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PubMed2005

Isolation and characterization of the mating-type locus of the barley pathogen Pyrenophora teres and frequencies of mating-type idiomorphs within and among fungal populations collected from barley landraces.

Pyrenophora teres f. sp. teres mating-type genes (MAT-1: 1190 bp; MAT-2: 1055 bp) have been identified. Their predicted proteins, measuring 379 and 333 amino acids, respectively, are similar to those of other Pleosporales, such as Pleospora sp., Cochliobolus sp., Alternaria alternata, Leptosphaeria maculans, and Phaeosphaeria nodorum. The structure of the MAT locus is discussed in comparison with those of other fungi. A mating-type PCR assay has also been developed; with this assay we have analyzed 150 isolates that were collected from 6 Sardinian barley landrace populations. Of these, 68 were P. teres f. sp. teres (net form; NF) and 82 were P. teres f. sp. maculata (spot form; SF). Within each mating type, the NF and SF amplification products were of the same length and were highly similar in sequence. The 2 mating types were present in both the NF and the SF populations at the field level, indicating that they have all maintained the potential for sexual reproduction. Despite the 2 forms being sympatric in 5 fields, no intermediate isolates were detected with amplified fragment length polymorphism (AFLP) analysis. These results suggest that the 2 forms are genetically isolated under the field conditions. In all of the samples of P. teres, the ratio of the 2 mating types was consistently in accord with the 1:1 null hypothesis. This ratio is expected when segregation distortion and clonal selection among mating types are absent or asexual reproduction is rare. Overall, sexual reproduction appears to be the major process that equalizes the frequencies of the 2 mating types within populations.

Amino Acid Sequence↗
PubMed1990

Prediction of rates of inbreeding in selected populations.

A method is presented for the prediction of rate of inbreeding for populations with discrete generations. The matrix of Wright's numerator relationships is partitioned into 'contribution' matrices which describe the contribution of the Mendelian sampling of genes of ancestors in a given generation to the relationship between individuals in later generations. These contributions stabilize with time and the value to which they stabilize is shown to be related to the asymptotic rate of inbreeding and therefore also the effective population size, Ne approximately 2N/(mu 2r + sigma 2r), where N is the number of individuals per generation and mu r and sigma 2r are the mean and variance of long-term relationships or long-term contributions. These stabilized values are then predicted using a recursive equation via the concept of selective advantage for populations with hierarchical mating structures undergoing mass selection. Account is taken of the change in genetic parameters as a consequence of selection and also the increasing 'competitiveness' of contemporaries as selection proceeds. Examples are given and predicted rates of inbreeding are compared to those calculated in simulations. For populations of 20 males and 20, 40, 100 or 200 females the rate of inbreeding was found to increase by as much as 75% over the rate of inbreeding in an unselected population depending on mating ratio, selection intensity and heritability of the selected trait. The prediction presented here estimated the rate of inbreeding usually within 5% of that calculated from simulation.

Animals↗
PubMed1979

Dextran anaphylactoid reaction in Sprague-Dawley CFY rats.

From a closed colony of randomly-bred Sprague-Dawley CFY rats about 23% failed to respond to intravenous dextran with the characteristic generalized anaphylactoid reaction, but still exhibited an inflammatory response when dextran was given into the foot pad. Brother-sister mating of rats showing the most expressed generalized reaction (reactor rats) yielded good responder offsprings, while the non-reactors had descendants completely unresponsive to systemic dextran. Brother-sister mating of selected non-reactor rats led to a gradual decrease in dextran paw oedema in the subsequent generations, and after the third mating, a complete local non-reactivity developed. In these rats the intradermal injection of dextran failed to increase vascular permeability, while the inflammatory response evoked by histamine, 5-HT, bradykinin, and compound 48/80 remained unchanged as compared to that of the reactor animals. These result show that the anaphylactoid reaction in Sprague-Dawley CFY rats is under genetic control.

Anaphylaxis↗
PubMed1993

Absence of quadratic relationships between genetic evaluations for somatic cell scores and udder linear traits.

