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.     

Ant-Repelling Pollinators of the Myrmecophytic <Emphasis Type="Italic">Macaranga winkleri</Emphasis> (Euphorbiaceae)

Many plants have mutualistic relationships with ants, whereby plants provide food and/or nesting sites for the symbiotic ants, and in turn the ants protect the host plants by excluding herbivores. While the ants are useful as guards, they may negatively affect host reproduction by excluding pollinators. Here we studied this potential conflict in the myrmecophytic Macaranga winkleri pollinated by the thrips Dolichothrips fialae. Behavioural responses of ant guards to pollinator thrips and their chemicals, and related chemical analyses, provide evidence that thrips deter ant-guards by secreting droplets containing ant-repelling n-decanoic acid from their anuses. This is the first report of insect pollinators repelling their host’s symbiotic guard ants to perform pollination. This is a novel strategy by which a plant host avoids interference with pollination by ant-guards in an ant–plant mutualism. The acquisition of a pollination system that is resistant to ant attacks may have facilitated the evolution of myrmecophytes in the genus Macaranga.     

Fire Elicits an Adaptive Reproductive Strategy Shift from Host Plant Quantity to Quality in a Capital Breeding Species

Capital breeding species, those that do not acquire resources over their reproductive period, are hypothesized to have more flexible reproductive strategies than income breeding species, enabling the former to better cope with environmental changes. Yet, empirical study of this life history attribute in a changing environment is rare. Hemileuca eglanterina (Saturniidae), a strict capital breeding, day-flying moth, should employ a different reproductive strategy to exploit temporary increases in host plant nutrient quality following fire. In wetlands, where one half was burned and the other left unburned, the number of eggs/clutch was positively correlated with host plant abundance in the absence of fire, suggesting that H. eglanterina uses a resource abundance matching reproductive strategy by default. However, following fire, H. eglanterina laid greater numbers of eggs/clutch and did not adjust clutch size to host plant abundance, appearing to shift to a host plant quality based reproductive strategy. Coinciding with the fire-induced shift in reproductive strategy, host plants from burned habitat contained a greater proportion of N-containing compounds in their foliage than plants from unburned habitat, and larvae fed only leaves from the burned habitat had significantly greater survival than siblings fed unburned foliage. These results suggest the shift in reproductive strategy by H. eglanterina following fire was adaptive and that capital breeding species can cope with sudden environmental changes via alternative reproductive strategies.     

Drought‐induced xylem pit membrane damage in aspen and balsam poplar

Drought induces an increase in a tree's vulnerability to a loss of its hydraulic conductivity in many tree species, including two common in western Canada, trembling aspen (Populus tremuloides) and balsam poplar (Populus balsamifera). Termed ‘cavitation fatigue’ or ‘air‐seeding fatigue’, the mechanism of this phenomenon is not well understood, but hypothesized to be a result of damage to xylem pit membranes. To examine the validity of this hypothesis, the effect of drought on the porosity of pit membranes in aspen and balsam poplar was investigated. Controlled drought and bench dehydration treatments were used to induce fatigue and scanning electron microscopy (SEM) was used to image pit membranes for relative porosity evaluations from air‐dried samples after ethanol dehydration. A significant increase in the diameter of the largest pore was found in the drought and dehydration treatments of aspen, while an increase in the percentage of porous pit membranes was found in the dehydration treatments of both species. Additionally, the location of the largest pore per pit membrane was observed to tend toward the periphery of the membrane.     

A tightly regulated expression system for <Emphasis Type="Italic">E. coli</Emphasis> using supersaturated silicic acid

Objective

To develop a new expression system regulated by a ferric uptake regulator in which silicic acid is used as an inducer.

Results

Fur box (binding site for Fur) was substituted for the lac operator to regulate the expression of GFP with the lac promoter. Since the addition of supersaturated silicic acid invokes iron deficiency, supersaturated silicic acids were used as an inducer. GFP expression was dependent on silica concentration, and the expression level without silica was negligible. Basal expression level of this lac-Fur system was extremely low and, hence, lytic enzyme gene E from bacteriophage ?X174 could be retained in this system. Furthermore, the expression of genes of interest was spontaneously initiated as the cell density increased and the costs of the inducer are considerably less than IPTG.

Conclusion

The combination of lac promoter and Ferric uptake repressor allowed the protein expression by supersaturated silicic acid as an inducer in an easy and cost-effective way.

     

4-Vinylphenol production from glucose using recombinant <Emphasis Type="Italic">Streptomyces mobaraense</Emphasis> expressing a tyrosine ammonia lyase from <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis>

Objectives

To find a novel host for the production of 4-vinylphenol (4VPh) by screening Streptomyces species.

Results

The conversion of p-coumaric acid (pHCA) to 4VPh in Streptomyces mobaraense was evaluated using a medium containing pHCA. S. mobaraense readily assimilated pHCA after 24 h of cultivation to produce 4VPh. A phenolic acid decarboxylase, derived from S. mobaraense (SmPAD), was purified following heterologous expression in Escherichia coli. SmPAD was evaluated under various conditions, and the enzyme’s k_cat/K_m value was 0.54 mM ^?1 s^?1. Using intergenetic conjugation, a gene from Rhodobacter sphaeroides encoding a tyrosine ammonia lyase, which catalyzes the conversion of l-tyrosine to p-coumaric acid, was introduced into S. mobaraense. The resulting S. mobaraense transformant produced 273 mg 4VPh l^?1 from 10 g glucose l^?1.

