Genetic and dietary adaptation to malaria in human populations

Plasmodial invasion places a severe oxidant stress on parasitized erythrocytes which can result in red cell damage and removal within the reticuloendothelial system or lysis, thus interrupting the parasitic cycle. The basis of a number of genetic adaptations to malaria--including the hemoglobin variants, the thalassemias, and glucose-6-phosphate dehydrogenase deficiency--is an increased sensitivity of the variant erythrocytes to the oxidant stress of plasmodial parasitization. It is suggested that dietary adaptations of traditional cusines in human populations living in areas where malaria is endemic augment this oxidant stress. It appears that there are three components of this adaptive dietary pattern in most tropical populations: the consumption of 'oxidant fuels', moderate to high iron intake, and limitation of dietary antioxidant intake or storage. It is argued that this dietary pattern maximizes iron-mediated free radical production in parasitized erythrocytes and thus provides a form of diet-mediated antimalarial prophylaxis. African pastoral populations that are heavy consumers of milk appear to manifest a different adaptive pattern involving low intakes of para-aminobenzoic acid, vitamin E, and iron. Periodic food restriction may also contribute to this antimalarial effect.     

Similarities in butterfly emergence dates among populations suggest local adaptation to climate

Phenology shifts are the most widely cited examples of the biological impact of climate change, yet there are few assessments of potential effects on the fitness of individual organisms or the persistence of populations. Despite extensive evidence of climate‐driven advances in phenological events over recent decades, comparable patterns across species' geographic ranges have seldom been described. Even fewer studies have quantified concurrent spatial gradients and temporal trends between phenology and climate. Here we analyse a large data set (~129 000 phenology measures) over 37 years across the UK to provide the first phylogenetic comparative analysis of the relative roles of plasticity and local adaptation in generating spatial and temporal patterns in butterfly mean flight dates. Although populations of all species exhibit a plastic response to temperature, with adult emergence dates earlier in warmer years by an average of 6.4 days per °C, among‐population differences are significantly lower on average, at 4.3 days per °C. Emergence dates of most species are more synchronised over their geographic range than is predicted by their relationship between mean flight date and temperature over time, suggesting local adaptation. Biological traits of species only weakly explained the variation in differences between space‐temperature and time‐temperature phenological responses, suggesting that multiple mechanisms may operate to maintain local adaptation. As niche models assume constant relationships between occurrence and environmental conditions across a species' entire range, an important implication of the temperature‐mediated local adaptation detected here is that populations of insects are much more sensitive to future climate changes than current projections suggest.     

Divergent selection on flowering time contributes to local adaptation in Mimulus guttatus populations

The timing of when to initiate reproduction is an important transition in any organism's life cycle. There is much variation in flowering time among populations, but we do not know to what degree this variation contributes to local adaptation. Here we use a reciprocal transplant experiment to examine the presence of divergent natural selection for flowering time and local adaptation between two distinct populations of Mimulus guttatus. We plant both parents and hybrids (to tease apart differences in suites of associated parental traits) between these two populations into each of the two native environments and measure floral, vegetative, life-history, and fitness characters to assess which traits are under selection at each site. Analysis of fitness components indicates that each of these plant populations is locally adapted. We obtain striking evidence for divergent natural selection on date of first flower production at these two sites. Early flowering is favored at the montane site, which is inhabited by annual plants and characterized by dry soils in midsummer, whereas intermediate (though later) flowering dates are selectively favored at the temperate coastal site, which is inhabited by perennial plants and is almost continually moist. Divergent selection on flowering time contributes to local adaptation between these two populations of M. guttatus, suggesting that genetic differentiation in the timing of reproduction may also serve as a partial reproductive isolating barrier to gene flow among populations.     

Repeatability of adaptation in experimental populations of different sizes

The degree to which evolutionary trajectories and outcomes are repeatable across independent populations depends on the relative contribution of selection, chance and history. Population size has been shown theoretically and empirically to affect the amount of variation that arises among independent populations adapting to the same environment. Here, we measure the contribution of selection, chance and history in different-sized experimental populations of the unicellular alga Chlamydomonas reinhardtii adapting to a high salt environment to determine which component of evolution is affected by population size. We find that adaptation to salt is repeatable at the fitness level in medium (N_e = 5 × 10⁴) and large (N_e = 4 × 10⁵) populations because of the large contribution of selection. Adaptation is not repeatable in small (N_e = 5 × 10³) populations because of large constraints from history. The threshold between stochastic and deterministic evolution in this case is therefore between effective population sizes of 10³ and 10⁴. Our results indicate that diversity across populations is more likely to be maintained if they are small. Experimental outcomes in large populations are likely to be robust and can inform our predictions about outcomes in similar situations.     

