Heritability of male outcrossing ability in the simultaneous hermaphrodite, Bulinus truncatus (Gastropoda: Planorbidae)

The heritability of phally, a dichotomous trait defined by the functional state of the male reproductive tract, was measured in a laboratory population of the simultaneous hermaphrodite snail Bulinus truncatus by means of a breeding experiment and a selection experiment. Euphallic individuals develop a fully functional male and female tract and are capable of receiving and donating sperm. In aphallic individuals the male tract does not develop fully, preventing sperm donation. There was no evidence of a heritable component to phally in the breeding experiment, but the selection experiment demonstrated a slight heritable effect. In both experiments there was more variation in the observed proportion of euphallics than expected by chance alone and no evidence of line or family effects, implicating environmental determination of male outcrossing ability even under controlled laboratory conditions. Previous studies of populations of B. truncatus reported that the proportion of euphallics was under strong genetic control. We suggest that there may be population differences in the extent of environmental control over phally, analogous to that reported for sex determination.     

SEX RATIO VARIATION IN THE LESSONIA NIGRESCENS COMPLEX (LAMINARIALES,PHAEOPHYCEAE): EFFECT OF LATITUDE,TEMPERATURE, AND MARGINALITY1

Little is known about variation of sex ratio, the proportion of males to females, in natural populations of seaweed, though it is a major determinant of the mating system. The observation of sexual chromosomes in kelps suggested that sex is partly genetically determined. However, it is probably not purely genetic since the sex ratio can be modified by environmental factors such as salinity or temperature. In this paper, sex ratio variation was studied in the kelp Lessonia nigrescens Bory complex, recently identified as two cryptic species occurring along the Chilean coast: one located north and the other south of the biogeographic boundary at latitude 29°–30° S. The life cycle of L. nigrescens is characterized by an alternation of microscopic haploid gametophytic individuals and large macroscopic fronds of diploid sporophytes. The sex ratio was recorded in progenies from 241 sporophytic individuals collected from 13 populations distributed along the Chilean coast in order (i) to examine the effect of an environmental gradient coupled with latitude, and (ii) to compare marginal populations to central populations of the two species. In addition, we tested the hypothesis that the sex ratios of the two cryptic species would be affected differently by temperature. First, our results demonstrate that sex ratio seems to be mainly genetically determined and temperature can significantly modify it. Populations of the northern species showed a lower frequency of males at 14°C than at 10°C, whereas populations of the southern species showed the opposite pattern. Second, both species displayed an increased variation in sex ratio at the range limits. This greater variation at the margins could be due either to differential mortality between sexes or to geographic parthenogenesis (asexual reproduction).     

VARIATION IN ENVIRONMENTAL AND GENOTYPIC SEX-DETERMINING MECHANISMS ACROSS A LATITUDINAL GRADIENT IN THE FISH,MENIDIA MENIDIA

Models of environmental sex determination (ESD) usually assume that genetic influences on sex are polygenic, but the validity of this (or any other) form of genotype-environment interaction is virtually unknown. In the Atlantic silverside, Menidia menidia, sex is determined by an interaction between temperature and genotype and the response of sex ratio to temperature differs among populations from different latitudes. We examined the genetic basis of this pattern by measuring among family variation in the proportion of females, F/(F + M), within and among high (21°C) and low (15°C) temperatures for two populations: one from Nova Scotia (NS) where the level of ESD is low, and another from South Carolina (SC) where the level of ESD is high. In NS fish, temperature had a significant influence on sex ratio in only 1 of 23 families. The distribution of the fraction of females within temperatures for families from NS was highly heterogeneous and tended to fall into distinct classes (0.0, 0.25, 0.5, 1.0) like that expected from Mendelian segregation of a major sex factor(s). In contrast, temperature had a highly significant influence on sex ratio in all SC families examined (N = 24). Family sex ratios within temperatures were highly heterogeneous and, at least at 15°C, did not conform to simple Mendelian ratios. At 21°C, the proportion of females in most SC families was near zero and so the underlying sex tendencies of different families could not be discerned. Based on a previous study, mid-latitude fish appear to have an intermediate form of sex determination: simple Mendelian sex-ratio patterns exist and there is a moderate thermal influence on sex ratio in most but not all families. We suggest that sex determination in M. menidia is controlled by an interaction between major genetic factors, polygenic factors, and temperature and that the relative importance of each component differs with latitude. High latitude populations appear to have evolved a major sex-determining factor(s) that overrides the effect of temperature, and this factor(s) is lacking in low latitude populations.     

