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1.
    
Local adaptation can be a potent force in speciation, with environmental heterogeneity leading to niche specialization and population divergence. However, local adaption often requires nonrandom mating to generate reproductive isolation. Population divergence in sensory properties can be particularly consequential in speciation, affecting both ecological adaptation and sexual communication. Pundamilia pundamila and Pundamilia nyererei are two closely related African cichlid species that differ in male coloration, blue vs. red. They co‐occur at rocky islands in southern Lake Victoria, but inhabit different depth ranges with different light environments. The species differ in colour vision properties, and females exert species‐specific preferences for blue vs. red males. Here, we investigated the mechanistic link between colour vision and preference, which could provide a rapid route to reproductive isolation. We tested the behavioural components of this link by experimentally manipulating colour perception – we raised both species and their hybrids under light conditions mimicking shallow and deep habitats – and tested female preference for blue and red males under both conditions. We found that rearing light significantly affected female preference: shallow‐reared females responded more strongly to P. pundamilia males and deep‐reared females favoured P. nyererei males – implying that visual development causally affects mate choice. These results are consistent with sensory drive predictions, suggesting that the visual environment is key to behavioural isolation of these species. However, the observed plasticity could also make the species barrier vulnerable to environmental change: species‐assortative preferences were weaker in females that were reared in the other species’ light condition.  相似文献   

2.
    
Trichomes, or leaf hairs, are epidermal extensions that take a variety of forms and perform many functions in plants, including herbivore defence. In this study, I document genetically determined variation, within‐generation plasticity, and a direct role of trichomes in herbivore defence for Mimulus guttatus. After establishing the relationship between trichomes and herbivory, I test for transgenerational effects of wounding on trichome density and herbivore resistance. Patterns of interannual variation in herbivore density and the high cost of plant defence makes plant–herbivore interactions a system in which transgenerational phenotypic plasticity (TPP) is apt to evolve. Here, I demonstrate that parental damage alters offspring trichome density and herbivore resistance in nature. Moreover, this response varies between populations. This is among the first studies to demonstrate that TPP contributes to variation in nature, and also suggests that selection can modify TPP in response to local conditions.  相似文献   

3.
Body size affects life history, the ecological niche of an organism and its interactions with other organisms. Resultantly, marked differences in body size between related organisms are often an indication of a species boundary. This is particularly evident in the Gehyra variegata species complex of geckos, which displays differential body sizes between genetically divergent species, but high levels of intraspecific morphological conservatism. We report on a Gehyra population that displays extraordinary body size differentiation in comparison with other G. variegata species. We used morphological and environmental data to show this population is phenotypically and ecologically distinct from its parapatric congener Gehyra lazelli and that morphology and ecology are significantly correlated. Contrastingly, mtDNA analysis indicates paraphyly between the two groups, and allele frequencies at six microsatellite loci show no population structure concordant with morpho‐/ecotype. These results suggest either ecological speciation or environmentally induced phenotypic polymorphism, in an otherwise morphologically conservative group.  相似文献   

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5.
    
The relative roles of natural and sexual selection in promoting evolutionary lineage divergence remains controversial and difficult to assess in natural systems. Local adaptation through natural selection is known to play a central role in promoting evolutionary divergence, yet secondary sexual traits can vary widely among species in recent radiations, suggesting that sexual selection may also be important in the early stages of speciation. Here, we compare rates of divergence in ecologically relevant traits (morphology) and sexually selected signalling traits (coloration) relative to neutral structure in genome‐wide molecular markers and examine patterns of variation in sexual dichromatism to explore the roles of natural and sexual selection in the diversification of the songbird genus Junco (Aves: Passerellidae). Juncos include divergent lineages in Central America and several dark‐eyed junco (J. hyemalis) lineages that diversified recently as the group recolonized North America following the last glacial maximum (ca. 18,000 years ago). We found an accelerated rate of divergence in sexually selected characters relative to ecologically relevant traits. Moreover, sexual dichromatism measurements suggested a positive relationship between the degree of colour divergence and the strength of sexual selection when controlling for neutral genetic distance. We also found a positive correlation between dichromatism and latitude, which coincides with the geographic axis of decreasing lineage age in juncos but also with a steep ecological gradient. Finally, we found significant associations between genome‐wide variants linked to functional genes and proxies of both sexual and natural selection. These results suggest that the joint effects of sexual and ecological selection have played a prominent role in the junco radiation.  相似文献   

6.
    
