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At least 919 records · Page 51Linked to original sources
PubMed2001

Female remating in Drosophila ananassae: bidirectional selection for remating speed.

In Drosophila ananassae, artificial selection was carried out for fast and slow remating speed for 10 generations. Response to selection resulted in rapid divergence in remating time in each of two replicates of both fast and slow lines. There were significant differences in mean remating time in females among fast, slow, and control lines. Regression coefficients for both fast and slow lines are significantly different from zero. The realized heritability over 10 generations of selection is from 0.26 to 0.33 for two replicates of fast line and from 0.23 to 0.27 for two replicates of slow line. These findings suggest that female remating time in D. ananassae is under polygenic control. Remating frequency of females showed a correlated response in both fast and slow lines. At generation 10, correlated response to selection was also investigated. Mating propensity of D. ananassae of fast and slow lines was observed in an Elens-Wattiaux mating chamber. Fifteen pairs per test showed that on the average, the fast lines (11.20, 11.60) were more successful in mating than those of slow (6.40, 5.60) and control (8.00) lines. Productivity of once-mated females was measured in terms of number of progeny produced per female and the results of productivity analysis indicate that females of fast lines (157.83, 130.83) produced more progeny compared with slow (72.70, 85.83) and control (109.23) lines.

Animals↗
PubMed1997

Genetic selection strategies: computer modeling.

There are four primary factors to consider in genetic selection strategies: 1) accuracy of selection, 2) selection intensity, 3) effective population size, and 4) mating system. Current theory indicates that optimum response to selection is achieved by maximizing the first three factors and using a mating systems that allows optimization of reproductive characteristics in dam lines and production characteristics in sire lines. However, with limited resources, compromises among the first three factors are needed. Simulations are useful for examining those compromises. Unrealistic simplifying assumptions are necessary for analytic theoretical results and thus do not address real world breeding problems. Using simulations, the relationship between selection accuracy, which is increased by use of family selection indices or Best Linear Unbiased Prediction (BLUP), and response to selection was examined. Results show that those procedures place a great restriction on effective population size, which offsets most of their advantage, i.e., there is too little emphasis on effective population size. A revision of the methodology and a reappraisal of the results of selection theory for optimization of genetic response is required. Another relationship that is of fundamental importance in breeding programs is that between selection intensity and effective population size. Analytical results for the additive case have been developed but have never been extended to heterotic traits. A gene level simulation program was developed to examine that relationship. Results show that the optimal selection strategy depends on the trait being selected. For additive traits and in the short term (20 generations), one should maximize selection intensity. For heterotic traits, an intermediate proportion (25% of each sex) gives optimal response. In all breeding strategies, primary attention must be given to the rate of inbreeding, which is increased by increasing either accuracy of selection or selection intensity. Inbreeding reduces response to selection in two ways. First, for both additive and nonadditive traits, inbreeding is a measure of the amount of random genetic drift that has occurred. Genetic drift causes loss of favorable alleles. Once lost, those alleles can never be recovered and thus genetic drift lowers the selection limit. Second, for heterotic traits, inbreeding results in a depression of the mean caused by directional dominance.

Animals↗
PubMed2006

Advanced methods for handling and preparation of stallion semen.

Clinical reproduction in the horse more closely parallels human clinical reproduction than in other domestic farm animals. Horse breeders rarely include fertility as a selection criterion when making mating decisions; in most breeds, there is no licensing or approval of stallions. This has led to a significant number of stallions in the breeding pool that possess desirable performance traits but are subfertile for a variety of reasons, some of them genetically transmitted between generations. Therefore, semen characteristics can vary greatly among stallions within the breeding population. A champion stallion is not gelded or culled for poor semen quality or the inability of his spermatozoa to withstand semen preservation techniques. Rather, equine theriogenologists go to great lengths to maximize reproductive performance using any and all means available. Therefore, advanced methods for processing and selecting stallion semen provide the clinician with valuable tools for handling poor-quality semen or for obtaining spermatozoa for assisted reproduction procedures.