Conclusion

A novel strain suitable for the production of 4VPh and potentially other aromatic compounds was isolated.

     

Mode of action of leucocin K7 produced by <Emphasis Type="Italic">Leuconostoc mesenteroides</Emphasis> K7 against <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> and its potential in milk preservation

Objectives

To investigate the mode of action of leucocin K7 against Listeria monocytogenes and to assess its inhibitory effect on Lis. monocytogenes in refrigerated milk.

Results

A bacteriocin-producing strain, Leuconostoc mesenteroides K7, was isolated from a fermented pickle. The bacteriocin, leucocin K7, exhibited antagonistic activity against Lis. monocytogenes with an MIC of 28 µg/ml. It was sensitive to proteaseS and displayed good thermal stability and broad active pH range. Leucocin K7 had no effect on the efflux of ATP from Lis. monocytogenes but triggered the efflux of K⁺ and the intracellular hydrolysis of ATP. It also dissipated the transmembrane electrical potential completely and transmembrane pH gradient partially. It 80 AU/ml inhibited the growth of Lis. monocytogenes by 2.3–3.9 log units in milk; when combined with glycine (5 mg/ml), it completely eliminated viable Lis. monocytogenes over 7 days

Conclusion

Leucocin K7 shows different mode of action from nisin and may have potential application in milk preservation.

     

Contribution of direct electron transfer mechanisms to overall electron transfer in microbial fuel cells utilising <Emphasis Type="Italic">Shewanella oneidensis</Emphasis> as biocatalyst

Objectives

To investigate the contribution of direct electron transfer mechanisms to electricity production in microbial fuel cells by physically retaining Shewanella oneidensis cells close to or away from the anode electrode.

Results

A maximum power output of 114 ± 6 mWm^?2 was obtained when cells were retained close to the anode using a dialysis membrane. This was 3.5 times more than when the cells were separated away from the anode. Without the membrane the maximum power output was 129 ± 6 mWm^?2. The direct mechanisms of electron transfer contributed significantly to overall electron transfer from S. oneidensis to electrodes, a result that was corroborated by another experiment where S. oneidensis cells were entrapped in alginate gels.

Conclusion

S. oneidensis transfers electrons primarily by direct electron transfer as opposed to mediated electron transfer.

     

Conversion of glycerol to 1,3-dihydroxyacetone by glycerol dehydrogenase co-expressed with an NADH oxidase for cofactor regeneration

Objectives

To investigate the efficiency of a cofactor regeneration enzyme co-expressed with a glycerol dehydrogenase for the production of 1,3-dihydroxyacetone (DHA).

Results

In vitro biotransformation of glycerol was achieved with the cell-free extracts containing recombinant GlyDH (glycerol dehydrogenase from Escherichia coli), LDH (lactate dehydrogenase form Bacillus subtilis) or LpNox1 (NADH oxidase from Lactobacillus pentosus), giving DHA at 1.3 g l^?1 (GlyDH/LDH) and 2.2 g l^?1 (GlyDH/LpNox1) with total turnover number (TTN) of NAD⁺ recycling of 6039 and 11100, respectively. Whole cells of E. coli (GlyDH–LpNox1) co-expressing both GlyDH and LpNox1 were constructed and converted 10 g glycerol l^?1 to DHA at 0.2–0.5 g l^?1 in the presence of zero to 2 mM exogenous NAD⁺. The cell free extract of E. coli (GlyDH–LpNox) converted glycerol (2–50 g l^?1) to DHA from 0.5 to 4.0 g l^?1 (8–25 % conversion) without exogenous NAD⁺.

Conclusions

The disadvantage of the expensive consumption of NAD⁺ for the production of DHA has been overcome.

     

Enhancement of production and activity of alkaline zinc metalloprotease from <Emphasis Type="Italic">Salinivibrio proteolyticus</Emphasis> using low intensity direct electric current and zinc nanoparticles

Objectives

To improve the production and activity of an alkaline zinc metalloprotease from Salinivibrio proteolyticus in response to ZnSO₄ (ionic and nanoparticle forms) and low intensity direct electric current (LIDC).

Results

A DC of 50 µA for 10 min increased enzyme production from 35 to 53 U ml^?1 when applied to the stationary phase bacterial cells. Zn²⁺ improved enzyme production better than zinc nanoparticles (52 vs. 43.5 U ml^?1). Zinc nanoparticles (0.5 mM) added to an enzyme reaction mixture containing casein (0.65 %) and 20 mM Tris/HCl buffer (pH 8) improved enzyme activity more than Zn²⁺ (42 vs. 36 U ml^?1).

Conclusion

LIDC exposure (50 µA, 10 min) to the stationary phase bacterial cells increases metalloprotease production in Salinivibrio. A low concentration of zinc nanoparticles (0.5 mM) increases maximum enzyme activity.