Ecological limits to phenotypic plasticity (PP), induced by simultaneous biotic and abiotic factors, can prevent organisms from exhibiting optimal plasticity, and in turn lead to decreased fitness. Herbivory is an important biotic stressor and may limit plant functional responses to challenging environmental conditions such as shading. In this study we investigated whether plant functional responses and PP to shade are constrained by herbivory, and whether such constraints are due to direct effects based on resource limitation by considering ontogeny. We used as a model system the relict tree Prunus lusitanica and implemented an indoor experiment to quantify the response of saplings of different ages to shade and herbivory. We measured five functional traits and quantitatively calculated PP. Results showed that herbivory did not constrain functional responses or PP to shade except for shoot:root ratio (SR), which, despite showing a high PP in damaged saplings, decreased under shade instead of increasing. Damaged saplings of older age did not exhibit reduced constraints on functional responses to shade and generally presented a lower PP than damaged saplings of younger age. Our findings suggest that herbivory‐mediated constraints on plant plasticity to shade may not be as widespread as previously thought. Nonetheless, the negative effect of herbivory on SR plastic expression to shade could be detrimental for plant fitness. Finally, our results suggest a secondary role of direct effects (resource‐based) on P. lusitanica plasticity limitation. Further studies should quantify plant resources in order to gain a better understanding of this seldom‐explored subject.  相似文献   

7.
    
Heterozygosity has been positively associated with fitness and population survival. However, the relationship between heterozygosity and adaptive phenotypic plasticity (i.e., plasticity which results in fitness homeostasis or improvement in changing environments) is unclear and has been poorly explored in seaweeds. In this study, we explored this relationship in the clonal red seaweed, Gracilaria chilensis by conducting three growth rate plasticity experiments under contrasting salinity conditions and by measuring heterozygosity with five microsatellite DNA markers. Firstly, we compared growth rate plasticity between the haploid and diploid phases. Secondly, we compared growth rate plasticity between diploids with different numbers of heterozygous loci. Finally, we compared growth rate plasticity between diploid plants from two populations that are expected to exhibit significant differences in heterozygosity. We found that, (i) diploids displayed a higher growth rate and lower growth rate plasticity than haploids, (ii) diploids with a higher number of heterozygous loci displayed lower growth rate plasticity than those exhibiting less heterozygosity, and (iii) diploid sporophytes from the population with higher heterozygosity displayed lower growth rate plasticity than those with lower heterozygosity. Accordingly, this study suggests that heterozygosity is inversely related to growth rate plasticity in G. chilensis. However, better genetic tools in seaweeds are required for a more definitive conclusion on the relationship between heterozygosity and phenotypic plasticity.  相似文献   

8.
    
  1. The future increase in the atmospheric CO2 concentration is likely to affect the growth and performance of submerged freshwater macrophytes because of higher concentrations of free CO2 in the water at air equilibrium. We measured the plastic responses to free CO2 and light for several traits of four invasive aquatic plants (Elodea canadensis, Egeria densa, Hydrilla verticillata and Ceratophyllum demersum) that use bicarbonate.
  2. The plants were grown in standard culture media at either high (HiC, c. 50 μmol L?1) or low concentrations of free CO2 (LowC, c. 19 μmol L?1) combined with high (HiL, c. 150 μmol m?2 s?1) or low (LowL, c. 21 μmol m?2 s?1) light intensity in a 2 × 2 factorial experiment. We compared the relative growth rate (RGR), several morphological traits, the photosynthetic response to light intensity and the bicarbonate uptake capacity of the four species. For every trait measured, we established plasticity indices for light and CO2 availability.
  3. Light intensity had a greater effect than CO2 concentration on all species. The RGR of all four species was higher at high light intensity, and photosynthetic light responses acclimated to low light with a lower light compensation point, and with higher concentrations of photosynthetic pigments and quantum yield. The bicarbonate uptake capacity was generally highest at the high light intensity and high concentrations of free CO2. Plasticity indices for light intensity were consistently higher than for CO2 availability in all four species.
  4. As the growth and photosynthesis of the four invasive bicarbonate users were only slightly affected by the CO2 availability in air‐equilibrated water, the future rise in atmospheric CO2 is unlikely to exacerbate their invasive behaviour and may even reduce their competitiveness against species unable to use bicarbonate, especially at limiting light.
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9.
    
