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Sexual selection & mating systems

Explore the dynamics of male competition and female choice in marine vertebrates, diving deep into sexual selection theories, mating systems like polygyny and monogamy, and alternative male strategies. Discover how behaviors and characteristics maximize mating chances, with a focus on pipefishes and seahorses. Witness fascinating examples from the marine world, shedding light on reproductive strategies and challenges faced by different species.

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Sexual selection & mating systems

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  1. Marine Vertebrates: Lecture 16 Sexual selection & mating systems

  2. 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 Why do males usually compete, while females choose?

  3. 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

  4. 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

  5. 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?

  6. 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?

  7. Gulf pipefish ♀ ♂

  8. Broad-nose pipefish ♀ ♂ Photo: Institute of Biology of the Southern Seas, Ukraine

  9. Hippocampus spp. Pair(Same genus as W. Australian seahorse • Note similar size and coloration of pair. www.divegallery.com

  10. 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.

  11. Polygyny • Female defense polygyny • Example: Northern elephant seals Photo: www.driftersister.com Photo: www.wetasschronicles.com

  12. Male-male competition and sexual dimorphism (seals)NOTE: Each point represents a species

  13. Polygyny • Lek polygyny • Example: Marine iguanas Photo: Martin Wikelski

  14. Polygyny: Cetacea • Sperm whales • Highly skewed sex ratios on mating grounds • Sexual dimorphism & battle scars • Females: synchronous estrus • Adaptive value?

  15. 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

  16. 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

  17. Alternative male strategies • Plainfin midshipmen • Dominant male features and behavior • Sneaker male features and behavior Photo: Cornell University

  18. 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

  19. California Sheephead and sex reversal California sheephead female Photo: UC Santa Cruz California sheephead male Photo: V. Sanchez

  20. Other sex reversers: bluehead wrasse Bluehead wrasse, intial phase Bluehead wrasse, terminal phase male Photo: P. Humann

  21. 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

  22. Monogamy: alternate hypotheses • Danger “theory” • Leaving  increases chance of dying if predation rates are high. • Example: Blue-spotted jawfish www.reefcorner.com

  23. Social vs. genetic monogamy • Video: blue-footed boobie www.amazingjourneys.net

  24. 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

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