Biodiversity Challenge: It’s What’s on the Inside that Counts
In the picture above, with a little bit of training, you can count the diversity of seaweed species on one hand. For most, this seems like a ‘low biodiversity’ system especially if you’ve ever poked around on rocky shores of the west coast of the United States.
But what if you were to think smaller, go inside those seaweeds, into the nucleus of their cells, and measure the variation of the molecules there – the variation in the genetic code (DNA). Throughout Earth’s history changes to the genetic code, big and small, have produced the amazing array of life on this planet. DNA ultimately drives how organisms look, function, and interact with their environment and other organisms. For these reasons genetic diversity, to me and other scientists in this field, is the most fundamental level of biodiversity.
It may be easy to understand how genetic diversity is important in single species, particularly endangered charismatic animals such as elephant seals and condors. When population sizes drop too low, genetic diversity may be reduced, and the already threatened species becomes even more vulnerable. This is because reduced genetic diversity means less variation to deal with pressures such as extreme climatic events or disease. In populations with greater genetic diversity there may be a greater variety of ‘genetic codes’, some less vulnerable than others, leaving the population with a ‘buffer’ of individuals that can make it through tough times.
But can genetic diversity have influences beyond a single species? Imagine kelp forests, coral reefs, and seagrass beds – what do you think of? Likely the kelp, corals, and grass! These ecosystems are dominated and supported by just a single or a few species. If individual kelps function or have different traits because of genetic variation then basic principles of biodiversity science may apply – higher genetic diversity of these key organisms could lead to greater productivity, stability, and/or resilience of the entire ecosystem they support. Given the importance of many of these types of ecosystems for services such as fisheries, tourism, and coastline stability, conserving genetic diversity could provide benefits to humans as well.
Genetic diversity–ecosystem function research is still in its early stages, and there are lots of open, unanswered questions. There is a need for more empirical evidence from a wider variety of organisms and ecosystems to understand the generality of the effects of genetic diversity. Genetic diversity of a species can change from population to population and from generation to generation and how this influences the effects of genetic diversity on communities and ecosystems is little understood. Since genetic diversity is a currency of evolution, this area of research may help bridge the gap between evolutionary biology and ecology. The number of unanswered questions and the links between different disciplines make it an exciting time to be involved in genetic diversity-ecosystem function research!
1 November 2013
You know, intraspecific genetic diversity is probably one of the hardest angles to pitch: everyone can “see” diversity of species, populations, habitats, etc. but you can’t really visualize genetic diversity. As you put it so well, Kylla, when I look at a seagrass bed, I see seagrass.(Ok that’s not fair, really I’m looking at amphipods but its only recently that we began to think about their genetic diversity, so we’ll stick to seagrass). Thanks for putting some good talking points out there!
My question for you is: how do we convince people to conserve genetic diversity? If I want to conserve species diversity, I can give people pictures of various organisms and say “Keep that, it’s good.” Unless genotypically different individuals are also phenotypically different (quite within the realm of possibility), then it becomes “Keep ALL of this one thing, because we’re not sure how much genetic variation there is within this population and which individuals carry it.” Genetic testing is still difficult for many organisms, and cost-prohibitive even in cases where good primers are available. What do you think? Can a case be made?
Ah, good, tough, question! The fact that people cannot see genetic diversity, on top of the slim likelihood that people remember what they learned about genetics in their biology classes, makes this one of the more difficult topics to talk about in outreach settings. At least it has been in my experience.
But I do think a case can be made. I think one critical factor is how genetic diversity is defined and in what way it is deemed “important”. For example, Hughes & Stachowicz 2004 and Reusch et al. 2005 both nicely demonstrate that genotypic diversity per se enhanced resistance/recovery from disturbance. In order to get published these research groups had to genotype the sample population to demonstrate they indeed had different clones, but a conservation group would not necessarily need to do the same. If a group was restoring seagrass beds, a little information about the biology (and maybe genetics) of a system can inform the sampling. From the research I am familiar with, I would probably not sample just one patch in one bed for all my donor seagrass. Sampling shoots that are fairly far apart or maybe even from different sites should generate a reasonable amount of genotypic diversity to outplant. It may take a little more effort but if it increases success of restoration efforts it is probably worth it.
