Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae)

Abstract

The endemic Hawaiian lobeliads are exceptionally species rich and exhibit striking diversity in habitat, growth form, pollination biology and seed dispersal, but their origins and pattern of diversification remain shrouded in mystery. Up to five independent colonizations have been proposed based on morphological differences among extant taxa. We present a molecular phylogeny showing that the Hawaiian lobeliads are the product of one immigration event; that they are the largest plant clade on any single oceanic island or archipelago; that their ancestor arrived roughly 13 Myr ago; and that this ancestor was most likely woody, wind-dispersed, bird-pollinated, and adapted to open habitats at mid-elevations. Invasion of closed tropical forests is associated with evolution of fleshy fruits. Limited dispersal of such fruits in wet-forest understoreys appears to have accelerated speciation and led to a series of parallel adaptive radiations in Cyanea, with most species restricted to single islands. Consistency of Cyanea diversity across all tall islands except Hawai`i suggests that diversification of Cyanea saturates in less than 1.5 Myr. Lobeliad diversity appears to reflect a hierarchical adaptive radiation in habitat, then elevation and flower-tube length, and provides important insights into the pattern and tempo of diversification in a species-rich clade of tropical plants.

The quest to resolve recent radiations: Plastid phylogenomics of extinct and endangered Hawaiian endemic mints (Lamiaceae)

“…Phylogenies of the Hawaiian mints have been reconstructed from datasets composed of commonly used DNA sequence markers, including cpDNA and nuclear ribosomal 5S non-transcribed spacer and external transcribed spacer regions (Lindqvist and Albert, 2002;Roy et al, 2013), which are rapidly evolving in many other species (Baldwin and Markos, 1998;Shaw et al, 2005;Small et al, 1998), but they fail to resolve relationships among the Hawaiian mints. A similar pattern of low genetic diversity has been noted in other recent radiations of Hawaiian plants (Appelhans et al, 2014;Baldwin and Sanderson, 1998;Cronk et al, 2005;Givnish et al, 2009;Givnish et al, 2013). Given this low diversity in recent radiations, large amounts of data are clearly required to increase resolution.…”

Ancient diversification of Hyposmocoma moths in Hawaii

“…The Hawaiian biota boasts extremely high endemism, not only on the species level, but on higher taxonomic levels as well. All major groups of organisms include endemic Hawaiian genera 10,11,26 , and the existence of so many endemic higher taxa implies long isolation from their continental relatives.…”

“…This suggests that most endemic lineages that formerly occurred on the oldest islands did not persist, and diminishes the role that these atolls and pinnacles played in generating the archipelago's present diversity, despite their greater size in the distant past. Only four extant lineages of plants or animals [7][8][9][10] are thought to have colonized the Hawaiian archipelago before the emergence of Kauai, but since all the living species in these apparently ancient lineages are currently restricted to the youngest islands, prior residence in the Hawaiian chain can only be inferred based on divergence time estimates. Moreover, very few of today's species radiations have extant representatives on the NWHI, implying widespread extinction of ancient groups that never reached the younger islands, and thus extensive lineage turnover between islands greater than and those less than 5 Myr old.…”

Speciation Has a Spatial Scale That Depends on Levels of Gene Flow

“…This has especially been argued in the specific context of oceanic islands (Diamond 1977;Paulay 1994;Ranker et al 1994;Parent and Crespi 2006;Whittaker and Fernandez-Palacios 2007;Gillespie and Baldwin 2009;Givnish et al 2009), where there are many examples of spectacular radiations of taxa with normally poor dispersal abilities but a propensity for passive longdistance dispersal (e.g., weevils on Rapa [Paulay 1985] and snails on Bonin [Chiba 1999]). Diamond (1977) argued more specifically that dispersal ability might determine the threshold island area necessary for within-island speciation to take place, but this idea remains untested.…”