Fabrizio Panebianco and Emanuele Serrelli: A Niche Construction Model with Reaction Norms

Overview Niche Construction Plasticity Reactions Norm NCRN: Basic and Population NCRN and Economics Formalization

A Niche Construction Model with ReactionNorms

Fabrizio Panebianco and Emanuele Serrelli

University of Milano - Bicocca

May 6, 2011

CISEPS ANNUAL REPORT

Cultural Evolution Project

Outline

• Niche construction• as a neglected major biological process• as modification and innovation of existing models

• Something missing in NC models: phenotypic plasticity

• NCRN model: a niche construction model with reactionnorm

• Basic and population NCRN Models

• NCRN, cultural evolution, and economical modeling

• First Formalization

Niche Construction: «the selection pressures to which anorganism is exposed exist partly as a consequence of the nicheconstructing activities of past and present generations oforganisms»(Laland et al. (1996), p.294)

That the activities of organisms lead to environmental modifications, on

both on a local and global scale, can hardly be doubted; so much is

obvious to even the most casual observer of the natural world. . . . if

everyone agrees that niche-construction, i.e. organism-induced

modification of the environment, occurs, why does orthodox evolutionary

theory fail to take account of it? (Okasha 2005, p. 1).

• Laland KN, Odling-Smee FJ, Feldman MW (1996). On theevolutionary consequences of niche construction. Journal ofEvolutionary Biology 9: 293-316.

• Laland KN, Odling-Smee FJ, Feldman MW (1999). Theevolutionary consequences of niche construction and its implicationsfor ecology. Proceedings of the National Academy of Sciences USA96:10242- 47.

• NC models are modification of multiplicative model (two loci)

• Locus E (alleles E, e), Locus A (alleles A, a), Resources R

• Frequency in E influences R, R influences A’s contribution to fitness

The analysis confirms that niche construction can be a potent

evolutionary agent by generating selection that leads to the fixation of

otherwise deleterious alleles, supporting stable polymorphisms where none

are expected, eliminating what would otherwise be stable polymorphisms,

and generating unusual evolutionary dynamics. Even small amounts of

niche construction, or niche construction that only weakly affects

resource dynamics, can significantly alter both ecological and

evolutionary patterns. (Laland et al. 1999, p. 10242).

Phenotypic Plasticity

• The term phenotypic plasticity describes the property of agenotype to generate phenotypic variation in response to agiven range of environmental conditions.

• Various measures of plasticity exist and can be united withinthe framework of a polynomial function: the norm ofreaction.

• NC models do not allow factors other than genotypes toparticipate in the production of phenotypes.

• Niche construction advocates always consider the classic ideaof an influence on the population’s gene pool (frequency ofalleles that correspond to determinate phenotypic traits orbehaviours).

NC vc NCRN• Reaction Norm (G)≡ The rule imposed by the genotype,

that determines the phenotype expressed in the population asa function of the environment and other factors, can beintended in different ways: it can go from simple mechanicalreaction rules up to complex algorithms considering aspects ofthe environment, or from population either seen in the presentor preceding generation.

• Differences: Phenotypic outcome affects the environment.Current phenotype undergoes selection, which affects onpopulation size. Future phenotypic outcomes depend on theenvironment by reaction norm, which takes into account atleast the resource available in the environment and populationsize.

• Common Feature: Aggregate Effect. NC models areconstitutively concerned with selection pressures, and whileselection pressures act on individuals, sorting them throughgenerations, they make sense only at population level.

Basic and Population NCRN Models

• The work with a basic NCRN model would be focused on theexploration of the dynamics resulting from different kinds ofreaction norms with no variation of G across the population.

• Although basic NCRN studies seem insensitive to theparticular explanation for the ubiquity of G, such studiesmight yield some results about the kinds of evolutionarynorms that exhibit evolutionary stability. NCRN studies canbe thought as preparatory to population models with multiplereaction norms (e.g. G1 and G2).

NCRN, cultural evolution, and economical modeling

• Reaction norm and Rational Choice are both Rules thatshare the picking of an element from a set of possibilitiesaccording to external constraints.

• This picked up element is respectively the phenotype and thechosen action.

• NCRN models introduce NC in a way that closes a gapbetween biological and economic modeling.

• NC models traits are cultural and genetic, and both kinds aremodeled by means of loci and alleles, where alleles correspondto phenotypic alternatives that are fixed and there is no roomfor plasticity.

First Formalization

• Resources Rt ,

• Population mass mt ,

• Genotype G , (reaction norm)

• Phenotype At ,

At : (Rt , mt , G ) 7→ [0, Rt ]Bt : (mt , At) 7→ <+

Ct : (Rt , At) 7→ <+

Ft : (Bt − Ct) 7→ <+

Rt : (Rt−1, At−1) 7→ <+

mt : (mt−1, Ft−1) 7→ <+

Fabrizio Panebianco and Emanuele Serrelli: A Niche Construction Model with Reaction Norms

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