BIO220-Slides-Lecture3-W2012 - Sexual Selection &...

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Unformatted text preview: Sexual Selection & Female Choice 1 satin bowerbird males v=tJ32_ijdmLo 2 Leks males in groups of 10 - 20 displaying Sage grouse 3 Female Choice •  Introduction to the problem •  Examples of female choice in action •  The benefit of female choice (direct and indirect benefits) •  Why do they choose arbitrary traits? •  Summary 4 Female Choice big females may prefer big males. •  Any female trait (behaviour, morphology) that biases the mating success of males toward the preferred type •  We will use mating bias, female preference, female choice to mean the same thing •  No implied sense of beauty •  Male choice is simply the reverse 5 Visual stimulation Acoustical stimulation •  •  •  •  •  •  •  •  •  •  •  Scorpionfly Barn swallow Long-tailed widowbird Satin bower bird Cichlid fish Field cricket Jungle fowl Tactile stimulation Field cricket Woodhouse s toad Great reed warbler Túngara frog Olfactory stimulation •  Mouse •  Cockroach •  Moth •  Sierra dome spider 6 Female Choice 7 Widow Birds 8 Tail Manipulation Experiment QUESTION: •  Are long tails preferred by females? EXPERIMENT: •  Manipulate tail length 9 Experiment •  •  •  •  Natural tail length (N) Reduced tail length (R) Elongated tail length (L) Sham surgery (S) cut off glued on cut the tail off and glue it onto the same bird, just to make sure mating success will not be affected by tail cutting PREDICTIONS: Mating success •  L > N > R •  N = S 10 Results Nest # per male 2 same tail length 1 Prior to treatment 0 R N S L 11 Results Nest # per male 2 After treatment 1 the surgery is not affecting mating success b/c N=S 0 R Females prefer long tails. N S L 12 Female Preference of Eyespots in Peacock Tails EXPERIMENT: Reduction of eyespot number13 Change in number of copulations Results 1 small increase, not important 0 Females count eye spots and prefer them. -1 -2 -3 -4 Experimental reduce eye spots Control 14 Female Preference of Complex Calls in Túngara Frog 15 Females prefer complex calls Sonogram Oscillogram Whining bring females into the pond. Whine Multiple chucks Call complexity 1 chuck When females are in the pond, they prefer multiple chucks. 16 frequency of sound (pitch) amplitude (how loud it is) Frog-eating bat are also attracted to whiny males Bats prefer complex calls too! 17 The Problem of Female Choice Why are male elaborations common? •  Females prefer them •  Therefore selection for elaboration Why do females prefer certain traits? •  One of the biggest problems in evolutionary ecology 18 Hypotheses for Female Choice (non-exclusive) •  Direct benefits: involve direct natural selection on the female •  Indirect benefits: involve genetic benefits to her offspring Elaboration means the male probably has good genes. 19 Hypotheses for Female Choice Direct Benefits •  Female preferences are side effect of other forces shaping female behaviour •  Selection of resources (PI) rather than male Eg. food, Male trait may indicate the male has the resources the female needs. territory attributes •  Male trait is indicator (or badge) of parental investment (PI) 20 Female Preference for Males with Resources a tiny sperm with a lot of food. Nutritious spermataphores (sperm, protein) Mormon cricket Katydid 21 Darryl Gwynne Hanging fly 22 Copulation duration (min) Results an increase relationship Body size of nuptial prey 23 an increasing relationship (X 1000) Number sperm transferred Results Copulation duration (min) 24 Selection for Male Traits as Indicators of PI •  •  •  •  Territory quality Parental care Defense Lack of parasites (STDs) Ornaments indicate the degree of parental care. 25 Hypotheses for Female Choice Indirect Benefits •  Females prefer male traits that indicate high genetic quality (good genes)? •  If so, offspring from matings with preferred males should have higher fitness 26 Peacock Display Size is an Indicator of Good Genes? Males with fewer eye spots should produce offspring that have low survival rate. 27 Preference for Good Genes % Chick survival to age 2 yrs 60 50 40 30 20 10 125 130 135 140 145 150 Display size 28 There is few data on this, so this might not be important. 1 Females are the ones that produce large gametes. 