We are soon to be wrapping up several analyses and starting some new ones. I want to mention one analysis that never really got off the ground, but it’s a good idea. My intern Jana asked me a great question: Does a female vampire bat inherit some of her food-sharing partners from her mother?
This question has some really interesting theoretical work behind it. I looked into my PhD data a bit, but unfortunately, I don’t have the necessary sample size. Food sharing most often occurs among females, and I have focused my data collecting on females, but there were only 4 females born during my PhD study. And I have only poor data for the 15 males born during my study (I’ll say more about that sex ratio bias in another blogpost).
Anyhow, to look into Jana’s question, I just now measured the average donation rate to bat A from all 37 possible donors, then compared that metric for bat A’s mom. If you just look at whether bats have more similar sharing networks to their moms versus all other bats, you find that females (n=4) do, while the males (n=15) do not. But this does not prove anything. We should expect that females should have more similar connections to all other females just because females are more similar to females in general when it comes to food-sharing. So this might have nothing to do with maternal bonds. What we really want to know is: Is the sharing network of female bat A more similar to bat A’s mother than to the mothers of bats B, C, or D?
Answer: Nope. That was only true in one case. Under perfect social inheritance, the rankings of similarity of the four bats to their own mom should have been all 1st place (out of 4). Instead the rankings were 4th (last), 4th (last), 1st, and 3rd. Clearly, it’s too few observations to draw conclusions, but there’s nothing very striking here.
As we collect more data from more bats, it will be interesting to do a more powerful comparison of the sharing networks of mothers and their adult daughters. With more data, we can also ask whether adult bats with many sharing partners have adult offspring with many sharing partners.
In the next few months, we hope to be looking at how bats form new food-sharing relationships with strangers. And we also have three more new pups.
Here’s a picture of the Rachel Page Bat Lab/Family in Gamboa:
And here’s a preliminary association network of female (red) and male (blue) frog-eating bats (Trachops cirrhosus) based on 4 years of roost capture data (more on that coming soon!).
Finally, some results of some recent cool papers:
Are there different cooperative social structure types? Or do animals socialize along a gradient? There are types! “Using phylogenetically informed comparative analyses, we found strong evidence indicating that not all reproductive arrangements within social groups are viable in nature and that in societies with multiple reproductives, selection favours instead taxon-specific patterns of decrease in the proportion of breeders as a function of group size.”
Do bacteria within your own gut cooperate with each other? Yes: “Using in vitro systems and gnotobiotic mouse colonization models, we find that extracellular digestion of inulin increases the fitness of B. ovatus owing to reciprocal benefits when it feeds other gut species such as Bacteroides vulgatus. This is a rare example of naturally-evolved cooperation between microbial species.”
Do individuals choose to cooperate based on expected payoffs? “We experimentally created a situation of high conflict in communally nursing house mice, by using a genetic tool to create a difference in birth litter sizes. Females in the high conflict situation (unequal litter sizes at birth) showed a reduced propensity to give birth as part of a communal nest, therefore adjusting their cooperativeness to the circumstances.”
Do individuals pay attention and change their behavior depending on their own dominance status relative to that of others? “In this study, it is shown that male mice form linear dominance hierarchies characterized by individuals attacking in bursts. Temporal pairwise-correlation analysis reveals that non-dominant individuals avoid behaving aggressively concurrently with an aggressively behaving alpha male. This anti-correlation is only found with alpha males and is greater for more despotic alpha males. It is concluded that less dominant individuals modulate their aggressive behaviour in response to their social context, resulting in an attentional group structure.”