Evolutionary Connectionism: Algorithmic Principles Underlying the Evolution of Biological Organisation in Evo-Devo,Evo-Eco and Evolutionary Transitions

The mechanisms of variation, selection and inheritance, on which evolution by natural selection depends, are not fixed over evolutionary time. Current evolutionary biology is increasingly focussed on understanding how the evolution of developmental organisations modifies the distribution of phenotypic variation, the evolution of ecological relationships modifies the selective environment, and the evolution of reproductive relationships modifies the heritability of the evolutionary unit. The major transitions in evolution, in particular, involve radical changes in developmental, ecological and reproductive organisations that instantiate variation, selection and inheritance at a higher level of biological organisation. However, current evolutionary theory is poorly equipped to describe how these organisations change over evolutionary time and especially how that results in adaptive complexes at successive scales of organisation (the key problem is that evolution is self-referential, i.e. the products of evolution change the parameters of the evolutionary process). Here we first reinterpret the central open questions in these domains from a perspective that emphasises the common underlying themes. We then synthesise the findings from a developing body of work that is building a new theoretical approach to these questions by converting well-understood theory and results from models of cognitive learning. Specifically, connectionist models of memory and learning demonstrate how simple incremental mechanisms, adjusting the relationships between individually-simple components, can produce organisations that exhibit complex system-level behaviours and improve the adaptive capabilities of the system. We use the term “evolutionary connectionism” to recognise that, by functionally equivalent processes, natural selection acting on the relationships within and between evolutionary entities can result in organisations that produce complex system-level behaviours in evolutionary systems and modify the adaptive capabilities of natural selection over time. We review the evidence supporting the functional equivalences between the domains of learning and of evolution, and discuss the potential for this to resolve conceptual problems in our understanding of the evolution of developmental, ecological and reproductive organisations and, in particular, the major evolutionary transitions.     

Estimating abdominal adipose tissue with DXA and anthropometry

Objective: To identify an anatomically defined region of interest (ROI) from DXA assessment of body composition that when combined with anthropometry can be used to accurately predict intra‐abdominal adipose tissue (IAAT) in overweight/obese individuals. Research Methods and Procedures: Forty‐one postmenopausal women (age, 49 to 66 years; BMI, 26 to 37 kg/m²) underwent anthropometric and body composition assessments. ROI were defined as quadrilateral boxes extending 5 or 10 cm above the iliac crest and laterally to the edges of the abdominal soft tissue. A single‐slice computed tomography (CT) scan was measured at the L3 to L4 intervertebral space, and abdominal skinfolds were taken. Results: Forward step‐wise regression revealed the best predictor model of IAAT area measured by CT (r² = 0.68, standard error of estimate = 17%) to be: IAAT area (centimeters squared) = 51.844 + DXA 10‐cm ROI (grams) (0.031) + abdominal skinfold (millimeters) (1.342). Interobserver reliability for fat mass (r = 0.994; coefficient of variation, 2.60%) and lean mass (r = 0.986, coefficient of variation, 2.67%) in the DXA 10‐cm ROI was excellent. Discussion: This study has identified a DXA ROI that can be reliably measured using prominent anatomical landmarks, in this case, the iliac crest. Using this ROI, combined with an abdominal skinfold measurement, we have derived an equation to predict IAAT in overweight/obese postmenopausal women. This approach offers a simpler, safer, and more cost‐effective method than CT for assessing the efficacy of lifestyle interventions aimed at reducing IAAT. However, this warrants further investigation and validation with an independent cohort.     

A novel Candida albicans skin test antigen: efficacy and safety in man

Yeast phase Candida albicans (ATCC No. 10231) was grown in a nonantigenic medium, harvested and lyophilized. Ammonium sulfate fractions of an aqueous extract of the lyophilized cells were evaluated and the fraction yielding the highest specific delayed cutaneous reactivity in sensitized guinea-pigs was used to prepare a C. albicans skin test antigen (CASTA). The safety of the antigen was evaluated by measuring immediate and delayed (0.25, 6, 24, 48 and 72 h) cutaneous reactions in atopic and nonatopic human subjects. The outcome of three repetitive monthly Mantoux skin tests with 0.01-1 microgram antigen doses was used to test for booster effects in 14 subjects and to estimate a safe initial test antigen dose. The utility of a single skin test as a measure of cell-mediated immunity was evaluated in 40 healthy subjects. Reactor rates (greater than or equal to 2 mm, 48 h) of 40% and 85% were detected, respectively, with doses of 0.0316 and 1 microgram. Using a skin test reaction diameter greater than or equal to 5 mm at 48 h, the reactor rate was 50% for the 1-microgram dose. The only adverse reaction (45 mm, 0.25 h) was detected with the 1-microgram dose in an atopic subject who also exhibited exquisite scratch test reaginic hypersensitivity to C. albicans allergen. The prevalence of other adverse reactions to this antigen compared favorably with that to other antigens used for recall antigen testing. These studies suggest the 1-microgram CASTA dose can be used for effective, safe recall antigen skin tests.     