Animals↗
PubMed2002

Parasites as a viability cost of sexual selection in natural populations of mammals.

Sexual selection in mammals has resulted in the evolution of sexual size dimorphism (SSD), with males usually being the larger sex. Comparative analyses indicate that the evolution of SSD is associated with the evolution of male-biased mortality, suggesting a possible causal link between the two. Here, we use a comparative approach to investigate the possible role of parasites in generating this relation. We show that there is a robust association between male-biased parasitism and the degree of sexual selection, as measured by mating system (monogamous or polygynous) and by the degree of SSD. There is also a positive correlation, across taxa, between male-biased mortality and male-biased parasitism. These results are consistent with the hypothesis that parasites contribute to the observed association between SSD and male-biased mortality.

Aggression↗
PubMed1972

The evolutionary development of modifier genes.

The main findings of a study of the evolution of modifier gene frequencies in models of deterministic population genetics are presented. A wide variety of random mating systems are subject to selection with modifiers operating, in different cases, on mutation rates, dominance, migration between subpopulations, and linkage between other loci. In all these instances the modifier frequencies evolve in such a way as to maximize the mean fitness of the population at equilibrium. This is remarkable since, except for the dominance modifier, the modifier genes are selectively neutral in the sense that they do not affect the fitness of their individual carriers. In nonrandom mating systems the mean fitness concept is not well defined, and there does not appear to be such a simple principle governing the evolution of modifier frequencies. In assortative mating systems modifiers favoring reduced assortment propensities tend to increase. In contrast, for selfing-outcrossing systems modifiers favoring increased selfing tend to increase.

Alleles↗
PubMed1998

Evolutionarily Stable Reproductive Strategies in Sexual Organisms. Part V-Joint Effects of Parent-offspring Conflict and Sibling Conflict in Perennial Plants.

We develop a general treatment of the joint effects of parent-offspring conflict (conflict between broods) and sibling conflict (conflict within broods) in perennial plants. Parent-offspring conflict as well as sibling conflict are examined in the context of an integrated analysis of reproductive allocation, sex allocation, and the amount of resources invested in each offspring. We find that under a wide range of conditions the selected seed size is independent of reproductive effort or sex allocation. To the extent that the relationships between gamete output and resource investment are linear for both sex functions, the separate treatment of reproductive effort, sex allocation, and offspring size-number compromise in modern life-history theories is well justified, regardless of which side, parents or offspring, controls the allocation to individual seed offspring. We show that incorporation of sibling conflict results in even larger seed size, which in turn leads to even lower reproductive effort, than under pure parent-offspring conflict. If the costs of increased provisioning of selfish offspring are entirely borne by their brood mates, then offspring are selected to solicit parental care as long as they continue to benefit individually from more resources.Copyright 1998 Academic Press Limited

Journal Article↗
PubMed2006

Size breeds success: multiple paternity, multivariate selection and male semelparity in a small marsupial, Antechinus stuartii.

Mating in the marsupial genus Antechinus is a synchronous annual event that is characterized by monoestry in females and abrupt postmating mortality in males. Male semelparity (multiple copulations during a single breeding season per lifetime) is often assumed to occur as a consequence of the intense mating effort expended by males in the rut, but the forces selecting for this remain elusive. Here, we investigate selection in male brown antechinus, Antechinus stuartii, and test two hypotheses for the evolution of semelparity: intermale competition and sperm competition. If intermale competition drives semelparity, we predicted that males would be under strong selection for large body size. If sperm competition is important, we predicted that selection would be strongest on scrotal size, a surrogate for testes volume. Using microsatellite markers, we found that 92% of females in free-living conditions mated with multiple males, producing litters of eight that had up to four fathers. These observations confirm the potential for sperm competition. Using selection analysis, we then found paternity success in 119 males to be related most strongly to body mass and scrotal size, thus providing support for both hypotheses. Large males presumably experience increased paternity success by gaining more matings or prolonged copulations via mate guarding, while large testes may allow increased sperm investment per copulation. Increased levels of free corticosteroid hormones in males facilitate the extreme mating effort during the short period of rut, but lead to immune suppression and consequently to the phenomenon of postmating mortality.

