Population structure in Neotropical plants: integrating pollination biology, topography and climatic niches

Animal pollinators mediate gene flow among plant populations, but, in contrast to well-studied topographic and (Pleistocene) environmental isolating barriers, their impact on population genetic differentiation remains largely unexplored. Comparatively investigating how these multifarious factors drive microevolutionary histories is, however, crucial for better resolving macroevolutionary patterns of plant diversification. We here combined genomic analyses with landscape genetics and niche modelling across six related Neotropical plant species (424 individuals across 33 localities) differing in pollination strategy to test the hypothesis that highly mobile (vertebrate) pollinators more effectively link isolated localities than less mobile (bee) pollinators. We found consistently higher genetic differentiation (FST) among localities of bee- than vertebrate-pollinated species with increasing geographic distance, topographic barriers and historic climatic instability. High admixture among montane populations further suggested relative climatic stability of Neotropical montane forests during the Pleistocene. Overall, our results indicate that pollinators may differentially impact the potential for allopatric speciation, thereby critically influencing diversification histories at macroevolutionary scales.

Anthropogenic restocking of gharial individuals prevents genetic isolation of gharial population in Girwa River, India by geographic barriers imposed by a barrage

Gharial (Gavialis gangeticus) is a critically endangered fresh water crocodile endemic to the Indian subcontinent. The species has suffered > 95% decline in population and habitat size. A small population of gharials comprising of 50 breeding adults is resident in a 20 Km stretch of the River Girwa in Katerniaghat wildlife sanctuary, India. Gharials in this 20 Km stretch have been genetically isolated since 1976 by a barrage that functions as a barrier to gene flow. A captive rear and release program has been initiated since 1979 under Project Crocodile for restocking declining wild gharial populations. Thousands of gharial eggs were collected from gharial populations at Girwa and Chambal Rivers. Hatchlings from the collected eggs were captive reared at a common location in Kukrail Gharial Centre, India and released back to multiple gharial populations including the isolated population at Girwa. This restocking programme was not preceded by a genetic screening of captive animals or wild populations to identify genetic diversity and genetic structure of both captive and wild animals. In this study we investigate whether release of captive reared gharials into the resident population at Girwa River has prevented genetic isolation caused due to barriers imposed by the barrage. Using a combination of empirical analysis using microsatellite markers and a systematic review of data from previous workers on molecular characterization of gharial populations, we analysed genetic differentiation in gharial populations at Girwa and Chambal. We found similar genetic variability in gharial populations of Girwa and Chambal. There was low inter population genetic differentiation and evidences of genetic migration between the two populations. Our findings indicate that anthropogenic intervention via release of captive animals has compensated for the genetic isolation in Girwa population caused by the barrage.

Unangan (Aleut) Migrations

There were diverse causes and demographic and evolutionary consequences of migration of the Unangan (a.k.a. Aleut) people in their expansion from Siberia through the Aleutian archipelago. The causes included subsistence patterns, volcanic eruptions that destroyed island econiches, climatic changes that calmed the seas and made interisland migrations possible, and cultural contacts as well as forcible relocations. The consequences of the migrations included an intimate relationship between genetics, as revealed by mitochondrial DNA, and geography; loss of genetic diversity due to population fission along kin groups; creation of genetic barriers due to periodic climatic limitations to migrations; population genetic differentiation due to kin migration and founder effect; and admixture with Russian administrators and military in the western and central islands and with fishermen of English and Scandinavian ancestry in the eastern islands.

ISSR markers and population differentiations in Erodium ciconium (L.) L'hér ex Aiton

Erodium ciconium is an important grazing plant and a source of protein supplements to straw for ruminants in semideserts and wastelands of the Middle East. There is no information on its population genetic structure, genetic diversity, and morphological variability in Iran. We performed molecular data for knowing the population differentiation in this species. For this study, we used 110 randomly collected plants from 15 geographical populations in 6 provinces of Iran. AMOVA test revealed significant genetic difference among the studied populations and also revealed that, 63% of total genetic variability was due to within population diversity while, 37% was due to among population genetic differentiation. Mantel test showed positive significant correlation between genetic distance and geographical distance of the studied populations. Networking, STRUCTURE analyses revealed some degree of gene flow among these populations. Bangladesh J. Plant Taxon. 28(1): 61-73, 2021 (June)

Geography is more important than life history in the recent diversification of the tiger salamander complex

The North American tiger salamander species complex, including its best-known species, the Mexican axolotl, has long been a source of biological fascination. The complex exhibits a wide range of variation in developmental life history strategies, including populations and individuals that undergo metamorphosis; those able to forego metamorphosis and retain a larval, aquatic lifestyle (i.e., paedomorphosis); and those that do both. The evolution of a paedomorphic life history state is thought to lead to increased population genetic differentiation and ultimately reproductive isolation and speciation, but the degree to which it has shaped population- and species-level divergence is poorly understood. Using a large multilocus dataset from hundreds of samples across North America, we identified genetic clusters across the geographic range of the tiger salamander complex. These clusters often contain a mixture of paedomorphic and metamorphic taxa, indicating that geographic isolation has played a larger role in lineage divergence than paedomorphosis in this system. This conclusion is bolstered by geography-informed analyses indicating no effect of life history strategy on population genetic differentiation and by model-based population genetic analyses demonstrating gene flow between adjacent metamorphic and paedomorphic populations. This fine-scale genetic perspective on life history variation establishes a framework for understanding how plasticity, local adaptation, and gene flow contribute to lineage divergence. Many members of the tiger salamander complex are endangered, and the Mexican axolotl is an important model system in regenerative and biomedical research. Our results chart a course for more informed use of these taxa in experimental, ecological, and conservation research.

