Polyembryony

The evolution of polyembryony and the potential evolutionary advantages that may entail have been studied. In parasitoid wasps, there are several hypotheses surrounding the evolutionary advantages of polyembryony, one of them being that it allows female wasps that are small in size to increase the number of potential offspring in comparison to wasps that are mono embryonic. There are limitations to monoembryony, but with this method of development, multiple embryos can be derived from each of the individual eggs that are laid. == Vertebrates ==

Armadillos are the most well studied vertebrate that undergoes polyembryony, with six species of armadillo in the genus Dasypus that are always polyembryonic. The nine banded armadillo, for instance, always gives birth to four identical young. There are two conditions that are expected to promote the evolution of polyembryony: the mother does not know the environmental conditions of her offspring as in the case of parasitoids, or a constraint on reproduction. == Invertebrates ==

A more striking example of the use of polyembryony as a competitive reproductive tool is found in the parasitoid Hymenoptera, family Encyrtidae. The progeny of the splitting embryo develop into at least two forms, those that will develop into adults and those that become a type of soldier, called precocious larvae. From one egg, these insects can produce over thousands of offspring. Through genotype analysis and molecular data, it has been suggested that polyembryony happens in the entire bryozoan order Cyclostomatida. == Plants ==

The term is also used in botany to describe the phenomenon of multiple seedlings emerging from one embryo. Around 20 genera of gymnosperms undergo polyembryony, termed "cleavage polyembryony," where the original zygote splits into many identical embryos. Antonie van Leeuwenhoek first described polyembryony in 1719 when the seed in Citrus was observed to have two germinating embryos. In Citrus, polyembryony is genetically controlled by a shared polyembryony locus among the species, determined by single-nucleotide polymorphism in the genotypes sequenced. The variation within the species of citrus is based on the amount of embryos that develop, the impact of the environment, and gene expression. As with other species, due to the many embryos developing in close proximity, competition occurs, which can cause variation in seed success or vigor. seeds with more than one embryo ==See also==