Genetic basis and breeding application of clonal diversity and dual reproduction modes in polyploid Carassius auratus gibelio

A unisexual species is generally associated with polyploidy, and reproduced by a unisexual reproduction mode, such as gyno- genesis, hybridogenesis or parthenogenesis. Compared with other unisexual and polyploid species, gibel carp (Carassius au- ratus gibelio) has a higher ploidy level of hexaploid. It has undergone several successive rounds of genome polyploidy, and experienced an additional, more recent genome duplication event. More significantly, the dual reproduction modes, including gynogenesis and sexual reproduction, have been demonstrated to coexist in the polyploid gibel carp. This article reviews the genetic basis concerning polyploidy origin, clonal diversity and dual reproduction modes, and outlines the progress in new va- riety breeding and gene identification involved in the reproduction and early development. The data suggests that gibel carp are under an evolutionary trajectory of diploidization. As a novel evolutionary developmental (Evo-Devo) biology model, this work highlights future perspectives about the functional divergence of duplicated genes and the sexual origin of vertebrate animals.

Evolutionary traits and functional roles of chemokines and their receptors in the male pregnancy of the Syngnathidae

Vertebrates have developed various modes of reproduction,some of which are found in Teleosts.Over 300 species of the Syngnathidae(seahorses,pipefishes and seadragons)exhibit male pregnancies;the males have specialized brood pouches that provide immune protection,nourishment,and oxygen regulation.Chemokines play a vital role at the mammalian maternal–fetal interface;however,their functions in fish reproduction are unclear.This study revealed the evolutionary traits and potential functions of chemokine genes in 22 oviparous,ovoviviparous,and viviparous fish species through comparative genomic analyses.Our results showed that chemokine gene copy numbers and evolutionary rates vary among species with different modes of reproduction.Syngnathidae lost cxcl13 and cxcr5,which are involved in key receptor–ligand pairs for lymphoid organ development.Notably,Syngnathidae have site-specific mutations in cxcl12b and ccl44,suggesting immune function during gestation.Moreover,transcriptome analysis revealed that chemokine gene expression varies among Syngnathidae species with different types of brood pouches,suggesting adaptive variations in chemokine functions among seahorses and their relatives.Furthermore,challenge experiments on seahorse brood pouches revealed a joint immune function of chemokine genes during male pregnancy.This study provides insights into the evolutionary diversity of chemokine genes associated with different reproductive modes in fish.

Production of asexual and sexual offspring in the triploid sexual planarian Dugesia ryukyuensis

Certain freshwater planarians reproduce asexually as well as sexually,and their chromosomal ploidies include polyploidy,aneuploidy and mixoploidy.Previously,we successfully performed an experiment in which a clonal population produced by asexual reproduction of the Dugesia ryukyuensis(OH strain)switched to the sexual mode of reproduction.Worms of this strain are triploid with a pericentric inversion on Chromosome 4.The worms were switched to sexual reproduction after being fed with sexually mature Bdellocephala brunnea,which is a sexually reproducing species.The resulting sexualized OH strain produced cocoons filled with several eggs.Two putative factors,Mendelian factor(s)and chromosomal control(s),have been proposed as determining the reproductive mode.The present study demonstrated that inbreeding of the resultant sexualized worms produced the following four types of offspring through sexual reproduction:diploid asexual worms,triploid asexual worms,diploid sexual worms and triploid sexual worms.The chromosomal mutation on Chromosome 4 was inherited by these offspring independent of their reproductive mode.These results provide two important pieces of information:(i)the putative genetic factor was not necessarily inherited in a Mendelian fashion;and(ii)the reproductive mode is not regulated by chromosomal changes such as polyploidy or chromosomal mutations.This suggests that asexuality in D.ryukyuensis is regulated by an unknown factor(s)other than a Mendelian factor or a chromosomal control.