Evolution of Autonomous Selfing in Marginal Habitats: Spatiotemporal Variation in the Floral Traits of the Distylous Primula wannanensis

Outcrossing plant species are more likely to exhibit autonomous selfing in marginal habitats to ensure reproduction under conditions of limited pollinator and/or mate availability. Distyly is a classical paradigm that promotes outcrossing; however, little is known about the variation in floral traits associated with distylous syndrome in marginal populations. In this study, we compared the variation in floral traits including stigma and anther height, corolla tube length, herkogamy, and corolla diameter between the central and peripheral populations of the distylous Primula wannanensis, and assessed the variation of floral traits at early and late florescence stages for each population. To evaluate the potential consequences of the variation in floral traits on the mating system, we investigated seed set in each population under both open-pollinated and pollinator-excluded conditions. The flower size of both short- and long-styled morphs was significantly reduced in late-opening flowers compared with early opening flowers in both central and peripheral populations. Sex-organ reciprocity was perfect in early opening flowers; however, it was largely weakened in the late-opening flowers of peripheral populations compared with central populations. Of these flowers, disproportionate change in stigma height (elongated in S-morph and shortened in L-morph) was the main cause of reduced herkogamy, and seed set was fairly high under pollinator-excluded condition. Our results provide empirical support for the hypothesis on the evolution of delayed autonomous selfing in marginal populations of distylous species. Unsatisfactory pollinator service is likely to have promoted reproductive assurance of distylous plants with largely reduced herkogamy mimicking “homostyles.”

Variation in intraspecific demography drives localised concordance but species-wide discordance in responses to Plio-Pleistocene climatic change

Understanding how species biology may facilitate resilience to climate change remains a critical factor in detecting and protecting species at risk of extinction. Many studies have focused on the role of particular ecological traits in driving species responses, but less so on demographic history and levels of standing genetic variation. We used environmental and genomic datasets to reconstruct the phylogeographic histories of two ecologically similar and largely co-distributed freshwater fishes to assess the degree of concordance in their responses to Plio-Pleistocene climatic changes. Although several co-occurring populations demonstrated concordant demographic histories, idiosyncratic population size changes were found at the range edges of the more spatially restricted species. Discordant responses between species were associated with low standing genetic variation in peripheral populations. This might have hindered adaptive potential, as documented in recent population declines and extinctions of the two species. Our results highlight both the role of spatial scale in the degree of concordance in species responses to climate change, and the importance of standing genetic variation in facilitating range shifts. Even when ecological traits are similar between species, long-term genetic diversity and historical population demography may lead to discordant responses to ongoing and future climate change.

Flowering and quality of seeds and pollen in endangered populations of Betula humilis

Key message Lowered pollen and seed quality of B. humilis compared to its widespread tree relatives may threaten its populations at the southwestern edge of the species range. Abstract Inability to produce vital propagules is the main threat to the persistence of rare plants at the edges of species distribution. In the present investigation, factors responsible for the low germinability of shrub birch (Betula humilis) seeds in the peripheral populations were analysed. As shrub birch populations are found in phosphorus (P)-limited peatlands with high groundwater levels, the impact of groundwater PO43− ion contents and groundwater table for B. humilis flowering was also studied. Qualities of the B. humilis seeds and pollen were compared to those of tree congeners silver birch (B. pendula) and downy birch (B. pubescens), which usually represent a high reproductive performance. We revealed that the poor germination ability of B. humilis seeds was caused by the high proportions of empty seeds (44.8%) and seeds with partially developed embryos (47.3%). The insufficient numbers of viable seeds may be a consequence of low-quality shrub birch pollen, as only 1.6% of pollen grains sprouted. The germinability of shrub birch pollen was significantly lower than that of Betula tree pollen; thus, there is a risk of pollination of B. humilis female flowers by pollen grains of tree birches. Positive relationships between the P concentrations in seeds and seed germinability were revealed in tree birches, but not in B. humilis. The availability of PO43− ions in the groundwater did not affect B. humilis flowering, but male inflorescences were more numerous in stands with higher groundwater levels. Consequently, the maintenance of peatlands is crucial for the efficient sexual reproduction of shrub birches.

