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PubMed1987

Characterization of species and strains of Theileria.

A variety of methods is now available for characterizing species and strains of Theileria. For many practical purposes involving field control of theileriosis, characterization on a broad basis may be sufficient, but in other areas much more precise characterization is required. Such precision can be usefully exploited only when cloned parasite populations are involved, and methods to improve parasite characterization and parasite cloning should be developed concurrently. The current methods of immunization against theileriosis involve the use of live parasite populations which are generally poorly defined and, in addition, have the capacity to undergo biological change (by selection, mutation or genetic recombination) within hosts and vectors. Such changes may be difficult to define and identify, but could have profound effects on immunization strategies. Improved methods of parasite characterization and selection, which are now becoming available, will enable parasite stocks for immunization to be identified and selected more precisely, and any biological changes that occur can be monitored. Improved methods of parasite characterization will also open the way to a better understanding of Theileria genetics and the mechanisms of heritability, which appear to differ in some fundamental ways from patterns of Mendelian inheritance. Controlled matings between selected and defined populations of parasites can be envisaged, with the aim of producing hybrid parasites for immunization. In addition, the prospects of modifying the theilerial genome by genetic manipulation become very real: transfection vectors tailored by restriction enzymes could be used to insert or modify gene sequences to develop parasites with appropriate sets of characters. It may also be possible to identify parasite genes which trigger the cytotoxic response which is so important in immunity (Eugui and Emery, 1981; Emery et al., 1981; Preston et al., 1983). Such genes might then be transfected into bovine host lymphocytes to generate immunity against the whole parasite (Iams, 1985). The gene products which are responsible for stimulating immune responses could also be synthesized artificially and used for vaccination. Methods of characterizing Theileria range from Giemsa's staining to DNA hybridization; all have a role to play, and by judicious selection of appropriate methods for particular circumstances, it is becoming possible to characterize theilerial parasites very precisely. Improved methods of characterization can, in turn, lead to a better understanding of parasite biology and to the development of improved methods of immunization and control.

Animals↗
PubMed1980

The effects of increased phenotypic variance on the evolutionary outcomes of generalized major-gene models.

The study of generalized major-gene models has been extended to accommodate selective, assortative mating mechanisms. In this formulation the consequences of amplified phenotypic variance on the major gene frequency are investigated. It is shown that the rate of approach to the equilibrium state is slowed under attenuated assortative mating tendencies and/or with increased environmental noise. Also, an increased phenotypic variance induces more skewness in the nature of the gene frequencies, i.e. a less 'central' polymorphic expression. Where strong positive assortative mating occurs, a population fixation state results. Negative assortment generally facilitates the stability of a 'central' polymorphism.

Alleles↗
PubMedDate not supplied

An optimized approach for the assessment of sexual behavior in male rats.

The improvement and optimization of methods used to detect reproductive disorders in experimental animals are among the main challenges facing researchers in this field. The conventional method for testing male sexual behavior uses ovariectomized females rendered sexually receptive by injection of estradiol benzoate and progesterone prior to testing. The receptive females are then mated with exposed male rats during the dark phase of the cycle under dim red light followed by direct visual and momentary observation of the mating activity. The ovariectomized females may respond differently to hormonal injection (individual differences), leading to variations in the intensity of lordosis. Additionally, the data obtained by the direct visual and momentary evaluation of copulatory activity are very subjective and may produce inaccurate results. In the optimized method, the sexual cycles of female rats are determined, and only those in estrus are selected and mated with sexually experienced male rats. The mating activity is videotaped, enabling the correct observation and evaluation of the different components of mating behavior. This method fosters animal welfare by avoiding surgical intervention and enables the videotape to be kept as permanent documentation.

Animals↗
PubMed2005

Sexual selection for male dominance reduces opportunities for female mate choice in the European bitterling (Rhodeus sericeus).

