Mating Systems

1. Mating Systems Psychology 3107

2. Introduction • For the most part, males’ involvement in mating, well, ends after the mating • Females pay for the mating a lot more • Physiologically • Post birth/hatch care • Therefore, we should expect Polygyny where males have more than one mate • Male variance > female variance

3. Polygyny • There are several theories about polygyny • Resource defense polygyny • Male defends some good resource • Example, hummingbirds • The resource is some nectar giving flower

4. Hummingbirds • Male sets up territory • Excludes other males • Basically, the male exchanges letting females feed in exchange for copulations • Sort of like nuptial gifts in some sinsects, but the ‘gift’ is stationary • Females then set up breeding territory withing male’s teritorry

5. Polygyny Threshold • Polygyny may occur when the ‘polygyny threshold’ is crossed • Example here is migratory songbirds • Males arrive, set up territories • Females choose mates

6. Polygyny Threshold • When differences in qualities of available territories crosses the polygyny threshold, then polygyny results • It is more profitable for the female to become a secondary female with a high end male, then a primary femle with a mid range

7. What about monogamy • Monogamy should happen if: • Curves are far apart • Curves are flat • In other words, little variation in quality of males and their territories • Verner and Wilson did a really cool study that looked at these ideas

8. Verner and Wilson • Marsh birds • Quality varies greatly vs • Non Marsh birds • Not so much variation • Prediction is that there should be much more monogamy in non marsh living songbirds

9. So, what happened • Marsh species  44 % are polygynous • Non Marsh  2 % are polygynous • You can also get female defense polygyny • Males basically guard the females • Good example here is in Bison

10. But you said we’d talk about monogamy… • OK, OK…… • When should mongamy happen? • When the young are in need of lots of parental care • When Territories or resources are poor • When females actually enforce it! • Some ‘monogamous’ species aren’t…..

11. Extra Pair Copulations • Happens a lot in birds • Ummm, happens a lot in people • ‘sperm competition’ • Usually when female is unguarded or when male can get away with it….. • Sperm Wars

12. Polyandry • One female, many males • Exceedingly rare • Usually only happens when there is complete sex role reversal • Sea horses • Spotted sandpipers

13. Conclusions • Many theories as to why different animals have different mating systems • Polygyny is by far the most common • When you think about it, the system correlates nicely with the gametes!