Publications

Staminodes are infertile stamens that have evolved numerous times across angiosperms; however, little is known about the evolutionary transitions of staminodes, especially among close relatives. We studied staminode evolution in Mentzelia section Bartonia to determine how many times staminodes have been gained or lost. A maximum-likelihood approach identified ten transitions, in which staminodes evolved at least five times and were reversible. We then examined the consequences of the evolution of staminodes by quantifying how staminodes affect visitation rates. A population of Mentzelia multiflora was used in an experimental study in which visitation of control flowers (staminodes present) was compared to that of treatment flowers (staminodes removed). The only pollinator was Apis mellifera (Apidae), which hovered above and landed on control flowers significantly more often than treatment flowers. Despite the preference for landing on staminodial flowers, once landed, pollinators spent an equal time on control and treatment flowers. We hypothesize that the increased visitation of staminodial flowers probably offsets the loss of the reproductive function in stamens.

Abstract Aim To determine the historical dynamics of colonization and whether the relative timing of colonization predicts diversification rate in the species-rich, murine rodent communities of Indo-Australia. Location Indo-Australian Archipelago including the Sunda shelf of continental Asia, Sahul shelf of continental Australia, the Philippines and Wallacea of Indonesia. Taxon Order Rodentia, Family Muridae. Methods We used a fossil-calibrated molecular phylogeny and Bayesian biogeographical modelling to infer the frequency and temporal sequence of biogeographical transitions among Sunda, Sahul, the Philippines and Wallacea. We estimated diversification rates for each colonizing lineage using a method-of-moments estimator of net diversification and Bayesian mixture model estimates of diversification rate shifts. Results We identified 17 biogeographical transitions, including nine originating from Sunda, seven originating from Sulawesi and broader Wallacea and one originating from Sahul. Wallacea was colonized eight times, the Phillipines five times, Sunda twice and Sahul twice. Net diversification rates ranged from 0.2 to 2.12 species/lineage/My with higher rates in secondary and later colonizers than primary colonizers. The highest rates were in the genus Rattus and their closest relatives, irrespective of colonization history. Main Conclusions Our inferences from murines demonstrate once again the substantial role of islands as sources of species diversity in terrestrial vertebrates of the IAA with most speciation events occurring on islands. Sulawesi and broader Wallacea have been a major source of colonists for both island and continental systems. Crossings of Wallace's Line were more common than subsequent transitions across Lydekker's Line to the east. While speciation following colonization of oceanic archipelagos and large islands is consistent with adaptive radiation theory and ideas regarding ecological opportunity, we did not observe a strong signal of incumbency effects. Rather, subsequent colonists of landmasses radiated unhindered by previous radiations.

Premise of research. The evolution of lineages on continental edaphic islands has been an important determinant of diversification. To understand the complexities of continental edaphic diversification, the historical, biogeographic, and ecological aspects of the diversification process must be studied, even when the relative contributions of ecological and nonecological processes are difficult to differentiate. To decipher the ecological determinants of diversification on continental edaphic islands, we examined the diversification of the plant genus Paronychia (Caryophyllaceae) that occurs on sandhills across the three ecological axes that follow: habitat, soil chemistry, and bioclimate.Methodology. A phylogenetic hypothesis of Paronychia was reconstructed, and ecological variables were measured in natural populations to determine the key axes of diversification. We tested an allopatric model that made predictions based on new habitat formation as sea levels lowered and sand ridges formed, as well as an ecological divergence hypothesis. Ecological variation was summarized with principal component analyses and subjected to several phylogenetic diversification models. Ecological niche modeling approaches were applied to determine whether species were ecologically diversifying across a bioclimate axis.Pivotal results. Although Paronychia is ecologically conservative in occurring on sandy, dry, and open soils, we identified substantial ecological variation, in which individuals occupied greater ecological space within rather than between species. Despite substantial variation, species had not partitioned into unique ecological space. Instead, we found that allopatric speciation based on the geological appearance of habitats was supported and is a key determinant of diversity.Conclusions. Our findings highlight the role of phylogenetic niche conservatism and allopatric speciation for similar, yet disjunct, habitats as species diversified across continental edaphic islands. Despite species occupying similar niche space, our results suggest that niche envelopes can be quite broad and that diversity is dependent on the extent of habitat isolation.

PREMISE OF THE STUDY: A repeated pattern of American amphitropical disjunct species or sister species distributed on either side of the equator has long-fascinated botanists, but the modes of these disjunctions remain untested. We evaluated diaspore morphology to generate hypotheses on probable dispersal mechanisms.METHODS: The sizes and structures of diaspores, habit, habitat, distribution, and dispersal units were collected for 108 species from literature searches and herbarium specimens. Variation was evaluated with summary statistics, χ2 tests with Monte Carlo simulations, ANOVAs, and the nonparametric Mann–Whitney test.KEY RESULTS: Seeds were the dispersing diaspore in 38.0% of the species, 45.4 were dispersed as fruits, and the remaining were dispersed as infructescences or spores. Diaspores were epizoochorous (52.8%), anemochorous (20.4%), achorous (15.7%), endozoochorous (8.3%), and hydrochorous (2.8%). Epizoochory was significantly greater than expected. Zoochory occurred more frequently than expected when considering achorous diaspores as animal-dispersed. Most species were associated with wetland, woodland, and grassland habitats. An ANOVA revealed that diaspores associated with hydrochory were larger and anemochory was smaller; all other syndromes were not significantly different.CONCLUSIONS: Botanists have long-held the assumption that bird migrations are responsible for amphitropical disjunctions. Our results support this hypothesis, with the majority of these events occurring by external attachment of small fruits. However, our results also indicate that anemochory might play a greater role in producing amphitropical distributions than previously thought and at a greater rate than endozoochory or hydrochory.

We combined new sequence data for more than 300 muroid rodent species with our previously published sequences for up to five nuclear and one mitochondrial genes to generate the most widely and densely sampled hypothesis of evolutionary relationships across Muroidea. An exhaustive screening procedure for publically available sequences was implemented to avoid the propagation of taxonomic errors that are common to supermatrix studies. The combined data set of carefully screened sequences derived from all available sequences on GenBank with our new data resulted in a robust maximum likelihood phylogeny for 900 of the approximately 1,620 muroids. Several regions that were equivocally resolved in previous studies are now more decisively resolved, and we estimated a chronogram using 28 fossil calibrations for the most integrated age and topological estimates to date. The results were used to update muroid classification and highlight questions needing additional data. We also compared the results of multigene supermatrix studies like this one with the principal published supertrees and concluded that the latter are unreliable for any comparative study in muroids. In addition, we explored diversification patterns as an explanation for why muroid rodents represent one of the most species-rich groups of mammals by detecting evidence for increasing net diversification rates through time across the muroid tree. We suggest the observation of increasing rates may be due to a combination of parallel increases in rate across clades and high average extinction rates. Five increased diversification-rate-shifts were inferred, suggesting that multiple, but perhaps not independent, events have led to the remarkable species diversity in the superfamily. Our results provide a phylogenetic framework for comparative studies that is not highly dependent upon the signal from any one gene.