Sire genetic evaluations for lactation average somatic cell scores from first and second lactation daughters were regressed in separate models on genetic evaluations for udder linear traits. Somatic cell scores were from Pennsylvania DHIA, and udder linear scores were from the Holstein Association of America classifications of first lactation cows in the northeastern US excluding Pennsylvania. The independent data files for calculation of genetic evaluations included 108,632 cows from 301 sires with udder linear scores and 58,235 cows from the same 301 sires with somatic cell scores. Sire genetic evaluations for higher udders, stronger fore udder attachments, closer teat placement, and shorter teats were associated with lower somatic cell scores. Quadratic relationships between genetic evaluations for the udder traits and somatic cell scores were not important. Quadratic components were significant only for somatic cell scores and teat length. Evaluations for intermediate teat length tended to be associated with higher somatic cell score evaluations. Selection and mating for intermediate udder depth, fore udder attachment, and front teat placement scores are not as effective in reducing somatic cell scores as selection for higher udders, stronger fore udders, and closer front teats.

Animals↗
PubMed2002

Evolutionary experiments on mate recognition in the Drosophila serrata species complex.

It is becoming increasingly apparent that at least some aspects of the evolution of mate recognition may be amenable to manipulation in evolutionary experiments. Quantitative genetic analyses that focus on the genetic consequences of evolutionary processes that result in mate recognition evolution may eventually provide an understanding of the genetic basis of the process of speciation. We review a series of experiments that have attempted to determine the genetic basis of the response to natural and sexual selection on mate recognition in the Drosophila serrata species complex. The genetic basis of mate recognition has been investigated at three levels: (1) between the species of D. serrata and D. birchii using interspecific hybrids, (2) between populations of D. serrata that are sympatric and allopatric with respect to D. birchii, and (3) within populations of D. serrata. These experiments suggest that it may be possible to use evolutionary experiments to observe important events such as the reinforcement of mate recognition, or the generation of the genetic associations that are central to many sexual selection models.

Animals↗
PubMed2006

Assortative preferences and discrimination by females against hybrid male song in the grasshoppers Chorthippus brunneus and Chorthippus jacobsi (Orthoptera: Acrididae).

The grasshoppers Chorthippus brunneus and Chorthippus jacobsi are highly differentiated for male mating signals, and form a mosaic hybrid zone in northern Spain. At some sites within this zone, many hybrids are observed. At others, few hybrids are observed. Such bimodal sites may reflect recent contacts between parental genotypes, or local variation in levels of assortative mating or selection against hybrids. Playback of 12 parental and F1 male songs to 296 parental and hybrid females revealed positive assortative preferences in C. brunneus and C. jacobsi females, supporting a direct role of male mating signals in female choice. However, all female genotypic classes showed reduced responsiveness to F1 male songs. Such sexual selection against hybrids is consistent with the narrow cline width observed in the field for song characters relative to morphology. These results have implications for the genetic structure of the hybrid zone and for models of speciation by reinforcement.

Animal Communication↗
PubMed1997

Straight-line movement and competitive mate searching in prairie rattlesnakes, Crotalus viridis viridis

Males compete in various ways for mating and reproductive success. Phylogenetic factors and local ecology affect female spatial and temporal distributions, which in turn influence the form of male competition, sexual selection and mating systems. In prairie rattlesnake, Crotalus viridis viridispopulations where (1) males seek females during a brief reproductive period, (2) females are relatively few, and (3) females are widely and unpredictably distributed spatially into small discrete clusters, males should show efficient mate searching more so than time-consuming 'handling' (e.g. fighting, mate persuasion). Natural history studies and computer and mathematical modelling generate this expectation. This long-term field study of prairie rattlesnakes in Wyoming indicated that straight-line (i.e. fixed-bearing) movement by males is critical for mate location and, thus, for mating success. Males that searched along straight-line paths located and mated with more females than those having less straight movement paths. Fighting was observed rarely, and no relationship was found between males' success at mate location and body mass and/or snout-vent length. Thus a range of traits may mediate competition and mating success among male snakes.

Journal Article↗
PubMedDate not supplied

Does fitness erode in the absence of selection? An experimental test with Tribolium.

