Maui Nui Research Articles

Cladogenesis and reticulation in the Hawaiian endemic mints (Lamiaceae)

The Hawaiian endemic mints, which comprise 58 species of dry-fruited Haplostachys and fleshy-fruited Phyllostegia and Stenogyne, represent a major island radiation that likely originated from polyploid hybrid ancestors in the temperate North American Stachys lineage. In contrast with considerable morphological and ecological diversity among taxa, sequence variation in the nrDNA 5S non-transcribed spacer was found to be remarkably low, which when analyzed using standard parsimony resulted in a lack of phylogenetic resolution among accessions of insect-pollinated Phyllostegia and bird-pollinated Stenogyne. However, many within-individual nucleotide polymorphisms were observed, and under the assumption that they could contain phylogenetic information, these ambiguities were recoded as new character states. Substantially more phylogenetic structure was obtained with these data, including the resolution of most Stenogyne species into a monophyletic group with an apparent recent origin on O’ahu (⩽3.0 My) or the Maui Nui island complex (⩽2.2 My). Subsequent diversification appears to have involved multiple inter-island dispersal events. Intergeneric placements for a few morphotypes, seemingly misplaced within either Phyllostegia or Stenogyne, may indicate reticulation as one polymorphism-generating force. For a finer scale exploration of hybridization, preliminary AFLP fragment data were examined among putative hybrids of Stenogyne microphylla and S. rugosa from Mauna Kea, Hawai’i, that had been identified based on morphology. Cladistic analysis (corroborated by multivariate correspondence analysis) showed the morphologically intermediate individuals to group in a strongly supported monophyletic clade with S. microphylla. Therefore, reticulation could be both historic and active in Stenogyne, and perhaps a force of general importance in the evolution of the Hawaiian mints. The relatively greater extent of lineage-sorted polymorphisms in Stenogyne may indicate selective differentiation from other fleshy-fruited taxa, perhaps through the agency of highly specialized bird pollinators that restricted gene flow with other Hawaiian mint morphotypes.

Patterns of Endangerment in the Hawaiian Flora

The Hawaiian flora, because of its great isolation, high levels of endemism, known lineages, and high rates of endangerment, offers unique opportunities to explore patterns of endangerment related to phylogeny, ecological and life history traits, and geographic patterns. Nine percent of the native flora of 1159 taxa are already extinct, and 52.5% are at risk (extinct, endangered, vulnerable, or rare). Risk is strongly associated with limited geographic distribution at several scales: endemic taxa (native only to the Hawaiian Islands) are at far greater risk than indigenous taxa (with both Hawaiian and extra-Hawaiian ranges); single-island endemics are more at risk than multi-island endemics; small islands have the highest proportion of endemic taxa at risk; and endemics with more limited habitat distributions (elevation, community type) are more at risk. Historic population density is a strong predictor of risk, and taxa with low historic population densities are at greatest risk with rapid anthropogenic changes. Among the major islands, Maui Nui has the highest percent of taxa that are extinct. Kaua'i has the lowest percent of extinct taxa and the highest proportion of single-island endemic taxa that are rare. Endemic taxa at risk are associated with distributions in shrublands, forests, bogs, and cliff habitats. Endemic taxa with distributions in low elevation dry habitats have the highest proportion of taxa at risk, but the greatest absolute numbers of taxa at risk have distributions in mesic lowland and montane forests, and in wet montane forests. The life history patterns associated with risk are complicated, and inclusion of the effects of evolutionary relationships (lineages) changes some of these patterns. Species level analyses without respect to lineage shows risk associated with monomorphic (hermaphroditic) breeding systems and bird pollination because of the large number of hermaphroditic, bird-pollinated species in the Campanulaceae. Analyses incorporating the effect of lineage greatly reduce the impact of large lineages and result in an association of risk with insect pollination, and no effect of breeding system. There is no association of lineage size and the percent of taxa at risk within the lineage; endemic taxa from lineages with large radiations are at no greater risk than endemic single-taxon lineages. The percentages of taxa at risk at the family level in the Hawaiian Islands and worldwide (excluding Hawaiian taxa) are positively correlated, although flowering plant families in the Hawaiian Islands have a much greater proportion of taxa at risk. Some of the approaches described here may be useful to predict geographical and biological patterns of endangerment in island and island-like ecosystems under increasing pressures of endangerment and extinction.

Evaluation of Relationships within the Endemic Hawaiian Platynini (Coleoptera: Carabidae) Based on Molecular and Morphological Evidence

Relationships among 69 species of Hawaiian Platynini, a monophyletic beetle radiation, was investigated based on evidence from five data partitions, comprising mitochondrial and nuclear DNA sequences (cytochrome oxidase II, 624 bp; cytochrome b, 783 bp; 28S rDNA, 668 bp; wingless; 441 bp) and morphology (206 features of external and internal anatomy). Results from individual and combined data analyses generally support the monophyly of three putative divisions within Platynini in Hawaii: Division 0 (Colpocaccus species group), Division 1 (Blackburnia species group), and Division 2 (Metromenus species group). However, relationships within and among these three divisions differ from previous morphological hypotheses. An extensive series of sensitivity analyses was performed to assess robustness of recovered clades under a variety of weighted parsimony conditions. Sensitivity analyses support the monophyly of Divisions 0 and 1, but were equivocal for the monophyly of Division 2. A phylogeny based on combined data suggests at least four independent losses/reductions of platynine flight wings. The combined analysis provides corroboration for biogeographic hypotheses, including (1) colonization of Kauai by Hawaiian Platynini with subsequent dispersal and colonization along the island chain from Oahu to Maui Nui to Hawaii Island and (2) incongruent area relationships among Eastern Molokai, West Maui, and Haleakala for two species triplets.