Resource allocation in a simultaneously hermaphroditic slug with phally polymorphism

The theory of resource allocation assumes that a resource not allocated to one function may be reallocated to another. Thus, in hermaphroditic species, an individual that suppresses the use of one sex function may free resources for the other sex function. We determined the relative importance of male copulatory organs in terms of their fraction of the total dry body weight and tested whether in the pulmonate land slug Deroceras laeve (Müller), individuals that lack the male copulatory organs (aphallics) reallocate this resource towards the female structures and/or towards life-history traits. To this end, we raised 13 families under uniparental reproduction and compared growth, length of the juvenile period, number of eggs produced, percentage of hatched eggs and hatching time among a- and euphallics. We also measured the reproductive and sex allocation of all individuals. Six out of 13 families contained no euphallic individuals. In the other seven families, the proportion of euphallic individuals ranged from 0.13 to 0.43. There was an enormous variation in life-history traits and reproductive and sex allocation among individuals, even among individuals of the same family. Allocation to the male function was very low in euphallic slugs (i.e. 1.35% of the total body dry mass and 12.33% of the total reproductive dry mass). Our results did not reveal a reallocation from the lost male function towards the female function, nor towards one of the life-history traits. Finally, we propose a scenario that could explain the maintenance of phally polymorphism in D. laeve.     

Effect of elevation on sexual reproduction in alpine populations of Saxifraga oppositifolia (Saxifragaceae)

Self-compatibility in high arctic and alpine areas is regarded as an adaptation to low pollinator abundance. However, high genetic variability as a consequence of outcrossing is, with regard to population persistence, favorable in highly stochastic environments such as tundra habitats. To evaluate these contradictory scenarios, I performed in situ pollination experiments to examine the breeding system of the predominant outcrosser Saxifraga oppositifolia in ten populations at two different elevations in the Swiss Alps. Pollinator limitation was detected at both elevations, but fruit set in naturally pollinated flowers was only slightly less at the higher elevation. Increased pollinator limitation at high compared with low elevation thus could not be demonstrated in this experiment. Hand-crossings yielded equal mean proportion seed set at both elevations, and so did hand-selfings. This constant pattern of the breeding system in S. oppositifolia indicates selective factors that lead to the maintenance of a high level of outcrossing even in high-elevation populations. Based on sex allocation models, it was expected that a high ovule number should be selectively advantageous in a plant-pollinator system where chance visitation or selfing play important roles. However, female reproductive offer in terms of ovule number per flower did not change from low to high elevation. Since neither increased pollinator limitation nor increased seed set in selfed flowers was found at high compared with low elevation, the prerequisites for testing the hypothesis were not given. This study contradicts the hypothesis that inimical environmental factors in alpine or arctic habitats necessarily select for increased selfing rates in a preferentially outcrossing species like S. oppositifolia. Received: 28 April 1997 / Accepted: 20 October 1997     

The Genetical and Environmental Determination of Phally Polymorphism in the Freshwater Snail Bulinus Truncatus

In some species of self-fertile pulmonate snails, two sexual morphs co-occur in natural populations: regular individuals and aphallic individuals that cannot transmit sperm to other snails. Purely aphallic populations therefore reproduce obligatorily by selfing. Understanding the evolution of aphally and selfing in these snails requires a precise knowledge of phally determination. In this paper, we investigate the genetic and environmental determination of aphally in Bulinus truncatus by a survey of the family (offspring) aphally ratio of 233 individuals originating from seven natural populations and a study of the reaction norm of the family aphally ratio to temperature using 60 individuals from 10 selfed lineages of one population. Our results indicate a high genetic variability for the determination of aphally between populations and within some populations, associated with a high level of genetic determination. Our second experiment indicates a significant temperature and lineage effect though no interaction between these two effects. We discuss our results in the framework of threshold models developed for dimorphic traits with polygenic inheritance. We propose that the sexual morph of an individual at a given temperature is determined by a temperature threshold value depending on both the individual genotype and probabilistic processes.     

Evidence of thermolabile sex determination in pejerrey*

Temperature regimes of 17 ± 1°C and 21 ±1°C early in development of pejerrey Odontesthes bonariensis produced nearly all females, whereas at 25 ± 1°C variable, sometimes male-biased sex-ratios were obtained. The critical period of thermolabile sex determination seemed to occur between 25 and 50 days post-hatch (about 11 and 21 mm s.i.) at low temperatures (17–20°C) and between 0 and 25 days (about 7 and 15 mm) at high temperatures (22–25°C). The likelihood of expression of temperature-dependent sex determination in natural populations and the possible adaptive significance of environmental sex determination in pejerrey are discussed.     

