Polyembryony
Encyclopedia
Polyembryony is the phenomenon of two or more embryo
s developing from a single fertilized egg (in humans, identical twins). Polyembryony occurs regularly in many plants and animals. The nine banded armadillo, for instance, usually gives birth to four identical young. Polyembryony is best known among parasitoid
insects of the order Hymenoptera
, families Encyrtidae
, Dryinidae
, Platygasteridae and Braconidae
. The term is also used in botany
to describe the phenomenon of two seedlings emerging from one seed
.
In plants, polyembryony often gives rise to the enigma of a single offspring.
The mechanism underlying this phenonomena is programmed cell death
(PCD) which removes all but one embryo. PCD serves to halt competition among monozygotic embryos in order to ensure survival of one embryo. 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. These latter larvae patrol the host and kill any other parasitoids they find with the exception of their siblings, usually sisters.
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s developing from a single fertilized egg (in humans, identical twins). Polyembryony occurs regularly in many plants and animals. The nine banded armadillo, for instance, usually gives birth to four identical young. Polyembryony is best known among parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
insects of the order Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, families Encyrtidae
Encyrtidae
Encyrtidae is a large family of parasitic wasps, with some 3710 described species in some 455 genera . The larvae of the majority are primary parasitoids on Hemiptera, though other hosts are attacked, and details of the life history can be variable Encyrtidae is a large family of parasitic wasps,...
, Dryinidae
Dryinidae
Dryinidae is a family of hymenopteran insects with about 1,400 described species found worldwide. These are solitary wasps whose larvae are parasitoids on other insects. The only known hosts are Hemiptera, especially leafhoppers....
, Platygasteridae and Braconidae
Braconidae
Braconidae is a family of parasitoid wasps and one of the richest families of insects. Between 50,000 and 150,000 species exist worldwide. The species are grouped into about 45 subfamilies and 1,000 genera, some important ones being: Ademon, Aphanta, Asobara, Bracon hebetor, Cenocoelius, Chaenusa,...
. The term is also used in botany
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
to describe the phenomenon of two seedlings emerging from one seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
.
In plants, polyembryony often gives rise to the enigma of a single offspring.
The mechanism underlying this phenonomena is programmed cell death
Programmed cell death
Programmed cell-death is death of a cell in any form, mediated by an intracellular program. PCD is carried out in a regulated process which generally confers advantage during an organism's life-cycle...
(PCD) which removes all but one embryo. PCD serves to halt competition among monozygotic embryos in order to ensure survival of one embryo. A more striking example of the use of polyembryony as a competitive reproductive tool is found in the parasitoid Hymenoptera family Encyrtidae
Encyrtidae
Encyrtidae is a large family of parasitic wasps, with some 3710 described species in some 455 genera . The larvae of the majority are primary parasitoids on Hemiptera, though other hosts are attacked, and details of the life history can be variable Encyrtidae is a large family of parasitic wasps,...
. 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. These latter larvae patrol the host and kill any other parasitoids they find with the exception of their siblings, usually sisters.