Animals↗
PubMed1967

Linkage and segregation of unselected markers in matings of Nocardia erythropolis with Nocardia canicruria.

The segregation of unselected genes expressing resistance or susceptibility to acriflavine, erythromycin, streptomycin, and tetracycline was analyzed in selected prototrophic recombinants resulting from matings of Nocardia erythropolis and N. canicruria. The organisms were shown to be functionally haploid and appeared to contain not more than one genome. It was postulated that all observed genes were present in a linear linkage group. The ordering of the genes in N. erythropolis was: tetB10 eryB9 his-3 purA1 acr-2 strA1 (respectively, resistance to tetracycline and erythromycin, deficiency for histidine and for purine, and resistance to acriflavine and streptomycin). The ordering of the genes in N. canicruria was: purB2 tetA9 eryA7 acr-11 strB2 (respectively, deficiency for purine, and resistance to tetracycline, erythromycin, acriflavine, and streptomycin). Excluding the genes for acriflavine resistance, acr-2 and acr-11, resistance loci in N. erythropolis were not allelic to and showed lateral displacement from genes controlling phenotypically similar resistance in N. canicruria. Evidence for some lack of homology between N. erythropolis and N. canicruria genomes was found. Recombination phenomena between the nocardial species was postulated to occur as a result of formation of a heterogenomic zygote in which new combinations were produced. Production of selectable, haploid recombinants was ascribed to subsequent haploidization of the zygote.

Chromosome Mapping↗
PubMed2001

The influence of parental relatedness on reproductive success.

The relationship between fitness and parental similarity has been dominated by studies of how inbreeding depression lowers fecundity in incestuous matings. A widespread implicit assumption is that adult fitness (reproduction) of individuals born to parents who are not unusually closely related is more or less equal. Examination of three long-lived vertebrates, the long-finned pilot whale, the grey seal and the wandering albatross reveals significant negative relationships between parental similarity and genetic estimates of reproductive success. This effect could, in principle, be driven by a small number of low quality, inbred individuals. However, when the data are partitioned into individuals with above average and below average parental similarity, we find no evidence that the slopes differ, suggesting that the effect is more or less similar across the full range of parental similarity values. Our results thus uncover a selective pressure that favours not only inbreeding avoidance, but also the selection of maximally dissimilar mates.

Animals↗
PubMed2004

Labile male morphology and intraspecific male polymorphism in the Philotrypesis fig wasps.

We investigate the evolution of male morphology in the fig wasps belonging to the genus Philotrypesis (Chalcidoidea, Sycorectinae). We first reconstruct the phylogenetic relationships of Philotrypesis associated with African figs using nuclear and mitochondrial DNA. We then determine male morphotypes in the species included in our phylogeny and show that intraspecific polymorphism is common. Most species present two types of males and some species have up to three types. These morphotypes are believed to represent alternative mating tactics: some males show morphological adaptations to fighting, others are winged dispersers and others are small sneakers. Mapping out these variations onto our phylogeny reveals that the combination of morphs changes randomly along the branches of the tree. Both parsimony and likelihood approaches indicate that there has been at least one transition from dimorphism to trimorphism, several gains and losses of the small morph and two independent acquisitions of the winged morph. Using maximum likelihood analyses of character evolution, we estimate transition rates for each morph and show that the evolution of each type of morph are not correlated and that forward and backward transition rates are not significantly different. Our results altogether suggest that male morphology is evolutionary labile, it responds quickly to selection imposed by the mating environment. This study, also suggests that seemingly complex phenotypes, such as winged males, can evolve several times and can even be recreated after having been lost.

Animals↗
PubMed2002

Female mice mate preferentially with non-parasitized males.

