Tuesday, 6 April 2010

When it doesn't matter where you're from

ResearchBlogging.orgPeople move animals around. It's what we do. Why are there Elk on Afognak island? Some guy thought it was a good idea at the time. Wildlife managers in the past were some of the biggest conduits for moving animals around, frequently en mass, back before biology really caught up with the profession. We can cite plenty of examples where moving animals around to do population rescues was a bad thing - the Arabian Oryx got both inbreeding and outbreeding depression at once! And there's others, still.

Why? We predict animals to be generally well adapted to their environment, or well adapted to it pre-human mucking around. What it takes to be a good Elk in Hungary is very different from what it takes to be a good Elk in Norway. Norway is pretty different from Hungary.

Quick side note: Names are confusing, even to a professional Here, I'm talking about what North Americans call Elk, or Wapiti. What Europeans call Elk is Alces alces, or what North Americans call "Moose." They call NA-Elk "Red Deer." In any event, it's Cervus elaphus. North American elk are sometimes called Cervus canadensis, but frankly, I think that's a load of hooey. But that's an argument for another day. When I say "Elk," I mean Cervus elaphus or C. canadensis.

Just reading my explanation of the nomenclature makes me want to get a stiff drink!

"Strangely" enough, the situation I just gave to you as a hypothetical happened. So, the question is... does it matter? Does putting Hungary blood in Norway animals make them maladapted? Well, Haanes et al. studied whether these long-distance translocations hurt a population on an island called Otterøya. What a wonderfully Norwegian looking name! The population on Otterøya was down to 12-14 individuals, 3 or 4 or which were stags. Since Elk tend to have very skewed reproductive success in the males (meaning, either you're the big bull and get plenty of reproduction, or you get little-none), it means you can basically 2 or 3 individuals contribution into the next generations. That brings it down to 9-12 individuals who contributed their genes to the next generation.

To avoid expatriation, 17 German•Hungarian 'Hybrid' elk were brought in for a population rescues. I say 'hybrid', because supposedly those are different subspecies. I have issues with that, which I'll outline later. Regardless, the population exploded, shooting up to 100 Elk in 10 years, and even higher since. Obviously, the population rescue worked. But what's the long-term consequences of the German•Hungarian animals' introduction? It could be that the Elk are less successful than they would be, if they didn't introduce that linage.

Well, Haanes et al. decided to take a two-prong approach. First, they took blood/tissue from Elk on Otterøya, they sampled Elk on mainland Norway, and they sampled 20 Elk in Hungary. They took DNA from all of them. They would have loved to sample the German Elk, but since the translocation, the rest of the German Elk were bottlenecked, translocated some more, and probably experienced some introgression. Basically, they're not the same Elk anymore. Finally, they measured body characteristics for the various populations, hijacking some datasets to do so. I'm fine with that; it's hard to get good data on hunter-derrived samples because hunters bias their hunts to tasty/big animals.

I'll skip ahead to the results. First, using STRUCTURE, they found a best solution of `there are two populations. The program STRUCTURE tries to assign individuals to populations without knowing anything about where they're from. It doesn't make assumptions in that regard (although it can, if you tell it to). I've put the STRUCTURE bar-plots next to this paragraph. Each vertical bar represents an individual, and each colour represents one population assignment. So a half red, half green vertical bar represents 50% assignment to both red and green cluster. Next, they found that their mtDNA showed that there was a hybrid origin of the elk. The morphometric measurements suggest that body size is large in the Otterøya Elk. Take together, the message is "Hybridization happened! But it looks like things went well for them."

First, I'm not sure that their various elk are deserving of subspecific designation. I'm not too familiar with the lit on Eurasian Red Deer, but Europe is where a lot of taxonomy was developed, so they've gone through and divided Europe up with a fine tooth comb. Just about everything has its own subspecies over there, and I'm not sure legitimately so. The reason why this matters is that a subspecies implies a whole lot more adaptation than just two unconnected, remote populations. I do see that other people are skeptical of the taxonomic assignments. Taxonomy matters.

