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PubMed2001

Intrasexual selection predicts the evolution of signal complexity in lizards.

Sexual selection has often been invoked in explaining extravagant morphological and behavioural adaptations that function to increase mating success. Much is known about the effects of intersexual selection, which operates through female mate choice, in shaping animal signals. The role of intrasexual selection has been less clear. We report on the first evidence for the coevolution of signal complexity and sexual size dimorphism (SSD), which is characteristically produced by high levels of male male competition. We used two complementary comparative methods in order to reveal that the use of complex signals is associated with SSD in extant species and that historical increases in complexity have occurred in regions of a phylogenetic tree characterized by high levels of pre-existing size dimorphism. We suggest that signal complexity has evolved in order to improve opponent assessment under conditions of high male male competition. Our findings suggest that intrasexual selection may play an important and previously underestimated role in the evolution of communicative systems.

Animal Communication↗

PubMed2005

Identification of novel binding partners for tuberous sclerosis complex 2 (TSC2) by yeast two-hybrid approach.

AIM: To identify novel tuberous sclerosis complex (TSC2) binding partners by yeast two-hybrid screening. METHODS: The yeast two-hybrid system DupLEX-A developed by OriGene Technologies and Mouse embryo and HeLa cells cDNA libraries were used in this study. The "bait" constructs, containing full-length and truncated form of TSC2 were prepared. The expression of all constructs in yeast was confirmed by immunoblotting with specific anti-LexA antibodies. The suitability of generated constructs for screening was tested in autoactivation and nuclear translocation assays. Screening of mouse embryo and HeLa cDNA libraries with selected baits was carried out according to manufacturer's recommendations. Positive clones were selected using double selection procedure and further confirmed in mating assay. Isolated cDNA clones were identified by automated DNA sequencing and database searching. RESULTS: Extensive screening of two cDNA libraries from mouse embryo and HeLa cells with TSC2 baits led to the isolation of 102 positives clones. The specificity of interaction between TSC2 and binding proteins of selected clones was confirmed by mating assay for 83 clones. Sequencing of these clones indicated that they encode already known and novel TSC2-binding partners. CONCLUSION: The isolation of several known TSC2-binding partners, such as several isoforms of 14-3-3, demonstrates the validity of generated bait constructs and screening conditions. In addition, we have found a number of novel interactors, which encode cytoskeletal proteins and signaling molecules, such as Ser/Thr phosphatases.

Animals↗

PubMed1988

The evolution of human intrasexual competition: tactics of mate attraction.

Darwin's theory of sexual selection suggests that individuals compete with members of their own sex for reproductively relevant resources held by members of the opposite sex. Four empirical studies were conducted to identify tactics of intrasexual mate competition and to test four evolution-based hypotheses. A preliminary study yielded a taxonomy of tactics. Study 1 used close-friend observers to report performance frequencies of 23 tactics to test the hypotheses. Study 2 replicated Study 1's results by using a different data source and subject population. Study 3 provided an independent test of the hypotheses in assessing the perceived effectiveness of each tactic for male and female actors. Although the basic hypotheses were supported across all three studies, there were several predictive failures and unanticipated findings. Discussion centers on the heuristic as well as predictive role of evolutionary theory, and on implications for other arenas of intrasexual competition.

Achievement↗

PubMed2000

Mutational analysis suggests that activation of the yeast pheromone response mitogen-activated protein kinase pathway involves conformational changes in the Ste5 scaffold protein.

