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  1. Abstract

    Mitochondrial genomes are known for their compact size and conserved gene order, however, recent studies employing long-read sequencing technologies have revealed the presence of atypical mitogenomes in some species. In this study, we assembled and annotated the mitogenomes of five Antarctic notothenioids, including four icefishes (Champsocephalus gunnari,C. esox,Chaenocephalus aceratus, andPseudochaenichthys georgianus) and the cold-specializedTrematomus borchgrevinki. Antarctic notothenioids are known to harbor some rearrangements in their mt genomes, however the extensive duplications in icefishes observed in our study have never been reported before. In the icefishes, we observed duplications of the protein coding geneND6, two transfer RNAs,and the control region with different copy number variants present within the same individuals and with someND6duplications appearing to follow the canonical Duplication-Degeneration-Complementation (DDC) model inC. esoxandC. gunnari. In addition, using long-read sequencing and k-mer analysis, we were able to detect extensive heteroplasmy inC. aceratusandC. esox. We also observed a large inversion in the mitogenome ofT. borchgrevinki, along with the presence of tandem repeats in its control region. This study is the first in using long-read sequencing to assemble and identify structural variants and heteroplasmy in notothenioid mitogenomes and signifies the importance of long-reads in resolving complex mitochondrial architectures. Identification of such wide-ranging structural variants in the mitogenomes of these fishes could provide insight into the genetic basis of the atypical icefish mitochondrial physiology and more generally may provide insights about their potential role in cold adaptation.

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    Free, publicly-accessible full text available December 1, 2024
  2. Barbour, Alan G. (Ed.)
    A major focus of host-microbe research is to understand how genetic differences, of various magnitudes, among hosts translate to differences in their microbiomes. This has been challenging for animal hosts, including humans, because it is difficult to control environmental variables tightly enough to isolate direct genetic effects on the microbiome. Our work in stickleback fish is a significant contribution because our experimental approach allowed strict control over environmental factors, including standardization of the microbiome from the earliest stage of development and unrestricted co-housing of fish in a truly common environment. Furthermore, we measured host genetic variation over 2,000 regions of the stickleback genome, comparing this information and microbiome composition data among fish from very similar and very different genetic backgrounds. Our findings highlight how differences in the host genome influence microbiome diversity and make a case for future manipulative microbiome experiments that use host systems with naturally occurring genetic variation. 
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  3. Seadragons are a remarkable lineage of teleost fishes in the family Syngnathidae, renowned for having evolved male pregnancy. Comprising three known species, seadragons are widely recognized and admired for their fantastical body forms and coloration, and their specific habitat requirements have made them flagship representatives for marine conservation and natural history interests. Until recently, a gap has been the lack of significant genomic resources for seadragons. We have produced gene-annotated, chromosome-scale genome models for the leafy and weedy seadragon to advance investigations of evolutionary innovation and elaboration of morphological traits in seadragons as well as their pipefish and seahorse relatives. We identified several interesting features specific to seadragon genomes, including divergent noncoding regions near a developmental gene important for integumentary outgrowth, a high genome-wide density of repetitive DNA, and recent expansions of transposable elements and a vesicular trafficking gene family. Surprisingly, comparative analyses leveraging the seadragon genomes and additional syngnathid and outgroup genomes revealed striking, syngnathid-specific losses in the family of fibroblast growth factors (FGFs), which likely involve reorganization of highly conserved gene regulatory networks in ways that have not previously been documented in natural populations. The resources presented here serve as important tools for future evolutionary studies of developmental processes in syngnathids and hold value for conservation of the extravagant seadragons and their relatives. 
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  4. null (Ed.)
  5. Abstract

    Gynogenetic embryos – those inheriting only maternal DNA – can be experimentally created by fertilizing eggs with radiation‐treated sperm containing inactivated paternal chromosomes. Diploidy in the zygotes can be maintained through prevention of the second meiosis or restored by preventing the first mitosis after the maternal chromosome complement has been replicated. These gynogenetic organisms are useful in many fields including aquaculture, evolutionary biology and genomics. Although gynogenetic organisms have been created in numerous species, the completeness of uni‐parental inheritance has often been assumed rather than thoroughly quantified across the genome. Instead, when tests of uni‐parental inheritance occur, they typically rely on well‐studied genetically determined phenotypes that represent a very small sub‐set of the genome. Only assessing small genomic regions for paternal inheritance leaves the question of whether some paternal contributions to offspring might still have occurred. In this study, the authors quantify the efficacy of creating gynogenetic diploid three‐spined stickleback fish (Gasterosteus aculeatus). To this end, the authors mirrored previous assessments of paternal contribution using well‐studied genetically determined phenotypes including sex and genetically dominant morphological traits but expanded on previous studies using dense restriction site‐associated DNA sequencing (RAD‐seq) markers in parents and offspring to assess paternal inheritance genome‐wide. In the gynogenetic diploids, the authors found no male genotypes underlying their phenotypes of interest – sex and dominant phenotypic traits. Using genome‐wide assessments of paternal contribution, nevertheless, the authors found evidence of a small, yet potentially important, amount of paternally “leaked” genetic material. The application of this genome‐wide approach identifies the need for more widespread assessment of paternal contributions to gynogenetic animals and promises benefits for many aspects of aquaculture, evolutionary biology and genomics.

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