Timothy K. Lowrey

Allozyme Divergence and Evolution in Tetramolopium (Compositae: Astereae) on the Hawaiian Islands

Tetramolopium is a genus of shrubby to suffrutescent perennial Compositae known only from New Guinea and the Hawaiian Islands. Evidence from biogeography suggests the genus was introduced into Hawaii from New Guinea recently, and perhaps originated from a single introduction. The morphological and ecological diversity of Tetramolopium in the Hawaiian Islands suggest there has been rapid divergence associated with adaptive radiation. Despite the diversity, all taxa are completely interfertile with fertile F1, F2, and F3 hybrids having been obtained. An electrophoretic study of allozymes revealed little divergence at 22 genes coding soluble enzymes. The mean genetic identity for pairwise comparisons of 19 populations from seven species is 0.95, a very high value normally obtained for conspecific plant populations. The results for Tetramolopium contrast sharply with other instances of high genetic identity between species, where taxa are similar morphologically and usually reproductively isolated. The enzyme data also support the hypothesis of recent, rapid divergence in Hawaiian Tetramolopium.

Molecular and morphological reassessment of relationships within the Vittadinia group of Astereae (Asteraceae)

Morphological and ITS (internal transcribed spacer) sequence data for 40 species of the Austral-Pacific genera Camptacra, Kippistia, Minuria, Peripleura, Tetramolopium, and Vittadinia as well as one semiherbaceous species of Olearia were subjected to cladistic analysis, separately and together. Minuria, Peripleura, and Tetramolopium are paraphyletic as currently defined. Tetramolopium vagans from Australia appears to represent an undescribed genus. Both Kippistia suadefolia and Peripleura diffusa show close affinity to Minuria species, and Minuria macrorhiza appears to contain two distinct but closely related species. Vittadinia and the remaining species of Tetramolopium and Peripleura form a strong affinity group. The distribution of indels and the combined analysis each provide evidence that the Hawaiian and Cook Island species of Tetramolopium are descended from New Guinea species. The combined analysis also suggests that the Cook Island species T. mitiaroense is sister to the Hawaiian clade. Olearia arguta groups strongly with Camptacra and shows no close affinity with either of the arborescent species of Olearia used to root these analyses. Marked homoplasy among morphological characters indicates why generic delimitation in the group has been problematic.

Genetics of adaptive radiation in Hawaiian and Cook Islands species of Tetramolopium (Asteraceae; Astereae). I. Nuclear RFLP marker diversity.

Thirty-three nuclear RFLP (restriction fragment length polymorphism) probes were used to study genetic diversity in Hawaiian and Cook Islands species of Tetramolopium for comparison with previous morphological and isozyme studies and to provide greater resolution of the events associated with adaptive radiation in the genus. Levels of RFLP diversity are greater than those reported for isozymes, yet are still low in comparison to continental species. Genetic differentiation is greatest among species in sections rather than among sections and is concordant with the hypothesis of phyletic sorting of initial variability as suggested for morphological traits. Hypothesized introgression between T. lepidotum and T. filiforme is supported, but the evidence suggests bidirectional gene flow. Systematic relationships derived from the data agree with hypotheses based on morphology in the placement of populations within their respective species and the recognition of three main lineages within Hawaii. Inclusion of the Cook Islands species, however, renders section Tetramolopium paraphyletic, contradicting morphological, ecological, and crossing evidence. Interpreting these results in light of evidence from previous studies, the genetic diversity and relationships seen among species and sections of Hawaiian and Cook Islands Tetramolopium reflect the recent and rapid evolution of this group, limited addition of new variability, and phyletic sorting.