It gets trickier if particular alleles or values of genetic diversity are the metrics of genetic diversity. Williams 2001 demonstrated that seagrass transplant success was greatest when heterozygosity at two particualr markers was high. Stachowicz et al 2013 show that particular values of relatedness yield the highest productivity in seagrass plots. How are conservation groups supposed use this type of information? As you mention, genetic testing at this scale (for restoration efforts) would be cost prohibitive. But maybe this information can still be used to guide restoration plans. In the Williams study at least one of the markers was linked to a phenotypic trait (rate of flowering) which could be used to inform donor selection for restoration. In terms of the Stachowicz study, maybe this means even more spatially explicit donor sampling (e.g., selecting some shoots near each other and some shoots far away from each other).
If genetic diversity is linked to phenotypic diversity I think it makes it even easier, especially if the trait(s) is morphological (macroscopic) in some way. Since molecular studies are fairly recent, scientists have been using phenotypic diversity and differentiation as a proxy for genetics for over a century and is much cheaper than genetic testing. Zhu et al. 2000 tested disease resistance and yield of monocultures and polycultures of rice clones based on their disease-tolerance phenotypes. Although the genetics of these clones is known, given the importance of rice (now and historically) my bet is farmers probably understood the clone-phenotype connection a long time ago. On a side note, I think that for genetic diversity to important ecologically there has to be some connection to phenotype.
To make the case to conserve “genetic diversity” you have to *see* the positive outcome of genetic diversity. In the case of seagrass research, it would be easy to show data and pictures comparing high and low diversity plots. This along with knowledge of the biology of the system you could then make recommendations about what should/could be conserved. If you work in a system in which the genetics is unknown then there is a little more hand waving involved but you can take information from similar organisms as a start, and again phenotypic studies can/may be just as informative but less costly.
I actually think in any conservation effort (species, habitat, genetic, etc.) donors, decision makers, voters, etc. all put a lot of trust in the information provided by scientists. Typically we say “see this species/habitat/ecosystem, keep all of it over here because its good”. We may provide data and pictures of success to show why those things are important but ultimately non-scientists involved in the process do not know about the details of the observations and experiments that allowed us to make that “keep it, its good” statement – the same goes for conservation of genetic diversity.
All of this is a long winded way of saying some knowledge on the biology of an organism (reproductive mode/rate, phenotypic and/or genotypic diversity and differentiation, population dynamics, etc.) and a few well designed experiments can provide a lot of information for conservation efforts and importance of genetic diversity in a system. It doesn’t necessarily have to involve expensive and expansive genetic sampling. Making the case is up to the scientist, just as in protecting any other level of biodiversity. Additionally, conservation efforts (seem to) are becoming more informed efforts rather than willy-nilly “save this forest here for politcal reasons” – genetic information is just one more piece of the large conservation puzzle.
Hey Kylla, thanks for writing such a long and thoughtful reply.
To extend your seagrass examples, Laura Reynolds, formerly of UVA, did some excellent work looking at seagrass restoration success for her dissertation work (see her 2012 paper here: http://dx.doi.org/10.1371/journal.pone.0038397). She found that higher genetic diversity of seagrass transplants and/or seeds translated to higher primary productivity, higher invertebrate biomass (aka more habitat), and greater nutrient retention.
What’s most interesting is that the source populations for the restoration were genetically distinct because they were geographically distinct (some from the Chesapeake Bay proper–right outside my window, in fact–and some from the Eastern Shore, where the restoration was taking place). This could be an easily understood argument for conservationists: protecting geographically distinct populations, as they are likely to be genetically distinct as well. However, there are lots of caveats to this argument, first and foremost that seagrasses are relatively sedentary (although seagrass seed dispersal can be on the order of 100s of kms). Laura did some other work looking at population connectedness in relation to currents and dispersal, but I’m not sure if that work is published yet.
Anyways, thanks for the food for thought. I didn’t know Jay had published his work on closely related stands of eelgrass maximizing biomass (an opposite trend to what is predicted from theory). I remember him presenting that at ESA a few years ago and scratching my head…