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PubMed1994

Benefit to male sailfin mollies of mating with heterospecific females.

Female gynogens reproduce clonally but rely on sperm from heterospecific males to initiate embryogenesis. It has been assumed that males gain no benefit from such matings; thus, selection should favor males that avoid them. Here it is shown that males gain a benefit by mating with female gynogens in an asexual-sexual complex of fish. The sexual females increase their preference for males whom they observe consorting with female gynogens. Thus, gynogenetic species might persist because selection favors males to be sexually parasitized.

Animals↗
PubMed2001

Context-dependent genetic benefits from mate choice.

Adaptive mate preferences are generally assumed to be static and open-ended, favouring the most extreme expression of display traits. In contrast to this view, three new studies show that genetic benefits from mate choice can be context-dependent. Thus, there might be short-term fluctuations in selection on mate preferences. The crucial question then is, are plastic mate preferences an optimal evolutionary outcome?

Journal Article↗
PubMed1999

Mice with early onset of death (EOD) due to lupus glomerulonephritis.

Both MRL-lpr/lpr (lpr) and BXSB mice fall victim to autoimmune disease as a function of age. To combine their properties, brother-sister mating of (female lpr x male BXSB)F1 mice was done. Mice for mating were selected according to indicators of early onset of glomerulonephritis and subsequent early death (i.e., EOD). This mating was continued for more than 16 generations. The EOD mice thus established had homozygous H-2k/k, lpr/lpr, and possible yaa/- (in the case of males). The average life span of males was 83 days while that of females was 126 days. After 12 weeks of age, the majority (> 80%) of male EOD mice were characterized by the abnormality of urine due to glomerulonephritis. We then characterized how glomerulonephritis was evoked, especially in terms of expanding lymphocyte subsets in various immune organs. Similar to the case of parental lpr mice, the major expanding cells were CD4-8-B220+ TCRint cells in the immune organs and kidney. In addition, myeloid cells were found to infiltrate the kidney. This massive infiltration of both TCRint cells and myeloid cells might be responsible for the onset of acute glomerulonephritis. Even after more than 50 generations, these EOD mice still carry both lpr and yaa genes. These results suggest that EOD mice might be a very useful tool for the study of acute lupus glomerulonephritis which is evoked by the genetic abnormalities.

Acute Disease↗
PubMed1997

Effect of total allelic relationship on accuracy of evaluation and response to selection.

Total allelic relationship (TA) as a possible alternative to the pedigree-derived additive genetic relationship (RA) is defined. The TA measures the actual allelic identity between individuals for loci segregating for the trait concerned. Its value was studied by simulation in populations of different family structure, different numbers of loci, different numbers of alleles per locus, and different heritability levels. The alternative types of relationship matrices were used in mixed model equations to derive best linear unbiased prediction estimates (EBV) of breeding values (BV). Accuracies of evaluations were calculated as correlations of EBV with true breeding values. In populations with random selection and mating, EBVTA derived using TA had higher accuracies than EBVRA derived using RA. In populations with selection, EBVTA was more accurate and resulted in higher responses than selection on EBVRA. We conclude that not accounting for variation in average measures of relationship and identity in state can be important sources of variance of prediction error, and taking account of them increases the accuracy of selection.

Alleles↗
PubMed2004

Social behavior: how do fish find their shoal mate?

Fish form social aggregations called shoals which often consist of fish with similar morphologies. Experiments using zebrafish pigment variants demonstrate that fish can select shoal mates solely on the basis of their color patterns, and that early experience plays a key role in determining these shoaling preferences.

Animals↗
PubMed1995

The reduction principle for recombination under density-dependent selection.

In diploid random mating populations with constant viability selection, genetic modifiers of recombination, introduced near equilibria that exhibit genetic association, invade if they reduce recombination. In this study we combine ecological and standard populations genetics in a haploid multilocus model that includes density-dependent regulation of population size and weak density-dependent differential selection among the multilocus genotypes. An allele that affects recombination among the genes contributing to the ecological selection, introduced near a stable equilibrium of the ecological-genetic system, invades if it reduces a weighted average of the recombination rates among pairs of loci under selection. This generalizes the Reduction Principle for the evolution of recombination (M. W. Feldman and U. Liberman, Proc. Nat. Acad. Sci. USA 83, 4824-4827, 1986; L. A. Zhivotovsky, W. M. Feldman, and F. B. Christiansen, Theor. Popul. Biol. 44, 225-245, 1993). It is also shown that the stronger the extent of density-dependence, the weaker the selection for reduced recombination.

Alleles↗
PubMed1984

[The effects of rat selection and reproduction on learning ability in the offspring].

