Natural selection contributes to geographic patterns of thermal plasticity in Plantago lanceolata

Novel host plant use by a specialist insect depends on geographic variation in both the host and herbivore species

Understanding the circumstances under which insect herbivores will adopt a novel host plant is a longstanding question in basic and applied ecology. While geographic variation in host use can arise through differences in both herbivore preference and plant characteristics, there is a tendency to attribute geographic variation in host use to regional differences in herbivore preference alone. This is especially true for herbivores specialized to one or a few plant species. We compared how geographic variation in herbivore preference and host plant origin shape regional differences in host plant use by the specialized herbivore, Euphydryas phaeton. In parts of its range, E. phaeton uses only a native host, Chelone glabra, while in others, it also uses an introduced host, Plantago lanceolata. We offered female butterflies from each region the non-native host plant sourced from both regions and compared their oviposition behavior. The non-native host was almost universally rejected by butterflies in the region where only the native plant is used. In the region where butterflies use both hosts, females accepted non-native plants from their natal region twice as often as non-native plants from the other region where they are not used. Acceptance differed substantially among individual butterflies within regions but not among plants within regions. Thus, both individual preference and regional differences in both the insect and non-native host contributed to the geographic variation in different ways. These results highlight that, in addition to herbivore preference, regional differences in perceived plant suitability may be an important driver of diet breadth.

Pattern of Adaptive Divergence in Zingiber kawagoii Hayata (Zingiberaceae) along a Narrow Latitudinal Range

Ecological and evolutionary processes linking adaptation to environment are related to species’ range shifts. In this study, we employed amplified-fragment-length-polymorphism-based genome scan methods to identify candidate loci among Zingiber kawagoii populations inhabiting varying environments distributed at low to middle elevations (143–1488 m) in a narrow latitudinal range (between 21.90 and 25.30° N). Here, we show evidence of selection driving the divergence of Z. kawagoii. Twenty-six F_ST outliers were detected, which were significantly correlated with various environmental variables. The allele frequencies of nine F_ST outliers were either positively or negatively correlated with the population mean F_ST. Using several independent approaches, we found environmental variables act in a combinatorial fashion, best explaining outlier genetic variation. Nonetheless, we found that adaptive divergence was affected mostly by annual temperature range, and it is significantly positively correlated with latitude and significantly negatively correlated with the population mean F_ST. This study addresses a latitudinal pattern of changes in annual temperature range (which ranged from 13.8 °C in the Lanyu population to 18.5 °C in the Wulai population) and emphasizes the pattern of latitudinal population divergence closely linked to the allele frequencies of adaptive loci, acting in a narrow latitudinal range. Our results also indicate environmentally dependent local adaptation for both leading- and trailing-edge populations.

Transgenerational Genetic Effects Help Explain Latitudinal Variation in Seed Mass and Germination Timing in Plantago lanceolata

We know little about the underlying genetic control of phenotypic patterns of seed traits across large-scale geographic and environmental gradients. Such knowledge is important for understanding the evolution of populations within species and for improving species conservation. Therefore, to test for genetic variation in Plantago lanceolata, we made reciprocal crosses between northern and southern genotypes that span the species’ range in Europe. The results provide evidence of transgenerational genetic effects on seed mass and germination timing. Northern mothers produced larger seeds with delayed germination, in contrast to southern mothers, which produced smaller seeds with accelerated germination. A maternal latitude affected both the seed coat, solely maternal tissue, and embryo/endosperm tissues. Thus, latitudinal variation in seed size and germination timing can be explained, in part, by the direct influence of maternal genotype, independent of zygotic genes that parents pass directly to the embryo and endosperm. Data suggest that researchers exploring the existence and evolution of large-scale geographic variation within species test for transgenerational genetic effects. In addition, data suggest that transgenerational control of seed traits should be considered when developing procedures designed to facilitate species conservation and restoration.

Into the range: a latitudinal gradient or a center-margins differentiation of ecological strategies in Arabidopsis thaliana?

BACKGROUND AND AIMS

Determining within-species large-scale variation in phenotypic traits is central to elucidate the drivers of species' ranges. Intraspecific comparisons offer the opportunity to understand how trade-offs and biogeographical history constrain adaptation to contrasted environmental conditions. Here we test whether functional traits, ecological strategies from the CSR scheme and phenotypic plasticity in response to abiotic stress vary along a latitudinal or a center- margins gradient within the native range of Arabidopsis thaliana.

METHODS

We experimentally examined the phenotypic outcomes of plant adaptation at the center and margins of its geographic range using 30 accessions from southern, central and northern Europe. We characterized the variation of traits related to stress tolerance, resource use, colonization ability, CSR strategy scores, survival and fecundity in response to high temperature (34 °C) or frost (- 6 °C), combined with a water deficit treatment.

KEY RESULTS

We found evidence for both a latitudinal and a center-margins differentiation for the traits under scrutiny. Age at maturity, leaf dry matter content, specific leaf area and leaf nitrogen content varied along a latitudinal gradient. Northern accessions presented a greater survival to stress than central and southern accessions. Leaf area, C-scores, R-scores and fruit number followed a center-margins differentiation. Central accessions displayed a higher phenotypic plasticity than northern and southern accessions for most studied traits.

CONCLUSIONS

Traits related to an acquisitive/conservative resource-use trade-off followed a latitudinal gradient. Traits associated with a competition/colonization trade-off differentiated along the historic colonization of the distribution range and then followed a center-margins differentiation. Our findings pinpoint the need to consider the joint effect of evolutionary history and environmental factors when examining phenotypic variation across the distribution range of a species.

