Geographic variation in diapause incidence, life-history traits, and climatic adaptation in Drosophila melanogaster

In Drosophila melanogaster, exposure of females to low temperature and shortened photoperiod can induce the expression of reproductive quiescence or diapause. Diapause expression is highly variable within and among natural populations and has significant effects on life-history profiles, including patterns of longevity, fecundity, and stress resistance. We hypothesized that if diapause expression is associated with overwintering mechanisms and adaptation to temperate environments, the frequency of diapause incidence would exhibit a latitudinal cline among natural populations. Because stress resistance and reproductive traits are also clinal in this species, we also examined how patterns of fecundity and longevity varied with geography and how stress resistance and associated traits differed constitutively between diapause and nondiapause lines. Diapause incidence was shown to vary predictably with latitude, ranging from 35% to 90% among natural populations in the eastern United States Survivorship under starvation stress differed between diapause and nondiapause lines; diapause phenotypes were also distinct for total body triglyceride content and the developmental distribution of oocytes in the ovary following stress exposure. Patterns of longevity, fecundity, and ovariole number also varied with geography. The data suggest that, for North American populations, diapause expression is functionally associated with overwintering mechanisms and may be an integral life-history component in natural populations.     

Environmental heterogeneity and the maintenance of genetic variation for reproductive diapause in Drosophila melanogaster

Drosophila melanogaster has colonized temperate habitats on multiple continents over a historical time period, and many traits vary predictably with latitude. Despite considerable attention paid to clinal variation in Drosophila, the mechanisms generating such patterns in nature remain largely unidentified. In D. melanogaster, the expression of reproductive diapause can be induced by exposure to low temperatures and shortened photoperiods. Both diapause expression itself and the underlying genetic variance for diapause expression have widespread impacts on organismal fitness, and diapause incidence exhibits a 60% cline in frequency in the eastern United States. The major aim of this study was to evaluate whether the relative fitness of diapause and nondiapause genotypes varies predictably with environment. In experimental population cages in the laboratory, the frequency of genotypes that express diapause increased over time when flies were exposed to environmental stress, whereas the frequency of nondiapause genotypes increased when flies were cultured under benign control conditions. Other fitness traits correlated with the genetic variance for diapause expression (longevity, mortality rates, stress resistance, lipid content, preadult viability, fecundity profiles, and development time) also diverged between experimental treatments. Similarly, sampling of isofemale lines from natural populations revealed that the frequency of diapause incidence cycled over time in seasonal habitats: diapause expression was at high frequency following the winter season and subsequently declined throughout the summer months. In contrast, diapause expression was low and temporally homogeneous in isofemale line collections from human-associated urban habitats. These data suggest that genetic variation underlying the diapause-nondiapause dichotomy may be actively maintained by selection pressures that vary spatially and temporally in natural populations.     

Spatially varying selection shapes life history clines among populations of Drosophila melanogaster from sub‐Saharan Africa

Clines in life history traits, presumably driven by spatially varying selection, are widespread. Major latitudinal clines have been observed, for example, in Drosophila melanogaster, an ancestrally tropical insect from Africa that has colonized temperate habitats on multiple continents. Yet, how geographic factors other than latitude, such as altitude or longitude, affect life history in this species remains poorly understood. Moreover, most previous work has been performed on derived European, American and Australian populations, but whether life history also varies predictably with geography in the ancestral Afro‐tropical range has not been investigated systematically. Here, we have examined life history variation among populations of D. melanogaster from sub‐Saharan Africa. Viability and reproductive diapause did not vary with geography, but body size increased with altitude, latitude and longitude. Early fecundity covaried positively with altitude and latitude, whereas lifespan showed the opposite trend. Examination of genetic variance–covariance matrices revealed geographic differentiation also in trade‐off structure, and Q_ST‐F_ST analysis showed that life history differentiation among populations is likely shaped by selection. Together, our results suggest that geographic and/or climatic factors drive adaptive phenotypic differentiation among ancestral African populations and confirm the widely held notion that latitude and altitude represent parallel gradients.     