Ste5 is essential for pheromone response and binds components of a mitogen-activated protein kinase (MAPK) cascade: Ste11 (MEKK), Ste7 (MEK), and Fus3 (MAPK). Pheromone stimulation releases Gbetagamma (Ste4-Ste18), which recruits Ste5 and Ste20 (p21-activated kinase) to the plasma membrane, activating the MAPK cascade. A RING-H2 domain in Ste5 (residues 177-229) negatively regulates Ste5 function and mediates its interaction with Gbetagamma. Ste5(C177A C180A), carrying a mutated RING-H2 domain, cannot complement a ste5Delta mutation, yet supports mating even in ste4Delta ste5Delta cells when artificially dimerized by fusion to glutathione S-transferase (GST). In contrast, wild-type Ste5 fused to GST permits mating of ste5Delta cells, but does not allow mating of ste4Delta ste5Delta cells. This differential behavior provided the basis of a genetic selection for STE5 gain-of-function mutations. MATa ste4Delta ste5Delta cells expressing Ste5-GST were mutagenized chemically and plasmids conferring the capacity to mate were selected. Three independent single-substitution mutations were isolated. These constitutive STE5 alleles induce cell cycle arrest, transcriptional activation, and morphological changes normally triggered by pheromone, even when Gbetagamma is absent. The first, Ste5(C226Y), alters the seventh conserved position in the RING-H2 motif, confirming that perturbation of this domain constitutively activates Ste5 function. The second, Ste5(P44L), lies upstream of a basic segment, whereas the third, Ste5(S770K), is situated within an acidic segment in a region that contacts Ste7. None of the mutations increased the affinity of Ste5 for Ste11, Ste7, or Fus3. However, the positions of these novel-activating mutations suggested that, in normal Ste5, the N terminus may interact with the C terminus. Indeed, in vitro, GST-Ste5(1-518) was able to associate specifically with radiolabeled Ste5(520-917). Furthermore, both the P44L and S770K mutations enhanced binding of full-length Ste5 to GST-Ste5(1-518), whereas they did not affect Ste5 dimerization. Thus, binding of Gbetagamma to the RING-H2 domain may induce a conformational change that promotes association of the N- and C-terminal ends of Ste5, stimulating activation of the MAPK cascade by optimizing orientation of the bound kinases and/or by increasing their accessibility to Ste20-dependent phosphorylation (or both). In accord with this model, the novel Ste5 mutants copurified with Ste7 and Fus3 in their activated state and their activation required Ste20.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Blockade of CD86 signaling facilitates a Th2 bias at the maternal-fetal interface and expands peripheral CD4+CD25+ regulatory T cells to rescue abortion-prone fetuses.

Intervention in B7 (CD80/CD86)/B7-ligand (CD28/CTLA-4) pathways is an effective way of preventing unwanted immune responses, such as allograft rejection. Pregnancy maintenance represents maternal tolerance to the fetal allograft, which is accompanied by a type 2 helper cell (Th2) bias at the maternal-fetal interface. Here, the costimulatory signal of CD86 was selectively blocked, and that of CD80 was kept unimpaired by administration of anti-murine CD86 monoclonal antibody at the early gestational stage in abortion-prone CBA/JxDBA/2 matings and normal pregnant CBA/JxBALB/c matings. It was demonstrated that in vivo blockade of CD86 costimulation could suppress maternal immune attack to the fetus by shifting cytokines from Th1 predominance to Th2 bias at the maternal-fetal interface, and expanding peripheral CD4+CD25+ regulatory T cells, which play an important role in the development and maintenance of maternal-fetal tolerance. Furthermore, the expression of CD28 and its ligands CD80/CD86 on peripheral lymphocytes was down-regulated, whereas that of CTLA-4 was up-regulated, which might facilitate the suppressive effect of CD4+CD25+ regulatory T cells on the alloreactive T cells. The maternal-fetal immunotolerance induced by CD86 blockade decreased fetal resorption in CBA/JxDBA/2 matings, but did not affect normal pregnant CBA/JxBALB/c matings. These results suggest that selective blockade of CD86 costimulation leads to maternal immune tolerance to embryo antigen, and might contribute to a rational immunoregulatory regimen for recurrent spontaneous abortion.

Abortion, Spontaneous↗

PubMed1997

Mate choice: from sexual cues to cognitive adaptations.

