Biology subjects

Landis, J. B.

Publications and source records attributed to Landis, J. B..

24 records · Page 2Linked to original sources

bioRxiv2020

Migration through a major Andean ecogeographic disruption as a driver of genotypic and phenotypic diversity in a wild tomato species

The large number of species on our planet arises from the phenotypic variation and reproductive isolation occurring at the population level. In this study, we sought to understand the origins of such population-level variation in defensive acylsugar chemistry and mating systems in Solanum habrochaites - a wild tomato species found in diverse Andean habitats in Ecuador and Peru. Using Restriction-Associated-Digestion Sequencing (RAD-seq) of 50 S. habrochaites accessions, we identified eight population clusters generated via isolation and hybridization dynamics of 4-6 ancestral populations. Estimation of heterozygosity, fixation index, isolation by distance, and migration probabilities, allowed identification of multiple barriers to gene flow leading to the establishment of extant populations. One major barrier is the Amotape-Huancabamba Zone (AHZ) - a geographical feature in the Andes with high endemism, where the mountainous range breaks up into isolated microhabitats. The AHZ was associated with emergence of alleles for novel reproductive and acylsugar phenotypes. These alleles led to the evolution of self-compatibility in the northern populations, where alleles for novel defense-related enzyme variants were also found to be fixed. We identified geographical distance as a major force causing population differentiation in the central/southern part of the range, where S. habrochaites was also inferred to have originated. Findings presented here highlight the role of the diverse ecogeography of Peru and Ecuador in generating new, reproductively isolated populations, and enhance our understanding of the microevolutionary processes that lay a path to speciation.

plant biology↗

bioRxiv2020

Chromosome fusions shape an ancient UV sex chromosome system

Non-recombining sex chromosomes, like the mammalian Y, often lose genes and accumulate transposable elements, a process termed degeneration1,2. The correlation between suppressed recombination and degeneration is clear in animal XY systems1,2, but the absence of recombination is confounded with other asymmetries between the X and Y. In contrast, UV sex chromosomes, like those found in bryophytes, experience symmetrical population genetic conditions3,4. Here we test for degeneration in the bryophyte UV sex chromosome system through genomic comparisons with new female and male chromosome-scale reference genomes of the moss Ceratodon purpureus. We show that the moss sex chromosomes evolved over 300 million years ago and expanded via two chromosomal fusions. Although the sex chromosomes show signs of weaker purifying selection than autosomes, we find suppressed recombination alone is insufficient to drive gene loss on sex-specific chromosomes. Instead, the U and V sex chromosomes harbor thousands of broadly-expressed genes, including numerous key regulators of sexual development across land plants.

evolutionary biology↗

bioRxiv2020

Plastome phylogenomic study of Gentianeae (Gentianaceae): widespread gene tree discordance and its association with evolutionary rate heterogeneity of plastid genes

BackgroundPlastome-scale data have been prevalent in reconstructing the plant Tree of Life. However, phylogenomic studies currently based on plastomes rely primarily on maximum likelihood (ML) inference of concatenated alignments of plastid genes, and thus phylogenetic discordance produced by individual plastid genes has generally been ignored. Moreover, structural and functional characteristics of plastomes indicate that plastid genes may not evolve as a single locus and are experiencing different evolutionary forces, yet the genetic characteristics of plastid genes within a lineage remain poorly studied. ResultsWe sequenced and annotated ten plastome sequences of Gentianeae. Phylogenomic analyses yielded robust relationships among genera within Gentianeae. We detected great variation of gene tree topologies and revealed more than half of the genes, including one (atpB) of the three widely used plastid markers (rbcL, atpB and matK) in phylogenetic inference of Gentianeae, are likely contributing to phylogenetic ambiguity of Gentianeae. Estimation of nucleotide substitution rates showed extensive rate heterogeneity among different plastid genes and among different functional groups of genes. Comparative analysis suggested that the ribosomal protein (RPL and RPS) genes and the RNA polymerase (RPO) genes have higher substitution rates and genetic variations in Gentianeae. Our study revealed that just one (matK) of the three (matK, ndhB and rbcL) widely used markers show high phylogenetic informativeness (PI) value. Due to the high PI and lowest gene-tree discordance, rpoC2 is advocated as a promising plastid DNA barcode for taxonomic studies of Gentianeae. Furthermore, our analyses revealed a positive correlation of evolutionary rates with genetic variation of plastid genes, but a negative correlation with gene-tree discordance under purifying selection. ConclusionsOverall, our results demonstrate the heterogeneity of nucleotide substitution rates and genetic characteristics among plastid genes providing new insights into plastome evolution, while highlighting the necessity of considering gene-tree discordance into phylogenomic studies based on plastome-scale data.

evolutionary biology↗

bioRxiv2020

Genome wide sequencing provides evidence of adaptation to heterogeneous environments for the ancient relictual Circaeaster agrestis (Circaeasteraceae, Ranunculales)

