A Molecular Dynamics Study of Monomer Melt Properties of Cyanate Ester Monomer Melt Properties.

The objective of this work was to computationally predict the melting temperature and melt properties of thermosetting monomers used in aerospace applications. In this study, we applied an existing voids method by Solca. to examine four cyanate ester monomers with a wide range of melting temperatures. Voids were introduced into some simulations by removal of molecules from lattice positions to lower the free-energy barrier to melting to directly simulate the transition from a stable crystal to amorphous solid and capture the melting temperature. We validated model predictions by comparing melting temperature against previously reported literature values. Additionally, the torsion and orientational order parameters were used to examine the monomers' freedom of motion to investigate structure-property relationships. Ultimately, the voids method provided reasonable estimates of melting temperature while the torsion and order parameter analysis provided insight into sources of the differing melt properties between the thermosetting monomers. As a whole, the results shed light on how freedom of molecular motions in the monomer melt state may affect melting temperature and can be utilized to inspire the development of thermosetting monomers with optimal monomer melt properties for demanding applications.

Extensive hybridization and past introgression between divergent lineages in a quasi-clonal hermaphroditic fish: Ramifications for species concepts and taxonomy.

Extreme inbreeding is expected to reduce the incidence of hybridization, serving as a prezygotic barrier. Mangrove rivulus is a small killifish that reproduces predominantly by self-fertilization, producing highly homozygous lines throughout its geographic range. The Bahamas and Caribbean are inhabited by two highly diverged phylogeographic lineages of mangrove rivulus, Kryptolebias marmoratus and a 'Central clade' closely related to K. hermaphroditus from Brazil. The two lineages are largely allopatric, but recently were found in syntopy on San Salvador, Bahamas, where a single hybrid was reported. To better characterize the degree of hybridization and the possibility of secondary introgression, here we conducted a detailed genetic analysis of the contact zone on San Salvador. Two mixed populations were identified, one of which contained sexually mature hybrids. The distribution of heterozygosity at diagnostic microsatellite loci in hybrids showed that one of these hybrids was an immediate offspring from the K. marmoratus x Central clade cross, whereas the remaining five hybrids were products of reproduction by self-fertilization for 1-3 generations following the initial cross. Two hybrids had mitochondrial haplotypes of K. marmoratus and the remaining four hybrids had a haplotype of the Central clade, indicating that crosses go in both directions. In hybrids, alleles of parental lineages were represented in equal proportions suggesting lack of recent backcrossing to either of the parental lineages. However, sympatric populations of two lineages were less diverged than allopatric populations, consistent with introgression. Results are discussed in terms of applicability of the biological species concept for isogenic, effectively clonal, organisms.

Natural hybridization between divergent lineages in a selfing hermaphroditic fish.

By definition, mating between individuals is infrequent in highly selfing organisms, and so too, therefore, hybridization should be rare between genetically divergent lineages in predominantly self-fertilizing species. Notwithstanding these expectations, here we report a remarkable case of natural hybridization between highly diverged phylogeographic lineages of the mangrove rivulus, a small killifish that reproduces predominantly by self-fertilization and typically is found as highly homozygous lines in most parts of its extensive geographical range. Two distinctive genetic lineages (Kryptolebias marmoratus and a 'Central clade' closely related to K. hermaphroditus) previously were not known in sympatry, but were found by us to co-occur on San Salvador, Bahamas. Genetic analyses of a mitochondrial and multiple nuclear markers determined the direction of a cross producing a hybrid fish. Furthermore, we show that this hybrid individual was viable, as it successfully reproduced by self-fertilization for two generations. Additional sampling of this population will be necessary to determine if backcrossing of hybrids to the parental lineages occurs in nature and to analyse whether such backcross progeny are viable. Application of the biological species concept (BSC) is traditionally difficult in clonally reproducing organisms. Our results show that although mangrove rivulus fish are mostly highly selfing in nature (resulting in isogenic, effectively clonal and homozygous progeny), classification within this taxonomic complex need not be incompatible with the BSC.

A novel terrestrial fish habitat inside emergent logs.

