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PubMed2005

Genetic structure of an endangered Portuguese semiferal pony breed, the Garrano.

The present study intends to survey the genetic variability of an endangered semiferal Portuguese native pony breed, the Garrano. Thirteen microsatellite markers were examined in 277 animals born in 1998, belonging to eight subpopulations corresponding to eight northern Portuguese geographic regions. Mean heterozygosity (H(o)) in the Garrano breed was 0.732, ranging from 0.531 to 0.857 across subpopulations. Allelic frequencies and diversity differed significantly between regions, suggesting the existence of genetic differentiation within the breed confirmed by the population differentiation estimator F(ST). Allele sharing genetic distance (Dps) was used to determine the relationship between the analyzed subpopulations, some of which are diverging significantly from the others. Relationships among six Iberian horse breeds (including the Garrano) were assessed through the restricted maximum likelihood method, which clusters the Garrano with another Celtic pony, the Spanish Asturcon, traditionally bred in geographical continuity with the Garrano. Results reveal a statistically significant deficit of heterozygotes within the Garrano breed (F(IT) = 0.031, p < 0.05). Regular monitoring should therefore be implemented so that the effect of genetic drift within subpopulations, enhanced by inbreeding, may be successfully minimized.

Alleles↗
PubMed2005

A spatial model to estimate habitat fragmentation and its consequences on long-term persistence of animal populations.

The increasing use of the landscape by humans has led to important diminutions of natural surfaces. The remaining patches of wild habitat are small and isolated from each other among a matrix of inhospitable land-uses. This habitat fragmentation, by disabling population movements and stopping their spread to new habitats, is a major threat to the survival of numerous plant and animal species. We developed a general model, adaptable for specific species, capable of identifying suitable habitat patches within fragmented landscapes and investigating the capacity of populations to move between these patches. This approach combines GIS analysis of a landscape, with spatial dynamic modeling. Suitable habitat is identified using a threshold area to perimeter ratio. Potential movement pathways of species between habitat patches are modeled using a cellular automaton. Habitat connectivity is estimated by overlaying habitat patches with movement pathways. The maximum potential population is calculated within and between connected habitat patches and potential risk of inbreeding within meta-populations is considered. The model was tested on a sample map and applied to scenario maps of predicted land-use change in the Peoria Tri-county region (IL). It (1) showed area of natural area alone was insufficient to estimate the consequences on animal populations; (2) underscored the necessity to use approaches investigating the effect of land-use change spatially through the landscape and the importance of considering species-specific life history characteristics; and (3) highlighted the model's potential utility as an indicator of species likelihood to be affected negatively by land-use scenarios and therefore requiring detailed investigation.

Animals↗
PubMed2005

Population genetic structure of two columnar cacti with a patchy distribution in eastern Brazil.

The genetic variability and population genetic structure of six populations of Praecereus euchlorus and Pilosocereus machrisii were investigated. The genetic variability in single populations of Pilosocereus vilaboensis, Pilosocereus aureispinus, and Facheiroa squamosa was also examined. All of these cacti species have a patchy geographic distribution in which they are restricted to small areas of xeric habitats in eastern Brazil. An analysis of genetic structure was used to gain insights into the historical mechanisms responsible for the patchy distribution of P. euchlorus and P. machrisii. High genetic variability was found at the populational level in all species (P=58.9-92.8%, A(p)=2.34-3.33, H(e)=0.266-0.401), and did not support our expectations of low variability based on the small population size. Substantial inbreeding was detected within populations (F(IS)=0.370-0.623). In agreement with their insular distribution patterns, P. euchlorus and P. machrisii had a high genetic differentiation (F(ST)=0.484 and F(ST)=0.281, respectively), with no evidence of isolation by distance. Accordingly, estimates of gene flow (N(m)) calculated from F(ST) and private alleles were below the level of N(m)=1 in P. machrisii and P. euchlorus. These results favored historical fragmentation as the mechanism responsible for the patchy distribution of these two species. The genetic distance between P. machrisii and P. vilaboensis was not compatible with their taxonomic distinction, indicating a possible local speciation event in this genus, or the occurrence of introgression events.

Alleles↗
PubMed2006

Longevity differences among lines artificially selected for developmental time and wing length in Drosophila buzzatii.

We assessed the indirect response of longevity in lines selected for wing length (WL) and developmental time (DT). Longevity in selection lines was compared to laboratory control lines and the offspring of recently collected females. Wild flies (W lines), flies from lines selected for fast development (F lines), and for fast development and large wing length (L lines) outlived control laboratory lines (C lines) and lines selected for fast development and short wing (S lines). The decline in longevity in S lines is in line with the idea that body size and longevity are correlated and may be the result of the fixation of alleles at loci affecting pleiotropically the two traits under selection and longevity. In addition, inbreeding and artificial selection affected the correlation between wing length and longevity that occurs in natural populations of Drosophila buzzatii, suggesting that correlations between traits are not a perdurable feature in a population.

