Biology subjects

Weigel, B. L.

Publications and source records attributed to Weigel, B. L..

4 recordsLinked to original sources

bioRxiv2024

Population genomics reveals strong impacts of genetic drift without purging and guides conservation of bull and giant kelp

Kelp forests are declining in many parts of the northeast Pacific1-4. In small populations, genetic drift can reduce adaptive variation and increase fixation of recessive deleterious alleles5-7, but natural selection may purge harmful variants8-10. To understand evolutionary dynamics and inform restoration strategies, we investigated genetic structure and the outcomes of genetic drift and purging by sequencing the genomes of 429 bull kelp (Nereocystis luetkeana) and 211 giant kelp (Macrocystis pyrifera sensu lato11; cf. 12) from the coastlines of British Columbia and Washington. We identified 6-7 geographically and genetically distinct clusters in each species. Low effective population size was associated with low genetic diversity and high inbreeding coefficients (including increased selfing rates), with extreme variation in these genetic health indices among bull kelp populations but more moderate variation in giant kelp. We found no evidence that natural selection is purging putative recessive deleterious alleles in either species. Instead, genetic drift has fixed many such alleles in small populations of bull kelp, leading us to predict (1) reduced within-population inbreeding depression in small populations, which may be associated with an observed shift toward increased selfing rate, and (2) hybrid vigour in crosses between small populations. Our genomic findings imply several strategies for optimal sourcing and crossing of populations for restoration and aquaculture, but which require experimental validation. Overall, our work reveals strong genetic structure and suggests that conservation strategies should consider the multiple health risks faced by small populations whose evolutionary dynamics are dominated by genetic drift.

evolutionary biology↗

bioRxiv2024

Taxonomy and phylogeny of the family Suberitidae (Porifera: Demospongiae) in California

This study presents a comprehensive taxonomic revision of the family Suberitidae (Porifera: Demospongiae) for California, USA. We include the three species previously known from the region, document two additional species previously known from other regions, and formally describe four new species as Pseudosuberites latke sp. nov., Suberites californiana sp. nov., Suberites kumeyaay sp. nov., and Suberites agaricus sp. nov. Multi-locus DNA sequence data is presented for seven of the nine species, and was combined with all publicly available data to produce the most comprehensive global phylogeny for the family to date. By integrating morphological and genetic data, we show that morphological characters may be sufficient for regional species identification but are likely inadequate for global classification into genera that reflect the evolutionary history of the family. We therefore propose that DNA sequencing is a critical component to support future taxonomic revisions.

zoology↗

bioRxiv2022

The diversity and functional capacity of microbes associated with coastal phototrophs

Coastal marine phototrophs exhibit some of the highest rates of primary productivity in the world. They have been found to host a diverse set of microbes, many of which may impact the biology of their phototroph hosts through metabolisms that are unique to microbial taxa. Here we characterized the metabolic functions of phototroph-associated microbial communities using metagenomes collected from 2 species of kelp (Laminaria setchellii and Nereocystis luetkeana) and 3 marine angiosperms (Phyllospadix scouleri, P. serrulatus and Zostera marina), including the rhizomes of two surfgrass species (Phyllospadix spp.) and the seagrass Zostera marina, and the sediments surrounding P. scouleri and Z. marina. Using metagenomic sequencing, we describe 72 metagenome assembled genomes (MAGs) that potentially benefit from being associated with macrophytes and may contribute to macrophyte fitness through their metabolic gene content. All host-associated metagenomes contained genes for the use of dissolved organic matter from hosts and vitamin (B1, B2, B7, B12) biosynthesis. Additionally, we found a range of nitrogen metabolism genes that transform dissolved inorganic nitrogen into forms that may be more available to the host. The rhizosphere of surfgrass and seagrass contained genes for anaerobic microbial metabolisms, including nifH genes associated with nitrogen fixation, despite residing in a well-mixed and oxygenated environment. The range of oxygen environments engineered by macrophytes likely explains the diversity of both oxidizing and reducing microbial metabolisms, and contributes to the functional capabilities of microbes and their influence on carbon and nitrogen cycling in nearshore ecosystems. ImportanceKelps, seagrasses and surfgrasses are ecosystem engineers on rocky shorelines where they show remarkably high levels of primary production. Through analysis of their associated microbial communities, we found a variety of microbial metabolisms that may benefit the host, including nitrogen metabolisms and the production of B vitamins. In turn, these microbes have the genetic capability to assimilate the dissolved organic compounds released by their phototroph hosts. We describe a range of oxygen environments associated with surfgrass, including low-oxygen microhabitats in their rhizomes that host genes for nitrogen fixation. The tremendous productivity of coastal phototrophs is likely due in part to the activities of associated microbes and an increased understanding of these associations is needed.

ecology↗

bioRxiv2020

Spatial organization of the kelp microbiome at micron scales

Macroalgae are colonized by complex and diverse microbial communities that are distinct from those on inert substrates, suggesting intimate symbioses that likely play key roles in both macroalgal and bacterial biology. Canopy-forming kelp fix teragrams of carbon per year in coastal kelp forest ecosystems, yet little is known about the structure and development of their associated microbial communities. We characterized the spatial organization of bacterial communities on blades of the canopy-forming kelp Nereocystis luetkeana using fluorescence in situ hybridization and spectral imaging with a probe set combining phylum, class and genus-level probes to target >90% of the microbial community. We show that kelp blades host a dense microbial biofilm, generally less than 20 m thick, in which disparate microbial taxa live in close contact with one another. The biofilm is spatially differentiated, with tightly clustered cells of the dominant symbiont Granulosicoccus sp. (Gammaproteobacteria) close to the kelp surface and filamentous Bacteroidetes and Alphaproteobacteria relatively more abundant near the biofilm-seawater interface. Further, a community rich in Bacteroidetes colonized the interior of kelp tissues. Microbial community structure and cell density increased along the length of the kelp blade, from sparse microbial colonization of newly produced tissues at the meristematic base of the blade to an abundant microbial biofilm on older tissues at the blade tip. Finally, kelp from a declining population hosted fewer microbial cells compared to kelp from a stable population, indicating that biofilms are characteristic of health and that biofilm loss may be related to the condition of the host. ImportanceThe microbial community coating the surfaces of macroalgae may play a key but underexplored role both in the biology of the macroalgal host and in the biogeochemistry of the coastal ocean. We show that photosynthetic blades of the canopy-forming kelp Nereocystis luetkeana host a complex microbial biofilm that is both dense and spatially differentiated. Microbes of different taxa are in intimate cell-to-cell contact with one another; microbial cells invade the interior of kelp cells as well as cover their external surfaces; and a subset of the surface microbiota projects into the water column. These results highlight the potential for metabolic interactions between key members of the kelp microbiome as well as between microbes and their host. The dense layer of microbes coating the surface of the kelp blade is well-positioned to mediate interactions between the host and surrounding organisms and to modulate the chemistry of the surrounding water column.

microbiology↗