If parasitic infection is a driving force in female mate choice, then females should preferentially select parasite-free males. The role of infection on female mate choice in mammals was assessed using a 3-chambered apparatus. A female CD-1 mouse was allowed to choose between 2 tethered male mice, 1 uninfected and 1 infected with 200 larvae (L3) of the intestinal nematode Heligmosomoides polygyrus. Both uninfected and infected males were equally receptive to the oestrous females, and females did not differ in the number of visits and time spent exploring the 2 males. Female time preference was not a useful predictor of ultimate mate choice, whereas first mount preference of the female was a reliable indicator. Results indicate that female mice preferentially mated with uninfected males as evidenced by first ejaculation choice, but that male infection status did not significantly affect female reproductive success. Interestingly, litters sired by infected males contained a significantly higher percentage of females suggesting that parasite-induced hormonal changes may alter the sex ratio of the offspring. This study provides the first direct evidence of the impact of parasitic infection on mammalian mate choice.

Animals↗
PubMed2004

Male accessory gland size and the evolutionary transition from single to multiple mating in the fungus-gardening ants.

Polyandry in hymenopteran social insects is surprisingly rare, despite its likely colony-level fitness benefits. Ordinarily, a male's fitness will be at odds with that of a colony when the genetic representation within it is diluted by multiple mating by the queen. Consequently, males are expected to be under selection to limit female re-mating, for example via secretions of their accessory glands. I hypothesized that if accessory glands in some way regulate female mating frequency, an evolutionary transition from single to multiple mating would likely be accompanied with a change in the morphology of the accessory glands. The accessory gland morphology was examined in the fungus-gardening ants, which have made a single transition from single to multiple mating. The evolution of polyandry within this clade corresponds to the loss of male accessory glands, lending tentative support to the idea that they may be involved in regulating mating frequency.

Animals↗
PubMed2000

Runaway sexual selection when female preferences are directly selected.

We introduce models for the runaway coevolution of female mating preferences and male display traits. The models generalize earlier results by allowing for direct natural selection on the preference, arbitrary forms of mate choice, and fairly general assumptions about the underlying genetics. Results show that a runaway is less likely when there is direct selection on the preference, but that it is still possible if there is a sufficiently large phenotypic correlation between the female's preference and the male's trait among mated pairs. Comparison of three preference functions introduced by Lande (1981) shows that open-ended preferences are particularly prone to a runaway, and that absolute preferences require very large differences between females in their preferences. We analyze the causes of the runaway seen in a model developed by Iwasa and Pomiankowski (1995).

Animals↗
PubMed1990

Mutants of Enterococcus faecalis deficient as recipients in mating with donors carrying pheromone-inducible plasmids.

From Enterococcus faecalis cells containing random chromosomal insertions of Tn916, strains resistant to a lytic phage were selected and tested for conjugal mating ability. The phage-resistant strains all showed decreased recipient ability (Con-) in broth matings with donors carrying pheromone-inducible plasmids. These strains were normal with respect to donor ability in broth matings and recipient ability in filter matings. The data suggest that the mutants are deficient in the binding substance receptor for the pheromone-induced donor aggregation substance. These mutants contained multiple insertions of Tn916, and none of the individual insertions from the mutant strains were capable of generating the phenotype. Analysis of cell envelope lipoteichoic acids and protein revealed changes in both associated with the Con- phenotype.

Bacteriophages↗
PubMedDate not supplied

The effect of thermal stress on the mating behavior of three Drosophila species.