SEX RATIO SELECTION AND THE EVOLUTION OF ENVIRONMENTAL SEX DETERMINATION IN LABORATORY POPULATIONS OF MENIDIA MENIDIA

What happens when a population with environmental sex determination (ESD) experiences a change to an extreme environment that causes a highly unbalanced sex ratio? Theory predicts that frequency-dependent selection would increase the proportion of the minority sex and decrease the level of ESD in subsequent generations. We empirically modeled this process by maintaining five laboratory populations of a fish with temperature-dependent sex determination (the Atlantic silverside, Menidia menidia) in extreme constant temperature environments that caused highly skewed sex ratios to occur initially. Increases in the minority sex consistently occurred from one generation to the next across all five populations, first establishing and then maintaining a balanced sex ratio until termination of the experiment at 8 to 10 generations. The extent to which the level of ESD changed as balanced sex ratios evolved, however, was not consistent. Two populations that experienced high temperatures each generation displayed a loss of ESD, and in one of these ESD was virtually eliminated. This suggests that temperature-insensitive, sex-determining genes were being selected. In populations maintained in low temperature environments, however, the level of ESD did not decline. Instead, the response of sex ratio to temperature was adjusted upward or downward, perhaps by selection of sex-determining genes sensitive to higher (or lower) temperatures. The two different outcomes at low versus high temperatures occurred independent of the geographic origin of the founding population. Our results demonstrate that ESD is capable of evolving in response to selection.     

Consequences of inbreeding for offspring fitness and gender in Silene vulgaris,a gynodioecious plant

Abstract In gynodioecious plants, hermaphrodite and female plants co‐occur in the same population. In these systems gender typically depends on whether a maternally inherited cytoplasmic male sterility factor (CMS) is counteracted by nuclear restorer alleles. These restorer alleles are often genetically dominant. Although plants of the female morph are obligatorily outcrossing, hermaphrodites may self. This selfing increases homozygosity and may thus have two effects: (1) it may decrease fitness (i.e. result in inbreeding depression) and (ii) it may increase homozygosity of the nuclear restorer alleles and therefore increase the production of females. This, in turn, enhances outcrossing in the following generation. In order to test the latter hypothesis, experimental crosses were conducted using individuals derived from four natural populations of Silene vulgaris, a gynodioecious plant. Treatments included self‐fertilization of hermaphrodites, outcrossing of hermaphrodites and females using pollen derived from the same source population as the pollen recipients, and outcrossing hermaphrodites and females using pollen derived from different source populations. Offspring were scored for seed germination, survivorship to flowering and gender. The products of self‐fertilization had reduced survivorship at both life stages when compared with the offspring of outcrossed hermaphrodites or females. In one population the fitness of offspring produced by within‐population outcrossing of females was significantly less than the fitness of offspring produced by crossing females with hermaphrodites from other populations. Self‐fertilization of hermaphrodites produced a smaller proportion of hermaphroditic offspring than did outcrossing hermaphrodites. Outcrossing females within populations produced a smaller proportion of hermaphrodite offspring than did crossing females with hermaphrodites from other populations. These results are consistent with a cytonuclear system of sex determination with dominant nuclear restorers, and are discussed with regard to how the mating system and the genetics of sex determination interact to influence the evolution of inbreeding depression.     

Sex differences in host defence interfere with parasite‐mediated selection for outcrossing during host–parasite coevolution

The Red Queen hypothesis proposes that coevolving parasites select for outcrossing in the host. Outcrossing relies on males, which often show lower immune investment due to, for example, sexual selection. Here, we demonstrate that such sex differences in immunity interfere with parasite‐mediated selection for outcrossing. Two independent coevolution experiments with Caenorhabditis elegans and its microparasite Bacillus thuringiensis produced decreased yet stable frequencies of outcrossing male hosts. A subsequent systematic analysis verified that male C. elegans suffered from a direct selective disadvantage under parasite pressure (i.e. lower resistance, decreased sexual activity, increased escape behaviour), which can reduce outcrossing and thus male frequencies. At the same time, males offered an indirect selective benefit, because male‐mediated outcrossing increased offspring resistance, thus favouring male persistence in the evolving populations. As sex differences in immunity are widespread, such interference of opposing selective constraints is likely of central importance during host adaptation to a coevolving parasite.     

