Genetic control of male production in Daphnia pulex

Abstract

Daphnia normally reproduce by cyclical parthenogenesis, with offspring sex being determined by environmental cues. However, some females have lost the ability to produce males. Our results demonstrate that this loss of male-producing ability is controlled by a dominant allele at a single locus. We identified the locus by comparing whole-genome sequences of 67 nonmale-producing (NMP) and 100 male-producing (MP) clones from 5 Daphnia pulex populations, revealing 132 NMP-linked SNPs and 59 NMP-linked indels within a single 1.1-Mb nonrecombining region on chromosome I. These markers include 7 nonsynonymous mutations, all of which are located within one unannotated protein-coding gene (gene 8960). Within this single gene, all of the marker-linked NMP haplotypes from different populations form a monophyletic clade, suggesting a single origin of the NMP phenotype, with the NMP haplotype originating by introgression from a sister species, Daphnia pulicaria. Methyl farnesoate (MF) is the innate juvenile hormone in daphnids, which induces the production of males and whose inhibition results in female-only production. Gene 8960 is sensitive to treatment by MF in MP clones, but such responsiveness is greatly reduced in NMP clones. Thus, we hypothesize that gene 8960 is located downstream of the MF-signaling pathway in D. pulex, with the NMP phenotype being caused by expression change of gene 8960.

Speciation inDaphnia

“…These nonmale producers have a genetic basis which can be traced back to introgression with D . pulicaria (Ye et al, 2019).…”

The life history fitness of F1 hybrids of the microcrustaceans Daphnia pulex and Daphnia pulicaria (Crustacea, Anomopoda)

“…If F 1 s occur in nature, it is likely that some of the hybrids would survive regardless of the direction of selection and facilitate gene flow between these two species. As a matter of fact, introgression from D. pulicaria to D. pulex has been linked to the cause of two phenotypic changes, namely the origin of obligate asexual reproduction (Xu et al, 2015) and the suppression of male production (Ye et al, 2019). We note that most previous studies used only a few characteristic molecular markers (e.g., allozyme locus LDH) for species identification (e.g., Hebert et al, 1989; Hebert & Crease, 1983).…”

Evolutionary novelty in the apoptotic pathway of aphids

“…It is worth noting that, while IAP expansion might be involved in aphid-specific polyphenisms, it does not seem to be a hallmark of all arthropod polyphenisms. Indeed, even though A. mellifera , L. migratoria , or D. pulex present well-known polyphenisms ( 56 , 57 ), they show no IAP expansion.…”