Selection may act on the weakest link in fitness to change how a species adapts to an environmental stress. For many species, this limitation may be reproduction. After adult Drosophila melanogaster, Drosophila simulans, and Drosophila mojavensis males were exposed to varying levels of thermal stress well below those that endanger life, courtship and mating frequency declined. The regression coefficients of both courtship and mating success did not differ significantly between D. melanogaster and D. simulans males. In contrast, significant differences were present between the two cosmopolitan species and D. mojavensis. Courtship frequency decreased at a much slower rate in D. mojavensis than in D. melanogaster and D. simulans, and while heat-stressed D. mojavensis males continued to court, many did not mate. In the cosmopolitan species, courting males almost always mated successfully. Courtship behaviors, including wing waving, were observed in D. mojavensis at temperatures that prohibited flight, while flight, courtship, and mating were knocked out simultaneously in D. melanogaster. One possible explanation for decreased flight ability and courtship success may be the reduced heat shock response in the flight muscle tissue because Hsp70 expression was lowest in the thoracic tissue of both D. melanogaster and D. mojavensis.

Adaptation, Physiological↗
PubMed1982

Effects of a novel dopamine-receptor agonist RDS-127 (2-N,N-di-n-propylamino-4,7-dimethoxyindane), on hormone levels and sexual behavior in the male rat.

Selective changes in the mating pattern occurred 30 minutes following administration of RDS-127 (3.0 mg/kg, IP) to sexually experienced adult male rats. Marked decreases in intromission frequency and ejaculation latency were observed. These data indicate a potent effect upon conummatory mechanisms underlying copulatory behavior. The lack of effect upon arousal state was further demonstrated utilizing a "mounting test" (in which the penis is anesthetized by topical application of tetracaine hydrochloride). No difference in mounting behavior was seen. Seminal plugs were noted in a large percentage of treated animals at the time of anesthetic application. Additionally, a six-fold decrease in plasma prolactin and a lesser decrement in plasma luteinizing hormone were evident. Finally, in sexually experienced castrate animals, RDS-127 induced mounting in two thirds and intromissive and ejaculatory patterns in one third of the treated animals, 35 days postcastration. These effects were greatly attenuated by 56 days postcastration. The selective alteration of consummatory mechanisms, with little or no effect upon arousal status, suggests a neurochemical separation of these two components in the intact male rat.

Animals↗
PubMed2004

Sexual conflict over mating in a spider: increased fecundity does not compensate for the costs of polyandry.

Female multiple mating (polyandry) is a widespread but costly behavior that remains poorly understood. Polyandry may arise when whatever benefits females accrue from multiple mating outweigh the costs, or males manipulate females against the females' best interests. In a polyandrous spider Stegodyphus lineatus females may mate with up to five males, but behave aggressively toward additional males after the first mating. Female aggressiveness may act to select for better quality males. Alternatively, females may try to avoid superfluous matings. To test these alternatives, we allocated females into single-mating (SM) and double-mating treatments. Double-mated females either accepted (DM) or rejected (RE) the second male. DM females laid more eggs, but did not produce more offspring than SM and RE females. Offspring of DM females were smaller at dispersal than offspring of SM and RE females. Also, nest failure was significantly more common in DM females. Paternal variables did not influence female reproductive success, whereas maternal body condition explained much of the variation. We show that polyandry is costly for females despite the production of larger clutches and suggest that multiple mating results from male manipulation of female remating behavior.

Aggression↗
PubMed1996

Seasonal dynamics of dental sexual dimorphism in the Atlantic stingray Dasyatis sabina

Cartilaginous fishes continuously replace their teeth throughout their life (polyphyodonty) and often show a sexually dimorphic dentition that was previously thought to be an invariant sex character. Radial vector analysis of tooth shape in the polyphyodontic stingray Dasyatis sabina across a consecutive 24 month period shows a stable molariform morphology for females but a periodic shift in male dentition from a female-like molariform to a recurved cuspidate form during the reproductive season. The grip tenacity of the male dentition is greater for the cuspidate form that occurs during the mating season than for the molariform dentition that occurs during the non-mating season. Dental sexual dimorphism and its sex-dependent temporal plasticity probably evolved via polyphyodontic preadaptation under selective pressures on both sexes for increased feeding efficiency and sexual selection in males to maximize mating success. These phenomena are important considerations for the identification and classification of cartilaginous fishes and possibly other polyphyodontic vertebrates in the fossil record.

Journal Article↗