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PubMed2003

A direct experimental test of founder-flush effects on the evolutionary potential for assortative mating.

Founder-flush speciation models propose that population bottlenecks can enhance evolutionary potential for reproductive isolation. To test this prediction, we subjected bottlenecked (three-pair founder-flush) and nonbottlenecked populations of the housefly to 18 generations of selection for assortative mating. After the selection regime, we analysed videotaped courtship bouts in these lines to identify correlated responses to the selection protocol. The realized heritabilities for assortative mating for both the bottlenecked and nonbottlenecked treatments were very low, but still significant. The founder-flush populations had thus responded to selection as well as the nonbottlenecked populations, although not significantly greater (i.e. total increases in assortative mating were 9.6 and 8.6%, respectively). Multivariate analyses on the courtship repertoires found that, although both bottlenecked and nonbottlenecked treatments attained similar levels of assortative mating, the treatments exhibited different evolutionary solutions in their correlated responses. Specifically, the bottlenecked lines demonstrated a significantly more diverse set of evolutionary trajectories (i.e. significant shifts along the second principal component for courtship). This suggests that the bottlenecked lines had greater potential for the evolution of novel phenotypes as predicted by founder-induced speciation models. Our results, however, cannot distinguish whether the more variable evolutionary responses resulted from increased heritabilities in courtship components, reduced potential to follow the convergent evolutionary trajectories noted for the nonbottlenecked lines, or some combination of both general processes in determining the resultant multivariate phenotype.

Animals↗
PubMed1986

Selection for increased mutation rates with fertility differences between matings.

Previous studies of mutation modification have considered models in which selection is a result of viability differences that are sex symmetric. The results of a numerical study of a model in which selection is a result of fertility differences between mated pairs demonstrate that the type of selection to which a population is subject can have a significant impact on the evolution of various parameters of the genetic system. When the fertility of matings between individuals with different genotypes exceeds the fertility of at least some of the matings between individuals with the same genotype, selection may favor increased rates of mutation, in contrast to the results from all existing constant viability models with random mating and infinite population size. Increased mutation rates are most frequently favored when forward and back mutation occur at approximately equal rates and when the modifying locus is loosely linked to the selected locus. We present one example in which selection favors increased rates of mutation even though the selection scheme is reducible to one of differential viability between the sexes.

Alleles↗
PubMed1969

Polymorphism resulting from the mating advantage of rare male genotypes.

An algebraic model is presented for selection by the mating advantage of rare genotypes. In accordance with the results of recent experiments, the selective advantage is formulated as inversely proportional to genotype frequency. The model applies to any number of alleles at an autosomal locus or at a sex-linked locus, and it provides for a different intensity of selection for each genotype in each sex. The frequency of an allele under this selection proceeds to a stable, nontrivial equilibrium when any one of the genotypes carrying the allele and any one of those carrying another allele possess some degree of the advantage which varies inversely with genotype frequency. The changes in gene frequency are not affected by the mating system, being, for instance, the same with random mating as with inbreeding. With low values for the selection parameters, genetic polymorphisms could be maintained with little selection apparent except at rather low or rather high gene frequencies. The rare genotype advantage may be a significant element among the mechanisms which maintain the extensive genetic polymorphisms of natural populations.

Animals↗
PubMed2004

Changes along the male reproductive axis in response to social context in a gonochoristic gobiid, Zosterisessor ophiocephalus (Teleostei, Gobiidae), with alternative mating tactics.

Sexual selection has given rise, in several taxa, to intrasexual variation in male phenotype. While evolutionary studies have provided explanations of the adaptive function of this dramatic male phenotypic diversity, the proximate control of its expression has still to be completely understood. Several observations, primarily from sex-changing species, indicated a major role of social interactions in reproductive axis regulation and consequently in the expression of alternative male phenotypes. Here we documented changes along the male reproductive axis in response to social context in a gonochoristic species, the grass goby Zosterisessor ophiocephalus, where fully functional alternative male mating tactics appear to be expressed as an ontogenetic gradient. In the grass goby, larger and older males dig a nest and perform parental care, while smaller males sneak fertilization during territorial male spawning. Territorial males are characterized by a higher number of gonadotropin-releasing hormone (GnRH) neurons in forebrain preoptic area, smaller testes, larger seminal vesicles, and viscous ejaculates that last longer and contain fewer sperm than those of sneakers. To experimentally investigate the role of social factors in inducing changes along the male reproductive axis, sneakers were tested in two different situations: nesting alone or with ripe females. Sneakers that mated and performed parental care showed dramatic changes in brain, reproductive apparatus morphology, and ejaculate traits. GnRH-immunoreactive cells in forebrain preoptic area increased in number, reaching values typical of wild-caught parental males. Testes size decreased while seminal vesicle size increased and ejaculates showed lower sperm densities. These results were discussed within the framework of the social transduction hypothesis, which predicts that social experience should mediate, through a cascade of internal processes, shifts between morphs throughout life.