The channel-forming protein proaerolysin remains a dimer at low concentrations in solution

Proaerolysin, the proform of the channel-forming protein aerolysin, is secreted as a dimer by Aeromonas sp. The protein also exists as a dimer in the crystal, as well as in solution, at least at concentrations in the region of 500 microg/ml. Recently it has been argued that proaerolysin becomes monomeric at concentrations below 100 microg/ml and that only the monomeric form of the protoxin can bind to cell surface receptors (Fivaz, M., Velluz, M.-C., and van der Goot, F. G. (1999) J. Biol. Chem. 274, 37705-37708). Here we show, using non-denaturing polyacrylamide electrophoresis, chemical cross-linking, and analytical ultracentrifugation, that proaerolysin remains dimeric at the lowest concentrations of the protein that we measured (less than 5 microg/ml) and that the dimeric protoxin is quite capable of receptor binding.     

VE-cadherin: adhesion at arm's length

VE-cadherin was first identified in the early 1990s and quickly emerged as an important endothelial cell adhesion molecule. The past decade of research has revealed key roles for VE-cadherin in vascular permeability and in the morphogenic events associated with vascular remodeling. The details of how VE-cadherin functions in adhesion became apparent with structure-function analysis of the cadherin extracellular domain and with the identification of the catenins, a series of cytoplasmic proteins that bind to the cadherin tail and mediate interactions between cadherins and the cytoskeleton. Whereas early work focused on the armadillo family proteins -catenin and plakoglobin, more recent investigations have identified p120-catenin (p120^ctn) and a related group of armadillo family members as key binding partners for the cadherin tail. Furthermore, a series of new studies indicate a key role for p120^ctn in regulating cadherin membrane trafficking in mammalian cells. These recent studies place p120^ctn at the hub of a cadherin-catenin regulatory mechanism that controls cadherin plasma membrane levels in cells of both epithelial and endothelial origin. endothelial cell; cytoskeleton; -catenin; p120^ctn; cell adhesion; vascular endothelial cadherin     

Food hoarding is increased by food deprivation and decreased by leptin treatment in Syrian hamsters

Compensatory increases in food intake are commonly observed after a period of food deprivation in many species, including laboratory rats and mice. Thus it is interesting that Syrian hamsters fail to increase food intake after a period of food deprivation, despite a fall in plasma leptin concentrations similar to those seen in food-deprived rats and mice. In previous laboratory studies, food-deprived Syrian hamsters increased the amount of food hoarded. We hypothesized that leptin treatment during food deprivation would attenuate food-deprivation-induced increases in hoarding. Baseline levels of hoarding were bimodally distributed, with no hamsters showing intermediate levels of hoarding. Both high (HH) and low hoarding (LH) hamsters were included in each experimental group. Fifty-six male hamsters were either food deprived or given ad libitum access to food for 48 h. One-half of each group received intraperitoneal injections of leptin (4 mg/kg) or vehicle every 12 h during the food-deprivation period. Within the HH group, the hoarding score increased significantly in food-deprived but not fed hamsters (P < 0.05). Leptin treatment significantly decreased hoarding in the food-deprived HH hamsters (P < 0.05). The LH hamsters did not increase hoarding regardless of whether they were food deprived or had ad libitum access to food. These results are consistent with the idea that HH hamsters respond to energetic challenges at least in part by changing their hoarding behavior and that leptin might be one factor that mediates this response.     

Dispersal of viviparity across contact zones in Iberian populations of fire salamanders (Salamandra) inferred from discordance of genetic and morphological traits

Abstract.— We used partial sequences of the cytochrome b mitochondrial DNA (mtDNA) gene, obtained from 76 individuals representing 45 populations of Iberian Salamandra salamandra plus 15 sequences of additional species of Salamandra and related genera, to investigate contact zones. These zones, identified by earlier allozymic and morphological analyses, are between populations of viviparous (S. s. bernardezi and S. s. fastuosa ) and ovoviviparous (S. s. gallaica and S. s. terrestris ) salamanders. The distribution of mtDNA and nuclear markers is mostly concordant at one contact zone (between S. s. gallaica and S. s. bernardezi ), but at another (between S. s. fastuosa and S. s. terrestris ) the markers are offset by about 250 km. The observed geographic variation fits a model of mtDNA capture. Among the potential mechanisms responsible for such discordance we favor a combination of range shifts due to climatic fluctuations and biased genetic admixture across moving contact zones. We apply our findings to the issue of possible homoplasy in the evolution of viviparity and conclude that viviparity likely arose only once within S. salamandra .