Understanding the capacity for different species to reduce their susceptibility to climate change via phenotypic plasticity is essential for accurately predicting species extinction risk. The climatic variability hypothesis suggests that spatial and temporal variation in climatic variables should select for more plastic phenotypes. However, empirical support for this hypothesis is limited. Here, we examine the capacity for ten Drosophila species to increase their critical thermal maxima (CTMAX) through developmental acclimation and/or adult heat hardening. Using four fluctuating developmental temperature regimes, ranging from 13 to 33 °C, we find that most species can increase their CTMAX via developmental acclimation and adult hardening, but found no relationship between climatic variables and absolute measures of plasticity. However, when plasticity was dissected across developmental temperatures, a positive association between plasticity and one measure of climatic variability (temperature seasonality) was found when development took place between 26 and 28 °C, whereas a negative relationship was found when development took place between 20 and 23 °C. In addition, a decline in CTMAX and egg‐to‐adult viability, a proxy for fitness, was observed in tropical species at the warmer developmental temperatures (26–28 °C); this suggests that tropical species may be at even greater risk from climate change than currently predicted. The combined effects of developmental acclimation and adult hardening on CTMAX were small, contributing to a <0.60 °C shift in CTMAX. Although small shifts in CTMAX may increase population persistence in the shorter term, the degree to which they can contribute to meaningful responses in the long term is unclear.  相似文献   

10.
    
Both constitutive and inducible antipredator strategies are ubiquitous in nature and serve to maximize fitness under a predation threat. Inducible strategies may be favored over constitutive defenses depending on their relative cost and benefit and temporal variability in predator presence. In African temporary ponds, annual killifish of the genus Nothobranchius are variably exposed to predators, depending on whether larger fish invade their habitat from nearby rivers during floods. Nonetheless, potential plastic responses to predation risk are poorly known. Here, we studied whether Nothobranchius furzeri individuals adjust their life history in response to a predation threat. For this, we monitored key life history traits in response to cues that signal the presence of predatory pumpkinseed sunfish (Lepomis gibbosus). While growth rate, adult body size, age at maturation, and initial fecundity were not affected, peak and total fecundity were higher in the predation risk treatment. This contrasts with known life history strategies of killifish from permanent waters, which tend to reduce reproduction in the presence of predators. Although our results show that N. furzeri individuals are able to detect predators and respond to their presence by modulating their reproductive output, these responses only become evident after a few clutches have been deposited. Overall our findings suggest that, in the presence of a predation risk, it can be beneficial to increase the production of life stages that can persist until the predation risk has faded.  相似文献   

11.
    
Circadian clocks have evolved independently in all three domains of life, suggesting that internal mechanisms of time‐keeping are adaptive in contemporary populations. However, the performance consequences of either discrete or quantitative clock variation have rarely been tested in field settings. Clock sensitivity of diverse segregating lines to the environment remains uncharacterized as do the statistical genetic parameters that determine evolutionary potential. In field studies with Arabidopsis thaliana, we found that major perturbations to circadian cycle length (referred to as clock period) via mutation reduce both survival and fecundity. Subtler adjustments via genomic introgression of naturally occurring alleles indicated that clock periods slightly >24 hr were adaptive, consistent with prior models describing how well the timing of biological processes is adjusted within a diurnal cycle (referred to as phase). In segregating recombinant inbred lines (RILs), circadian phase varied up to 2 hr across months of the growing season, and both period and phase expressed significant genetic variances. Performance metrics including developmental rate, size and fruit set were described by principal components (PC) analyses and circadian parameters correlated with the first PC, such that period lengths slightly >24 hr were associated with improved performance in multiple RIL sets. These experiments translate functional analyses of clock behaviour performed in controlled settings to natural ones, demonstrating that quantitative variation in circadian phase is highly responsive to seasonally variable abiotic factors. The results expand upon prior studies in controlled settings, showing that discrete and quantitative variation in clock phenotypes correlates with performance in nature.  相似文献   

12.
    