Evolutionary psychologists have successfully combined sexual selection theory and empirical research to compile lists of sexual attractiveness cues used in human mate choice. But a list of inputs is not the same as a normative or descriptive model of a psychological adaptation. We need to shift from cataloguing sexual cues to modelling cognitive adaptations for mate choice. This theoretical chapter addresses how to make this transition in three parts. The introduction discusses four general problems with cue cataloguing as an evolutionary psychology research strategy: animals' promiscuous flexibility of cue use; cue use being marginal to cognition; cue use being marginal to the hard game-theoretical aspects of mate choice; and cue use being uninformative about the exact adaptive functions of mate choice. The middle section develops six critiques of current mate choice research: the obsession with sex difference; the over-emphasis on physical rather than behavioural cues; the assumption of weighted linear models of cue integration; the avoidance of game-theoretical problems of mutual choice and assortative mating; the neglect of co-evolution between mate choice heuristics and the cues that they select; and the failure to understand that mate choice is only worth doing if potential mates show significant genetic variance. The conclusion outlines a new normative and descriptive framework for mate choice, centred on the use of brutally efficient search heuristics that exploit the informational structure of human genotypes, phenotypes and populations to make good mate choices.

Adaptation, Psychological↗

PubMed2002

Active formation of mixed-species grouse leks: a role for predation in lek evolution?

Behavioural ecologists have interpreted avian leks as products of sexual selection, in which males display socially to increase their opportunities to mate. However, without invoking reproductive queuing or kin selection, this paradigm does not necessarily explain why many males that fail to mate participate in leks. An alternative solution, that males also aggregate to reduce predation, has previously lacked compelling support. We show that mixed-species leks, comprising two congeneric grouse, form when single males or small groups of one species, the greater prairie chicken Tympanuchus cupido, join leks of another, the sharp-tailed grouse T. phasianellus. We documented the process by observing lek dynamics and comparing group sizes between mixed- and single-species leks. Joining implies that prairie chickens benefit from displaying with sharp-tailed grouse. The numbers of females of each species attending a lek increased with the number of conspecific, but not heterospecific, males. This suggests that the joining of heterospecifics is unlikely to increase mating opportunities, and leaves lowered predation risk as the most likely benefit of associating with heterospecifics. Active formation of mixed-species leks therefore suggests that predation may be sufficient to drive lek formation. The benefits of participation in mixed leks may be asymmetrical because prairie chickens display more and are less vigilant than sharp-tailed grouse.

Animals↗

PubMed2000

Competitive speciation in quantitative genetic models.

We study sympatric speciation due to competition in an environment with a broad distribution of resources. We assume that the trait under selection is a quantitative trait, and that mating is assortative with respect to this trait. Our model alternates selection according to Lotka-Volterra-type competition equations, with reproduction using the ideas of quantitative genetics. The recurrence relations defined by these equations are studied numerically and analytically. We find that when a population enters a new environment, with a broad distribution of unexploited food sources, the population distribution broadens under a variety of conditions, with peaks at the edge of the distribution indicating the formation of subpopulations. After a long enough time period, the population can split into several subpopulations with little gene flow between them.

Animals↗

PubMed1999

Gene ste20 controls amiloride sensitivity and fertility in Schizosaccharomyces pombe.

It has been shown previously that amiloride, a widely used diuretic drug, inhibits growth in Schizosaccharomyces pombe. Here we show that the drug also alleviates repression by various nutrients of mating and sporulation in fission yeast. We selected spontaneous mutants that are amiloride-resistant and unable to mate and sporulate. One of them defines the gene ste20. This gene has been cloned and sequenced. It codes for a putative protein of 1309 amino acids. Its sequence does not provide any clues to its function. In contrast to the wild-type, mutants defective in this gene can grow in a medium containing 40 microm amiloride, do not arrest in G(1), and do not induce ste11 expression upon nitrogen starvation and thus are sterile. In addition the ste20 mutants are methylamine-sensitive, exhibit enhanced medium acidification and are defective in the utilization of gycerol as a carbon source.

