On January 28, 2005, I sent the following to EvolDir: Dear colleagues, I vaguely recall seeing a paper some years ago, perhaps 10-15, which suggested that the ratio of Ne/N is smaller the larger is N. Can anybody give me this reference? Many, many thanks to all who responded! The responses I received are given below for the benefit of all. Bill 1. (This message actually identified the paper I vaguely recalled:) From: Charles Goodnight Yup. That would be me (among others) that wrote that. It turns out that there is a strong negative relationship between N and Ne/N. We confirmed this experimentally, and found qualitative agreement with published data (although differences in methodology among studies precluded convincing quantitative comparisons). Aside: Note the census numbers for the gallon populations. Those counts almost killed me. Pray, L. A., C. J. Goodnight, L. Stevens, G. Yan, and J. M. Schwartz. 1996. The effect of population size on effective population size. Genetical Research 68:151-156. 2. From: Paul Moran Is that Frankham 95 Genetical Research 66:95-107? It seems, however, that the apparent influence of N is related to mixing harmonic and arithmetic means rather than an inherent biological phenomenon. Robin will check my interpretation on that. He wrote about this issue in a recent book chapter, and he and Steven Kalinowski published a paper in Conservation Biology (16:129-136). 3. From: Robin Waples Robin.Waples@noaa.gov Perhaps you are thinking of Vucetich and Waite 1998 Conserv Biol. 12:1023-1030 or Vucetich et al. 1997 Evolution 51:2015-2019. They showed that Ne/N declines to an asymptote as one considers a longer time series. However, this is the case only if one defines long term Ne/N as the harmonic mean Ne divided by the arithmetic mean N. Hedgecock (1994) suggested Ne/N might be very small in some marine species. This hypothesis is controversial, but some recent genetic estimates of Ne in marine species support this idea. Ne and Tajima (1981) suggested Ne/N might be low in species with large N such as insects, but I don't think they provided any data. Hedgecock, D. 1994. Does variance in reproductive success limit effective population sizes of marine organisms? Pp. 122-134 in A. R. Beaumont, ed. Genetics and evolution of aquatic organisms. Chapman and Hall, London. 4. From: Paul Moran Thanks, Robin. As an example of your point about Ne in marine populations (other than oysters), Lorenz Hauser's work on New Zealand snapper showed a really small Ne/N ratio (I've forgotten just how small, but I remember being impressed when I saw him present those data). Hauser L, Adcock G.J., Smith P.J., Bernal Ramirez J.H., Carvalho G.R.(2002) Loss of microsatellite diversity and low effective population size in an overexploited population of New Zealand snapper (Pagrus auratus). Proceedings of the National Academy of Sciences 99, 11742-11747. 5. From: Masatoshi Nei Dear Bill, Maybe you are referring to the Nei and Graur paper, which was published in Evolutionary Biology in 1984. In this paper we estimated the census size in a crude way and effective size from average heterozygosity. You can get a copy of this paper from my website, which is given at the bottom of the signature page of this email. You can see that Ne/N ratio is smaller for large N. 6. From: Nicky Rivers Dear Bill regarding your question below, I dont know the paper but would be interested to know of the reference if you find it - could you post the replies on evoldir? However there is a useful section in R. Frankham, J.D. Ballou and D.A. Briscoe's book 'Introduction to Conervation Genetics' which talks about the influences on Ne/N (p241-251), however it doesnt say that larger N per se influences the ratio, but does say fluctuations in popn size, overlapping generations, unequal sex ratio, variations in family size and outbreeding are important factors influencing the Ne/N ratio, so perhaps it is not as simple as the larger the N, the smaller the Ne/N ratio? Nicola Rivers 7. From: Rich Strauss No, but to the extent that Ne is roughly constant among populations (or time), then Ne/N and N are proportional to reciprocals. Rich Strauss C. William Birky, Jr. Professor of Ecology and Evolutionary Biology Member, Graduate Interdisciplinary Programs in Genetics Biological Sciences West 1041 E. Lowell University of Arizona Tucson, AZ 85721 Office phone: 520-626-6513 Lab phone: 520-626-5108 Fax: 520-621-9190 Email: birky@u.arizona.edu birky@u.arizona.edu