Evolutionary Biology Pays Off

This forum is for the discussion of the evidence for evolution. Anyone is welcome to post, however, scripture is not allowed. As the title says, Science Only please!

Moderator: Moderators

Evolutionary Biology Pays Off

Postby Timothy Chase » Wed Mar 21, 2007 7:27 pm

A lot of times, people who are sympathetic towards creationism will argue that evolutionary biology has no practical value. Given this, I think it might be nice to keep track of some of the stories which show how our knowledge of evolution pays off and even saves lives.

Now of course there are examples involving our understanding of bacteria, lateral gene transfer between bacteria, the life cycles of phages and why you might want to avoid taking antibiotics for e coli, etc. But here is something a little different - which may save lives - and which doesn't at least directly involve bacteria, but which depends upon our knowledge of evolution in at least a couple of ways.

Glow In The Dark GM Mosquitoes Prevent Spread Of Malaria
Main Category: Tropical Diseases News
Article Date: 20 Mar 2007 - 6:00 PDT
http://www.medicalnewstoday.com/healthn ... wsid=65601


Feel free to comment - or add other stories here. Later, if we have a list of such stories it will make writing articles or letters to the editor a little easier when this sort of question comes up.
User avatar
Timothy Chase
 
Posts: 532
Joined: Sat Oct 07, 2006 4:59 pm

Postby Paula Thomas » Thu Mar 22, 2007 2:20 pm

Good idea Tim.

But we should bare in mind that utility does not necessarily equal truth!

Paula
Paula Thomas
 
Posts: 290
Joined: Fri Dec 01, 2006 12:51 pm
Location: London, UK

Postby Timothy Chase » Thu Mar 22, 2007 7:57 pm

wilmot wrote:Good idea Tim.

But we should bare in mind that utility does not necessarily equal truth!

Paula

Granted.

With me, when I hear about some discovery and they start getting into the medical implications or whatnot I have to work not to just zone it out. I want to understand. It is the theoretical aspects which genuinely interest me. But this isn't how most people work, and when you speak with someone, it is important to keep in mind their context, the level of their understanding and how they understand things - as well as their interests. Part of the art of communication.
User avatar
Timothy Chase
 
Posts: 532
Joined: Sat Oct 07, 2006 4:59 pm

Postby marc » Sat Mar 24, 2007 7:58 pm

Scientists manipulate the genome of a mosquito and design transgenic mosquitoes that are resistant to the Plasmodium parasite.

It is not surprising that the mosquito lives longer and has more offspring. If you cure any animal of a parasitic infection and you will find the same result.

This is great news for the mosquito (and for people) but I have a bit of trouble seeing this as a pay off of evolution biology. It seems to me that this is a practical application of genetic engineering not evolution.
Marc
marc
 
Posts: 5
Joined: Wed Dec 06, 2006 2:47 pm

Postby Timothy Chase » Sun Mar 25, 2007 2:02 am

Sorry, Marc - my wife was interviewing in a different part of town today and we took a bit of time getting back.

Actually, I think you may be a assuming a bit too much, though, as far as the negative effects of parasitic infection is concerned. For example, there are plenty of phages which actually benefit their bacterial hosts. Likewise, you would be at a distinct disadvantage without the kilogram of bacteria you have in your lower gut - as it helps to process your food. Now this is not to say that plasmodium benefits its mosquito host. I honestly don't know. But there is no reason to assume that it is actually detrimental to the mosquito host. In fact, as both undoubtedly maintain relatively large populations, one would expect coevolution such that at worse, the plasmodium would be asymptomatic with little or no effect upon its mosquito host.

Setting this aside for the moment, one should ask why in the first place we would consider fitness costs. The reason is obviously that we know that natural selection is an effective force, and if the transgenic mosquito is to displace the established population of mosquitos, it must have distinct advantage, either in terms of fitness or fecundity, or preferably both. As such, we are putting a fairly essential principle of evolutionary theory into practice.

However, we also know that a natural species will typically be relatively close to a local optima - particularly if it maintains a large population. The larger the population, the more efficient the process of natural selection and the narrower the range over which detrimental mutations will be tolerated by the environment. Mosquitos maintain large populations in what is a fairly stable environment. Ergo, they should be close to the local optima.