Amiloride↗

PubMed2001

Reinforcement of genetic coherence in a two-locus model.

BACKGROUND: In order to maintain populations as units of reproduction and thus enable anagenetic evolution, genetic factors must exist which prevent continuing reproductive separation or enhance reproductive contact. This evolutionary principle is called genetic coherence and it marks the often ignored counterpart of cladistic evolution. Possibilities of the evolution of genetic coherence are studied with the help of a two-locus model with two alleles at each locus. The locus at which viability selection takes place is also the one that controls the fusion of gametes. The second locus acts on the first by modifying the control of the fusion probabilities. It thus acts as a mating modifier whereas the first locus plays the role of the object of selection and mating. Genetic coherence is enhanced by modifications which confer higher probabilities of fusion to heterotypic gametic combinations (resulting in heterozygous zygotes) at the object locus. RESULTS: It is shown that mutants at the mating modifier locus, which increase heterotypic fusions but do not lower the homotpyic fusions relative to the resident allele at the object locus, generally replace the resident allele. Since heterozygote advantage at the object locus is a necessary condition for this result to hold true, reinforcement of genetic coherence can be claimed for this case. If the homotypic fusions are lowered, complex situations may arise which may favor or disfavor the mutant depending on initial frequencies and recombination rates. To allow for a generalized analysis including alternative models of genetic coherence as well as the estimation of its degrees in real populations, an operational concept for the measurement of this degree is developed. The resulting index is applied to the interpretation of data from crossing experiments in Alnus species designed to detect incompatibility relations.

Alleles↗

PubMed2004

Sexual selection: harem size and the variance in male reproductive success.

Sexual selection is potentially stronger than natural selection when the variance in male reproductive fitness exceeds all other components of fitness variance combined. However, measuring the variance in male reproductive fitness is difficult when nonmating males are absent, inconspicuous, or otherwise difficult to find. Omitting the nonmating males inflates estimates of average male reproductive success and diminishes the variance, leading to underestimates of the potential strength of sexual selection. We show that, in theory, the proportion of the total variance in male fitness owing to sexual selection is approximately equal to H, the mean harem size, as long as H is large and females are randomly distributed across mating males (i.e., Vharem=H). In this case, mean harem size not only provides an easy way to estimate the potential strength of sexual selection but also equals the opportunity for sexual selection, I(mates). In nature, however, females may be overdispersed with Vharem H. We show that H+(k-1) is a good measure of the opportunity for sexual selection, where k is the ratio Vharem/H. A review of mating system data reveals that in nature the median ratio for Vharem/H is 1.04, but as H increases, females tend to become more aggregated across mating males with V(harem) two to three times larger than H.

Animals↗

PubMed2006

A multilocus-multiallele analysis of frequency-dependent selection induced by intraspecific competition.

The study of the mechanisms that maintain genetic variation has a long history in population genetics. We analyze a multilocus-multiallele model of frequency- and density-dependent selection in a large randomly mating population. The number of loci and the number of alleles per locus are arbitrary. The n loci are assumed to contribute additively to a quantitative character under stabilizing or directional selection as well as under frequency-dependent selection caused by intraspecific competition. We assume the strength of stabilizing selection to be weak, whereas the strength of frequency dependence may be arbitrary. Density-dependence is induced by population regulation. Our main result is a characterization of the equilibrium structure and its stability properties in terms of all parameters. It turns out that no equilibrium exists with more than two alleles segregating per locus. We give necessary and sufficient conditions on the strength of frequency dependence to ensure the maintenance of multilocus polymorphism. We also give explicit formulas on the number of polymorphic loci maintained at equilibrium. These results are based on the assumption that selection is sufficiently weak compared with recombination, so that linkage equilibrium can be assumed. If additionally the population size is assumed to be constant, we prove that the dynamics of the model form a generalized gradient system. For the model in its general form we are able to derive necessary and sufficient conditions for the stability of the monomorphic equilibria. Furthermore, we briefly analyze a special symmetric two-locus two-allele model for a constant population size but allowing for linkage disequilibrium. Finally, we analyze a single diallelic locus with dominance to illustrate the complications that can occur if the assumption of additivity is relaxed.

