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PubMed2002

Alpaca semen characteristics previous to a mating period.

Increasing the knowledge of the semen characteristics in the alpaca will contribute to understanding one of the many factors that affect the poor fertility rate in this species. Ten adult male alpacas, 2.6-10 years of age, average weight 64.7 +/- 4.7 kg were used. The animals were distributed randomly into two groups of five each and submitted alternatively to two semen collections, using an artificial vagina and sexually receptive females. For the first semen collection the animals had a sexual rest period of about 90 and 45 days before the second. Duration of semen collection, color and volume of ejaculate were recorded, and sperm concentration and morphology (light microscopy) were evaluated. Descriptive statistical analyses were used for each variable, considering all samples obtained (n= 19). An analysis of variance for animal groups and opportunity of collection were used for quantitative variables. Most frequent color was opalescent white (84.2%). There were no statistical differences among male groups or between semen collections. The average values and standard deviations for the quantitative variables were: 12.3 +/- 7.2 min for semen collection time, 1.8 +/- 0.8 ml for ejaculate volume, (17.6 +/- 26.1) x 10(6) sperm/ml for sperm concentration and 34.0 +/- 52.2 x 10(6) for total number of sperm per ejaculate. The percentage of normal spermatozoa was 51.0 +/- 12.4%. From the total abnormalities, that of mid piece segment (14.4%) was the most frequent. These results indicate that male alpaca have poor semen quality, when compared with other domestic species. Nevertheless, for the evaluation of male alpaca as breeders it would be necessary to create a protocol for the selection of them, where phenotypic, behavioral and seminogram aspects are considered. The values reported herein define the characteristics of the alpaca semen that could be considered as the initial base of the seminal analysis to select male alpacas before mating.

Animals↗
PubMed1997

Mating type switching in yeast controlled by asymmetric localization of ASH1 mRNA.

Cell divisions that produce progeny differing in their patterns of gene expression are key to the development of multicellular organisms. In the budding yeast Saccharomyces cerevisiae, mother cells but not daughter cells can switch mating type because they selectively express the HO endonuclease gene. This asymmetry is due to the preferential accumulation of an unstable transcriptional repressor protein, Ash1p, in daughter cell nuclei. Here it is shown that ASH1 messenger RNA (mRNA) preferentially accumulates in daughter cells by a process that is dependent on actin and myosin. A cis-acting element in the 3'-untranslated region of ASH1 mRNA is sufficient to localize a chimeric RNA to daughter cells. These results suggest that localization of mRNA may have been an early property of the eukaryotic lineage.

Actins↗
PubMed2001

Consequences of life history for inbreeding depression and mating system evolution in plants.

Many plants are perennial, but most studies of inbreeding depression and mating system evolution focus on annuals. This paper extends a population genetic model of inbreeding depression due to recessive deleterious mutations to perennials. The model incorporates life history and mating system variation, and multiplicative selection across many genetic loci. In the absence of substantial mitotic mutation, perennials have higher mean fitness and lower, or even negative, inbreeding depression than annuals with the same mating system. As in annuals, self fertilization exposes deleterious recessive mutations to selection, increasing mean fitness and decreasing inbreeding depression. Including mitotic mutation decreases mean fitness while increasing inbreeding depression. Perenniality introduces a kind of selective sieve, such that strongly recessive mutations contribute disproportionately to mean fitness and inbreeding depression. In the presence of high mitotic mutation, this selective sieve may provide a mechanistic basis for high inbreeding depression observed in some long lived perennials. Without substantial mitotic mutation, it is difficult to reconcile genetically based models of inbreeding depression with the empirical generalization that perennials outcross while related annuals self fertilize.

Biological Evolution↗
PubMed1999

Sexual selection resulting from extrapair paternity in collared flycatchers.

