Haystack Model Research Articles

The Evolution of Preferences in a Haystack Model with Finite Populations

The Evolution of Preferences in a Haystack Model with Finite Populations

Formalizing Tag-Based Metadata With the Brick Ontology

Current efforts establishing semantic metadata standards for the built environment span academia, industry and standards bodies. For these standards to be effective, they must be clearly defined and easily extensible, encourage consistency in their usage, and integrate cleanly with existing industrial standards, such as BACnet. There is a natural tension between informal tag-based systems that rely upon idiom and convention for meaning, and formal ontologies amenable to automated tooling. We present a qualitative analysis of Project Haystack, a popular tagging system for building metadata, and identify a family of inherent interpretability and consistency issues in the tagging model that stem from its lack of a formal definition. To address these issues, we present the design and implementation of the Brick+ ontology, a drop-in replacement for Brick with clear formal semantics that enables the inference of a valid Brick model from an informal Haystack model, and demonstrate this inference across five Haystack models.

Effect of inbreeding on sex ratio in the apple snail Pomacea canaliculata

ABSTRACT Female-biased sex ratios are adaptive in populations founded by a small number of individuals and are mainly due to local mate competition (the haystack model). However, little empirical support for this theory exists and, with the exception of terrestrial vertebrates and arthropods, very little is known about the possible mechanisms for biased sex ratios under this model in animals. The highly invasive freshwater snail Pomacea canaliculata usually reproduces in small temporary water bodies and is characterized by genetically based variable brood sex ratios. We conducted a mating experiment to test the prediction that sex ratio is biased towards females in inbred populations. Inbred lines (pairing of a male and a female from the same brood) and outcrossed lines (pairing of a male and a female from different broods) were reared in the lab, and sex ratios were compared between these two breeding types for three generations (the F1 generation was produced by outcrossing only). As predicted, the sex ratios of the inbred lines showed greater bias towards females (average proportion of males per generation was 0.38–0.40) than the outcrossed lines (0.45–0.55). The female-biased sex ratios of P. canaliculata may facilitate rapid population growth and may thus enhance the invasive capacity of this snail. Female-biased sex ratios under metapopulation structures, as predicted by the haystack models, may be more common than previously considered.

Gene-drive-mediated extinction is thwarted by population structure and evolution of sib mating.

Background and objectivesGenetic engineering combined with CRISPR technology has developed to the point that gene drives can, in theory, be engineered to cause extinction in countless species. Success of extinction programs now rests on the possibility of resistance evolution, which is largely unknown. Depending on the gene-drive technology, resistance may take many forms, from mutations in the nuclease target sequence (e.g. for CRISPR) to specific types of non-random population structures that limit the drive (that may block potentially any gene-drive technology).MethodologyWe develop mathematical models of various deviations from random mating to consider escapes from extinction-causing gene drives. A main emphasis here is sib mating in the face of recessive-lethal and Y-chromosome drives.ResultsSib mating easily evolves in response to both kinds of gene drives and maintains mean fitness above 0, with equilibrium fitness depending on the level of inbreeding depression. Environmental determination of sib mating (as might stem from population density crashes) can also maintain mean fitness above 0. A version of Maynard Smith’s haystack model shows that pre-existing population structure can enable drive-free subpopulations to be maintained against gene drives.Conclusions and implicationsTranslation of mean fitness into population size depends on ecological details, so understanding mean fitness evolution and dynamics is merely the first step in predicting extinction. Nonetheless, these results point to possible escapes from gene-drive-mediated extinctions that lie beyond the control of genome engineering.Lay summaryRecent gene drive technologies promise to suppress and even eradicate pests and disease vectors. Simple models of gene-drive evolution in structured populations show that extinction-causing gene drives can be thwarted both through the evolution of sib mating as well as from purely demographic processes that cluster drive-free individuals.

Carrot or Stick? The Evolution of Reciprocal Preferences in a Haystack Model

We study the evolution of both characteristics of reciprocity: the willingness to reward and the willingness to punish. First, both preferences for rewarding and preferences for punishing can survive provided that individuals interact within separate groups. Second, rewarders survive only in coexistence with self-interested preferences, but punishers either vanish or dominate the population entirely. Third, the evolution of preferences for rewarding and the evolution of preferences for punishing influence each other decisively. Rewarders can invade a population of self-interested players. The existence of rewarders enhances the evolutionary success of punishers, who then crowd out all other preferences. (JEL C71, C72, C73, D64, K42)

Efficient social contracts and group selection

We consider the Stag Hunt in terms of Maynard Smith’s famous Haystack model. In the Stag Hunt, contrary to the Prisoner’s Dilemma, there is a cooperative equilibrium besides the equilibrium where every player defects. This implies that in the Haystack model, where a population is partitioned into groups, groups playing the cooperative equilibrium tend to grow faster than those at the non-cooperative equilibrium. We determine under what conditions this leads to the takeover of the population by cooperators. Moreover, we compare our results to the case of an unstructured population and to the case of the Prisoner’s Dilemma. Finally, we point to some implications our findings have for three distinct ideas: Ken Binmore’s group selection argument in favor of the evolution of efficient social contracts, Sewall Wright’s Shifting Balance theory, and the equilibrium selection problem of game theory.

