Evolutionary and ecological forces influencing population diversification in Bornean montane passerines.

The mountains of Borneo are well known for their high endemicity and historical role in preserving Southeast Asian rainforest biodiversity, but the diversification of populations inhabiting these mountains is poorly studied. Here we examine the genetic structure of 12 Bornean montane passerines by comparing complete mtDNA ND2 gene sequences of populations spanning the island. Maximum likelihood and Bayesian phylogenetic trees and haplotype networks are examined for common patterns that might signal important historical events or boundaries to dispersal. Morphological and ecological characteristics of each species are also examined using phylogenetic generalized least-squares (PGLS) for correlation with population structure. Populations in only four of the 12 species are subdivided into distinct clades or haplotype groups. Although this subdivision occurred at about the same time in each species (ca. 0.6-0.7Ma), the spatial positioning of the genetic break differs among the species. In two species, northeastern populations are genetically divergent from populations elsewhere on the island. In the other two species, populations in the main Bornean mountain chain, including the northeast, are distinct from those on two isolated peaks in northwestern Borneo. We suggest different historical forces played a role in shaping these two distributions, despite commonality in timing. PGLS analysis showed that only a single characteristic-hand-wing index-is correlated with population structure. Birds with longer wings, and hence potentially more dispersal power, have less population structure. To understand historical forces influencing montane population structure on Borneo, future studies must compare populations across the entirety of Sundaland.

Model selection as a tool for phylogeographic inference: an example from the willow Salix melanopsis.

Phylogeographic inference has typically relied on analyses of data from one or a few genes to provide estimates of demography and population histories. While much has been learned from these studies, all phylogeographic analysis is conditioned on the data, and thus, inferences derived from data that represent a small sample of the genome are unavoidably tenuous. Here, we demonstrate one approach for moving beyond classic phylogeographic research. We use sequence capture probes and Illumina sequencing to generate data from >400 loci in order to infer the phylogeographic history of Salix melanopsis, a riparian willow with a disjunct distribution in coastal and the inland Pacific Northwest. We evaluate a priori phylogeographic hypotheses using coalescent models for parameter estimation, and the results support earlier findings that identified post-Pleistocene dispersal as the cause of the disjunction in S. melanopsis. We also conduct a series of model selection exercises using IMa2, Migrate-n and ∂a∂i. The resulting ranking of models indicates that refugial dynamics were complex, with multiple regions in the inland regions serving as the source for postglacial colonization. Our results demonstrate that new sources of data and new approaches to data analysis can rejuvenate phylogeographic research by allowing for the identification of complex models that enable researchers to both identify and estimate the most relevant parameters for a given system.

Speciational history of North American Haemorhous finches (Aves: Fringillidae) inferred from multilocus data.

We investigated species relationships and timing of speciation in North American Haemorhous finches by using a mitochondrial phylogeographic approach combined with a multilocus species tree reconstruction. Haemorhous purpureus and H. cassinii were strongly supported as sister taxa, and H. mexicanus was sister to H. purpureus+H. cassinii. Our divergence times indicated that diversification within Haemorhous occurred progressively from the Late Miocene into the Pleistocene. Our inferred pattern of speciation demonstrates the complexity of the origins of North American birds, and provides additional evidence that a single cause for speciation in closely related North American birds, such as Late Pleistocene glacial-interglacial cycles, is unlikely.

A numerical study on flow and pollutant transport in Singapore coastal waters.

Intensive economic and shipping activities in Singapore Strait have caused Singapore coastal waters to be under high risk of water pollution. A nested three-dimensional unstructured-grid SUNTANS model is applied to Singapore coastal waters to simulate flow and pollutant transport. The small domain (~50m resolution) Singapore coastal model is nested within a large domain (~200m resolution) regional model. The nested model is able to predict water surface elevations and velocities with high R(2) values of 0.96 and 0.91, respectively. Model results delineate the characteristics of circulation pattern in Singapore coastal waters during the Northeast and Southwest monsoons. The pollutants are modeled as passive tracers, and are released at six key sailing locations Points 1-6 in Singapore coastal waters and are named as Passive Tracers 1-6, respectively. Our results show that the rate of dispersion is twice as large for the Northeast monsoon compared to the Southwest monsoon due to differences in large-scale monsoons and small-scale local winds. The volume averaged concentration (VAC) diminishes faster and the local flushing time is shorter during the Northeast monsoon than the Southwest monsoon. Dispersion coefficients K and the VAC decreasing rate are maximum for Tracers 2 and 3 with shortest local flushing time due to the strong surrounding currents and abrupt bathymetry changes near Senang and St. John Islands. Dispersion coefficients K and the VAC decreasing rate are minimum for Tracer 1 due to weak currents induced by the semi-enclosed coastline near Tuas. It is found that both the lateral dispersion coefficient Ky and the compound dispersion coefficient K obey a "4/3-law", which defines a linear correlation between dispersion coefficients and 4/3-power of selected length scale.

Synthesis and Properties of New "Stimuli" Responsive Nanocomposite Hydrogels Containing Silver Nanoparticles.

Hydrogel nanocomposites containing silver nanoparticles of size 15⁻21 nm were prepared by diffusion and in-situ chemical reduction in chemically crosslinked polymers based on N-acryloyl-N'-ethyl piperazine (AcrNEP) and N-isopropylacrylamide (NIPAM). The polymer chains of the hydrogel network offered control and stabilization of silver nanoparticles without the need for additional stabilizers. The presence of silver nanoparticles and their size was quantified by UV-Vis absorption spectroscopy and scanning electron microscopy. The nanocomposite hydrogels were responsive to pH and temperature changes of the external environment. The equilibrium weight swelling ratio of the hydrogel nanocomposite was lower in comparison with the precursor hydrogel. Silver nanoparticles present in the nanocomposite offered additional physical crosslinking which influenced media diffusion and penetration velocity. The release of silver nanoparticles from the hydrogel matrix in response to external pH changes was studied. The rate of release of silver nanoparticles was higher in a solution of pH 2.5 due to maximum swelling caused by ionization of the gel network. No significant release of nanoparticles was observed in a solution of pH 7.