It’s hard to hunt with babies on your back!

In nature, animals are often faced with limited resources (i.e. time and energy). When faced with this problem, there are often compromises in the amount of time and energy an animal can devote to a particular activity at any given time. Activities associated with reproduction (e.g. mate searching, copulation, pregnancy, offspring care) can be time consuming and energetically expensive. This is especially true for viviparous (live-bearing) females. During pregnancy, females often experience significant increases in body mass. In addition, the continuous allocation of nutrients to offspring throughout pregnancy is also energetically taxing for females. These reproductive costs are known to negatively impact a female’s ability to move efficiently. I was interested in whether these reproductive costs also increase the difficulty of capturing and subduing prey. Using Arizona Bark Scorpions (Centruroides sculpturatus), Dr. Javier A Rodríguez-Robles and I tested whether reproduction had a negative impact on the predatory efficiency of females. As part of our experiment, we recorded how long it took female bark scorpions to successfully capture and subdue a prey item (Common House Cricket). We compared the prey handling times of female scorpions at different reproductive stages 1) Non-pregnant, 2) Pregnant, and 3) females exhibiting maternal care (i.e. carrying offspring on their backs).

Female Arizona Bark Scorpion stinging a cricket.

Female Arizona Bark Scorpion stinging a cricket.

What we found was that pregnancy did not significantly reduce the predatory efficiency of female Arizona Bark Scorpions. In fact, pregnant females were just as good at catching prey as non-pregnant females. However, females experienced a decrease in their predatory abilities during the maternal care period and they were unable to capture prey. We also wanted to see how long it took females to recover their predatory abilities after the maternal care period, so we removed the offspring from their backs and retested their prey handling abilities 24 hours and 28 days later. What we found was that 24 hours after offspring removal, females were unable to capture prey. However after 28 days, females were significantly better at catching prey compared to females carrying offspring and females 24 hours after offspring removal, but were still slower than non-pregnant and pregnant females. Our results demonstrate that female Arizona Bark Scorpions experience a tradeoff between caring for offspring and capturing prey. In addition, we also observed that reproduction can change the way in which female scorpions hunt for prey.

You can read all of the exciting details of our study in BMC Evolutionary Biology! (http://www.biomedcentral.com/1471-2148/13/197)

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