Identifying the Explanatory Weakness of Strong Altruism: The Needle in the ‘Haystack Model’

Evolutionary theorists have encountered difficulty in explaining how altruistic behavior can evolve. I argue that these theorists have made this task more difficult than it needs to be by focusing their efforts on explaining how nature could select for a strong type of altruism that has powerful selection forces working against it. I argue that switching the focus to a weaker type of altruism renders the project of explaining how altruism can evolve significantly less difficult. I offer a model of weak altruism that can avoid many of the difficulties that evolutionary accounts of altruism have traditionally faced.

Emergency Decisions, Cultural-Selection Mechanics, and Group Selection [and Comments and Reply

Emergency behaviors of nonliterate groups are taken as a useful starting point for demonstrating that decisions can be integrated more directly into cultural analysis and that the explanatory pay-offs can be far-reaching. The methodological feasibility of studying group decisions directly is explored through three exceptional tribal ethnographies with a focus on emergency adaptive problem solving and its implications for both cultural- and gene-selection theory. Urgently discussed decision alternatives become apprehensible to fieldworkers through open group debate, while the reproductive effects of decisions are readily assessed whenever groups act in unison. Implications for the development of a more effective theory of cultural microselection and a truly processual definition of culture in its guided phase are suggested. With respect to long-term genetic evolution, the implications of emergency decision making are extended to foragers, exploring special possibilities that enable genetic group selection to become robust when groups are egalitarian and engage in consensual problem solving. Prehistorically, the verdict is that group-selection effects were amplified at the same time that individual effects were suppressed. On this basis it is hypothesized that the genetic evolution of human cooperative and altruistic tendencies can be explained in part by selection at the level of groups rather than inclusive fitness

Hierarchical Levels of Spatial Structure and Their Consequences for the Evolution of Sex Allocation in Mites and Other Arthropods

Evolutionarily stable (ES) sex allocation strategies depend critically on how the population is structured with regard to competition for mates and resources. This structure is determined by spatial heterogeneity, dispersal, and colonization behavior. In mating groups lasting one generation where mating precedes female dispersal, female-biased sex ratios will be favored by mate competition, especially when the number of foundresses is small. When groups last several generations before dispersal takes place (haystack structure), relatedness among population members develops, and this can favor an extra female bias. However, when groups are permanent, with some dispersal in each generation (island structure), relatedness builds up without an effect on sex ratio bias because most competition takes place within groups. Current models of evolution under a haystack structure generally assume unlimited growth for a fixed number of generations (and hence no local density dependence), absence of substructure, and sex ratios that are inflexible over generations. These model limitations warrant scrutiny. Using extended versions of the haystack model, we show that, although local density depen- dence in the haystack population diminishes the sex ratio bias, strongly female-biased sex ratios are still possible if foundress numbers are low. It is also shown that substructure in the haystack by subdivision into one-generation mating groups promotes the female bias. Finally, it is shown that the ES sex ratio can change radically with generations within haystacks. When population growth is density dependent, the sex ratio of the last generation should be more female biased than in the preceding generations. In the case of haystacks subdivided into local mating groups, the sex ratio in the first generation should be less female biased than in the following generations. It is argued that a haystack structure is frequently found among small arthropods with a coloniz- ing lifestyle and that subdivision into one-generation mating groups may occur, for example, among plant-inhabiting mites. To illustrate these points, predatory mites of the family Phytoseii- dae are considered in more detail. Some species are found to exhibit a stronger female bias in their sex ratios than expected from local mating competition alone. This extra bias may well stem from selection in a haystack or subdivided haystack structure. Other phytoseiid species have a lifestyle that leads to more permanent subpopulations that have an island-like structure. As predicted, these species generally show less female-biased sex ratios.

Altruism in Mendelian Populations Derived from Sibling Groups: The Haystack Model Revisited

Altruism in Mendelian Populations Derived from Sibling Groups: The Haystack Model Revisited

Sex ratio under the haystack model: Polymorphism may occur

The haystack model describes a population which is subdivided in local mating groups. Female-biased sex ratios are known to occur under these circumstances. Analysis of this model, assuming that the sex ratio is under control of one gene with two alleles, acting in the mother, shows that a monomorphic evolutionary stable strategy (ESS) does not always exist, and that polymorphism can then be expected. In most cases this is caused by an effect of the gene action of alleles: no sex ratio exists capable of withstanding the invasion of rare “mutant” alleles of all possible degrees of dominance. A genetic analysis leads to different conclusions than a phenotypic analysis.

Sex ratio under the haystack model

This paper investigates the evolution of the sex ratio under an extension of the haystack model of Maynard Smith (1964). At the beginning of each season a stack is colonized by a number of fertilized females, and their offspring breed there for several generations until new haystacks are available for colonization. We intend this as a model for populations which undergo periodical population explosions and crashes. With mating before dispersal, the number of generations in the stack has little effect on the equilibrium sex ratio, but it has a marked effect with mating after dispersal. This model is then used to investigate the evolutionary stability of the mechanism of sex determination found in the wood lemming which leads to a population sex ratio of three females to one male.