Reproductive isolation of a new hybrid species, Senecio eboracensis Abbott & Lowe (Asteraceae)

Despite its role in homogenizing populations, hybridization has also been proposed as a means to generate new species. The conceptual basis for this idea is that hybridization can result in novel phenotypes through recombination between the parental genomes, allowing a hybrid population to occupy ecological niches unavailable to parental species. A key feature of these models is that these novel phenotypes ecologically isolate hybrid populations from parental populations, precipitating speciation. Here we present an alternative model of the evolution of reproductive isolation in hybrid populations that occurs as a simple consequence of selection against incompatibilities. Unlike previous models, our model does not require small population sizes, the availability of new niches for hybrids or ecological or sexual selection on hybrid traits. We show that reproductive isolation between hybrids and parents evolves frequently and rapidly under this model, even in the presence of ongoing migration with parental species and strong selection against hybrids. Our model predicts that multiple distinct hybrid species can emerge from replicate hybrid populations formed from the same parental species, potentially generating patterns of species diversity and relatedness that mimic adaptive radiations.

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Genetic divergence and the number of hybridizing species affect the path to homoploid hybrid speciation

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1809685115 ◽

2018 ◽

Vol 115 (39) ◽

pp. 9761-9766 ◽

Cited By ~ 13

Author(s):

Aaron A. Comeault ◽

Daniel R. Matute

Keyword(s):

Genetic Diversity ◽

Reproductive Isolation ◽

Genetic Divergence ◽

Adaptive Systems ◽

Parental Species ◽

Hybrid Speciation ◽

Hybrid Species ◽

Empirical Question ◽

Homoploid Hybrid

Hybridization is often maladaptive and in some instances has led to the loss of biodiversity. However, hybridization can also promote speciation, such as during homoploid hybrid speciation, thereby generating biodiversity. Despite examples of homoploid hybrid species, the importance of hybridization as a speciation mechanism is still widely debated, and we lack a general understanding of the conditions most likely to generate homoploid hybrid species. Here we show that the level of genetic divergence between hybridizing species has a large effect on the probability that their hybrids evolve reproductive isolation. We find that populations of hybrids formed by parental species with intermediate levels of divergence were more likely to mate assortatively, and discriminate against their parental species, than those generated from weakly or strongly diverged parental species. Reproductive isolation was also found between hybrid populations, suggesting differential sorting of parental traits across populations. Finally, hybrid populations derived from three species were more likely to evolve reproductive isolation than those derived from two species, supporting arguments that hybridization-supplied genetic diversity can lead to the evolution of novel “adaptive systems” and promote speciation. Our results illustrate when we expect hybridization and admixture to promote hybrid speciation. Whether homoploid hybrid speciation is a common speciation mechanism in general remains an outstanding empirical question.

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Natural hybridization between two butterfly bushes in Tibet: dominance of F1 hybrids promotes strong reproductive isolation

10.21203/rs.3.rs-42245/v2 ◽

2020 ◽

Author(s):

Rongli Liao ◽

Weibang Sun ◽

Yongpeng Ma

Keyword(s):

Reproductive Isolation ◽

Parental Species ◽

Morphological Characters ◽

Natural Hybridization ◽

Hybrid Origin ◽

F1 Hybrids ◽

Evolutionary Significance ◽

Sympatric Populations ◽

Hybrid Species ◽

Intergenic Spacers

Abstract Background: F1 hybrids acting as a bridgehead for producing later generation hybrids can have evolutionary significance through strengthening reproductive isolation or facilitating gene flow between parental species, depending on whether backcrossing can occur. It had been suggested that the Tibetan plant Buddleja wardii was a hybrid species between B. alternifolia and B. crispa based on their sympatric distributions and the morphological characters in last century. Till now however, we still have limited evidence to prove key issues to B. wardii, like if it is of hybrid origin indeed and whether it is currently a true hybrid species already.Results: In the present study, two sympatric populations of these three taxa were examined and compared using four nuclear genes and three chloroplast intergenic spacers, as well as with 10 morphological characters. Our results suggest that at both sites B. × wardii was likely to be a hybrids between B. alternifolia and B. crispa, and moreover, most of the hybrids present were confirmed to be F1s. This was further supported by morphology as no transgressive characters were detected. B. crispa was found to be the maternal parent in one population (BH), while in the second population (TJ), it was difficult to distinguish the hybridization direction due to shared haplotypes of cpDNA between B. alternifolia and B. crispa. Conclusions: These results provide evidence that the natural hybrids between B. alternifolia and B. crispa mainly comprise F1 hybrids, which have subsequently been given the name B. wardii. The F1 hybrids have also contributed to strong reproductive isolation between parental species.