In the absence of natural selection, average fitness in the population is expected to decline due to the accumulation of deleterious mutations. Replicate populations of flour beetles (Tribolium confusum) were maintained for 22 generations in the virtual absence of selection (random mating, favorable environment, excess of food, and mortality of only 3%). Larva-to-adult survivorship rates were similar in the stock population and selection-free populations. In contrast, starvation resistance of adult beetles from selection-free populations was significantly reduced (by more than 2% per generation). When tested in the favorable environment, beetles in one selection-free population had significantly slower development and smaller sizes of females than beetles from the stock population. Since such changes in these fitness components are usually maladaptive, they indicate possible erosion of fitness under relaxed selection at the rate of 0.1-0.2% per generation. No fitness erosion was detectable in the second selection-free population.

Animals↗
PubMedDate not supplied

The microevolution of mouse salivary androgen-binding protein (ABP) paralleled subspeciation of Mus musculus.

Mouse salivary androgen-binding protein (ABP) is a major secretory product of the submaxillary glands. Although it is a common salivary protein among rodents generally, the function of ABP has yet to be determined. Here we report a comparison of the DNA coding sequences and putative amino acid sequences they determine for the three common alleles of the Alpha subunit gene (Abpa), alleles that appear to be diagnostic for the three subspecies of Mus musculus. Three other unique sequences were found in the species M. caroli, M. spretus, and M. spicilegus. Comparison of the six sequences shows that 8 of the 20 base substitution sites produce a high degree of variability in amino acids 32, 33, 36, and 39, a variability that creates unique sequence combinations in each species and subspecies. We compare the possibilities that selection or genetic drift caused this unusual microevolution and argue that selection is the more likely explanation. We speculate on the potential significance of this with respect to the proposal that ABP is involved in assortive mate kin selection.

Alleles↗
PubMed1998

Inbreeding and reproduction in mice divergently selected for response to a dietary toxin.

This study was conducted to determine whether inbreeding coefficients of selected parents or of progeny differed between lines of mice selected for increased or decreased responsiveness to a nutritional toxicosis. A second objective was to determine whether the influence of inbreeding of parents and/or progeny on reproductive traits differed between those lines. Mice were selected divergently for 8 generations for the effect on post-weaning growth of endophyte-infected fescue seed in their diet. Forty pairs (or in Generation 7, 20 pairs) were selected and mated per generation in each line. Inbreeding increased 0.5 to 0.6% per generation in both lines, a rate close to that predicted from genetic theory. Inbreeding coefficients of selected parents were not higher in the susceptible than in the resistant line. A difference would have been expected if the inbreeding coefficient had been correlated with susceptibility to toxicosis. The magnitudes of inbreeding depression for reproductive traits did not differ significantly between lines. The average inbreeding coefficient of the potential litter tended to be higher in nonfertile than fertile matings (P = 0.10), but inbreeding coefficients of sires and dams did not differ between successful and unsuccessful matings. Inbred litters tended to be born earlier than noninbred litters (P = 0.10). Inbred dams produced smaller litters than noninbred dams (main effect P < 0.05) but only when the litter also was inbred (interaction P < 0.01). Sex ratio was not influenced by inbreeding of sire, dam or litter, but there was a higher proportion of male progeny in the susceptible than in the resistant line (P = 0.01). To avoid reduced reproductive fitness, laboratory animal populations should be managed to minimize inbreeding of progeny and dam.

Animals↗
PubMed2003

Sexual selection, antennae length and the mating advantage of large males in Asellus aquaticus.

In crustacean species with precopulatory mate-guarding, sexual size dimorphism has most often been regarded as the consequence of a large male advantage in contest competition for access to females. However, large body size in males may also be favoured indirectly through scramble competition. This might partly be the case if the actual target of selection is a morphological character, closely correlated with body size, involved in the detection of receptive females. We studied sexual selection on body size and antennae length in natural populations of Asellus aquaticus, an isopod species with precopulatory mate guarding. In this species, males are larger than females and male pairing success is positively related to body size. However, males also have longer antennae, relative to body size, than females, suggesting that this character may also be favoured by sexual selection. We used multivariate analysis of selection to assess the relative influences of body size and antennae length in five different populations in the field. Selection gradients indicated that, overall, body size was a better predictor of male pairing success than antennae length, although some variation was observed between sites. We then manipulated male antennae length in a series of experiments conducted in the lab, and compared the pairing ability of males with short or long antennae. Males with short antennae were less likely to detect, orient to, and to pair with a receptive female compared with males with long antennae. We discuss the implications of our results for studies of male body size and sexual dimorphism in relation to sexual selection in crustaceans.