Animals↗
PubMed1975

Selection for high adult body weight in Drosophila populations with different structures.

Selection for high adult body weight in Drosophila melanogaster was practiced for 18 generations in three selection lines. These lines were genetically similar and of equal size but different in population structure. One line represented a large mass-selected, random-mating population, while the other two lines simulated large populations that had been subdivided into partial isolates or demes. Mass selection and random mating occurred within each deme. These two subdivided lines were different only in the rate of effective migration among the demes (5% and 10%). Selection intensities of approximately 20% were applied to these populations. A fourth line served as a random mating control. Heritability of adult body weight in the base population was estimated to be 0.58 plus or minus 0.22. The results indicate that significantly greater responses were achieved in the subdivided lines than in the large mass-selected line, in spite of the fact that larger selection differentials were applied to the latter. No significant differences in response were observed between the two subdivided lines. Wright (1930, 1931) postulated that selection would be most efficient in subdivided populations with limited interdeme migration. The present findings appear to support this theory.

Animals↗
PubMed1988

Use of a modified Marchand cage to study mating and swarming behavior in Culex tarsalis, with reference to colonization.

Selective pressures in laboratory rearing may account for the poor field mating of laboratory reared Culex tarsalis males. Previous studies of swarming behavior of field collected Cx. tarsalis had to be done in the field since such adults did not exhibit normal swarming in cages. Field collected individuals did not swarm normally nor mate effectively in cages. Normal swarming behavior by field collected mosquitoes, subsequent mating, and insemination were observed in a cage modified from a design by Marchand (1985). The use of such a cage could reduce one type of selective mating pressure involved in the colonization of mosquito species.

Animals↗
PubMed1984

Effects of concurrent lactation and postpartum mating on reproductive performance in mice selected for large litter size.

Reproductive and maternal performance of a line of mice selected for large first parity litter size (L+) and a control line (K) were compared under two mating systems: (1) postpartum mating (PP), in which females undergo concurrent gestation and lactation, and (2) postweaning mating (PW), in which females wean their litter before being remated. Females were evaluated in their first two parities. Litters in each line were standardized at birth to 4, 8, 12 or 16 pups in parity 1, and to 10 pups in parity 2. Concurrent gestation had no adverse effect on postnatal maternal performance in parity 1 of either line. In parity 2, both L+ and K declined in reproductive and postnatal maternal performance in PP compared with PW. The pattern of delayed implantation as number of pups nursed increased was similar in both lines under the PP regimen. Several interactions indicated that reproductive performance of L+ was more adversely affected than in K under postpartum mating. Pup mortality was greater in L+ than K under PP but not under PW. In the PP regimen, L+ dams nursing 12 and 16 pups had a lower mating success rate and dams nursing 16 pups had a smaller litter size and higher pup mortality than did K dams. Thus, when L+ dams nurse their natural litter, frequently exceeding 16 pups, their reproductive advantage over K dams observed in PW would be eliminated in PP. If the differences in the first two litters reflect subsequent parities, lifetime reproductive performance in the PP environment would be reduced in the high fecundity line. High fecundity appears to depend upon the environment of selection.

Animals↗
PubMed1985

Evolution of mating preference and sexual dimorphism.

A quantitative genetic model of the joint evolution of female mating preferences and sexual dimorphism in homologous characters of the sexes is described for polygamous species with no male parental effort, such that mating preferences are selectively neutral and evolve only by indirect selection on genetically correlated characters. The male character and the homologous female character are each under stabilizing natural selection toward an optimum phenotype. At an evolutionary equilibrium the female character under natural selection is at its optimum, whereas there is a line of possible equilibria between female mating preferences and the male character. The line of equilibria may be stable or unstable, depending on the intensity of natural selection, the type of mating preferences, and the inheritance of the characters. Various mechanisms for maladaptive evolution of mating preferences and sexual dimorphism are discussed.

Animals↗
PubMed2006

Reversed selection responses in small populations of the housefly (Musca domestica L.).