Aging↗
PubMed2005

A survey of pig production systems in the rain forest of the Pacific coast Colombia.

A questionnaire-based survey was conducted in small-scale pig farms in the rain forest of the Colombian Pacific coast in order to study aspects of reproduction, nutrition and productivity. A total of 124 farmers was interviewed. They owned, on average, 13.6 pigs, including 2.3 sows, mainly of the Zungo breed. Pigs are reared in extensive systems and are allowed to wander freely in search of food. The sows produce, on average, 9.6 piglets/litter but, owing to poor sanitary conditions, 1.5 are born dead and only 6.3 are weaned alive. Two-thirds of the sows have five litters or more and the boars are also kept for a long time. This leads to high consanguinity rates within the herd and low productivity. Diets are based on maize, banana, tubers (taro, cassava) and fruits (peach palm, among others), and are rich in energy but poor in protein and minerals. The lack of protein and mineral sources appears to be the main limiting factor of these extensive production systems. Tree forages could partially solve the problem but are used by only 2% of the farmers. It is concluded that decreasing inbreeding, better piglet management and provision of balanced diets are areas that require immediate improvement.

Animal Husbandry↗
PubMed1988

On the evolution of genetic incompatibility systems. IV. Modification of response to an existing antigen polymorphism under partial selfing.

A 2-locus model of the evolution of self-incompatibility in a population practicing partial selfing is presented. An allele is introduced at a modifier locus which influences the strength of the rejection reaction expressed by the style in response to antigens recognized in pollen. Two causes of inbreeding depression are investigated. First, offspring viability depends solely on the source (self or non-self) of the fertilizing pollen. Second, offspring viability declines with the expression of recessive deleterious alleles, segregating at a third (disease) locus, which exhibit an imperfect association with antigen alleles. Evolutionary changes occurring at the disease locus are not considered in this study. The condition under which a modifier allele that intensifies the incompatibility reaction increases when rare depends upon the number of antigens, the frequency of recessive deleterious alleles at the disease locus, and the level of association between the antigen locus and the disease locus. It is the improvement of viability among offspring derived by outcrossing, rather than the prevention of self-fertilization, that may represent the primary evolutionary function of genetic incompatibility systems.

Biological Evolution↗
PubMed1991

On the concept of effective number.

A generalized conceptual basis for Wright's notion of effective size is presented. The concept is applied to the calculation of effective numbers based on the rate of change of genetic variability. With particular reference to the inbreeding, the eigen value, and the newly introduced "diversity" effective size, the use of the concept as a means for discrimination between and identification of various effective sizes is demonstrated.

Biometry↗
PubMed1988

Evidence of loss of a suggested genetic polymorphism in the blood potassium contents of zoo-living Barbary sheep Ammotragus lervia (Pallas 1777).

1. Concentrations of potassium and iron were measured in blood samples of 15 zoo-living Barbary sheep by atomic absorption spectrophotometry. 2. In analogy with the situation in Ovis it is suggested that a blood potassium polymorphism is also found in Ammotragus. 3. However, in the Frankfurt line at least, one of the presumed alleles is likely to be lost due to inbreeding.

Animals↗
PubMed1992

Genetic variability and rodent models of human aging.

Inbred strains, outbred strains, and natural populations of rodents differ greatly in the amount and nature of the genetic variability they possess. Consequently, as models of human aging they vary with respect to the areas of research to which they are best suited. Inbred strains, in which all individuals are genetically identical, are best suited as models of specific disease processes and for manipulations involving tissue transplantation. Their lack of genetic variability, however, and the disruption of genetic linkage groups that occurs during inbreeding limit their value as models of more general aging processes. Outbred strains exhibit large interindividual genetic variation--a result of ongoing random accumulation of deleterious alleles with late ages of action. This makes them ideal models for studying the diversity of pathologic lesions, connections between pathologies, and susceptibility to pathologic lesions that collectively produce the reductions in reproductive capacity, physiological efficiency, and viability that are characteristic of aging. Natural populations also may exhibit relatively large amounts of interindividual genetic variability. However, difficulties with husbandry, variable parasite loads, and complex population genetics can compromise their suitability as models of human aging. Ultimately, a consideration of the range of animal models available and a more careful matching of the goals of a study with the genetic system of the model will prove fruitful to gerontology.

Aging↗
PubMed2006

Evolution of plant breeding systems.

