Sex Ratio Equilibrium Extension 2
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WHAT IS IT
This is the second extension in a series of NetLogo models about population dynamics, population genetics and evolutionary biology developed by Sugat Dabholkar for the Designing & Constructing Models With Multi-Agent Languages, a course offered by Prof. Uri Wilensky at the School of Education and Social Policy in the Northwestern University.
This is an extension of the model Sex Ratio Equilibrium, where the core phenomenon that is modeled is the sex-ratio equilibrium in sexually reproducing organisms. Most of the sexually reproducing organisms have sex-ratio 1:1. Fisher (1930) explained the rational based on natural selection, irrespective of particular mechanism of sex-determination, which is known as Fisher’s first principle (Hamilton, 1967).
This extension allows independent violation of Fisher's assumptions of biparentism as well as Mendelian inheritance. It allows disentangling parental influence on sex-determination and inheritance of sex-determination mechanism. It captures emergence of Non-Fisherian Sex Ratios or extraordinary sex-ratios (Hamilton, 1967) and allows exploration of effects of variation in differences in parental influence on sex-determination and inheritance of sex-determination mechanism.
HOW IT WORKS
This is a population dynamics model, where individuals mate, give birth, die. The demographics changes in the population and sex ratio are captured in the model.
There are two types of individuals in the model: Males (Indicated by green color) Females (Indicated by blue color if not carrying a child and indicated by orange color if carrying a child)
At every time-step the individuals: Age and check if dead - probability of dying increases with age Move Search-a-partner – (Only males). This procedure involves mating, which is dependent on mating-chance. If agents mate, the female carries. (For simplicity, mating chance incorporate conception-chance as well.) Reproduce – (Only for females)
Each male and female carries a trait called male-child-chance. This determines the probability of a child being male. In this extension, weighted influence of parents on the determination of the sex of child can be set using a slider. A child inherits this trait, male-child-chance from its parents with a mutation. The mutation is implemented by choosing the value for the trait from a random-normal distribution with mean equal to weighted average of male-child-chance of the parents. These two weights can be set separately.
HOW TO USE IT
Click the SETUP button to set up the population.
You can use sliders to choose the following parameters when you SETUP.
INI-NUMBER : initial number of individuals in the population. INI-SEX-RATIO : initial female-proportion in the population INI-AVERAGE-MALE-CHILD-CHANCE : initial average male child chance of all the individuals in the population GESTATION-PERIOD : number of 'ticks' a female is going to carry a child MAX-LITTER-SIZE : maximum number of children a female would give birth to after she completes gestation LONGEVITY : maximum 'ticks' an individual lives MATING-CHANCE : probability that a female mates with a male when a male finds a female partner
SEX-DETERMINATION-WEIGHT: This slider determines the influence on sex determination of a child by its parents. 0 means the sex determination of a child is fully influenced by the mother and 1 means the sex determination of a child is fully influenced by the father.
INHERITANCE-WEIGHT: This slider determines influence on inheritance of the child sex-determination trait to the offspring.
Click the GO button to start the simulation.
THINGS TO NOTICE
When you run the model, notice how changes in the SEX-DETERMINATION-WEIGHT and INHERITANCE-WEIGHT sliders result in evolution of different sex-ratios. Changes in INHERITANCE-WEIGHT has significant impact on the stable sex-ratios, whereas changes in SEX-DETERMINATION-WEIGHT has little impact on the stable sex-ratios. Also notice that extreme values if the INHERITANCE-WEIGHT result in unstable population.
THINGS TO TRY
Change the other parameters and see if you can get to a stable extraordinary sex ratio for extreme values of INHERITANCE-WEIGHT.
EXTENDING THE MODEL
This model implements search of partner by a male, see if you can change it and make it a female action. You can add a variety of features related to evolutionary population genetics and sex ratio equilibrium studies, such as different mortality rates for males and females, sexual selection by females.
RELATED MODELS
Red Queen, Fish Tank Genetic Drift, Plant Speciation
CREDITS AND REFERENCES
Hamilton, W. D. (1967). Extraordinary sex ratios. Science, 156(3774), 477-488 Fisher, R. A. (1930). The genetical theory of natural selection: a complete variorum edition. Oxford University Press.
