Trophic egg

A trophic egg, in most species that produce them, usually is an unfertilised egg because its function is not reproduction but nutrition; in essence it serves as food for offspring hatched from viable eggs. The production of trophic eggs has been observed in a highly diverse range of species, including fish, amphibians, spiders and insects. The function is not limited to any particular level of parental care, but occurs in sub-social species of insects as well as in Leptodactylus fallax, a species of frog known for its close parental care.

Parents of some species deliver trophic eggs directly to their offspring, whereas some other species simply produce the trophic eggs after laying the viable eggs; they then leave the trophic eggs where the viable offspring are likely to find them.

The mackerel sharks present the most extreme example of proximity between reproductive eggs and trophic eggs; their viable offspring feed on trophic eggs in utero.

Despite the diversity of species and life strategies in which trophic eggs occur, all trophic egg functions are similarly derived from similar ancestral functions, which once amounted to the sacrifice of potential future offspring in order to provide food for the survival of rival (usually earlier) offspring. In more derived examples the trophic eggs are not viable, being neither fertilised, nor even fully formed in some cases, so they do not represent actually potential offspring, although they still represent parental investment corresponding to the amount of food it took to produce them.


Trophic eggs are not always morphologically distinct from normal reproductive eggs; however if there is no physical distinction there tends to be some kind of specialised behaviour in the way that trophic eggs are delivered by the parents.

In some beetles, trophic eggs are paler in colour and softer in texture than reproductive eggs, with a smoother surface on the chorion.[1] It has also been found that trophic eggs in ants have a less pronounced reticulate pattern on the chorion.[2]

The morphological differences may arise due to the fact that mothers invest less energy in the production of trophic eggs than viable eggs.

Summary of cross-species morphology and behaviour


Species (Family) Trophic eggs (TE) morphologically distinct? Specialised Behaviour in delivery of TEs?
Vertebrates Tree frogs (Dendrobatidae, Leptodactylidae, Hylidae) No Yes (repeated TE laying)
Bagrus meridionalis (Bagridae) ? Yes (repeated TE laying)
Latimeria chalumnae (Coelacanthidae) Yes Yes (TEs supplied continually in oviduct)
Insects Adomerus triguttulus (Cydnidae) Yes Yes (repeated TE laying)
Anurogryllus muticus (Gryllidae) Yes Yes (repeated TE laying)
Eusocial insects Various ants (Formicidae); queen-produced eggs Yes Yes (delivery to offspring)
Various ants (Formicidae); worker-produced eggs Yes Yes (delivery to offspring)
Other invertebrates Several polychaete worms (Spionidae) Yes ?
Amaurobius ferox (Amaurobiidae) ? Yes (laid after offspring hatch)
Coelotes terrestris (Agelenidae) ? Yes (laid after offspring hatch)
Several prosobranch gastropods (Buccinidae, Calyptraeidae, Muricidae) Yes Yes


Adaptive plasticity

The behaviour of trophic egg-laying species depends highly on their environment and can be modified via adaptive plasticity in response to environmental variation. The ratio of trophic to viable eggs is determined by the availability of resources, although the absolute number of trophic eggs does not always change.[4] The production of fewer viable eggs ensures that each hatched nymph will have a larger provision of trophic eggs; and therefore give each individual an enhanced chance of survival when external resources are limited. Females can adaptively adjust the egg ratio in response to environmental drivers prior to oviposition.

Reproductive success

When resources are limited, the presence of trophic eggs greatly increases the maturation and survival rates of offspring. There are some species such as the subsocial burrower bug Canthophorus niveimarginatus (Heteroptera: Cydnidae) whose offspring cannot survive at all without the provision of trophic eggs. The nymphs starve to death because trophic eggs are the only thing they are able to feed on.[5] However, when other suitable sources of food are plentiful, feeding on trophic eggs has little effect on brood success.[6]

Sibling cannibalism, common in many spider species, is not affected by the proportion of trophic eggs, since viable eggs are oviposited and hatch synchronously, before trophic eggs are laid. In the spider Amaurobius ferox, trophic eggs are laid the day after spiderlings emerge from their egg sac. The mother’s reproductive behaviour is modified by the behaviour of her offspring, and their presence inhibits the second generation of eggs from maturing; instead they are released as infertile trophic eggs. Converting the second generation into food for the first ultimately boosts the mother’s reproductive success.[7]

Evolutionary theory

There are no concrete explanations for the evolution of trophic eggs. The two main conflicting arguments are:

  1. They are an evolved maternal phenotype
  2. They are simply a failed generation of offspring, produced as a result of reproductive stochasticity.