As such, when we genetically modify the mosquito, this will tend to have a detrimental effect upon the genetically modified mosquitos. And as such, transgenic mosquitos will tend to be selected against.

This is in fact a major problem which Marrelli was well aware of.

Padet Siriyasatien and Usavadee Thavara wrote:Fitness cost

Fitness cost is defined as the relative success with which a genotype transmits its genes to the next generation (Marrelli et al., 2006). There are two major components of the fitness cost, survival and reproduction, which can be evaluated by analyzing several parameters, such as fecundity, fertility, larval biomass productivity, developmental rate, adult emergence, male ratio and mating competitiveness. Fitness of genetically modified mosquitoes can be reduced from the negative effect of transgene products such as fluorescent markers and antipathogen proteins or from insertional mutagenesis after a transposition event (Catteruccia et al., 2003; Marrelli et al., 2006). Catteruccia et al. (2003) demonstrated that the reductions of fitness of the transgenic An. stephensi mosquitoes is caused by the expression of an exogenous gene and the mutations from the insertion of the transgene. The
fitness cost of transgenic Ae. aegypti mosquitoes has been examined by Irvin et al. (2004), the results show that fitness of transgenic mosquitoes were reduced significantly compared to not-transgenic mosquitoes. The fitness of the genetically modified mosquitoes should therefore be evaluated under laboratory conditions for planning release strategies.


Genetically Modified Mosquitoes: A New Strategy to Control Mosquito Borne Diseases
Padet Siriyasatien and Usavadee Thavara
Thai Journal of Veterinary Medicine 36(4): 9-19.


Consequently, after having created a transgenic, we need to be able to measure the effects of fitness and fecundity - the same way that we already have been in some of our empirical studies of the process of evolution - in order to determine whether we have succeeded in creating a rare transgenic which has found a higher local optima so that it will have a selective advantage against the native species.

But we should also ask: how is it possible for them to genetically modify mosquitos in the first place? And the answer is: the same way nature has largely been modifying multicellular life over the past billion years and life for the past four billion - viruses. Lateral gene transfer. In the case of multicellular life, this is generally by means of retroviruses which take up residence in the genome of their host as a provirus through infection, and then are passed on from generation to generation by means of vertical gene transfer - or inheritance.

So lets see... We are genetically modifying the mosquito by means of retroviral insertion, we realise that both the plasmodium and mosquito host are most likely well-coadapted such that the infection of the mosquito is asymptomatic, we recognise that transgenic organisms will typically be less fit than the natural organisms which we might seek to displace, we are measuring the effects of fitness and fecundity to determine whether a given transgenic organism is likely to displace its natural counterpart, we need to know whether the two are likely to interbreed, etc..

Seems to me that we have actually learned a great deal by studying evolution and are applying it in a way that has the potential of saving millions of lives. Moreover, given global warming, this could be of considerable significance for those who are living at the higher latitudes in the coming decades - even if one assumes that saving lives in the tropics doesn't already carry a great deal of weight in terms of their priorities. (I actually hope that the latter is a false assumption, but wouldn't care to presume too much.)
User avatar
Timothy Chase
 
Posts: 532
Joined: Sat Oct 07, 2006 4:59 pm

Postby Timothy Chase » Sun Mar 25, 2007 2:50 am

Unfortutately the article is subscription only at this point, but I found the abstract which is already available on the web...

Mauro T. Marrelli, et al. wrote:Abstract

The introduction of genes that impair Plasmodium development into mosquito populations is a strategy being considered for malaria control. The effect of the transgene on mosquito fitness is a crucial parameter influencing the success of this approach. We have previously shown that anopheline mosquitoes expressing the SM1 peptide in the midgut lumen are impaired for transmission of Plasmodium berghei. Moreover, the transgenic mosquitoes had no noticeable fitness load compared with nontransgenic mosquitoes when fed on noninfected mice. Here we show that when fed on mice infected with P. berghei, these transgenic mosquitoes are more fit (higher fecundity and lower mortality) than sibling nontransgenic mosquitoes. In cage experiments, transgenic mosquitoes gradually replaced nontransgenics when mosquitoes were maintained on mice infected with gametocyte-producing parasites (strain ANKA 2.34) but not when maintained on mice infected with gametocyte-deficient parasites (strain ANKA 2.33). These findings suggest that when feeding on Plasmodium-infected blood, transgenic malaria-resistant mosquitoes have a selective advantage over nontransgenic mosquitoes. This fitness advantage has important implications for devising malaria control strategies by means of genetic modification of mosquitoes.