Extrapair paternity has been suggested to represent a potentially important source of sexual selection on male secondary sexual characters, particularly in birds with predominantly socially monogamous mating systems. However, relatively few studies have demonstrated sexual selection within single species by this mechanism, and there have been few attempts to assess the importance of extrapair paternity in relation to other mechanisms of sexual selection. We report estimates of sexual selection gradients on male secondary sexual plumage characters resulting from extrapair paternity in the collared flycatcher Ficedula albicollis, and compare the importance of this form of sexual selection with that resulting from variation in mate fecundity. Microsatellite genotyping revealed that 15% of nestlings, distributed nonrandomly among 33% of broods (N=79), were the result of extrapair copulations. Multivariate selection analyses revealed significant positive directional sexual selection on two uncorrelated secondary sexual characters in males (forehead and wing patch size) when fledgling number was used as the measure of fitness. When number of offspring recruiting to the breeding population was used as the measure of male fitness, selection on these traits appeared to be directional and stabilizing, respectively. Pairwise comparisons of cuckolded and cuckolding males revealed that males that sired young through extrapair copulations had wider forehead patches, and were paired to females that bred earlier, than the males that they cuckolded. Path analysis was used to partition selection on these traits into pathways via mate fecundity and sperm competition, and suggested that the sperm competition pathway accounted for between 64 and 90% of the total sexual selection via the two paths. The selection revealed in these analyses is relatively weak in comparison with many other measures of selection in natural populations. We offer some explanations for the relatively weak selection detected. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Reproductive toxicity studies in rats with rimexolone, a corticoid ophthalmic suspension.

Rimexolone is a potent anti-inflammatory corticosteroid with a lower potential for elevating intraocular pressure, relative to other ophthalmic steroids, and is indicated for postsurgical inflammation and uveitis. Fertility and peri/postnatal toxicities were evaluated at oral gavage doses of 50, 150 or 500 mg/kg, and developmental toxicity at 100, 500, or 1000 mg/kg. In the fertility study, male rats were treated daily beginning 4 weeks prior to mating and females were treated daily beginning 2 weeks prior to mating, and through gestation day 6. Females were necropsied on gestation day 15 and males were necropsied after 10 weeks of exposure. In males, dose-related reductions in mean body weights, body weight gains, and food consumption occurred in all groups. In the 500 mg/kg females, mean body weights were reduced during gestation, and there was an increase in early resorptions and concomitant decrease in viable fetuses at this level. There were no effects on copulation or fertility indices, or on the number of corpora lutea and implantation sites. The no-observed-effect level (NOEL) for fertility and reproductive effects was 150 mg/kg. In the developmental toxicity study, female rats were treated daily from gestation days 6 through 17, necropsied on gestation day 20 and fetuses were evaluated. Maternal toxicity occurred at 500 and 1000 mg/kg as indicated by reduced maternal body weights and body weight gains. However, there was no indication of a developmental effect on fetuses due to rimexolone. The NOEL was 1000 mg/kg for the developing fetuses. In the peri/postnatal toxicity study, female rats were treated daily from gestation day 6 through lactation day 20 and necropsied. F1 developmental and behavioral parameters were evaluated. Selected F1 animals were mated at 12 weeks, allowed to deliver, and necropsied on lactation day 21. At 500 mg/kg, F0 maternal body weights were reduced during gestation and lactation, and F1 pup weights were reduced during lactation and the growth phase. There were no effects on the F1 fertility or reproductive capabilities, or on F2 developmental parameters. The NOEL for the F0 females and F1 offspring was 150 mg/kg. Together, these studies indicate that, unlike some corticosteroids, rimexolone does not produce developmental or reproductive toxicity in rats.

Administration, Topical↗
PubMed1990

Divergent selection for body weight and yolk precursor in Coturnix coturnix japonica. 8. A summary of correlated responses.

Correlated response data accompanying 19 generations of selection for increased (HW) or decreased (LW) 4-wk BW and increased (HP) or decreased (LP) total plasma P were summarized. Similarly, 11 generations of selection of sublines derived from the original Lines HW and LP were also analyzed. Sublines were maintained through selection of males for increased 4-wk BW and females for the respective high or low plasma P. The randombred control (RBC1) was stable for BW early in egg production, BW change from early to late in production, wet and dry liver weights, 120-day egg production, and ova weight. A linear decrease in BW was found for the RBC1 line late in egg production, egg and respective component weights, and ova number. Body weight early and late in the production period for original Lines HW and LW was different from the RBC1 line. Wet liver weight increased for the HW line while dry liver weights declined in the original Lines LW, HP, and LP. Egg weights were greater in Line HW and lower in Lines LW, HP, and LP than in the RBC1 line. Yolk weight increased in Line HW and decreased in Lines LW and LP. Albumen weight was reduced in Line LP while shell weight was increased in Line HW and decreased in Line HP. Egg production, from onset to 120 days, decreased in Lines HW and LW when compared to the RBC1 line. Line LP had more follicles in rapid development than Line RBC1. The sublines responded similarly to their line of origin differing only in the magnitude of response. This was a reflection of the mating scheme, which placed selection pressure on BW of males and plasma P in females.

