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April 21, 2020  |  

Divergent evolutionary trajectories following speciation in two ectoparasitic honey bee mites.

Multispecies host-parasite evolution is common, but how parasites evolve after speciating remains poorly understood. Shared evolutionary history and physiology may propel species along similar evolutionary trajectories whereas pursuing different strategies can reduce competition. We test these scenarios in the economically important association between honey bees and ectoparasitic mites by sequencing the genomes of the sister mite species Varroa destructor and Varroa jacobsoni. These genomes were closely related, with 99.7% sequence identity. Among the 9,628 orthologous genes, 4.8% showed signs of positive selection in at least one species. Divergent selective trajectories were discovered in conserved chemosensory gene families (IGR, SNMP), and Halloween genes (CYP) involved in moulting and reproduction. However, there was little overlap in these gene sets and associated GO terms, indicating different selective regimes operating on each of the parasites. Based on our findings, we suggest that species-specific strategies may be needed to combat evolving parasite communities. © The Author(s) 2019.


April 21, 2020  |  

Characterization of a male specific region containing a candidate sex determining gene in Atlantic cod.

The genetic mechanisms determining sex in teleost fishes are highly variable and the master sex determining gene has only been identified in few species. Here we characterize a male-specific region of 9?kb on linkage group 11 in Atlantic cod (Gadus morhua) harboring a single gene named zkY for zinc knuckle on the Y chromosome. Diagnostic PCR test of phenotypically sexed males and females confirm the sex-specific nature of the Y-sequence. We identified twelve highly similar autosomal gene copies of zkY, of which eight code for proteins containing the zinc knuckle motif. 3D modeling suggests that the amino acid changes observed in six copies might influence the putative RNA-binding specificity. Cod zkY and the autosomal proteins zk1 and zk2 possess an identical zinc knuckle structure, but only the Y-specific gene zkY was expressed at high levels in the developing larvae before the onset of sex differentiation. Collectively these data suggest zkY as a candidate master masculinization gene in Atlantic cod. PCR amplification of Y-sequences in Arctic cod (Arctogadus glacialis) and Greenland cod (Gadus macrocephalus ogac) suggests that the male-specific region emerged in codfishes more than 7.5 million years ago.


April 21, 2020  |  

Comparative genomic and phylogenetic analyses of Populus section Leuce using complete chloroplast genome sequences

Species of Populus section Leuce are distributed throughout most parts of the Northern Hemisphere and have important economic and ecological significance. However, due to frequent hybridization within Leuce, the phylogenetic relationship between species has not been clarified. The chloroplast (cp) genome is characterized by maternal inheritance and relatively conservative mutation rates; thus, it is a powerful tool for building phylogenetic trees. In this study, we used the PacBio SEQUEL software to determine that the cp genome of Populus tomentosa has a length of 156,558 bp including a long single-copy region (84,717 bp), a small single-copy region (16,555 bp), and a pair of inverted repeat regions (27,643 bp). The cp genome contains 131 unique genes, including 37 transfer RNAs, 8 ribosomal RNAs, and 86 protein-coding genes. We compared the cp genomes of seven species of section Leuce and identified five cp DNA markers with >?1% variable sites. Phylogenetic analyses revealed two evolutionary branches for section Leuce. The species with the closest relationship with P. tomenstosa was P. adenopoda, followed by P. alba. These cp genome data will help to determine the cp evolution of section Leuce and further elucidate the origin of P. tomentosa.


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