Breeding systems are important, and often neglected, aspects of the natural biology of organisms, affecting homozygosity and thus many aspects of their biology, including levels and patterns of genetic diversity and genome evolution. Among the different plant mating systems, it is useful to distinguish two types of systems: 'sex systems', hermaphroditic versus male/female and other situations; and the 'mating systems' of hermaphroditic populations, inbreeding, outcrossing or intermediate. Evolutionary changes in breeding systems occur between closely related species, and some changes occur more often than others. Understanding why such changes occur requires combined genetical and ecological approaches. I review the ideas of some of the most important theoretical models, showing how these are based on individual selection using genetic principles to ask whether alleles affecting plants' outcrossing rates or sex morphs will spread in populations. After discussing how the conclusions are affected by some of the many relevant ecological factors, I relate these theoretical ideas to empirical data from some of the many recent breeding system studies in plant populations.

Biological Evolution↗
PubMed2006

Recombination and the evolution of mutational robustness.

Mutational robustness is the degree to which a phenotype, such as fitness, is resistant to mutational perturbations. Since most of these perturbations will tend to reduce fitness, robustness provides an immediate benefit for the mutated individual. However, robust systems decay due to the accumulation of deleterious mutations that would otherwise have been cleared by selection. This decay has received very little theoretical attention. At equilibrium, a population or asexual lineage is expected to have a mutation load that is invariant with respect to the selection coefficient of deleterious alleles, so the benefit of robustness (at the level of the population or asexual lineage) is temporary. However, previous work has shown that robustness can be favoured when robustness loci segregate independently of the mutating loci they act upon. We examine a simple two-locus model that allows for intermediate rates of recombination and inbreeding to show that increasing the effective recombination rate allows for the evolution of greater mutational robustness.

Animals↗
PubMed2006

A pedigree-analysis approach to the descriptive epidemiology of autosomal-recessive disorders.

We describe a pedigree-analysis approach to estimating descriptive epidemiological parameters for autosomal-recessive disorders when the ancestral source of the disorder is known. We show that the expected frequency of carriers in a cohort equals the gene contribution of the ancestral source to that cohort, which is equivalent to the direct (additive) genetic relationship of that ancestor to the cohort. Also, the expected incidence of affected foetuses ranges from (1/2)F* to F*, where F* is the mean partial inbreeding coefficient (due to the ancestor) of the cohort. We applied this approach to complex vertebral malformation (CVM) in Holstein-Friesians in Australia, for which the ancestral source is a USA-born bull, Carlin-M Ivanhoe Bell. The estimated frequency of carriers was 2.47% for the 1992-born and 4.44% for the 1997-born cohort of Holstein-Friesian cows in Australia. The estimated incidence of affected foetuses/calves was considerably less than one per thousand, ranging from 0.0024 to 0.0048% for the 1992-born cohort, and from 0.0288 to 0.0576% for the 1997-born cohort. These incidences correspond to expected numbers of affected female foetuses/calves ranging from 2 to 4 for the 1992-born cohort and from 28 to 56 for the 1997-born cohort. This approach is easy to implement using software that is readily available.

Animals↗
PubMed2004

Screening and analysis of porcine endogenous retrovirus in Chinese Banna minipig inbred line.

Pigs have been the most likely animal as the source of cells, tissues, and organs for xenotransplantation. But the use of pigs in xenotransplantation is associated with the risk of porcine endogenous retrovirus (PERV) transmission. Previous studies have identified that the proviruses are integrated into the genome of normal pigs and that virus particles released from the porcine cells can infect human cells in vitro. As a unique inbred pig, Banna minipig inbred (BMI) has a huge potential value for xenotransplantation and medical research. It has been the focal experimental animal for pig-to-human xenotransplantation in China, due to its clear genetic background and tiny individual differences. To evaluate whether the potential risk of PERV exists in inbred pigs, a series of screening experiments were performed herein. The results of PCR with primers specific for gag, pol, and env showed that proviruses existed in the genome of BMI, and the PERV subtypes were PERV-A and PERV-B. PERV mRNA was expressed functionally in BMI. Positive results of an RT assay identified that PERV in BMI had potential infectivity, but the concentration of PERV reverse transcriptase in BMI was almost 20 times lower than that of HIV. These results suggested that gag, pol and env genes of PERV were not lost during inbreeding, which created favorable conditions to produce viral particles that could possibly infect human cells in xenotransplantation.

Animals↗
PubMed2000

The influence of self-fertilization and pairing on life-history traits in the freshwater snail Bulinus forskalii (Gastropoda, planorbidae).

