Some animals have a lot of sex, I mean a LOT of sex.  I study a type of beetle that is like that, where females will mate possibly dozens of times a day with a dozen different males.  Now, this may sound like a quirky or humorous research topic, but if you think about it, it just doesn’t make sense.  Here we have these beetles which only live a few months, but still need to eat a lot of food and lay a lot of eggs, but are spending a huge chunk of their time having sex.  For the females, one mating gives them more than enough sperm to fertilize her eggs for weeks, if not her whole life, so these extra matings seem almost a waste of time.  Every extra mating means less food meaning less eggs meaning less offspring, which is the exact type of situation that would not be favored by natural selection.  Why, then, do females mate with so many males despite no obvious benefit and some obvious cost?

Well, having sex with a bunch of guys may not give you more offspring, it might give you better offspring.  The sperm from different male beetles may fight it out inside the female, with the best male’s sperm winning and the female getting good, Ivy League-bound quality children.  Or, female may mate so much because they keep running into better, hunkier males who would give hunkier kids.  Or, instead of getting super-good kids, the female gets a whole bunch of different kids from different fathers (this was actually on Maury once with a paternity test of human twins).

• Orsetti, D.M. In prep. Copulation time and sperm transfer in Leptintoarsa decemlineata. 
• Orsetti, D.M. In prep. Size affects copulation behavior, but not female choice, in Leptinotarsa decemlineata. 
• Orsetti, D.M., P.C. Frost. In prep. Ecological stoichiometry and behavioral ecology; how do elemental ratios affect interactions among organisms? 
• Orsetti, D.M., R.L. Rutowski. 2003. No material benefits, and a fertilization cost, for multiple matings by female leaf beetles (Leptinotarsa decemlineata). Animal Behavior 66: 477-484. 
• Orsetti, D.M. 2000. Multiple mating by female Colorado potato beetles (Leptinotarsa decemlineata). M.S. Thesis. Arizona State University. Tempe, AZ, USA.