The capacity of restored plant populations to adapt to new environmental challenges depends on within‐population genetic variation. We examined how much genetic and environmentally based variation for fitness‐associated traits exists within populations of two native grasses commonly used for restoration in California. We were also interested in understanding how phenotypic expression of genetic variation for these traits varies with growth environment. Thirty maternal families of Elymus glaucus (Blue wild rye) and Nassella pulchra (Purple needlegrass) were sampled from both coastal and interior populations and reciprocally transplanted into three replicated common gardens with and without interspecific competition at each site. Reproductive output of families differed both among years and with competition treatments. Phenotypic expression of genetic variation in culm production differed among populations and was very low when families were grown with interspecific competition. Without interspecific competition, the degree of genetic determination peaked in year two in both species (8.4 and 15.1% in E. glaucus and N. pulchra, respectively). Significant genetic differences in reproduction and phenotypic plasticity were found among N. pulchra subpopulations sampled less than 3 km apart, further highlighting the importance of thoroughly sampling available genetic variation in populations used for restoration. The variable and generally low expression of genetic variation indicates that rates of adaptation in restored populations of these native grasses may vary temporally and may be especially slow within competitive environments.  相似文献   

13.
    
In the threespine stickleback Gasterosteus aculeatus model system, phenotypes are often classified into three morphs according to lateral plate number. Morph identity has been shown to be largely genetically determined, but substantial within‐morph variation in plate number exists. In this study, we test whether plate number has a plastic component in response to salinity in the low‐plated morph using a split‐clutch experiment where families were split in two, one half raised in water at 0 and the other at 30 ppt salt. We find a small salinity‐induced plastic effect on plate number in an unexpected direction, opposite to what we predicted: Fish raised in freshwater on average have slightly more plates than fish raised in saltwater. Our results confirm that heritability of plate number is high. Additionally, we find that variance in plate number at the family level can be predicted from other family level traits, which might indicate that epistatic interactions play a role in creating the observed pattern of lateral plate number variation.  相似文献   

14.
    
Models of speciation by sexual selection propose that male–female coevolution leads to the rapid evolution of behavioural reproductive isolation. Here, we compare the strength of behavioural isolation to ecological isolation, gametic incompatibility and hybrid inviability in a group of dichromatic stream fishes. In addition, we examine whether any of these individual barriers, or a combined measure of total isolation, is predicted by body shape differences, male colour differences, environmental differences or genetic distance. Behavioural isolation reaches the highest values of any barrier and is significantly greater than ecological isolation. No individual reproductive barrier is associated with any of the predictor variables. However, marginally significant relationships between male colour and body shape differences with ecological and behavioural isolation are discussed. Differences in male colour and body shape predict total reproductive isolation between species; hierarchical partitioning of these two variables' effects suggests a stronger role for male colour differences. Together, these results suggest an important role for divergent sexual selection in darter speciation but raise new questions about the mechanisms of sexual selection at play and the role of male nuptial ornaments.  相似文献   

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16.
    
Both traits and the plasticity of these traits are subject to evolutionary change and therefore affect the long‐term persistence of populations and their role in local communities. We subjected clones from 12 different populations of Alnus glutinosa, located along a latitudinal gradient, to two different temperature treatments, to disentangle the distribution of genetic variation in timing of bud burst and bud burst plasticity within and among genotypes, populations, and regions. We calculated heritability and evolvability estimates for bud burst and bud burst plasticity and assessed the influence of divergent selection relative to neutral drift. We observed higher levels of heritability and evolvability for bud burst than for its plasticity, whereas the total phenological heritability and evolvability (i.e. combining timing of bud burst and bud burst plasticity) suggest substantial evolutionary potential with respect to phenology. Earlier bud burst was observed for the low‐latitudinal populations than for the populations from higher latitudes, whereas the high‐latitudinal populations did not show the expected delayed bud burst. This countergradient variation can be due to evolution towards increased phenological plasticity at higher latitudes. However, because we found little evidence for adaptive differences in phenological plasticity across the latitudinal gradient, we suggest differential frost tolerance as the most likely explanation for the observed phenological patterns in A. glutinosa.  相似文献   

17.
    