Relationships between plant density,outcrossing rates and seed set in natural and experimental populations of Scabiosa columbaria

Outcrossing rates were estimated in both natural and experimental populations of Scabiosa columbaria, a self-compatible, entomophilous, gynodioecious, protandrous perennial. In natural populations, estimates of the outcrossing rate in hermaphrodites were near to one and ranged from 0.84 ± 0.07 to 1.12 ± 0.11. The effect of plant density on outcrossing rates was studied in two experimental populations of 27 individuals. Contrary to expectation the estimates of the outcrossing rate in hermaphrodites were about 100% for both densities. However, in the sparse population, the fraction of developed seeds of plants used to estimate outcrossing rates was significantly lower than of plants in the dense population (0.41 ± 0.06 and 0.68 ± 0.08, respectively). Artificial pollinations of these plants in the greenhouse showed that the fraction of developed seeds was 0.60 ± 0.01 and 0.83 ± 0.05 after self- and cross-pollination, respectively. The combined results suggested that the differential success of self- and cross-pollination might have caused equalization of the outcrossing rates in the experimental populations, despite different plant densities. The implications of the results for conservation biology are discussed.     

The evolution of phally polymorphism in Bulinus truncatus (Gastropoda,Planorbidae): the cost of male function analysed through life-history traits and sex allocation

In the hermaphrodite freshwater snail Bulinus truncatus, two sexual morphs, euphallic (regular hermaphrodites) and aphallic individuals without a male copulatory organ, co-occur at various ratios in natural populations. Both aphallic and euphallic individuals can reproduce by selfing, but when outcrossing aphallic individuals can only play the female role. A comparison of life-history traits and sex allocation in these two forms provides the opportunity to investigate the evolution and maintenance of sexual polymorphisms. This study was performed to test whether a reallocation of resources from the lost male function to the female function occurs in aphallic snails at the level of both sex organs (sex allocation) and life-history traits. In a first experiment we compared life-history traits over a whole life-cycle under selfing between the two sexual morphs. In a second experiment, the sex organs were weighed to test for a difference in sex allocation between the two morphs. No difference in resource allocation to female function between the two morphs was observed in either experiment. This is in contrast to patterns frequently observed in sexually polymorphic plants, and in a previous study performed on aphally in the same snail species. We discuss the genetic and physiological hypotheses that could explain these results, and their consequences for the evolution and maintenance of phally polymorphism in B. truncatus.     

High temperature causes masculinization of genetically female medaka by elevation of cortisol

In poikilothermic vertebrates, sex determination is sometimes influenced by environmental factors such as temperature. However, little is known about the molecular mechanisms underlying environmental sex determination. The medaka (Oryzias latipes) is a teleost fish with an XX/XY sex determination system. Recently, it was reported that XX medaka can be sex‐reversed into phenotypic males by high water temperature (HT; 32–34°C) treatment during the sex differentiation period. Here we report that cortisol caused female‐to‐male sex reversal and that metyrapone (an inhibitor of cortisol synthesis) inhibited HT‐induced masculinization of XX medaka. HT treatment caused elevation of whole‐body levels of cortisol, while metyrapone suppressed the elevation by HT treatment during sexual differentiation. Moreover, cortisol and 33°C treatments inhibited female‐type proliferation of germ cells as well as expression of follicle‐stimulating hormone receptor (fshr) mRNA in XX medaka during sexual differentiation. These results strongly suggest that HT induces masculinization of XX medaka by elevation of cortisol level, which, in turn, causes suppression of germ cell proliferation and of fshr mRNA expression. Mol. Reprod. Dev. 77: 679–686, 2010. © 2010 Wiley‐Liss, Inc.     

Life history characteristics of the western flower thrips,Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), under fluctuating conditions of temperature or relative humidity

