Social evolution of toxic metal bioremediation in Pseudomonas aeruginosa

Bacteria are often iron-limited, and hence produce extracellular iron-scavenging siderophores. A crucial feature of siderophore production is that it can be an altruistic behaviour (individually costly but benefitting neighbouring cells), thus siderophore producers can be invaded by non-producing social ‘cheats’. Recent studies have shown that siderophores can also bind other heavy metals (such as Cu and Zn), but in this case siderophore chelation actually reduces metal uptake by bacteria. These complexes reduce heavy metal toxicity, hence siderophore production may contribute to toxic metal bioremediation. Here, we show that siderophore production in the context of bioremediation is also an altruistic trait and can be exploited by cheating phenotypes in the opportunistic pathogen Pseudomonas aeruginosa. Specifically, we show that in toxic copper concentrations (i) siderophore non-producers evolve de novo and reach high frequencies, and (ii) producing strains are fitter than isogenic non-producing strains in monoculture, and vice versa in co-culture. Moreover, we show that the evolutionary effect copper has on reducing siderophore production is greater than the reduction observed under iron-limited conditions. We discuss the relevance of these results to the evolution of siderophore production in natural communities and heavy metal bioremediation

Comparative evidence for strong phylogenetic inertia in precloacal signalling glands in a species-rich lizard clade

Background: The precloacal glands of lizards are responsible for the secretion of pheromones involved in chemical-based interactions, such as male territoriality and female mate choice. However, in spite of the significance of these structures for social and sexual communication, their evolution remains poorly studied. Previous research has suggested that the number of precloacal glands may reflect adaptive variation because a higher number of these organs increases the potential rate of secretion, compensating for the impact of extreme environmental conditions on the optimal quantity of secretions smeared on the substrate. Therefore, the number of precloacal glands may be expected to exhibit convergent evolution in response to similar environments. Nevertheless, the only available evidence testing this prediction ignored potential effects of shared phylogenetic history on the evolution of this trait. Hypotheses: (1) Lizard precloacal gland number evolves adaptively in response to variation in environmental conditions, experiencing convergent patterns independent of phylogenetic relationships. (2) Species with a wider geographical distribution exhibit higher variance in the number of precloacal glands as a response to variation along environmental gradients. Organisms: Liolaemus lizards, one of the largest and most ecologically diverse vertebrate genera. Methods: Phylogenetic comparative methods. Regression analyses based on phylogenetic independent contrasts, and on raw data at intra-clade level. Historical estimates based on ancestral state reconstructions from explicit phylogenetic hypotheses. Results: Precloacal glands are constrained by phylogenetic relationships. In contrast to previous work, we found no evidence for independent convergent events along the phylogenetic history of this lineage. Environmental conditions failed to predict the number of glands in species of the Liolaemus genus in both current and reconstructed ancestral states. Conclusions: Our phylogenetically controlled comparative analysis fails to support the hypothesis that the number of precloacal emitter glands in lizards is the product of adaptive evolution. © 2008 Tom Tregenza.</p

popdemo: an R package for population demography using projection matrix analysis

Effective population management requires accurate predictions of future population dynamics and how they may be manipulated to achieve management goals.2. The R package popdemo provides software tools for novel analytical methods that aim to enhance the predictive power of basic population projection matrix models. These include indices of transient population dynamics and transfer function analyses.3. We use a case study to demonstrate the use and importance of these methods for population management and briefly discuss their potential application outside population ecology.</p

The evolution of body size under environmental gradients in ectotherms: why should Bergmann's rule apply to lizards?