Connectivity in Spanish metapopulation of Dupont’s lark may be maintained by dispersal over medium-distance range and stepping stones

Background Dupont’s Lark is an endangered bird, whose fragmented distribution in Europe is entirely restricted to Spain. This lark, suffering pronounced population decline and range contraction, inhabits steppes that have long been used for grazing sheep and are now threatened by rural abandonment and land use changes. Thus, for conservation of the lark, increasing knowledge about the connectivity of the Spanish metapopulation and identifying the most important connectivity nodes are crucial. Methods The study was carried out in Spain, using over 16,000 Dupont’s Lark georeferenced observations. We used distance buffers to define populations and subpopulations, based on the available scientific information. We identified potential stepping stones using a MaxEnt probability of presence model. Connectivity was assessed using Conefor software, using the centroid of each subpopulation and stepping stone as nodes. Each node was assigned a quantitative attribute based on total habitat area, within-node habitat quality and internal fragmentation. We evaluated different connectivity scenarios by potential movement thresholds (5–20–100 km) and presence or absence of stepping stones in the network. Results Dupont’s Lark Iberian metapopulation comprises 24 populations and 100 subpopulations, plus 294 potential stepping stones. Movement thresholds and stepping stones had a strong influence in the potential network connectivity. The most important nodes are located in the core of the metapopulation, which shows connectivity among subpopulations in the different indices and scenarios evaluated. Peripheral populations are more isolated and require stepping stones or medium (20 km) or long (100 km) potential movement thresholds to join the network. Discussion Metapopulation connectivity may be greater than expected, thanks to stepping stones and potential medium-distance movements. Connectivity is crucial for conservation and can be increased by preserving or improving adequate habitat in the most important nodes. Given the current species decline, steppe habitat should be urgently protected from land use changes and agriculture intensification, at least in the critical subpopulations and stepping stones. Long-term conservation of steppe lands and Dupont’s Lark in Spain requires the recovery of traditional grazing and more research on juvenile dispersion. Meanwhile, the conservation of potentially critical stepping stones should be incorporated to management plans.

Microhabitat Selection and Population Density of Nehalennia Speciosa Charpentier, 1840 (Odonata: Coenagrionidae) in a Peripheral Microrefugium

Peripheral populations of boreal tyrphophilic animals and plants often occupy relict Alpine peatlands, which act as microrefugia. Ecological conditions within local peatlands can lead to uncommon adaptations, highly valuable for the long-term conservation of species and habitats. The pigmy damselfly (Nehalennia speciosa) is an endangered Odonata distributed in Central and Eastern Europe with peripheral populations in the Alps. We investigated the microscale species-habitat association and the conservation status of one of these populations in a relict raised bog. We applied dynamic N-mixture models to assess population ecology and density, while disentangling predictors’ effect on ecological and observation process. We counted N. speciosa individuals in spring 2018 along with vegetation, water, soil and weather conditions during surveys. Final model resulted reliable according to performance measures. Spatial variation in N. speciosa abundance was driven by vegetation type, with a strong selection for flooded hollows where C. rostrata, R. alba and S. palustris vegetation occupy acidic and oligotrophic shallow pools. Population density showed a peak in the first decade of June and increased with accumulation of superficial water. Detection probability was generally low and decreased further when wind blew. The reduced ecological plasticity of the species imperil the species to habitat and climate changes, which will be particularly threatening for its peripheral Alpine populations in the near future, causing water imbalance and rapid vegetation turnover within the peatlands’ fragile microhabitat. The studied peat bog could thus be retained a key future microrefugium for the long-term conservation of tyrphopilous wildlife and habitats.

Genetic load and extinction in peripheral populations: the roles of migration, drift and demographic stochasticity

We analyse how migration from a large mainland influences genetic load and population numbers on an island, in a scenario where fitness-affecting variants are unconditionally deleterious, and where numbers declines with increasing load. Our analysis shows that migration can have qualitatively different effects, depending on the total mutation target and fitness effects of deleterious variants. In particular, we find that populations exhibit a genetic Allee effect across a wide range of parameter combinations, when variants are partially recessive, cycling between low-load (large-population) and high-load (sink) states. Migration further reduces load in the sink state (by increasing heterozygosity) but increases load in the large-population state (by hindering purging). We identify various critical parameter thresholds at which one or other stable state collapses, and discuss how these thresholds are influenced by the genetic vs. demographic effects of migration. Our analysis is based on a 'semi-deterministic' analysis, which accounts for genetic drift but neglects demographic stochasticity. We also compare against simulations which account for both demographic stochasticity and drift. Our results clarify the importance of gene flow as a key determinant of extinction risk in peripheral populations, even in the absence of ecological gradients.