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Natural Hybridization between Two Butterfly Bushes in Tibet: Dominance of F1 Hybrids Promotes Strong Reproductive Isolation

10.21203/rs.3.rs-42245/v1 ◽

2020 ◽

Author(s):

Rongli Liao ◽

Weibang Sun ◽

Yongpeng Ma

Keyword(s):

Reproductive Isolation ◽

Parental Species ◽

Morphological Characters ◽

Natural Hybridization ◽

Hybrid Origin ◽

F1 Hybrids ◽

Evolutionary Significance ◽

Sympatric Populations ◽

Hybrid Species ◽

Intergenic Spacers

Abstract Background: F1 hybrids acting as a bridgehead for producing later generation hybrids can have evolutionary significance through strengthening reproductive isolation or facilitating gene flow between parental species, depending on whether backcrossing can occur. It had been suggested that the Tibetan plant Buddleja wardii was a hybrid species between B. alternifolia and B. crispa based on their sympatric distributions and the morphological characters in last century. Till now however, we still have limited evidence to prove key issues to B. wardii, like if it is of hybrid origin indeed and whether it is currently a true hybrid species already.Results: In the present study, two sympatric populations of these three taxa were examined and compared using four nuclear genes and three chloroplast intergenic spacers, as well as with 10 morphological characters. Our results suggest that at both sites B. × wardii was likely to be a hybrids between B. alternifolia and B. crispa, and moreover, most of the hybrids present were confirmed to be F1s. This was further supported by morphology as no transgressive characters were detected. B. crispa was found to be the maternal parent in one population (BH), while in the second population (TJ), it was difficult to distinguish the hybridization direction due to shared haplotypes of cpDNA between B. alternifolia and B. crispa. Conclusions: These results provide evidence that the natural hybrids between B. alternifolia and B. crispa mainly comprise F1 hybrids, which have subsequently been given the name B. wardii. The F1 hybrids have also contributed to strong reproductive isolation between parental species.

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Light environment influences mating behaviours during the early stages of divergence in tropical butterflies

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2021.0157 ◽

2021 ◽

Vol 288 (1947) ◽

Author(s):

Alexander E. Hausmann ◽

Chi-Yun Kuo ◽

Marília Freire ◽

Nicol Rueda-M ◽

Mauricio Linares ◽

...

Keyword(s):

Reproductive Isolation ◽

Close Relative ◽

Putative Hybrid ◽

Hybrid Species ◽

Video Footage ◽

Signal Perception ◽

Sensory Environment ◽

Visual Attraction ◽

Selection For ◽

Mating Cues

Speciation is facilitated when traits under divergent selection also act as mating cues. Fluctuations in sensory conditions can alter signal perception independently of adaptation to the broader sensory environment, but how this fine-scale variation may constrain or promote behavioural isolation has received little attention. The warning patterns of Heliconius butterflies are under selection for aposematism and act as mating cues. Using computer vision, we extracted behavioural data from 1481 h of video footage, for 387 individuals. We show that the putative hybrid species H. heurippa and its close relative H. timareta linaresi differ in their response to divergent warning patterns, but that these differences are strengthened with increased local illuminance. Trials with live individuals reveal low-level assortative mating that is sufficiently explained by differences in visual attraction. Finally, results from hybrid butterflies are consistent with linkage between a major warning pattern gene and the corresponding behaviour, though the differences in behaviour we observe are unlikely to cause rapid reproductive isolation as predicted under a model of hybrid trait speciation. Overall, our results reveal that the contribution of ecological mating cues to reproductive isolation may depend on the immediate sensory conditions during which they are displayed to conspecifics.

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