Sperm-Dependent Parthenogenesis and Hybridogenesis in Teleost Fishes

Abstract

In so-called unisexual teleost fishes, a broad spectrum of evolutionary stages with varying amounts of sexual elements has evolved. These range from pure sperm-dependent parthenogenesis (gynogenesis) without or with different amounts of paternal leakage to hybridogenesis with hemiclonal diploid gametogenesis or genome elimination followed by meiosis (meiotic hybridogenesis). All of these phenomena are of hybrid origin. Many of these fish form complexes which involve the coexistence of one or more sexually reproducing species with derived all-female forms that have various ploidy levels and reproductive modes, including gynogenesis, (meiotic) hybridogenesis and sexual reproduction. In teleosts, parthenogenetic reproduction is strictly dependent on sperm to initiate embryonic development. As opposed to true parthenogenesis, sperm-dependent parthenogenetic teleost lineages must primarily coexist with their "sperm donor", usually males from a parental sexual lineage or from a related sexual species. In some systems, gynogens were able to escape from their initial sperm donors ("host switch") and therefore, to enlarge their ranges and ecological niches. Sperm donors normally do not contribute genetically to the next generation. However, paternal leakage is observed in many systems contributing differing amounts of genetic material (from microchromosomes to entire chromosome sets) allowing interaction between genomes of different origin. Hybridogenesis is similar to gynogenesis in depending upon coexistence with sexual species but incorporates recombined genetic material by true fertilization. While hybridogens usually form clonal gametes, some triploids are capable of genome elimination followed by a normal diploid meiosis. Sperm-dependent parthenogenesis and hybridogenesis

Laboratory synthesis of an independently reproducing vertebrate species

“…Inherent to the hemiclonal mechanism of hybridogenetic reproduction, eggs only contain one of the parental genomes and diploidy must be restored via fertilization by sperm from sympatric males each generation. Even in clonally reproducing (i.e., gynogenetic) unisexual salamanders and fish where the sperm genome is not incorporated into the offspring, sperm from a related species is required to trigger embryogenesis in eggs carrying the full somatic chromosome complement (37,38). This absolute requirement for males from related sexual species is shared by all unisexual anamniotes and prevents establishment of reproductively independent unisexual species in these taxa.…”

Massive mortality of Prussian carp Carassius gibelio in the upper Elbe basin associated with herpesviral hematopoietic necrosis (CyHV-2)

“…This is known as gynogenesis and it leads to all-female offspring, each of which is considered a clone of the mother (Lamatsch & Stöck 2009). …”

Spontaneous speciation by ploidy elevation: Laboratory synthesis of a new clonal vertebrate

“…One simple possibility is that successful elevation to higher ploidy is a rare event and is facilitated in unisexual amphibians and fish because of their continuing dependence on sperm to initiate the onset of development. In unisexual fish, for example, this often leads to variable amount of paternal leakage that ranges from microchromosomes to a whole genome set (17). However, in some circumstances, hybrids between parthenogenetic and sexual reptiles are very common [e.g., as high as 50% (12)], suggesting that this alone is not the whole story.…”