Abstract Environmental stress is a fundamental facet of life and a significant driver of natural selection in the wild. Gene expression diversity may facilitate adaptation to environmental changes, ...without necessary genetic change, but its role in adaptive divergence remains largely understudied in Neotropical systems. In Amazonian riparian forests, species distribution is predominantly influenced by species' waterlogging tolerance. The flooding gradient delineates distinct wetland forest types, shaping habitats and species characteristics. Here we investigated the molecular basis of environmental stress response in a tropical ground‐herb species ( Ischnosiphon puberulus ) to environmental variation in Amazonian riparian forests. We compared environmental variables and gene expression profiles from individuals collected in two forest types: Igapó and Terra firme in the Amazonian riparian forests. Predictable seasonal flooding poses a significant challenge in Igapó compared to Terra firme environments, with the former presenting higher water column height and longer flooding duration. Our findings suggest that contrasting environmental conditions related to flooding regimes are important drivers of population genetic differentiation and differential gene expression in I. puberulus . Enriched gene ontology terms highlight associations with environmental stresses, such as defence response, water transport, phosphorylation, root development, response to auxin, salicylic acid and oxidative stress. By uncovering key environmental stress response pathways conserved across populations, I. puberulus offers novel genetic insights into the molecular basis of plant reactions to environmental constraints found in flooded areas of this highly biodiverse neotropical ecosystem.
Studies on insular organisms provide an important framework for investigating patterns of genetic differentiation and reproductive isolation. By focusing on populations of the same species, we have ...the opportunity to study the mechanisms operating during the earliest stages of speciation, as reproductive barriers can be examined among divergent lineages in a geographic context. We investigated the genetic differentiation and the evolution of early stages of intrinsic postmating reproductive isolation between continental and insular populations of
Epidendrum fulgens
, a neotropical orchid distributed in southeastern Brazil. Genetic diversity and structure were estimated for both nuclear and plastid markers by using genetic differentiation measures and model-based assignment test. Furthermore, two components of reproductive isolation were examined by analyzing fruit set and seed viability in interpopulation crosses. Strong plastid genetic structure (
F
ST
= 0.679) was found between insular and remaining populations, indicating that
E
.
fulgens
reduced gene flow via seed dispersal, although significant nuclear genetic structure was lower (
D
ST
= 0.179), likely due to the smaller effective population size of the plastid genome. Significant differences in seed viability between self- and cross-pollinated plants were found, indicating the occurrence of inbreeding depression in all populations. Seed viability was significantly lower in crosses between insular and remaining populations, suggesting a late postzygotic reproductive barrier due to low migration associated with genetic drift (i.e., bottleneck) and its consequences. Our results confirm the importance of islands as drivers for populational differentiation and suggest a central role for outbreeding depression during the early stages of lineage diversification.
Aim
Ancient climatic fluctuations are invoked as the main driving force that generates the astonishing biodiversity in ancient mountains. As a result, endemism and spatial turnover are usually high ...and few species are widespread amongst entire mountain ranges, precluding the understanding of origins of macroevolutionary patterns. Here, we used a species endemic to, but widespread in, one of the most species‐rich ancient mountains in the globe to test how environmental changes acted on and how their macroevolutionary patterns were shaped.
Location
Espinhaço Range, Eastern Brazil.
Taxon
Vriesea oligantha species complex (Bromeliaceae).
Methods
We compiled data for plastidial regions and nuclear microsatellites to assess genetic diversity, population structure, migration rates and phylogenetic relationships. Using temperature and precipitation variables, we modelled suitable areas for the present and the past, estimating corridors between isolated populations. We also implemented Bayesian demographic analyses to estimate ancient populations dynamics. Finally, we tested if population structure is driven by isolation by environment or by distance using a Bayesian modelling approach.
Results
Our results showed that the intraspecific divergence events of V. oligantha are older than those associated with the latest Pleistocene climatic oscillations, supporting the view that Quaternary climatic fluctuations are key components for understanding its population differentiation processes. Species distribution modelling estimated corridors between populations in the past, as also shown in the demographic analyses, depicting a major spatial reorganization during colder climates. Besides, the high genetic structure estimated results from both models of isolation by distance and by environment.
Main conclusions
V. oligantha is a remarkable model to test the effects of climatic oscillations over the biological community, since this species originated in the early‐Pleistocene, prevailing over several cycles of climatic fluctuations until today. The estimated demographic dynamics of V. oligantha agrees with the species‐pump mechanism, suggesting it as the main cause of speciation within the Espinhaço Range. Moreover, the phylogeographic patterns of V. oligantha reflect previously recognised spatial and temporal macroevolutionary patterns in the Espinhaço Range, providing insights into how microevolutionary processes may have given rise to this astonishing mountain biodiversity.
PDF