| 1. |
- Bechsgaard, Jesper, et al.
(författare)
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Evidence for Faster X Chromosome Evolution in Spiders
- 2019
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Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 36:6, s. 1281-1293
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Tidskriftsartikel (refereegranskat)abstract
- In species with chromosomal sex determination, X chromosomes are predicted to evolve faster than autosomes because of positive selection on recessive alleles or weak purifying selection. We investigated X chromosome evolution in Stegodyphus spiders that differ in mating system, sex ratio, and population dynamics. We assigned scaffolds to X chromosomes and autosomes using a novel method based on flow cytometry of sperm cells and reduced representation sequencing. We estimated coding substitution patterns (dN/dS) in a subsocial outcrossing species (S. africanus) and its social inbreeding and female-biased sister species (S. mimosarum), and found evidence for faster-X evolution in both species. X chromosome-to-autosome diversity (piX/piA) ratios were estimated in multiple populations. The average piX/piA estimates of S. africanus (0.57 [95% CI: 0.55–0.60]) was lower than the neutral expectation of 0.75, consistent with more hitchhiking events on X-linked loci and/or a lower X chromosome mutation rate, and we provide evidence in support of both. The social species S. mimosarum has a significantly higher piX/piA ratio (0.72 [95% CI: 0.65–0.79]) in agreement with its female-biased sex ratio. Stegodyphus mimosarum also have different piX/piA estimates among populations, which we interpret as evidence for recurrent founder events. Simulations show that recurrent founder events are expected to decrease the piX/piA estimates in S. mimosarum, thus underestimating the true effect of female-biased sex ratios. Finally, we found lower synonymous divergence on X chromosomes in both species, and the male-to-female substitution ratio to be higher than 1, indicating a higher mutation rate in males.
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| 2. |
- Junghanns, Anja, et al.
(författare)
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Physiological Adaptations to Extreme Maternal and Allomaternal Care in Spiders
- 2019
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Some semelparous species show terminal investment by suicidal offspring provisioning. This requires internal cellular disintegration for the production of regurgitated food and in preparation for the sacrifice of the female body to the offspring, however, we have limited insights into the extent and costs of such physiological modifications. Extreme provisioning is hypothesized to be limited to reproducing individuals because it requires physiological alterations triggered by reproduction. However, non-reproducing helpers-at-the-nest have been shown to engage in suicidal provisioning, prompting us to ask whether helpers undergo similar physiological alterations to brood provisioning as mothers, which would represent an adaptation to cooperative breeding. Using an experimental approach, we investigated the physiological consequences of extended maternal care in the solitary spider Stegodyphus lineatus and the cooperative breeder S. dumicola, and whether non-reproducing helpers (virgin allomothers) in S. dumicola show physiological adaptations to brood provisioning. To identify costs of offspring provisioning, we determined the energy expenditure (standard metabolic rate; SMR) and tissue disintegration over the course of brood care. In both species, brood care is associated with elevated SMR, which was highest in allomothers. Brood care results in progressive disintegration of midgut tissue, which also occurred in allomothers. On experimental offspring removal, these responses are reversible but only until the onset of regurgitation feeding, marking a physiological “point-of-no-return.” The mechanism underlying the onset of physiological responses is unknown, but based on our finding of mature eggs in mothers and allomothers, as opposed to the undeveloped eggs in virgins of the solitary species, we propose that oocyte maturation is a central adaptation in non-reproducing helpers to provide terminal allomaternal care.
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| 3. |
- Schwager, Evelyn E., et al.
(författare)
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The house spider genome reveals an ancient whole-genome duplication during arachnid evolution
- 2017
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Ingår i: BMC Biology. - : BIOMED CENTRAL LTD. - 1741-7007. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Background: The duplication of genes can occur through various mechanisms and is thought to make a major contribution to the evolutionary diversification of organisms. There is increasing evidence for a large-scale duplication of genes in some chelicerate lineages including two rounds of whole genome duplication (WGD) in horseshoe crabs. To investigate this further, we sequenced and analyzed the genome of the common house spider Parasteatoda tepidariorum.Results: We found pervasive duplication of both coding and non-coding genes in this spider, including two clusters of Hox genes. Analysis of synteny conservation across the P. tepidariorum genome suggests that there has been an ancient WGD in spiders. Comparison with the genomes of other chelicerates, including that of the newly sequenced bark scorpion Centruroides sculpturatus, suggests that this event occurred in the common ancestor of spiders and scorpions, and is probably independent of the WGDs in horseshoe crabs. Furthermore, characterization of the sequence and expression of the Hox paralogs in P. tepidariorum suggests that many have been subject to neo-functionalization and/or sub-functionalization since their duplication.Conclusions: Our results reveal that spiders and scorpions are likely the descendants of a polyploid ancestor that lived more than 450 MYA. Given the extensive morphological diversity and ecological adaptations found among these animals, rivaling those of vertebrates, our study of the ancient WGD event in Arachnopulmonata provides a new comparative platform to explore common and divergent evolutionary outcomes of polyploidization events across eukaryotes.
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