Limits to adaptation in asexual populations

In asexual populations, the rate of adaptation is basically limited by the frequency and properties of spontaneous beneficial mutations. Hence, knowledge of these mutational properties and how they are affected by particular evolutionary conditions is a precondition for understanding the process of adaptation. Here, we address how the rate of adaptation of asexual populations is limited by its population size and mutation rate, as well as by two factors affecting the fraction of mutations that confer a benefit, i.e. the initial adaptedness of the population and the variability of the environment. These factors both influence which mutations are likely to occur, as well as the probability that they will ultimately contribute to adaptation. We attempt to separate the consequences of these basic population features in terms of their effect on the rate of adaptation by using results from evolution experiments with microorganisms.     

Genetic variations in Tibetan populations and high-altitude adaptation at the Himalayas

Modern humans have occupied almost all possible environments globally since exiting Africa about 100,000 years ago. Both behavioral and biological adaptations have contributed to their success in surviving the rigors of climatic extremes, including cold, strong ultraviolet radiation, and high altitude. Among these environmental stresses, high-altitude hypoxia is the only condition in which traditional technology is incapable of mediating its effects. Inhabiting at >3,000-m high plateau, the Tibetan population provides a widely studied example of high-altitude adaptation. Yet, the genetic mechanisms underpinning long-term survival in this environmental extreme remain unknown. We performed an analysis of genome-wide sequence variations in Tibetans. In combination with the reported data, we identified strong signals of selective sweep in two hypoxia-related genes, EPAS1 and EGLN1. For these two genes, Tibetans show unusually high divergence from the non-Tibetan lowlanders (Han Chinese and Japanese) and possess high frequencies of many linked sequence variations as reflected by the Tibetan-specific haplotypes. Further analysis in seven Tibetan populations (1,334 individuals) indicates the prevalence of selective sweep across the Himalayan region. The observed indicators of natural selection on EPAS1 and EGLN1 suggest that during the long-term occupation of high-altitude areas, the functional sequence variations for acquiring biological adaptation to high-altitude hypoxia have been enriched in Tibetan populations.     

Walking speed adaptation ability of Myzus persicae to different temperature conditions

Walking speeds were calculated for nine clones of the peach potato aphid Myzus persicae collected from three countries along a latitudinal cline of its European distribution from Sweden to Spain (Sweden, UK and Spain), and the effects of collection origin and intra and intergenerational acclimation were investigated. Walking speeds declined with decreasing temperature, with maximum performance at temperatures closest to acclimation temperature (fastest median walking speed of 5.8 cm min(-1) was recorded for clone UK 3, collected from the UK, at 25°C after acclimating to 25°C for one generation). Following acclimation at both 20°C and 25°C, walking ceased (as indicated by median walking speeds of 0.0 cm min(-1)) at temperatures as high as 7.5°C and 12.5°C. However, acclimation at 10°C enabled mobility to occur to temperatures as low as 0°C. There was no relationship between mobility and latitude of collection, suggesting that large scale mixing of aphids may occur across Europe. However, clonal variation was suggested, with clone UK 3 outperforming the majority of other clones across all temperatures at which mobility was maintained following acclimation at 10°C for one and three generations and at 25°C for one generation. The Scandinavian clones consistently outperformed their temperate and Mediterranean counterparts at the majority of temperatures following acclimation for three generations at 25°C.     

