sexual selection & mating systems
DESCRIPTION
Why do males usually compete, while females choose? Hypothesis 1: “Eggs are expensive, sperm is cheap!” More energy invested per egg than per sperm Females: limited by egg production Males: limited by number of matesTRANSCRIPT
![Page 1: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/1.jpg)
Marine Vertebrates: Lecture 16
Sexual selection & mating systems
![Page 2: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/2.jpg)
Why do males usually compete, while females
choose?• Hypothesis 1: “Eggs are expensive, sperm
is cheap!” More energy invested per egg than per sperm
• Females: limited by egg production
• Males: limited by number of mates
![Page 3: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/3.jpg)
Is sperm really cheap?
• It often takes a large number of sperm to fertilize a single egg, due to
Hostile environment within female Sperm competition among males
![Page 4: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/4.jpg)
Why do males usually compete, while females
choose?• Hypoth. 2 (R.
Trivers): Individual with the most total parental investment chooses.
Often the female (i.e. mammals)
Sometimes the male…
Photo: pbs.org
![Page 5: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/5.jpg)
Sexual selection• Characteristics/behaviors are
selected for that maximize the chances of acquiring mates.
• What are some of these
characteristics?
• Which gender is likely to have the most obvious sexually-selected characteristics?
![Page 6: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/6.jpg)
Sexual selection and polyandry in pipefishes and
sea horses • Why pipefish and seahorses? • Question
Is there a relationship between the type of mating system and degree of sexual selection?
• Species Gulf pipefish: Polyandry (no polygyny) Dusky pipefish: Polygynandrous Broad-nosed pipefish: Polygynandrous W. Australian seahorse: Monogamous
• Expected results?
![Page 7: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/7.jpg)
Gulf pipefish
♀
♂
![Page 8: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/8.jpg)
Broad-nose pipefish
Photo: Institute of Biology of the Southern Seas, Ukraine
♀
♂
![Page 9: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/9.jpg)
Hippocampus spp. Pair(Same genus as W. Australian
seahorse•Note similar size
and coloration of pair.
www.divegallery.com
![Page 10: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/10.jpg)
Mating systems Polygyny: One male mates with several
females• Why considered the male “default”?
Monogamy: One male mates with one female• Social vs. genetic monogamy
Polyandry: One female mates with several males
Polygynandry: Male mates with >1 female, female mates with >1 male.
![Page 11: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/11.jpg)
Polygyny•Female defense polygyny
Example: Northern elephant seals
Photo: www.driftersister.com Photo: www.wetasschronicles.com
![Page 12: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/12.jpg)
Male-male competition and sexual dimorphism (seals)
NOTE: Each point represents a species
![Page 13: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/13.jpg)
Polygyny•Lek polygyny
Example: Marine iguanas
Photo: Martin Wikelski
![Page 14: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/14.jpg)
Polygyny: Cetacea
•Sperm whales Highly skewed sex
ratios on mating grounds
Sexual dimorphism & battle scars
Females: synchronous estrus•Adaptive value?
![Page 15: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/15.jpg)
Polygyny: Cetacea
•Humpback whales Skewed sex ratios Asynchronous
ovulation Asynchronous
arrival on mating grounds
Paternity studies•Many males with
no offspring•No male with >3
![Page 16: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/16.jpg)
Polygyny? Orcas
• Matrilineal groups Males associate with mother’s group
• Mate outside groups (based on genetic studies using “skin darts” for sampling)
www.pacificwhaler.com
![Page 17: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/17.jpg)
Alternative male strategies
Photo: Cornell University
•Plainfin midshipmen Dominant male
features and behavior
Sneaker male features and behavior
![Page 18: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/18.jpg)
Alternative male strategies•Salmon
Dominant males•Top two in
photo
Jacks (smaller, less time at sea)•Bottom photo by Ian Fleming
yusukekoseki.michikusa.jp/research.htm
![Page 19: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/19.jpg)
California Sheephead and sex reversal
California sheephead female Photo: UC Santa Cruz
California sheephead male Photo: V. Sanchez
![Page 20: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/20.jpg)
Other sex reversers: bluehead wrasse
Bluehead wrasse, terminal phase male
Photo: P. Humann
Bluehead wrasse, intial phase
![Page 21: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/21.jpg)
Monogamy: alternate hypotheses
• Mate assistance: it takes two parents to raise the offspring
Example: Adelie penguins
Both parents needed for chick survival
Photo: Karen Haberman
![Page 22: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/22.jpg)
Monogamy: alternate hypotheses
• Danger “theory”
Leaving increases chance of dying if predation rates are high.
Example: Blue-spotted jawfish www.reefcorner.com
![Page 23: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/23.jpg)
Social vs. genetic monogamy
•Video: blue-footed boobie
www.amazingjourneys.net
![Page 24: Sexual selection & mating systems](https://reader036.vdocument.in/reader036/viewer/2022062311/5a4d1b217f8b9ab059995495/html5/thumbnails/24.jpg)
Polyandry/Polygynandry
•Potential advantages of multiple matings by females? Females reproductive success limited
by mates rather than gametes (rare)•Example: polyandrous pipefish
Higher rates of conception (i.e. % of eggs fertilized)
Good genes hypothesis: Insures the highest quality mate/offspring
Genetic variability among offspring Material benefits