Now here's a Situation.

May 23, 2011

Eva Gusnowski

The battle of the sexes continues to rage on. However, this time it seems to have moved a little bit further off of the beaten path…
situation, species extinction, male aggression
Let’s face it: females and their eggs are a limiting resource in sexual reproduction. Because a female adds more content to their gametes than males (sperm is pretty much only DNA) and also are likely to have to incubate and ultimately take care of the developing zygote, females tend to exercise a higher degree of mate selection than males. However, this in turn means males have an increased tendency to spread their seed around the block and increased competition between males. This increased competition has resulted in the evolution of certain male traits, such as high numbers of sperm produced, overly aggressive behavior and also investment in weaponry.   “Sexual weaponry,” you might ask? Yes, sexual weaponry indeed. When male-male competition results in a decrease in female viability, it is referred to as a “tragedy of the commons” because population survival is decreased.
The emerging problem is therefore how the development of these male-male competition traits ultimately affects the survival of the species.  An individual might survive, but if female viability is decreased and the species begins to go extinct, what good is the individual? How far can the benefits for the individual be taken before it overtakes the benefits for the population?
A study in seed beetles attempted to answer these questions. The males of this species of beetle have a tendency towards aggressive behavior: the most aggressive males fertilize the most eggs, and are themselves more genetically successful.  How do they do this? Remember when I mentioned sexual weaponry earlier? Seed beetle males have a barbed penis that prevents the female from leaving during a sexual encounter. It is quite obvious that a female is likely to sustain serious injury during sexual intercourse (just look at that picture!), and therefore the most aggressive males and those with the longest genital spikes are likely to inflict the most damage.
male seed beetle penis, science in seconds, male aggression
A study in 2009 directly demonstrated that the length of male genital spikes is positively correlated to the fertilization success of that individual: longer spikes equals more successful. Sadly, the length of male genital spikes is also positively correlated to harm to the females. So size really does matter, just not in the way that everyone once thought.
And just FYI, sexual harassment of females by males has most definitely been shown to impose a cost on females in terms of reduced fecundity and survival (check out this study in lizards), even though these males don’t necessarily have a barbed penis. 
beetle, situation, science in seconds
So dearest “The Situation,”
Please pull your shirt down. You are literally killing us. 



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