COPYRIGHT AND LICENSE
Copyright 2006 Uri Wilensky.
This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at uri@northwestern.edu.
Comments and Questions
globals [ sex-ratio-list ;; global-variable to track time-series data (for behavior space experiment) ] breed [males male] breed [females female] ;; females-own [ partner carrying? ;; boolean to track if a female is carrying a child after mating male-child-chance ;; this is a probability of giving birth to a male child temp-male-child-chance ;; a variable to store male-chind-chance for a particular father-mother pair child-male-child-chance ;; it is the inherited male-child-chance by a child gestation ;; a veriable to track time of carrying a child till a female reachers gesatation-period age ] males-own [ partner male-child-chance child-male-child-chance age ] ;;set-up pupulation of males and females to setup ca create-males round ( ( 1 - ini-sex-ratio ) * ini-number ) [ setxy random-xcor random-ycor set shape "male" set color green set male-child-chance random-normal ini-average-male-child-chance 0.1 ;; males are assinged initial male-child-chance from a random-normal distribution set age 0 set partner nobody ] create-females round ( ini-sex-ratio * ini-number ) [ setxy random-xcor random-ycor set color blue set shape "female" set carrying? false set partner nobody set male-child-chance random-normal ini-average-male-child-chance 0.1 ;; females are assinged initial male-child-chance from a random-normal distribution ] set sex-ratio-list [] reset-ticks end to go if not any? turtles [stop] ask males [ check-if-dead move search-a-partner ] ask females [ check-if-dead if not carrying? [move] reproduce ] update-sex-ratio-list tick end to move rt random 60 lt random 60 fd 1 end to search-a-partner if count females in-radius 1 with [not carrying?] = 1 and count other males in-radius 1 = 0 [ ;; spatial restriction is used to incorporate density-dependant growth rate set partner one-of females in-radius 1 with [not carrying?] ] if partner = nobody [stop] ifelse [partner] of partner != nobody [ set partner nobody stop ;; just in case two males find the same partner ] [ ifelse random-float 1 < mating-chance [ ask partner [ set partner myself set carrying? true set color orange ;; color oragne indicates carrying female set child-male-child-chance ( ( 1 - inheritance-weight ) * male-child-chance ) + ( inheritance-weight * ( [male-child-chance] of myself ) ) ;; this is inherited male-child-chance by a child (determined by father and mother according to inheritance-weight) set temp-male-child-chance ( ( 1 - sex-determination-weight ) * male-child-chance ) + ( sex-determination-weight * ( [male-child-chance] of myself ) ) ;; sex of a child is determined by male-child-chance (determined by father and mother according to sex-determination-weight) ] set partner nobody ] [ set partner nobody ] ] end to reproduce if carrying? [ ifelse gestation = gestation-period [ ;; genstation-period can be set. When it's over, a female gives birth to a a child, starts afrest and can have a new partner set gestation 0 set carrying? false set color blue set partner nobody repeat random max-litter-size + 1 [ ifelse random-float 1 < temp-male-child-chance [ ;; sex of a child is determined by male-child-chance hatch 1 [ set breed males set shape "male" set color green set male-child-chance random-normal child-male-child-chance 0.1 set age 0 ] ][ hatch 1 [ set male-child-chance random-normal child-male-child-chance 0.1 set age 0 ] ] ] ][ set gestation gestation + 1 ] ] end to check-if-dead ifelse random-float longevity < age [ die ][ set age age + 1 ] end ;; reporting procedures for plotting and for behaviorspace experiments to-report female-percentage ifelse any? turtles [ report ( count females / count turtles ) * 100 ] [ report 0 ] end to-report average-male-child-chance ifelse any? males [ report mean [male-child-chance] of males ] [ report 0 ] end to update-sex-ratio-list if ticks > 10000 [ set sex-ratio-list lput female-percentage sex-ratio-list ] end to-report average-sex-ratio ifelse length sex-ratio-list > 0 [ report precision mean sex-ratio-list 2] [report 0] end to-report sd-sex-ratio ifelse length sex-ratio-list > 0 [ report precision standard-deviation sex-ratio-list 2] [report 0] end
There is only one version of this model, created over 9 years ago by Sugat Dabholkar.
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