This study analyses the basic reproductive biology of the schistosonie-vector snail Bulinus forskalli. This hermaphroditic species can self-fertilize. Variation of the mating system was analysed in two populations from Cameroon in a three-step experiment. (i) The fecundity (number of eggs and of egg capsules) of isolated virgin individuals from both populations was followed over a month, as well as the survival of offspring from these individuals. Estimates of these parameters were intermediate. Our results also indicate that inbreeding depression has a maximum value of about one-half in both populations. No difference was observed between populations for both the overall fecundity of adults and survival of offspring. (ii) Individuals were then paired either within, or between populations over three successive days, and the number of copulations recorded. Copulations were observed in all situations, including between-population pairs. No significant dlifference in the number of copulations per pair was detected. However, this value decreased with time, and reciprocal copulations were significantly less numerous between than within populations. (iii) Individuals that successfully copulated as female in (ii) were isolated, and their fecundity was followed over 3 weeks. The fecundity of individuals that had been maintained isolated over the whole experiment served as a control. No significant difference was on the whole detected. Our results collectively suggest that the individuals from the two populations studied are rather selfers, confirming that B. forskalii is a preferentially selfing species. There is also some pre-zygotic isolation against crosses between populations.

Animals↗
PubMed1999

Inherited arrhythmias in the dog: potential experimental models of cardiac disease.

Centuries of inbreeding the domestic dog has resulted in numerous spontaneous breed-specific and familial diseases of all body systems [1]. Although few animal models of spontaneous arrhythmic death exists [2] veterinary cardiologists have recognized potentially inherited arrhythmias in the dog for years. The purpose of this paper is to describe the proven inherited, and the likely inherited, arrhythmias diagnosed commonly in the dog with the intent to provide information of potential models for investigation of primary arrhythmias. Additionally, examples of common arrhythmias that are secondary to inherited cardiac disease in the dog will be provided.

Animals↗
PubMed2002

Computer simulations to determine the efficacy of different genome resource banking strategies for maintaining genetic diversity.

Genome resource banks (GRBs) and assisted reproductive techniques are increasingly recognized as useful tools for the management and conservation of biodiversity, including endangered species. Cryotechnology permits long-term storage of valuable genetic material. Although, the actual application to endangered species management requires technical knowledge about sperm freezing and thawing, a systematic understanding of the quantitative impacts of various germ plasm storage and use scenarios is also mandatory. In this study, various GRB strategies were analyzed using the historical data from three managed populations of endangered species with varied pedigrees (Eld's deer, Przewalski's horse, and Sumatran tiger). The following types of sperm banks were assessed: (1) a "Wild Bank" consisting of sperm (i.e., genes) from 5 to 10 males unrelated to the managed population and to each other; and (2) a "Best Male" bank containing sperm from only the most genetically valuable males alive in the ex situ population at the time the bank was established. These different bank types were then used to evaluate the effectiveness of different bank usage frequencies. The efficiency of each scenario was assessed by examining the level of inbreeding and gene diversity in the population. Overall, a sperm usage frequency of five times per year was determined to be the most efficient and "wild banks" were highly successful at enhancing genetic diversity. The value of a GRB established from the ex situ population depends on how closely related the banked males are to future generations. A GRB will have significantly less benefit when banked males also produce many successful offspring, or when donors are already genetically over-represented in the population at the time of establishing the GRB.

Animals↗
PubMedDate not supplied

The effective number of a population that varies cyclically in size. II. Overlapping generations.

We consider haploid and dioecious age-structured populations that vary over time in cycles of length k. Results are obtained for both autosomal and sex-linked loci if the population is dioecious. It is assumed that k is small in comparison with numbers of haploid individuals (or of numbers of males and females) in any generation of a cycle. The inbreeding effective population size N(e) is then approximately given by the expression [T summation operator (k-1)(j=0)1/[N(e)(j)T(j)]](-1), where N(e)(j) and T(j) are, respectively, the effective population size and generation interval that would hold if the population was at all times generated in the same way as at time j. The constant T, which is the effective overall generation interval, is defined to be k times the harmonic mean of the quantities T(j). Our expressions for T and N(e), in terms of N(e)(j) and T(j), are general, but the N(e)(j)s are derived under the assumption that offspring are produced according to Poisson distributions.

Alleles↗
PubMed2003

Evolution of disassortative and assortative mating preferences based on imprinting.

A two-locus haploid model of sexual selection is investigated to explore evolution of disassortative and assortative mating preferences based on imprinting. In this model, individuals imprint on a genetically transmitted trait during early ontogeny and choosy females later use those parental images as a criterion of mate choice. It is assumed that the presence or absence of the female preference is determined by a genetic locus. In order to incorporate such mechanisms as inbreeding depression and heterozygous advantage into our haploid framework, we assume that same-type matings are less fertile than different-type mating. The model suggests that: if all the females have a disassortative mating preference a viability-reducing trait may be maintained even without the fertility cost of same-type matings; a disassortative mating preference can be established even if it is initially rare, when there is a fertility cost of same-type matings. Further, an assortative mating preference is less likely to evolve than a disassortative mating preference. The model may be applicable to the evolution of MHC-disassortative mating preferences documented in house mice and humans.

Animals↗