Biology subjects

Marhaver, K. L.

Publications and source records attributed to Marhaver, K. L..

3 recordsLinked to original sources

bioRxiv2026

Baseline microbiomes of the pillar coral Dendrogyra cylindrus reveal novel taxa and regional differences

The pillar coral Dendrogyra cylindrus is a rare but iconic member of Caribbean reefs that has suffered range-wide losses. D. cylindrus is highly susceptible to stony coral tissue loss disease (SCTLD), and the outbreak has contributed to the functional extinction of Floridas population of pillar corals. The coral microbiome can impact the health and disease resistance of coral colonies, yet little is known about what constitutes the core microbiome of D. cylindrus. This information is crucial for comparisons of healthy and diseased tissue in pathogen identification studies and can be applied to restoration efforts as a coral health metric. Therefore, we characterized the microbiomes of D. cylindrus colonies ahead of the SCTLD disease front in Belize and Curacao. The most prevalent members of the D. cylindrus microbial community were bacteria for which taxonomy could not be assigned confidently beyond the level of domain as well as the putatively endosymbiotic genera Endozoicomonas, Ca. Amoebophilus, and Spiroplasma. The coral reefs of Belize and Curacao represent distinct Caribbean marine ecoregions, and we documented regional differences in strains among predominant bacterial taxa. The understudied microbiome of D. cylindrus harbors unique bacterial lineages that are in danger of extinction along with its critically endangered coral host, and these bacterial lineages may be important bioindicators during restoration efforts. IMPORTANCETropical corals face global extinction if average temperatures rise by 2{degrees}C (3.6{degrees}F), which may occur as soon as 2050. Included in the loss of charismatic macrofauna like the majestic pillar coral is the loss of the biological and genetic diversity of its symbionts. Here we examined the bacterial and archaeal communities associated with Caribbean pillar corals and found that the microbiome was dominated by taxonomically unclassified and putatively endosymbiotic taxa. Endosymbiotic bacteria, which live inside the coral tissue, are likely to have evolved unique adaptations to become symbionts and may be important to the health and success of pillar corals in ecosystem restoration efforts.

microbiology↗

bioRxiv2020

Juvenile corals inherit mutations acquired during the parents lifespan

128 years ago, August Weismann proposed that the only source of inherited genetic variation in animals is the germline1. Julian Huxley reasoned that if this were true, it would falsify Jean-Baptiste Lamarcks theory that acquired characteristics are heritable2. Since then, scientists have discovered that not all animals segregate germline cells from somatic cells permanently and early in development3. In fact, throughout their lives, Cnidaria4-6 and Porifera7 maintain primordial stem cells that continuously give rise to both germline and somatic cells. The fate of mutations generated in this primordial stem cell line during adulthood remains an open question. It was unknown whether post-embryonic mutations could be heritable in animals8-10--until now. Here we use two independent genetic marker analyses to show that post-embryonic mutations are inherited in the coral Acropora palmata (Cnidaria, Anthozoa). This discovery upends the long-held supposition that post-embryonic genetic mutations acquired over an animals lifetime in non-germline tissues are not heritable2. Over the centuries-long lifespan of a coral, the inheritance of post-embryonic mutations may not only change allele frequencies in the local larval pool but may also spread novel alleles across great distances via larval dispersal. Thus, corals may have the potential to adapt to changing environments via heritable somatic mutations10. This mechanism challenges our understanding of animal adaptation and prompts a deeper examination of both the process of germline determination in Cnidaria and the role of post-embryonic genetic mutations in adaptation and epigenetics of modular animals. Understanding the role of post-embryonic mutations in animal adaptation will be crucial as ecological change accelerates in the Anthropocene.

evolutionary biology↗

bioRxiv2018

SUCCESSFUL DEMONSTRATION OF ASSISTED GENE FLOW IN THE THREATENED CORAL ACROPORA PALMATA ACROSS GENETICALLY-ISOLATED CARIBBEAN POPULATIONS USING CRYOPRESERVED SPERM

Global change will compromise the population sizes, species ranges, and survival of economically-important plants and animals, including crops, aquaculture species, and foundational ecosystem builders. Scleractinian reef-building corals are a particular concern because they are slow-growing, long-lived, environmentally-sensitive, and concentrated in the warmest regions of the ocean. Assisted Gene Flow (AGF) is considered a viable tool to help natural plant and animal populations, including corals, adapt to changing environments. Our goal was to test for the first time whether cryopreserved coral sperm could be used to facilitate assisted gene flow between genetically-isolated populations of a Caribbean coral. We collected, pooled, and cryopreserved coral sperm from the threatened Caribbean coral Acropora palmata in the western Caribbean (Key Largo, FL), central Caribbean (Rincon, Puerto Rico), and eastern Caribbean (Curacao). Alongside freshly-collected sperm from Curacao, the cryopreserved sperm from each of these populations was used for in vitro fertilization experiments with freshly-collected eggs from Curacao. Across five egg donors, average fertilization success was 91 to 99% for CUR x CUR (fresh sperm) crosses, 37 to 82% for CUR x CUR (frozen sperm) crosses, 3 to 19% for CUR x FL (frozen sperm) crosses and 0 to 24% for CUR x PR (frozen sperm) crosses. Notably, fertilization was achieved in all four categories of crosses, showing for the first time through direct evidence that populations of A. palmata are reproductively compatible, and that genetic diversity can be transferred from one population to another for the purposes of assisted gene flow. The resulting larvae were reared in Curacao for up to 7 days, then the swimming larvae were transported to Florida for settlement and grow-out at two separate facilities, which achieved larval settlement rates of 37 to 60% across all cohorts. Larvae were reared and settled in Florida to acclimate them to the ambient water quality, microbial environment, and temperature regimes of the western genetic A. palmata population as early in their life cycle as possible. At one month, over 54% all settlers had survived, including over 3500 settlers from CUR x CUR (frozen sperm), 1200 settlers from CUR x FL (frozen sperm), and 230 settlers from CUR x PR (frozen sperm). These experiments represent the first-ever pan-Caribbean coral crosses produced in captivity and the first direct evidence that geographically-separated and genetically-isolated populations of any Caribbean coral are reproductively compatible. Moreover, with over 4700 A. palmata settlers produced using cryopreserved sperm, this represents the largest living wildlife population ever created from cryopreserved material. Together, these findings demonstrate that cryopreservation of coral sperm can enable efficient, large-scale assisted gene flow in corals. This form of assisted migration can not only help to preserve the population-level genetic diversity of extant coral populations but also help to increase population resilience to global change.

zoology↗