Second, I draw your attention to the STRUCTURE plots. I've seen this sort of plot before, where my most likely solution is lower than what my true apparent tree is. I suspect STRUCTURE focuses on lower k values, stopping at some high level divide and not going any deeper. For example, I have one data set where both the highest likelyhood solution and Evanno's ∆K method solve for K=2, when in fact I have very clear structure, and structure we expect to find, at K=5. I think STRUCTURE is biased to the deepest divisions.

Still on the STRUCTURE topic, I think the Hungarian sample was just too low. Sample size matters. Fogelqvist et al. (2010) argues that 8-10 is enough in STRUCTURE. I think that might be true in selfing organisms, but I seriously question whether that's enough in most of the organisms I'm working in. Obviously, the thing to do would be to do a simulation study, which I haven't done. 20 for Hungary, for such fine scale differences, feels too small. And I wonder if how spatially distant they're sampling their populations is biasing their very high He (which is ~.8, astronomical for a mammal.) And they have a ton of private alleles too, which I have a hard time explaining - is it just a function of northern animals being lower diversity? Or maybe a function of Fennoscandian isolation - but that would support a model where Norway has something closer to a sub-specific division. And look at the number of haplotypes in the below table. I wish they rarifacted...

Finally, how do we know body size isn't environmentally induced? In my own experience, Caribou seem to follow a few different life history strategies that we've lumped into 'ecotypes.' In general, folks have found that the sedentary type is smaller. However, these aren't genetic differences, but instead diversity that seems to lie among all Caribou. The first or second generation migrants should be more like wherever they end up growing up, and plausibly not retain their sedentary phenotype. I'm hesitant to use body mass as a marker of success for supposed hybrids, for this reason. Better would be rumpfat, ovarian markers (for reproduction), etc. It's clear from the census alone, though, that these animals are doing quite well.

Too often, us in the conservation world take too much of an adaptionalist point of view. This is amusing because what we work with to get at population demographic history is almost entirely neutral markers. But few people I know will be too enthusiastic about neutral hypotheses of genomic evolution! This serves as a good counter-example to many of our examples of translocations being bad. Did Norwegian Elk lose a little bit of adaptation to their environment? It's possible, but these results wouldn't support that. Or if they did, they're currently "adapted enough" to make a good go at being Elk in Norway. Even if those crazy Europeans call Elk the wrong name. ;)

As usual, here's the abstract:
For several centuries, game management has involved translocations of non-native individuals of many species to reinforce local native populations. However, there are few quantitative studies of potentially negative effects on population viability as expected when taxa with different local adaptations hybridise. The European red deer has been subject to particularly many translocations. Around 1900, a total of 17 red deer of Hungarian (Cervus elaphus hippelaphus) and German (C. e. germanicus) ori- gin were introduced onto the island of Otterøya in Norway where few native red deer (C. e. atlanticus) remained (n ~ 13). To assess interbreeding, the present stock on Otterøya and the indigenous Norwegian and Hungarian populations were characterised in 14 microsatellite loci and in the control region of mtDNA. An intermediate level of genetic variation in the Otterøya population and the pres- ence of population specific alleles from both the indigenous Norwegian and the Hungarian population demonstrate that the introduced red deer interbred with the native. Even distributions of one indigenous and one non-indigenous mtDNA haplotype in the Otterøya population and two point estimates of admixture indicate similar genetic con- tributions from the two parental populations into the hybrid stock. Low numbers of migrants identified with Bayesian assignment tests demonstrate low recent gene flow from Otterøya into the Norwegian mainland population. The Otterøya hybrid stock has grown vastly in numbers during recent decades, suggesting a high population viability. We observed that the body mass of red deer on Otterøya was similar or greater than in adjacent indigenous Norwegian stocks, indicating that population performance has not been reduced in the hybrid stock and that gene flow probably has not had any negative effects.
Haanes, H., Røed, K., Mysterud, A., Langvatn, R., & Rosef, O. (2010). Consequences for genetic diversity and population performance of introducing continental red deer into the northern distribution range Conservation Genetics DOI: 10.1007/s10592-010-0048-1

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