Genetic basis of adaptation: flowering time in Arabidopsis thaliana

 We have mapped QTLs (quantitative trait loci) for an adaptive trait, flowering time, in a selfing annual, Arabidopsis thaliana. To obtain a mapping population we made a cross between an early-summer, annual strain, Li-5, and an individual from a late over-wintering natural population, Naantali. From the backcross to Li-5 298 progeny were grown, of which 93 of the most extreme individuals were genotyped. The data were analysed with both interval mapping and composite interval mapping methods to reveal one major and six minor QTLs, with at least one QTL on each of the five chromosomes. The QTL on chromosome 4 was a major one with an effect of 17.3 days on flowering time and explaining 53.4% of the total variance. The others had effects of at most 6.5 days, and they accounted for only small portions of the variance. Epistasis was indicated between one pair of the QTLs. The result of finding one major QTL and little epistasis agrees with previous studies on flowering time in Arabidopsis thaliana and other species. That several QTLs were found was expected considering the large number of possible candidate loci. In the light of the suggested genetic models of gene action at the candidate loci, epistasis was to be expected. The data showed that major QTLs for adaptive traits can be detected in non-domesticated species. Received: 15 January 1997/Accepted: 21 February 1997     

Parallel flowering time clines in native and introduced ragweed populations are likely due to adaptation

As introduced species expand their ranges, they often encounter differences in climate which are often correlated with geography. For introduced species, encountering a geographically variable climate sometimes leads to the re‐establishment of clines seen in the native range. However, clines can also be caused by neutral processes, and so it is important to gather additional evidence that population differentiation is the result of selection as opposed to nonadaptive processes. Here, we examine phenotypic and genetic differences in ragweed from the native (North America) and introduced (European) ranges. We used a common garden to assess phenotypic differentiation in size and flowering time in ragweed populations. We found significant parallel clines in flowering time in both North America and Europe. Height and branch number had significant clines in North America, and, while not statistically significant, the patterns in Europe were the same. We used SNP data to assess population structure in both ranges and to compare phenotypic differentiation to neutral genetic variation. We failed to detect significant patterns of isolation by distance, geographic patterns in population structure, or correlations between the major axes of SNP variation and phenotypes or latitude of origin. We conclude that the North American clines in size and the parallel clines seen for flowering time are most likely the result of adaptation.     

Genetic and epigenetic variations associated with adaptation to heterogeneous habitat conditions in a deciduous shrub

Environmentally induced phenotypic plasticity is thought to play an important role in the adaption of plant populations to heterogeneous habitat conditions, and yet the importance of epigenetic variation as a mechanism of adaptive plasticity in natural plant populations still merits further research. In this study, we investigated populations of Vitex negundo var. heterophylla (Chinese chastetree) from adjacent habitat types at seven sampling sites. Using several functional traits, we detected a significant differentiation between habitat types. With amplified fragment length polymorphisms (AFLP) and methylation‐sensitive AFLP (MSAP), we found relatively high levels of genetic and epigenetic diversity but very low genetic and epigenetic differences between habitats within sites. Bayesian clustering showed a remarkable habitat‐related differentiation and more genetic loci associated with the habitat type than epigenetic, suggesting that the adaptation to the habitat is genetically based. However, we did not find any significant correlation between genetic or epigenetic variation and habitat using simple and partial Mantel tests. Moreover, we found no correlation between genetic and ecologically relevant phenotypic variation and a significant correlation between epigenetic and phenotypic variation. Although we did not find any direct relationship between epigenetic variation and habitat environment, our findings suggest that epigenetic variation may complement genetic variation as a source of functional phenotypic diversity associated with adaptation to the heterogeneous habitat in natural plant populations.     

Genetic polymorphisms of proteins in different breeds and different populations of chickens

Six polymorphic protein systems in 15 chicken breeds have been investigated. In the Silkie breed another variant of G3 proteins (G₃ A^F Silkie) has been observed characterized by higher electrophoretic mobility than G₃ A. The frequencies of individual alleles in various lines and different generations have been determined in two breeds (White Leghorn and White Cornish).     

Genetic differentiation in life history between Daphnia galeata populations: an adaptation to local predation regimes?

