Difference between Polyandry and Polygyny?

1. Snake Mating Systems, Behavior, and Evolution: The Revisionary Implications of Recent FindingsRivas, Jesus A., Burghardt, Gordon M. (2005). Snake Mating Systems, Behavior and Evolution: The Revisionary Implications of Recent Findings. Journal of Comparative Psychology. 119(4), 447-454.Laura Cain, Taylor Casillas, Sarah Fukui and Nick O’BrienPsychology of Sex DifferencesOctober 20, 2010

2. Difference between Polyandry and Polygyny? • Polyandry: A mating pattern in which a female mates with more than one male in a single breeding season. • Polygyny: few males monopolize access to many females • Benefit = mate with more females, spread genes • Ex: male elephant seals (dominant one gets to mate) • Previous to this study, it was widely believed that the primary form of reproduction in snakes is polygyny • Males have upper hand/advantage (sexual selection) • In mating (male-male competition) • Attractiveness to females (body size, morphological behavior, physiological attributes)

3. Framework for understanding diversity of mating systems • Relies on… • Degree males can monopolize • Distribution of resources • Availability of mates • Thus… sexual selection > for the sex that benefits more from increased number of matings (more offspring) • Polygyny = for males • Four types of polygyny that were believed to accompany all snakes • Female defense (mate guarding) • Hot-spot • Prolonged male searching • Explosive mating assemblage

4. Initial research on snake mating systems • Disproportionate Research • done on one species • in a specific climate and location- inaccurate findings • Diverse data for comparative findings unavailable • Poor database/invalid research due to: • Secretive nature of snakes & other difficulties • Contrary to prejudiced info available, polyandry has been found to be the primary, if not universal form of mating system in snakes, not polygyny • Snakes are the first species in which polyandry best describes their mating system

5. Findings on snake mating systems • Contrary to prejudiced info available, Polyandry has been found to be the primary, if not universal form of mating system in snakes, not polygyny • Snakes are the first animal in which polyandry documented • Evidence: males spend more time courting and mating • Choosier (larger more fertile female) • Less reproductive investment • Female multiple mating: found in all species (anaconda not the rare exception anymore) • Males are smaller than females (would be opposite if polygyny) • Males rarely if ever feed during reproductive period • Suffer higher mortality rate

7. Evidence for polyandry in snakes • Garter snake • DNA and molecular studies proved several sires in the litters of garter snakes • Even with molecular methods to assess paternity( have found that multiple paternity is the norm for snakes), the word polyandry was still avoided • Although this species still recognized as polygynous • Female Green Anaconda • One female lays in mud or water • 13 males come over • Coil around her and attempt to mate • This mating can last for up to a month • Males may stay with female until the end of her attractive period http://www.youtube.com/watch?v=7TF7d4jvays

8. Female Snakes • OSR (operational sex ratio) = <1:1 for most snake species • OSR is the ratio of available females to available males • Female snakes: large reproductive investment • Can’t always mate every year • Leads to male-biased OSR • potential for females to mate numerous times

9. Conclusion • Snakes are more likely to exhibit polygynandry (group mating) or polyandry than polygyny • Polgynandry is similar to promiscuity • When looking at their ancestors and sister taxa, evidence for polyandry or serial monogamy • Explains paradoxical behavioral differences • Ex: lack of territoriality or male-based sexual size dimorphism