Stress-induced recombination and the mechanism of evolvability

The concept of evolvability is controversial. To some, it is simply a measure of the standing genetic variation in a population and can be captured by the narrow-sense heritability (h²). To others, evolvability refers to the capacity to generate heritable phenotypic variation. Many scientists, including Darwin, have argued that environmental variation can generate heritable phenotypic variation. However, their theories have been difficult to test. Recent theory on the evolution of sex and recombination provides a much simpler framework for evaluating evolvability. It shows that modifiers of recombination can increase in prevalence whenever low fitness individuals produce proportionately more recombinant offspring. Because recombination can generate heritable variation, stress-induced recombination might be a plausible mechanism of evolvability if populations exhibit a negative relationship between fitness and recombination. Here we use the fruit fly, Drosophila melanogaster, to test for this relationship. We exposed females to mating stress, heat shock or cold shock and measured the temporary changes that occurred in reproductive output and the rate of chromosomal recombination. We found that each stress treatment increased the rate of recombination and that heat shock, but not mating stress or cold shock, generated a negative relationship between reproductive output and recombination rate. The negative relationship was absent in the low-stress controls, which suggests that fitness and recombination may only be associated under stressful conditions. Taken together, these findings suggest that stress-induced recombination might be a mechanism of evolvability.     

Using information theory as a substitute for stepwise regression in ecology and behavior

In ecological and behavioral research, drawing reliable conclusions from statistical models with multiple predictors is usually difficult if all predictors are simultaneously in the model. The traditional way of handling multiple predictors has been the use of threshold-based removal-introduction algorithms, that is, stepwise regression, which currently receives considerable criticism. A more recent and increasingly propagated modelling method for multiple predictors is the information theoretic (IT) approach that quantifies the relative suitability of multiple, potentially non-nested models based on a balance of model fit and the accuracy of estimates. Here, we examine three shortcomings of stepwise regression, subjective critical values, model uncertainty, and parameter estimation bias, which have been suggested to be avoided by applying information theory. We argue that, in certain circumstances, the IT approach may be sensitive to these issues as well. We point to areas where further testing and development could enhance the performance of IT methods and ultimately lead to robust inferences in behavioral ecology.     

Biliverdin-based egg coloration is enhanced by carotenoid supplementation

Avian eggshell color is remarkably variable among and within species and its possible function has long been controversial. Female birds use biliverdin pigment to color their eggs blue and green. Although evidence is accumulating that blue-green eggshell coloration is costly to produce, the exact mechanisms underlying its expression are little studied. Biliverdin pigment is involved in important maintenance functions such as immune and antioxidant defenses and shows similar properties to carotenoid pigments. Carotenoids play a role as immunoenhancers and have the potential to ameliorate the impact of oxidative processes, although their antioxidant function could be minor for some bird species. Important life-history components can be limited by carotenoid availability, including sexual displays and fecundity. Here we explored if biliverdin-based eggshell pigmentation was affected by carotenoid availability in a seabird, by performing a carotenoid supplementation experiment in female blue-footed boobies (Sula nebouxii) after laying their first egg. In this species, blue eggshell color is associated with incubation patterns, and carotenoid availability affects the crucial trade-off between female foot ornamentation and fecundity. We found that under natural conditions, there was a decline in eggshell color with laying order, suggesting pigment limitation for females. However, carotenoid-supplemented females had enhanced second egg coloration compared to controls, and the color increase was independent of their previous pigment allocation to the first egg. Our results suggest that biliverdin-based eggshell coloration is costly to produce and can be alleviated by current carotenoid availability.     