2 Females are limited to resources. Males are limited to access to large gametes. If the male is investing a lot in offspring, males choose females. Summary •  Introduction to the problem •  Examples of female choice •  The benefit of female choice (direct and indirect benefits) 29 Parental Investment (PI) Theory Robert Trivers (1972): •  Sexes differ in their reproductive investment •  Members of the sex that invest little in offspring will compete among themselves to mate with members of the sex that invest more in offspring 30 Expectations and Examples •  High male PI •  Male choice •  Female/female competition •  •  •  •  Giant water bugs Pipefish Katydids Spotted sand piper •  Plover •  Others bird 31 Pipefish 32 Pipefish Sex Roles and Mating System •  Male reproductive success limited by size of their brood pouch Males brood eggs. Females insert the eggs into male's brood pouch. •  Female reproductive success limited by access to males •  Females compete for access to males •  Sexual selection on female size and ornamentation 33 Female inserts eggs into pouch Brood pouch Copulation 34 Male providing safety and O2 Full Brood Pouch 35 Birth 36 Offspring Fry Father 37 Sexual Dimorphism in Pipefish Male Female Large and colorful females produce more eggs. 38 Experimental Evidence of Sex Role Reversal •  Question: Do males exercise mate choice? •  Prediction: Males will prefer large highly fecund females 39 # preferred by males Results 10 8 6 4 2 small large Female body length 40 # preferred by males Results 10 8 6 4 2 small large Female fold size large ornament small ornament 41 Darryl Gwynne Darryl Gwynne Katydids Sex role can change in katydids. Male produce spermatophores and call the females. In high resource envi, males will produce spermatophores easily, and females can choose among males. In low, females need resources from males. Males with spermato phores can choose competing females. 42 Relative PI and Flexible Sex Roles in Katydids As ambient resource levels decline: •  Male availability declines (resource limited) •  Female need for male resources increases Predictions at low resources: •  Male choice of females •  Female-female competition 43 Results: Sex Role Reversal Food Abundant Food Scarce Calling males: 6.6 Matings per female: 0.7 1.3 Male choice: <0.1 0.4 Female competition: 0.0 0.2 Males are competing. 0.4 Not calling because can't make spermatophores. Male rejects 40% females 44 So, what about sexual selection in humans? Our mate preferences are determined by culture a lot. this is more symmetrical. most people prefer symmetrical faces. 45 Mate Choice in Mice and Humans: the MHC What is MHC? •  Major Histocompatibility Complex •  Called HLA in humans •  MHC loci code for the antigen recognition system of the immune response •  Lots of genetic variation at MHC loci is GOOD MHCs is involved with recognizing antigens. Diverse MHC is good. 46 Do mice choose mates based on MHC? Reasons why such mate choice might evolve: •  To avoid inbreeding •  To increase the genetic variation at MHC loci in their offspring Sense in mice and what MHC loci they have is related. 47 House mice prefer to mate with individuals of a different MHC-type Male mate choice preference Female mate choice preference 1 0.8 0.8 0.6 % % 1 0.6 0.4 0.4 0.2 0.2 0 0 Same Different Female's Genotype Same Different Male s genotype Mate choice is based on differences in odour That correspond with differences in MHC 48 When females are brooding, they are attracted to similar MHCs, because offsprings have similar MHCs Do humans choose mates based on MHC? Reasons why such mate choice might evolve? •  To avoid inbreeding •  To increase the genetic variation at MHC loci in their offspring 49 intensity attractiveness Results: dissimilar similar dissimilar similar •  All these women were NOT taking birth control pills •  The pill simulates hormonal levels present during pregnancy •  Perhaps women who ARE taking the pill have a different preference (e.g., nesting response in mice) Females smell males' t shirts. and rate intensity and attractiveness 50 attractiveness intensity dissimilar similar dissimilar similar •  Women on the pill tended to prefer similar MHC types!! •  Consider the implications this has for choosing a mate while you are using the pill and then going off the pill (!!) 51 Next Lecture: Social Behaviour 52 ...
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