Dear All, I wish to thank all the people who reply to my request: this was very interesting and I really enjoy. I add the replies and some references below. Best wishes, Nicolas Poulet ## Some references ## Gannett L. 2004. The biological reification of race. British Journal for the Philosophy of Science 55: 323-345. Hedrick PW, and Kalinowski ST. 2000. Inbreeding depression in conservation biology. Annual Review of Ecology and Systematics 31: 139-62. Kinlan BP, and Gaines SD. 2003. Propagule dispersal in marine and terrestrial environments: a community perspective. Ecology 84: 2007 -2020. Mills LS, and Allendorf FW. 1996. The one-migrant-per-generation rule in conservation and management. Conservation Biology 10: 1509-1518. Palumbi SR. 2001. The ecology of marine protected areas. In: Bertness MD, Gaines SM and Hixon ME, eds. Marine Community Ecology. Sunderland, Mass: Sinauer Associates. 509-530. Palumbi SR. 2003. Population genetics, demographic connectivity, and the design of marine reserves. Ecological Applications 13: S146-S158. Palumbi SR. 2004. Marine reserves and ocean neighborhoods: The spatial scale of marine populations and their management. Annual Review of Environmental Resources 29: 31-68. Saccheri IJ, and Brakefield PM. 2002. Rapid spread of immigrant genomes into inbred populations. Proceedings of the Royal Society of London Series B - Biological Sciences 269: 1073-8. Vucetich JA, and Waite TA. 2000. Is one migrant per generation sufficient for the genetic management of fluctuating populations? Animal Conservation 3: 261-266. Waples RS, and Gaggiotti O. In press. What is a population? An empirical evaluation of some genetic methods for identifying the number of gene pools and their degree of connectivity. Molecular Ecology. Waples RS. 1998. Separating the wheat from the chaff: patterns of genetic differentiation in high gene flow species. Journal of Heredity 89: 438-450. Wang J. 2004. Application of the one-migrant-per-generation rule to conservation and management. Conservation Biology 18: 332-343. Westemeier RL, Brawn JD, Simpson SA, Esker TL, Jansen RW, Walk JW, Kershner EL, Bouzat JL, and Paige KN. 1998. Tracking the long-term decline and recovery of an isolated population. Science 282: 1695-8. Whitlock MC, and McCauley DE. 1999. Indirect measures of gene flow and migration: FST not equal to 1/(4Nm + 1). Heredity 82 ( Pt 2): 117-25. ## The replies ## ********* >From Jeff Markert Dear Nicolas, I think you ask some excellent questions in your evoldir post, I'll fill you in on my conclusions from my struggles with the same issue. I'm not sure I have a definite view yet, and I would be interested to see what you learn from your evoldir post. First, the idea about homogenization of is an important one. I believe there is a 1980's paper by Slatkin that suggests even one migrant every second generation is sufficient to prevent populations from diverging through genetic drift alone. There are at least two important caveats: One is that selection could act differently in the two populations, and could lead to divergence in both phenotypes and marker loci even with low or moderate levels of gene flow. It's basically a balancing act between the homogenizing effects of gene exchange and the differentiating effects of selection. The second is that if two populations start out as separate gene pools and then for some reason start exchanging migrants, then they will become homogeneous. However the time it takes for them to become the same (expressed in generations) is proportional to the number of individuals. For insects or other animals with very high population sizes, the effects of moderate levels of gene flow can be insignificant because it would take so long for homogeneity to be restored that the biogeographic scenario would often be quite likely to change over that time period. The effect of migration on population dynamics is an important one. A good place to start exploring this might be a paper by Westemeier et al (Science 282 pp 1695) on the genetic rescue of some genetically depauperate populations. We discussed this paper in a course last year, and I came away wondering whether the "rescue" effect was entirely due to a change in the genetics, or due to a change in the demographics because additional individuals were added to the population. It's likely both, but since you can't do controlled experiments on endangered populations it would be difficult to disentangle the genetic effects from population dynamics outside of the laboratory. I wonder whether there might be an experimental conservation