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PubMed2005

Tension versus ecological zones in a two-locus system.

Previous theories show that tension and ecological zones are indistinguishable in terms of gene frequency clines. Here I analytically show that these two types of zones can be distinguished in terms of genetic statistics other than gene frequency. A two-locus cline model is examined with the assumptions of random mating, weak selection, no drift, no mutation, and multiplicative viabilities. The genetic statistics for distinguishing the two types of zones are the deviations of one- or two-locus genotypic frequencies from Hardy-Weinberg equilibrium (HWE) or from random association of gametes (RAG), and the deviations of additive and dominance variances from the values at HWE. These deviations have a discontinuous distribution in space and different extents of interruptions in the ecological zone with a sharp boundary, but exhibit a continuous distribution in the tension zone. Linkage disequilibrium enhances the difference between the deviations from HWE and from RAG for any two-locus genotypic frequency.

Ecosystem↗
PubMed2004

Are men and women really so different?

Distinct differences in the behaviour and preferences of men and women have conventionally been attributed to Trivers' powerful insights regarding the impact of parental investment on sexual selection and mating systems. This has spawned a huge literature about the evolutionary significance of human sex differences. But are men and women really so different? An elegant new study shows that men and women are strikingly similar in their mate preferences. Have conventional models blinded us to the obvious, and precluded the posing of far more interesting questions?

Journal Article↗
PubMedDate not supplied

Relationship between broiler chicken haematocrit-selected parents and their progeny, with regard to haematocrit, mortality from ascites and bodyweight.

A previous work of this group demonstrated that the relative haematocrit value of broilers is inherited and may serve as an indicator to susceptibility to the ascites syndrome in cold-stressed broilers. In this study, a full-pedigreed population was produced from male and female grandparent breeding stock that was selected by haematocrit and by normal selection parameters. Matings were made between low (L), medium (M) and high (H) haematocrit parents: L x L, M x M, and H x H. In their progeny, both before and after cold exposure, there was a statistically linear relationship between actual haematocrit and their H, M and L grouping (P<0.0001); heritability of the haematocrit was high (0.46-0.81). Both the low haematocrit parent and progeny groups showed an increased bodyweight. Exposure of the progeny from all the parental groups to an ascites-predisposing cold environment caused similar losses from ascites in the progeny of all three groups. Although this finding was not the same as in the previous trial where the H haematocrit group was associated with high ascites mortality, it is hypothesized that other factors, such as arterial blood saturation with oxygen, interacted in these birds at genetic or environmental levels.

Animals↗
PubMed1990

Behavioral adaptations to pathogens and parasites: five strategies.

The ever present threat of viral, bacterial, protozoan and metazoan parasites in the environment of wild animals is viewed as responsible for the natural selection of a variety of behavioral patterns that enable animals to survive and reproduce in this type of environment. Several lines of research, some quite recent, point to five behavioral strategies that vertebrates utilize to increase their personal or inclusive fitness in the face of parasites (broadly defined to include pathogens). These are: 1) avoidance of parasites; 2) controlled exposure to parasites to potentiate the immune system; 3) behavior of sick animals including anorexia and depression to overcome systemic febrile infections; 4) helping sick animals; 5) sexual selection for mating partners with the genetic endowment for resistance to parasites. The point is made that to consider a behavioral pattern as having evolved to serve a parasite control function the parasite or causative agent should be shown to adversely impact the animal's fitness and the behavior in question must be shown to help animals, or their offspring or group mates, in combating their exposure, or reducing their vulnerability, to the parasite.

Adaptation, Psychological↗
PubMed1989

The consequences of heterogamy and homogamy on the similarity between spouses.

Humans in many societies are known to mate, or marry, assortatively for a number of characters such as eye colour, height, IQ and place of birth. In this assortment an element of active choice may be involved. It is not known whether this choice is genetic. Two models of human mate choice are examined in which both males and females can express a mating preference. In the first, 'sexual' preferences can be expressed for any phenotype not necessarily one's own; in the second, preferences are only expressed for an individual's own phenotype. The results of the examination indicate how much active choice would be needed to account for the observed correlations between human mates, and suggest whether human mating preferences are more likely to be sexual or assorting.

Choice Behavior↗
PubMed1990

Endogamy among the Dogon of Boni, Mali.

This paper examines factors influencing endogamy in a Dogon population in Mali. Situated in Boni district, this population of about 5000 individuals is distributed over fifteen villages located on four independent massifs. This population is strongly endogamous (only 4% of all marriages are contracted with neighbouring ethnic groups), and each massif shows high endogamy. The roles of lineage, residence in the same village, and geographical distance in mating choice are examined. These different factors are successively analysed using log-linear statistical models and the results offer a more precise interpretation of endogamy in this population.