Frankliniella occidentalis (Pergande) is a major insect pest of greenhouse crops such as leaf vegetables, flowers and vegetable fruits worldwide. The life history characteristics of F. occidentalis were investigated at control temperature and humidity (27.3 ± 0.54 °C, 79.9 ± 2.79% RH) (mean ± SD), a 10 °C-range fluctuation in temperature (27.1 ± 5.28 °C, 81.5 ± 4.03% RH), a 20 °C-range fluctuation in temperature (26.5 ± 10.09 °C, 80.4 ± 5.76% RH), a 20%-range fluctuation in humidity (26.8 ± 0.37 °C, 80.7 ± 9.55% RH) and a 30%-range fluctuation in humidity (27.3 ± 0.41 °C, 76.3 ± 15.28% RH). Overall, the life history traits of F. occidentalis were more negatively affected by fluctuating environmental conditions. The impact of temperature fluctuation was more severe than that of humidity fluctuation. Additionally, the degree of impact increased as the fluctuation range of the temperature increased, while the reverse trend was observed with humidity fluctuations. With the 20 °C-range fluctuation in temperature, F. occidentalis died at the 1st instar larval stage. The offspring’s sex ratio was significantly higher at the 20%- and 30%-range fluctuations in humidity (0.47 and 0.49, respectively) compared to the control (0.35) and at the 10 °C-range fluctuation in temperature (0.33). From the fertility life table analysis, the intrinsic rate of increase (r) was higher at the 30%-range fluctuation in humidity and control conditions as 0.218 and 0.205, respectively. At the 10 °C-range fluctuation in temperature conditions, r was significantly lower as 0.169. High fluctuations in temperature and low fluctuations in humidity appear to be the best conditions for controlling F. occidentalis populations in greenhouses.     

Intersexuality in the amphipod Gammarus duebeni results from incomplete feminisation by the vertically transmitted parasitic sex ratio distorter Nosema granulosis

We investigated the effects of parasitism and temperature on the production of intersexes in the amphipod Gammarus duebeni from a field population at Cumbrae, Scotland. There was significant temporal variation in intersex frequency which ranged from 0.5 to 5.2% in monthly field collections. Prevalence of Nosema granulosis, a feminising microsporidian parasite, also varied temporally and there was a significant correlation between parasite prevalence and intersex frequency in the field. Intersexes (16.3 ± 0.4 mg) were larger than true females (14.8 ± 0.1 mg) but produced fewer eggs thus demonstrating a cost of intersexuality. Intersexes were less likely to be paired than true females. In a breeding experiment, only females infected by N. granulosis produced intersex offspring. Temperature had no effect on intersex frequency. Intersexes therefore appear to be the result of incomplete feminisation by N. granulosis in this population. These results contrast with previous studies of G. duebeni from different populations which found that intersexes were the result of abnormal development under environmental sex determination. We suggest that intersexuality may be induced by both environmental and parasitic factors in populations of G. duebeni. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fitness‐consequences of geitonogamous selfing in a clonal marine angiosperm (Zostera marina)

Plant mating systems have received considerable attention because the proportion of selfed vs. outcrossed progeny is an important evolutionary factor. In clonally reproducing plants, geitonogamous selfing between distant ramets belonging to the same genet is expected to be widespread, yet empirical data are sparse. Nothing is known about between‐ramet selfing in aquatic flowering plants with subaqueous pollen transfer, most of which display pronounced clonal reproduction. From two locations in the western Baltic Sea, I present data on the effects of patch isolation and clonal diversity on the outcrossing rate of eelgrass, Zostera marina L., based on the genotypes of maternal plants and recently fertilized ovules scored at eight microsatellite loci. There were no differences in outcrossing rates between vegetation patches and continuous meadow although patches were nearly always composed of single genets. Quantitative effects of clonal diversity were present in the continuous vegetation where a significant positive correlation between genet diversity and the proportion of outcrossed offspring was detected (Kendall’s τ=0.82, P=0.0017). On a population‐scale as well, the genotypic diversity was positively correlated with outcrossing. The relative fitness of selfed offspring was low (ω ± 95% confidence interval=0.56 ± 0.032 and 0.322 ± 0.15) indicating that geitonogamy incurred substantial fitness costs. Selfing rates in Z. marina may not be in evolutionary equilibrium because of spatial and temporal heterogeneity of clonal size and diversity. The high prevalence of dioecy in seagrasses may have evolved to avoid the fitness costs associated with geitonogamy.     

EXPERIMENTAL EVOLUTION OF HSP70 EXPRESSION AND THERMOTOLERANCE IN DROSOPHILA MELANOGASTER

To examine whether recent evolutionary history affects the expression of Hsp70, the major heat-induced-heat shock protein in Drosophila melanogaster, we measured Hsp70 expression, thermotolerance, and hsp70 gene number in replicate populations undergoing laboratory evolution at different temperatures. Despite Hsp70's ancient and highly conserved nature, experimental evolution effectively and replicably modified its expression and phenotype (thermotolerance). Among five D. melanogaster populations founded from a common ancestral population and raised at three different temperatures (one at 18°C, two each at 25°C and 28°C) for twenty years, Hsp70 expression varies in a consistent pattern: the replicate 28°C lines expressed 30–50% less Hsp70 than the other lines at a range of inducing temperatures. This modification was refractory to acclimation, and correlated with thermotolerance: the 28°C lines had significantly lower inducible tolerance of 38.5°C and 39°C. We verified the presence of five hsp70 genes in the genome of each line, excluding copy number variation as a candidate molecular basis of the evolved difference in expression. These findings support the ability of Hsp70 levels in D. melanogaster populations to change over microevolutionary time scales and implicate constancy of environmental temperature as a potentially important selective agent.     

