BIO220-Slides-Lecture2-W2012(1) - 0 The Evolution of Sexual...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 0 The Evolution of Sexual Differences (Dimorphisms) •  The puzzle of conspicuous ornaments •  Darwin’s answer (hypothesis) •  Origin of sexual differences •  Male-male competition 1 Sexual dimorphism: conspicuous ornaments non-breeding male breeding male Frigate Bird female Widow Birds Sexual dimorphism: conspicuous behaviours female Greater Sage-Grouse Sexual dimorphism: armaments elephant seals fighting for the beach Peacock Displays Survival of the Fittest? Peacock Displays: Survival of the Fittest? + Mating Success - Survival (predation) energetic cost 6 darwin calls this Sexual Selection 7 bias of females Sense of Beauty 8 Sexual Selection … depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction. – Charles Darwin mating Sexually selected traits function solely to enhance mating success It is a subset of natural selection but it can be useful to consider them separately Natural selection Sexual selection In males, # of mates determines # of offspring Survival + Reproductive rate + Number of mates + FITNESS 10 Fitness in Males & Females Reproductive rate Survival male fitness FITNESS Mating success usually females usually males 11 The origin of sexual differences Why sexual selection? Why two sexes? Anisogamy! Unequal-sized gametes expensive eggs makes female have the right to choose good males For a new species, females are the ones that produce large gametes. eye Anisogamy SPERM •  Inexpensive •  Many •  Small EGG •  Resource-rich •  Few •  Large 13 Parental Investment Theory Robert Trivers (1972): by definition •  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 14 The Difference Between the Sexes MALES FEMALES •  Tiny, mobile gametes (sperm) •  Large, resource-rich gametes (egg) •  Fitness limited by access to fertilizable gametes •  Fitness limited by access to resources Competition among males for mates Choosing among males for mates 15 Males Limited by Access to Females Number of offspring strong selection for males to have many mates Males limited by the quantity of resources to produce more eggs Females Number of mates 16 A Test: Bateman Curves female insects can store sperms from many males Total number of offspring 150 Male 100 Female 50 0 0 1 2 Number of mates 3 4 17 Comparison of Maximum Number of Offspring Produced During Lifetime Species Male Female Elephant seal Red deer Man Kittiwate gull 100 24 888 26 8 14 69 28 monogamous 1 male - 1 female 18 Sexual Selection Intrasexual selection •  Male-male competition Intersexual selection •  Female choice 19 Intrasexual Selection: Male-Male Competition FORMS: Pre-copulatory # of copulations copulation does not mean successful fertilization Post-copulatory success of copulations (sperm competition) 20 Manifestations of Male-Male Competition •  Fighting behaviour •  Territoriality •  Social status •  Sperm competition 21 Fighting either for dominance or terratory 22 Social Status Walrus High ranking male gets all or most copulations 23 displays Elephant Seals fighting on the beach, establish dominance females come up to the beach lower dominance males chase females to mate with them before they go back to sea 24 very high selection for dominance 25 Sperm Competition •  •  •  •  •  •  •  Mate guarding Sperm removal Copulation duration Sperm plugs Traumatic insemination Anti-aphrodisiacs Other bed bugs 26 Mate Guarding male guarding another female 27 Mate guarding in dragon & damselflies genitalia bring up the female to copulatory organs sometimes males don't release the female 28 Sperm Competition •  •  •  •  • •  Mate guarding Sperm removal Copulation duration Sperm plugs Anti-aphrodisiacs Other 29 Copulation Duration extend the period of copulation more sperms, and guarding the female 30 Sperm removal in damselflies remove last male's sperms horn uninflated inflated barbs whip 31 Bean Weevils - damages the female scrape the walls of reproductive tracts - may facilitate movement of oviposition signals into the female (reducing sperm competition) spines some proteins 32 33 Female Choice 34 ...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online