05/24/2026
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Here, researchers investigated an unusual reproductive event in the normally biparental cichlid fish ๐ถ๐ฆ๐โ๐๐ก๐๐๐๐๐๐ ๐๐๐๐๐ก๐๐ ๐, in which a female produced offspring without a male. Using whole-genome sequencing data, the authors analysed whether reproduction occurred via selfing or parthenogenesis by comparing patterns of heterozygosity with those from a wild, genetically diverse ๐ถ๐ฆ๐โ๐๐ก๐๐๐๐๐๐ ๐๐๐๐๐ก๐๐ ๐ family collected in Lake Tanganyika and a closely related in**ed ๐ถ๐ก๐๐๐๐โ๐๐๐๐๐ ๐๐๐๐กโ๐๐๐๐๐ family.
The study provides rare genomic evidence of selfing in a vertebrate and suggests that such alternative reproductive modes may be overlooked rather than truly absent. The findings contribute to a broader understanding of how alternative reproductive strategies evolve in vertebrate lineages.
Extract from paper - "The regular mode of s*xual reproduction is biparental in vertebrates and is also predominant for cichlids as well as the here investigated species ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐. The percentage of heterozygous sites (Table S1) was higher in the wild ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐ parental individuals (20.10 ยฑ 2.85%) and the uniparental female (15.42%) than in the in**ed ๐ถ๐ก. ๐๐๐๐กโ๐๐๐๐๐ parents (5.71 ยฑ 0.08%), supporting that biparental s*xual reproduction is the predominant reproductive mode in ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐, with selfing representing a facultative mode under certain environmental conditions or reproductive constraints.
There are a few reported cases of selfing in fishes, specifically, in the mangrove killifish ๐พ๐๐ฆ๐๐ก๐๐๐๐๐๐๐ ๐๐๐๐๐๐๐๐ก๐ข๐ and ๐พ. โ๐๐๐๐๐โ๐๐๐๐๐ก๐ข๐ , and in the cichlid fish ๐ต๐๐๐๐ก๐๐โ๐๐๐๐๐ ๐๐๐๐๐๐๐๐๐ ๐๐๐๐ . In natural populations of ๐พ. ๐๐๐๐๐๐๐๐ก๐ข๐ , males are rare and many individuals are simultaneous hermaphrodites that reproduce via selfing. In cichlids, s*x determination is controlled by highly dynamic s*x chromosomes, and s*x change can occur in some species. However, whether ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐ is capable of s*x change during its lifetime is so far unknown. Moreover, Svensson et al., 2016 reported a functional hermaphrodite first-generation hybrid capable of selfing, obtained by crossing two s*xually reproducing ๐๐ข๐๐๐๐๐๐๐๐ species. Therefore, selfing may be possible in cichlids under certain conditions. Notably, natural hybridization has been observed along a narrow hybrid zone between the northerly distributed ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐ and its southern sister species ๐ถ๐ฆ. ๐๐๐๐๐๐๐๐ ๐. Yet, our uniparental ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐ female shows heterozygosity estimates comparable to those of the wild parents, originating from outside the hybrid zone, making a hybrid origin unlikely as elevated heterozygosity would be expected under recent hybridization.
By using selfing as an adaptive strategy, organisms can assure reproduction when males are unavailable. In contrast to as*xual reproduction, selfing may also be more efficient to purge deleterious recessive mutations. Facultative selfing is therefore expected to be favoured in systems where mating opportunities are unpredictable or spatially constrained. In cichlids, such conditions may be influenced by life-history traits and temporal or spatial environmental heterogeneity shaping reproductive opportunities. ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐ is one of the larger Lake Tanganyika cichlids, reaching a total length of 35 cm, and inhabits deeper rocky habitats where it typically occurs in social groups consisting of a dominant male and multiple females. Such a social structure, combined with spatial segregation in patchily distributed habitats in the northern part of the lake, may lead to periods of limited mate access for some individuals.
In addition, ๐ถ๐ฆ. ๐๐๐๐๐ก๐๐ ๐ is a maternal mouthbrooder with a long brooding period of approximately 40 days and low fecundity, increasing costs of reproductive failure when mating opportunities are rare or unpredictable. Under these conditions, facultative selfing could represent an alternative reproductive strategy that ensures reproductive output when males are unavailable, particularly in isolated or low density habitats. Beyond these short-term fitness benefits, reproductive flexibility may also have longer-term evolutionary consequences. Given that variation in life-history traits is discussed to contribute to diversification in adaptive radiations, our results suggest that such reproductive flexibility may constitute an additional mechanism facilitating rapid speciation.
Future studies should therefore address two complementary questions: under which ecological and social conditions โ such as low population density, reduced habitat connectivity, or skewed s*x ratios โ alternative reproductive modes are expressed, and whether such flexibility ultimately promotes or constrains diversification in adaptive radiations."
* Correction to above extract, noted by Alan Smith in comments - In the Svenson et al paper the selfing fish was a ๐๐ข๐๐๐๐๐๐๐๐ x ๐๐๐๐โ๐๐๐๐๐ hybrid, not two ๐๐ข๐๐๐๐๐๐๐๐ species as stated.
