Biology subjects

Koch, H. R.

Publications and source records attributed to Koch, H. R..

3 recordsLinked to original sources

bioRxiv2025

Morphological plasticity in a reef-building coral is context-dependent and trades off with resistance to thermal stress

In sessile, long-lived organisms, such as reef-building corals, phenotypic plasticity may play a key role in mitigating the impacts of climate change. Plasticity is often context-dependent and has costs and limits, ultimately resulting in adaptive, neutral, or maladaptive effects. However, our understanding of the mechanisms that maintain variation in, and therefore drive the evolution of, plasticity is still limited. We use a field-based transplant experiment to show context-dependent tradeoffs to morphological plasticity in Acropora cervicornis under real-world conditions driven by climate change. We find that while morphological plasticity is neutral under some conditions, it trades off with thermal tolerance during moderate temperature stress during a marine heatwave. Additionally, we find that plasticity changes over time, underlining the importance of its temporal dynamics in long-lived organisms. Our results demonstrate a key role for environmental change in the eco-evolutionary dynamics of plasticity by demonstrating context-dependent costs under real-world thermal stress.

evolutionary biology↗

bioRxiv2023

Genome assemblies and genetic maps highlight chromosome-scale macrosynteny in Atlantic acroporids

BackgroundCorals belong to the Cnidaria, an early branching phylum of metazoans. Over the course of their long evolutionary history, they have adapted to changing environments, such as rising sea levels and increasing ocean temperatures. While their history speaks to their evolutionary capacity, it is less clear how quickly they may respond to rapid changes. A critical aspect of adaptive capacity is the structure of their genome and the genetic diversity contained within. FindingsHere, we present chromosome-scale genome assemblies and genetic linkage maps of two critically endangered coral species, Acropora palmata and A. cervicornis, the two extant Atlantic acroporid corals. Genomes of both species were resolved into 14 chromosomes with comparable assembly sizes (A. palmata, 287Mb; A. cervicornis, 305Mb). Gene content, repeat content, gene collinearity and macrosynteny were largely preserved between the Atlantic acroporids but a 2.5 Mb inversion and 1.4 Mb translocation were detected between two of the chromosome pairs. Macrosynteny and gene collinearity decreased when comparing Atlantic with Pacific acroporids. Paracentric inversions of whole chromosome arms characterized A. hyacinthus, specifically. In the larger context of cnidarian evolution, the four acroporids and another scleractinian coral with chromosome-resolved genome assemblies retained six of 21 cnidarian ancestral linkage groups, while also privately sharing numerous ALG fission and fusion events compared to other distantly related cnidarians. Genetic linkage maps were built using a 30K genotyping array with 105 offspring in one family for A. palmata and 154 offspring across 16 families for A. cervicornis. The A. palmata consensus linkage map spans 1,013.42 cM and includes 2,114 informative markers. The A. cervicornis consensus map spans 927.36 cM across 4,859 markers. A. palmata and A. cervicornis exhibited similarly high sex-averaged genome-wide recombination rates (3.53 cM/Mb and 3.04 cM/Mb, respectively) relative to other animals. In our gamete-specific maps, we found pronounced sex-based differences in recombination, known as heterochiasmy, in this simultaneous hermaphrodite, with both species showing recombination rates 2-2.5X higher in eggs compared to sperm. ConclusionsThe genomic resources presented here are the first of their kind available for Atlantic coral species. These data sets revealed that adaptive capacity of endangered Atlantic corals is not limited by their recombination rates, with both species exhibiting high recombination rates and heterochiasmy. Nevertheless, the two sister species maintain high levels of macrosynteny and gene collinearity between them. The few large-scale rearrangements detected deserve further study as a potential cause of fertilization barriers between the species. Together, the assemblies and genetic maps presented here now enable genome-wide association studies and discovery of quantitative trait loci; tools that can aid in the conservation of these endangered corals.

evolutionary biology↗

bioRxiv2021

The coral symbiont Candidatus Aquarickettsia is variably abundant in threatened Caribbean acroporids and transmitted horizontally.

The aquatic symbiont "Candidatus Aquarickettsia rohweri" infects a diversity of non-bilaterian metazoan phyla. In the threatened coral Acropora cervicornis, Aquarickettsia proliferates in response to increased nutrient exposure, resulting in suppressed growth and increased disease susceptibility and mortality. This study evaluated the extent, as well as the ecology and evolution of Aquarickettsia infecting the Caribbean corals: Ac. cervicornis and Ac. palmata and their hybrid ( Ac. prolifera). The bacterial parasite Aquarickettsia was found in all acroporids, with host and sampling location impacting infection magnitude. Phylogenomic and genome-wide single nucleotide variant analysis found Aquarickettsia clustering by region, not by coral taxon. Fixation analysis suggested within coral colonies, Aquarickettsia are genetically isolated to the extent that reinfection is unlikely. Relative to other Rickettsiales, Aquarickettsia is undergoing positive selection, with Florida populations experiencing greater positive selection relative to the other Caribbean locations. This may be due to Aquarickettsia response to increased nutrient stress in Florida, as indicated by greater in situ replication rates in these corals. Aquarickettsia did not significantly codiversify with either coral animal nor algal symbiont, and qPCR analysis of gametes and juveniles from susceptible coral genotypes indicated absence in early life stages. Thus, despite being an obligate parasite, Aquarickettsia must be horizontally transmitted via coral mucocytes, an unidentified secondary host, or a yet unexplored environmentally mediated mechanism. Importantly, the prevalence of Aquarickettsia in Ac. cervicornis and high abundance in Florida populations suggests that disease mitigation efforts in the US and Caribbean should focus on preventing early infection via horizontal transmission.

microbiology↗