Identification of general patterns of sex-biased expression inDaphnia, a genus with environmental sex determination

Abstract

1Daphnia reproduce by cyclic-parthenogenesis, where phases of asexual reproduction are 2 intermitted by sexual production of diapause stages. This life cycle, together with 3 environmental sex determination, allow the comparison of gene expression between genetically 4 identical males and females. We investigated gene expression differences between males and 5 females in four genotypes of Daphnia magna and compared the results with published data on 6 sex-biased gene expression in two other Daphnia species, each representing one of the major 7 phylogenetic clades within the genus. We found that 42 % of all annotated genes showed sex-8 biased expression in D. magna. This proportion is similar both to estimates from other Daphnia 9 species as well as from species with genetic sex determination, suggesting that sex-biased 10 expression is not reduced under environmental sex determination. Among 7453 single copy, 11 one-to-one orthologs in the three Daphnia species, 707 consistently showed sex-biased 12 expression and 675 were biased in the same direction in all three species. Hence these genes 13 represent a core-set of genes with consistent sex-differential expression in the genus. A 14 functional analysis identified that several of them are involved in known sex determination 15 pathways. Moreover, 75 % were overexpressed in females rather than males, a pattern that 16 appears to be a general feature of sex-biased gene expression in Daphnia. 17 18 species with genetic sex determination, suggesting that sex-biased expression is not necessarily 26 reduced under environmental sex determination. 27 28

Sex-Biased Gene Expression and Isoform Profile of Brine Shrimp Artemia franciscana by Transcriptome Analysis

“…In case of crustaceans, transcriptomic analysis of the Norway lobster Nephrops norvegicus in multiple tissues showed a higher number of male-specific transcripts compared with females [ 14 ]. However, the opposite results appeared in Pacific white shrimp Litopenaeus vannamei and water flea Daphnia species [ 65 , 66 , 67 ]. Thus, further discussion on the evolutionary rates of sex-biased genes in crustaceans is indicated.…”

Sex differences in the strength of selection under facultative sex

“…A substantial proportion of genes is only expressed in a fraction of population members or in some generations. One of the most obvious cases of such conditional gene expression are the numerous genes with male and female specific expression (Mank 2017;Molinier et al 2018). In many situations (but not all, see Harts et al 2014), sex-specificity translates into a simple expectation of a 'tug-of-war' where the overall selection coefficient can be computed by averaging over the sex-specific effects.…”

“…Arguably the most common situation of conditional gene expression is related to sex-linked expression, with thousands of genes being reported to have sex-linked expression (Parsch and Ellegren 2013;Mank 2017;Molinier et al 2018). Conditional expression can be even more extreme when sex-linked gene expression occurs in facultatively sexual species, i.e.…”

Transcriptome analysis of different life-history stages and screening of male-biased genes in Daphnia sinensis

“…Male-biased expression is enriched for cuticle and protease function [14]. Huylmans et al (2016) and Molinier et al (2018) analyzed the sex-biased genes between the female and male of Daphnia galeata and Daphnia magna, respectively [15,16]. Moreover, the female-biased genes of Daphnia sinensis might contribute to maintaining rapid production of parthenogenetic females, and nutrient uptake for the growth of neonates [17].…”