Sexual selection involves two main mechanisms: intrasexual competition for mates and intersexual mate choice. We experimentally separated intrasexual (male-male interference competition) and intersexual (female choice) components of sexual selection in a freshwater fish, the European bitterling (Rhodeus sericeus). We compared the roles of multiple morphological and behavioural traits in male success in both components of sexual competition, and their relation to male reproductive success, measured as paternity of offspring. Body size was important for both female choice and male-male competition, though females also preferred males that courted more vigorously. However, dominant males often monopolized females regardless of female preference. Subordinate males were not excluded from reproduction and sired some offspring, possibly through sneaked ejaculations. Male dominance and a greater intensity of carotenoid-based red colouration in their iris were the best predictors of male reproductive success. The extent of red iris colouration and parasite load did not have significant effects on female choice, male dominance or male reproductive success. No effect of parasite load on the expression of red eye colouration was detected, though this may have been due to low parasite prevalence in males overall. In conclusion, we showed that even though larger body size was favoured in both intersexual and intrasexual selection, male-male interference competition reduced opportunities for female choice. Females, despite being choosy, had limited control over the paternity of their offspring. Our study highlights the need for reliable measures of male reproductive success in studies of sexual selection.

Animals↗
PubMed1988

STE2 protein of Saccharomyces kluyveri is a member of the rhodopsin/beta-adrenergic receptor family and is responsible for recognition of the peptide ligand alpha factor.

We have cloned the gene for the alpha-factor receptor of the yeast Saccharomyces kluyveri by using the Saccharomyces cerevisiae receptor gene (c-STE2) as a probe. The nucleotide sequence of the S. kluyveri gene (k-STE2) shows that its predicted polypeptide contains seven hydrophobic segments capable of spanning a lipid bilayer and thus that, like c-STE2, it appears to be a member of the rhodopsin/beta-adrenergic receptor family. The k-STE2 polypeptide is 50% identical to that coded by c-STE2, with high conservation (greater than 67%) in the putative membrane-spanning domains. The carboxyl-terminal amino acid sequences are not similar, but both are very hydrophilic and rich in serine and threonine residues. The k-STE2 gene is functional in S. cerevisiae: it reverses the mating defect of an S. cerevisiae mutant defective in its STE2 gene. S. cerevisiae strains expressing k-STE2 rather than c-STE2 exhibit the mating-factor selectivity characteristic of S. kluyveri: better response to S. kluyveri alpha factor than to S. cerevisiae alpha factor. (S. cerevisiae normally responds much better to its own alpha-factor peptide than to the related alpha-factor peptide of S. kluyveri.) This observation demonstrates that the STE2 gene is responsible for ligand selectivity and provides additional evidence that the STE2 protein is the receptor for alpha factor.

Amino Acid Sequence↗
PubMed2005

The evolution of intratetrad mating rates.

Intratetrad mating, the fusion of gametes formed in a single meiosis, has unusual consequences for genetic diversity, especially in genome regions linked to mating type loci. Here we investigate the fate of modifier alleles that alter the rate of intratetrad mating, under models of heterozygote advantage and of genetic load resulting from recurrent mutation. In both cases, intratetrad mating is favored if the recombination rate between the selected locus and mating type is less than the frequency of lethal recessive alleles at that locus in the population. Positive feedback often accelerates the invasion of modifiers to the intratetrad mating rate. Recombination rate and intratetrad mating rate exert indirect selection on one another, resulting in a cascading decline in outcrossing, even in the absence of any cost of sex. However, under recurrent mutation, alleles for obligate intratetrad mating invade only very slowly, perhaps explaining why outcrossing can persist at low frequencies in a largely intratetrad mating population.

Biological Evolution↗
PubMed2006

Repeatability of extra-pair mating in tree swallows.

Models of sexual selection assume that female mating preferences are heritable and, thus, repeatable for individual females across multiple mating episodes. Previous studies of the repeatability of female preference have examined individuals in captivity and focused presumably on social mate choice. However, extra-pair mating is widespread and can also influence sexual selection. We examined the repeatability of extra-pair mating in a wild population of tree swallows (Tachycineta bicolor) by experimentally inducing females to lay two clutches in rapid succession within the same season. We found that the proportion of extra-pair young and the number of extra-pair sires were highly repeatable for individual females. However, the repeatability of specific extra-pair sires was low. We suggest that this unusual pattern of mating may be due to females maximizing the heterozygosity of their offspring.

Animals↗
PubMed1993

Marriage selection and age patterns of mortality: a mathematical investigation.

