b2900 lab 5 sex sel LAB FILE w24 yrt WORD

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Feb 20, 2024

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B2900 L5: S exual selection and tradeoffs Lab File (w inter 2024) 1 Biology 2900 Lab 5: Sexual selection and tradeoffs Value: 5% of your total b2900 mark (marked out of 18.75) Assignment: this file (with completed questions) uploaded to the brightspace lab 5 assignment folder Due: 24 hr after your lab session Please bring your own device (laptop). Recommended readings: (From Evolution 4 th Edition by Futuyma and Kirkpatrick – available as pdf on brightspace) Natural Selection (pg. 59), What are females and males? (pg. 249-259), How to be fit (pg. 275-278), Number of offspring and Life histories and mating strategies (p.286) Objectives To allow students to analyze and interpret a variety of peacock train empiri- cal data for evidence of sexual selection and tradeoffs. At the end of this lab, you will have gained knowledge/experience writing a hypothesis, analyzing empirical sample data using RStudio and interpreting it to determine if the hypothesis is supported. Students will also consider a range of supplemental data to assess the validity of the sexual selection the- ory. Assignment Overview During this lab, you will formulate a hypothesis to the lab problem/question based on the background material below, the supplementary material pro- vided on brightspace and the in-lab video. Then, using the sample data in the l5_dataset.csv file (available on brightspace) and the specific instructions in the lab5file.rmd file (available on brightspace), you will generate graphs and perform statistical analysis in RStudio. The graphs and analysis will be interpreted by answering the questions below (staring on page 5). Students are encouraged to work in pairs BUT must complete their OWN re- ports. At the end of lab 5, upload ONE file containing the: - problem/question, - hypothesis, - results (3 graphs generated in RStudio) - Answered questions to the lab 5 assignment folder on bright space.

B2900 L5: S exual selection and tradeoffs Lab File (w inter 2024) 2 Background As discussed Iab 4, a species is a group of organisms that can mate and produce fertile offspring. Charles Darwin described two types of driving forces that act on species; hunger and sex. The need for organisms to com- pete to eat in order to survive is explained by his theory of natural selection (lab 4). The need for organisms to reproduce in order to perpetuate them- selves is explained by his theory of sexual selection (topic of today’s lab). Natural selection is the non-random survival of individuals that are better adapted (ie. have a higher fitness) to their environment. This differential (higher) survivorship indirectly translates to differential (higher) reproduction with higher fitness individuals passing on proportionally more “survival” alle- les (and resultant characters) than lower fitness individuals. Sexual selection While higher survivorship leads to higher reproduction, there is a more direct process. Sexual selection is entirely based on individual differences that in- crease their ability to attract a mate, successfully copulate, and produce off- spring. Thus, more reproductively fit individuals produce proportionally more offspring (and thereby pass on more alleles) than less reproductively fit individuals. Sexual selection specifically acts on secondary sex characters, which de- velop as an animal approaches breeding age and are only connected to mat- ing success. These are distinguished from primary sex characters, which con- stitute male and female reproductive organs present at birth and are essen- tial for/directly connected to the act of reproduction itself. As in natural se- lection, sexually selected characters have a genetic basis and are inherited by offspring. Sexual selection consists of 2 types; contest competition (also referred to as intrasexual selection or male-male competition) and attractiveness competi- tion (also referred to as intersexual selection, female choice or mate choice). Contest competition This type of sexual selection involves individuals of the same sex (usually males) physically competing with each other for access to mates (or for re- sources that will attract mates). This competition leads to the evolution of characters commonly called anatomical weapons or armaments. An example is male elk fighting other males for access to females during the mating sea- son, the male with the bigger antlers having a better chance of winning the fight and reproducing. Note that while this is similar to individuals physically competing for food (natural selection), here they are specifically competing for mates (sexual selection).

B2900 L5: S exual selection and tradeoffs Lab File (w inter 2024) 3 Attractiveness competition This type of sexual selection involves individuals of the same sex (usually males) competing peacefully with one another by engaging in visual, acous- tic, or behavioural displays to increase the likelihood of being selected as a mate by the opposite sex. This type of competition is responsible for the evo- lution of colour and morphology of plumage, acoustic signals, odours or courtship dances; collectively described as ornaments. An example is a fe- male peafowl (peahen) choosing to mate with the male peafowl (peacock) bearing the largest and most colourful tail feathers. Important implications/consequences of sexual selection Natural selection continually strives to make organisms better adapted (thereby enabling higher survivorship) to their current environment. During contest competition, even though the main goal is reproduction (and not sur- vival), development of armaments presumably enables organisms to better survive as they can use these anatomical weapons while physically compet- ing for food. However, this is not the case for attractiveness competition. It leads to the evolution of characters that have no direct survival value and in- stead serve solely to attract potential partners. In fact, these characters come at an expense, debilitating rather than facili- tating an organism's survival. These are referred to as tradeoffs and de- fined as characters that come with both a fitness benefit and a fitness cost. Examples of attractiveness characters in birds include enlarged/brightly coloured feathers, loud/unique mating calls/songs and/or obvious courtship dances. The tradeoffs include being more conspicuous to predators; adding weight thereby reducing their ability to fly away from predators; and expend- ing more energy to grow these structures/perform the actions. But, if females continually prefer to mate with attractive males, then the ad- vantage of beauty can outweigh the advantages of survival. This persistent female preference counteracts limitations imposed by natural selection and highlights the sexual selection-natural selection equilibrium. Thus, exagger- ated sexual characters will keep becoming more extravagant to the point where disadvantages (higher mortality) outweigh the advantages (higher re- productive success). Importantly (in attractiveness competition), character development in males and preference for such characters by females means that females actively drive the evolution of morphological and/or behavioural characters of males. By preferentially selecting males with certain characters, females select which alleles are transmitted to the next generation. This process is com- monly referred to as female choice and male modification.

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