Siblicide

I continue to question the interpretation of "fatal sibling aggression" and active brood reduction as a means of maximizing productivity[…]. To me, the data clearly indicate a simple response to food availability, with the oldest young passively out-competing its smaller sibling for a limited resource. I still have not seen data to support "siblicide" as a strategy.

Oophagy and adelphophagy, which are forms of embryonic cannibalism, occur in both cartilaginous and bony fishes. They are variations on the tactic of siblicide (Mock, 1984) as a reproductive strategy. In oophagy, embryos feed upon sibling eggs. […] Adelphophagy, literally eating one's brother, is also known in sharks as intrauterine embryonic cannibalism[…].

Obligate siblicide is best known in various eagles, boobies, and pelicans. All lay two eggs, hatching is asynchronus, and usually the elder sib kills its younger sib soon after hatch. From the parent's perspective, the second egg/chick serves as insurance against the unexpected failure of the first[…]. Interestingly, obligate siblicide seems to be independent of prevailing food at the time of the junior sibling[']s demise.

If siblicides are victim-based, a mother clearly cannot improve her fitness by producing fewer eggs. Less obviously, mothers may eventually be able to gain by laying more, until eventually they are constrained by the costs of eggs.

One of the more recent examinations of siblicide cases is [John M.] Dawson and [Patrick A.] Langan's Special Report on Murder in Families, published through the Bureau of Justice Statistics (1994). […] According to their findings, 85% of siblicide offenders and 73% of siblicide victims were male. […] Alcohol was reported to play a role in approximately one half of the siblicides in Dawson and Langan's study.

Infanticide, siblicide, cannibalism, rape, and lethal combat have been documented in many kinds of animals.