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Genetic Problems (genetic + problem)
Selected AbstractsInbreeding depression and founder diversity among captive and free-living populations of the endangered pink pigeon Columba mayeriANIMAL CONSERVATION, Issue 4 2004Kirsty J. Swinnerton The endemic pink pigeon has recovered from less than 20 birds in the mid-1970s to 355 free-living individuals in 2003. A major concern for the species' recovery has been the potential genetic problem of inbreeding. Captive pink pigeons bred for reintroduction were managed to maximise founder representation and minimise inbreeding. In this paper, we quantify the effect of inbreeding on survival and reproductive parameters in captive and wild populations and quantify DNA sequence variation in the mitochondrial d-loop region for pink pigeon founders. Inbreeding affected egg fertility, squab, juvenile and adult survival, but effects were strongest in highly inbred birds (F,0.25). Inbreeding depression was more apparent in free-living birds where even moderate levels of inbreeding affected survival, although highly inbred birds were equally compromised in both captive and wild populations. Mitochondrial DNA haplotypic diversity in pink pigeon founders is low, suggesting that background inbreeding is contributing to low fertility and depressed productivity in this species, as well as comparable survival of some groups of non-inbred and nominally inbred birds. Management of wild populations has boosted population growth and may be required long-term to offset the negative effects of inbreeding depression and enhance the species' survival. [source] Evolutionary, behavioural and molecular ecology must meet to achieve long-term conservation goalsMOLECULAR ECOLOGY, Issue 18 2009J. SCOTT KEOGH Founder populations in reintroduction programmes can experience a genetic bottleneck simply because of their small size. The influence of reproductive skew brought on by polygynous or polyandrous mating systems in these populations can exacerbate already difficult conservation genetic problems, such as inbreeding depression and loss of adaptive potential. Without an understanding of reproductive skew in a target species, and the effect it can have on genetic diversity retained over generations, long-term conservation goals will be compromised. In this issue of Molecular Ecology, Miller et al. (2009a) test how founder group size and variance in male reproductive success influence the maintenance of genetic diversity following reintroduction on a long-term scale. They evaluated genetic diversity in two wild populations of the iconic New Zealand tuatara (Fig. 1), which differ greatly in population size and genetic diversity, and compared this to genetic diversity in multiple founder populations sourced from both populations. Population viability analysis on the maintenance of genetic diversity over 400 years (10 generations) demonstrated that while the loss of heterozygosity was low when compared with both source populations (1,14%), the greater the male reproductive skew, the greater the predicted losses of genetic diversity. Importantly however, the loss of genetic diversity was ameliorated after population size exceeded 250 animals, regardless of the level of reproductive skew. This study demonstrates that highly informed conservation decisions could be made when you build on a solid foundation of demographic, natural history and behavioural ecology data. These data, when informed by modern population and genetic analysis, mean that fundamental applied conservation questions (how many animals should make up a founder population?) can be answered accurately and with an eye to the long-term consequences of management decisions. Figure 1. ,Large adult male tuatara attacking a smaller male. Photo by Jeanine Refsnider. [source] Female-biased dispersal, low female recruitment, unpaired males, and the extinction of small and isolated bird populationsOIKOS, Issue 2 2001Svein Dale Small and isolated populations are usually assumed to be at a high risk of extinction due to environmental or demographic stochasticity, genetic problems, or too little immigration. In birds, natal dispersal is usually female-biased, but the consequences of such a pattern on vulnerability to extinction of isolated populations has not received much attention before. In this paper I derive predictions as to how female-biased natal dispersal may differentially affect the extinction risk of populations and species with contrasting distributions, migratory behaviours, life histories and mating systems. Female-biased dispersal will lead to male-biased sex ratios in small, isolated or fragmented populations, in particular because recent research has shown that females often have a limited ability to search for mates and may therefore effectively be lost from the breeding population if they disperse into areas empty of conspecifics. I reviewed published studies on birds and found that a high proportion of unpaired males is common in isolated populations or populations in small habitat fragments. Dispersal of females may therefore increase the vulnerability