Animals↗
PubMed2003

Sexual selection, antennae length and the mating advantage of large males in Asellus aquaticus.

In crustacean species with precopulatory mate-guarding, sexual size dimorphism has most often been regarded as the consequence of a large male advantage in contest competition for access to females. However, large body size in males may also be favoured indirectly through scramble competition. This might partly be the case if the actual target of selection is a morphological character, closely correlated with body size, involved in the detection of receptive females. We studied sexual selection on body size and antennae length in natural populations of Asellus aquaticus, an isopod species with precopulatory mate guarding. In this species, males are larger than females and male pairing success is positively related to body size. However, males also have longer antennae, relative to body size, than females, suggesting that this character may also be favoured by sexual selection. We used multivariate analysis of selection to assess the relative influences of body size and antennae length in five different populations in the field. Selection gradients indicated that overall body size was a better predictor of male pairing success than antennae length, although some variation was observed between sites. We then manipulated male antennae length in a series of experiments conducted in the laboratory, and compared the pairing ability of males with short or long antennae. Males with short antennae were less likely to detect, orient to and to pair with a receptive female compared to males with long antennae. We discuss the implications of our results for studies of male body size and sexual dimorphism in relation to sexual selection in crustaceans.

Animals↗
PubMed1997

Genetic analysis of default mating behavior in Saccharomyces cerevisiae.

Haploid Saccharomyces cerevisiae cells find each other during conjugation by orienting their growth toward each other along pheromone gradients (chemotropism). However, when their receptors are saturated for pheromone binding, yeast cells must select a mate by executing a default pathway in which they choose a mating partner at random. We previously demonstrated that this default pathway requires the SPA2 gene. In this report we show that the default mating pathway also requires the AXL1, FUS1, FUS2, FUS3, PEA2, RVS161, and BNI1 genes. These genes, including SPA2, are also important for efficient cell fusion during chemotropic mating. Cells containing null mutations in these genes display defects in cell fusion that subtly affect mating efficiency. In addition, we found that the defect in default mating caused by mutations in SPA2 is partially suppressed by multiple copies of two genes, FUS2 and MFA2. These findings uncover a molecular relationship between default mating and cell fusion. Moreover, because axl1 mutants secrete reduced levels of a-factor and are defective at both cell fusion and default mating, these results reveal an important role for a-factor in cell fusion and default mating. We suggest that default mating places a more stringent requirement on some aspects of cell fusion than does chemotropic mating.

DNA-Binding Proteins↗
PubMed2003

The effects of selection for early (day) and late (dusk) mating lines of hybrids of Bactrocera tryoni and Bactrocera neohumeralis.

Bactrocera neohumeralis and Bactrocera tryoni are closely related tephritid fruit fly species. B. neohumeralis mates throughout the day (in bright light) and B. tryoni mates at dusk. The two species can also be distinguished by the colour of their calli (prothoracic sclerites) which are brown and yellow, respectively. The F1 hybrids can mate both in bright light just before dusk and during dusk and have calli that are partly brown and partly yellow. The F2 hybrids have a wider range of callus patterns and mating occurs more widely in the day as well as at dusk. We directly selected hybrid stocks for mating time, creating 'early' (day-mating) and 'late' (dusk-mating) lines. As an apparently inadvertent consequence, the two types of line respectively had predominantly brown and predominantly yellow calli and thus came to closely resemble the original two species in both behaviour and appearance. Lines that were evenly selected (half for day and half for dusk) essentially retained the mating pattern of F2 hybrids. Selection for callus colour alone also affected the distribution of mating times in a predictable way. We propose a genetical model to account for the results and discuss them in the light of the apparent maintenance of species integrity in nature.