Darwin’s “tug-of-war” vs. starlings’ “horse-racing”: how adaptations for sequential encounters drive simultaneous choice

Charles Darwin aided his private decision making by an explicit deliberation, famously deciding whether or not to marry by creating a list of points in a table with two columns: “Marry” and “Not Marry”. One hundred seventy-two years after Darwin’s wedding, we reconsider whether this process of choice, under which individuals assign values to their options and compare their relative merits at the time of choosing (the tug-of-war model), applies to our experimental animal, the European Starling, Sturnus vulgaris. We contrast this with the sequential choice model that postulates that decision-makers make no comparison between options at the time of choice. According to the latter, behaviour in simultaneous choices reflects adaptations to contexts with sequential encounters, in which the choice is whether to take an opportunity or let it pass. We postulate that, in sequential encounters, the decision-maker assigns (by learning) a subjective value to each option, reflecting its payoff relative to background opportunities. This value is expressed as latency and/or probability to accept each opportunity as opposed to keep searching. In simultaneous encounters, choice occurs through each option being processed independently, by a race between the mechanisms that generate option-specific latencies. We describe these alternative models and review data supporting the predictions of the sequential choice model.     

Sex-specific fitness consequences of dispersal in Siberian jays

In most birds, natal dispersal is female-biased, but the selective pressures leading to this pattern have rarely been explored with comprehensive data on lifetime reproductive success. In territorial birds, the benefit of philopatry should be higher for males than for females when males establish territories for which knowledge about the local environment is important. As females may use male characteristics for mate choice, and hence indirectly for territory choice, the benefit from the direct knowledge of the local environment may be lower for females than males. We tested this hypothesis using data from a long-term study of group living corvids, the Siberian jays (Perisoreus infaustus). In this species, the socially dominant offspring delay dispersal while the sub-dominant offspring leave the family group directly after reaching independence. Our results show that natal dispersal distance (a proxy for local knowledge) was related to sex and dispersal timing (a proxy for “quality”): Females and early dispersers traveled further on average than males and delayed dispersers. Furthermore, dispersal distance and timing were negatively related to the number of recruits produced over an individual’s lifetime in males, but not in females. Hence, the results support the hypothesis that the female-biased natal dispersal found in this and other bird species may come about through higher lifetime reproductive success of philopatric males than females.     

Movement and memory: different cognitive strategies are used to search for resources with different natural distributions

Recent attempts to integrate function and mechanism have resulted in an appreciation of the relevance of forager psychology to understanding the functional aspects of foraging behaviour. Conversely, an acknowledgement of the functional diversity of learning mechanisms has led to greater understanding of the adaptive nature of cognition. In this paper, we present data from three experiments suggesting that noisy miner birds use different cognitive strategies when searching for foods with different distributions. When searching for nectar, an immobile, readily depleted resource, birds spontaneously attend to fine-scale spatial information and use a spatial memory-based strategy that is efficient in a novel context and largely resistant to disruptions to movement. When searching for invertebrates, a mobile, clumped and cryptic resource, birds employ a strategy whose efficiency increases with increased task familiarity, is vulnerable to disruptions to their movement and may rely more on memory for movement rules than memory for location information. Previous reports of adapted cognition have reported performance differences between species (for example, better spatial cognitive performance in storing versus non-storing birds). Ours is the first study to demonstrate that differences in cognitive strategy (as opposed to just enhanced performance) occur within a single species in different foraging contexts. As well as providing an example of how specially adapted cognitive mechanisms might work, our data further emphasise the importance of jointly considering functional and mechanistic aspects to fully understand the adaptive complexities of behaviour.     

Natural Food and the Pastoral: A Sentimental Notion?

The term natural is effective in the marketing of a wide variety of foods. This ambiguous term carries important meaning in Western culture. To challenge an uncritical understanding of natural with respect to food and to explore the ambiguity of the term, the development of Western ideas of nature is first discussed. Personification and hypostasization of nature are given special emphasis. Leo Marx’s idea of the pastoral design in literature is then used to explore the meaning of natural as applied to food, emphasizing Marx’s distinction between a sentimental and a complex pastoral. The latter is applied to natural as a means of collapsing a dichotomy of man and nature to the idea of second nature. From this perspective an understanding of the industrialization of the food system and the importance of local and organic food are considered. The extent to which processed foods might properly be considered natural is raised and discussed for several common foods. Although marketing of natural foods might make us think that we consume nature, I suggest that what is consumed is more appropriately second nature. I suggest that in order to maintain a critical perspective about one’s relationship to the natural world, everyone should make an attempt to experience the complex pastoral with respect to at least something that is consumed as food. When nature is understood as second nature in the context of a complex pastoral, the question of whether a food or ingredient is to be considered natural is replaced by deliberative thought based on our best knowledge and judgment, and the result will be less constrained by ideology.     

