Social Cliques and Old Boys Clubs in Wild Chimpanzees

We humans are not as far removed from our primate cousins as we’d like to think.  A recently published paper in my favorite journal (Behavioral Ecology and Sociobiology) shows that there are hidden complexities to the food signalling calls of wild chimpanzees that mirror the actions taken by members of our species.

Just what is a food signalling call?

It’s any vocalization or behavior that serves to communicate to others that a food source has been found…and if you’re a hungry human or any other animal, you’ve got to decide carefully with whom you’d like to share it.

As humans, we’re not likely to send out a food-sharing call to just anyone who happens to be within ear shot.  If we’ve found something great, chances are we’re only interested in sharing with ‘socially important individuals’, people with whom we are closely associated.  After all, if you do something nice for members of your immediate social group, it strengthens the group bond and should translate into some reciprocal assistance at a later time.  Reminiscent of those cliques you experienced in high school, there is also a form of social rejection of non-members.  If you’re not a part of the club, you aren’t invited to take part in the ‘members only’ benefits…whatever they may be.

It turns out that in wild chimpanzees the same logic applies.  Males form stable, long-term social relationships with other males that are extremely important for day to day functions like group defense, territory establishment and social grooming.  Over six hundred hours of behavioral observations of these animals in Ugandan tropical forests confirmed that males sometimes produce special ‘rough grunt’ food calls about the quality of a food source.  However, they ONLY produce those calls if another ‘socially important’ male is nearby.  If the audience consistsof lower ranking individuals or even of oestrous (reproductive) females, males do not produce any rough grunt vocalizations.

There you have it:  Social cliques and old boys clubs are alive and well in primate orders other than our own!

Cited: Slocombe, K. E. et al.  June, 2010. Production of food-associated calls in wild male chimpanzees is dependent on the composition of the audience. Behav. Ecol. Sociobiol.

Size really does matter! Well endowed male earwigs have their cake and eat it too…

Many animal species employ a polyandrous sexual system, where one female mates with many males and stores sperm in a specialized storage organ.  Since fertilization doesn’t take place immediately (in some cases females can store viable sperm for several weeks), males actively compete to contribute to her sperm bank, regardless of whether it requires another deposit.  So what does it take to be reproductively successful as a male in a polyandrous sexual system?  There is a vast diversity of answers to this question, although one can discuss a few major themes.  First, be big.  Females generally prefer dominant males, who are generally associated with dominant genes (representing a large degree of biological fitness).  Second, be forceful. Males of many species have evolved complex structures for grasping, holding and subduing females in order to successfully transfer his seed. Third, be quick.  Some males have evolved strategies to be reproductively successful in a competitive environment by getting the deed done before any competing males realize he’s done it.  In addition, females that are busy mating have less time for other activities like feeding, finding shelter, and watching for predators.

So what is the best strategy if you are an Australian earwig (Euborellia brunneri)?  It turns out that none of the aforementioned strategies is involved.  Successful male earwigs are neither the biggest nor the most forceful.  They are also the ones who take the longest to achieve successful sperm transfer.  What is going on here?

It turns out that there is great disparity between males of this species with respect to the size of their genitalia.  Some males have extremely exaggerated sperm-transfer appendages (longer than their entire bodies), and some do not.  It’s important to clarify that just because a male has a longer penis, he isn’t necessarily bigger overall.  Genital size may be simply a heritable trait (hence the ‘sexy son’ hypothesis), if you’re dad had a great big schlong then it’s likely that you will too.  In a series of experiments designed to test the preferences of females for well endowed vs not-so-well-endowed males, researchers found that females overwhelmingly chose to mate with the former.

Evolutionarily speaking, this situation represents an interesting conundrum.  Here’s why:

1. As I mentioned above, males with longer appendages (virgae) are NOT necessarily bigger than males with shorter ones, so traditional arguments about females preferring dominant (larger) males do not apply here.
2. Males do not mate forcefully with females through coersion, so she has an active choice in her sexual partnerships (regardless of the endowment of her partner).  She is free to walk away (and end copulation) at any time.
3. Males with longer appendages deposit their sperm more deeply into a females’ reproductive tract, which means it takes them longer to reproduce than a male with a shorter member.

So why do females prefer the males with the largest genitalia?  The authors suggest that the elongation is an antagonistic adaptation that increases male control through sensory exploitation.  And I quote:

“During copulation, the genitalia of certain males may elicit more favorable female responses through superior mechanical or stimulatory interaction with the female reproductive tract.”

Do you really need a translation here?  Probably, since it’s kind of hard to believe:  male earwigs with giant members are titilating their partners into submission while they take their sweet time depositing their sperm.  Kind of like earwig porn really…Ok perhaps that’s an exaggeration, but the authors do reiterate that the male genital phenotypes that are most successful in sperm competition (those that can reach further into the females’ reproductive tract) are also mediated by mating benefits from the female.  Females allow well-endowed males to occupy a greater amount of time during mating, perhaps due to some form of sensory exploitation from his giant, stimulating sexual organ.

Just when you think you can generalize about sexual strategies in the animal kingdom, one comes along that seems to fly in the face of clearly defined categories.

Awesome.

Lieshout, E. (2010). Male genital length and mating status differentially affect mating behaviour in an earwig Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-010-1021-1

Are Headlines Hogwash? Part III

Blackburn, J., Mitchell, M., Blackburn, M., Curtis, A., & Thompson, B. (2010). Evidence of Antibiotic Resistance in Free-Swimming, Top-Level Marine Predatory Fishes Journal of Zoo and Wildlife Medicine, 41 (1), 7-16 DOI: 10.1638/2007-0061.1

This week’s installment of ‘Are Headlines Hogwash’ brings us to an article from Discovery News this past June.  Here’s the headline:

ANTIBIOTICS BREEDING ‘SUPER BUGS’ IN SHARKS, FISH

I should also add that the first line of the article reads:

“It’s one of the scariest things about modern society — ever since we declared war on bacteria with the widespread use of penicillin in the 1940s, microbes have been adapting, gaining resistance to our drugs, coming back stronger and more vicious than before…”

Superbugs!  Antibiotic Resistance!  Stop the Presses! No wait…start the presses! Uh – hold on… is there really any truth to this dire headline?

She says:   There’s a shred of truth to it.

The research described here did indeed find evidence of bacterial resistance.  Here’s the rundown:  scientists wiped the bums of several large fish species including seven sharks and one teleost, and isolated the bacteria that were found.  This was done at six separate (widespread) locations.  The bacteria were characterized by their gram-stain morphology, and then tested against 13 different drugs for possible resistance.

Antibiotic resistant bacteria were found in all species, and at all sites, for at least one of the drugs tested.  *However, the authors note that when gram stain morphology of the bacteria is included in the analysis the incidence of resistance decreases dramatically.  This is because a gram negative bacteria will OBVIOUSLY be resistant to an antibiotic designed for a gram positive one.