Please cite Heredity as the source of the following items. If publishing online, please carry a hyperlink to http://www.nature.com/hdy/index.html.

This month we find out if inbreeding spells doom for endangered populations, whether bottlenecks can lead to degeneration of genes, how X chromosome influences sperm length and much more.

You say Inbred, we say adapted.

Click here to read the paper

Researchers find nearly extinct species of Goodeid fish is inbred in the wild.

The significance of genetic and non-genetic factors in driving extinction has been debated at length. In a paper published as Advanced Online Publication on 28 February 2007, Prof. Michael Ritchie and colleagues compared the genetic diversity, using microsattelite loci, of wild populations of two nearly extinct species of Goodeid fish (Z.tequila and A.splendens) with samples from captive stocks. They found that genetic diversity indices, such as alleic richness, were significantly higher in the wild than in captive populations for both species. Both species also showed evidence of exponential population decline, but the evidence in Z.tequila was stronger. However, the wild Z.tequila population, the only known extant population, showed indications that its genetic variability had declined from its probable ancestral levels.

The authors considered the implications of their findings for the conservation of critically endangered populations. They proposed that “the viability of wild stocks should not be compromised by attempts to increase their genetic diversity in the absence of evidence of inbreeding depression. [Such attempts] may promote the spread of deleterious alleles adapted to captivity.” In the case of Z.tequila, the wild population has survived at least 15 years of such severe isolation that it has probably undergone an amount of local adaptation. Any rescue attempts that introduce captive stocks could mean a sad trade-off said Ritchie and colleagues. “[We] risk breaking down a locally adapted genome (and one purged of deleterious alleles) by introducing alleles adapted to captivity, or risk local extinction due to [unpredictable] environmental changes to which this genetically impoverished population cannot adapt.

Click here to read the paper or click here to comment on this article.

Other articles published Advanced Online Publication:

 X chromosome influences sperm length in the stalk-eyed fly Cyrtodiopsis dalmanni

 Habitat size and the genetic structure of a cyclical parthenogen, Daphnia magna

 Multivariate segregation analysis for quantitative traits in line crosses

 Efficiency of triple test cross for detecting epistasis with marker information

 Meiotic recombination in Turnera (Turneraceae): extreme sexual difference in rates, but no evidence for recombination suppression associated with the distyly (S) locus

 Fluctuating asymmetry and genetic variability in the roe deer (Capreolus capreolus): a test of the developmental stability hypothesis in mammals using neutral molecular markers

 Dos and don'ts of testing the geographic mosaic theory of coevolution

 Recent degeneration of an old duplicated flowering time gene in Brassica nigra

 The genetic basis of interspecific differences in genital morphology of closely related carabid beetles

 The effect of non-additive genetic interactions on selection in multi-locus genetic models

 Evolutionary dynamics of multilocus microsatellite arrangements in the genome of the butterfly Bicyclus anynana, with implications for other Lepidoptera

Posted by Ogechi Okoli at 04:04 PM | Permalink | Comments (0) | TrackBacks (0)

After reading with interest the recent paper by Axenovich et al. (Heredity 98:99-105) and the commentary on it by R F Nespolo (Heredity 98:63-64), Philip Hedrick has written this short commentary on their findings that puts their conclusions in a familiar context for the readers of Heredity.

Paper by Axenovich et al http://www.nature.com/hdy/journal/v98/n2/abs/6800908a.html

News and Commentary by R F Nespolo http://www.nature.com/hdy/journal/v98/n2/full/6800925a.html

Cycling selection for litter size in arctic foxes

PW Hedrick

Various evolutionary scenarios have been suggested to explain the regular numerical cycles in some microtine rodents (Nespolo, 2007). The numbers of arctic foxes in inland populations also have approximately four-year cycles in response to the cycles in numbers of small rodents, mainly voles and lemmings. Using a detailed pedigree of captive animals, Axenovich et al. (2007) concluded that the variation in arctic fox number was mainly the result of variation in litter size determined primarily by polymorphism at a major gene. To explain the maintenance of this polymorphism, they presented a model in which the recessive genotype had the highest litter size in bad years and the lowest litter size in good years (Table 1a). In their model, “In years with low food supply, the survival rate of the small litters produced by A2A2 mothers was assumed to be k-times higher than that of large litters produced by A1A1 and A1A2 mothers.”
These litter sizes can be given as standardized relative fitnesses as in Table 1b. The conditions for genetic polymorphism for this model was first given by Haldane and Jayakar (1963) in which they showed that a polymorphism was maintained when the arithmetic mean fitness of genotype A2A2 over generations is greater than 1 and the geometric mean fitness of A2A2 is less than 1. To meet these conditions, assuming that there are three bad years to every good year (Axenovich et al. 2007), then 1.666 < k < 1.718, a range of 0.052, which encompasses the k = 1.7 value given as a stable polymorphism example by Axenovich et al. (2007). Or for a stable polymorphism with standardized fitness, 1.111 < k' < 1.145, a range of only about 3%. In other words, the conditions for polymorphism maintenance with dominance and cyclic fitness variation are quite restrictive (Hedrick et al. 1976).