Genetic variance for diapause expression and associated life histories in Drosophila melanogaster

The dipteran Drosophila melanogaster can express a form of reproductive quiescence or diapause when exposed to low temperature and shortened photoperiod. Among natural populations in the eastern United States, the frequency of lines that express reproductive diapause in the laboratory varies substantially and predictably with latitudinal origin. The goals of the present study were twofold: (1) to examine the impact of genetic variance for diapause expression on multiple traits associated with organismal fitness; and (2) to evaluate the potential for fitness trade-offs between diapause and nondiapause phenotypes that may result in the observed cline. Even prior to diapause entry or expression, inbred lines that express and do not express reproductive diapause in laboratory assays were constitutively distinct for life span, age-specific mortality rates, fecundity profiles, resistance to cold and starvation stress, lipid content, development time, and egg-to-adult viability. Furthermore, estimates of genetic correlations based on line means revealed significant differentiation for genetic variance/covariance matrices between diapause and nondiapause lines. The data indicate the potential for life-history trade-offs associated with variation for the diapause phenotype. The observed cline in diapause incidence in the eastern United States may be generated by these tradeoffs and the associated spatial and/or temporal variation in relative fitness of these two phenotypes in natural populations.     

Does artificial selection on diapause incidence cause correlational changes in other life‐history traits? Case study in a spider mite population

Theoretical studies suggest that the timing of entering hibernation by arthropods has large effects on long-term fitness, incurring strong selection pressure on diapause attributes every year. On the other hand, diapause attributes are often genetically correlated with other important life-history traits such as fecundity or development time. To understand the evolutionary process of life cycle formation, there is a need to investigate not only diapause attributes themselves but also their genetic association with other life-history traits. The Kanzawa spider mite, Tetranychus kanzawai Kishida (Acari: Tetranychidae), is a small herbivore that lives on the undersurface of host plant leaves. This mite has been investigated for the mode of inheritance of diapause attributes, but scarcely for genetic correlations with other life-history traits. Here, I investigated whether diapause proneness, measured as the proportion of diapausing females under short-day conditions, is genetically correlated with fecundity or development time under long-day conditions using artificial selection experiments. Diapause incidence responded to the selection for both increasing and decreasing directions, suggesting that high genetic variance in diapause proneness is maintained in the study population. However, the change in proportion of diapausing females during the selection period was not associated with responses in fecundity or development time. These results suggest that diapause proneness and other life-history traits have different genetic backgrounds, and thus diapause proneness may freely evolve without being constrained by changes in other life-history traits.     

Altitudinal variation of demographic life-history traits does not mimic latitudinal variation in natterjack toads (Bufo calamita)

In anuran amphibians, age- and size-related life-history traits vary along latitudinal and altiudinal gradients. In the present study, we tested the hypothesis that altitudinal and latitudinal effects cause similar responses by assessing demographic life-history traits in nine Bufo calamita populations inhabiting elevations from sea level to 2270 m. Skeletochronologically determined age at maturity and longevity increased at elevations exceeding 2000 m, but female potential reproductive lifespan (PRLS) did not increase with altitude, as it did with latitude. Integrating the available evidence, it was found that lifetime fecundity of natterjacks decreased at the upper altitudinal range because PRLS was about the same as in lowland populations but females were smaller. In contrast, small size of northern females was compensated for by increased PRLS which minimised latitudinal variation of lifetime fecundity. Thus, this study provides evidence that altitudinal effects on life-history traits do not mimic latitudinal effects. Life-history trait variation along the altitudinal gradient seems to respond directly to the shortening of the annual activity period. As there is no evidence for increasing mortality in highland populations, reduced lifetime fecundity may be the ultimate reason for the natterjacks' inability to colonise elevations exceeding 2500 m.     

Large-scale intraspecific variation in life-history traits of European freshwater fish

Aims To test the magnitude and direction of the effects of large‐scale environmental factors (latitude and habitat type: lotic or lentic) on the intraspecific variations in multiple life‐history traits, across multiple European freshwater fish species. To test the relevance of defining species traits by quantifying the magnitude of interspecific vs. intraspecific variability in traits. Location Europe. Methods We obtained estimates of 11 fish traits from published sources for 1089 populations of 25 European freshwater fish species. Traits were: longevity, maximal length, growth rate, asymptotic length, mortality rate, age and length at maturation, fecundity, egg size, gonadosomatic index, and length of breeding season. We described population habitats by latitude and habitat type (lotic or lentic), when available. For each species we tested the combined effect of latitude and habitat type on the intraspecific variation of each trait using analysis of covariance (ancova ). We compared the intraspecific variation in traits with the variation between species using an analysis of variance (anova ) for each trait, all species pooled. Results We found a consistent effect in direction of latitude on six traits, but we showed that this effect is not always significant across species. Higher‐latitude populations often grew more slowly, matured later, had a longer life span and a higher maximal and asymptotic length, and allocated more energy to reproduction than populations at lower latitudes. By contrast, we noted only a slight effect of habitat type on the intraspecific variation in traits, except for Salmo trutta. All traits varied significantly between species. However, traits such as growth rate, mortality rate and length of breeding season varied more between populations than between species, whereas fecundity and traits associated with body length varied more between species. Main conclusions Latitude, in contrast to habitat type, is an important factor influencing several traits of geographically widely dispersed populations of multiple European freshwater fish species. Species traits that vary more between species than between populations are attractive variables for understanding and predicting the responses of stream fish communities to their environment.     