Food Insecurity in Pakistan: Causes and Policy Response

There is evidence of continued food insecurity and malnutrition in Pakistan despite significant progress made in terms of food production in recent years. According to “Vision 2030” of the Planning Commission of Pakistan, about half of the population in the country suffers from absolute to moderate malnutrition, with the most vulnerable being children, women, and elderly among the lowest income group. The Government of Pakistan has been taking a series of policy initiatives and strategic measures to combat food insecurity issues. These range from increasing production to food imports, implementation of poverty reduction strategies, nutritional improvement programs, as well as provision of social safety nets. The article aims to instill some fresh thinking into the debate regarding the challenges of food security. It underscores the limitations of hitherto policy response, and suggests crucial measures to improve the present grim scenario. Policy makers, planners, practitioners, and academicians in countries with comparable socio-political and economic setup can view this discussion as a case study and may apply the findings in their domain accordingly.     

Local Perception of Environmental Change in a Semi-Arid Area of Northeast Brazil: A New Approach for the Use of Participatory Methods at the Level of Family Units

The diversity of plant resources in the Brazilian semi-arid region is being compromised by practices related to agriculture, pastures, and forest harvesting, especially in areas containing Caatinga vegetation (xeric shrublands and thorn forests). The impact of these practices constitutes a series of complex factors involving local issues, creating a need for further scientific studies on the social-environmental dynamics of natural resource use. Through participatory methods, the present study analyzed people’s representations about local environmental change processes in the Brazilian semi-arid region, taking into consideration local production systems, natural resources, and their importance. Environmental historical graphs were developed with nine local families to analyze landscape changes with regard to cultivated areas and pastures, and their relationship with the availability of native vegetation. Punctuation exercises were performed to observe the importance of each unit that supplied native and cultivated resources. The availability of native resources in the environment is subject to stability, as observed by a majority of the local families. The role of the production units (crops and pastures) was emphasized by most families in the study, especially because of the need for products for subsistence needs and income generation. The current decline of such practices is a consequence of an exodus of field workers and also relates to the conservation of native species that otherwise would have been deforested in favor of agricultural practices.     

Continuing Issues in the Limitations of Pesticide Use in Developing Countries

The rationale for pesticide use in agriculture is that costs associated with pesticide pollution are to be justified by its benefits, but this is not so obvious. Valuing the benefits by simple economic analysis has increased pesticide use in agriculture and consequently produced pesticide-induced “public ills.” This paper attempts to explore the research gaps of the economic and social consequences of pesticide use in developing countries, particularly with an example of Nepal. We argue that although the negative sides of agricultural development, for example- soil, water, and air pollution; pest resistance and resurgence; bioaccumulation, bio-magnification; and loss of biodiversity and ecosystem resilience caused by the use of pesticides in agriculture, are “developmental problems” and are “unintentional,” the magnitude may be increased by undervaluing the problems in the analysis of its economic returns. Despite continuous effort for holistic system analyses for studying complex phenomena like pesticides impacts, the development within the academic science has proceeded in the opposite direction that might have accelerated marginalization of the third world subsistence agricultural communities. We hypothesize that, if these adversities are realized and accounted for, the benefits from the current use of pesticides could be outweighed by the costs of pollution and ill human health. This paper also illustrates different pathways and mechanisms for marginalization. In view of potential and overall negative impacts of pesticide use, we recommend alternative ways of controlling pests such as community integrated pest management (IPM) along with education and training activities. Such measures are likely to reduce the health and environmental costs of pesticide pollution, and also enhance the capabilities of third world agricultural communities in terms of knowledge, decision making, innovation, and policy change.