"In this paper, we use simulation models to demonstrate the complexity of the relationship between the marriage selection process and the resulting RMRs [relative mortality ratios]. In particular, we show that marriage selection alone can produce a relative mortality ratio which remains large and relatively constant at ages far beyond the marriage span....Our general objective...is to determine the range of age patterns of relative mortality which could, in theory, result from marriage selection on the basis of health characteristics. We also evaluate the effects of variations in the marriage selection mechanisms on the resulting mortality patterns.... We develop and apply several simple mathematical models of the marriage selection process. In order to distinguish the potential consequences of marriage selection from marriage protection, we consider hypothetical populations in which causal effects are absent.... We begin by considering an extremely simple marriage selection process and subsequently explore a more realistic selection model based on recent death and marriage rates for Japan."

Age Factors↗
PubMed2000

The number of farm mates influences social and maintenance behaviours of Japanese Black cows in a communal pasture.

The objective of the present study was to investigate optimal group size in cattle in communal pastures where cattle from various farms are turned out: (1) to ascertain if cows derived from each farm form an affiliative group and (2) to investigate the effect of the number of farm mates on social and maintenance behaviours when farm mates form an affiliative group. Farm mates were defined as cows from the same farm. A total of 27 cows having zero, one, two to four, or sixteen farm mates were selected as focal animals in two communal pastures. Each focal animal was followed by an individual observer for 8 h from sunrise. The nearest neighbour and the distance to the nearest neighbour were recorded at 10-min intervals, and maintenance behaviours at 1-min intervals; social behaviours and participants were recorded continuously. Most focal animals frequently choose cows from the same farm as their nearest neighbours allogroomed with these farm mates significantly more (P<0.001). Two focal animals did not form affiliative groups with farm mates. The mean distance to the nearest neighbours, whether farm mates or non-farm mates from focal animals having one and two to four farm mates was shorter than cows turned out with no farm mate (1.4 vs. 1.9 times as long as a cow's body length, P<0.05). Cows having two to four farm mates performed (7.8 s/h/cow, P=0.06) and received allogrooming more (9.8 s/h/cow) and escaped less during agonistic encounters (0.1 frequencies/h/cow, P<0.01) than ones having other numbers of farm mates. The mean duration of grazing behaviour per bout tended to increase with the number of farm mates (5.2 to 10.3 min, P<0.05). The mean duration of recumbency behaviour of cows having two to four farm mates (44.0 min/bout) was longer than the ones having other numbers of farm mates. Social and maintenance behaviours of cows having 16 farm mates were like those having zero or one farm mates, which suggested that the social bond among them was weak. It is concluded that a group of cows having two to four farm mates, that is, a group size of three to five cows, may be optimal for a stable life in a communal pasture.

Journal Article↗
PubMed2003

Endocrine correlates of sexual behavior in the Mohor gazelle (Gazella dama mhorr).

In this study, we quantitatively examined male sexual behavior in relation to fecal estrogen and progesterone concentrations in female Mohor gazelles. We investigated the hypothesis that, during natural mating, males detect cues relating to the potential for successful conception and pregnancy. Time series analysis revealed that males could detect the approach of estrus 2-3 days before female fecal estrogens and estrogen/progestagen (E/P) ratio reached their peak values. Males also paid closer attention to those females excreting higher fecal estrogen concentrations. Mounting and copulation frequencies were positively correlated with both peri-ovulatory fecal estrogen concentrations, and the frequency of pre-copulatory courtship behaviors. These data suggested that males invest their reproductive effort selectively by mating the most fertile females, assuming that estrogen is a valid index of fertility. This assumption was investigated by examining sequential phases of the reproductive cycle for evidence that oocytes and follicles produced in a more estrogenic environment would lead to the formation of the most competent corpora lutea, thereby maximizing the chance of sustaining pregnancy. Associations between sexual behavior and hormone excretion support the hypothesis that males may use this mechanism to assess female fertility.

Animals↗
PubMed1996

Discrete clutch sizes, local mate competition, and the evolution of precise sex allocation.

