José A. Castro

Bayesian estimation of post-Messinian divergence times in Balearic island lizards

Phylogenetic relationships and timings of major cladogenesis events are investigated in the Balearic Island lizards Podarcislilfordi and P.pityusensis using 2675bp of mitochondrial and nuclear DNA sequences. Partitioned Bayesian and Maximum Parsimony analyses provided a well-resolved phylogeny with high node-support values. Bayesian MCMC estimation of node dates was investigated by comparing means of posterior distributions from different subsets of the sequence against the most robust analysis which used multiple partitions and allowed for rate heterogeneity among branches under a rate-drift model. Evolutionary rates were systematically underestimated and thus divergence times overestimated when sequences containing lower numbers of variable sites were used (based on ingroup node constraints). The following analyses allowed the best recovery of node times under the constant-rate (i.e., perfect clock) model: (i) all cytochrome b sequence (partitioned by codon position), (ii) cytochrome b (codon position 3 alone), (iii) NADH dehydrogenase (subunits 1 and 2; partitioned by codon position), (iv) cytochrome b and NADH dehydrogenase sequence together (six gene-codon partitions), (v) all unpartitioned sequence, (vi) a full multipartition analysis (nine partitions). Of these, only (iv) and (vi) performed well under the rate-drift model. These findings have significant implications for dating of recent divergence times in other taxa. The earliest P.lilfordi cladogenesis event (divergence of Menorcan populations), occurred before the end of the Pliocene, some 2.6Ma. Subsequent events led to a West Mallorcan lineage (2.0Ma ago), followed 1.2Ma ago by divergence of populations from the southern part of the Cabrera archipelago from a widely-distributed group from north Cabrera, northern and southern Mallorcan islets. Divergence within P.pityusensis is more recent with the main Ibiza and Formentera clades sharing a common ancestor at about 1.0Ma ago. Climatic and sea level changes are likely to have initiated cladogenesis, with lineages making secondary contact during periodic landbridge formation. This oscillating cross-archipelago pattern in which ancient divergence is followed by repeated contact resembles that seen between East-West refugia populations from mainland Europe.

Population structure and mitochondrial DNA gene flow in Old World populations of Drosophila subobscura

An extensive survey of mitochondrial DNA (mtDNA) restriction polymorphism in 156 isofemale lines from 29 different geographic populations of Drosophila subobscura distributed throughout the Old World was carried out. Ten restriction enzymes were used, five of which revealed restriction site polymorphism. Of the 31 restriction sites detected, 13 were found to be polymorphic. Comparisons with the mtDNA map of Drosophila yakuba indicate that the variable sites are mainly concentrated in protein genes, especially those corresponding to the NADH complex. A total of 13 different haplotypes were observed, two of which (haplotypes I and II) are quite frequent and widely distributed throughout the populations, whereas the other 11 with the exception of VIII, which deserves special attention, are each restricted to one population only and occur at low frequencies. The observed distribution of haplotypes, corroborated by a parsimonious unrooted tree, suggests an ancient origin of haplotypes I and II in the continent.In order to compare genetic structure according to mtDNA and allozymes, the 10 populations with higher population sizes were studied for 10 polymorphic allozymes also. One striking result is the high degree of population structure of the mtDNA when compared to that obtained for allozymes. If an island model is assumed, estimates of gene flow give values of 0.013 and 1.89 migrants per generation for mtDNA and allozymes, respectively. What is apparent from these estimates is that Drosophila subobscura populations are effectively subdivided for mtDNA genes at migration rates at which nuclear genes (allozymes) are almost panmictic.

An Evaluation of Video-to-Video Face Verification

Person recognition using facial features, e.g., mug-shot images, has long been used in identity documents. However, due to the widespread use of web-cams and mobile devices embedded with a camera, it is now possible to realize facial video recognition, rather than resorting to just still images. In fact, facial video recognition offers many advantages over still image recognition; these include the potential of boosting the system accuracy and deterring spoof attacks. This paper presents an evaluation of person identity verification using facial video data, organized in conjunction with the International Conference on Biometrics (ICB 2009). It involves 18 systems submitted by seven academic institutes. These systems provide for a diverse set of assumptions, including feature representation and preprocessing variations, allowing us to assess the effect of adverse conditions, usage of quality information, query selection, and template construction for video-to-video face authentication.

Biometric Template Protection Using Universal Background Models: An Application to Online Signature

Data security and privacy are crucial issues to be addressed for assuring a successful deployment of biometrics-based recognition systems in real life applications. In this paper, a template protection scheme exploiting the properties of universal background models, eigen-user spaces, and the fuzzy commitment cryptographic protocol is presented. A detailed discussion on the security and information leakage of the proposed template protection system is given. The effectiveness of the proposed approach is investigated with application to online signature recognition. The given experimental results, evaluated on the public MCYT signature database, show that the proposed system can guarantee competitive recognition accuracy while providing protection to the employed biometric data.

Unsupervised clustering method to detect microsaccades.

Microsaccades, small involuntary eye movements that occur once or twice per second during attempted visual fixation, are relevant to perception, cognition, and oculomotor control and present distinctive characteristics in visual and oculomotor pathologies. Thus, the development of robust and accurate microsaccade-detection techniques is important for basic and clinical neuroscience research. Due to the diminutive size of microsaccades, however, automatic and reliable detection can be difficult. Current challenges in microsaccade detection include reliance on set, arbitrary thresholds and lack of objective validation. Here we describe a novel microsaccade-detecting method, based on unsupervised clustering techniques, that does not require an arbitrary threshold and provides a detection reliability index. We validated the new clustering method using real and simulated eye-movement data. The clustering method reduced detection errors by 62% for binocular data and 78% for monocular data, when compared to standard contemporary microsaccade-detection techniques. Further, the clustering methods reliability index was correlated with the microsaccade-detection error rate, suggesting that the reliability index may be used to determine the comparative precision of eye-tracking devices.