to extinction of small or isolated populations, or populations at the periphery of a species' distribution range. I also predict that vulnerability to extinction should be greater for migratory than for resident species and greater for short-lived than for long-lived species because of differences in the time available for females to locate unpaired males. Further, extinction risk may also be greater for birds than for mammals due to differences in which sex disperses and patterns of parental care. Finally, mating system will also affect vulnerability to extinction when natal dispersal leads to biased sex ratios. I review available evidence for these predictions (e.g. songbird declines in North America) and discuss implications for conservation. [source] Christianity, health, and genetics,AMERICAN JOURNAL OF MEDICAL GENETICS, Issue 1 2009David H. Smith Abstract Health is an intrinsic value that Christians should respect, but it is not the highest value. Christians should be willing to jeopardize their own health for the health of others, and should repudiate any idea that genetic problems are the result of sin. Rather, sin leads us to make genetic problems harder to live with than they should be. © 2009 Wiley-Liss, Inc. [source] Azoospermia and Sertoli-cell-only syndrome: hypoxia in the sperm production site due to impairment in venous drainage of male reproductive systemANDROLOGIA, Issue 5 2010Y. Gat Summary Sertoli-cell-only (SCO) syndrome, or germ cell aplasia, is diagnosed on testicular biopsy when germ cells are seen to be absent without histological impairment of Sertoli or Leydig cells. It is considered a situation of irreversible infertility. Recent studies have shown that varicocele, a bilateral disease, causes hypoxia in the testicular microcirculation. Destruction of one-way valves in the internal spermatic veins (ISV) elevates hydrostatic pressure in the testicular venules, exceeding the pressure in the arteriolar system. The positive pressure gradient between arterial and venous system is reversed, causing hypoxia in the sperm production site. Sperm production deteriorates gradually, progressing to azoospermia. Our prediction was that, if genetic problems are excluded, SCO may be the final stage of longstanding hypoxia which deteriorates sperm production in a progressive process over time. This would indicate that SCO is not always an independent disease entity, but may represent deterioration of the testicular parenchyma beyond azoospermia. Our prediction is confirmed by histology of the seminiferous tubules demonstrating that SCO is associated with extensive degenerative ischaemic changes and destruction of the normal architecture of the sperm production site. Adequate treatment of bilateral varicocele by microsurgery or by selective sclerotherapy of the ISV resumes, at least partially, the flow of oxygenated blood to the sperm production site and restored sperm production in 4 out of 10 patients. Based on our findings the following statements can be made: (i) SCO may be related in part of the cases to persistent, longstanding testicular parenchymal hypoxia; (ii) germ cells may still exist in other areas of the testicular parenchyma; and (iii) if genetic problems are excluded, adequate correction of the hypoxia may restore very limited sperm production in some patients. [source] Measuring and interpreting genetic structure to minimize the genetic risks of translocationsAQUACULTURE RESEARCH, Issue 1 2000M S. Johnson Genetic subdivision of a species indicates the potential for local adaptation, and the genetic differences among populations are a key component of genetic diversity. Molecular genetic markers are generally used to assess the extent and pattern of subdivision. These traits provide an abundance of simple genetic markers, and they allow comparisons across studies. However, the connection of molecular genetic variation to local adaptation and, hence, to possible genetic problems of translocation, is weak. In the extreme case of no genetic subdivision, there is no reason to expect genetic problems with translocation. Where there is deep genetic structure, indicating substantial evolutionary independence of sets of populations, translocations may threaten basic components of genetic diversity. Between these extremes, however, predicting genetic problems of translocations is extremely difficult. The molecular markers used to measure genetic structure indicate where there has been opportunity for local adaptation, but they are not directly related to such adaptation. The relationship of the level of genetic divergence to genetic incompatibilities is very loose, although quantitative tests are scarce. However, studies of reproductive isolation between species illustrate the fundamental inadequacy of using measures of genetic divergence to predict interactions between populations. Although it is tempting to use simple measures as predictors, such use may provide a false sense of scientific rigour. There is no substitute for direct tests for variation in ecologically relevant traits and possible genetic incompatibilities among populations. [source] | ||||||||||