The energy costs of sexual dimorphism in mole-rats are morphological not behavioural.

Different reproductive strategies of males and females may lead to the evolution of differences in their energetic costs of reproduction, overall energetic requirements and physiological performances. Sexual dimorphism is often associated with costly behaviours (e.g. large males might have a competitive advantage in fighting, which is energetically expensive). However, few studies of mammals have directly compared the energy costs of reproductive activities between sexes. We compared the daily energy expenditure (DEE) and resting metabolic rate (RMR) of males and females of two species of mole-rat, Bathyergus janetta and Georychus capensis (the former is sexually dimorphic in body size and the latter is not) during a period of intense digging when males seek females. We hypothesized that large body size might be indicative of greater digging or fighting capabilities, and hence greater mass-independent DEE values in males of the sexually dimorphic species. In contrast to this prediction, although absolute values of DEE were greater in B. janetta males, mass-independent values were not. No differences were apparent between sexes in G. capensis. By comparison, although RMR values were greater in B. janetta than G. capensis, no differences were apparent between the sexes for either species. The energy cost of dimorphism is most likely to be the cost of maintenance of a large body size, and not the cost of behaviours performed when an individual is large.

Modulation of surface charge, particle size and morphological properties of chitosan-TPP nanoparticles intended for gene delivery

This work investigates the polyanion initiated gelation process in fabricating chitosan-TPP (tripolyphosphate) nanoparticles in the size range of 100-250 nm intended to be used as carriers for the delivery of gene or protein macromolecules. It demonstrates that ionic gelation of cationic chitosan molecules offers a flexible and easily controllable process for systematically and predictably manipulating particle size and surface charge which are important properties in determining gene transfection efficacy if the nanoparticles are used as non-viral vectors for gene delivery, or as delivery carriers for protein molecules. Variations in chitosan molecular weight, chitosan concentration, chitosan to TPP weight ratio and solution pH value were examined systematically for their effects on nanoparticle size, intensity of surface charge, and tendency of particle aggregation so as to enable speedy fabrication of chitosan nanoparticles with predetermined properties. The chitosan-TPP nanoparticles exhibited a high positive surface charge across a wide pH range, and the isoelectric point (IEP) of the nanoparticles was found to be at pH 9.0. Detailed imaging analysis of the particle morphology revealed that the nanoparticles possess typical shapes of polyhedrons (e.g., pentagon and hexagon), indicating a similar crystallisation mechanism during the particle formation and growth process. This study demonstrates that systematic design and modulation of the surface charge and particle size of chitosan-TPP nanoparticles can be readily achieved with the right control of critical processing parameters, especially the chitosan to TPP weight ratio. (c) 2005 Elsevier B.V. All rights reserved.

High Speed FPGA-based implementations of Delayed-LMS filters

A variation of the least means squares (LMS) algorithm, called the delayed LMS (DLMS) algorithm is an ideally suited to achieve highly pipelined, adaptive digital filter implementations. The paper presents an efficient method of determining the delays in the DLMS filter and then transferring these delays using retiming in order to achieve fully pipelined circuit architectures for FPGA implementation. The method has been used to derive a series of retimed delayed LMS (RDLMS) architectures, which considerable reduce the number of delays and convergence time and give superior performance in terms of throughput rate when compared to previous work. Three circuit architectures and three hardware shared versions are presented which have been implemented using the Virtex-II FPGA technology resulting in a throughout rate of 182 Msample/s.

Signal-to-Noise Ratio Analysis for Nonlinear N-ary Phase Filters

The problem of recognising targets in non-overlapping clutter using nonlinear N-ary phase filters is addressed. Using mathematical analysis, expressions were derived for an N-ary phase filter and the intensity variance of an optical correlator output. The N-ary phase filter was shown to consist of an infinite sum of harmonic terms whose periodicity was determined by N. For the intensity variance, it was found that under certain conditions the variance was minimised due to a hitherto undiscovered phase quadrature effect. Comparison showed that optimal real filters produced greater SNR values than the continuous phase versions as a consequence of this effect.