Adaptation to a seasonally varying environment: a strong latitudinal cline in reproductive diapause combined with high gene flow in Drosophila montana

Adaptation to seasonal changes in the northern hemisphere includes an ability to predict the forthcoming cold season from gradual changes in environmental cues early enough to prepare for the harsh winter conditions. The magnitude and speed of changes in these cues vary between the latitudes, which induces strong selection pressures for local adaptation.We studied adaptation to seasonal changes in Drosophila montana, a northern maltfly, by defining the photoperiodic conditions leading to adult reproductive diapause along a latitudinal cline in Finland and by measuring genetic differentiation and the amount of gene flow between the sampling sites with microsatellites. Our data revealed a clear correlation between the latitude and the critical day length (CDL), in which half of the females of different cline populations enter photoperiodic reproductive diapause. There was no sign of limited gene flow between the cline populations, even though these populations showed isolation by distance. Our results show that local adaptation may occur even in the presence of high gene flow, when selection for locally adaptive life-history traits is strong. A wide range of variation in the CDLs of the fly strains within and between the cline populations may be partly due to gene flow and partly due to the opposing selection pressures for fly reproduction and overwinter survival. This variation in the timing of diapause will enhance populations' survival over the years that differ in the severity of the winter and in the length of the warm period and may also help them respond to long-term changes in environmental conditions.     

ON THE LOW HERITABILITY OF LIFE-HISTORY TRAITS

Life-history traits such as longevity and fecundity often show low heritability. This is usually interpreted in terms of Fisher's fundamental theorem to mean that populations are near evolutionary equilibrium and genetic variance in total fitness is low. We develop the causal relationship between metric traits and life-history traits to show that a life-history trait is expected to have a low heritability whether or not the population is at equilibrium. This is because it is subject to all the environmental variation in the metric traits that affect it plus additional environmental variation. There is no simple prediction regarding levels of additive genetic variance in life-history traits, which may be high at equilibrium. Several other patterns in the inheritance of life-history traits are readily predicted from the causal model. These include the strength of genetic correlations between life-history traits, levels of nonadditive genetic variance, and the inevitability of genotype-environment interaction.     

Spatiotemporal dynamics and genome‐wide association analysis of desiccation tolerance in Drosophila melanogaster

Water availability is a major environmental challenge to a variety of terrestrial organisms. In insects, desiccation tolerance varies predictably over spatial and temporal scales and is an important physiological determinant of fitness in natural populations. Here, we examine the dynamics of desiccation tolerance in North American populations of Drosophila melanogaster using: (a) natural populations sampled across latitudes and seasons; (b) experimental evolution in field mesocosms over seasonal time; (c) genome‐wide associations to identify SNPs/genes associated with variation for desiccation tolerance; and (d) subsequent analysis of patterns of clinal/seasonal enrichment in existing pooled sequencing data of populations sampled in both North America and Australia. A cline in desiccation tolerance was observed, for which tolerance exhibited a positive association with latitude; tolerance also varied predictably with culture temperature, demonstrating a significant degree of thermal plasticity. Desiccation tolerance evolved rapidly in field mesocosms, although only males showed differences in desiccation tolerance between spring and autumn collections from natural populations. Water loss rates did not vary significantly among latitudinal or seasonal populations; however, changes in metabolic rates during prolonged exposure to dry conditions are consistent with increased tolerance in higher latitude populations. Genome‐wide associations in a panel of inbred lines identified twenty‐five SNPs in twenty‐one loci associated with sex‐averaged desiccation tolerance, but there is no robust signal of spatially varying selection on genes associated with desiccation tolerance. Together, our results suggest that desiccation tolerance is a complex and important fitness component that evolves rapidly and predictably in natural populations.     

Can life history predict the effect of demographic stochasticity on extinction risk?

