Sympatric speciation in palms on an oceanic island

Abstract

The origin of species diversity has challenged biologists for over two centuries. Allopatric speciation, the divergence of species resulting from geographical isolation, is well documented. However, sympatric speciation, divergence without geographical isolation, is highly controversial. Claims of sympatric speciation must demonstrate species sympatry, sister relationships, reproductive isolation, and that an earlier allopatric phase is highly unlikely. Here we provide clear support for sympatric speciation in a case study of two species of palm (Arecaceae) on an oceanic island. A large dated phylogenetic tree shows that the two species of Howea, endemic to the remote Lord Howe Island, are sister taxa and diverged from each other well after the island was formed 6.9 million years ago. During fieldwork, we found a substantial disjunction in flowering time that is correlated with soil preference. In addition, a genome scan indicates that few genetic loci are more divergent between the two species than expected under neutrality, a finding consistent with models of sympatric speciation involving disruptive/divergent selection. This case study of sympatric speciation in plants provides an opportunity for refining theoretical models on the origin of species, and new impetus for exploring putative plant and animal examples on oceanic islands.

High-Dimensional Fitness Landscapes and Speciation

“…Some of them are based on a model of adaptive radiation which is intended to be more abstract and general Vose 2005, 2009). Other attempts use models tailored for particular case studies such as cichlids in a crater lake (Barluenga et al 2006;), palms on an oceanic island Savolainen et al 2006), snails on seashores (Hollander et al 2005(Hollander et al , 2006Sadedin et al 2008), and butterflies in jungles (Duenez-Guzman et al 2009;Mavárez et al 2006). The general setup in all these models is similar.…”

Genomic and phenotypic divergence unveil microgeographic adaptation in the Amazonian hyperdominant tree Eperua falcata Aubl. (Fabaceae)

“…Microgeographic adaptation driven by a bundle of abiotic and biotic factors may be an initial step towards tree specialization and ecological (sympatric) speciation (Savolainen et al 2006;Feder et al 2012). In this study we provide support for this process at the intra-populational level in an Amazonian tree species.…”

“…This phenomenon has been repeatedly observed in annual plants growing in strongly contrasting yet geographically adjacent habitats, particularly in cases with large differences in soil composition (Bradshaw 1960;Jain and Bradshaw 1966;Antonovics and Bradshaw 1970;Antonovics 2006;Gould et al 2014); in some cases, molecular evidence also supports adaptation to habitat mosaics (Turner et al 2010;Fustier et al 2017). In the case of Howea palm trees, Savolainen et al (2006) have elegantly provided cogent evidence of a link between adaptation to habitat mosaics and sympatric speciation. The process underlying these instances of adaptation with gene flow has been dubbed 'microgeographic adaptation', whereby adaptive divergence occurs at geographical scales of the same order of magnitude as gene dispersal distance (Richardson et al 2014) .…”

Hybridization masks speciation in the evolutionary history of the Galápagos marine iguana

“…In birds, most phylogenetic studies of species occurring on single islands rejected sister-species relationships, thereby ruling out within-island speciation [52]. Only small-sized or less mobile organisms, such as palms, provide unambiguous examples of sympatric speciation on small volcanic islands [6]. Given that marine iguanas are large and vagile reptiles, the observed incipient speciation event, occurring in less than 30 000 years on a small island, is unexpected.…”

“…Therefore, these systems can be seen as evolutionary laboratories, and provide a more simplified framework to study evolutionary processes than mainland settings. Prime examples of island-based evolutionary research include well-known adaptive radiations [2][3][4]], Mayr's classical work on allopatric species formation [5] and compelling accounts of within-island speciation [6][7][8]. However, island systems do not only provide useful settings to study diversification processes leading to speciation-they also reveal insights into the processes which counteract speciation, such as hybridization.…”