Biology subjects

Berbel-Filho, W. M.

Publications and source records attributed to Berbel-Filho, W. M..

5 recordsLinked to original sources

bioRxiv2026

Ancestral gene flow shaped the singular origin of the Amazon molly

The evolutionary origins of asexuality remain poorly understood, despite extensive research on its ecological and evolutionary consequences. Asexuality often arises through hybridization between species with intermediate genomic divergence, implying that hybrid-induced asexuality may be partly repeatable. The Amazon molly (Poecilia formosa), the first asexual vertebrate known to science, challenges this view: repeated experimental crosses between its extant parental species have failed to recreate a stable Amazon molly-like lineage. This apparent paradox gave rise to the Rare Formation Hypothesis, which proposes that stable asexuality requires an exceptionally specific genomic combination. Here, we combine experimental crosses, molecular cytogenetics, and population genomics to test whether ancestral introgression before the hybrid speciation event set the stage for the singular origin of the Amazon molly. We show that most experimental hybrids are viable but sexual, but that a subset of F1 hybrids produce unreduced eggs through a mechanism distinct from that of the Amazon molly. Population genomic analyses reveal that introgression between parental species likely predated the formation of the Amazon molly, and shared homozygous tracts across Amazon molly genomes support inheritance from admixed progenitors. Together, our findings reconcile the repeatable and contingent views of the origin of asexuality, suggesting that ancestral introgression may be the missing mechanism assembling the rare genomic combinations required for seemingly unrepeatable evolutionary innovations, including the emergence of asexual species.

evolutionary biology↗

bioRxiv2023

Why Do Hybrids Turn Down Sex?

Asexual reproduction is ancestral in prokaryotes; the switch to sexuality in eukaryotes is one of the major transitions in the history of life. The study of the maintenance of sex in eukaryotes has raised considerable interest for decades and is still one of evolutionary biologys most prominent question. The observation that many asexual species are of hybrid origin have led some to propose that asexuality in hybrids results from sexual processes being disturbed because of incompatibilities between the two parental species genomes. This proximate theory appears difficult in real life, as it requires fundamental reproductive traits to be profoundly altered without collapsing individuals fertility. Repeated failures to produce asexual Amazon Molly in the lab through crossing experiments show that we are still in need of an evolutionary explanation. Here, we present a mathematical model and propose an adaptive route for the evolution of asexuality from previously sexual hybrids. Under smaller reproductive alterations, we show that asexuality can evolve to rescue hybrids reproduction. Importantly, we highlight that when incompatibilities only affect the fusion of sperm and eggs genomes, unreduced meiosis and paternal genome elimination can evolve separately, greatly facilitating the overall evolutionary route.

evolutionary biology↗

bioRxiv2020

More than meets the eye: syntopic and morphologically similar mangrove killifish species show different mating systems and patterns of genetic structure along the Brazilian coast

Different mating systems can strongly affect the extent of genetic diversity and population structure among species. Given the increased effects of genetic drift on reduced population size, theory predicts that species undergoing self-fertilization should have greater population structure than outcrossed species, however demographic dynamics may affect this scenario. The mangrove killifish clade is composed of the two only known examples of self-fertilising species among vertebrates (Kryptolebias marmoratus and K. hermaphroditus). A third species in this clade, K. ocellatus, inhabits mangrove forests in southeast Brazil, however its mating system and patterns of genetic structure have been rarely explored. Here, we examined the genetic structure and phylogeographic patterns of K. ocellatus along its distribution, using mitochondrial DNA and microsatellites to compare its patterns of genetic structure with the predominantly selfing and often syntopic, K. hermaphroditus. Our results indicate that K. ocellatus reproduces mainly by outcrossing across much of its known range, with no current evidence of selfing, despite being an androdioecious species. Our results also reveal a stronger population subdivision in K. ocellatus compared to K. hermaphroditus, contrary to the theoretical predictions based on reproductive biology of the two species Our findings indicate that, although morphologically similar, K. ocellatus and K. hermaphroditus had remarkably different evolutionary histories when colonising the same mangrove areas in south-eastern Brazil, with other factors (e. g. time of colonisation, dispersal/establishment capacity) having more profound effects on the current population structuring of those species than differences in mating systems.

evolutionary biology↗

bioRxiv2020

Additive and non-additive epigenetic signatures of hybridisation between fish species with different mating systems

Hybridisation is a major source of evolutionary innovation. However, several prezygotic and postzygotic factors influence its likelihood and evolutionary outcomes. Differences in mating systems can have a major effect on the extent and direction of hybridisation and introgression. In plants, epigenetic mechanisms help to stabilize hybrid genomes and contribute to reproductive isolation, but the relationship between genetic and epigenetic changes in animal hybrids is unclear. We analysed the extent of a unique case of natural hybridisation between two genetically distant mangrove killifish species with different mating systems, Kryptolebias hermaphroditus (self-fertilising) and K. ocellatus (outcrossing), and the methylation patterns of their hybrids. Hybridisation rate between the species ranged between 14% and 26%. Although co-existing parental species displayed highly distinct genetic (microsatellites and SNPs) and methylation patterns (37,000 differentially methylated cytosines), our results indicate that F1 hybrids are viable and able to backcross with parental species. Hybrids had predominantly intermediate methylation patterns (88.5% of the sites) suggesting additive effects, as expected from hybridisation between genetically distant species. Differentially methylated cytosines between hybrids and both parental species (5,800) suggest that introgressive hybridisation may play a role in generating novel genetic and epigenetic variation which could lead to species diversification. We also found a small percentage of non-additive epigenetic effects which might act as an evolutionary bet-hedging strategy and increase fitness under environmental change.

evolutionary biology↗

bioRxiv2019

Local parasite pressures and host genotype may modulate epigenetic diversity in a mixed-mating fish

Parasite-mediated selection is one of the main drivers of genetic variation in natural populations. The persistence of asexual reproduction and self-fertilization, however, challenges the notion that low genetic variation and inbreeding compromise the hosts ability to respond to pathogens. DNA methylation represents a potential mechanism for generating additional adaptive variation under low genetic diversity. We compared genetic diversity (microsatellites and AFLPs), variation in DNA methylation (MSAFLPs), and parasite loads in three populations of Kryptolebias hermaphroditus, a unique mixed-mating (partially self-fertilising) fish, to analyse the potential adaptive value of DNA methylation in relation to genetic diversity and parasite loads. We found strong genetic population structuring, as well as differences in parasite loads and methylation levels among sampling sites and selfing lineages. Globally, the interaction between parasites and inbreeding with selfing lineages influenced DNA methylation, but parasites seemed more important in determining methylation levels at the local scale.

zoology↗