Demographic stochasticity is important in determining extinction risks of small populations, but it is largely unknown how its effect depends on the life histories of species. We modeled effects of demographic stochasticity on extinction risk in a broad range of generalized life histories, using matrix models and branching processes. Extinction risks of life histories varied greatly in their sensitivity to demographic stochasticity. Comparing life histories, extinction risk generally increased with increasing fecundity and decreased with higher ages of maturation. Effects of adult survival depended on age of maturation. At lower ages of maturation, extinction risk peaked at intermediate levels of adult survival, but it increased along with adult survival at higher ages of maturation. These differences were largely explained by differences in sensitivities of population growth to perturbations of life-history traits. Juvenile survival rate contributed most to total demographic variance in the majority of life histories. Our general results confirmed earlier findings, suggesting that empirical patterns can be explained by a relatively simple model. Thus, basic life-history information can be used to assign life-history-specific sensitivity to demographic stochasticity. This is of great value when assessing the vulnerability of small populations.     

Genotype-by-environment interactions and adaptation to local temperature affect immunity and fecundity in Drosophila melanogaster

Natural populations of most organisms harbor substantial genetic variation for resistance to infection. The continued existence of such variation is unexpected under simple evolutionary models that either posit direct and continuous natural selection on the immune system or an evolved life history "balance" between immunity and other fitness traits in a constant environment. However, both local adaptation to heterogeneous environments and genotype-by-environment interactions can maintain genetic variation in a species. In this study, we test Drosophila melanogaster genotypes sampled from tropical Africa, temperate northeastern North America, and semi-tropical southeastern North America for resistance to bacterial infection and fecundity at three different environmental temperatures. Environmental temperature had absolute effects on all traits, but there were also marked genotype-by-environment interactions that may limit the global efficiency of natural selection on both traits. African flies performed more poorly than North American flies in both immunity and fecundity at the lowest temperature, but not at the higher temperatures, suggesting that the African population is maladapted to low temperature. In contrast, there was no evidence for clinal variation driven by thermal adaptation within North America for either trait. Resistance to infection and reproductive success were generally uncorrelated across genotypes, so this study finds no evidence for a fitness tradeoff between immunity and fecundity under the conditions tested. Both local adaptation to geographically heterogeneous environments and genotype-by-environment interactions may explain the persistence of genetic variation for resistance to infection in natural populations.     

LABORATORY EVOLUTION OF LIFE-HISTORY TRAITS IN THE BEAN WEEVIL (ACANTHOSCELIDES OBTECTUS): THE EFFECTS OF DENSITY-DEPENDENT AND AGE-SPECIFIC SELECTION

Four types of laboratory populations of the bean weevil (Acanthoscelides obtectus) have been developed to study the effects of density-dependent and age-specific selection. These populations have been selected at high (K) and low larval densities (r) as well as for reproduction early (Y) and late (O) in life. The results presented here suggest that the r- and K-populations (density-dependent selection regimes) have differentiated from each other with respect to the following life-history traits: egg-to-adult viability at high larval density (K > r), preadult developmental time (r > K), body weight (r > K), late fecundity (K > r), total realized fecundity (r > K), and longevity of males (r > K). It was also found that the following traits responded in statistically significant manner in populations subjected to different age-specific selection regimes: egg-to-adult viability (O > Y), body weight (O > Y), early fecundity (Y > O), late fecundity (O > Y), and longevity of females and males (O > Y). Although several life-history traits (viability, body weight, late fecundity) responded in similar manner to both density-dependent and age-specific selection regimes, it appears that underlying genetic and physiological mechanisms responsible for differentiation of the r/K and Y/O populations are different. We have also tested quantitative genetic basis of the bean weevil life-history traits in the populations experiencing density-dependent and age-specific selection. Among the traits traded-off within age-specific selection regimes, only early fecundity showed directional dominance, whereas late fecundity and longevity data indicated additive inheritance. In contrast to age-specific selecton regimes, three life-history traits (developmental time, body size, total fecundity) in the density-sependent regimes exhibited significant dominance effects. Lastly, we have tested the congruence between short-term and long-term effects of larval densities. The comparisons of the outcomes of the r/K selection regimes and those obtained from the low- and high-larval densities revealed that there is no congruence between the selection results and phenotypic plasticity for the analyzed life-history traits in the bean weevil.     