๐ฅ๐ฒ๐๐ฒ๐ฎ๐ฟ๐ฐ๐ต ๐ง๐ถ๐๐น๐ฒ
Genomic evidence for facultative selfing in the cichlid fish ๐ถ๐ฆ๐โ๐๐ก๐๐๐๐๐๐ ๐๐๐๐๐ก๐๐ ๐
Open-access (preprint) - https://www.biorxiv.org/content/10.64898/2026.05.13.724898v1
๐ช๐ต๐ฎ๐ ๐ถ๐ ๐ฎ ๐ฃ๐ฟ๐ฒ๐ฝ๐ฟ๐ถ๐ป๐ ๐ฃ๐๐ฏ๐น๐ถ๐ฐ๐ฎ๐๐ถ๐ผ๐ป?
https://www.biorxiv.org/content/what-unrefereed-preprint
๐๐ถ๐๐ฎ๐๐ถ๐ผ๐ป
M. Efe Uysal, Daniela Souza-Costa, Allison Marks, Adrian Indermaur, Wolfgang Gessl, Walter Salzburger, Julia M. I. Barth, Genomic evidence for facultative selfing in the cichlid fish ๐ถ๐ฆ๐โ๐๐ก๐๐๐๐๐๐ ๐๐๐๐๐ก๐๐ ๐. bioRxiv 2026.05.13.724898; doi: https://doi.org/10.64898/2026.05.13.724898
๐๐ฏ๐๐๐ฟ๐ฎ๐ฐ๐
Organisms have evolved a remarkable diversity of reproductive strategies in response to environmental variations and selective pressures. Although most vertebrates do reproduce biparentally, rare alternative modes such as selfing (self-fertilization) and different forms of parthenogenesis exist, but remain poorly characterized. Here, we investigated an unusual reproductive event in the normally biparental cichlid fish ๐ถ๐ฆ๐โ๐๐ก๐๐๐๐๐๐ ๐๐๐๐๐ก๐๐ ๐, in which a female produced offspring in the absence of a male. Using whole-genome sequencing data, we analyzed whether reproduction occurred via selfing or parthenogenesis by comparing patterns of heterozygosity with those from a wild, genetically diverse ๐ถ. ๐๐๐๐๐ก๐๐ ๐ family collected in Lake Tanganyika and a closely related in**ed ๐ถ๐ก๐๐๐๐โ๐๐๐๐๐ ๐๐๐๐กโ๐๐๐๐๐ family. The uniparental family exhibited reduced genetic diversity, elevated relatedness, and genome-wide patterns of homozygosity distinct from those expected under parthenogenesis or inbreeding, but consistent with self-fertilization. Our study provides rare genomic evidence of selfing in a vertebrate and suggests that such alternative reproductive modes may be overlooked rather than truly absent. These findings contribute to a broader understanding of how alternative reproductive strategies evolve in vertebrate lineages.
๐ฆ๐ถ๐ด๐ป๐ถ๐ณ๐ถ๐ฐ๐ฎ๐ป๐ฐ๐ฒ The overwhelming majority of vertebrates reproduce s*xually, requiring a male and a female to produce genetically distinct offspring. Yet, rare alternative modes involving only a single parent such as as*xual parthenogenesis (โvirgin birthโ) or self-fertilization challenge this paradigm. Among these, selfing is exceptionally uncommon and poorly studied in vertebrates. Here, we unveiled - based on genomic analyses - the reproductive strategy of a member of the extraordinarily diverse cichlid fish radiation in Lake Tanganyika that reproduced in captivity in the absence of a male. By comparing patterns of genome-wide heterozygosity with both wild and in**ed reference families, we identified a rare case of selfing. This finding adds to the limited records of selfing in vertebrates and expands current understanding of reproductive diversity, highlighting the power of whole-genome sequencing to distinguish among alternative reproductive mechanisms.
๐ฃ๐ต๐ผ๐๐ผ ๐๐ฟ๐ฒ๐ฑ๐ถ๐
Top - Portrait photo of male ๐ถ๐ฆ๐โ๐๐ก๐๐๐๐๐๐ ๐ ๐. (aquarium raised). Shutterstock stock photo, cropped.
Bottom - During canonical meiosis, DNA replication is followed by two successive divisions (meiosis I and II) to produce haploid gametes (a). Diploidy is restored in s*xual reproduction either by fusion of gametes from two individuals (outcrossing), maintaining genome-wide heterozygosity, or by fusion of two independent gametes from the same individual (selfing), resulting in genome-wide reduction and stochastic redistribution of heterozygosity (b). In as*xual (parthenogenetic) reproduction, diploidy is restored without fertilisation, either via mitotic divisions (apomixis) producing clonal offspring with fully retained heterozygosity, or via altered meiosis (automixis) (c). Automixis comprises distinct cytological mechanisms with characteristic genomic outcomes: Fusion of meiotic products (d) can occur after meiosis I (central fusion), reuniting homologs and retaining high heterozygosity, particularly in regions of low recombination (e.g., near centromeres), or after meiosis II (terminal fusion), where fusion of sister chromatids results in extensive homozygosity. Alternatively, in automixis, diploidy can be restored through modification of meiotic division itself (e): Suppression of meiosis I (first division restitution, FDR) prevents homolog segregation and largely preserves heterozygosity, whereas suppression of meiosis II (second division restitution, SDR) allows homolog segregation but retains sister chromatids, resulting in partial loss of heterozygosity with recombination-dependent patterns. In premeiotic endoreplication, genome duplication prior to meiosis leads to pairing of identical copies, effectively bypassing homolog interactions and preserving heterozygosity. Finally, postmeiotic genome duplication (gamete duplication) (f) restores diploidy by doubling a haploid genome, resulting in complete homozygosity. Percentages display retained heterozygosity (H).
ยฉ 2026 the Author(s). Published on bioRxiv Preprint Server. This paper is released under a Creative Commons Attribution 4.0 International (CC-BY-4.0) licence.
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