How Jealous Can One Beetle Get? Collin Ainslie Jealousy is one of the most frustrating emotions someone can deal with, it not only affects you, but it affects those around you. Jealousy isn’t exclusive to humans though, it can be seen all over the animal king, even in beetles. In Male burying beetles extend, not reduce, parental care duration when reproductive competition is high from P.E. Hopwood et. al. a group of scientists wanted to see just how jealousy affects male beetles. Nicrophorus vespilloides (Figure 1) are a cool species of beetles that are native to the United Kingdom who are famously called “burying beetles” because of some of their more unique habits. These beetles are known for burying animal carcasses for their children. What they do is find a small rodent carcass then mate and lay their eggs within it and bury it (Figure 2). As gross as this may sound, it serves as a great food source for their children once they hatch within the carcass. Now how exactly can jealousy affect something as bizarre as this ritual? Well, that is exactly what Dr. Hopwood, and his fellow scientists studied within their experiment. They wanted to see how competition between beetles can lead to changes in parental investment among males within a community. Figure 1: An Image of Nicrophorus vespilloides in the wild (Pendleton) There is some background information that can really help with understanding how these burying beetle’s work. Parental investment is the idea that parents invest time and resources into their children, an example of this would be a mom or dad taking a day off work to take his/her kids to an amusement park (Zimmer 2016). In the animal kingdom parental investment is different than this. Parental investment is almost entirely dominated by the mother providing care for the children through providing food, nourishment and often protection while the father leaves to explore other avenues. This is often the father leaving to find another mate. This remains true for our trusty beetles; the fathers often will mate with the mother and then leave. Competition is also super important to how animals interact and reproduce. Competition is when two or more animals compete for a common interest, this could be food, land or who they want to mate with (Zimmer 2016). In a majority of the animal kingdom, competition is dominated by males competing for the attention of a female to mate (Zimmer 2016). A human example of this would be two guys trying to impress a girl at the gym by seeing who bench presses more. The burying beetles are no different than these average gym bros, the males will have to compete for the chance to mate with the “dominant” female within the community. The competition between males will often determine who the female wants to have children with. The mating between the male and female beetle is also complex. How Jealous Can One Beetle Get? Collin Ainslie The male and female beetles’ mate and then lay the eggs within a carcass of a dead animal then bury it underground (Clutton-Brock 2017). In addition to this, female burying beetles have mechanisms to store sperm for prolonged periods of time that allows them to be pickier of their mates (Hopwood 2015). Now that the groundwork has been laid, how does competition affect parental investment of a father Nicrophorus vespilloides? In Dr. Hopwood’s study, they wanted to find out how competition impacts a father burying beetle parental investment, or what happens when a father beetle gets jealous of other male beetles. The hypothesis tested is that prolonged father investment will lead to an increased paternity, meaning that prolonged father investment is a method in protecting his mates and future offspring. If the hypothesis is true, there should be an increased parental investment when competition is present. Figure 2: Two Nicrophorus vespilloides partaking in activities in an animal carcass. (Eklund) To test this, they gathered 200 wild beetles from their native environments in the United Kingdom, had them mate, and produced viable lab born beetles, 246 to be exact. These lab viable beetles were then assigned to their study groups. In conjunction, miniature environments were set up to best represent the beetle’s native environment, these also included cameras to capture what occurred in the study groups. 24 hours before the beetles were placed within their study groups, the females had to mate with males not being used in the experiment. This is to ensure that the females can breed in either a monogamous group or without a male being present. Once the females had mated, the beetles were divided up into the study groups. There were four study groups used were, female bias, male bias, no sex bias, and no current extrapair competition with each group designed to see how competition affects beetles. The female bias group has a 3:1 female to male ratio and the male bias group with a 3:1 male to female ratio designed to show male competition. No sex bias includes a 2:2 female and male ratio while the no current extrapair competition group has a 1:1 female to male ratio. In addition, each study group had only one animal carcass to use. The cameras then recorded the beetle’s interaction around the carcass and the parental care given. The number of times they mated was recorded and parental care was measured as the amount of time the parent spent with the eggs before hatching and dispersal of the larvae. How Jealous Can One Beetle Get? Collin Ainslie The data gathered from the experiments was in support of the hypothesis. When male Nicrophorus vespilloides had more competition, they increased their paternity. They increased their paternity through investing more into their children and guarding their mate. This wasn’t the only way in which the males could increase their paternity though. When there were higher amounts of competition, males would mate with females more, up to seven times. In addition, when there were multiple females and less competition between males, males would mate with multiple females as another means of increasing their paternity. Another interesting take away from the experiment was that as competition increases, the number of children born decreases. The hypothesized explanation was a shortage of resources. The most interesting finding from this study is that there was really no benefit to the children if the father invested more. When children from varying amounts of father investment were compared, there were no real benefits to having father investment. Nicrophorus vespilloides is one of the most interesting beetle species in the world. They are called burying beetles because of their gross ritual of laying eggs in animal carcasses which are then buried. Just like humans, these beetles can feel jealousy. Males will change they the way they act when other males are present and this them jealous. To better understand this, Dr. Hopwood and his team did an experiment to study how jealousy affects a male’s parental investment into his offspring. They did this by making the males jealous through having the males compete for a mate. From this, they determined that males would increase their parental investment when competition is high or are jealous of other male beetles. This increase in investment is a method for the male to increase their paternity through protecting their offspring and mate. How Jealous Can One Beetle Get? Collin Ainslie Citations (1) Hopwood PE, Moore AJ, Tregenza T, Royle NJ. Male burying beetles extend, not reduce, parental care duration when reproductive competition is high. J Evol Biol. 2015 Jul;28(7):1394-402. doi: 10.1111/jeb.12664. Epub 2015 Jun 17. Erratum in: J Evol Biol. 2016 Jan;29(1):226. PMID: 26033457. (2) Zimmer, Carl. “12.2: Parental Investment & 12.3: Family Conflicts.” Evolution: Making Sense of Life, edited by Douglas J Emlen, Second ed., W. H. Freeman and Company, 2016, pp. 756–770. (3) Zimmer, Carl. “11.2 Sexual Selection” Evolution: Making Sense of Life, edited by Douglas J Emlen, Second ed., W. H. Freeman and Company, 2016, pp. 685–709. (4) Clutton-Brock T. 2017 Reproductive competition and sexual selection. Phil. Trans. R. Soc. B 372: 20160310. http://dx.doi.org/10.1098/rstb.2016.0310 (5) Benowitz KM, McKinney EC, Moore AJ. Difference in parenting in two species of burying beetle, Nicrophorus orbicollis and Nicrophorus vespilloides. J Ethol. 2016;34(3):315-319. doi:10.1007/s10164-016-0477-5 (6) Pendleton, Trevor, and Dilys Pendleton. “Nicrophorus Vespilloides.” Eakringbirds.com, www.eakringbirds.com/eakringbirds3/nicrophorusvespilloides01.jpg. (7) Eklund, Calle. “Nicrophorus Vespilloides Burying Beetle.” Entomologytoday.org, entomologytoday.org/nicrophorus-vespilloides-burying-beetle/.