Reports of new habitats for a major group of organisms are rare. Fishes display diverse adaptations for temporary (amphibious) existence on land, but to our knowledge, none have ever been reported regularly living inside emergent logs. Here, we show that the mangrove killifish, Kryptolebias marmoratus, a species previously known to emerse (leave the water) regularly, is now known to emerse and aggregate in large numbers inside decaying mangrove logs that have been "galleried" by terrestrial insects. This behavior has now been documented in both Belize, Central America, and Florida, U.S.A., populations and represents the first known case of fishes entering terrestrial woody material. The dense packing of fish in the narrow log galleries may imply a novel social context in which intraspecific aggressive behaviors are reduced, possibly mediated by the physiological limitations imposed within this restrictive habitat.

Altered development and reproduction in mosquitofish exposed to pulp and paper mill effluent in the Fenholloway River, Florida USA.

Female mosquitofish exposed to pulp and paper mill effluent (PME) in the Fenholloway River, Florida, USA have masculinized secondary sex characteristics and altered aromatase enzyme activity. We and others have shown that the Fenholloway River PME contains androgenic and progestogenic substance(s). The present study was designed to test the hypothesis that the development and reproductive health of PME-exposed Fenholloway River mosquitofish are altered compared to mosquitofish living in Econfina River, which is the reference site. Fish were collected on a single day from both sites in June and August 1999 and January and June 2000. We compared standard length, anal fin length and segment number; body, liver, and gonad mass; and number of eggs and embryos from Fenholloway and Econfina River mosquitofish. The data were analyzed collectively for generalized site effect, for site effects during reproductive and nonreproductive seasons, and for repeatability of site effects between years. Mosquitofish exposed to PME in the Fenholloway River were generally smaller in length and mass, anal fin segment number was greater, and the number of embryos, but not oocytes, was significantly decreased compared to the reference site fish. Anal fin length and segment number and liver and testis masses were generally greater in Fenholloway compared to the Econfina River males. The importance of this study is that we have documented masculinized development and decreased embryo production in PME-exposed mosquitofish and that these site effects are generally consistent across seasons and between years.

Characterizing coral condition using estimates of three-dimensional colony surface area.

Coral reefs provide shoreline protection, biological diversity, fishery harvests, and tourism, all values that stem from the physically-complex coral infrastructure. Stony corals (scleractinians) construct and maintain the reef through deposition of calcium carbonate. Therefore, assessment of coral reefs requires at least some measurement endpoints that reflect the biological and physical condition of stony corals. Most monitoring programs portray coral quantity as live coral cover, which is the two-dimensional proportion of coral surface to sea floor viewed from above (planar view). The absence of the third dimension, however, limits our ability to characterize coral reef value, physiology, health and sustainability. A three-dimensional (3D) approach more realistically characterizes coral structure available as community habitat and, when combined with estimates of live coral tissue, quantifies the amount of living coral available for photosynthesis, growth and reproduction. A rapid coral survey procedure that coupled 3D coral quantification with more traditional survey measurements was developed and tested in the field. The survey procedure relied on only three underwater observations--species identification, colony size, and proportion of live tissue--made on each colony in the transect. These observations generated a variety of metrics, including several based on 3D colony surface area, that are relevant to reef management.

Aromatase activity in the ovary and brain of the eastern mosquitofish (Gambusia holbrooki) exposed to paper mill effluent.

Studies have shown that female mosquitofish living downstream of a paper mill located on the Fenholloway River, Florida, have masculinized secondary sex characteristics, including altered anal fin development and reproductive behavior. Masculinization can be caused by exposure to androgens in the water or from an alteration in aromatase activity in the fish. We hypothesized that aromatase activity would be inhibited by a component(s) of the paper mill effluent. Aromatase inhibition could masculinize the hormonal profile and, subsequently, secondary sex characteristics of the exposed females. Therefore, we predicted that ovarian and brain aromatase activity would be lower in the female mosquitofish from the Fenholloway River compared with the reference site, the Econfina River. Adult females were collected and standard length, body mass, anal fin length, and segment number were measured. Ovarian and brain aromatase activity were determined using a tritiated water assay. Fenholloway females had masculinized anal fin development as indicated by an increase in the number of segments in the longest anal fin ray (p < 0.0001), yet the length of the ray did not differ between sites (p = 0.95). Fenholloway females exhibited higher ovarian (p = 0.0039) and brain (p = 0.0003) aromatase activity compared with reference site fish. These data do not support aromatase inhibition as the mechanism for masculinization, suggesting that the masculinization of the Fenholloway female mosquitofish is due to androgenic contaminants. Future studies should examine the relationship between aromatase enzyme activity and exposure to environmental androgens.