The study of local adaptation sheds some light on the evolutionary process and particularly that of speciation. Local adaptation involves populations that are specifically adapted to peculiarities of their local environment. These adaptations may result in limiting gene flow between populations that are differently adapted. I am studying a species of Picture-winged Drosophila endemic to the Island of Hawaiʻi that appears to be distributed in a way consistent with local adaptations to temperature differences that fall along altitude gradients.
A critical element in a study of adaptation is a continuous long-term data set for a variety of climate data for a high resolution network of monitors distributed around the island in order to determine differences between localities of populations that appear to not share gene flow. Population structure in general is affected by a variety of climatic factors. The marine environment provides an excellent example of how factors like current direction and speed, salinity, etc can affect the dispersal of larvae. In collaboration with Bob Nishimoto (DLNR-DAR Hawaiʻi Island), and Mike Fitzsimons (LSU), we are studying the population structure of endemic gobies (Oʻopu). This amphidromous fish spends two-three months, during its larval phase, in the ocean before returning to the stream environment.
The population structure of the Oʻopu is a result of climatic factors that determine the distribution of larvae while in the ocean and affect the likelihood of return to different streams. Understanding local adaptation as a process has profound implications to human health since humans, like all other life, are the product of many historical adaptations. For instance, it has been suggested that some human populations are more susceptible to diseases like Type II Diabetes as a result of an ancestry that selected for the ability to quickly accumulate fat. Such a phenotype would be beneficial in an environment subject to episodes of feast and famine but very detrimental in an environment that is characterized by plentiful high calorie food.
The genetic structure and evolutionary history of an endemic anchialine species, the shrimp Halocaridina rubra Holthuis, 1963 (Crustacean: Decapoda: Atyidae), was investigated across its range in the Hawaiian archipelago using mitochondrial (e.g., cytochrome oxidase subunit I and large subunit ribosomal) gene sequences. A survey of 573 individuals collected from 34 sites on the islands of Hawaiʻi, Maui, and Oʻahu revealed 13 distinct genetic groups belonging to eight divergent lineages.
In general, a Halocaridina genetic group or lineage was restricted to a particular region of a single Hawaiian Island, with no individuals being exchanged between them. This pattern stems from a combination of intrinsic organismal properties such as large egg size, abbreviated development, restricted larval habitat and larval feeding mode, and extrinsic obstacles to gene flow in the form of a marine barrier and geologic features that compartmentalize the islands’ aquifers.
The phylogeographic structuring on and between islands suggests that evolutionary diversification in Halocaridina is driven by population fragmentation, isolation, and subsequent diversification in the aquifers of the Hawaiian Islands. Calibration of cytochrome oxidase subunit I sequence divergence between sister Halocaridina lineages to the geologic age of Kilauea volcano on Hawaiʻi implies that diversification in the genus is proceeding at a short-term rate of 20% per million years. The examined mitochondrial genes were generally inadequate for inferring phylogenetic relationships between the Halocaridina lineages.