Further, Axenovich et al. (2007) concluded that the “male effect was negligible” at this gene, indicating that selection is only occurring in females and not in males. Female-only selection can be modeled using the standardized fitnesses given in Table 1c. In this case, the conditions for a stable polymorphism, 1.056 < k'' < 1.063, are even more restrictive, encompassing a range of less than 0.7%. In other words, it appears unlikely that litter sizes and subsequent survival of the pups are so finely balanced that they meet these very limited conditions for a balanced polymorphism under cycling selection.
It is possible that other types of balancing selection with broader conditions for stable polymorphism, such differential selection at different locations or genotype-specific habitat selection (Hedrick et al., 1986; Hedrick, 2006), or some kind frequency-dependent selection, may also be acting so that the conditions for stability are less restrictive. Or, as suggested by Axenovich et al. (2007), the farmed foxes analyzed for litter size may have inherited the allele for small litter size from coastal populations which have small litters and reproduce every year and the allele for large litter size from inland populations which large litters sizes but do not reproduce every year. If this putative litter size gene can be located and the different alleles characterized molecularly, perhaps the type of balancing selection, or other explanation, can be identified. These concerns do not detract from the fascinating statistical conclusion of Axenovich et al. (2007) that the best genetic model to explain the observed bimodal litter size in arctic foxes is one with a single major gene.

PW Hedrick is at the School of Life Sciences, Arizona State University, Tempe, Arizona 85287-4501, USA.

e-mail: philip.hedrick@asu.edu

Axenovich TI, Zorkoltseva IV, Akberdin IR, Beketov SV, Kashtanov SN, Zakharov IA, Borodin PM (2007). Inheritance of litter size at birth in farmed arctic foxes (Alopex lagopus, Canidae, Carnivora). Heredity 98: 99-105.

Haldane JBS, Jayakar SD (1963). Polymorphism due to selection of varying direction. J. Genet. 58: 237-242.

Hedrick PW (1986). Genetic polymorphism in heterogeneous environments: A decade later. Ann. Rev. Ecol. Syst. 17: 535-566.

Hedrick PW (2006). Genetic polymorphism in heterogeneous environments: The age of genomics. Ann. Rev. Ecol. Evol. Syst. 37: 67-93.

Hedrick PW, Ginevan ME, Ewing EP (1976). Genetic polymorphism in heterogeneous environments. Ann. Rev. Ecol. Syst. 7: 1-32.

Nespolo RF (2007). A complex population dynamic explained by a single-locus Mendelian model for litter size. Heredity 98: 63-64.

Paper by Axenovich et al http://www.nature.com/hdy/journal/v98/n2/abs/6800908a.html

News and Commentary by R F Nespolo http://www.nature.com/hdy/journal/v98/n2/full/6800925a.html

Posted by Haroon Ashraf at 01:39 PM | Permalink | Comments (0) | TrackBacks (0)

Please reply to this post to comment on a paper published in Heredity.

Posted by Richard Nichols at 02:44 PM | Permalink | Comments (1) | TrackBacks (0)

There is a widespread view that peer-review could be improved, using the opportunities provided by the web; see here: http://blogs.nature.com/peer-to-peer/

Another model is to publish papers accompanied by referees’ comments, and correspondence columns offer an analogous forum to air legitimate differences of scientific opinion.

This blog will attempt to combine some of the better aspects of these approaches. It will evolve in the light of Heredity readers and authors’ recommendations, but I have in mind that we will use it to

1) Publish rapid feedback on papers that have appeared in Heredity: the paper is wrong because … , readers should also see paper x because … . i.e. something like a correspondence section of a journal, but with the merit of being very fast and brief. The more incisive or interesting comments could be published in print.
2) Publish comments provided for public consumption by the referees: the paper is controversial because … but I recommend publication because … .
3) To publish discussion on the editorial direction of the journal. In large part the content of Heredity is determined by what is submitted, but the News & Commentaries, Short Reviews and Special Issues are commissioned. Are we neglecting important areas?

Contributions will be screened before being posted. Please reply to the appropriate topics to contribute.

Posted by Richard Nichols at 02:36 PM | Permalink | Comments (0) | TrackBacks (0)

Are there areas of Genetics in which Heredity should publish more (or fewer) News and Commentaries, Reviews or Special issues?

Reply to this post, to suggest future directions.

Posted by Richard Nichols at 02:25 PM | Permalink | Comments (2) | TrackBacks (0)