Migration pulsedness alters patterns of allele fixation and local adaptation in a mainland-island model

Gene flow, through allele migration and spread, is critical in determining patterns of population genetic structure, divergence and local adaptation. While evolutionary theory has typically envisioned gene flow as a continuous connection among populations, many processes can render it fluctuating and intermittent. We analyze mathematically a stochastic mainland-island model in continuous time, in which migration occur as recurrent ''pulses''. We derive simple analytical approximations regarding how migration pulsedness affects the effective migration rates across a range of selection and dominance scenarios. Predictions are validated with stochastic simulations and summarized with graphical interpretations in terms of fixation probabilities. We show that migration pulsedness can decrease or increase gene flow, respectively above or below a selection threshold that is s~-1/N for additive alleles and lower for recessive deleterious alleles. We propose that pulsedness may leave a genomic detectable signature, by differentially affecting the fixation rates of loci subjected to different selection regimes. The additional migration created by pulsedness is called a ''pulsedness'' load. Our results indicate that migration pulsedness, and more broadly temporally variable migration, is important to consider for evolutionary and population genetics predictions. Specifically, it would overall be detrimental to the local adaptation and persistence of small peripheral populations.

Life in the desert: habitat spatial complexity, gene flow, and functional connectivity in Ivesia webberi

Habitat protection, by itself, is not sufficient to conserve range-restricted species with disjunct populations. Indeed, it becomes critical to characterize gene flow among the populations and factors that influence functional connectivity in order to design effective conservation programs for such species. In this study, we genotyped 314 individuals of Ivesia webberi, a United States federally threatened Great Basin Desert perennial forb using six microsatellite loci, to estimate genetic diversity and population genetic structure, as well as rates and direction of gene flow among 16 extant I. webberi populations. We assessed the effects of Euclidean distance, landscape features, and ecological dissimilarity on the genetic structure of the sampled populations, while also testing for a relationship between I. webberi genetic diversity and diversity in the vegetative communities. The results show low levels of genetic diversity overall (He = 0.200–0.441; Ho = 0.192–0.605) and high genetic differentiation among populations. Genetic diversity was structured along a geographic gradient, congruent with patterns of isolation by distance. Populations near the species’ range core have relatively high genetic diversity, supporting a central-marginal pattern, while peripheral populations have lower genetic diversity, significantly higher genetic distances, higher relatedness, and evidence of genetic bottlenecks. Genotype cluster admixture results support a predominant west to east gene flow pattern for populations near the species’ range center, as well as smaller genotype clusters with a narrow north to south distribution and little admixture, suggesting that dispersal direction and distance vary on the landscape. Pairwise genetic distance strongly correlates with actual evapotranspiration and precipitation, indicating a role for isolation by environment, which the observed phenological mismatches among the populations also support. The significant correlation between pairwise genetic distance and dissimilarity in the soil seed bank suggest that annual regeneration of the floristic communities contributes to the maintenance of genetic diversity in I. webberi.

Sibling species as a result of microevolution (a case study of Lepidoptera)

This article is devoted to the problems of diagnosis and taxonomy of sibling species in Lepidoptera of different taxonomic groups. The most important advances in understanding the reality of species include: species are real and objectively exist; each species has specific spatial characteristics and its own biological time, which may not coincide with the physical one. The main criteria for the reality of a species include the following: a certain stability in space and time, isolation from the surrounding world, a certain opposition to the environment; material continuity over time; a certain degree of indivisibility; the presence of special, distinctive properties in relation to other similar systems; the presence of a certain number of degrees of freedom in relation to higher taxa; the presence of a given set of individuals of a lower order, a certain hierarchy of individuals; continuity in space and time. Through the construction of a natural system of phenotypes of the wing pattern, it is possible to build a system of groups of populations of a species and create a population taxonomy, while the phenotype should act as a reliable diagnostic feature of a specific population or groups of populations. In the landscape complex of Lepidoptera populations of a particular geographic region, as a rule, only one of the available forms is the most often found, which is also the most often collected and described as typical. All other forms are found in populations with a lower frequency, so they can be described as atypical, up to giving them the status of new species. This applies primarily to European populations of Lepidoptera, individuals of which were once accepted by taxonomists as typical and therefore received the status of nominative species and subspecies. Individuals from populations at the border of ranges, for example, from mountainous areas, are most often described as new taxa. Quite often, polytypical Lepidoptera species have a wide phenotypic diversity of the wing pattern, which makes rare forms in central populations often found in peripheral populations of the range. Therefore, the species of Lepidoptera should be considered in the light of a biological concept. Based on an integrated approach to studying the phenotypic variability of the wing pattern, it is possible to carry out taxonomic studies of Lepidoptera populations and the separation of sibling species.