Animals↗
PubMed1977

Regions of stable equilibria for models of differential selection in the two sexes under random mating.

The equilibrium structure of models of differential selection in the sexes is investigated. It is shown that opposing additive selection leads to stable polymorphic equilibria for only a restricted set of selection intensities, and that for weak selection intensities must be of approximately the same magnitude in the sexes. General models of opposing directional selection, with arbitrary dominance, are investigated by considering simultaneously the stability properties of the trivial equilibria and the curve along which multiple roots appear. Numerical calculations lead us to infer that the average degree of dominance determines the equilibrium characteristics of models of opposing selection. It appears that if the favored alleles are, on the average, recessive, there may be multiple polymorphic equilibria, whereas only a single polymorphic equilibrium can occur when the favored alleles are, on the average, dominant. The principle that the average degree of dominance controls equilibrium behavior is then extended to models allowing directional selection in one sex with overdominance in the other sex, by showing that polymorphism is maintained if and only if the average fitness in heterozygotes exceeds one.

Animals↗
PubMed2001

Reversible frequency-dependent switches in male mate choice.

Current sexual-selection theories predict that mating should occur preferentially with the highest-quality partner, and assume that for distinguishing among potential mates the choosy sex applies an internal representation of the characteristics of the desired mate, i.e. a template. Binary choice experiments were performed to test male mate choice between two different female colour morphs in the damselfly Ischnura elegans. Choice experiments were conducted before and after an habituation period, during which males were exposed to only one female colour morph. Given the choice between the two female morphs, males did exhibit a choice for the most recently experienced female morph. This is the first evidence for a reversible switch in mate choice in a frequency-dependent way. In contrast with previous studies on mate choice, template formation in male I. elegans seems not to be based on quality. Switching mate choice in a frequency-dependent manner, choosing the most common morph, probably allows males to minimize their search efforts and to maximize fitness.

Animals↗
PubMed1988

The influence of premating feed intake on the reproductive performance of gilts.

In an attempt to improve the reproductive performance of gilts mated at puberty, 70 Yorkshire x Landrace gilts were allocated at 120 d of age and 60 kg body weight to one of two treatments. Restricted gilts were fed 2.0 kg d-1 of a diet formulated to provide 18% crude protein and 14.5 MJ DE kg-1 from selection until mated at their first estrus (n = 35). Flushed gilts were fed 2.0 kg d-1 of the same diet from 120 to 150 d of age, but then had their feed intake increased to 3.5 kg d-1 until mated at their first estrus (n = 35). An additional group of gilts (control fed; n = 33) were fed 3.0 kg d-1 from selection until they were bred at their third estrus in order to investigate the influence of feed restriction on the onset of puberty. During gestation all gilts were fed 1.8 to 2.2 kg d-1 of a 16.8% crude protein diet having 13.7 MJ DE kg-1. Control fed gilts were younger (p less than 0.05) at puberty (150 d) than restricted (165 d) or flushed gilts (165 d). There was no difference in subsequent litter size between the restricted and flushed gilts (7.7 and 8.0, respectively). It is concluded that the institution of a flushing nutritional regime in the prepubertal period will not enhance piglet production from gilts mated at puberty.

Animal Feed↗
PubMed2000

Pectoral fins and paternal quality in sticklebacks.

Sexual selection through female mate choice exerts a strong selection pressure on males' sexual traits, particularly when direct benefits are involved. In species with male parental care, one would expect sexual selection to favour paternal quality, for instance through selection on morphological structures which promote quality. We experimentally studied the influence of pectoral fins on paternal quality in male three-spined sticklebacks (Gasterosteus aculeatus L.). After reductions of fin area to different degrees, similar-sized males had to perform a complete reproductive cycle in enclosures in the field. The collected data on fanning behaviour and egg development showed that a reduction in pectoral fin size affected paternal quality probably through an increased beat frequency of the pectorals. Thus, pectoral fins can potentially signal paternal quality to choosy females.

Animals↗