Natural selection and quantitative genetics of life-history traits in Western women: A twin study

Whether contemporary human populations are still evolving as a result of natural selection has been hotly debated. For natural selection to cause evolutionary change in a trait, variation in the trait must be correlated with fitness and be genetically heritable and there must be no genetic constraints to evolution. These conditions have rarely been tested in human populations. In this study, data from a large twin cohort were used to assess whether selection Will cause a change among women in contemporary Western population for three life-history traits: age at menarche, age at first reproduction, and age at menopause. We control for temporal variation in fecundity (the baby boom phenomenon) and differences between women in educational background and religious affiliation. University-educated women have 35% lower fitness than those with less than seven years education, and Roman Catholic women have about 20% higher fitness than those of other religions. Although these differences were significant, education and religion only accounted for 2% and 1% of variance in fitness, respectively. Using structural equation modeling, we reveal significant genetic influences for all three life-history traits, with heritability estimates of 0.50, 0.23, and 0.45, respectively. However, strong genetic covariation with reproductive fitness could only be demonstrated for age at first reproduction, with much weaker covariation for age at menopause and no significant covariation for age at menarche. Selection may, therefore, lead to the evolution of earlier age at first reproduction in this population. We also estimate substantial heritable variation in fitness itself, with approximately 39% of the variance attributable to additive genetic effects, the remainder consisting of unique environmental effects and small effects from education and religion. We discuss mechanisms that could be maintaining such a high heritability for fitness. Most likely is that selection is now acting on different traits from which it did in pre-industrial human populations.

Identification of causal relationships among traits related to drought resistance in Stylosanthes scabra using QTL analysis

Previous studies have shown that a negative relationship exists between transpiration efficiency (TE) and carbon isotope discrimination (Delta) and between TE and specific leaf area (SLA) in Stylosanthes scabra, A glasshouse experiment was conducted to confirm these relationships in an F-2 population and to study the causal nature of these relationships through quantitative trait loci (QTL) analysis, One hundred and twenty F-2 genotypes from a cross between two genotypes within S. scabra were used. Three replications for each genotype were maintained through vegetative propagation, Water stress was imposed by maintaining plants at 40% of field capacity for about 45 d. To facilitate QTL analysis, a genetic linkage map consisting of 151 RAPD markers was developed, Results from this study show that Delta was significantly and negatively correlated with TE and biomass production. Similarly, SLA showed significant negative correlation with TE and biomass production, Most of the QTL for TE and Delta were present on linkage groups 5 and 11. Similarly, QTL for SLA, transpiration and biomass productivity traits were clustered on linkage groups 13 and 24, One unlinked marker was also associated with these traits, There were several markers coincident between different traits, At all the coincident QTL, the direction of QTL effects was consistent with phenotypic data, At the coincident markers between TE and Delta, high alleles of TE were associated with low alleles of Delta. Similarly, low alleles of SLA were associated with high alleles of biomass productivity traits and transpiration. At the coincident markers between trans-4-hydroxy-N-methyl proline (MHP) and relative water content (RWC), low alleles of MHP were associated with high alleles of RWC, This study suggests the causal nature of the relationship between TE and Delta. Phenotypic data and QTL, data show that SLA was more closely associated with biomass production than with TE, This study also shows that a cause-effect relationship may exist between SLA and biomass production.

Biology and conservation of the rare New Zealand land snail Paryphanta busbyi watti (Mollusca, Pulmonata)