Optimal sex allocation under a population structure with local mate competition has been studied mainly in deterministic models that are based on the assumption of continuous clutch sizes; Hamilton's (1967) model is the classic example. When clutch sizes are small, however, this assumption is not appropriate. When taking the discrete nature of eggs into account it becomes critically important whether females control only the mean sex ratio ("binomial" females) or the variance as well ("precise" females). As both types of sex ratio control have been found, it is of interest to investigate their evolutionary stability. In particular, it may be questioned whether perfect control of the sex ratio is always favoured by natural selection when mating groups are small. Models based on discrete clutch sizes are developed to determine evolutionarily stable (ES) sex ratios. It is predicted that when all females are of the binomial type they should produce a lower proportion of daughters than predicted by Hamilton's model, especially when clutch size and foundress number are small. When all females are of the precise type, the ES number of sons should generally be either a stable mixed strategy or a pure strategy, but there are special cases (for two foundresses and particular clutch sizes) where the ES number of sons lies in a trajectory of neutrally stable mixed strategies; the predicted mean sex ratios can be either higher or lower than predicted by Hamilton's model. The existence of ES mixed strategies implies that individual females do not necessarily have to produce sex ratios with perfect precision; some level of imperfection can be tolerated (i.e., will not be selected against). When the population consists of both binomial and precise females, the latter always have a selective advantage. This advantage of precision does not disappear when precision approaches fixation in the population. The latter result contradicts the conclusions of Taylor and Sauer (1980) which is due to their way of expressing selective advantage; they define selective advantage as the between-generation increase per allele, which will always become vanishingly small when an allele reaches fixation, irrespective of fitness differences.

Animals↗
PubMed1999

A tradeoff between immunocompetence and sexual ornamentation in domestic fowl.

Females often select their mates on the basis of the size or intensity of sexual ornaments, and it is thought that such traits are reliable indicators of male quality because the costliness of these traits prevents cheating. The immunocompetence handicap hypothesis is a recently proposed mechanistic explanation of these costs and states that males carry ornaments at the expense of their resistance to disease and parasites. The tradeoff between immunocompetence and sexual ornamentation was hypothesized to arise as a consequence of the dual effect of androgens on ornamentation (+) and immune function (-). To test this hypothesis, we compared comb size between male domestic chickens Gallus domesticus of lines divergently selected for antibody responses to sheep erythrocytes (three lines: selected for low response or high response and a control line). The importance of comb size in inter- and intrasexual selection is well established, and comb size is strongly dependent on testosterone level. Comb size was larger in the males of the low line than in the high line, and comb size of control males was intermediate, indicating a tradeoff between ornamentation and immunocompetence. Testosterone (T) levels varied in a similar fashion (TLow > TControl > THigh), suggesting that this hormone could mediate the tradeoff between ornamentation and immunocompetence. These results support the idea that a tradeoff with immune function may constrain the expression of secondary sexual ornaments.

Animals↗
PubMed1984

Mating behavior and brain biogenic amine concentrations in chickens treated with parachlorophenylalanine (PCPA).

Four experiments were conducted to determine the effect of parachlorophenylalanine (PCPA) on the male mating behavior of a line of chickens genetically selected for low mating frequency and to determine the effect on brain concentrations of 5-hydroxytryptamine, dopamine (DA) and norepinephrine (NE). Mating behavior was not affected by moderate levels (less than 64 mg/kg) of PCPA, and decreased significantly when higher levels (100 mg/kg) of the drugs were administered. Results suggest that elevated brain serotonin titers were not causing the low mating frequency associated with the selected line. Birds receiving higher levels of PCPA exhibited a lethargy which persisted for approximately ten days after withdrawal of the drug. Serotonin, DA, and NE were all significantly reduced in the brains of birds receiving PCPA (30 mg/kg).

Animals↗
PubMed2005

Competitive divergence in non-random mating populations.

A haploid model of frequency-dependent selection and assortative mating is introduced and analyzed for the case of a single multiallelic autosomal locus. Frequency-dependent selection is due to intraspecific competition mediated by a quantitative character under stabilizing or directional selection. Assortment is induced by the same trait. We analyze the equilibrium structure and the local stability properties of all possible equilibria. In the limit of weak selection we obtain global stability properties by finding a Lyapunov function. We provide necessary and sufficient conditions for the maintenance of polymorphism in terms of the strength of stabilizing selection, intraspecific competition and assortment. Our results also include criteria for the ability of extreme types to invade the population. Furthermore, we study the occurrence of disruptive selection and provide necessary and sufficient conditions for intraspecific divergence to occur.

