Islands contain some of the most remarkable yet imperiled plants anywhere on Earth. Despite remarkable ecological/morphological diversity, insular endemics often retain the ability to hybridize and produce vigorous, fertile progeny. This study over several generations of synthetic interspecific hybrids between two species endemic to the Canary Islands shows that gene exchange between species can produce novel traits, transgressive phenotypes and novel combinations of features not seen in their parents. Results of this study provide experimental evidence of the potential of hybridization to promote diversification and possibly generate stabilized hybrid derivatives in plants in an oceanic archipelago.
Premise
The mating system has profound consequences, not only for ecology and evolution, but also for the conservation of threatened or endangered species. Unfortunately, small populations are difficult to study owing to limits on sample size and genetic marker diversity. Here, we estimated mating system parameters in three small populations of an island plant using genomic genotyping. Although self‐incompatible (SI) species are known to often set some self‐seed, little is known about how “leaky SI” affects selfing rates in nature or the role that multiple paternity plays in small populations.
Methods
We generalized the BORICE mating system program to determine the siring pattern within maternal families. We applied this algorithm to maternal families from three populations of Tolpis succulenta from Madeira Island and genotyped the progeny using RADseq. We applied BORICE to estimate each individual offspring as outcrossed or selfed, the paternity of each outcrossed offspring, and the level of inbreeding of each maternal plant.
Results
Despite a functional self‐incompatibility system, these data establish T. succulenta as a pseudo‐self‐compatible (PSC) species. Two of 75 offspring were strongly indicated as products of self‐fertilization. Despite selfing, all adult maternal plants were fully outbred. There was high differentiation among and low variation within populations, consistent with a history of genetic isolation of these small populations. There were generally multiple sires per maternal family. Twenty‐two percent of sib contrasts (between outcrossed offspring within maternal families) shared the same sire.
Conclusions
Genome‐wide genotyping, combined with appropriate analytical methods, enables estimation of mating system and multiple paternity in small populations. These data address questions about the evolution of reproductive traits and the conservation of threatened populations.
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Premise: Plants endemic to oceanic archipelagos are suitable for studying evolution, being isolated on substrates of different ages. Evolution has been recent, rendering traditionally employed sequences insufficiently variable for resolving relationships. This study includes sampling in the genus Tolpis (Asteraceae) from the Azores, Madeira, and Cape Verde, and expands upon an earlier study demonstrating the efficacy of multiplexed shotgun genotyping (MSG) for resolving relationships in Canarian Tolpis. Methods: Genomic libraries for 90 accessions of Tolpis and two from the outgroup were generated for genotyping individuals using MSG. Loci were de novo assembled with iPyrad, which clusters MSG loci within and between samples. A maximum likelihood phylogeny was generated with RAxML. Ancestral area reconstruction was inferred using R package BioGeoBEARS. Results: MSG data recovered a highly resolved phylogeny from population to interarchipelago levels. Ancestral area reconstruction provided biogeographic hypotheses for the radiation of Macaronesian Tolpis. Conclusions: Four major clades were resolved. The Madeiran endemic T. macrorhiza is sister to other Tolpis. Species from the Canaries, Cape Verdes, and the continent are sister to T. succulenta from Madeira, which has a sister subclade of Azorean populations composed of T. succulenta and T. azorica. Population-level resolution suggests unrecognized taxa on several archipelagos. Ancestral reconstruction suggests initial dispersal from the continent to Madeira, with dispersal to the Azores, then
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