Transcript Mating Systems and Behaviors in Snakes

Snake Mating Systems,
Behavior, and Evolution: The
Revisionary Implications of
Recent Findings
Rivas, 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’Brien
Psychology of Sex Differences
October 20, 2010
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)
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
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Female defense (mate guarding)
Hot-spot
Prolonged male searching
Explosive mating assemblage
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
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
QuickTime™ and a
decompressor
are needed to see this picture.
•
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
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
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