Biology subjects

Kayal, E.

Publications and source records attributed to Kayal, E..

6 recordsLinked to original sources

bioRxiv2025

Population Genomics Informs Conservation Strategies for Critically Endangered Kokia Species in Hawaii

Island endemic species are particularly vulnerable to extinction due to their limited geographic ranges and small population sizes. Kokia is a genus found exclusively in the Hawaiian Islands, whose species were once major components of local forests but have experienced significant population reductions due to habitat destruction and the consequences of invasive species. Although conservation of Kokia species has been an ongoing topic for over a century, records regarding historical efforts are sparse. Recently generated genomes for each of the three extant species provide the foundation for understanding genetic diversity and population structure for future conservation work. Whole genome resequencing of K. cookei (n = 23 samples), K. drynarioides (n = 92), and K. kauaiensis (n = 45) suggests that K. drynarioides has the lowest overall diversity, reflecting propagation from a limited part of the remaining gene pool, whereas K. kauaiensis exhibits the most diversity. Diversity in the primarily graft-propagated K. cookei is higher than expected, and slightly higher than in the free-living K. drynarioides. Notably, our analyses identified a source of novel variation in K. cookei in a cultivated plant historically labeled K. drynarioides. Population structure analyses reveal a single population for K. cookei, but three groups for each of the other two species. Importantly, our analyses identify clusters of related individuals, reflected in genetic distance and clustering metrics, which provide valuable information for increasing diversity in managed populations and in ex situ conservation collections. These results provide a genomic framework for ongoing efforts in restoring and maintaining diversity in these critically endangered Hawaiian species.

genomics↗

bioRxiv2025

Two Spore Types in a Marine Parasite of Dinoflagellates

Marine alveolates (MALVs) are diverse, primarily parasitic micro-eukaryotes that significantly impact marine ecosystems. The life cycles of most MALVs remain elusive and the role of sexual reproduction in these organisms is a key question that may determine their ecological success. In this study we focus on a widespread dinoflagellate parasite of bloom-forming dinoflagellates, Amoebophrya. After infection, we identified two distinct spores, differing in size, ultrastructure, swimming behavior, lifespan, gene expression, and metabolite composition. The smaller spores serve as infectious propagules, equipped with an apical complex for host invasion. They exhibit a distinct, shorter, and straighter swimming pattern, likely optimized for an extended lifespan while enhancing dispersion and chance for host encounters. Transcriptomic analysis reveals that these smaller spores are primed for efficient protein synthesis upon initiating a new infection. Conversely, the larger spores cannot infect new hosts and are characterized by the expression of meiotic genes, underscoring their sexual nature. They have a shorter lifespan, exhibit more tortuous movement, along display condensed chromosomes, signaling readiness for mating. Interestingly, infected hosts already express meiotic genes, and a single infected host only produces progeny of the same spore type, suggesting that cell fate is determined prior to spore release. Our study provides one of the first formal demonstrations of a sexually specialized cell in MALVs. Isolating compatible strains for cross-breeding and understanding how environmental conditions favor each reproductive route are the next key questions for elucidating the ecological success of MALVs in marine waters. Significance StatementMarine alveolates (MALVs) are ecologically significant parasites that impact carbon cycling, causing major disease outbreaks affecting fisheries and aquaculture, and influencing the dynamics of harmful algal blooms. Despite their diversity and wide host range, much of our knowledge comes from environmental DNA, leaving important aspects of their biology, such as their life cycles, largely unknown. This study provides the first evidence of sexual reproduction in MALVs, linking spore polymorphism to infective or sexual routes. This discovery is crucial as sexual reproduction increases genetic diversity and adaptability, aiding MALVs resilience in changing environments. Understanding MALVs reproductive strategies deepens our insight into their ecological roles and their broader impact on marine ecosystems.

microbiology↗

bioRxiv2024

Assessment of the Genetic Diversity of Atlantic Bottlenose Dolphin (Tursiops truncatus) Strandings in the Mississippi Sound (USA)

The common bottlenose dolphin (Tursiops truncatus) is a key marine mammal species in the northern Gulf of Mexico, playing an essential role as a top predator. This study focuses on the genetic diversity and population structure of bottlenose dolphins stranded in the Mississippi Sound from 2010 to 2021. A total of 511 tissue samples (muscle, liver, lung, kidney, and brain) were collected from stranded dolphins, and mitochondrial DNA (mtDNA) was extracted for analysis. Using high-throughput sequencing methods, 417 samples were successfully amplified and sequenced, producing 386 complete mitogenomes. Genetic diversity metrics, such as nucleotide and haplotype diversity, were calculated, and population structure was inferred for both mitochondrial control region (mtCR) and whole mitogenome sequences. Using the whole mitogenome, the study identified four genetically distinct populations within the Mississippi Sound, demonstrating regional variation in dolphin populations. Notably, some individuals likely originated from populations outside the sampled area. The use of whole mitogenomes allowed for improved resolution of genetic diversity and population differentiation compared to previous studies using partial mtDNA sequences. These findings provide critical insights into the genetic structure of bottlenose dolphins in the region and highlight the value of using stranded animals for population genetic studies.

