NATURAL HISTORY

The Hawaiian Islands are the most isolated high islands in the world, being 3,200 km from the nearest major landmass (Carson and Clague, 1995).  The islands are formed in the middle of the Pacific plate as it moves 8.6 – 9.2 cm/yr to the northwest over a hot spot with a relatively fixed position (Wilson, 1963) (Clague and Darymple, 1987).  The resulting chain of islands has the youngest active volcanoes to the southeast and older features to the northwest.  As new high islands are formed the older islands are reduced by subsidence, erosion, slumping , and landslides, to low islands, atolls, and finally submerged seamounts. Organisms can persist for longer than the island onwhich they originally arrived by colonizing new islands as they emerge, the "stepping-stone" hypothesis.

Colonization date estimation
The serial formation and K-Ar dating of the Hawaii Islands provides an ideal context for estimating the age of endemic species radiations.  By fixing the date of putative inter-island cladogenic events the age of deeper nodes on a cladogram can be estimated.  The ages of many lineages of plants and animals in Hawaii have been estimated using the molecular clock and biogeographic dating.  Price and Clague (2002) , reviewed plant and animal lineages for which colonization dates have been estimated, proposing that the majority of lineages are no older than the oldest current  high island, Kauai.  Kauai marks the end of a previous period of low lava flow and the formation of relatively small and low elevation islands.  They believed that the ~3 Mya period of low island formation after Necker (8 Mya) created a bottleneck that prevented the majority of lineages from successfully colonizing from the previous high islands.

Penalized likelihood PL (Sanderson, 2002) was used to estimate the deepest divergence among the endemic species and between the endemic species and the nearest outgroup sampled. 

The lowest estimate for the root node, and therefore time of Hawaiian colonization, was 6.49 Mya and the highest estimate was 8.97 Mya.  Estimates of the divergence time between the Hawaiian taxa and the nearest outgroup varied between 10.00 Mya and 13.71 Mya, for the same calibration schemes as above.  The nearest outgroups included in the analysis are probably not the nearest extant relatives and provide a maximum divergence time only. 

The results suggest that the endemic Hawaiian Nitidulidae colonized the Hawaiian Islands before the formation of the present high islands, between Gardiner and Nihoa Islands , and successfully colonized Kauai and the younger present high islands.

Price, J. P., and D. A. Clague. 2002. How Old is the Hawaiian Biota? Geology and Phylogeny Suggest Recent Divergence. Proc. R. Soc. Lond. B 269:2429-2435.

Sanderson, M. J. 2002. Estimating Absolute Rates of Molecular Evolution and Divergence Times: A Penalized Likelihood Approach. Mol. Biol. Evol. 19:101-109.