Alleles↗

PubMed1998

Selective breeding of rats for high and low motor activity in a swim test: toward a new animal model of depression.

Because low motor activity ina swim test has been found to represent "depression-like" behavior in the rat, Sprague-Dawley (SD) albino rats were selectively bred for low motor activity (low struggling time/high floating time) in a swim test, while others were bred for high motor activity (high struggling time/low floating time). Eighty-four male and 42 female SD rats were initially purchased from Charles-River Breeding Laboratories in 1987, their behavior assessed in a 15-min swim test, and selective breeding carried out by mating those male and female rats that showed either low or high levels of motor activity in the test; results from behavioral testing of the first 18 generations produced by this selective breeding process are reported here. Two rat lines have been obtained, Swim Low-Active (SwLo) and Swim High-Active (SwHi) rats, which differ dramatically in swim-test behavior--SwLo rats show little struggling and much floating, while SwHi rats show the reverse. Activity scores of individual SwLo and SwHi rats now show no overlap. Selective breeding has produced bidirectional changes; that is, SwLo rats are considerably less active than randomly bred Sprague-Dawley albino rats, while SwHi rats are considerably more active than randomly bred rats. Measuring activity of SwLo and SwHi rats in other situations--ambulation in the home cage, open-field activity, exploratory activity in a novel, home cage-like situation, and immobility in the Porsolt swim test--revealed that differences are most pronounced when animals respond to acute challenges; under these conditions, SwHi rats show active, assertive behavior, whereas SwLo rats show a distinct absence of this type of response. When SwLo rats from the 8th to the 11th generations were given antidepressant medication [desipramine, (DMI), a tricyclic, or phenelzine, an MAO inhibitor], chronic but not acute administration of both drugs increased swim-test activity of SwLo rats. Buspirone, an anxiolytic, did not increase activity of SwLo rats. Use of animals selectively bred for high and low activity in the swim test may represent a new tool for studying physiological processes relevant to affective disorders and for testing antidepressant drugs/treatments.

Animals↗

PubMed2002

Sexual selection on multivariate phenotype in wild and mass-reared Ceratitis capitata (Diptera: Tephritidae).

Males with a larger thorax and narrower face were found to be favoured by directional sexual selection in a previous field cage experiment where Ceratitis capitata males from the Seib 6-96 genetic sexing strain competed with wild males from Alto Valle (Patagonia) for the possession of wild females. Targets of sexual selection, however, might differ between wild and laboratory females as a response to adaptation to mass-rearing conditions. To evaluate possible divergences on the targets of sexual selection as a by-product of adaptation to mass-rearing conditions, field cage tests were performed with both wild and laboratory females. To avoid possible bias due to correlation among the measured traits (eye length [EL], face width [FW], head width [HW], and thorax length [TL]), a multivariate analysis was applied. Consistent with the previous experiment, the results indicated that TL and FW are probable targets of directional sexual selection independently of female strain. However, laboratory females were less selective than wild ones. Additionally, correlational sexual selection was detected acting on the multivariate phenotype. The effects of correlational selection overlap with those of directional selection on each single trait. The analysis of mating pair characteristics showed patterns that do not match the expectations for a random mating system. The current analysis indicates that during mating pair formation two processes overlap. On the one hand, sexual selection favours males with larger size (TL) and narrower faces (FW). This effect occurs in both wild and laboratory females. In addition, assortative mating based on both phenotype and origin was also observed.

Animals↗

PubMed1983

Canine hip dysplasia in German Shepherd Dog-Greyhound crossbreeds.