If they have evolved (and are now distinct) from functionless by-products of failed reproduction, then trophic eggs should be more easily available and provide more nutrients to the offspring than their evolutionary predecessors. There seems to be clear evidence of this adaptation in many species. This can be seen in mothers making an effort to distribute trophic eggs to their offspring; and/or eggs which are specialised for the nutritional needs of the offspring. However, in many species, the two types of egg are indistinguishable. Various hypotheses could potentially be tested to determine whether trophic eggs are indeed an evolved phenotype.[3]

It has been suggested that trophic egg-laying evolved as a consequence of limited egg size, since larger eggs with more nutrient supply would require the mother to have a larger body size. Thus, the production of more eggs, some of which are not intended to reach maturity. It is relatively simple for the mother to adjust the ratio of fertilised to non-fertilised eggs, in response to environmental conditions.

An alternative to trophic egg-laying is sibling cannibalism; however this requires the mother to regulate the synchrony of hatching times. However, in this case eggs which are not eaten would continue to develop. If it is difficult for the mother to achieve this synchrony, trophic eggs are a sensible alternative in ensuring that the offspring that hatches will be fed sufficiently.



  1. Ento, K; Araya, K; Kudo, S (2008). "Trophic egg provisioning in a passalid beetle (Coleoptera)". European Journal of Entomology. 105: 99–104.
  2. Koedam, D; Velthausz, P H; v d Krift, T; Dohmen, M R; Sommeijer, M J (2008). "Morphology of reproductive and trophic eggs and their controlled release by workers in Trigona (Tetragonisca) angustula llliger (Apidae, Meliponinae)". Physiological Entomology. 21: 289–296. doi:10.1111/j.1365-3032.1996.tb00867.x.
  3. 1 2 Perry, J; Roitberg, B D (2006). "Trophic egg laying: hypotheses and tests". Oikos. 112: 706–714. doi:10.1111/j.0030-1299.2006.14498.x.
  4. 1 2 Kudo, S; Nakahira, T (2005). "Trophic-egg production in a subsocial bug: adaptive plasticity in response to resource conditions". Oikos. 111: 459–464. doi:10.1111/j.1600-0706.2005.14173.x.
  5. Baba, N; Hironaka, M; Hosokawa, T; Mukai, H; Nomakuchi, S; Ueno, T (2011). "Trophic eggs compensate for poor offspring feeding capacity in a subsocial burrower bug". Biology Letters. 7: 194–196. doi:10.1098/rsbl.2010.0707.
  6. Kudo, S; Nakahira, T (2004). "Effects of trophic-eggs on offspring performance and rivalry in a sub-social bug". Oikos. 107: 28–35. doi:10.1111/j.0030-1299.2004.13169.x.
  7. Won Kim, K; Roland, C (2000). "Trophic egg laying in the spider, Amaurobius ferox: mother–offspring interactions and functional value". Behavioural Processes. 50: 31–42. doi:10.1016/S0376-6357(00)00091-7.
  8. Peters, John M.; Queller, David; Imperatriz-Fonseca, Vera L.; Roubik, David W.; Strassmann, Joan (1999). "Mate Number, kin selection and social conflicts in stingless bees and honeybees". The Royal Society.
  9. Dietemann, V; Peeters, C (2000). "Queen influence on the shift from trophic to reproductive eggs laid by workers of the ponerine ant Pachycondyla apicalis". Insectes Sociaux. 47: 223–228. doi:10.1007/PL00001707.
  10. Won Kim, K; Roland, C (2000). "Trophic egg laying in the spider, Amaurobius ferox: mother–offspring interactions and functional value". Behavioural Processes. 50: 31–42. doi:10.1016/S0376-6357(00)00091-7.
  11. Kitching, R L (2000). Food Webs and Container Habitats: The Natural History and Ecology of Phytotelmata. Cambridge University Press. pp. 55–56.
  12. Gibson, R; Buley, K (2004). "Maternal Care and Obligatory Oophagy in Leptodactylus fallax: A New Reproductive Mode in Frogs". Copeia. 1: 128–135. doi:10.1643/CE-02-091R2.
  13. Hoar, W S; Randall, D J (1988). The Physiology of Developing Fish: Viviparity and posthatching juveniles. Academic Press. pp. 43–71.

Further reading

This article is issued from Wikipedia - version of the 6/6/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.