Niche construction through germination cueing: life-history responses to timing of germination in Arabidopsis thaliana

Germination responses to seasonal conditions determine the environment experienced by postgermination life stages, and this ability has potential consequences for the evolution of plant life histories. Using recombinant inbred lines of Arabidopsis thaliana, we tested whether life-history characters exhibited plasticity to germination timing, whether germination timing influenced the strength and mode of natural selection on life-history traits, and whether germination timing influenced the expression of genetic variation for life-history traits. Adult life-history traits exhibited strong plasticity to season of germination, and season of germination significantly altered the strength, mode, and even direction of selection on life-history traits under some conditions. None of the average plastic responses to season of germination or season of dispersal were adaptive, although some genotypes within our sample did exhibit adaptive responses. Thus, recombination between inbred lineages created some novel adaptive genotypes with improved responses to the seasonal timing of germination under some, but not all, conditions. Genetically based variation in germination time tended to augment genetic variances of adult life-history traits, but it did not increase the heritabilities because it also increased environmentally induced variance. Under some conditions, plasticity of life-history traits in response to genetically variable germination timing actually obscured genetic variation for those traits. Therefore, the evolution of germination responses can influence the evolution of life histories in a general manner by altering natural selection on life-history traits and the genetic variation of these traits.     

Natural selection on fecundity variance in subdivided populations: kin selection meets bet hedging

In a series of seminal articles in 1974, 1975, and 1977, J. H. Gillespie challenged the notion that the "fittest" individuals are those that produce on average the highest number of offspring. He showed that in small populations, the variance in fecundity can determine fitness as much as mean fecundity. One likely reason why Gillespie's concept of within-generation bet hedging has been largely ignored is the general consensus that natural populations are of large size. As a consequence, essentially no work has investigated the role of the fecundity variance on the evolutionary stable state of life-history strategies. While typically large, natural populations also tend to be subdivided in local demes connected by migration. Here, we integrate Gillespie's measure of selection for within-generation bet hedging into the inclusive fitness and game theoretic measure of selection for structured populations. The resulting framework demonstrates that selection against high variance in offspring number is a potent force in large, but structured populations. More generally, the results highlight that variance in offspring number will directly affect various life-history strategies, especially those involving kin interaction. The selective pressures on three key traits are directly investigated here, namely within-generation bet hedging, helping behaviors, and the evolutionary stable dispersal rate. The evolutionary dynamics of all three traits are markedly affected by variance in offspring number, although to a different extent and under different demographic conditions.     

Both costs and benefits of sex correlate with relative frequency of asexual reproduction in cyclically parthenogenic Daphnia pulicaria populations

Sexual reproduction is generally believed to yield beneficial effects via the expansion of expressed genetic variation, which increases the efficiency of selection and the adaptive potential of a population. However, when nonadditive gene action is involved, sex can actually impede the adaptive progress of a population. If selection promotes coupling disequilibria between genes of similar effect, recombination and segregation can result in a decrease in expressed genetic variance in the offspring population. In addition, when nonadditive gene action underlies a quantitative trait, sex can produce a change in trait means in a direction opposite to that favored by selection. In this study we measured the change in genotypic trait means and genetic variances across a sexual generation in four populations of the cyclical parthenogen Daphnia pulicaria, which vary predictably in their incidence of sexual reproduction. We show that both the costs and benefits of sex, as measured by changes in means and variances in life-history traits, increase substantially with decreasing frequency of sex.     

Phenology and fecundity in 11 sympatric pioneer species of Macaranga (Euphorbiaceae)in Borneo

Reproductive traits of tropical tree species vary predictably in relation to successional stage, but this variation may be due to the species' phylogenetic histories rather than selective pressures imposed by regeneration requirements. Reproductive phenology, tree size at the onset of reproduction, and fecundity of 11 sympatric, closely related Macaranga species were studied to investigate within-species variation in reproductive traits in relation to resource availability, and among-species variation in relation to other life-history traits (shade tolerance, seed size and maximum tree size, H(max)) and consequently the requirements for forest-gap colonization. Nine species reproduced in synchronous episodes, and two species reproduced continuously over 32 mo. Episodic reproduction was most intense in 1992 following a severe drought. For several species, reproductive trees had greater light availability, lower fecundity in lower light levels, and lower growth rates than nonreproductive trees, reflecting resource-limited reproduction. Among species, H(max) was negatively correlated with shade tolerance and seed size. Tree size at the onset of reproduction and fecundity was strongly linked to this axis of life-history variation, but phenological pattern was not. Absolute tree size at the onset of reproduction was positively correlated with H(max) and negatively correlated with shade tolerance. Relative size at reproductive onset was not correlated with shade tolerance or H(max). Fecundity ranged four orders of magnitude among species and was correlated positively with H(max) and negatively with seed size and shade tolerance. The interrelationships among these reproductive and other life-history traits are strongly correlated with the species' requirements for gap colonization.     