O_LIInvestigating the interaction between environmental heterogeneity and local adaptation is critical to understand the evolutionary history of a species, providing the premise for studying the response of organisms to rapid climate change. However, for most species how exactly the spatial heterogeneity promotes population divergence and how genomic variations contribute to adaptive evolution remain poorly understood. C_LIO_LIWe examine the contributions of geographical and environmental variables to population divergence of the relictual, alpine herb Circaeaster agrestis, as well as genetic basis of local adaptation using RAD-seq and plastome data. C_LIO_LIWe detected significant genetic structure with an extraordinary disequilibrium of genetic diversity among regions, and signals of isolation-by-distance along with isolation-by-resistance. The populations were estimated to begin diverging in the late Miocene, along with a possible ancestral distribution of the Hengduan Mountains and adjacent regions. Both environmental gradient and redundancy analyses revealed significant association between genetic variation and temperature variables. Genome-environment association analyses identified 16 putatively adaptive loci related to biotic and abiotic stress resistance. C_LIO_LIOur genome wide data provide new insights into the important role of environmental heterogeneity in shaping genetic structure, and access the footprints of local adaptation in an ancient relictual species, informing conservation efforts. C_LI

evolutionary biology↗

bioRxiv2020

The draft genome of the endangered, relictual plant Kingdonia uniflora (Circaeasteraceae, Ranunculales) reveals potential mechanisms and perils of evolutionary specialization

Kingdonia uniflora, an alpine herb, has an extremely narrow distribution and represents a model for studying evolutionary mechanisms of species that have adapted to undisturbed environments for evolutionary long periods of time. We assembled a 1,004.7-Mb draft genome (encoding 43,301 genes) and investigated the evolutionary history of K. uniflora, along with mechanisms related to its endangered status. Phylogenomic analyses based on 497 single copy genes confirmed the sister relationship between K. uniflora and Circaeaster agrestis, which were estimated to have diverged around 52 Mya. Proliferation of LTR retrotransposons in K. uniflora is estimated to occur around 2.7 Mya, coinciding with one recent uplift of the Hengduan Mountains between the late Miocene and late Pliocene. Across 12 species of monocots, early-diverging eudicots and core eudicots, K. uniflora showed significant overrepresentation in gene families associated with DNA repair and underrepresentation in gene families associated with stress response. Most of the plastid ndh genes were found to be lost not only in the plastome but also in the nuclear genome of K. uniflora. During the evolutionary process, the overrepresentation of gene families involved in DNA repair could help asexual K. uniflora reduce the accumulation of deleterious mutations, while at the same time, reducing genetic diversity which is important in responding to environment fluctuations. The underrepresentation of gene families related to stress response and functional loss of ndh genes could be due to lack or loss of ability to respond to environmental changes caused by long-term adaptation to a relatively stable ecological environment.

genomics↗

bioRxiv2019

Accelerated diversification correlated with functional traits shapes extant diversity of the early divergent angiosperm family Annonaceae

BackgroundA major goal of phylogenetic systematics is to understand both the patterns of diversification and the processes by which these patterns are formed. Few studies have focused on the ancient, species-rich Magnoliales clade and its diversification pattern. Within Magnoliales, the pantropically distributed Annonaceae are by far the most genus-rich and species-rich family-level clade, with c. 110 genera and c. 2,400 species. We investigated the diversification patterns across Annonaceae and identified traits that show varied associations with diversification rates using a time-calibrated phylogeny of 835 species (34.6% sampling) and 11,211 aligned bases from eight regions of the plastid genome (rbcL, matK, ndhF, psbA-trnH, trnL-F, atpB-rbcL, trnS-G, and ycf1). Two hypotheses that might explain patterns of diversification--the museum model and heterogeneous diversification rates--are also evaluated.\n\nResultsTwelve rate shifts were identified using BAMM: in Annona, Artabotrys, Asimina, Drepananthus, Duguetia, Goniothalamus, Guatteria, Uvaria, Xylopia, the tribes Miliuseae and Malmeeae, and the Desmos-Dasymaschalon-Friesodielsia-Monanthotaxis clade (which collectively account for over 80% of the total species richness in the family). TurboMEDUSA and method-of-moments estimator analyses showed largely congruent results. A positive relationship between species richness and diversification rate is revealed using PGLS. We further explore the possible role of selected traits (habit, pollinator trapping, floral sex expression, pollen dispersal unit, anther septation, and seed dispersal unit) in shaping diversification patterns, based on inferences of BiSSE, MuSSE, HiSSE, and FiSSE analyses. Our results suggest that the liana habit, the presence of circadian pollinator trapping, androdioecy, and the dispersal of seeds as single-seeded monocarp fragments are closely correlated with higher diversification rates; pollen aggregation and anther septation, in contrast, are associated with lower diversification rates.\n\nConclusionOur results show that the high species richness in Annonaceae is likely the result of recent increased diversification rather than the steady accumulation of species via the museum model. BAMM, turboMEDUSA, and the method-of-moments estimator all indicate heterogeneity in diversification rates across the phylogeny, with different traits associated with shifts in diversification rates in different Annonaceae clades.

evolutionary biology↗