GENETIC DIFFERENTIATION IN THE FLORIDA SUBSPECIES OF HELIANTHUS DEBILIS (ASTERACEAE)

Techniques of horizontal starch gel electrophoresis were employed to estimate levels of genetic variation within and genetic differentiation among populations of the three Florida subspecies of Helianthus debilis. The subspecies are H. d. debilis, H. d. vestitus, and H. d. tardiflorus. These taxa are very similar with respect to levels of genetic variability. The average values across all populations for proportion of polymorphic loci (25.5%) and number of alleles per polymorphic locus (2.35) are comparable to those found in other outcrossing plants. The average frequency of heterozygotes per locus (0.05) is lower than that found in other outcrossers. Local populations within each subspecies are genetically very similar. The average genetic distance between local populations is D = 0.010 ± 0.001. Subspecies vestitus and subspecies tardiflorus are also genetically very similar (D = 0.015 ± 0.001). However, subspecies debilis is differentiated from both subspecies vestitus (D = 0.121 ± 0.006) and subspecies tardiflorus (D = 0.103 ± 0.005). This genetic differentiation parallels morphological differentiation. The average genetic distance among all three subspecies is D = 0.080 ± 0.003. A moderate amount of genetic differentiation accompanies the process of subspeciation in Helianthus debilis.     

Reproductive correlates of mating system variation in Eichhornia paniculata (Spreng.) Solms (Pontederiaceae)

Comparative studies of related plant species indicate that evolutionary shifts in mating systems are accompanied by changes in reproductive attributes such as flower size, floral morphology, and pollen/ovule ratio. Recent theoretical work suggests that patterns of investment in reproduction should also change with the mating system. In a glasshouse study, we investigated the extent to which mating system differences among populations of Eichhornia paniculata (Pontederiaceae) were correlated with changes in allocation to male and female function, floral display, and the regulation of investment in reproduction through fruit and ovule abortion. Significant differences in the amount of biomass allocated to reproductive structures were evident among six populations of E. paniculata. As predicted by sex allocation theory, the proportion of dry weight allocated to male function decreased with the outcrossing rate of populations. Six of the eight attributes used to characterize floral display also differed significantly among populations. However, with the exception of two attributes describing the number of flowers produced by inflorescences, these were not correlated with outcrossing rate. Levels of fruit and ovule abortion were determined in two populations with contrasting mating systems under different nutrient and pollination treatments. Virtually all fruits initiated by plants from a self-fertilizing population were matured, while the amount of fruit abortion in an outcrossing population increased with flower production. Ovule abortion was low in both populations. Our results demonstrate that the evolution of self-fertilization in E. paniculata is associated with changes in investment to reproduction that normally distinguish selfing and outcrossing species.     

Local adaptation with high gene flow: temperature parameters drive adaptation to altitude in the common frog (Rana temporaria)

Both environmental and genetic influences can result in phenotypic variation. Quantifying the relative contributions of local adaptation and phenotypic plasticity to phenotypes is key to understanding the effect of environmental variation on populations. Identifying the selective pressures that drive divergence is an important, but often lacking, next step. High gene flow between high‐ and low‐altitude common frog (Rana temporaria) breeding sites has previously been demonstrated in Scotland. The aim of this study was to assess whether local adaptation occurs in the face of high gene flow and to identify potential environmental selection pressures that drive adaptation. Phenotypic variation in larval traits was quantified in R. temporaria from paired high‐ and low‐altitude sites using three common temperature treatments. Local adaptation was assessed using Q_ST–F_ST analyses, and quantitative phenotypic divergence was related to environmental parameters using Mantel tests. Although evidence of local adaptation was found for all traits measured, only variation in larval period and growth rate was consistent with adaptation to altitude. Moreover, this was only evident in the three mountains with the highest high‐altitude sites. This variation was correlated with mean summer and winter temperatures, suggesting that temperature parameters are potentially strong selective pressures maintaining local adaptation, despite high gene flow.