genetics literature on this. The obvious experiment to do would be to set up several genetically impoverished populations. To some you add genetic diversity by putting in an unrelated individual and removing one of the individuals from the impoverished population. You also add impoverished and "outbred" individuals to impoverished and outbred population (all appropriate controls, etc. ) in order to isolate the effects of simple demographics from genetic diversity. However if you did all this, if might turn out to be only relevant to the demographics and genetics of the laboratory animal. best wishes, Jeff Markert ______________________________ Jeffrey Markert, Ph. D. Oak Ridge / EPA Postdoctoral Fellow Atlantic Ecology Division 27 Tarzwell Drive Narragansett, RI 02882 Phone: (401) 782 3153 http://markert.fastmail.fm ******** >From Norman Johnson Dear Nicolas, First thing is that a few migrants per generation will homogenize allelic frequencies IF the alleles are neutral. If selection is involved, a few migrants may not be sufficient to homogenize populations. Whitlock and McCauley have a paper cautioning the use of using indirect measures to measure gene flow because the assumption of neutrality may not be met. Whitlock, M., and D. E. McCauley. 1999. Indirect measures of gene flow and migration: F-st does not equal 1/(4Nm+1). Heredity. 82:117-125. Adam Porter and I showed that hybrid incompatibility could arise given sufficient selection and the proper genetic architecture even in the face of considerable gene flow (Nm > 10). Porter, A. H. and N. A. Johnson. 2002. Speciation despite gene flow when developmental pathways evolve. Evolution 56: 2103-2111. >> What these "few migrants" mean from a population dynamic point of view?<< I'm not sure what you mean by dynamical. >> Are they sufficient to influence significantly the populations' growth rates?<< Probably not. Hope this helps Norman ***** >From Oscar Gaggiotti Dear Nicolas, Actually, the problem you mention is important but difficult to treat so, although any people are aware of it, few have attempted to discuss it. Robin Waples and I have addressed this problem in an article that will be published in Mol Ecol sometime soon. It is clear that the level of migration that determines whether two populations represent the same genetic pool or not is different from the one that determines if two populations have independent dynamics. In the article we discuss this issue so if you are interested I can send you a copy. Best regards, Oscar Oscar Gaggiotti Professor Equipe Genomique de Populations et Biodiversité LECA UMR CNRS 5553 Université Joseph Fourier BP 53 38041 GRENOBLE France Tel.: 33(0)4 76 51 41 15 Fax: 33(0)4 76 51 42 79 http://www2.ujf-grenoble.fr/leca/membres/WebPageOscar/Webpage.html http://www2.ujf-grenoble.fr/leca/projets/IMPBio/IMPBioFr.html ***** >From Bob O'Hara >In broader view, is it justified to consider the definition of a >population (and so its conservation/management) only from a genetic point of view? My answer is a definite "no". I've attached a paper discussing how populations are defined, and I talked about this problem at a workshop. I can send you the .pdf, but it's about 1.5Mb in size (too many photos!). >I would appreciate any comments, references, papers, point of view. I had the same problem finding articles: I guess it's time someone wrote one! Bob -- Bob O'Hara Department of Mathematics and Statistics P.O. Box 68 (Gustaf Hällströmin katu 2b) FIN-00014 University of Helsinki Finland Telephone: +358-9-191 51479 Mobile: +358 50 599 0540 Fax: +358-9-191 51400 WWW: http://www.RNI.Helsinki.FI/~boh/ Journal of Negative Results - EEB: www.jnr-eeb.org ******* >From Marc Kochzius Dear Nicolas, The questions you raised are exactly the ones we are currently discussing in our group. Below please find some references of papers, that discuss the problem (at least to some extend) of population genetics vs. population dynamics. If you want, I can sent you the pdf files of these papers. Cheers, Marc PALUMBI (2003) POPULATION GENETICS, DEMOGRAPHIC CONNECTIVITY, AND THE DESIGN OF MARINE RESERVES. Ecological Applications, 13(1) Supplement, 2003, pp. S146–S158 KINLAN & GAINES (2003) PROPAGULE DISPERSAL IN MARINE AND TERRESTRIAL ENVIRONMENTS: A COMMUNITY PERSPECTIVE. Ecology 84(8): 2007–2020 Waples, R. S. 1998. Separating the wheat from the chaff: patterns of genetic differentiation in high gene flow species. Journal of Heredity 89:438–450. Palumbi, S.R. 2001. The ecology of marine protected areas. In: Marine Community Ecology ed. by M.D. Bertness, S.M. Gaines, and M.E. Hixon.. Sunderland, Mass: Sinauer Associates, pp.509-530. Palumbi (2004) MARINE RESERVES AND OCEAN NEIGHBORHOODS: The Spatial Scale of Marine Populations and Their Management. Annu. Rev. Environ. Resour. 