The biology of Paryphanta busbyi watti, an endangered carnivorous land snail, was studied mostly by following large juvenile and adult snails with harmonic radar. The snails are nocturnally active and most (79%) hide during the day under leaf litter or in dense vegetation. Fecal analysis showed that the diet is primarily earthworms, but some cannibalism of smaller snails occurs. Empty shells appear to be an additional source of dietary calcium. Mating occurred most frequently between April and July. Mating snails stayed together for 4-7 days, and each pair reversed their positions at least twice. Four snails were first found mating 151-1240 d after they acquired adult shells, and 7 snails were observed mating a second time after 66-298 d. We found 8 nests and observed 6 snails ovipositing; 5 snails laid eggs in holes they dug and one laid eggs in a crevice between rocks. In 2 instances, oviposition was recorded 52 and 140 d after mating. Snails were estimated to lay on average similar to17.5 eggs per year in 3-5 clutches. Most oviposition was observed in August/September, but some occurred between November and February. Of the snails that died, pigs killed 13.6% and humans inadvertently killed another 13.6%. Other snails died from unknown causes mostly during the drier and warmer months, from November to April. This large land snail survives in the presence of introduced predators, but some life history traits could predispose it to a rapid decline in numbers if new predators arrive.

Multivariate quantitative genetics and the Lek Paradox: Genetic variance in male sexually selected traits of Drosophila serrata under field control

Single male sexually selected traits have been found to exhibit substantial genetic variance, even though natural and sexual selection are predicted to deplete genetic variance in these traits. We tested whether genetic variance in multiple male display traits of Drosophila serrata was maintained under field conditions. A breeding design involving 300 field-reared males and their laboratory-reared offspring allowed the estimation of the genetic variance-covariance matrix for six male cuticular hydrocarbons (CHCs) under field conditions. Despite individual CHCs displaying substantial genetic variance under field conditions, the vast majority of genetic variance in CHCs was not closely associated with the direction of sexual selection measured on field phenotypes. Relative concentrations of three CHCs correlated positively with body size in the field, but not under laboratory conditions, suggesting condition-dependent expression of CHCs under field conditions. Therefore condition dependence may not maintain genetic variance in preferred combinations of male CHCs under field conditions, suggesting that the large mutational target supplied by the evolution of condition dependence may not provide a solution to the lek paradox in this species. Sustained sexual selection may be adequate to deplete genetic variance in the direction of selection, perhaps as a consequence of the low rate of favorable mutations expected in multiple trait systems.

Divergent selection and the evolution of signal traits and mating preferences

Mating preferences are common in natural populations, and their divergence among populations is considered an important source of reproductive isolation during speciation. Although mechanisms for the divergence of mating preferences have received substantial theoretical treatment, complementary experimental tests are lacking. We conducted a laboratory evolution experiment, using the fruit fly Drosophila serrata, to explore the role of divergent selection between environments in the evolution of female mating preferences. Replicate populations of D. serrata were derived from a common ancestor and propagated in one of three resource environments: two novel environments and the ancestral laboratory environment. Adaptation to both novel environments involved changes in cuticular hydrocarbons, traits that predict mating success in these populations. Furthermore, female mating preferences for these cuticular hydrocarbons also diverged among populations. A component of this divergence occurred among treatment environments, accounting for at least 17.4% of the among- population divergence in linear mating preferences and 17.2% of the among-population divergence in nonlinear mating preferences. The divergence of mating preferences in correlation with environment is consistent with the classic by- product model of speciation in which premating isolation evolves as a side effect of divergent selection adapting populations to their different environments.

Measuring natural and sexual selection on breeding values of male display traits in Drosophila serrata

Fundamental to many theories of sexual selection is the expectation that sexual traits, which males use in an attempt to increase mating success, confer costs as well as benefits to individual males. Although evolution of exaggerated male traits is predicted to be halted, by costs applied by natural selection, there is a lack of empirical work devoted to quantitatively establishing whether natural selection opposes sexual selection generated by the preferences of females. In this study, we quantified natural and sexual selection gradients on breeding values for cuticular hydrocarbon (CHC) components of male contact pheromones in Drosophila serrata. As male sexual traits may often be environmentally condition dependent, breeding values were used in the selection analysis to remove the possibility of environmental correlations between the measured trait and fitness biasing estimates of selection. The direction of natural selection was found to oppose sexual selection on a subset of CHCs examined. Opposing natural and sexual selection suggests that further evolution of the male pheromone may in part be limited by costs associated with attractive male CHC blends.