Animals↗
PubMed2006

Dispersal is not female biased in a resource-defence mating ungulate, the European roe deer.

Dispersal is frequently more prevalent in one sex compared to the other. Greenwood proposed that patterns of sex-biased dispersal among birds and mammals are linked to their mating strategies. For species where males defend resources rather than females, he predicted female-biased dispersal, because males should remain at their birth site where they are familiar with the distribution of the resources that they must defend. Greenwood's hypothesis has been extensively supported among birds, where most species exhibit a resource-defence mating strategy. However, almost no equivalent information is available for mammals as males generally defend mates in this group. An exception is the European roe deer, a resource-defence mating ungulate. We thus tested Greenwood's hypothesis on this atypical mammalian model, looking for female-biased dispersal using sex-specific inter-individual genetic distances. We conclusively show that gene flow is not higher among females compared to males in the studied roe deer population, and hence that dispersal is not female-biased, suggesting that male mating strategy is not the primary selective force driving the evolution of dispersal in roe deer. We discuss the role of female mate choice and intra-sexual competition as possible alternative selective pressures involved.

Animal Migration↗
PubMed2003

MHC studies in nonmodel vertebrates: what have we learned about natural selection in 15 years?

Elucidating how natural selection promotes local adaptation in interaction with migration, genetic drift and mutation is a central aim of evolutionary biology. While several conceptual and practical limitations are still restraining our ability to study these processes at the DNA level, genes of the major histocompatibility complex (MHC) offer several assets that make them unique candidates for this purpose. Yet, it is unclear what general conclusions can be drawn after 15 years of empirical research that documented MHC diversity in the wild. The general objective of this review is to complement earlier literature syntheses on this topic by focusing on MHC studies other than humans and mice. This review first revealed a strong taxonomic bias, whereby many more studies of MHC diversity in natural populations have dealt with mammals than all other vertebrate classes combined. Secondly, it confirmed that positive selection has a determinant role in shaping patterns of nucleotide diversity in MHC genes in all vertebrates studied. Yet, future tests of positive selection would greatly benefit from making better use of the increasing number of models potentially offering more statistical rigour and higher resolution in detecting the effect and form of selection. Thirdly, studies that compared patterns of MHC diversity within and among natural populations with neutral expectations have reported higher population differentiation at MHC than expected either under neutrality or simple models of balancing selection. Fourthly, several studies showed that MHC-dependent mate preference and kin recognition may provide selective factors maintaining polymorphism in wild outbred populations. However, they also showed that such reproductive mechanisms are complex and context-based. Fifthly, several studies provided evidence that MHC may significantly influence fitness, either by affecting reproductive success or progeny survival to pathogens infections. Overall, the evidence is compelling that the MHC currently represents the best system available in vertebrates to investigate how natural selection can promote local adaptation at the gene level despite the counteracting actions of migration and genetic drift. We conclude this review by proposing several directions where future research is needed.

Animals↗
PubMed1979

Mating pheromones of Saccharomyces kluyveri: pheromone interactions between Saccharomyces kluyveri and Saccharomyces cerevisiae.

Saccharomyces kluyveri is a heterothallic yeast with two allelic mating types denoted as a-k and alpha-k by analogy with Saccharomyces cerevisiae and from the work described here. S. kluyveri produces mating pheromones analogous to those of S. cerevisiae, but which appear to have different specificity. S. kluyveri thus differs from S. cerevisiae, Hansenula wingei, and Schizosaccharomyces pombe in that it exhibits both strong constitutive agglutination and mating pheromones. alpha-k cells produce a pheromone ("alpha-k-factor") which causes a-k cells to arrest in the G1 phase of the cell cycle and to undergo a morphological change. After a period of time dependent on the concentration of alpha-k-factor, cells exposed to the factor resume cell division. alpha-k-factor has no effect on a-k/alpha-k diploids or on alpha-k cells, but at high concentration does induce G1 arrest of S. cerevisiaea cells (a-c). a-k cells produce a pheromone ("a-k-factor") which causes alpha-k cells to exhibit a morphological change. In addition, a-k cells exhibit the Bar phenotype with respect to alpha-k-factor. Partially purified preparations of S. cerevisiae alpha-factor are more active in inducing G1 arrest of a-k cells than of a-c cells. A more purified preparation of alpha-c-factor is less active against a-k cells than a-c cells, suggesting that an additional factor (KRE, kluyveri response enhancer) may be lost during purification. Attempts to mate S. kluyveri and S. cerevisiae cells by prototroph selection and by cell-to-cell mating have been unsuccessful with all combinations of mating types. Thus, S. cerevisiae and S. kluyveri are incompatible for mating even though their pheromones exhibit some physiological cross-reaction.