The diverse benefits of group living include protection against predators through dilution effects and greater group vigilance. However, intraspecific aggregation can decrease developmental rates and survival in prey species. We investigated the impact on tadpole development and behaviour of the interaction between population density and predation risk. Spotted tree frog (Litoria spenceri: Hylidae, Dubois 1984) tadpoles were kept at one of three different densities (two tadpoles per litre, five tadpoles per litre or 10 tadpoles per litre) until metamorphosis in the presence or absence of predatory cues. We aimed to determine the influence of population density, predation and the interaction of both factors in determining growth rates in tadpoles. Tadpoles were measured weekly to assess growth and development and filmed to quantify differences in activity and feeding frequency between groups. Generally, tadpoles housed without predators had longer developmental periods when housed with a predator, but there was no effect on tail length or total length. There was no effect of either predation cues or density on percentage of individuals feeding or moving. Although the effects of the presence of predators alone may appear to be less than the effects of the presence of competitors, the prioritisation of competitiveness over predator avoidance may increase vulnerability of tadpoles to the lethal threat of predators. This is particularly important in species such as L. spenceri, which is at risk from introduced fish predators.  相似文献   

18.
    
New World livebearing fishes (family Poeciliidae) have repeatedly colonised toxic, hydrogen sulphide‐rich waters across their natural distribution. Physiological considerations and life‐history theory predict that these adverse conditions should favour the evolution of larger offspring. Here, we examined nine poeciliid species that independently colonised toxic environments, and show that these fishes have indeed repeatedly evolved much larger offspring size at birth in sulphidic waters, thus uncovering a widespread pattern of predictable evolution. However, a second pattern, only indirectly predicted by theory, proved additionally common: a reduction in the number of offspring carried per clutch (i.e. lower fecundity). Our analyses reveal that this secondary pattern represents a mere consequence of a classic life‐history trade‐off combined with strong selection on offspring size alone. With such strong natural selection in extreme environments, extremophile organisms may commonly exhibit multivariate phenotypic shifts even though not all diverging traits necessarily represent adaptations to the extreme conditions.  相似文献   

19.
    
Phenotypic variation among individuals and species is a fundamental principle of natural selection. In this review, we focus on numerous experiments involving the model species Daphnia (Crustacea) and categorize the factors, especially secondary ones, affecting intraspecific variations in inducible defense. Primary factors, such as predator type and density, determine the degree to which inducible defense expresses and increases or decreases. Secondary factors, on the other hand, act together with primary factors to inducible defense or without primary factors on inducible defense. The secondary factors increase intraspecies variation in inducible defense, and thus, the level of adaptation of organisms varies within species. Future research will explore the potential for new secondary factors, as well as the relative importance between factors needs to be clarified.  相似文献   

20.
    
Although changes in magnitude of single traits responding to selective agents have been studied intensively, little is known about selection shaping networks of traits and their patterns of covariation. However, this is central for our understanding of phenotypic evolution as traits are embedded in a multivariate environment with selection affecting a multitude of traits simultaneously rather than individually. Here, we investigate inter‐ and intraspecific patterns of trait integration (trait correlations) in the larval abdomen of dragonflies as a response to a change in predator selection. Species of the dragonfly genus Leucorrhinia underwent a larval habitat shift from predatory fish to predatory dragonfly‐dominated lakes with an associated relaxation in selection pressure from fish predation. Our results indicate that the habitat‐shift‐induced relaxed selection pressure caused phenotypic integration of abdominal traits to be reduced. Intraspecific findings matched patterns comparing species from both habitats with higher abdominal integration in response to predatory fish. This higher integration is probably a result of faster burst swimming speed. The abdomen holds the necessary morphological machinery to successfully evade predatory fish via burst swimming. Hence, abdominal traits have to function in a tight coordinated manner, as maladaptive variation and consequently nonoptimal burst swimming would cause increased mortality. In predatory dragonfly‐dominated lakes, no such strong link between burst swimming and mortality is present. Our findings highlight the importance of studying multivariate trait relationships as a response to selection for understanding patterns of phenotypic diversification.  相似文献   

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