genomics↗

bioRxiv2024

Genomic diversity and evolution in the Hawaiian Islands endemic Kokia (Malvaceae)

Island species are highly vulnerable due to habitat destruction and their often small population sizes with reduced genetic diversity. The Hawaiian Islands constitute the most isolated archipelago on the planet, harboring many endemic species. Kokia is an endangered flowering plant genus endemic to these islands, encompassing three extant and one extinct species. Recent studies provided evidence of unexpected genetic diversity within Kokia. Here, we provide high quality genome assemblies for all three extant Kokia species, including an improved genome for K. drynarioides. All three Kokia genomes contain 12 chromosomes exhibiting high synteny within and between Kokia and the sister taxon Gossypioides kirkii. Gene content analysis revealed a net loss of genes in K. cookei compared to other species, whereas the gene complement in K. drynarioides remains stable and that of K. kauaiensis displays a net gain. A dated phylogeny estimates the divergence time from the last common ancestor for the three Kokia species at [~]1.2 million years ago (mya), with the sister taxa [K. cookei + K. drynarioides] diverging [~]0.8 mya. Kokia appears to have followed a stepping-stone pattern of colonization and diversification of the Hawaiian Archipelago, likely starting on low or now submerged older islands. The genetic resources provided may benefit conservation efforts of this endangered endemic genus.

genomics↗

bioRxiv2024

Acanthella acuta Mitochondrial DNA: Linear Architecture and Other Unique Features

While Acanthella acuta (Schmidt 1862), a common demosponge found in the Mediterranean Sea and Atlantic Ocean, is -- morphologically -- little distinguishable from other sponges, its mitochondrial DNA (mtDNA) is unique within the class. In contrast to all other studied demosponges, A. acuta mtDNA appears to be linear and displays several unusual features: inverted terminal repeats, group II introns in three mt-genes, and two unique ORFs. One of the ORFs (ORF1535) combines a DNA-polymerase domain with a DNA-directed RNA-polymerase domain, while the second bears no discernable similarity to any reported sequences. The group II intron within the cox2 gene is the first such intron reported in an animal. Our phylogenetic analyses indicate that the cox1 intron is related to similar introns found in other demosponges, while the cox2 intron is likely not of animal origin. The two domains found within ORF1535 do not share a common origin and, along with the cox2 intron, were likely acquired by horizontal transfer. The findings of this paper open new avenues of exploration in the understanding of mtDNA linearization within Metazoa. SignificanceThe transition from circular to linear mtDNA architecture is a rare and poorly understood phenomenon in animals. In addition, the few lineages that made this transition (Medusozoa, Calcarea, and Isopoda), adopted linear mt-DNA architecture early in their history, making it difficult to reconstruct the underlying events. The identification of linear mtDNA in Acanthella acuta not only provides an independent example of the origin of linear mtDNA architectures in animals but also an opportunity to investigate its evolution at a much shorter evolutionary time. In particular, the conservation of circular mtDNA in other studied species within the family Dictyonellidae highlights the need to investigate other species in the genus Acanthella, to better understand mtDNA linearization in A. acuta.

evolutionary biology↗

bioRxiv2021

Intracellular development and impact of a eukaryotic parasite on its zombified microalgal host in the marine plankton

Parasites are widespread and diverse in the oceanic plankton, and many of them infect single-celled algae for survival. How these parasites develop and scavenge energy within the host and whether the cellular organization and metabolism of the host is altered remain open questions. Combining quantitative structural and chemical imaging with time-resolved transcriptomics, we unveil dramatic morphological and metabolic changes of the parasite Amoebophrya (Syndiniales) during intracellular infection (e.g. 200-fold increase of mitochondrion volume), particularly following digestion of nutrient-rich host chromosomes. Some of these changes are also found in the apicomplexan parasites (e.g. sequential acristate and cristate mitochondrion, switch from glycolysis to TCA), thus underlining key evolutionary-conserved mechanisms. In the algal host, energy-producing organelles (chloroplast) remain intact during most of the infection, but sugar reserves diminish while lipid droplets increase. Thus, rapid infection of the host nucleus could be a zombifying strategy to digest nutrient-rich chromosomes and escape cytoplasmic defense while benefiting from the maintained C-energy production of the host cell.

cell biology↗