Molecular Ecology最新文献

Reef-building corals face continued declines due to climate change-amplified marine heatwaves. In addition to affecting coral heat tolerance, corals' algal endosymbionts (family Symbiodiniaceae) can reflect their prior heatwave exposure, although understanding is often limited to heatwave-induced shifts between symbiont genera. Here, we used ITS2 metabarcoding to characterise Symbiodiniaceae assemblages in 293 individuals of the common Indo-Pacific coral Acropora aff. digitifera in Palau (Western Pacific), between two outer-reef regions with contrasting heatwave histories. During the strongest recorded heatwaves, southwestern ‘hotspot’ reefs have typically accrued an additional 2°C-weeks of heat stress compared to thermal ‘refugia’ located 60 km north. In contrast to previous studies that observed declines in symbiont richness following heat stress, we found a greater diversity of symbiont taxa and low-abundance sequence variants in ‘hotspot’ corals, predominantly within the C40 lineage in genus Cladocopium. Combining these data with experimental heatwave performance from 168 of these corals revealed that approximately 10% of heat tolerance variability at hotspot reefs was associated with hosting different symbiont taxa. Compared to other hotspot corals, those hosting symbionts with the C15h sequence variant suffered bleaching mortality at 0.8°C-weeks lower heat stress. Despite higher variability in heat tolerance among corals from thermal refugia compared to hotspot reefs, we found no association between heat tolerance and the symbionts hosted by refugium corals. As the world's coral reefs are exposed to intensifying marine heatwaves under accelerating climate change, the low-abundance variants that characterise symbionts within genera or lineages may become increasingly important indicators of poor heatwave tolerance.

Marine microbial communities are structured by a complex interplay of deterministic and stochastic processes, yet how these vary across latitudes remains poorly understood. Most long-term microbial observatories are restricted to temperate regions, limiting our ability to assess latitudinal contrasts in microbial dynamics. Here, we compare coastal microbial communities from two contrasting marine time-series stations using standardised molecular protocols: a new tropical site in the Equatorial Atlantic (EAMO, 6° S) and a well-studied temperate site in the Mediterranean Sea (BBMO, 41° N). Monthly 16S and 18S rRNA gene sequencing of two size-fractions (0.22–3 μm and > 3 μm) over 41 months (from April 2013 to August 2016) revealed marked differences in taxonomic composition, temporal variability and ecological assembly processes. Temperate communities exhibited strong seasonal turnover, higher beta-diversity and tighter coupling with environmental variables such as temperature and daylength. In contrast, tropical communities were compositionally more stable and more governed by biotic factors and stochastic processes such as historical contingency and ecological drift. These patterns were consistent across taxonomic domains and size-fractions, though selection was generally stronger in prokaryotes and the smallest size-fraction. Co-occurrence networks at the temperate site were more densely connected and environmentally responsive compared to tropical networks, where stochastic processes and putative biological interactions gain prominence. This study highlights the importance of integrating observatories from underrepresented latitudes into global microbial monitoring efforts, particularly as climate change alters the amplitude and frequency of environmental drivers across the ocean.

Sympatric morphs provide valuable systems for studying incipient divergence despite incomplete reproductive isolation. In connected waterbodies with spatially heterogeneous habitats, one or more morphs may form metapopulation structures, generating eco-evolutionary dynamics unlike those in single lakes. We studied the phenotypic and genome-wide differentiation in Arctic charr (Salvelinus alpinus) in two Icelandic lakes: Thingvallavatn, known to harbour four distinct morphs, and a smaller downstream lake, Ulfljotsvatn. Our analyses confirm a single origin of charr polymorphism in this system, with all morphs present in both lakes. Relative morph abundances differ between the lakes: PL-charr dominate in Thingvallavatn, whereas LB-charr are most abundant in Ulfljotsvatn. Three morphs, large- (LB-), small (SB-) benthivorous and planktivorous (PL-) charr, are genetically distinct. The system likely forms a source-sink structure for both PL- and SB-charr, though migration rates from Thingvallavatn vary remarkably, resulting in distinct population dynamics. Conversely, LB-charr exhibit genetic differentiation between the lakes, suggesting the presence of a separate population in Ulfljotsvatn. While piscivorous (PI-) charr appear genetically similar to PL-charr, evidence suggests hybridisation between PI- and LB-charr in both lakes. Moreover, the higher hybridisation in the downstream lake likely contributes to the observed erosion of genetic separation between LB- and PL-charr in Ulfljotsvatn. These findings suggest that the complex interplay of habitat heterogeneity and morph-specific migrations shapes the coexistence and eco-evolutionary dynamics of sympatric charr morphs in the connected lakes. Our study highlights the importance of investigating early divergence in spatially complex systems to advance eco-evolutionary research.