Background. The impact of environmental gradients on the evolution of life history traits is a central issue in macroecology and evolutionary biology. A number of hypotheses have been formulated to explain factors shaping patterns of variation in animal mass. One such example is Bergmann's rule, which predicts that body size will be positively correlated with latitude and elevation, and hence, with decreasing environmental temperatures. A generally accepted explanation for this phenotypic response is that as body mass increases, body surface area gets proportionally smaller, which contributes to reduced rates of heat-loss. Phylogenetic and non-phylogenetic evidence reveals that endotherms follow Bergmann's rule. In contrast, while previous non-phylogenetic studies supported this prediction in up to 75 of ectotherms, recent phylogenetic comparative analyses suggest that its validity for these organisms is controversial and less understood. Moreover, little attention has been paid to why some ectotherms conform to this rule, while others do not. Here, we investigate Bergmann's rule in the six main clades forming the Liolaemus genus, one of the largest and most environmentally diverse genera of terrestrial vertebrates. A recent study conducted on some species belonging to four of these six clades concluded that Liolaemus species follow Bergmann's rule, representing the only known phylogenetic support for this model in lizards. However, a later reassessment of this evidence, performed on one of the four analysed clades, produced contrasting conclusions. Results. Our results fail to support Bergmann's rule in Liolaemus lizards. Non-phylogenetic and phylogenetic analyses showed that none of the studied clades experience increasing body size with increasing latitude and elevation. Conclusion. Most physiological and behavioural processes in ectotherms depend directly upon their body temperature. In cold environments, adaptations to gain heat rapidly are under strong positive selection to allow optimal feeding, mating and predator avoidance. Therefore, evolution of larger body size in colder environments appears to be a disadvantageous thermoregulatory strategy. The repeated lack of support for Bergmann's rule in ectotherms suggests that this model should be recognized as a valid rule exclusively for endotherms. © 2008 Pincheira-Donoso et al; licensee BioMed Central Ltd.</p

The evolution of body size under environmental gradients in ectotherms: why should Bergmann's rule apply to lizards?

Background. The impact of environmental gradients on the evolution of life history traits is a central issue in macroecology and evolutionary biology. A number of hypotheses have been formulated to explain factors shaping patterns of variation in animal mass. One such example is Bergmann's rule, which predicts that body size will be positively correlated with latitude and elevation, and hence, with decreasing environmental temperatures. A generally accepted explanation for this phenotypic response is that as body mass increases, body surface area gets proportionally smaller, which contributes to reduced rates of heat-loss. Phylogenetic and non-phylogenetic evidence reveals that endotherms follow Bergmann's rule. In contrast, while previous non-phylogenetic studies supported this prediction in up to 75 of ectotherms, recent phylogenetic comparative analyses suggest that its validity for these organisms is controversial and less understood. Moreover, little attention has been paid to why some ectotherms conform to this rule, while others do not. Here, we investigate Bergmann's rule in the six main clades forming the Liolaemus genus, one of the largest and most environmentally diverse genera of terrestrial vertebrates. A recent study conducted on some species belonging to four of these six clades concluded that Liolaemus species follow Bergmann's rule, representing the only known phylogenetic support for this model in lizards. However, a later reassessment of this evidence, performed on one of the four analysed clades, produced contrasting conclusions. Results. Our results fail to support Bergmann's rule in Liolaemus lizards. Non-phylogenetic and phylogenetic analyses showed that none of the studied clades experience increasing body size with increasing latitude and elevation. Conclusion. Most physiological and behavioural processes in ectotherms depend directly upon their body temperature. In cold environments, adaptations to gain heat rapidly are under strong positive selection to allow optimal feeding, mating and predator avoidance. Therefore, evolution of larger body size in colder environments appears to be a disadvantageous thermoregulatory strategy. The repeated lack of support for Bergmann's rule in ectotherms suggests that this model should be recognized as a valid rule exclusively for endotherms. © 2008 Pincheira-Donoso et al; licensee BioMed Central Ltd.</p

Comparative evidence for strong phylogenetic inertia in precloacal signalling glands in a species-rich lizard clade

