Why are Embryos so Tasty

TLDR: The prevalence of intense predation on eggs suggests that predators are important selective agents for egg characteristics.

Abstract: Recent decades of fieldwork have thoroughly established that the eggs of most animals are subject to intense predation. For example, temperate-zone open-nesting bird species lose about 35% of their eggs to predators (Lack 1954, 1968); among tropical species, the figure is as high as 50% (Ricklefs 1969). Indirect evidence from egg care and from life history characteristics of reptiles and amphibians (Tinkle et al. 1970) suggests high egg loss to predators. The same may be said for fish, and those with pelagic and demersal eggs have particularly high egg mortality from predation (Barnaby 1944; Foerster and Ricker 1941; Sette 1943). Losses of eggs of insects to predators and parasites are often high (e.g., Clausen 1940; Clark et al. 1967). While some animals appear to be specialists at eating eggs (e.g., Emydocephalus sea snakes [Voris 1966]; myrid bugs [Lord 1971]; mites [Lindquist 1969]; Dasypeltis terrestrial snakes [Ditmars 1910]; Trichogramma parasitic Hymenoptera [Clausen 1940]), almost all carnivores and many omivores regularly include many kinds of eggs in their diets. Humans not only consume large numbers of many species of vertebrate eggs, but \"at Lake Texcoco [Mexico] the natives collect the eggs of several species of corixid [bugs] by submerging a sheath of straw on stems of hay into the water where corixids are abundant. The egg-laden stems are later exposed to the sun, dried, and prepared as an edible delicacy\" (Peters and Ulbrich 1973). A single species of egg parasite, Trichogramnma minutum, has been reared from 162 species of insect eggs (Thompson 1958), which strongly suggests that insect eggs are generally palatable. The prevalence of intense predation on eggs suggests that predators are important selective agents for egg characteristics. Cryptic coloration of eggs of open-nesting birds is well documented (Cott 1952, 1953, 1954; Lack 1968). Egg protection by nesting on sea cliffs, islands, trees, or even near colonies of ants and wasps (Janzen 1969a; Meyers 1929, 1935; Moreau 1936, 1942) is commonplace. Frogs may lay their eggs on inaccessible foliage high over water (e.g., Pyburn and Glidewell 1971), and insects and fish display a wide variety of behaviors that render eggs inaccessible to predators.