SPATIAL AND TEMPORAL VARIATION IN SELECTION ON CORRELATED LIFE-HISTORY TRAITS AND PLANT SIZE IN CHAMAECRISTA FASCICULATA

Intraspecific studies of selection on multiple traits of a plant's life history provide insight as to how the composite life history of an organism evolves. Current understanding of selection on plant life-history traits is deficient in three important areas: 1) the effects of selection through correlated traits, 2) the effects of selection on a trait throughout the plant's lifetime, and 3) spatial and temporal variation in selection on plant life-history traits among populations and years. This study documents spatial and temporal variation in selection on three life-history and two morphological traits for two natural populations of Chamaecrista fasciculata, a native summer annual. Life-history and morphological traits (date of seedling emergence, size at establishment, size prior to reproduction, date of initial flowering, and date of initial fruit maturation) varied significantly between sites and/or years. Selection on traits varied either spatially, between sites and among transects within one site, or temporally, between years. In addition, life-history traits were phenotypically correlated among themselves and with morphological traits; correlations were generally constant over time and space. Indirect selection caused changes in means and variances in traits not under direct selection, but which were correlated with traits under selection. Selection on date of emergence varied in direction and magnitude among different life-cycle stages, while selection on other traits varied only in magnitude among life stages of the plant. This study documents the complexity of the selective process and the importance of considering multiple life stages and traits when studying the evolution of life-history traits.     

Negative genetic correlation between diapause duration and fecundity after diapause in a spider mite

Abstract.  1. Recently, the costs of diapause, i.e. the reduction of fecundity after diapause, have been examined from an evolutionary perspective.
2. The evolution of this trade-off should be clarified by quantitative genetic approaches, as theoretical studies address the evolution of multiple traits. Nevertheless, previous studies on the costs of diapause have been based on phenotypic correlations or experimental manipulations, whereas the genetic background underlying this trade-off remains unclear.
3. In the present study, a half-sib breeding design was used to examine the quantitative genetic relationships between diapause duration and post-diapause fecundity in the Kanzawa spider mite Tetranychus kanzawai Kishida (Acari: Tetranychidae).
4. The heritability of diapause duration, post-diapause total fecundity, and post-diapause early fecundity were 0.37, 0.14, and 0.11 respectively. Genetic correlations between diapause duration and post-diapause total fecundity, and between diapause duration and early fecundity were both significantly negative (–0.70 and –0.90 respectively). These results suggest that the cost of prolonging diapause duration is genetically based, and that these life-history traits respond to natural selection acting on them simultaneously.     

On the evolution of clonal plant life histories

Clonal plant life histories are special in at least four respects: (1) Clonal plants can also reproduce vegetatively, (2) vegetative reproduction can be realised with short or long spacers, (3) and it may allow to plastically place vegetative offspring in benign patches. (4) Moreover, ramets of clonal plants may remain physically and physiologically integrated. Because of the apparent utility of such traits and because ecological patterns of distribution of clonal and non-clonal plants differ, adaptation is a tempting explanation of observed clonal life-history variation. However, adaptive evolution requires (1) heritable genetic variation and (2) a trait effect on fitness, and (3) it may be constrained if other evolutionary forces are overriding selection or by constraints, costs and trade-offs. (1) The few studies undertaken so far reported broad-sense heritability for clonal traits. Variation in selectively neutral genetic markers appears as pronounced in populations of clonal as non-clonal plants. However, neutral markers may not reflect heritable variation of life-history traits. Moreover, clonal plants may have been sampled at larger spatial scales. Empirical information on the contribution of somatic mutations to heritable variation is lacking. (2) Clonal life-history traits were found to affect fitness. However, much of this evidence stems from artificial rather than natural environments. (3) The relative importance of gene flow, inbreeding, and genetic drift, compared with selection, in the evolution of clonal life histories is hardly explored. Benefits of clonal life-history traits were frequently studied and found. However, there is also evidence for constraints, trade-offs, and costs. In conclusion, though it is very likely, that clonal life-history traits are adaptive, it is neither clear to which degree this is the case, nor which clonal life-history traits constitute adaptations to which environmental factors. Moreover, evolutionary interactions among clonal life-history traits and between clonal and non-clonal ones, such as the mating system, are not well explored. There remains much interesting work to be done in this field – which will be particularly interesting if it is done in the field.