We studied the effect of selective reproduction on rats purchased from a breeder, so as to detect learning impairments in their offspring. The parent rats selected for mating were categorized as bright or dull in terms of learning ability on the basis of a learning test in a water maze or passive avoidance response (PAR). Offspring were tested in the same way as the selected rats, with their responses being compared for each generation. 1. The matings, consisting of bright X bright, bright X dull, dull X bright, dull X dull, resulted in a significant increase in the number of dull offspring of dull X dull from parents selected by water maze or PAR learning test. 2. Bright or dull mothers selected by PAR learning were treated with chlorpromazine 6 mg/kg (2 times/day/s.c.) on the 13th day of gestation. Afterwards, a slight increase in dull offspring of dull parents was seen. 3. These results indicate that in order to evaluate the learning ability of F1 in a reproductive test, it is first necessary to check the reaction of the parents, purchased F0, and to classify them as bright or dull.

Animals↗
PubMed2006

Genetic drift and selection effects of modified recurrent full-sib selection programs in two F2 populations of European flint maize.

Selection response of a modified recurrent full-sib (FS) selection scheme conducted in two European flint F(2) maize (Zea mays L.) populations was re-evaluated. Our objectives were to (1) determine the selection response for per se and testcross performance in both populations and (2) separate genetic effects due to selection from those due to random genetic drift. Modified recurrent FS selection was conducted at three locations using an effective population size N(e) = 32 and a selection rate of 25% for a selection index, based on grain yield and grain moisture. Recombination was performed according to a pseudo-factorial mating scheme. Selection response was assessed using a population diallel including the source population and advanced selection cycles, as well as testcrosses with unrelated inbred line testers and the parental F(1) generation. Selection response per cycle was significant for grain yield and grain moisture in both populations. Effects of random genetic drift caused only a small reduction in the selection response. No significant selection response was observed for testcrosses, suggesting that for heterotic traits, such as grain yield, a high frequency of favorable alleles in the elite tester masked the effects of genes segregating in the populations. We conclude that our modified recurrent FS selection is an alternative to other commonly applied intrapopulation recurrent selection schemes, and some of its features may also be useful for increasing the efficiency of interpopulation recurrent selection programs.

Crosses, Genetic↗
PubMed1997

Is sexual selection and species recognition a continuum? Mating behavior of the stalk-eyed fly Drosophila heteroneura.

If behavioral isolation between species can evolve as a consequence of sexual selection within a species, then traits that are both sexually selected and used as a criterion of species recognition by females should be identifiable. The broad male head of the Hawaiian picture-winged fly Drosophila heteroneura is a novel sexual dimorphism that may be sexually selected and involved in behavioral isolation from D. silvestris. We found that males with broad heads are more successful in sexual selection, both through female mate choice and through aggressive interactions. However, female D. heteroneura do not discriminate against hybrids on the basis of their head width. Thus, this novel trait is sexually selected but is not a major contributor to species recognition. Our methods should be applicable to other species in which behavioral isolation is a factor.

Animals↗
PubMed2002

Age-dependent sexual selection in bighorn rams.

Although mating systems and sexual selection have been intensively studied in ungulate model systems, very few studies have combined genetic paternity analysis with individual phenotypic data over several breeding seasons. We used microsatellite paternity analysis to determine the parentage of 83 bighorn sheep (Ovis canadensis) born between 1995 and 2000 at Ram Mountain, Alberta, Canada. We could assign the paternity of 64 lambs at a high level of statistical confidence (95%). Within each season, the most successful ram sired an average of 35.5% of the lambs with assigned paternity, and a single ram sired 26.1% of all lambs over the six mating seasons. Although a few large-horned, mature (age 8+ years) rams had very high reproductive success, younger rams sired ca. 50% of the lambs. Mixed-effects models indicated that mating success increases as a nonlinear function of age, with horn length increasingly positive in correlation with mating success in older rams. These results indicate that young or small rams possibly achieve mating success through alternative mating tactics that are less dependent on body and weapon size, such as coursing and blocking. Sexual selection is therefore likely to have age-dependent effects on traits such as agility, body and horn size.

Age Factors↗
PubMed1976

Design of experiments to estimate heritability when observations are available on parents and offspring.

The design of experiments to estimate heritability when data are available on both parents and offspring and the offspring data have a hierarchical structure is considered. Univariate maximum likelihood (ML) estimation is discussed, and extensions to the multivariate case are outlined. The efficiency of ML estimation is evaluated in cases where simple regression estimators are available. Optimum designs for ML estimation are given when various strategies of selecting and mating are followed. The variance of the heritability estimate can be approximately halved relative to designs in which no selection of parents is done.

Analysis of Variance↗
PubMed2004

Evidence for ecology's role in speciation.

