Biology subjects

Meusemann, K.

Publications and source records attributed to Meusemann, K..

7 recordsLinked to original sources

bioRxiv2022

Contribution of hybridization to the evolution of a derived reproductive strategy in ricefishes

Transitions between reproductive strategies are costly and involve major changes in life history, behaviour and morphology. Nevertheless, in Sulawesi ricefishes, pelvic-brooding evolved from transfer-brooding in two distantly related lineages within in the genera Adrianichthys and in Oryzias, respectively. Females of pelvic-brooding species carry their eggs attached to their belly until the fry hatches. Despite their phylogenetic distance, both pelvic-brooding lineages share a set of external morphological traits. A recent study found no direct gene-flow between pelvic-brooding lineages suggesting independent evolution of the derived reproductive strategy. It could, however, also be more complex. Pre-existing variation in an admixed population may enable the re-use of genetic variants when subjected to similar external selection pressure, resulting in similar phenotypes. We thus used a multi-species coalescent (MSC) model and D-statistics to identify gene-tree - species-tree incongruencies, to evaluate the evolution of pelvic-brooding with respect to inter-specific gene-flow not only between pelvic-brooding lineages, but between pelvic-brooding lineages and other Sulawesi ricefish lineages. We found a general network-like evolution in Sulawesi ricefishes and as previously reported, no gene-flow between the pelvic-brooding lineages. Instead, we found hybridization between the ancestor of pelvic-brooding Oryzias and the common ancestor of the four Oryzias species from Lake Poso, home of the pelvic-brooding Adrianichthys lineage. Further, indications of introgression were located within two confidence intervals of quantitative trait loci (QTL) associated with pelvic-brooding in O. eversi. We thus hypothesize that a mix of de novo mutations and (ancient) standing genetic variation shaped the evolution of pelvic-brooding. Significance statementThe evolution of pelvic-brooding in Oryzias eversi (Beloniformes:Adrianichthyidae), was recently described to be independent from another pelvic-brooding ricefish lineage (Adrianichthys) from Sulawesi. We confirmed these results, and detected no gene flow between the two distantly related pelvic-brooding lineages. Instead, we found ancient gene flow from another Orzyias lineage into the pelvic-brooding Oryzias lineage. One of the previously described QTL for pelvic brooding overlaps with a region of high introgression signal. Therefore, we assume that not only de novo mutations contributed to the evolution of pelvic-brooding in Orzyias, but that introduced ancient genetic variation was likely also recruited for the evolution of this derived brooding strategy.

evolutionary biology↗

bioRxiv2020

Disentangling the aging network of a termite queen

BackgroundMost insects are relatively short-lived, with a maximum lifespan of a few weeks, like the aging model organism, the fruit-fly Drosophila melanogaster. By contrast, the queens of social insects (termites, ants, some bees and wasps) can live for more than a decade. This makes social insects promising new models in aging research providing insights into how a long reproductive life can be achieved. Yet, aging studies on social insect reproductives are hampered by a lack of quantitative data on age-dependent survival and time series analyses that cover the whole lifespan of such long-lived individuals. We studied aging in queens of the drywood termite Cryptotermes secundus by determining survival probabilities over more than 15 years and performed transcriptome analyses for queens of known age that covered their whole lifespan. ResultsThe maximum lifespan of C. secundus queens was 13 years with a median maximum longevity of 11.0 years. Time course and co-expression network analyses of gene expression patterns over time indicated a non-gradual aging pattern. It was characterized by networks of genes that became differentially expressed only late in life, namely after an age of 10 years, which associates well with the median maximum lifespan for queens. These old-age gene networks reflect processes of physiological upheaval. We detected strong signs of stress, decline, defence and repair at the transcriptional level of epigenetic control as well as at the post-transcriptional level with changes in transposable element activity and the proteostasis network. The latter depicts an upregulation of protein degradation, together with protein synthesis and protein folding, processes which are often down-regulated in old animals. The simultaneous upregulation of protein synthesis and autophagy is indicative for a stress-response mediated by the transcription factor cnc, a homolog of human nrf genes. ConclusionOur results show non-linear senescence with a rather sudden physiological upheaval at old-age. Most importantly, they point to a re-wiring in the proteostatis network as central for explaining the long life of social insect queens.