Gossypium hirsutum is the world's most important source of cotton fibre, yet the diversity and population structure of its wild forms remain largely unexplored. The complex domestication history of G. hirsutum combined with reciprocal introgression with a second domesticated species, G. barbadense, has generated a wealth of morphological forms and feral derivatives of both species and their interspecies recombinants, which collectively are scattered across a large geographic range in arid regions of the Caribbean basin. Here we assessed genetic diversity within and among populations from two Caribbean islands, Puerto Rico (n = 43, five sites) and Guadeloupe (n = 25, one site), which contain putative wild or introgressed forms. Using whole-genome resequencing data and a phylogenomic framework derived from a broader genomic survey, we parsed individuals into feral derivatives and truly wild forms. Feral cottons display uneven levels of genetic and morphological resemblance to domesticated cottons, with diverse patterns of genetic variation and heterozygosity. These patterns are inferred to reflect a complex history of interspecific and intraspecific gene flow that is spatially highly variable in its effects. Wild cottons in both Caribbean islands appear to be relatively inbred, especially the Guadeloupe samples. Our results highlight the dynamics of population demographics in relictual wild cottons that experienced profound genetic bottlenecks associated with repeated habitat destruction superimposed on a natural ecogeographical distribution comprising widely scattered populations. These results have implications for conservation and utilisation of wild diversity in G. hirsutum.

Temperature is a key determinant of survival and distribution in ectothermic species, but how variation in thermal resilience is influenced by developmental transitions, life-history strategies, and their interaction with population-specific genomic variation is poorly understood. Using Chinook salmon (Oncorhynchus tshawytscha), an ecologically and culturally important species of conservation concern, we investigated how population-specific life histories influence thermal tolerance and its underlying genomic architecture. We assessed thermal tolerance using critical thermal maximum (CT_max), a nonlethal measure of acute thermal tolerance that determines the temperature at which fish can no longer maintain equilibrium during a thermal ramp. CT_max was measured in four populations representing two life-history types, stream-type and ocean-type, that differ in freshwater residency and age at smoltification. Stream-type populations exhibited lower CT_max than ocean-type populations in both freshwater and saltwater, revealing consistent life-history differences in thermal tolerance. Smoltification significantly reduced CT_max across all populations, indicating that physiological transformation for seawater readiness comes at a cost to thermal performance. Thermal tolerance was more variable in saltwater, highlighting the influence of environmental context on phenotypic expression. Although populations exhibited distinct genetic variants and expression profiles, all populations showed enrichment of common functional pathways, including the unfolded protein response and ion transport. These findings suggest that similar physiological outcomes are achieved through distinct regulatory architectures across life-history types and developmental stages. Together, our results provide insight into the polygenic nature of thermal tolerance in Chinook salmon, emphasising how life history, environment and genetic background interact to shape resilience to thermal stress.

Insects are highly reliant on chemical cues such as pheromones to facilitate communication and navigation. Some of the roles of pheromones include attracting and finding mates and conspecifics, and in these cases, we expect stabilising selection to dampen within-population pheromone variation. On the other hand, standing pheromone variation may lead to barriers to gene flow and saltational shifts that facilitate divergence and speciation. We investigated the relationships between pheromone variation and genetic variation in the spruce beetle, Dendroctonus rufipennis Kirby, a bark beetle that infests spruce. We found no convincing associations between genetic variation and pheromone variation in the spruce beetle. Instead, our results suggest that stabilising selection has acted to harmonise regional pheromone blends, including those of different sympatric clades, while pheromone blends differ regionally even within the same clade. Individual pheromone variation within regions cannot be attributed to phylogenetics and is instead partly explained by the identity of the natal tree, suggesting an environmental influence of host tree chemistry. Our results show that stabilising selection is not absolute, and that other opposing forces, such as co-evolution and environmental influences, could contribute to within-population variation.