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By: Nazifa Islam
Eating your own offspring seems…unthinkable, right? After reading the title, the most obvious explanation may be food shortage. However, that is not the case in many situations. Filial cannibalism is defined as an adult individual of a species consuming all or parts of its own species. Generally, this means their immediate offspring and it is most commonly observed in males.
Martin Vallon and Dr. Katja Heubel of Tübingen’s Institute of Evolution and Ecology have been studying personality differences between marine animal parental figures and how this serves a role in the practice of filial cannibalism. The Common Goby, a marine fish of up to 6 cm in length, was the main focus of the study.
After a female Common Goby (Pomatoschistus) lays her eggs, the male takes care of them. Males oftentimes go to great lengths to ensure proper nourishing and survival of their offspring – “survival of the fittest” beginning even before the eggs hatch.
Vallon and Heube observed that male caregivers who are more active are more likely to eat their offspring in order to compensate for their own lack of food and energy. A male’s tiredness could be thought of as normal since he oftentimes will look after several clutches of different females and will clean the nests.
Yet, it is not a shot in the dark or “pick any egg” type of deal. A male goby will usually pick among the youngest, least valuable egg(s) to consume. Vallon and Heubel attempted to explain the male’s cannibalism as a method to get rid of damaged eggs. Reducing the amount of eggs means that the remaining ones are better supplied with oxygen.
The younger eggs are more frequently eaten because they have less reproductive value than the older, more developed eggs, in which the male has already invested more time and effort. The older eggs have a greater chance of reaching the stage of independency and hatchlings. Researchers have also found that the younger eggs are more nourishing for the adult male.
Author Hope Klug, a graduate student at the University of Florida, and his colleague, Michael Bonsall, a student at the University of Oxford, wanted to determine if there were other reasons why cannibalism among marine animals would occur. They modeled different scenarios of “virtual organisms” with a computer.
The results of their study, funded by the Royal Society in England and the U.S. National Science Foundation, are detailed in the December issue of the journal, The American Naturalist. They found that cannibalism was found to increase the parent’s reproductive rate, apparently increasing male attractiveness.
Therefore, they initially overproduce offspring and then later “remove” some of the inferior offspring. This general competition for resources and nourishment within their own kind may limit the amount of energy and time spent for each egg. So basically the eggs are left with two choices…grow up fast or get eaten.
At face value, filial cannibalism seems unsettling, destructive, and counterproductive. But studying the fish’s behavior further, we can find out why some fish eat their own eggs – as an adaptive behavior, to ensure the survival of “superior” offspring.
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