Comparison of methods for rooting phylogenetic trees: A case study using Orcuttieae (Poaceae: Chloridoideae)

DNA sequence data (cpDNA trnL intron and nrDNA ITS1 and ITS2) were analyzed to identify relationships within Orcuttieae, a small tribe of endangered grasses endemic to vernal pools in California and Baja California. The tribe includes three genera: Orcuttia, Tuctoria, and Neostapfia. All three genera carry out C(4) photosynthesis but aquatic taxa of Orcuttia lack Kranz anatomy. The unusual habitat preference of the tribe is coupled with the atypical development of C(4) photosynthesis without Kranz anatomy. Furthermore, the tribe has no known close relatives and has been noted to be phylogenetically isolated within the subfamily Chloridoideae. In this study we examine the problem of inferring the root of the tribe in the absence of an identified outgroup, analyze the phylogenetic relationships of the constituent taxa, and evaluate the evolutionary development of C(4) photosynthesis. We compare four methods for inferring the root of the tree: (1) the outgroup method, (2) midpoint rooting, the imposition of a molecular clock for both (3) maximum likelihood (ML) and (4) Bayesian analysis. We examine the consequences of each method for the inferred phylogenetic relationships. Three of the methods (outgroup rooting and the ML and Bayesian molecular clock analyses) suggest that the root of Orcuttieae is between Neostapfia and the Tuctoria/Orcuttia lineage, while midpoint rooting gives a different root. The Bayesian method additionally provides information about probabilities associated with other possible root locations. Assuming that the true root of Orcuttieae is between Neostapfia and the Tuctoria/Orcuttia lineage, our data indicate Neostapfia and Orcuttia are both monophyletic, while Tuctoria is paraphyletic (with no synapomorphies in either dataset) and forming a grade between the other two genera and needs taxonomic revision. Our data support the hypothesis that Orcuttieae was derived from a terrestrial ancestor and evolved specializations to an aquatic environment, including C(4) photosynthesis without Kranz anatomy.

Evolutionary optimization of material properties of a tropical seed

Here, we show how the mechanical properties of a thick-shelled tropical seed are adapted to permit them to germinate while preventing their predation. The seed has evolved a complex heterogeneous microstructure resulting in hardness, stiffness and fracture toughness values that place the structure at the intersection of these competing selective constraints. Analyses of different damage mechanisms inflicted by beetles, squirrels and orangutans illustrate that cellular shapes and orientations ensure damage resistance to predation forces imposed across a broad range of length scales. This resistance is shown to be around the upper limit that allows cracking the shell via internal turgor pressure (i.e. germination). Thus, the seed appears to strike an exquisitely delicate adaptive balance between multiple selection pressures.

Genetic diversity in Chihuahuan Desert populations of creosotebush (Zygophyllaceae: Larrea tridentata)

We examined isozyme variation in the dominant Chihuahuan Desert shrub, Larrea tridentata (creosotebush), to determine the genetic variation within and among populations, the biogeographic relationships of populations, and the potential inbreeding in the species. We surveyed 17 populations consisting of 20 to 50 individuals per population along a 1600-km north-south transect across the Chihuahuan Desert. The southernmost population was near Villa Hidalgo, Mexico, and the northernmost near Isleta Pueblo, New Mexico. All 12 isozyme loci examined were polymorphic (H(t) = 0.416), with up to nine alleles per locus. Despite high levels of variation, we detected moderate inbreeding in L. tridentata populations. Most variation was found within rather than among populations (G(ST) = 0.118). Furthermore, recently established populations in the northern limits of the Chihuahuan Desert did not show decreased levels of genetic variation (H(o) = 0.336). A significant correlation was found between pairwise genetic and geographic distances (r = 0.305). Larrea tridentata showed and continues to show a massive range expansion into the arid and semi-arid regions of the American Southwest, but as shown by the high genetic variation, this expansion took place as a wave, rather than a series of founder events.