Wolbachia: Invasion biology in South Pacific butterflies

Wolbachia ensdosymbionts are well known for their ability to manipulate the population biology and development of their hosts. One of the less studied outcomes of Wolbachia infection with this symbiont is the selective killing of male embryos. Recent work on butterflies living on different South Pacific islands is beginning to help us understand the complexity of the co-evolutionary interactions between these partners.

Evidence for a global Wolbachia replacement in Drosophila melanogaster

Wolbachia are maternally inherited intracellular α-Proteobacteria found in numerous arthropod and filarial nematode species [1, 2 and 3]. They influence the biology of their hosts in many ways. In some cases, they act as obligate mutualists and are required for the normal development and reproduction of the host [4 and 5]. They are best known, however, for the various reproductive parasitism traits that they can generate in infected hosts. These include cytoplasmic incompatibility (CI) between individuals of different infection status, the parthenogenetic production of females, the selective killing of male embryos, and the feminization of genetic males [1 and 2]. Wolbachia infections of Drosophila melanogaster are extremely common in both wild populations and long-term laboratory stocks [6, 7 and 8]. Utilizing the newly completed genome sequence of Wolbachia pipientis wMel [9], we have identified a number of polymorphic markers that can be used to discriminate among five different Wolbachia variants within what was previously thought to be the single clonal infection of D. melanogaster. Analysis of long-term lab stocks together with wild-caught flies indicates that one of these variants has replaced the others globally within the last century. This is the first report of a global replacement of a Wolbachia strain in an insect host species. The sweep is at odds with current theory that cannot explain how Wolbachia can invade this host species given the observed cytoplasmic incompatibility characteristics of Wolbachia infections in D. melanogaster in the field [6].

Evolution of the genetic covariance between male and female components of mate recognition: An experimental test

The evolution of a positive genetic correlation between male and female components of mate recognition systems will result as a consequence of assortative mating and, in particular, is central to a number of theories of sexual selection. Although the existence of such genetic correlations has been investigated in a number of taxa, it has yet to be shown that such correlations evolve and whether they may evolve as rapidly as suggested by sexual selection models. In this study, I used a hybridization experiment to disrupt natural mate recognition systems and then observed the subsequent evolutionary dynamics of the genetic correlation between male and female components for 56 generations in hybrids between Drosophila serrata and Drosophila birchii. The genetic correlation between male and female components evolved from 0.388 at generation 5 to 1.017 at generation 37 and then declined to -0.040 after a further 19 generations. These results indicated that the genetic basis of the mate recognition system in the hybrid populations evolved rapidly. The initial rapid increase in the genetic correlation was consistent with the classic assumption that male and female components will coevolve under sexual selection. The subsequent decline in genetic correlation may be attributable to the fixation of major genes or, alternatively, may be a result of a cyclic evolutionary change in mate recognition.

The role of colour in signalling and male choice in the agamid lizard Ctenophorus ornatus

Bright coloration and complex visual displays are frequent and well described in many lizard families. Reflectance spectrometry which extends into the ultraviolet (UV) allows measurement of such coloration independent of our visual system. We examined the role of colour in signalling and mate choice in the agamid lizard Ctenophorus ornatus. We found that throat reflectance strongly contrasted against the granite background of the lizards' habitat. The throat may act as a signal via the head-bobbing and push-up displays of C. ornatus. Dorsal coloration provided camouflage against the granite background, particularly in females. C. ornatus was sexually dichromatic for all traits examined including throat UV reflectance which is beyond human visual perception. Female throats were highly variable in spectral reflectance and males preferred females with higher throat chroma between 370 and 400 nm. However, female throat UV chroma is strongly correlated to both throat brightness and chest UV chroma and males may choose females on a combination of these colour variables. There was no evidence that female throat or chest coloration was an indicator of female quality. However, female brightness significantly predicted a female's laying date and, thus, may signal receptivity. One function of visual display in this species appears to be intersexual signalling, resulting in male choice of females.