Evolutionary implications of recombination differences across diverging populations of Anopheles

Recombination is one of the main evolutionary mechanisms responsible for changing the genomic architecture of populations; and in essence, it is the main mechanism by which novel combinations of alleles, haplotypes, are formed. A clear picture that has emerged across study systems is that recombination is highly variable, even among closely related species. However, it is only until very recently that we have started to understand how recombination variation between populations of the same species impact genetic diversity and divergence. Here, we used whole-genome sequence data to build fine-scale recombination maps for nine populations within two species of Anopheles, Anopheles gambiae and Anopheles coluzzii. The genome-wide recombination averages were on the same order of magnitude for all populations except one. Yet, we identified significant differences in fine-scale recombination rates among all population comparisons. We report that effective population sizes, and presence of a chromosomal inversion has major contribution to recombination rate variation along the genome and across populations. We identified over 400 highly variable recombination hotspots across all populations, where only 9.6% are shared between two or more populations. Additionally, our results are consistent with recombination hotspots contributing to both genetic diversity and absolute divergence (dxy) between populations and species of Anopheles. However, we also show that recombination has a small impact on population genetic differentiation as estimated with FST. The minimal impact that recombination has on genetic differentiation across populations represents the first empirical evidence against recent theoretical work suggesting that variation in recombination along the genome can mask or impair our ability to detect signatures of selection. Our findings add new understanding to how recombination rates vary within species, and how this major evolutionary mechanism can maintain and contribute to genetic variation and divergence within a prominent malaria vector.

Genetic differentiation can be predicted from observational data for reproductive but not vegetative traits in a widespread short-lived plant

Phenotypic plasticity can mask population genetic differentiation, reducing the predictability of trait-environment relationships. In short-lived plants, reproductive traits may be more genetically determined due to their direct impact on fitness, whereas vegetative traits may show higher plasticity to buffer short-term perturbations. Combining a multi-treatment greenhouse experiment with global field observations for the short-lived Plantago lanceolata, we 1) disentangled the genetic and plastic responses of functional traits to a set of environmental drivers and 2) assessed the utility of trait-environment relationshisps inferred from observational data for predicting genetic differentiation. Reproductive traits showed distinct genetic differentiation that was highly predictable from observational data, but only when correcting traits for differences in their (labile) biomass component. Vegetative traits showed higher plasticity and contrasting genetic and plastic responses, leading to unpredictable trait patterns. Our study suggests that genetic differentiation may be inferred from observational data only for the traits most closely related with fitness.

Population genetic structure and gene flow in Alcea aucheri (Boiss.) Alef.: A potential medicinal plant

The genus Alcea, a member of Malvaceae family consists of approximately 75 species worldwide distributing mainly in South-West Asia. Among these, 33 species grow in Iran. Plants of the Alcea (or Althaea) are among important medicinal plants in Iranian traditional medicine. They have long been used in the treatment of health problems and diseases. Alcea aucheri (Boiss.) Alef. species are distributed in different habitats of Iran. There is no information on its population genetic structure, genetic diversity, and morphological variability in Iran. Therefore, due to the importance of these plant species, we performed a combination of morphological and molecular data for this species. For this study, we used 118 randomly collected plants from 10 geographical populations in 5 provinces. AMOVA test revealed significant genetic difference among the studied populations and also revealed that, 74% of total genetic variability was due to within population diversity while, 26% was due to among population genetic differentiation. Mantel test showed positive significant correlation between genetic distance and geographical distance of the studied populations. Networking, STRUCTURE analyses revealed some degree of gene flow among these populations.

Spatial Structure and Genetic Variation of a Mangrove Species (Avicennia marina (Forssk.) Vierh) in the Farasan Archipelago

Avicennia marina (Forssk.) Vierh is distributed in patches along the Farasan archipelago coast and is the most common mangrove species in the Red Sea. However, to date, no studies have been directed towards understanding its genetic variation in the Farasan archipelago. In this investigation, genetic variations within and among natural populations of Avicennia marina in the Farasan archipelago were studied using 15 microsatellite markers. The study found 142 alleles on 15 loci in nine populations. The observed (Ho) and expected (He) heterozygosity values were 0.351 and 0.391, respectively, which are much lower than those of earlier studies on A. marina in the Arabian Gulf. An inbreeding effect from self-pollination might explain its heterozygote deficiency. Population genetic differentiation (FST = 0.301) was similar to other mangrove species. Our findings suggest that the sea current direction and coastal geomorphology might affect genetic dispersal of A. marina. The more isolated populations with fewer connections by sea currents exhibited lower genetic variation and differentiation between populations. The genetic clustering of populations fell into three main groups—Group 1 (populations of Farasan Alkabir Island), Group 2 (populations of Sajid Island), and Group 3 (mix of one population of Farasan Alkabir Island and a population of Zifaf Island). More genetic variation and less genetic differentiation occurred when the population was not isolated and had a direct connection with sea currents. Both of these factors contributed to limited propagule dispersal and produced significant structures among the population. It is expected that the results of this research will be useful in determining policy and species-conservation strategies and in the rehabilitation of A. marina mangrove stands on the Farasan islands in an effort to save this significant natural resource.