Lipinska AP et al. (2016), Molecular evolution of candidate male reproduct...

ECB-ART-44429

BMC Evol Biol 2016 Jan 05;16:5. doi: 10.1186/s12862-015-0577-9.

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Molecular evolution of candidate male reproductive genes in the brown algal model Ectocarpus.

Lipinska AP , Van Damme EJ , De Clerck O .

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BACKGROUND: Evolutionary studies of genes that mediate recognition between sperm and egg contribute to our understanding of reproductive isolation and speciation. Surface receptors involved in fertilization are targets of sexual selection, reinforcement, and other evolutionary forces including positive selection. This observation was made across different lineages of the eukaryotic tree from land plants to mammals, and is particularly evident in free-spawning animals. Here we use the brown algal model species Ectocarpus (Phaeophyceae) to investigate the evolution of candidate gamete recognition proteins in a distant major phylogenetic group of eukaryotes. RESULTS: Male gamete specific genes were identified by comparing transcriptome data covering different stages of the Ectocarpus life cycle and screened for characteristics expected from gamete recognition receptors. Selected genes were sequenced in a representative number of strains from distant geographical locations and varying stages of reproductive isolation, to search for signatures of adaptive evolution. One of the genes (Esi0130_0068) showed evidence of selective pressure. Interestingly, that gene displayed domain similarities to the receptor for egg jelly (REJ) protein involved in sperm-egg recognition in sea urchins. CONCLUSIONS: We have identified a male gamete specific gene with similarity to known gamete recognition receptors and signatures of adaptation. Altogether, this gene could contribute to gamete interaction during reproduction as well as reproductive isolation in Ectocarpus and is therefore a good candidate for further functional evaluation.

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Species referenced: Echinodermata
Genes referenced: LOC100887844 LOC100893907 LOC115923812 mt-co3 pkd1l2a

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References [+] :

Altschul, Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. 1997, Pubmed

	Fig. 1. Species tree and species sexual compatibility. Maximum likelihood tree based on the cox3 gene from nine Ectocarpus strains and two Scytosiphon lomentaria specimens. Strains used in this study are marked with blue bars. ML bootstrap (left) and Bayesian posterior probability (right) values are shown. Red lines define species with prezygotic barriers to fertilization; dotted lines describe species with uncertain gamete compatibility; grey shading indicates pairwise d N /d S > 1 (PAML) (see Additional file 4)

	Fig. 3. Topology of Esi0130_0068 as predicted by Phyre2 and Blast2GO. The extracellular and cytoplasmic sides of the membrane are labeled and the beginning and end of each transmembrane helix are indicated by the residue index. Positively selected sites identified by PAML 4 are marked with orange arrows, sites identified by HyPhy are marked in blue