We compared the efficacy of artificial and natural selection processes in purging the genetic load of perpetually small populations. We subjected replicate lines of the housefly (Musca domestica L.), recently derived from the wild, to artificial selection for increased mating propensity (i.e., the proportion of male-female pairs initiating copulation within 30 min) in efforts to cull out the inbreeding depression effects of long-term small population size (as determined by a selection protocol for increased assortative mating). We also maintained parallel non-selection lines for assessing the spontaneous purge of genetic load due to inbreeding alone. We thus evaluated the fitness of artificially and 'naturally' purging populations held at census sizes of 40 individuals over the course of 18 generations. We found that the artificially selected lines had significant increases in mating propensity (up to 46% higher from the beginning of the protocol) followed by reversed selection responses back to the initial levels, resulting in non-significant heritabilities. Nevertheless, the 'naturally' selected lines had significantly lower fitness overall (a 28% reduction from the beginning of the protocol), although lower effective population sizes could have contributed to this effect. We conclude that artificial selection bolstered fitness, but only in the short-term, because the inadvertent fixation of extant genetic load later resulted in pleiotropic fitness declines. Still, the short-term advantage of the selection protocol likely contributed to the success of the speciation experiment since our recently-derived housefly populations are particularly vulnerable to inbreeding depression effects on mating behavior.

Animal Population Groups↗
PubMedDate not supplied

Genetic and environmental factors affecting mating type frequency in natural isolates of Tetrahymena thermophila.

In Tetrahymena thermophila mating type alleles specify temperature sensitive frequency distributions of multiple mating types. A-like alleles specify mating types I, II, III, V and VI, whereas B-like alleles specify mating types II through VII. We have characterized the mating type distributions specified by several A- and B-like genotypes segregated by genomic exclusion from cells isolated from a pond in northwestern Pennsylvania. The B-like genotypes are alike in specifying very low frequencies of mating type III, but differ with respect to the frequencies of other mating types, particularly II and VII. An A-like genotype specifies a high frequency of mating type III and is unstable in successive generations for the expression of mating type II, suggesting a possible modifier. Inter se crosses performed at 18 degrees C, 28 degrees C and 34 degrees C showed that each genotype specifies a frequency distribution that is uniquely affected by temperature. No mating type was affected the same way by temperature in all genotypes. In A/B heterozygotes, the B-like genotype exhibited partial dominance. The genotypes described here differ significantly from previously described genotypes from the same pond, indicating that there are numerous mating type alleles. For frequency-dependent selection to equalize mating type frequencies, it must act not only on complex multiple alleles but also on the response of mating type alleles to temperature.

Alleles↗
PubMed1998

Highly efficient assimilation of lactose by a metabolically engineered strain of Saccharomyces cerevisiae.

A diploid strain of Saccharomyces cerevisiae able to metabolize lactose with high efficiency has been obtained. Haploid strains of Saccharomyces able to grow on lactose were constructed by cotransformation with two genes of Kluyveromyces lactis required for the utilization of the sugar, LAC4 and LAC12, encoding beta-galactosidase and lactose permease respectively. Both genes were placed under the control of a galactose-inducible promoter and targeted to the rDNA encoding region (RDN1 locus) of the Saccharomyces genome. Lac+ transformants were selected on medium with lactose as the only carbon source. These transformants were mitotically stable, they maintained the Lac+ phenotype after growing in non-selective medium for more than 60 generations, but their growth was slow. We found that this lack of vigour was caused by their genetic background and not by a deficient expression of the heterologous genes. Therefore, their performance could be improved by crossing with a wild-type strain. Among the offspring of the crosses, two strains of opposite mating type were selected and mated to obtain a fast-growing Lac+ diploid. This diploid strain showed the typical fermentative behaviour of S. cerevisiae when it was grown in aerated liquid medium with glucose. In lactose medium, it exhibited a respiro-fermentative metabolism similar to that of K. lactis, with low ethanol production and high biomass yield.

Biomass↗
PubMed2006

Faster lizards sire more offspring: sexual selection on whole-animal performance.

Sexual selection operates by acting on variation in mating success. However, since selection acts on whole-organism manifestations (i.e., performance) of underlying morphological traits, tests for phenotypic effects of sexual selection should consider whole-animal performance as a substrate for sexual selection. Previous studies have revealed positive relationships between performance and survival, that is, natural selection, but none have explicitly tested whether performance may influence reproductive success (through more matings), that is, sexual selection. Performance predicts dominance in some species, implying the effects of sexual selection, but how it does so has not been established, nor is it certain whether performance might be a by-product of selection for something else, for example, elevated circulating testosterone levels. We investigated the potential for sexual selection on sprint speed performance in collared lizards (Crotaphytus collaris), considering the potential mediating effects of circulating hormone levels. Among territorial, adult male collared lizards, only sprint speed significantly predicted territory area and number of offspring sired as determined by genetic paternity analysis. Body size, head size, and hind limb length had no effect. Neither plasma testosterone levels nor corticosterone levels correlated with sprint speed, territory area, or number of offspring sired. Thus, our results provide a direct link between whole-animal performance and reproductive success, suggesting that intrasexual selection can act directly on sprint speed performance and drive the evolution of underlying morphological traits.