Animals↗
PubMed2000

The lipopolysaccharide of recipient cells is a specific receptor for PilV proteins, selected by shufflon DNA rearrangement, in liquid matings with donors bearing the R64 plasmid.

Shufflon DNA rearrangement selects one of seven PilV proteins with different C-terminal segments, which then becomes a minor component of the thin pili of Escherichia coli strains bearing the plasmid R64. The PilV proteins determine the recipient specificity in liquid matings. A recipient Escherichia coli K-12 strain was specifically recognized by the PilVA', -C, and -C' proteins, while E. coli B was recognized only by the PilVA' protein. To identify specific PilV receptors in the recipient bacterial cells, R64 liquid matings were performed using various E. coli K-12 waa (rfa) mutants and E. coli B transformants as recipient cells. E. coli K-12 waa mutants lack receptors for specific PilV proteins. E. coli B cells carrying waaJ or waaJKL genes of E. coli K-12 were recognized by donors expressing the PilVC' protein or the PilVC and -C' proteins, respectively, in addition to the PilVA' protein. Addition of E. coli K-12 or B lipopolysaccharide (LPS) specifically inhibited liquid matings. We conclude that the PilV proteins of the thin pili of R64-bearing donors recognize LPS molecules located on the surface of various recipient bacterial cells in liquid matings.

Bacterial Proteins↗
PubMed2006

Asymmetrical reinforcement and Wolbachia infection in Drosophila.

Reinforcement refers to the evolution of increased mating discrimination against heterospecific individuals in zones of geographic overlap and can be considered a final stage in the speciation process. One the factors that may affect reinforcement is the degree to which hybrid matings result in the permanent loss of genes from a species' gene pool. Matings between females of Drosophila subquinaria and males of D. recens result in high levels of offspring mortality, due to interspecific cytoplasmic incompatibility caused by Wolbachia infection of D. recens. Such hybrid inviability is not manifested in matings between D. recens females and D. subquinaria males. Here we ask whether the asymmetrical hybrid inviability is associated with a corresponding asymmetry in the level of reinforcement. The geographic ranges of D. recens and D. subquinaria were found to overlap across a broad belt of boreal forest in central Canada. Females of D. subquinaria from the zone of sympatry exhibit much stronger levels of discrimination against males of D. recens than do females from allopatric populations. In contrast, such reproductive character displacement is not evident in D. recens, consistent with the expected effects of unidirectional cytoplasmic incompatibility. Furthermore, there is substantial behavioral isolation within D. subquinaria, because females from populations sympatric with D. recens discriminate against allopatric conspecific males, whereas females from populations allopatric with D. recens show no discrimination against any conspecific males. Patterns of general genetic differentiation among populations are not consistent with patterns of behavioral discrimination, which suggests that the behavioral isolation within D. subquinaria results from selection against mating with Wolbachia-infected D. recens. Interspecific cytoplasmic incompatibility may contribute not only to post-mating isolation, an effect already widely recognized, but also to reinforcement, particularly in the uninfected species. The resulting reproductive character displacement not only increases behavioral isolation from the Wolbachia-infected species, but may also lead to behavioral isolation between populations of the uninfected species. Given the widespread occurrence of Wolbachia among insects, it thus appears that there are multiple ways by which these endosymbionts may directly and indirectly contribute to reproductive isolation and speciation.

Animals↗
PubMedDate not supplied

Bridewealth, marriage and fertility in the east-central states of Nigeria.

"The paper examines the determinants of high bridewealth in the east-central states of Nigeria, inhabited by the Igbo, and relates high bridewealth to rising age at marriage among both men and women. High and rising bridewealth in Igboland is associated with the prevailing economic situation, socio-economic status of bride's parents, raising incidence of self-selection of marital partners in place of arranged marriages, and particularly increasing female education.... Rising age at marriage in Igboland cannot be understood only on the basis of increasing urbanization, female education and employment opportunities, but also on the basis of rising bridewealth which reduces the tempo of marriage....The study ends with an investigation of the determinants of marital fertility through the use of a causal model that includes bridewealth, age at marriage and other socio-economic variables." (SUMMARY IN ITA AND FRE)

Africa↗