of direct hunting, habitat loss, and lesser resource availability 1,2.
Smaller populations show lesser genetic diversity, as seen in other systems1.
If pinniped populations declined, habitats moved to more remote areas and
foraging habits altered, the community compositions of sites along the Beagle
Channel and Fuegian archipelago likely would have changed. Food chain length in
human altered areas likely decreased as major predators were removed due to
cascading effects from the removal of major predators. More remote areas may
have seen increased niche selection pressures as seals dispersed from or were
eliminated due to human contact. A reduction in genetic diversity limits
resilience and the ability of organisms to adapt to disturbances such as
climate change and habitat destruction. Small populations are susceptible to
extinction as marine ecology is altered. As pinnipeds are removed, other marine
mammals such as dolphins may take advantage of the vacuum in the previously
occupied pinniped niche or apply pressure to vulnerable species.
There is an abundance of archaeological
sites near the Beagle Channel with hundreds of unanalyzed bones. I will analyze
two species of pinnipeds, South American fur seals (Arctocephalus australis) and Southern sea lions (Otaria flavescens)
commonly found in the archaeological sites. Only one site has had seal bone
analyzed for stable isotopes, though many other unanalyzed sites exist (see
Fig. 1). Several sites have not been excavated, and pre-human sites can be
identified in remote sensing surveys and fossil surveys. No ancient seals have
been sampled for ancient DNA, nor have any pre-human seals been analyzed. Radiocarbon
dating of the samples will show the timing of both potential shifts in the food
web and genetic changes.
Stable isotope geochemistry has been well
established as a method for identifying marine-terrestrial relationships3.
Bone collagen represents an excellent resource for representation of
animal diets over several years of the animal’s life. Using compound specific
amino acid analysis and bulk carbon, nitrogen and strontium stable isotopes as
measured from seal bone collagen, I will identify changes in diets between
localities of seals in the region, as well as potential changes in climate and
the environment at large. δ13C values will show habitat preferences
and trophic levels, δ15N will show changes in ocean productivity
over time as well as trophic levels, and δ34S will show benthic
versus pelagic differences in diets3. Through the isotopic analysis
of compound specific amino acids using δ15N I will be able to
differentiate trophic food web dynamics and baseline shifts in productivity. I
will characterize seal habitats and diets over time by identifying changes in
stable isotope values.
Ancient DNA will be critical in
identifying population structure and trends over time in seals1.
Since genetic diversity directly correlates with population size, an analysis
of genetic diversity over time can show how population demographics change. I
will construct phylogenetic networks to show genetic relationships between
populations of animals. A convenient way to measure population demographics
would be through statistical analysis of mitochondrial DNA haplotypes from
seals during various time periods. Previous studies5 have identified
the tRNA-Glu and cytochrome b genes
showing geographic variation in modern populations of O. flavescens and A.
australis and analysis of these genes in ancient populations will provide a
basis for comparison.
My research will shed light on how humans
have affected an understudied region of world, filling in a major gap in our
understanding of human altered ecosystems. The results of this study, showing
how humans altered seal habitat and populations, will have implications for the
conservation of endangered species and ecosystem functions in a high latitude
region where the effects of climate change are felt most. Identifying potential
differences or similarities between human-animal interactions in South America is
essential for a global perspective. A major goal of this research is to
elucidate how humans affect marine-terrestrial ecosystems to better understand
how animals reacted to human impacts. Working with colleagues from Argentina,
we can increase cross-cultural relationships.
Literature
Cited: 1.
De
Bruyn et al., 2009. PLoS - Genetics, 5(7), p. 1-11., 2. Gifford-Gonzalez D. 2011. University of California Press
Berkeley: Los Angeles and London; 221–242., 3. Newsome et al., 2010. Marine Mammal Science 26(3): 509–572. 4. Riccialdelli, et al., 2010. Marine
Ecology Progress Series 418: 235-248. 5.
Túnez, et al., 2007. Mammalian Biology-Zeitschrift für Säugetierkunde 72.4:
193-203, 6. Zangrando et al., 2014.
International Journal of Osteoarchaeology, 24(2), 231-244.
That brings us to this first trip. In the next five weeks, I'll be processing previously excavated bones from the oldest cave site in order to get a general idea of what the seal ecology is like, though I won't be able to crunch numbers until I get back. Of course I won't be accomplishing all the goals outlined in my proposal above, but this is a good first step. I'll have access to bones from about 270 individual seals and sea lions from various time frames, and primarily be focused on doing chemistry to prepare tiny chunks of bone collagen for the stable isotope analysis.
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| A pile of lab supplies I'm bringing with me. It's expensive to get this kind of stuff within Argentina |
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Traveling for a month plus to do research takes some preparation. I'm bringing a bunch of lab supplies and had to go through the official bureaucratic system for buying tickets, which is a pain but totally worth the trouble. Yesterday I flew out of Los Angeles, though a delayed flight to Houston caused me to miss my connecting flight to Buenos Aires. So I've been sitting in an airport slowly going crazy over an extra day of traveling, but that did give me some time to rest up and write this out. Tomorrow morning I'll be Buenos Aires, and later that day I'll be in Ushuaia. Stay tuned!
