Biology subjects

Krueger-Hadfield, S. A.

Publications and source records attributed to Krueger-Hadfield, S. A..

7 recordsLinked to original sources

bioRxiv2026

Environmentally-determined symbiont communities highlight flexibility of Aiptasia-algal symbiosis

The mechanisms driving host-symbiont associations across space and time in contemporary mutualisms can give insight into the capacity for symbiotic organisms to respond to environmental change. High specificity between partners can increase cooperation and facilitate efficient holobiont selection, whereas low specificity could reduce host benefit, but facilitate adaptive associations across heterogeneous environments. The present study explores specificity in natural populations of a cnidarian-algal model, Exaiptasia diaphana, across a latitudinal gradient to understand the genetic and environmental effects driving host-symbiont associations, and their relation to heritable and/or environmental symbiont acquisition. We found that symbiotic associations were extremely flexible in E. diaphana, regardless of transmission mode. E. diaphana were capable of associating with diverse symbiont communities across genetically identical hosts seeded with vertically transmitted symbionts, as well as across highly connected host populations which acquire symbionts horizontally. Host population connectivity was complex and unrelated to geographic distance, whereas symbiont community composition tracked the thermal gradient, potentially due to context dependent biotic interactions. These results indicate that in a flexible symbiosis, symbiont communities are environmentally-determined, suggesting the future of this symbiosis will likely depend on climate adaptation of symbionts.

ecology↗

bioRxiv2025

THE CONSEQUENCES OF PARTIAL CLONALITY ON THE SPATIOTEMPORAL GENETIC STRUCTURE OF THE RED ALGA CHONDRIA TUMULOSA (CERAMIALES, RHODOPHYTA)

The relative rates of sexual versus clonal reproduction partition genetic diversity but the quantification of these rates remains limited in natural populations. This knowledge gap is particularly acute among tropical macroalgae. Chondria tumulosa is a red macroalga that has been documented at high abundance in the three northernmost atolls in the Papah[a]naumoku[a]kea Marine National Monument. We sampled thalli at Manawai in 2021 and 2023, at Kuaihelani in 2022 and 2023, and at H[o]lanik[u] in 2023 to characterize the reproductive mode and patterns of gene flow. Tetrasporophytes overwhelmingly dominated at all sites, atolls, and years, although eight cystocarpic female gametophytes (<1%) were documented for the first time. We observed evidence of very high clonal rates, accompanied by an increase in homozygosity. Surprisingly, our temporal analyses suggested site-specific trends in the predominance of selfing, outcrossing, or clonality. A very small haploid proportion combined with high genetic drift likely rendered temporal analyses of genotypic frequencies challenging to implement and interpret whereby point estimates were a better reflection of reproductive mode variation. Genetic differentiation increased with geographic distance, with strong temporal and spatial structure. The patterns of genetic diversity and structure combined with the dominance of tetrasporophytes suggest that C. tumulosa thalli were introduced to this region, possibly via marine debris. Future studies should focus on identifying the native range to document the ecological and evolutionary shifts that have facilitated the rapid increase and spread of C. tumulosa and its potential similarities to other invasive haploid-diploid algae.

evolutionary biology↗

bioRxiv2025

THE HARD AND SOFT OF IT: THE ROLE OF SUBSTRATE IN PATTERNS OF PHASE DOMINANCE AND PHENOLOGY IN GRACILARIA VERMICULOPHYLLA

Despite the importance of the seasonal timing of life cycle events for understanding population dynamics, we lack information on the phenology of most macroalgal species. The red macroalga Gracilaria vermiculophylla is now common in both hard and soft bottom habitats following its invasion throughout the Northern Hemisphere. In sites with sufficient hard substratum, thalli are fixed by holdfasts to hard substrate. By contrast, in sites with soft substratum, thalli are free-living and either drift free-floating or anchored by the tube building polychaete Diopatra cuprea. The difference in substrate type has profound implications on the evolutionary ecology of G. vermiculophylla populations whereby the life cycle is disrupted in soft bottom habitats leading to tetrasporophytic dominance. To investigate these patterns across seasons, we determined the reproductive state via microscopy and phase via a sex-linked PCR assay for >4,800 thalli over the course of three years at hard and soft bottom sites with fixed and free-living G. vermiculophylla thalli, respectively, along the Eastern Shore of Virginia and Maryland. At hard bottom sites, most thalli were reproductive in the summer and sites were composed of gametophytes and tetrasporophytes, though there was a tetrasporophytic bias. By contrast, soft bottom sites were overwhelming tetrasporophyte dominated and fewer thalli were reproductive at any point in the year. Moreover, each soft bottom site displayed different patterns in the proportion of reproductive thalli, with G. vermiculophylla abundance fluctuating through time. Phenology surveys critical for understanding the spread of introduced macroalgae, including the on-going spread of G. vermiculophylla.

evolutionary biology↗

bioRxiv2024

Seasonality and inter-annual stability in the population genetic structure of Batrachospermum gelatinosum (Rhodophyta)