evolutionary biology↗

bioRxiv2020

Are fleas highly modified Mecoptera? Phylogenomic resolution of Antliophora (Insecta: Holometabola)

Insect orders have been defined and stable for decades, with few notable exceptions (e.g., Blattodea and Psocoptera). One of the few remaining questions of order-level monophyly is that of Mecoptera in respect to the phylogenetic placement of Siphonaptera (fleas). We used a large set of transcriptomic nucleotide sequence data representing 56 species and more than 3,000 single-copy genes to resolve the evolutionary history of Antliophora, including fleas (Siphonaptera), scorpionflies and relatives (Mecoptera), and true flies (Diptera). We find that fleas and mecopterans together are the sister group of flies. However, our data and/or analyses are unable to distinguish whether fleas are sister to a monophyletic Mecoptera, or whether they arose from within extant mecopteran families, rendering Mecoptera paraphyletic. We did not detect parameter bias in our dataset after applying a broad range of detection methods. Counter to a previous hypothesis that placed fleas within Mecoptera as the sister group to wingless boreids (snow fleas), we found a potential sister group relationship between fleas and the enigmatic family Nannochoristidae. Although we lack conclusive evidence, it seems possible that fleas represent the most-species rich group of modern mecopterans and that their parasitic lifestyle and morphological adaptations have simply made them unrecognizable in respect to their order-level classification.

evolutionary biology↗

bioRxiv2020

Transcriptomics provides a robust framework for the relationships of the major clades of cladobranch sea slugs (Mollusca, Gastropoda, Heterobranchia), but fails to resolve the position of the enigmatic genus Embletonia

BackgroundCladobranch sea slugs represent roughly half of the biodiversity of soft-bodied, marine gastropod molluscs (Nudibranchia) on the planet. Despite their global distribution from shallow waters to the deep sea, from tropical into polar seas, and their important role in marine ecosystems and for humans (as bioindicators and providers of medical drug leads), the evolutionary history of cladobranch sea slugs is not yet fully understood. Here, we amplify the current knowledge on the phylogenetic relationships by extending the cladobranch and outgroup taxon sampling using transcriptome data. ResultsWe generated new transcriptome data for 19 species of cladobranch sea slugs and two additional outgroup taxa. We complemented our taxon sampling with previously published transcriptome data, resulting in a final supermatrix covering 56 species from all but one accepted cladobranch superfamilies. Transcriptome assembly using six different assemblers, selection of those assemblies providing the largest amount of potentially phylogenetically informative sites, and quality-driven compilation of data sets resulted in three different supermatrices: one with a full coverage of genes per species (446 single-copy protein-coding genes) and two with a less stringent coverage (667 genes with 98.9% partition coverage and 1,767 genes with 86% partition coverage, respectively). We used these supermatrices to infer statistically robust maximum-likelihood trees. All analyses, irrespective of the data set, indicate maximum statistical support for all major splits and phylogenetic relationships on family level. The only discordance between the inferred trees is the position of Embletonia pulchra. Extensive testing using Four-cluster Likelihood Mapping, Approximately Unbiased tests, and Quartet Scores revealed that its position is not due to any informative phylogenetic signal, but caused by confounding signal. ConclusionsOur data matrices and the inferred trees inferred can serve as a solid foundation for future work on the taxonomy and evolutionary history of Cladobranchia. The correct placement of E. pulchra, however, proves challenging, even with large data sets. Moreover, quartet mapping shows that confounding signal present in the data is sufficient to explain the inferred position of E. pulchra, again leaving its phylogenetic position as an enigma.

evolutionary biology↗

bioRxiv2020

Transcriptomic signatures of ageing vary in solitary and social forms of an orchid bee