Consanguinity↗
PubMed1993

Availability of marriage partners in England and Wales: a comparison of three measures.

Measures of partner availability introduced by Goldman, Westoff & Hammerslough (1984) and by Veevers (1988) are described and a new measure of partner availability, the Iterated Availability Ratio, is introduced. The three measures are applied to 1981 Census data for England and Wales and their abilities to predict regional variations in age-specific marriage rates are compared.

Adult↗
PubMed1994

Education and assortative marriage in northern and urban Sudan: 1945-79.

This study examines the extent of assortative mating for education in Northern Sudan and urban Khartoum. More males than females were found at higher levels of education. Increasingly, people tend to marry persons of equal educational level, but the unequal educational opportunities for males and females have led to the emergence of educational exogamy in which members of different educational levels are more likely to marry from the adjacent educational category than from distant categories. The increasing level of education for both sexes, and especially for females, may in part explain the rising trend in age at marriage.

Adult↗
PubMed1997

International migration and biodemographical behaviour: a study of Italians in Belgium.

This paper describes the matrimonial and reproductive behaviour of Italians who migrated to Belgium after the Second World War. Migrants were either already married, or later became married, to other Italians. Among the children of migrants, men equally chose Italian or Belgian wives but women tended to prefer Italian partners. Italian-Belgian marriages were more frequent among the better educated groups. Family size is smaller among migrants marrying after migration and in heterogamous marriages. Significant differences in birth intervals are found when marriage occurred before or after migration, between generations, and between homogamous and heterogamous marriages.

Adult↗
PubMedDate not supplied

The major histocompatibility complex and the chemosensory signalling of individuality in humans.

The chemosensory identity of mice and rats is determined partly by polymorphic genes of the major histocompatibility complex (MHC). In inbred strains of mice, as well as in seminatural populations, MHC-associated mating preferences selectively influence reproductive success, thus serving to promote heterozygocity in the MHC. In order to determine whether MHC-associated chemosignals are present in humans, two studies were conducted. In a first study, olfactory identification of MHC-associated chemosignals was conducted on 12 trained rats' responses to the urine odors of humans. In a second study, MHC-associated olfactory cues in humans were analyzed by means of gas chromatography. The results indicate that the urine odors of humans are associated with the MHC and demonstrate that the profile of volatile components in the urine odors shows some association with the MHC. Furthermore, results show that a profile of some specific components, as well as a few ubiquitous volatiles, constitutes MHC-associated odor signals in humans.

Animals↗
PubMed2001

Host recognition by the tobacco hornworm is mediated by a host plant compound.

It is generally believed that animals make decisions about the selection of mates, kin or food on the basis of pre-constructed recognition templates. These templates can be innate or acquired through experience. An example of an acquired template is the feeding preference exhibited by larvae of the moth, Manduca sexta. Naive hatchlings will feed and grow successfully on many different plants or artificial diets, but once they have fed on a natural host they become specialist feeders. Here we show that the induced feeding preference of M. sexta involves the formation of a template to a steroidal glycoside, indioside D, that is present in solanaceous foliage. This compound is both necessary and sufficient to maintain the induced feeding preference. The induction of host plant specificity is at least partly due to a tuning of taste receptors to indioside D. The taste receptors of larvae fed on host plants show an enhanced response to indioside D as compared with other plant compounds tested.

Animals↗
PubMed2001

Strength and tempo of directional selection in the wild.

Directional selection is a major force driving adaptation and evolutionary change. However, the distribution, strength, and tempo of phenotypic selection acting on quantitative traits in natural populations remain unclear across different study systems. We reviewed the literature (1984-1997) that reported the strength of directional selection as indexed by standardized linear selection gradients (beta). We asked how strong are viability and sexual selection, and whether strength of selection is correlated with the time scale over which it was measured. Estimates of the magnitude of directional selection (absolute value of beta) were exponentially distributed, with few estimates greater than 0.50 and most estimates less than 0.15. Sexual selection (measured by mating success) appeared stronger than viability selection (measured by survival). Viability selection that was measured over short periods (days) was typically stronger than selection measured over longer periods (months and years), but the strength of sexual selection did not vary with duration of selection episodes; as a result, sexual selection was stronger than viability selection over longer time scales (months and years), but not over short time scales (days).

Animals↗