Nineteen German Shepherd Dog-Greyhound crossbreeds in 7 litters were evaluated by pathoanatomic and/or radiographic examination of their pelves when 12 to 24 months old (mean, 19 months). The prevalence of hip dysplasia in the crossbreeds was 42% (8/19). The prevalence of hip dysplasia in purebred German Shepherd Dog half-siblings in 16 litters produced by parents of the crossbreeds when mated to other German Shepherd Dogs was 35% (16/46). When numerical values were assigned to the pathoanatootmic and radiographic evaluations of the pelves, it was found that the severity of dysplastic changes in the crossbreeds were not significantly different from those changes in their purebred German Shepherd Dog half-siblings. It was concluded that selection for normal hips through mating German Shepherd Dogs with Greyhounds would be no more effective in lowering the prevalence of hip dysplasia than would selection within the German Shepherd Dog breed, which would be more desirable with regard to maintaining the standard of the breed.

Animals↗

PubMed2004

The Ustilago maydis a2 mating-type locus genes lga2 and rga2 compromise pathogenicity in the absence of the mitochondrial p32 family protein Mrb1.

The Ustilago maydis mrb1 gene specifies a mitochondrial matrix protein with significant similarity to mitochondrial p32 family proteins known from human and many other eukaryotic species. Compatible mrb1 mutant strains were able to mate and form dikaryotic hyphae; however, proliferation within infected tissue and the ability to induce tumor development of infected maize (Zea mays) plants were drastically impaired. Surprisingly, manifestation of the mrb1 mutant phenotype selectively depended on the a2 mating type locus. The a2 locus contains, in addition to pheromone signaling components, the genes lga2 and rga2 of unknown function. Deletion of lga2 in an a2Deltamrb1 strain fully restored pathogenicity, whereas pathogenicity was partially regained in an a2Deltamrb1Deltarga2 strain, implicating a concerted action between Lga2 and Rga2 in compromising pathogenicity in Deltamrb1 strains. Lga2 and Rga2 localized to mitochondria and Mrb1 interacted with Rga2 in the yeast two-hybrid system. Conditional expression of lga2 in haploid cells reduced vegetative growth, conferred mitochondrial fragmentation and mitochondrial DNA degradation, and interfered with respiratory activity. The consequences of lga2 overexpression depended on the expression strength and were greatly exacerbated in Deltamrb1 mutants. We propose that Lga2 interferes with mitochondrial fusion and that Mrb1 controls this activity, emphasizing a critical link between mitochondrial morphology and pathogenicity.

Amino Acid Sequence↗

PubMed2004

Selection on insect immunity in the wild.

The strength of selection on immune function in wild populations has only been examined in a few vertebrate species. We report the results from a study measuring selection on a key insect immune enzyme, phenoloxidase (PO), in a wild population of the damselfly Calopteryx xanthostoma. We followed individually marked males from the pre-reproductive adult phase and recorded their lifetime mating success. We found positive selection on PO activity in response to an immune insult, but no selection on wing-spot quality, a trait actively displayed to females during courtship. We suggest that positive selection on PO activity in the year of study may be explained by annual fluctuations in parasite loads.

Animals↗

PubMed1993

Within-family selection at an otherwise unselected locus in dairy cattle.

Identification of allelic variants with economic importance is feasible via molecular genetic techniques. This information can be used to increase the frequency of favourable alleles in dairy cattle. The effect of selection on the genotype within families in the early stages of life is examined. Three different strategies are considered: (1) random mating of bull sires with bull dams and with cows, with embryo selection of young bulls and all cows; (2) random mating of bull sires with bull dams, with embryo selection of young bulls only; (3) minimizing or avoiding matings between homozygotes for the unfavourable allele, with embryo selection of young bulls. Selection strategies assume the use of reproductive technologies such as embryo transfer to produce large family sizes for within-family selection to be practiced. All the three strategies increase the frequency of the favourable allele rapidly. Strategy 1 gives the fastest increase in the frequency of the favourable allele. The increase in the frequency of the favourable allele is slower under random mating (strategy 2) than under a negative assortative mating (strategy 3). This is a novel example of increased selection response with negative assortative mating.

Alleles↗