Temporal population genetic studies have investigated evolutionary processes, but few have characterized the temporal patterns of reproductive system variation. Yet, temporal sampling may improve our understanding of reproductive system evolution through assessing the relative rates of selfing, outcrossing, and clonality. In this study, we focus on the monoicous, haploid-diploid freshwater red alga Batrachospermum gelatinosum. This species has a perennial, microscopic diploid phase (chantransia) that produces an ephemeral, macroscopic haploid phase (gametophyte). Recent work focusing on single time point genotyping suggested high rates of intragametophytic selfing, though there was variation among sites. We expand on this work by genotyping 191 gametophytes from four sites with reproductive system variation at multiple time points within and among years. Intra-annual data suggest shifts in gametophytic genotypes present throughout the gametophytic season. We hypothesize this pattern is likely due to the seasonality of the life cycle and the timing of meiosis among the chantransia. Inter-annual patterns were characterized by consistent genotypic and genetic composition, indicating stability in the prevailing reproductive system through time. Yet, our study identified limits to which available theoretical predictions and analytical tools can resolve reproductive system variation using haploid data. There is a need to develop better tools to understand the evolution of sex by expanding our ability to characterize the spatiotemporal variation in reproductive systems across diverse life cycles.

evolutionary biology↗

bioRxiv2024

CLONALITY AND POLYPLOIDY CONTRIBUTE TO THE SPREAD OF AVRAINVILLEA LACERATA (BRYOPSIDALES, CHLOROPHYTA) IN HAWAI'I

The relative rates of sexual versus asexual reproduction influence the partitioning of genetic diversity within and among populations. During range expansions, uniparental reproduction often facilitates colonization and establishment. The arrival of the green alga Avrainvillea lacerata has caused shifts in habitat structure and community assemblages since its discovery in 1981 offshore of west Oahu, Hawai i. Field observations suggest this species is spreading via vegetative reproduction. To characterize the reproductive system of A. lacerata in Hawai i, we developed seven microsatellite loci and genotyped 321 blades collected between 2018 and 2023 from two intertidal sites at Maunalua Bay and Ewa Beach. We found one to four alleles at multiple loci, suggesting A. lacerata is tetraploid. Each site was characterized by high genotypic richness (R > 0.8). However, clonal rates were also high at both sites, suggesting vegetative spread of A. lacerata plays a significant role. The importance of clonal reproduction for the persistence of A. lacerata in Hawai i is consistent with the ecological data collected for this species, and observations of other abundant macroalgal invaders in Hawaii and other regions of the world. These data demonstrate the necessity for implementing appropriate population genetic methods and provide insights into the biology of this alga that will contribute to future studies on effective management strategies incorporating its reproductive system. This study represents one of the few investigating green algal population genetic patterns and contributes to our understanding of algal reproductive system evolution.

evolutionary biology↗

bioRxiv2023

THE RHODOEXPLORER PLATFORM FOR RED ALGAL GENOMICS AND WHOLE GENOME ASSEMBLIES FOR SEVERAL GRACILARIA SPECIES

Macroalgal (seaweed) genomic resources are generally lacking as compared to other eukaryotic taxa, and this is particularly true in the red algae (Rhodophyta). Understanding red algal genomes is critical to understanding eukaryotic evolution given that red algal genes are spread across eukaryotic lineages from secondary endosymbiosis and red algae diverged early in the Archaeplastids. The Gracilariales are highly diverse and widely distributed order whose species can serve as ecosystem engineers in intertidal habitats, including several notorious introduced species. The genus Gracilaria is cultivated worldwide, in part for its production of agar and other bioactive compounds with downstream pharmaceutical and industrial applications. This genus is also emerging as a model for algal evolutionary ecology. Here, we report new whole genome assemblies for two species (G. chilensis and G. gracilis), a draft genome assembly of G. caudata, and genome annotation of the previously published G. vermiculophylla genome. To facilitate accessibility and comparative analysis, we integrated these data in a newly created web-based portal dedicated to red algal genomics (https://rhodoexplorer.sb-roscoff.fr). These genomes will provide a resource for understanding algal biology and, more broadly, eukaryotic evolution.

genomics↗

bioRxiv2016

THE IDENTIFICATION OF SOURCE AND VECTOR OF A PROLIFIC MARINE INVADER

The source and vector of an introduced species inform its ecological and evolutionary history and may guide management that seeks to prevent future introductions. Surprisingly, few studies have successfully used genetic tools to independently inform the specific source and pathway of biological invasions. The ecological history of many introduced species, including their origins and vectors, is often based on suppositions or educated guesses. Here, we used mitochondrial and microsatellite genotyping to trace the invasion of the Asian seaweed Gracilaria vermiculophylla (Rhodophyta) along the three coastlines of the Northern Hemisphere to which it has been introduced: the western coast of North America, eastern coast of the United States and the coasts of Europe and northwest Africa. Analyzing 37 native and 53 introduced sites, we identified the Pacific coastline of northeastern Japan as the ultimate source of the Northern Hemisphere invasion. Coincidentally, most exports of the oyster Crassostrea gigas historically originated from this region and both species often grow in close proximity. Based on genetic signatures, each of the three coastlines likely received thalli directly from Japan, as well as material from another introduced coastline (i.e., a secondary invasion). Our ability to document a source region, which was enabled by a robust sampling of locations and loci that previous studies lacked, reflected strong phylogeographic structure along native coastlines. We suggest Gracilaria vermiculophylla is an important representative example of many species likely exported out of Japan by the oyster trade and its genetic signatures that may be a hallmark of oyster introduction legacies.

evolutionary biology↗