Crosses, Genetic↗
PubMed1981

[Selection of laboratory rats for fertility components in synchronized estrus using Suisychron-Praemix. 1. Effects of selection and synchronization].

The following results were obtained from experimental studies into effects of selection for fertility and into synchronised oestrus though eight generations of laboratory rats: -- The result of selection recordable from the population with selection only was better than that recorded from the population with selection and synchronised oestrus. This has been attributed to higher correlation between phenotype and genotype in the selection variant. -- Direct negative impact of synchronised oestrus on selection index was recorded from a population with random mating. -- The effects of synchronised oestrus regarding selection success were offset but not entirely ruled out by selection. -- Through the generations of both populations with synchronised oestrus the effects of synchronisation were lowered due to both physiological adaptation to Suisynchron application and contraselection with regard to suitability for synchronisation.

Animals↗
PubMed2004

Sexual selection on morphological and physiological traits and fluctuating asymmetry in the black scavenger fly Sepsis cynipsea.

Previous univariate studies of the fly Sepsis cynipsea (Diptera: Sepsidae) have demonstrated spatiotemporally variable and consequently overall weak sexual selection favouring large male size, which is nevertheless stronger on average than fecundity selection favouring larger females. To identify specific target(s) of selection on body size and additional traits possibly affecting mating success, two multivariate field studies of sexual selection were conducted. In one study using seasonal replicates from three populations, we assessed 15 morphological traits. No clear targets of sexual selection on male size could be detected, perhaps because spatiotemporal variation in selection was again strong. In particular, there was no (current) selection on male abdomen length or fore coxa length, the only traits for which S. cynipsea males are not smaller than females. Interestingly, copulating males had a consistently shorter fore femur base, a secondary sexual trait, and a wider clasper (hypopygium) gap, an external genital trait. In a second study using daily and seasonal replicates from one population, we included physiological measures of energy reserves (lipids, glucose, glycogen), in addition to hind tibia length and fluctuating asymmetry (FA) of all pairs of legs. This study again confirmed the mating advantage of large males, and additionally suggests independent positive influences of lipids (the long-term energy stores), with effects of glucose and glycogen (the short-term energy stores) tending to be negative. FA of paired traits was not associated with male mating success. Our study suggests that inclusion of physiological measures and genital traits in phenomenological studies of selection, which is rare, would be fruitful in other species.

Animals↗
PubMed2002

Temporally fluctuating selection of sex-limited signaling traits in the Texas field cricket, Gryllus texensis.

Gryllus texensis males produce acoustic mating signals and display extensive heritable variation in when and how much time they spend signaling throughout the night. The goal of this research is to elucidate the potential mechanism responsible for maintaining this heritable variation. Mating signals attract female crickets. In low-density spring populations females select males that signal most often; in high-density fall populations mating appears random with respect to signaling time. Mating signals also inadvertently attract acoustically orienting parasitoid flies; parasitoids are prevalent during the first half of the evening in the fall mating season. I hypothesized that mating signals are influenced by sex-limited temporally fluctuating selection. I predicted how mating signals would respond to this pattern of cyclical selection a priori, and then measured the sexual characters over four successive generations. I provide correlative evidence that mating signals appear to respond to sex-limited temporally fluctuating selection. These results indicate that sex-limited temporally fluctuating selection may play a role in the maintenance of variation in these sexual characters.

Animals↗
PubMed1985

Selection for weaning weight in Targhee sheep in two environments. II. Correlated effects.

Targhee sheep were selected for 120-d weight under irrigated pasture-drylot conditions at Davis (DW) and under range conditions at Hopland (HW). Unselected control lines were maintained in both environments (DC, HC1 and HC2). At Hopland, a line (DH) was maintained in which ewes were mated to Davis (DW) rams. Selection for 120-d weight was successful in both environments, with more improvement made in the drylot environment. The genetic improvement made in the drylot environment was expressed, although to a lesser degree, under range conditions. Correlated responses were analyzed. Birth weight increased significantly in all three selected lines; the increase was less in line DH than in the other two lines. In all selected lines, weights of ewes of all ages at mating increased significantly compared with their respective controls. Proportion of ewes lambing decreased (P less than .05) in line DH; the trend was negative but nonsignificant in line DW. Differences in litter size between lines within location were not significant. Lamb survival to weaning decreased in lines DW (P less than .05) and DH (P less than .01), compared with their respective controls; and the trend in HW was negative but nonsignificant. Fertility and survival data indicated that, under range conditions, the line selected under drylot conditions (DH) was less fit than the line selected under range conditions (HW). As a result of the decreases in lamb survival and fertility, none of the selected lines produced more total lamb weight weaned per ewe than the controls, in spite of the significant direct response to selection. Mature ewes of lines DH and DW produced less total lamb weight weaned per ewe (P less than .001 and P less than .05) than their respective controls. The results indicate that while single trait selection for growth rate to weaning results in heavier lambs, it does not increase and may decrease total lamb production per ewe.