29:31–68 Dr. Marc Kochzius Department of Biotechnology and Molecular Genetics Centre for Applied Gene Sensor Technology (CAG), FB2-UFT University of Bremen Leobener Strasse 28359 Bremen Germany Phone: +49 (0) 421-218-7225 (office) +49 (0) 421-218-7679 (Lab) Fax: +49 (0) 421-218-7578 Fish & Chips Project: www.fish-and-chips.uni-bremen.de POGEMAO Project: www.pogemao.uni-bremen.de CAG: www.gensensorik.uni-bremen.de/en/index.html Biotechnology: www.uft.uni-bremen.de/biotech/english/bmg_main.html Coral Reef Webpage: www.oceanium.de ***** >From Robin Waples Nicholas, A colleague passed this query on to me from the EvolDir. This is an interesting topic that hasn't had extensive treatment in the literature, although there are plenty of papers on migration and population genetic structure. I am attaching two of my papers that are relevant and might help. The first is an in press review paper for Molecular Ecology on the topic, What is a Population? , coauthored with Oscar Gaggiotti. It discusses both the ecological and evolutionary paradigms of a population and how to use genetic data to get insights into them. The second paper is from a few years ago and discusses the difficulty in drawing conclusions about population dynamics from genetic data. regarding your statement, "It is assumed that only few migrants per generation between two populations allow the homogenization of their genetic pools so that no genetic difference is revealed." This statement is not really true. More specifically, you might be able to find such statements in the literature, but they are misleading. One or more effective migrants per generation is sufficient to prevent (or make very unlikely) the fixation of different alleles in different populations, but that level will not homogenize allele frequencies. For example, even with 10 migrants per generation Fst will generally be > 0.02, which indicates modest allele frequency differences that can be highly significant if sample sizes are sufficiently large. As shown in the in press paper, current molecular methods provide very high power to detect small departures from panmixia. best wishes, Robin Waples ***** >From Paul Sunnucks Hi Nicolas you are right, it is a broad question(s)! 'It is assumed that only few migrants per generation between two populations allow the homogenization of their genetic pools so that no genetic difference is revealed.' Note that this is theoretical, and has some fairly strict limitations, including assumptions of panmixia and island model and applies only to NEUTRAL genetic variation. These are very important caveats. There has been some literature on how many migrants are generally required to produce 1 genetically effective migrants. Wang JL (2004) Application of the one-migrant-per-generation rule to conservation and management. CONSERVATION BIOLOGY 18 (2): 332-343 Vucetich JA, Waite TA (2000) Is one migrant per generation sufficient for the genetic management of fluctuating populations? ANIMAL CONSERVATION 3: 261-266 the outcomes approximately square with the Frankham meta-analysis estimate that the model Ne/N ratio for wildlife is in the ball park of 1/10. ie you need 10 migrants to get one effective one. 'What these "few migrants" mean from a population dynamic point of view? Are they sufficient to influence significantly the populations' growth rates?' Probably very dependent on lots of conditions, and you should not forget that the dichotomy between demographics and genetics is a false one. Fitness and hence population growth rates will depend on genetic factors. (Saccheri et al 1998 comes to mind). Talking of whom, you might find Saccheri IJ, Brakefield PM (2002) Rapid spread of immigrant genomes into inbred populations. Proceedings of the Royal Society of London Series B-Biological Sciences, 269, 1073-1078. interesting here. 'In broader view, is it justified to consider the definition of a population (and so its conservation/management) only from a genetic point of view?' No! At least because of the 'false dichotomy argument'. Paul Sunnucks -- Dr Paul Sunnucks Senior Lecturer in Zoology School of Biological Sciences Monash University, Melbourne Clayton Campus 3800 Victoria Australia ph + 61 3 9905 9593 fax + 61 3 9905 5613 email paul.sunnucks@sci.monash.edu.au webpage: http://www.biolsci.monash.edu.au/staff/sunnucks.html ***** Nicolas Poulet