To most humans, consuming another individual of the same species, much less one’s own children is deemed unthinkable. You might even consider from an evolutionary standpoint, isn’t this behavior pointless or destructive? However, to the amphibian species known as A. femoralis, cannibalism of unrelated groups of eggs or “clutches” is common practice. For A. femoralis females, cannibalism is actually an adaptive behavior that produces various benefits, necessary for survival. Cannibalism can lead to better access to food, reduce competition for offspring and provide more mating opportunities. Believe it or not, good parental care begins with eating other competition’s offspring to obtain better access to food and mates. This exciting finding leads us to our next question: what conditions or motivations allow for or inhibit clutch cannibalism?
In order to answer this question, several variables that influence clutch cannibalism were selected and tested in this experiment including the presence of a father, female oviposition state and female familiarity with their home environment. A. femoralis females were randomly assigned to four test conditions labeled “home”, “in out”, “in out M+”, and “in out M-”. The condition “home” involved removing a female from a familiar environment, adding an unrelated clutch and returning the same female to the terrarium. The condition “in out” referred to moving females to an unfamiliar terrarium, containing an unrelated clutch. The condition in “out M+” referred to when females cannibalize an unrelated clutch, in the presence of their father and consequently a clutch of their own is produced. The condition in “out M-” referred to when females are transferred to foreign terrarium, with an unrelated clutch in the presence of its father, and the father is shortly removed after clutch production. All of these different experimental conditions serve as potential opportunities in which A. femoralis females exhibit unrelated clutch cannibalism and test the longstanding theory that oviposition, familiarity with environment and (lack of) father presence all determine clutch cannibalism occurrence.
It is important to consider previous hypotheses made or causes attributed to cannibalism behavior, in order to understand the mechanisms by which clutch cannibalism occurs. Potential motivations for cannibalism behavior have been previously attributed to nutritional motivation. However this factor was discounted as being significant in this study, as all females received equal rations of food for all test conditions. The next prominent variable included reproductive benefits, which was disproved as parental care does not have a significant effect on clutch cannibalism. Predation or competition are not viable causes for clutch cannibalism, as females would need high rates of cannibalism in order to have a significant impact on competition. Ultimately, male presence and previous oviposition state were the two factors found to have a direct effect on unrelated clutch cannibalism in A. femoralis females.
Within this study, clutch cannibalism was observed across all experimental models, however, two principal factors including oviposition state and (lack of) father presence, drive its occurrence if at all. Having previous oviposition and father presence consistently reduced cannibalistic behavior across all models, these results propose that male territoriality and female reproductive state is imperative for clutch cannibalism. Big picture implications in this study should consider the role of male territoriality in the evolution of parental care. Surprisingly, a female’s familiarity with an environment was found to have no significance on clutch cannibalism, this could be due to variability or adaptiveness of these species in new environments. The cannibalistic behavior of the A. femoralis species is truly a rare yet fascinating phenomenon, by challenging the long held opinion labeling cannibalism as a maladaptive and destructive behavior.