Animals↗
PubMed2006

Advances in transgenic rat production.

Predictable and reproducible production of transgenic rats from a standardized input of egg donors and egg recipients is essential for routine rat model production. In the course of establishing a transgenic rat service, transgenic founders were produced from three transgenes in outbred Sprague-Dawley (SD) rats and four transgenes in inbred Fischer 344 (F344) rats. Key parameters that affect transgenesis efficiency were assessed, including superovulation treatments, methods to prepare pseudopregnant recipients, and microinjection technique. Five superovulation regimens were compared and treatment with 20 IU PMSG and 30 IU HCG was selected for routine use. Four methods to prepare pseudopregnant egg recipients were compared and estrus synchronization with LHRHa and mating to vasectomized males was selected as most effective. More than 80% of eggs survived microinjection when modified pronuclear microinjection needles and DNA buffers were used. The efficiencies of transgenic production in rats and C57BL/6J (B6J) mice were compared to provide a context for assessing the difficulty of transgenic rat production. Compared to B6J mice, SD rat transgenesis required fewer egg donors per founder, fewer pseudopregnant egg recipients per founder, and produced more founders per eggs microinjected. Similar numbers of injection days were required to produce founders. These results suggest that SD rat transgenesis can be more efficient than B6J mouse transgenesis with the appropriate technical refinements. Advances in transgenic rat production have the potential to increase access to rat models.

Animals↗
PubMed2004

Recent duplication and inter-locus gene conversion in major histocompatibility class II genes in a teleost, the three-spined stickleback.

Using a bacterial artificial chromosome (BAC) library, we analysed a 99.5 kb genomic segment containing the major histocompatibility class II genes of a teleost, the three-spined stickleback Gasterosteus aculeatus. Experiments with G. aculeatus have provided direct evidence for balancing selection by pathogens and mate choice driving MH class II beta polymorphism. Two sets of paralogous class II alpha genes and beta genes in a tandem arrangement were identified, designated Gaac-DAA/DAB and Gaac-DBA/DBB. Expression analysis of the beta genes using single-strand conformation polymorphism revealed that both gene copies are expressed. Based on an analysis of pairwise nucleotide polymorphisms, we estimate that the duplication into two paralogous class II loci occurred only 1.2-2.4 million years ago, 1-2 orders of magnitude more recently than in other fish, bird or mammalian species. At the 3'-direction of the classical MH loci, we identified another seven genes or gene fragments, two of which (small inducible cytokine, complement regulatory factor) are related to immune function in other vertebrates. None of these genes were associated with MH class II genes in zebrafish, suggesting a markedly different organisation of the MH class II region in sticklebacks, and presumably, across bony fishes. When the nucleotide substitution pattern of the novel class II beta genes was analysed together with a representative sequence sample isolated from fish in northern Germany (n=27), we found that the peptide binding region of the Gaac-DAB and Gaac-DBB loci had undergone an inter-locus gene conversion (P=0.007). In accordance, we found a 10- to 20-fold higher frequency of CpG-islands on the MH class II segment compared to other species, a feature that may be conducive for inter-locus recombination.

Amino Acid Sequence↗
PubMed2003

Non-equivalent loci and mutation-selection balance.

We consider the implications of mutationally non-equivalent loci for large populations of randomly mating diploid organisms under mutation-selection balance. Variation, across loci, of parameters such as the allelic mutational variance and the mutation rate, is shown to reduce the equilibrium genetic variance. This is proved to follow from the genetic variance contributed by a single locus having an underlying convexity. We give approximate results indicating the way small deviations of the mutational parameters, from their mean values, reduce the genetic variance. Numerical estimates of the size of the effect are given for more general variations of the parameters. Variation in the mutation rates has a significantly smaller effect than variation in the mutational variances. Under accepted parameter values, the reduction in genetic variance can be substantial.

Genetic Variation↗