Background: The precloacal glands of lizards are responsible for the secretion of pheromones involved in chemical-based interactions, such as male territoriality and female mate choice. However, in spite of the significance of these structures for social and sexual communication, their evolution remains poorly studied. Previous research has suggested that the number of precloacal glands may reflect adaptive variation because a higher number of these organs increases the potential rate of secretion, compensating for the impact of extreme environmental conditions on the optimal quantity of secretions smeared on the substrate. Therefore, the number of precloacal glands may be expected to exhibit convergent evolution in response to similar environments. Nevertheless, the only available evidence testing this prediction ignored potential effects of shared phylogenetic history on the evolution of this trait. Hypotheses: (1) Lizard precloacal gland number evolves adaptively in response to variation in environmental conditions, experiencing convergent patterns independent of phylogenetic relationships. (2) Species with a wider geographical distribution exhibit higher variance in the number of precloacal glands as a response to variation along environmental gradients. Organisms: Liolaemus lizards, one of the largest and most ecologically diverse vertebrate genera. Methods: Phylogenetic comparative methods. Regression analyses based on phylogenetic independent contrasts, and on raw data at intra-clade level. Historical estimates based on ancestral state reconstructions from explicit phylogenetic hypotheses. Results: Precloacal glands are constrained by phylogenetic relationships. In contrast to previous work, we found no evidence for independent convergent events along the phylogenetic history of this lineage. Environmental conditions failed to predict the number of glands in species of the Liolaemus genus in both current and reconstructed ancestral states. Conclusions: Our phylogenetically controlled comparative analysis fails to support the hypothesis that the number of precloacal emitter glands in lizards is the product of adaptive evolution. © 2008 Tom Tregenza.</p

On reducibility and ergodicity of population projection matrix models

1. Population projection matrices (PPMs) are probably the most commonly used empirical population models. To be useful for predictive or prospective analyses, PPM models should generally be irreducible (the associated life cycle graph contains the necessary transition rates to facilitate pathways from all stages to all other stages) and therefore ergodic (whatever initial stage structure is used in the population projection, it will always exhibit the same stable asymptotic growth rate).2. Evaluation of 652 PPM models for 171 species from the literature suggests that 24·7% of PPM models are reducible (parameterized transition rates do not facilitate pathways from all stages to all other stages). Reducible models are sometimes ergodic but may be non?ergodic (the model exhibits two or more stable asymptotic states with different asymptotic stable growth rates, which depend on the initial stage structure used in the population projection). In our sample of published PPMs, 15·6% are non?ergodic.3. This presents a problem: reducible–ergodic models often defy biological rationale in their description of the life cycle but may or may not prove problematic for analysis as they often behave similarly to irreducible models. Reducible–non?ergodic models will usually defy biological rationale in their description of the both the life cycle and population dynamics, hence contravening most analytical methods.4. We provide simple methods to evaluate reducibility and ergodicity of PPM models, present illustrative examples to elucidate the relationship between reducibility and ergodicity and provide empirical examples to evaluate the implications of these properties in PPM models.5. As a prevailing tool for population ecologists, PPM models need to be as predictive as possible. However, there is a large incidence of reducibility in published PPMs, with significant implications for the predictive power of such models in many cases. We suggest that as a general rule, reducibility of PPM models should be avoided. However, we provide a guide to the pertinent analysis of reducible matrix models, largely based upon whether they are ergodic or not.</p

Robust set-point regulation for ecological models with multiple management goals

Population managers will often have to deal with problems of meeting multiple goals, for example, keeping at specific levels both the total population and population abundances in given stage-classes of a stratified population. In control engineering, such set-point regulation problems are commonly tackled using multi-input, multi-output proportional and integral (PI) feedback controllers. Building on our recent results for population management with single goals, we develop a PI control approach in a context of multi-objective population management. We show that robust set-point regulation is achieved by using a modified PI controller with saturation and anti-windup elements, both described in the paper, and illustrate the theory with examples. Our results apply more generally to linear control systems with positive state variables, including a class of infinite-dimensional systems, and thus have broader appeal