Chaetopterid tubes from vent and seep sites: Implications for fossil record and evolutionary history of vent and seep annelids

Vestimentiferan tube worms living at deep-sea hydrothermal vents and cold seeps have been considered as a clade with a long and continuing evolutionary history in these ecosystems. Whereas the fossil record appears to support this view, molecular age estimates do not. The two main features that are used to identify vestimentiferan tubes in the fossil record are longitudinal ridges on the tube's surface and a tube wall constructed of multiple layers. It is shown here that chaetopterid tubes from modern vents and seeps—as well as a number of fossil tubes from shallow-water environments—also show these two features. This calls for a more cautious interpretation of tubular fossils from ancient vent and seep deposits. We suggest that: current estimates for a relatively young evolutionary age based on molecular clock methods may be more reliable than the inferences of ancient “vestimentiferans” based on putative fossils of these worms; not all of these putative fossils actually belong to this group; and that tubes from fossil seeps should be investigated for chitinous remains to substantiate claims of their potential siboglinid affinities.

rbcL sequences indicate a single evolutionary origin of multinucleate cells in the red algal tribe Callithamnieae.

In the Ceramiaceae, one of the largest families of the red algae, there are from 1 to 4000 nuclei in each vegetative cell, but each tribe is homogeneous with respect to the uninucleate/multinucleate character state, except for the Callithamnieae. The goals of this study were to analyze rbcL gene sequences to clarify the evolution of taxa within the tribe Callithamnieae and to evaluate the potential evolutionary significance of the development of multinucleate cells in certain taxa. The genus Aglaothamnion, segregated from Callithamnion because it is uninucleate, was paraphyletic in all analyses. Callithamnion (including Aristothamnion) was monophyletic although not robustly so, apparently due to variations between taxa in rate of sequence evolution. Morphological synapomorphies were identified at different depths in the tree, supporting the molecular phylogenetic analysis. The uninucleate character state is ancestral in this tribe. The evolution of multinucleate cells has occurred once in the Callithamnieae. Multiple nuclei in each cell may combine the benefits of small C values (rapid cell cycle) with large cells (permitting morphological elaboration) while maintaining a constant ratio of nuclear volume: cytoplasmic volume.

Software Release Planning: An Evolutionary and Iterative Approach

Abstract To achieve higher flexibility and to better satisfy actual customer requirements, there is an increasing tendency to develop and deliver software in an incremental fashion. In adopting this process, requirements are delivered in releases and so a decision has to be made on which requirements should be delivered in which release. Three main considerations that need to be taken account of are the technical precedences inherent in the requirements, the typically conflicting priorities as determined by the representative stakeholders, as well as the balance between required and available effort. The technical precedence constraints relate to situations where one requirement cannot be implemented until another is completed or where one requirement is implemented in the same increment as another one. Stakeholder preferences may be based on the perceived value or urgency of delivered requirements to the different stakeholders involved. The technical priorities and individual stakeholder priorities may be in conflict and difficult to reconcile. This paper provides (i) a method for optimally allocating requirements to increments; (ii) a means of assessing and optimizing the degree to which the ordering conflicts with stakeholder priorities within technical precedence constraints; (iii) a means of balancing required and available resources for all increments; and (iv) an overall method called EVOLVE aimed at the continuous planning of incremental software development. The optimization method used is iterative and essentially based on a genetic algorithm. A set of the most promising candidate solutions is generated to support the final decision. The paper evaluates the proposed approach using a sample project.

Early-type stars in the Galactic halo from the Palomar-Green survey - III. Completion of a magnitude range limited sample

High-resolution (R approximate to 40 000) echelle spectroscopic observations of 13 high-latitude early-type stars are presented. These stars comprise the final part of a complete magnitude range limited sample based on low-resolution spectroscopy of targets drawn from the Palomar-Green survey. The magnitude range under consideration is 13 less than or equal to B-PG less than or equal to 14.6, corresponding to an approximate distance limit for main-sequence B-type objects of 5 less than or equal to d less than or equal to 40 kpc. Three stars are found to be apparently normal, young stars, based on their positions on the (T-eff, log g) diagram, normal abundance patterns and relatively large projected rotational velocities. A further star, PG 1209+263, was found to belong to the chemically peculiar (CP) silicon star class of objects. The remainder are evolved subluminous stars lying on post- horizontal branch (post-HB) tracks, with the exception of PG 2120+062, which appears to be in a post-asymptotic giant branch evolutionary stage. For the young stars in the sample, we have derived distance and age estimates through comparison of the atmospheric parameters with recent theoretical evolutionary models. We discuss formation scenarios by comparing times-of- flight and evolutionary time-scales. It is found that all stars could have formed in the Galactic disc and been ejected from there soon after their birth, with the exception of PG 1209+263. The adopted proper motion is found to be a crucial factor in the kinematical analysis. We also present some number densities for young B-type halo stars, which indicate that they are extremely scarce objects.

B-type supergiants in the Small Magellanic Cloud: rotational velocities and implications for evolutionary models

High-resolution spectra for 24 SMC and Galactic B-type supergiants have been analysed to estimate the contributions of both macroturbulence and rotation to the broadening of their metal lines. Two different methodologies are considered, viz. goodness-of-fit comparisons between observed and theoretical line profiles and identifying zeros in the Fourier transforms of the observed profiles. The advantages and limitations of the two methods are briefly discussed with the latter techniques being adopted for estimating projected rotational velocities ( v sin i) but the former being used to estimate macroturbulent velocities. The projected rotational velocity estimates range from approximately 20 to 60 kms(-1), apart from one SMC supergiant, Sk 191, with a v sin i similar or equal to 90 km s(-1). Apart from Sk 191, the distribution of projected rotational velocities as a function of spectral type are similar in both our Galactic and SMC samples with larger values being found at earlier spectral types. There is marginal evidence for the projected rotational velocities in the SMC being higher than those in the Galactic targets but any differences are only of the order of 5 - 10 km s(-1), whilst evolutionary models predict differences in this effective temperature range of typically 20 to 70 km s(-1). The combined sample is consistent with a linear variation of projected rotational velocity with effective temperature, which would imply rotational velocities for supergiants of 70 kms(-1) at an effective temperature of 28 000 K ( approximately B0 spectral type) decreasing to 32 km s(-1) at 12 000 K (B8 spectral type). For all targets, the macroturbulent broadening would appear to be consistent with a Gaussian distribution ( although other distributions cannot be discounted) with an 1/e half-width varying from approximately 20 km s(-1) at B8 to 60 km s(-1) at B0 spectral types.

Epipolar geometry estimation based on evolutionary agents

This paper presents a novel approach based on the use of evolutionary agents for epipolar geometry estimation. In contrast to conventional nonlinear optimization methods, the proposed technique employs each agent to denote a minimal subset to compute the fundamental matrix, and considers the data set of correspondences as a 1D cellular environment, in which the agents inhabit and evolve. The agents execute some evolutionary behavior, and evolve autonomously in a vast solution space to reach the optimal (or near optima) result. Then three different techniques are proposed in order to improve the searching ability and computational efficiency of the original agents. Subset template enables agents to collaborate more efficiently with each other, and inherit accurate information from the whole agent set. Competitive evolutionary agent (CEA) and finite multiple evolutionary agent (FMEA) apply a better evolutionary strategy or decision rule, and focus on different aspects of the evolutionary process. Experimental results with both synthetic data and real images show that the proposed agent-based approaches perform better than other typical methods in terms of accuracy and speed, and are more robust to noise and outliers.