Phylogenetics of the genus Scaevola (Goodeniaceae): implication for dispersal patterns across the Pacific Basin and colonization of the Hawaiian Islands

Abstract

Scaevola, the only genus of Goodeniaceae that has extensively radiated outside of Australia, has dispersed throughout the Pacific Basin, with a few species reaching the tropical coastal areas of the Atlantic and Indian Oceans. Five Australian and most of the non-Australian species are placed in Scaevola section Scaevola based on their fleshy fruits, indeterminate inflorescences, and more arborescent habits. Analyses of ITS sequence data demonstrate that Scaevola is a monophyletic group if S. collaris is excluded and Diaspasis filifolia is included. The genus is Australian in origin, but there have been at least six separate dispersal events from Australia. Four of these dispersals each resulted in single extra-Australian species. The remaining two were followed by radiations that gave rise to large groups, each including one of the widespread strand species, S. taccada and S. plumieri. Remarkably, three of the six dispersals established species on the remote Hawaiian Archipelago, representing at present the largest number of colonizations by any flowering plant genus to these islands.

Progressive island colonization and ancient origin of Hawaiian Metrosideros (Myrtaceae)

“…Knowledge of whether these species are recent dispersers or are ancient lineages in the archipelago, or whether there have been single or multiple colonization events (e.g. Howarth et al 2003;Harbaugh & Baldwin 2007), is crucial to understanding the evolutionary history of the Hawaiian terrestrial ecosystem.…”

Dispersal potential of Scaevola crassifolia (Goodeniaceae) is influenced by intraspecific variation in fruit morphology along a latitudinal environmental gradient

“…The majority of Goodeniaceae genera are confined to the Australian continent, except for Scaevola, which is pantropical; 40 of 130 species are found outside Australia (Howarth et al 2003). These species occur throughout the coastal regions of the Pacific and Indian Oceans, including the tropical Americas, Africa, Philippines, China, Marquesas and Hawaiian Islands (Howarth et al 2003).…”

“…Capacity to undertake longdistance dispersal is likely to be increasingly important for the persistence of plant species as their ranges shift in response to continuing global climate change (Hughes 2000;Travis et al 2013). Dispersal via ocean currents can potentially result in long-distance dispersal, with recent phylogenetic and biogeographic studies leading to a resurgence of support for oceanic hydrochory as a means of long-distance dispersal of plants (Howarth et al 2003;de Queiroz 2005;Cousens et al 2008;Dawson and Hamner 2008;Kokubugata et al 2012). However, unlike Darwin's seminal studies of oceanic hydrochory (Darwin 1856(Darwin , 1859, recent hypotheses are generally not supported by evidence that fruits or seeds are capable of remaining buoyant and surviving in seawater for the extended periods required to achieve effective longdistance dispersal.…”

“…This capacity may result from or be enhanced by fruit morphology. For example, it has been hypothesised that the widespread distribution of S. taccada may be due to its fleshy exocarp (facilitating bird dispersal), or its corky mesocarp (facilitating buoyancy in water) (Lesko and Walker 1969;Howarth et al 2003). Certainly, the fruits of the widely distributed S. crassifolia and S. taccada are buoyant and survive in seawater for 42 and 120 days, respectively, without adverse effects on seed germination, demonstrating a capacity for oceanic dispersal (Lesko and Walker 1969;Guja et al 2010).…”

“…These species occur throughout the coastal regions of the Pacific and Indian Oceans, including the tropical Americas, Africa, Philippines, China, Marquesas and Hawaiian Islands (Howarth et al 2003). Phylogenetic relationships within Scaevola suggest three independent colonisation events from the Australian continent to the isolated Hawaiian Islands (Howarth et al 2003).…”