A New Species Of Tetramolopium (Asteraceae) from Mitiaro, Cook Islands: Biogeography, Phylogenetic Relationships, and Dispersal

Abstract A new species endemic to Mitiaro, Cook Islands, Tetramolopium mitiaroense, is described and illustrated. The species is most closely related to Hawaiian species of Tetramolopium section Tetramolopium. Tetramolopium mitiaroense shares an upright dwarf shrub habit with T. remyi and T. capillare but differs in possessing semi-succulent, linear-oblanceolate leaves versus sclerophyllous, involute, linear leaves for the latter two taxa. Tetramolopium sylvae also has succulent leaves but differs from T. mitiaroense in having a prostrate, rosette habit and spatulate leaves. A key is provided for all eastern Pacific species of Tetramolopium. Published morphological, molecular, and geological data are reviewed to assess relationships amongst Tetramolopium taxa in the eastern Pacific and elucidate the biogeographic pattern of dispersal. The data support the hypothesis that Tetramolopium was first dispersed to the Hawaiian Archipelago from New Guinea with a secondary dispersal event from the Hawaiian Islands to the Cook Islands. Available evidence indicates that the Pacific Golden-Plover is the probable agent of dispersal from the Hawaiian Islands to the Cook Islands.

Quantitative morphological variation inTetramolopium (Asteraceae) in Hawaii and the Cook Islands

Multivariate analyses of quantitative characters were undertaken to examine the pattern of variation resulting from adaptive radiation ofTetramolopium in Hawaii and to investigate the systematics of an undescribed species in the Cook Islands and a group of populations of uncertain affinity on Kalaupapa Peninsula in Hawaii. Taxa differentiated on quantitative characters in the absence of qualitative characters. Differentiation was observed in multiple characters which could be organized into a few principal components. The analyses supported the species rank of the Cook Islands plants. The relationship of the Kalaupapa Peninsula populations to the rest of the taxa needs further study.

LEAF ANATOMY OF ORCUTTIEAE (POACEAE: CHLORIDOIDEAE): MORE EVIDENCE OF C4 PHOTOSYNTHESIS WITHOUT KRANZ ANATOMY

ABSTRACT C4 photosynthesis without Kranz anatomy (single-cell C4 photosynthesis) occurs in only 0.003% of known species of C4 flowering plants. To add insight into the evolution of C4 photosynthesis, we studied the tribe Orcuttieae (Poaceae: Chloridoideae), which has species that can grow under both aquatic and terrestrial conditions, and utilize single-cell C4 photosynthesis when growing submerged. Carbon isotope ratios from aquatic, floating, and terrestrial leaves were in the range −12.25 to −14.31, suggesting that all species carry out C4 photosynthesis. Using light microscopy, we examined the anatomy of aquatic, floating and terrestrial leaves from eight of the nine species in the tribe to assess the pattern of evolution of C4 photosynthesis and Kranz anatomy among these vernal pool grasses. Kranz anatomy was present in all floating and terrestrial leaves of Orcuttia californica, O. inaequalis, O. pilosa, O. tenuis, O. viscida,Tuctoria greenei, T. mucronata, and Neostapfia colusana. Although carbon isotope data indicated C4 photosynthesis, aquatic leaves of all members of Orcuttia lacked Kranz anatomy, while aquatic leaves of Tuctoria and Neostapfia possessed Kranz anatomy. When considered in a phylogenetic context, these findings support previously proposed hypotheses suggesting that Orcuttieae are derived from a terrestrial ancestor and are now becoming more specialized to an aquatic environment.

How Baby Plants Avoid Getting Hurt and Blossom into Adulthood: The Story of a Tropical Seed

The seed shell of Mezzettia parviflora (Annonaceae), an understory tree from the lowland tropical rain forest of Malaysia, has an extraordinarily sophisticated structure. The shell is entirely made of sclerenchyma (mechanical support tissue) that is in all parts equally dense (about 95% of volume occupied by cell wall). Yet, differences in cell shape and orientation have a strong influence on fracture resistance. The structure appears designed to allow the seed to open for germination, but to limit predation by large animals.