Mitochondrial Phylogeny of Extant Hawaiian Tree Snails (Achatinellinae)

Hawaiian tree snails in the endemic subfamily Achatinellinae display a staggering variety of shell colors and banding patterns. Despite numerous attempts to classify this morphological variation, a conclusive phylogeny has not been proposed. To improve conservation efforts, we sought to better understand the species identities and phylogenetic relationships among the extant species of Achatinella and Partulina using partial mitochondrial 16S ribosomal DNA sequences. The reconstructed phylogeny showed a high degree of support for more recent branches, but gave little support to deeper nodes. The most confident branches challenge previous systematic arrangements of these snails, grouping species that previously had been placed into different subgenera. High levels of sequence divergence within some species may reflect the long-term isolation of subpopulations. Rapid rates of sequence divergence may have saturated base substitutions and contributed to the lack of resolution of higher-order relationships. We did not find support for the monophyly of the Achatinella species, nor thus for a single colonization of Oahu from Maui Nui.

Cladistic analysis, phylogeny and biogeography of the Hawaiian Platynini (Coleoptera: Carabidae)

The 128 known native Hawaiian species of the tribe Platynini are analysed cladistically. Cladistic analysis is based on 206 unit‐coded morphological characters, and also includes forty‐one outgroup taxa from around the Pacific Rim. Strict consensus of the multiple equally parsimonious cladograms supports the monophyly of the entire species swarm. The closest outgroup appears to be the south‐east Asian‐Pacific genus Lorostema Motschulsky, whose species are distributed from India and Sri Lanka to Tahiti, supporting derivation of the Hawaiian platynines from a source in the western or south‐western Pacific. The biogeographic relationships of the Hawaiian taxa are analysed using tree mapping, wherein items of error are minimized. The area cladogram found to be most congruent with the phylogenetic relationships, and most defensible based on underlying character data is {Kauai[Oahu(Hawaii{Lanai[East Maui(West Maui + Molokai)]})]}. This progressive vicariant pattern incorporates progressive colonization from Kauai, and vicariance of the former Maui Nui into the present islands of Molokai, Lanai, West Maui and East Maui. The evolution of flightlessness, tarsal structure, pronotal setation and bursal asymmetry are evaluated in the context of the cladogram. Brachyptery is a derived condition for which reversal is not mandated by the cladogram, although repeated evolution of reduced flight wings is required. Tarsal structure supports Sharp's (1903) recognition of Division 1 as a monophyletic assemblage, but exposes his Division 2 as a paraphyletic group requiring removal of the genus Colpocaccus Sharp. Pronotal setation is exceedingly homoplastic, and is not useful for delimiting natural groups. Left‐right asymmetry of the bursa copulatrix reversed twice independently, resulting in mirror‐image bursal configurations in B. rupicola and Prodisenochus terebratus of East Maui. The amount of character divergence is greater among species comprising Division 1 than among species of its sister group, the redefined Division 2. Based on superior fit of Division 1 relationships to the general biogeographic pattern, a greater speciation rate coupled with more extensive extinction is rejected as the cause for this greater divergence. Intrinsic differentiation in the processes underlying cuticular evolution appears to be more consistent with the observed biogeographic and morphological patterns.

Phylogeny of the Island Populations of the HawaiianDrosophila grimshawiComplex: Evidence from Combined Data

The picture-winged speciesDrosophila grimshawiis unique among HawaiianDrosophilain its wide geographic range, having populations on several islands of the Hawaiian archipelago. This distribution contrasts with the pattern of single-island endemism observed in most of the picture-winged group; significantly, it does not concur with predictions of the founder theory, where speciation is the typical outcome of founder events involving colonization of a new island. To examine this anomalous situation, we have taken a phylogenetic approach in an attempt to resolve the relationships among taxa and decipher the most probable colonization scenario. We have obtained both morphological and molecular data for all theD. grimshawipopulations as well as the closely related speciesD. pullipes,and two outgroup species, using scanning electron microscopy to score ultrastructural features of the chorion or eggshell, and PCR amplification and nucleotide sequencing to acquire sequence data onYp1,one of the threeYolk proteingenes. In addition, we have used available data on Yolk Protein electrophoretic pattern and jousting, oviposition, and mating behavioral characters. Analyses of these data sets, either individually or in combination, indicate that there are two separate and ecologically distinct clades within this species complex. One clade includes the Kauai and Oahu populations ofgrimshawi,as well as the closely related speciesD. pullipesfrom Hawaii, all of which are classified as ecological specialists with respect to their oviposition and breeding substrate. The other clade includes all the ecologically generalistgrimshawipopulations of the Maui Nui island complex. The phylogenetic results do not concur with the previously proposed hypothesis thatD. pullipesoriginated from a founder derived from the Maui Nui complex and further suggest that these taxa are in need of taxonomic revision.