Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Marine Vertebrates: Lecture 16 Sexual selection & mating systems 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 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 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 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? 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? Gulf pipefish ♀ ♂ Broad-nose pipefish ♀ ♂ Photo: Institute of Biology of the Southern Seas, Ukraine Hippocampus spp. Pair (Same genus as W. Australian seahorse • Note similar size and coloration of pair. www.divegallery.com 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. Polygyny • Female defense polygyny Example: Northern elephant seals Photo: www.driftersister.com Photo: www.wetasschronicles.com Male-male competition and sexual dimorphism (seals) NOTE: Each point represents a species Polygyny • Lek polygyny Example: Marine iguanas Photo: Martin Wikelski Polygyny: Cetacea • Sperm whales Highly skewed sex ratios on mating grounds Sexual dimorphism & battle scars Females: synchronous estrus • Adaptive value? 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 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 Alternative male strategies • Plainfin midshipmen Dominant male features and behavior Sneaker male features and behavior Photo: Cornell University 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 California Sheephead and sex reversal California sheephead female Photo: UC Santa Cruz California sheephead male Photo: V. Sanchez Other sex reversers: bluehead wrasse Bluehead wrasse, intial phase Bluehead wrasse, terminal phase male Photo: P. Humann 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 Monogamy: alternate hypotheses • Danger “theory” Leaving increases chance of dying if predation rates are high. Example: Bluespotted jawfish www.reefcorner.com Social vs. genetic monogamy • Video: blue-footed boobie www.amazingjourneys.net 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