Eusocial insect queens are remarkable in their ability to maximise both fecundity and longevity, thus escaping the typical trade-off between these two traits. In species exhibiting complex eusocial behaviour, several mechanisms have been proposed to underlie the remoulding of the trade-off, such as reshaping of the juvenile hormone pathway, or caste-specific susceptibility to oxidative stress. However, it remains a challenge to disentangle the molecular mechanisms underlying the remoulding of the trade-off in eusocial insects from caste-specific physiological attributes that have subsequently arisen due to their different life histories. Socially plastic species such as the orchid bee Euglossa viridissima represent excellent models to address the role of sociality per se in longevity as they allow direct comparisons of solitary and social individuals within a common genetic background. We present data on gene expression and juvenile hormone levels from young and old bees, from both solitary and social nests. We found 940 genes to be differentially expressed with age in solitary females, versus only 14 genes in social dominant females, and seven genes in subordinate females. We performed a weighted gene co-expression network analysis to further highlight candidate genes related to ageing in this species. Primary "ageing gene" candidates were related to protein synthesis, gene expression, immunity and venom production. Remarkably, juvenile hormone titres did not vary with age or social status. These results represent an important step in understanding the proximate mechanisms underlying the remodeling of the fecundity/longevity trade-off that accompanies the evolutionary transition from solitary life to eusociality. Significance statementThe remarkably long lifespan of the queens of eusocial insects despite their high reproductive output suggests that they are not subject to the widespread trade-off between fecundity and longevity that governs solitary animal life histories, yet surprisingly little is known of the molecular mechanisms underpinning their longevity. Using a socially plastic bee in which some individuals of a population are social whilst others are solitary, we identified hundreds of candidate genes and related gene networks that are involved in the remoulding of the fecundity/longevity tradeoff. As well as identifying candidate ageing genes, our data suggest that even in incipient stages of sociality there is a marked reprogramming of ageing; long live the queen.

evolutionary biology↗

bioRxiv2020

A minimum reporting standard for multiple sequence alignments

Multiple sequence alignments (MSAs) play a pivotal role in studies of molecular sequence data, but nobody has developed a minimum reporting standard (MRS) to quantify the completeness of MSAs in terms of completely-specified nucleotides or amino acids. We present an MRS that relies on four simple completeness metrics. The metrics are implemented in AliStat, a program developed to support the MRS. A survey of published MSAs illustrates the benefits and unprecedented transparency offered by the MRS.

bioinformatics↗

bioRxiv2019

No evidence for immune-gene specific signals of selection in termites

It has been hypothesized that selection pressure from pathogens plays an important role in shaping social evolution. Social behaviour, in particular brood care, is associated with pathogen pressure in wood-dwelling \"lower\" termites. Yet, generally pathogen pressure is low in wood-dwelling termite species that never leave the nest except for the mating flight. In comparison, pathogen pressure is higher in species that leave the nest to forage, and thus constantly encounter a diversity of microbes from their environment. We hypothesized that such differences in pathogen pressure are also reflected by differences in the intensity of natural selection on immune genes. We tested this hypothesis in a phylogenetic framework, analyzing rates of non-synonymous and synonymous substitutions on single-copy immune genes. Therefore, we leveraged recent genomic and transcriptomic data from eight termite species, representing wood-dwelling and foraging species as well as 14 additional species spanning the winged insects (Pterygota). Our results provide no evidence for a role of pathogen pressure in selection intensity on single-copy immune genes. Instead, we found evidence for a genome-wide pattern of relaxed selection in termites.\n\nLife Science Identifiers (as available Zoobank)Ephemera danica:\n\nurn:lsid:zoobank.org:act:06633F75-4809-4BB3-BDCB-6270795368D5\n\nCoptotermes sp.\n\nurn:lsid:zoobank.org:pub:D6724B7F-F27A-47DC-A4FC-12859ECA0C71\n\nBlattella germanica:\n\nrn:lsid:zoobank.org:pub:1EA126BA-E9D2-4AA6-8202-26BA5B09B8AD\n\nLocusta migratoria\n\nurn:lsid:zoobank.org:pub:D792A09E-844A-412A-BFCA-5293F8388F8C\n\nPeriplaneta americana (Blatta americana):\n\nurn:lsid:zoobank.org:act:95113A55-4C6D-4DC7-A0E5-620BACADFFE5\n\nApis mellifera:\n\nurn:lsid:zoobank.org:act:9082C709-6347-4768-A0DC-27DC44400CB2\n\nBombyx mori (Phalaena (Bombyx) mori)\n\nurn:lsid:zoobank.org:act:215466E3-E77F-46E9-8097-372837D7A375\n\nDrosophila melanogaster:\n\nurn:lsid:zoobank.org:act:5B39F0AA-270D-4AA8-B9A3-C36A3A265910

evolutionary biology↗