Matthias Stöck

A bisexually reproducing all-triploid vertebrate

Green toads are common in the Palaearctic region, where they have differentiated into several taxa. The toads exist with variable amounts of ploidy, similar to other anuran species or reptiles. In vertebrate biology, the very rare occurrence of triploidy is coupled with infertility or unisexuality, or requires the coexistence of individuals of different ploidy in a reproductive community. The reproduction of naturally occurring triploids has been reported to occur only through parthenogenesis, gynogenesis or hybridogenesis. The bisexual reproduction of pure triploids has been considered to be impossible because of the problem of equally distributing three chromosome sets in meiosis. Here we report geographically isolated populations of green toads (Bufo viridis complex) that are all-triploid and reproduce bisexually.

Post-Messinian evolutionary relationships across the Sicilian channel: mitochondrial and nuclear markers link a new green toad from Sicily to African relatives.

BackgroundLittle attention has been paid to the consequences of the last landbridge between Africa and Sicily on Mediterranean biogeography. Previous paleontological and scarce molecular data suggest possible faunal exchange later than the well-documented landbridge in the Messinian (5.3 My); however, a possible African origin of recent terrestrial Sicilian fauna has not been thoroughly tested with molecular methods. To gain insight into the phylogeography of the region, we examine two mitochondrial and two nuclear markers (one is a newly adapted intron marker) in green toads (Bufo viridis subgroup) across that sea barrier, the Strait of Sicily.ResultsExtensive sampling throughout the western Mediterranean and North Africa revealed a deep sister relationship between Sicilian (Bufo siculus n.sp.) and African green toads (B. boulengeri) on the mitochondrial and nuclear level. Divergence times estimated under a Bayesian-coalescence framework (mtDNA control region and 16S rRNA) range from the Middle Pliocene (3.6 My) to Pleistocene (0.16 My) with an average (1.83 to 2.0 My) around the Pliocene/Pleistocene boundary, suggesting possible land connections younger than the Messinian (5.3 My). We describe green toads from Sicily and some surrounding islands as a new endemic species (Bufo siculus). Bufo balearicus occurs on some western Mediterranean islands (Corsica, Sardinia, Mallorca, and Menorca) and the Apennine Peninsula, and is well differentiated on the mitochondrial and nuclear level from B. siculus as well as from B. viridis (Laurenti), whose haplotype group reaches northeastern Italy, north of the Po River. Detection of Calabrian B. balearicus haplotypes in northeastern Sicily suggests recent invasion. Our data agree with paleogeographic and fossil data, which suggest long Plio-Pleistocene isolation of Sicily and episodic Pleistocene faunal exchange across the Strait of Messina. It remains unknown whether both species (B. balearicus, B. siculus) occur in sympatry in northern Sicily.ConclusionOur findings on green toads give the first combined mitochondrial and nuclear sequence evidence for a phylogeographic connection across the Strait of Sicily in terrestrial vertebrates. These relationships may have implications for comparative phylogeographic research on other terrestrial animals co-occurring in North Africa and Sicily.

Sperm-Dependent Parthenogenesis and Hybridogenesis in Teleost Fishes

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.

A VERTEBRATE REPRODUCTIVE SYSTEM INVOLVING THREE PLOIDY LEVELS: HYBRID ORIGIN OF TRIPLOIDS IN A CONTACT ZONE OF DIPLOID AND TETRAPLOID PALEARCTIC GREEN TOADS (BUFO VIRIDIS SUBGROUP)*

The rise and consequences of polyploidy in vertebrates, whose origin was associated with genome duplications, may be best studied in natural diploid and polyploid populations. In a diploid/tetraploid (2n/4n) geographic contact zone of Palearctic green toads in northern Kyrgyzstan, we examine 4ns and triploids (3n) of unknown genetic composition and origins. Using mitochondrial and nuclear sequence, and nuclear microsatellite markers in 84 individuals, we show that 4n (Bufo pewzowi) are allopolyploids, with a geographically proximate 2n species (B. turanensis) being their maternal ancestor and their paternal ancestor as yet unidentified. Local 3n forms arise through hybridization. Adult 3n mature males (B. turanensis mtDNA) have 2n mothers and 4n fathers, but seem distinguishable by nuclear profiles from partly aneuploid 3n tadpoles (with B. pewzowi mtDNA). These observations suggest multiple pathways to the formation of triploids in the contact zone, involving both reciprocal origins. To explain the phenomena in the system, we favor a hypothesis where 3n males (with B. turanensis mtDNA) backcross with 4n and 2n females. Together with previous studies of a separately evolved, sexually reproducing 3n lineage, these observations reveal complex reproductive interactions among toads of different ploidy levels and multiple pathways to the evolution of polyploid lineages.