Transgenic malaria-resistant mosquitoes have a fitness advantage when feeding on Plasmodium-infected blood
Mauro T. Marrelli, Chaoyang Li , Jason L. Rasgon, and Marcelo Jacobs-Lorena
http://www.pnas.org/cgi/content/abstract/0609809104v1


Interestingly, the advantage which the transgenics have will be an advantage only where a substantial percentage of the vertebrate hosts of plasmodium are infected. Not sure whether this is by intention or not.
User avatar
Timothy Chase
 
Posts: 532
Joined: Sat Oct 07, 2006 4:59 pm

Evolutionary Biology Pays Off

Postby Dave Oldridge » Mon Mar 26, 2007 8:10 am

On 24 Mar 2007 at 14:58, marc wrote:

Scientists manipulate the genome of a mosquito and design
transgenic mosquitoes that are resistant to the Plasmodium
parasite.

It is not surprising that the mosquito lives longer and has more
offspring. If you cure any animal of a parasitic infection and
you will find the same result.

This is great news for the mosquito (and for people) but I have
a bit of trouble seeing this as a pay off of evolution biology.
It seems to me that this is a practical application of genetic
engineering not evolution.

These are small potatoes anyway. It's the forced evolution of
the rice seed crop by the Rice Institute in the Phillipines
that's keeping Asia fed right now. That's big potatoes (or
rather big rice).

They deliberately irradiate seeds and choose from the resulting
mutants for best resistance to insect pests along with good
nutrition for humans. They HAVE to do it this way to stay ahead
of the NATURAL evolution of the insect pests.



--

Dave Oldridge
ICQ 1800667
VA7CZ
Dave Oldridge+
Dave Oldridge
 
Posts: 159
Joined: Sat Oct 07, 2006 4:59 pm

Re: Evolutionary Biology Pays Off

Postby Timothy Chase » Mon Mar 26, 2007 1:48 pm

Dave Oldridge wrote:These are small potatoes anyway. It's the forced evolution of the rice seed crop by the Rice Institute in the Phillipines that's keeping Asia fed right now. That's big potatoes (or rather big rice).

They deliberately irradiate seeds and choose from the resulting mutants for best resistance to insect pests along with good nutrition for humans. They HAVE to do it this way to stay ahead of the NATURAL evolution of the insect pests.

Well, rice is one area we really need to pay attention to, specifically in terms of heat resistance. It is quite sensitive to higher temperatures, and as the temperature goes up it will be less well adapted to the areas in which it is currently grown. I know that this is something people are already concerned about - given how much of the world depends upon it.

Incidently, retroelements have been a major force in supplying us with the variation which made the domestication of rice possible - according to recent studies. I believe they are called "MITEs" - pretty tiny even by retroelement standards - although I would have to look it up just to be sure.
User avatar
Timothy Chase
 
Posts: 532
Joined: Sat Oct 07, 2006 4:59 pm

Postby Timothy Chase » Mon Mar 26, 2007 2:05 pm

MITEs - miniture inverted transposable elements. Actually they would appear not to be retroelements, although there is some question in this regard. In any case, the "inverted" mobility through transposition rather than retrotransposition, and yes, they are responsible for the much of the variation which made the rapid domestication of rice possible.

Moreover, it would appear that the Chinese are putting them to work today:

Mobilization of the Active MITE Transposons mPing and Pong in Rice by Introgression from Wild Rice (Zizania latifolia Griseb.)
Xiaohui Shan, Zhenlan Liu, Zhenying Dong, Yongming Wang, Yu Chen, Xiuyun Lin, Likun Long, Fangpu Han, Yingshan Dong and Bao Liu
MBE Advance Access published January 12, 2005
http://mbe.oxfordjournals.org/cgi/reprint/msi082v1.pdf
User avatar
Timothy Chase
 
Posts: 532
Joined: Sat Oct 07, 2006 4:59 pm


Return to Science Only

Who is online

Users browsing this forum: No registered users and 2 guests

cron