Comparison of genetic and morphological methods to detect the presence of American lobsters, Homarus americanus H. Milne Edwards, 1837 (Astacidea: Nephropidae) in Norwegian waters

American lobsters (Homarus americanus H. Milne Edwards, 1837) are imported live to Europe and should according regulations be kept in land-based tanks until sold. In spite of the strict regulations aimed specifically at preventing the introduction of this species into the NE Atlantic, several specimens of H. americanus have been captured in the wild, especially in Oslofjord, Norway since 1999. One of the great concerns is interbreeding between the introduced American species and the local European lobster, H. gammarus (Linnaeus, 1758). For this reason an awareness campaign was launched in 2000 focusing on morphologically "unusual" lobsters caught in local waters. Morphological characters have been based on colour and sub-ventral spines on the rostrum. Two samples of H. americanus were used for comparisons, as well as samples of European lobster from Oslofjord collected in 1992. Previous genetic analyses (allozymes, mtDNA and microsatellite DNA) have demonstrated that the American lobster is distinct from its European counterpart, with several additional alleles at many loci in addition to different allelic frequency distribution of alleles of "shared" alleles. During the present study, thirteen microsatellite loci were tested in the initial screening, and the three most discriminating loci (Hgam98, Hgam197b and Hgam47b) were used in a detailed comparison between the two species. A total of 45 unusual lobsters were reported captured from Ålesund (west) to Oslofjord (southeast) from 2001 to 2005 and these were analysed for the three microsatellite loci. Nine specimens were identified as American lobsters. Comparisons between morphological and genetic characteristics revealed that morphological differences are not reliable in discrimination the two species, or to identify hybrids. Further, some loci display almost no overlapping in allele frequency distribution for the reference samples analysed, thus providing a reliable tool to identify hybrids.

Tracing early stages of species differentiation: Ecological, morphological and genetic divergence of Galapagos sea lion populations

Background: Oceans are high gene flow environments that are traditionally believed to hamper the build-up of genetic divergence. Despite this, divergence appears to occur occasionally at surprisingly small scales. The Galápagos archipelago provides an ideal opportunity to examine the evolutionary processes of local divergence in an isolated marine environment. Galápagos sea lions (Zalophus wollebaeki) are top predators in this unique setting and have an essentially unlimited dispersal capacity across the entire species range. In theory, this should oppose any genetic differentiation.
Results: We find significant ecological, morphological and genetic divergence between the western colonies and colonies from the central region of the archipelago that are exposed to different ecological conditions. Stable isotope analyses indicate that western animals use different food sources than those from the central area. This is likely due to niche partitioning with the second Galápagos eared seal species, the Galápagos fur seal (Arctocephalus galapagoensis) that exclusively dwells in the west. Stable isotope patterns correlate with significant differences in foraging-related skull morphology. Analyses of mitochondrial sequences as well as microsatellites reveal signs of initial genetic differentiation.
Conclusion: Our results suggest a key role of intra- as well as inter-specific niche segregation in the evolution of genetic structure among populations of a highly mobile species under conditions of free movement. Given the monophyletic arrival of the sea lions on the archipelago, our study challenges the view that geographical barriers are strictly needed for the build-up of genetic divergence. The study further raises the interesting prospect that in social, colonially breeding mammals additional forces, such as social structure or feeding traditions, might bear on the genetic partitioning of populations.

Morphological and molecular characters reveal differentiation in a Neotropical social bee, Melipona beecheii (Apidae : Meliponini)

Morphometrics and DNA microsatellites were used to analyse the genetic structure of populations of the stingless bee M. beecheii from two extremes of its geographic range. The results showed that populations from Costa Rica and Yucatan exhibit substantial phenotypic and molecular differentiation. Bees from Yucatan were smaller and paler than those from Costa Rica. The value of multilocus F-ST = 0.280 (P <0.001) confirmed that there were significant molecular genetic differences between the two populations. Populations showed significant deviation from Hardy Weinberg equilibrium and the values of FIS (the inbreeding coefficient) were positive for Costa Rica = 0.416 and the Yucatan Peninsula = 0.193, indicating a lack of heterozygotes in both populations possibly due to inbreeding. The DNA sequence of 678 bp of the mitochondrial gene COI differed between populations by 1.2%. The results of this study should be considered in conservation programmes, particularly with regard to the movement of colonies between regions.