Multiple origins of tetraploid taxa in the Eurasian Bufo viridis subgroup

We used Q-banding and analyzed nucleolar organizing regions (NORs) to study the cytogenetic evolution of tetraploids within the Palearctic Bufo viridis subgroup, the only known amphibian complex comprising di-, tri- and tetraploid bisexually reproducing taxa. We examined three diploid (2n) nominal taxa (Bufo viridis viridis, B. v. turanensis, B. v. kermanensis) from five Eurasian localities and six tetraploid (4n) nominal taxa (B. oblongus, B. o. danatensis, B. pewzowi pewzowi, B. p. taxkorensis, B. p. unicolor, B. p. strauchi) from eight Central Asian localities. Homeologous chromosomes of 2n and 4n toads exhibit a similar morphology. Silver-staining and in situ hybridization revealed terminal NORs in the long arms of chromosomes 6 in all 2n but in only two out of four chromosomes 6 in all 4n taxa. Q-banding and a rapidly evolving mitochondrial marker suggest at least two origination events for Asian 4n toads: “Western Central Asian tetraploids’’ (B. oblongus Nikolsky, 1896) exhibit distinct differences within some chromosome quartets, which are divisible into pairs of chromosomes and may be allopolyploid. In contrast, “Central Asian tetraploids” (B. pewzowi Bedriaga, 1898) showed homogenous Q-banding patterns within each quartet, suggesting autopolyploidy. In Northeastern Iran, we discovered a zone of either common ancestry or hybridization of 2n and Western Central Asian 4n toads. This raises intriguing questions about how diploid and tetraploid taxa may evolve by exchanging genetic material.

Mosaicism in somatic triploid specimens of the Bufo viridis complex in the Karakoram with examination of calls, morphology and taxonomic conclusions

Abstract The discovery of triploidy in green toads from the Karakoram range and West Himalayas (Northern Pakistan) is reported. Somatic, mitotic metaphases comprising 33 conventionally and quinacrine mustard stained chromosomes are described. Meiotic metaphases and diakineses demonstrate the occurrence of different ploidy levels (diploid, triploid, tetraploid) in the male germ line of somatic triploid specimens. Flow cytometric data on DAPI stained blood samples from 54 specimens preliminarily seem to provide evidence for all‐triploid populations. The mean projection areas of 30 erythrocytes per specimen were measured. The analysis of 16 morphometric characters with univariate and multivariate methods and the comparison with published data exhibited differences of the present toads to both diploid and tetraploid toads from Middle Asia. Bioacoustic analyses revealed similarity of mating calls to those of tetraploid toads. A single specimen of Bufo (viridis) pseudoraddei Mertens 1971, was also found to be t...

Why comparing polyploidy research in animals and plants

transcriptomic shock’ [Buggs et al., 2011], rapid and repeated gene loss in young allopolyploids [Buggs et al., 2012b] as well as changes in polyploid gene expression [Roulin et al., 2012]. Schartl et al. [2013] hypothesize that paralog retention after ancient genome duplication may have supported the high level of behavioral complexity in some teleosts. A role of small RNAs in allopolyploid and hybrid gene expression has been suggested [Ignacio et al., 2012], which generate morphological variation and hybrid vigor as well as transgressive phenotypes with potential for adaptive evolution [Ng et al., 2012]. Latest studies propose a role of cis and trans -regulatory elements and chromatin modifications on gene expression diversity in allotetraploids [Shi et al., 2012]. Technological advances will soon also allow testing newly proposed mechanisms for gene expression in relation to cellular volume and genome size [Marguerat and Bähler, 2012]. Polyploidy is currently further studied regarding modifications of the cell cycle, biological networks, metabolic phenotypes, and in context to tumor biology [Mayfield-Jones et al., 2013]. Latest applications of research on ploidy changes include the creation of haploid mammalian pluripotent cell lines from which live transgenic mice could be produced [Li et al., 2012]. Despite its path-making character, not all the scientific progress depends on technology. Especially interactions between organisms of different ploidy levels ‘ Major botanical advances often suffer the worst of fates – the scientific community ignores them until they are independently ‘discovered’ or confirmed by zoologists. For example, the principles of inheritance, initially worked out in the garden pea were not generally accepted until verified in animals (Bateson 1902) ’ Rieseberg and Burke [2001]