A principal challenge in testing the role of natural selection in speciation is to connect the build-up of reproductive isolation between populations to divergence of ecologically important traits. Demonstrations of 'parallel speciation', or assortative mating by selective environment, link ecology and isolation, but the phenotypic traits mediating isolation have not been confirmed. Here we show that the parallel build-up of mating incompatibilities between stickleback populations can be largely accounted for by assortative mating based on one trait, body size, which evolves predictably according to environment. In addition to documenting the influence of body size on reproductive isolation for stickleback populations spread across the Northern Hemisphere, we have confirmed its importance through a new experimental manipulation. Together, these results suggest that speciation may arise largely as a by-product of ecological differences and divergent selection on a small number of phenotypic traits.

Alaska↗
PubMed1997

Sexual communication.

Sexual communication refers to the use of signals to promote or modulate sexual interaction. We suggest that these signals operate at three levels: (a) a primary level at which signals are used to increase the likelihood of sexual interaction between two individuals; (b) a secondary level at which signals inhibit inbreeding or facilitate outbreeding; and (c) a tertiary level at which signals allow selection among potential mates. Evidence is cited that the selective advantage of the primary, secondary and tertiary levels are, respectively, repair of DNA damage, masking of mutation, and selection for fitness in the mating partner. We illustrate how these advantageous processes are facilitated by sexual communication in bacteria, fungi, protozoa, insects, plants and vertebrates.

Adaptation, Physiological↗
PubMed1983

Linkage of quantitative variation of a serum protein (Sp) to the major histocompatibility complex of the rat.

An antiserum made in rabbits against a rat serum protein (provisionally designated Sp) has been used to establish the existence of a partially inbred line of animals that have low levels of this protein in their serum. This line of animals, the WRD line, was derived from a cross between a wild rat, WRF 6, and a rat of the F344 inbred strain. Offspring from this mating were selected for homozygosity at one wild major histocompatibility complex (MHC) haplotype and inbred for nine generations by brother-sister matings. When tested by immunodiffusion or rocket immunoelectrophoresis with a rabbit anti-rat Sp serum, the sera of these animals showed low levels of the protein when compared with other wild or inbred lines. Animals from the WRD line were backcrossed to the WF inbred strain and normal levels of the Sp protein were transmitted as an autosomal dominant trait. The gene controlling the serum levels of the protein is tightly linked to the MHC (RT1 complex) of the rat.

Animals↗
PubMed2000

Male and female mate choice affects offspring quality in a sex-role-reversed pipefish.

Where both sexes invest substantially in offspring, both females and males should discriminate between potential partners when choosing mates. The degree of choosiness should relate to the costs of choice and to the potential benefits to be gained. We measured offspring quality from experimentally staged matings with preferred and non-preferred partners in a sex-role-reversed pipefish, Syngnathus typhle L. Here, a substantial male investment in offspring results in a lower potential reproductive rate in males than in females, and access to males limits female reproductive success rather than vice versa. Thus, males are choosier than females and females compete more intensely over mates than do males. Broods from preferred matings were superior at escaping predation, when either males or females were allowed to choose a partner. However, only 'choosing' females benefited in terms of faster-growing offspring. Our results have important implications for mate-choice research: here we show that even the more competitive and less choosy sex may contribute significantly to sexual selection through mate choice.

Animals↗
PubMed1999

Selection under negative linkage disequilibrium. Random mating versus inbreeding.

A population resulting from the diallel cross of a set of elite inbred lines was selected under two strategies: (i) inbred strategy (IS) under brother-sister mating; and (ii) random strategy (RIS) under random mating. The final lines in both cases were completely inbred. RIS populations clearly responded better than IS populations. Although most of the RIS advantage was achieved in the second generation, the average response under the RIS strategy increased with respect to that of the IS strategy from the beginning to the end of the experiment. In general terms and on theoretical grounds this RIS advantage is expected only if the initial disequilibrium is negative. One of the final inbred lines performed significantly better than the sum of the two inbred ancestors, strongly suggesting a heterotic epistatic combination fixed in homozygosity. Strong negative disequilibrium and partial epistatic control of quantitative characters are to be expected in breeding programmes of self-pollinating crops. In all likelihood, recurrent selection under forced random mating in such crops would result in better responses.

Animals↗
PubMed1979

A model for population regulation with density- and frequency-dependent selection.

The life-cycle of a species with separate generations is divided into a 'reproduction phase' and a 'growing-up phase'. In the reproduction phase we assume random mating and selection due to genotype differences in fecundity of the parents and viability of the offspring. During the growing-up phase we assume a (deterministic) death process in continuous time with death rates for the genotypes which increase linearly with the genotype population sizes. In the absence of genotype differences the model gives logistic population regulation. With genotype differences the model generalizes the usual separate generations selection patterns. In addition to these we exhibit cases with three polymorphic equilibria or with a stable cycle.

Gene Frequency↗