Species of the water flea Daphnia exhibit constitutive as wellas phenotypically inducible anti-predator defence strategies,involving life history, morphological and behavioural traits.We explored the hypothesis of genetic differentiation in anti-predatordefence strategies using Daphnia clones originating from twodifferent water bodies: Tjeukemeer (the Netherlands) and FishPond (Belgium). Both water bodies are inhabited by zooplanktivorousfish. In contrast to Tjeukemeer, Fish Pond is also inhabitedby larvae of the phantom midge Chaoborus. The life history responsesof the two sets of clones to kairomones from fish (Perca), tokairomones from Chaoborus, and to a mixture of both were compared.Clones from Tjeukemeer and Fish Pond showed strong responsesto the presence of fish kairomone, with reductions in adultand neonate body length, in age at first reproduction and inthe total number of neonates produced during the first threeadult instars. Responses to Chaoborus kairomone were much lesspronounced, although there was a tendency towards an increasein the number of neonates in the first brood. Significant inter-populationgenetic differences were found for all the investigated traits.However, there was no indication for genetic adaptation of theFish Pond clones to negative size-selective predation by Chaoborus.Compared to Tjeukemeer clones, Fish Pond clones had a lowersize at first reproduction, produced smaller neonates and produceda higher number of neonates in their first brood. This suggestsadaptation to positive rather than to negative size selectivepredation. Genetic differences between populations were observedmainly for constitutive life history traits, rather than forphenotypic shifts in response to the presence of predator kairomones.     

Genetic diversity in Leavenworthia populations with different inbreeding levels.

Levels of neutral genetic diversity within and between populations were compared between outcrossing (self-incompatible) and inbreeding populations in the annual plant genus Leavenworthia. Two taxonomically independent comparisons are possible, since self-incompatibility has been lost twice in the group of species studied. Within inbred populations of L.uniflora and L.crassa, no DNA sequence variants were seen among the alleles sampled, but high diversity was seen in alleles from populations of the outcrosser L. stylosa, and in self-incompatible L. crassa populations. Diversity between populations was seen in all species. Although total diversity values were lower in the sets of inbreeding populations, between-population values were as high or higher, than those in the outcrossing taxa. Possible reasons for these diversity patterns are discussed. As the effect of inbreeding appears to be a greater than twofold reduction in diversity, we argue that some process such as selection for advantageous mutations, or against deleterious mutations, or bottlenecks occurring predominantly in the inbreeders, appears necessary to account for the findings. If selection for advantageous mutations is responsible, it appears that it must be some form of local adaptive selection, rather than substitution of alleles that are advantageous throughout the species. This is consistent with the finding of high between-population diversity in the inbreeding taxa.     

Odor-sampling time of mice under different conditions

Response accuracy and odor sample times on positive (S+) and negative (S-) trials were recorded for mice trained on a variety of go, no-go odor detection and discrimination tasks. Odor sample time was relatively stable over extended training on the same task, increased during acquisition of difficult tasks, relatively insensitive to reinforcement magnitude, and, in some cases, provided more information regarding task difficulty and discrimination than did response accuracy. Mice generally sampled longer on S- trials in simple odor detection tasks but longer on S+ trials in odor discrimination tasks.     

Local adaptation in rotifer populations

The adaptation of organisms to their environment has been a subject of study for a long time. One method to study adaptations in populations involves comparing contemporary populations of the same species under different selective regimes, in what is known as a ??local adaptation?? study. A previous study of the cyclically parthenogenetic rotifer Brachionus plicatilis found high heritabilities for some life-history traits. Some of these life-history traits significantly differed among six populations from Eastern Spain and data suggested some traits to have higher evolutionary rates than neutral genetic markers. Here, by studying the same B. plicatilis populations, we examine the variation and possible local adaptation of their main life-history traits, closely related to fitness, in relation to habitat salinity and temperature. These environmental factors have been shown to play a key role in the ecological differentiation among co-generic species of B. plicatilis. The results obtained in this study show that: (1) the seasonality of rotifer populations from Eastern Spain has profoundly influenced sexual reproduction strategies; (2) salinity is probably a key factor in the ecological specialization of some populations; and (3) rotifer populations harbour high variability in their fitness components.     

When similar ecological patterns in time emerge from different initial conditions: equifinality in the breeding performance of animal populations

In many behavioural, ecological and evolutionary trade-offs, patterns and trends, the same/similar outcomes are often expected from the different initial conditions. One of the most frequently encountered problems in ecology is how to disentangle two or more different hypotheses possibly explaining the emergence of an ecological pattern based on limited data that would fit both. Using previously published interaction patterns between floaters and breeders of an eagle population (Penteriani et al., 2006), it was possible to detect and to find an explanation to the singular case of the emergence of a similar ecological pattern under two very different scenarios, that is when different factors are affecting the intrinsic dynamic of a population.