Intense browsing by sika deer (Cervus nippon) drives the genetic differentiation of hairy nettle (Urtica thunbergiana) populations

Many studies have inferred the way in which natural selection, genetic drift and gene flow shape the population genetic structures, but very few have quantified the population differentiation under spatially and temporally varying levels of selection pressure, population fluctuation and gene flow. In Nara Park (6.6 km²), central Japan, where several hundred sika deer (Cervus nippon) have been protected for more than 1,200 years, heavily- or moderately-haired nettle (Urtica thunbergiana) populations have evolved probably in response to intense deer browsing. Here, we analysed the genetic structure of two Nara Park populations and five surrounding populations using amplified fragment length polymorphism markers. A total of 546 marker loci were genotyped from 210 individuals. A Bayesian method estimated 5.5% of these loci to be outliers, which are putatively under natural selection. Neighbour-joining, principal coordinates and Bayesian clustering analyses using all-loci, non-outlier loci and outlier loci datasets showed that the Nara Park populations formed a cluster distinct from the surroundings. These results indicate the genome-wide differentiation of the Nara Park populations from the surroundings. Moreover, these imply the following: (1) gene flow is limited between these populations and thus genetic drift is a major factor causing the differentiation; and (2) natural selection imposed by intense deer browsing has contributed to some extent to the differentiation. In conclusion, sika deer seems to have counteracted genetic drift to drive the genetic differentiation of hairy nettles in Nara Park. This study suggests that a single herbivore species could lead to genetic differentiation among plant populations.

Multiple modes of selection can influence the role of phenotypic plasticity in species' invasions: Evidence from a manipulative field experiment

In exploring the roles of phenotypic plasticity in the establishment and early evolution of invading species, little empirical attention has been given to the importance of correlational selection acting upon suites of functionally related plastic traits in nature. We illustrate how this lack of attention has limited our ability to evaluate plasticity's role during invasion and also, the costs and benefits of plasticity. We addressed these issues by transplanting clones of European-derived Plantago lanceolata L. genotypes into two temporally variable habitats in the species' introduced range in North America. Phenotypic selection analyses were performed for each habitat to estimate linear, quadratic, and correlational selection on phenotypic trait values and plasticities in the reproductive traits: flowering onset and spike and scape lengths. Also, we measured pairwise genetic correlations for our "colonists." Results showed that (a) correlational selection acted on trait plasticity after transplantation, (b) selection favored certain combinations of genetically correlated and uncorrelated trait values and plasticities, and (c) using signed, instead of absolute, values of plasticity in analyses facilitated the detection of correlational selection on trait value-plasticity combinations and their adaptive value. Based on our results, we urge future studies on species invasions to (a) measure correlational selection and (b) retain signed values of plasticity in order to better discriminate between adaptive and maladaptive plasticity.

Macroevolutionary variation and environmental correlates of scalation traits in Eurasian vipers (Serpentes: Viperinae)

Understanding how phenotypic variation across species is shaped by the combination of shared evolutionary history and environmental factors is key to elucidating the processes that underlie biodiversity. In reptiles, morphological traits have traditionally been used to delimit species and make systematic inferences. Recent studies highlight the possibility that phenotypic variation, particularly in scalation traits, might instead be driven by environmental factors and therefore not reflect the phylogenetic relationships among species. In this study, we combined morphological and ecological data in a macroevolutionary framework, in order to describe the morphological variation across species of Eurasian vipers (Serpentes: Viperinae), investigate the phylogenetic structure of scalation traits and test the contribution of environmental factors in shaping morphological patterns. We found considerable variation in all examined traits, which, in most cases, agreed with the phylogenetic relationships among species, reinforcing their usefulness for taxonomic inferences. Interestingly, however, the number of ventral scales exhibited lower phylogenetic signal and a tight association with environmental factors of geographical ranges, suggesting potential adaptive or developmental sources of variation in the trait. This is the first comparative study of macroevolutionary variation in scalation traits in Eurasian vipers, validating the use of most of them for systematic inferences, but also indicating possible environmental factors that might shape phenotypic variation across species.

Two reproductive traits show contrasting genetic architectures in Plantago lanceolata

In many species, temperature-sensitive phenotypic plasticity (i.e., an individual's phenotypic response to temperature) displays a positive correlation with latitude, a pattern presumed to reflect local adaptation. This geographical pattern raises two general questions: (a) Do a few large-effect genes contribute to latitudinal variation in a trait? (b) Is the thermal plasticity of different traits regulated pleiotropically? To address the questions, we crossed individuals of Plantago lanceolata derived from northern and southern European populations. Individuals naturally exhibited high and low thermal plasticity in floral reflectance and flowering time. We grew parents and offspring in controlled cool- and warm-temperature environments, mimicking what plants would encounter in nature. We obtained genetic markers via genotype-by-sequencing, produced the first recombination map for this ecologically important nonmodel species, and performed quantitative trait locus (QTL) mapping of thermal plasticity and single-environment values for both traits. We identified a large-effect QTL that largely explained the reflectance plasticity differences between northern and southern populations. We identified multiple smaller-effect QTLs affecting aspects of flowering time, one of which affected flowering time plasticity. The results indicate that the genetic architecture of thermal plasticity in flowering is more complex than for reflectance. One flowering time QTL showed strong cytonuclear interactions under cool temperatures. Reflectance and flowering plasticity QTLs did not colocalize, suggesting little pleiotropic genetic control and freedom for independent trait evolution. Such genetic information about the architecture of plasticity is environmentally important because it informs us about the potential for plasticity to offset negative effects of climate change.