Is My Student at the Other Side? Applying Biometric Web Authentication to E-Learning Environments

Despite of the advances in the e-learning domain during the last decades, there is a lack of suitable mechanism to carry out assessment with the appropriate measures to avoid cheating. Current LMSs do not provide the needed features to check that the intended student is taking the online exam by himself, or even to know if he has spent the whole session time in front of the computer. This paper presents a web-based application that offers biometric authentication based on face-recognition. This application, which can be easily integrated in currently available LMSs, is able to use face-recognition during access control, tracking and assessment. Thus it is possible to improve security during critical phases in the learning process (e.g. assessment).

Evolutionary analysis of genetic variation observed in citrus tristeza virus (CTV) after host passage.

Summary.We have studied the genetic variability in two genes (p18 and p20) from two groups of Citrus tristeza virus (CTV) isolates. One group (isolates T385, T317, T318, and T305) was derived from a Spanish source by successive host passages while the other (isolates T388 and T390) was obtained after aphid transmission from a Japanese source. A total of 274 sequences were obtained for gene p18 and 451 for p20. In the corresponding phylogenetic trees, sequences derived from the severe isolates (T318, T305, and T388) clustered together and separately from those derived from mild or moderate isolates (T385, T317, and T390), regardless of their geographic origin. Hierarchical analyses of molecular variance showed that up to 53% of the total genetic variability in p18 and up to 87% of the variation in p20 could be explained by differences in the pathogenicity features of the isolates. Neutrality tests revealed that different selection forces had been acting between isolates and between genes, with purifying selection being suggested for p18 from isolates T385 and T390 and for p20 from isolates T385, T317, and T388, and balancing selection for p18 from isolates T318, T305, and T388 and for p20 from isolates T318 and T390. Furthermore, several models of codon selection were observed, with purifying selection being the most notable one, compatible with low effective population size of the virus populations resulting from transmission bottlenecks. We found no evidence of recombination playing a significant role during p18 and p20 evolution in these isolates. These results suggest that hosts can be an important evolutionary factor for CTV isolates.

Security issues of Internet-based biometric authentication systems: risks of Man-in-the-Middle and BioPhishing on the example of BioWebAuth

Beside the optimization of biometric error rates the overall security system performance in respect to intentional security attacks plays an important role for biometric enabled authentication schemes. As traditionally most user authentication schemes are knowledge and/or possession based, firstly in this paper we present a methodology for a security analysis of Internet-based biometric authentication systems by enhancing known methodologies such as the CERT attack-taxonomy with a more detailed view on the OSI-Model. Secondly as proof of concept, the guidelines extracted from this methodology are strictly applied to an open source Internet-based biometric authentication system (BioWebAuth). As case studies, two exemplary attacks, based on the found security leaks, are investigated and the attack performance is presented to show that during the biometric authentication schemes beside biometric error performance tuning also security issues need to be addressed. Finally, some design recommendations are given in order to ensure a minimum security level.

Genetic variation within endemic Podarcis lizards from the Balearic Islands inferred from partial Cytochrome b sequences

Sequences of the cytochrome b gene were analysed for 47 samples of two species of Podarcis from the Balearic Islands (P. pityusensis from Pityuses and P. lilfordi, from Gymnesies archipelago). The average uncorrected distance between the two species studied was 9.7%. The sampled individuals from each species form reciprocally monophyletic units. Assuming an overall rate of change for cytochrome b of 2% per million years the nucleotide divergence of 9.7 ± 1.9% between P. lilfordi and P. pityusensis, could correspond to a divergence time of 4.95 ± 0.95 million years. The separation time between Gymnesies and Pityuses archipelagos according to geological hypotheses is around 5 million years, thus our results suggest the ancestors of the two present forms became isolated during this event. The most parsimonious networks suggest that currently accepted subspecies do not form monophyletic groups, and so should be reassessed. Despite our limited sampling the level of variability is much higher in P. lilfordi than P. pityusensis. Since they are sister taxa the relative age of each species is equal, therefore the differences might be due to historical population structure differences. However it seems that the forms on the islands are not genetically distinct units, implying that morphological differences are recent adaptations to their environments.

Quality-Based Score Normalization and Frame Selection for Video-Based Person Authentication

This paper addresses the incorporation of quality measures to video-based person authentication. A theoretical framework to incorporate quality measures in biometric authentication is exposed. Two different quality-based score normalization techniques are derived from this theoretical framework. Furthermore, a quality-based frame selection technique and a new face image quality measure are also presented. The ability of this quality measure and the proposed quality-based score normalization techniques and quality-based frame selection technique to improve verification performance is experimentally evaluated in a video-based face verification experiment on the BANCA Database.This paper addresses the incorporation of quality measures to videobased person authentication. A theoretical framework to incorporate quality measures in biometric authentication is exposed. Two different quality-based score normalization techniques are derived from this theoretical framework. Furthermore, a quality-based frame selection technique and a new face image quality measure are also presented. The ability of this quality measure and the proposed quality-based score normalization techniques and quality-based frame selection technique to improve verification performance is experimentally evaluated in a video-based face verification experiment on the BANCA Database.