Animals↗
PubMed1994

Selection by parasites for clonal diversity and mixed mating.

On theoretical grounds, coevolutionary interactions with parasites can select for cross-fertilization, even when there is a twofold advantage gained by reproducing through uniparental means. The suspected advantage of cross-fertilization stems from the production of genetically rare offspring, which are expected to be more likely to escape infection by coevolving enemies. In the present study, we consider the effects that parasites have on parthenogenetic mutants in obligately sexual, dioecious populations. Computer simulations show that repeated mutation to parthenogenesis can lead to the accumulation of clones with different resistance genotypes, and that a moderately diverse set of clones could competitively exclude the ancestral sexual subpopulation. The simulations also show that, when there are reasonable rates of deleterious mutation, Muller's ratchet combined with coevolutionary interactions with parasites can lead to the evolutionary stability of cross-fertilization. In addition, we consider the effects that parasites can have on the evolution of uniparental reproduction in cosexual populations. Strategy models show that parasites and inbreeding depression could interact to select for evolutionarily stable reproductive strategies that involve mixtures of selfed and outcrossed progeny.

Animals↗
PubMed1988

The evolution of mate choice in a fluctuating environment.

This paper analyzes the evolutionary dynamics of a locus controlling the degree of female mating preference in a temporally fluctuating environment. Preference for mating with males with respect to their genotypes at a locus that is subject to temporally varying natural selection pressure is considered first. With weak selection and free recombination between the choice locus and the selected locus, preference for mating with heterozygotes appears to be favored. With strong selection, preference for homozygous mates may be favored. In each case, choice alleles may increase from very low initial frequencies to near fixation, in contrast to previous models of mate choice in varying environments. Linkages between the two loci has complex effects on the strength and direction of selection for mate choice. Preference for mating with males with the currently fitter genotypes at the locus under natural selection is also modelled. Provided that the environmental period is not too short, a rare allele conferring such preference may be favored and spread to fixation. Strong natural selection, tight linkage and a short environmental period may produce polymorphism for the level of mate choice.

Alleles↗
PubMed2002

Improving male mating competitiveness and survival in the field for medfly, Ceratitis capitata (Diptera: Tephritidae) SIT programs.

The success of the sterile insect technique (SIT) depends critically upon mating between released sterilized males and wild females. In Hawaii, improvements in the efficiency of sterile males were attempted on two separate fronts--mating enhancement and survival improvement. In the former, two methods have been investigated--selective breeding and aromatherapy. In the latter, flies which survived in field cages for several days were selected and bred to produce progeny with enhanced survival ability compared to control flies. Regarding mating selection, standard laboratory-reared males that successfully mated with wild females in field cages were allowed to breed. F1 offspring were inbred, then the selection procedure was repeated for four additional cycles. In the aromatherapy procedure, laboratory-reared males were exposed to ginger root oil for several hours 1 day prior to testing in field cages. Compared to controls, the selected flies improved the mating competitiveness of male flies ca. 3-fold, irradiation reduced this increase to ca. 2.5-fold. Exposing the selected, hybrid strain raised the fitness of the lab males to ca. 9-fold that of wild males. In the ongoing survival selection study, we have obtained lines in which the selected males survived ca. 2-fold better than laboratory control males over several days in an outdoor field cage, with food and water provided. The goal is to combine the traits of higher survival and mating ability into a single strain for SIT release.

Animals↗
PubMed2006

Reconciling sexual selection to species recognition: a process-based model of mating decision.

Mating signals often encode information important for both species recognition and mate quality assessment and endure selection pressures that combine both stabilizing and directional components. Here, we present a family of models of mate preference for multiple-message signals. Our models are process based rather than purely normative, they assume the existence of one (or more) "utility function" that order signals along a scale of perceived appropriateness, and interpret preferences either as the differential probability of signals recognition or as the combined effect of differential recognition and direct comparison between signal alternatives. These models show the critical role played by the proximate mechanisms of information processing in influencing the ultimate function of female mate choice. They show that if preferences are an emergent property of the way animals recognize signals then species recognition and mate quality assessment are expected to constrain each other severely and to limit the overall discrimination power of the system. In contrast, if preferences result from two computational processes, recognition and comparison, the constraining effects of species recognition and mate quality assessment are sensibly reduced. In these cases, females may improve discrimination in mate quality by adopting permissive recognition rules and limiting the risks of heterospecific mating.

Animals↗