Inbreeding bad for invasives too

18 02 2010

I just came across this little gem of a paper in Molecular Ecology (not, by any stretch, a common forum for biodiversity conservation-related papers). It’s another one of those wonderful little experimental manipulation studies I love so much (see previous examples here and here).

I’ve written a lot before about the loss of genetic diversity as a contributing factor to extinction risk, via things like Allee effects and inbreeding depression. I’ve also posted blurbs about our work and that of others on what makes particular species prone to become extinct or invasive (i.e., the two sides of the same evolutionary coin). Now Crawford and Whitney bring these two themes together in their paper entitled Population genetic diversity influences colonization success.

Yes, the evolved traits of a particular species will set it up either to do well or very badly under rapid environmental change, and invasive species tend to be those with rapid generation times, defence mechanisms, heightened dispersal capacity and rapid growth. However, such traits generally only predict a small amount in the variation in invasion success – the other being of course propagule pressure (a composite measure of the number of individuals of a non-native species [propagule size] introduced to a novel environment and the number of introduction events [propagule number] into the new host environment).

But, that’s not all. It turns out that just as reduced genetic diversity enhances a threatened species’ risk of extinction, so too does it reduce the ‘invasiveness’ of a weed. Using experimentally manipulated populations of the weedy herb Arabidopsis thaliana (mouse-ear cress; see if you get the joke), Crawford & Whitney measured greater population-level seedling emergence rates, biomass production, flowering duration and reproduction in high-diversity populations compared to lower-diversity ones. Maintain a high genetic diversity and your invasive species has a much higher potential to colonise a novel environment and spread throughout it.

Of course, this is related to propagule pressure because the more individuals that invade/are introduced the more times, the higher the likelihood that different genomes will be introduced as well. This is extremely important from a management perspective because it means that well-mixed (outbred) samples of invasive species probably can do a lot more damage to native biodiversity than a few, genetically similar individuals alone. Indeed, most introductions probably don’t result in a successful invasion mainly because they don’t have the genetic diversity to get over the hump of inbreeding depression in the first place.

The higher genetic (and therefore, phenotypic) variation in your pool of introduced individuals, the great the chance that at least a few will survive and proliferate. This is also a good bit of extra proof for our proposal that invasion and extinction are two sides of the same evolutionary coin.

CJA Bradshaw

ResearchBlogging.orgCrawford, K., & Whitney, K. (2010). Population genetic diversity influences colonization success Molecular Ecology DOI: 10.1111/j.1365-294X.2010.04550.x

Bradshaw, C., Giam, X., Tan, H., Brook, B., & Sodhi, N. (2008). Threat or invasive status in legumes is related to opposite extremes of the same ecological and life-history attributes Journal of Ecology, 96, 869-883 DOI: 10.1111/j.1365-2745.2008.01408.x

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3 responses

29 03 2010
Inbreeding does matter « ConservationBytes.com

[…] is an important aspect of extinctions in free-ranging species (see also previous posts here and here) by Mr. Conservation Genetics himself, Professor Richard […]

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19 02 2010
Jeremy

Nice write-up. I pointed to it at our blog, where I said “I’d be willing to bet that if you could measure such a thing as invasiveness and persistence for crop varieties, where people, rather than nature, determine how many propagules survive and spread, the ones that are both widespread and long-lasting are also the ones with the most genetic diversity.”

Any thoughts on that?

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19 02 2010
CJAB

Thanks, Jeremy. I suspect that if threatened species have lower genetic diversity on average than their non-threatened congenerics, I suspect that a large sample of crop varieties would reveal the same trend – the widespread and persistent ones would have higher genetic diversity. Nice idea – might have to get a student to put just a database together to analyse this!

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