Parthenogenesis
It has Greek origin as “parthenos” which means “virgin birth”. Virgin birth means development of egg cell into an embryo without being fertilized by sperm. Hence parthenogenesis has been defined as the asexual reproduction in which organism developes from an unfertilized egg. Many insects reproduce by this mode of reproduction. This may occur due to lack of viable male to fertilise eggs.
- Parthenogenesis can be broadly grouped on the three bases:
- Based on natural occurrence
- Based on sex of offspring
- Based on division of germ cells
BASED ON NATURAL OCCURRENCE
(A) FACULTATIVE PARTHENOGENESIS
- Female can reproduce via sexual or asexual mode.
- Sexually reproducing female switch to asexual reproduction as the viable male is absent from the habitat.
- Automixis during reductional division i.e. meiosis enable the sexual animal to reproduce asexually.
- Mayfly exhibits facultative parthenogenesis.
(B) OBLIGATE PARTHENOGENESIS
- Female can reproduce only via asexual mode of reproduction.
- Few invertebrates solely reproduce asexually.
- Nematus oligospilus reproduce via parthenogenesis when it has been placed in Southern Hemisphere
BASED ON SEX OF OFFSPRING
(A) ARRHENOTOKY – The resultant of parthenogenesis is male offspring.
Example- Hymenoptera
(B) THELYTOKY – The resultant of parthenogenesis is female offspring.
Example- Aphids.
(C) DEUTEROTOKY – Male and female, both can me the resultants of parthenogenesis. Example- Cynipid wasp.
BASED ON DIVISION OF GERM CELLS
(A) HAPLO-DIPLOIDY – Germ cells undergoes complete meiosis to form oocyte which either fertilises to form female embryo or unfertilise to form male.
Example- Hymenoptera (Bees)
(B) APOMICTIC – Meiosis is absent. The egg cell is the resultant of mitotic division, thus egg has diploid genetic makeup and develops a diploid embryo.
Example- Aphids
(C) AUTOMICTIC – Germ cell undergoes Meiosis but chromosomes unable to separate at Anaphase -II or two nuclei fuse and diploid chromosome number is restored. Female produce as the resultant.
Example- Phasmids (stick insects).
Example: PARTHENOGENESIS IN Apis mellifera :
- They are colonial insect and are polymorphic as they exist in three forms i.e. (a) fertile Queen bee, (b) fertile male or Drone (c) Infertile worker bee.
- Queen bee mates several drones and receives millions of spermatozoa. Mating takes place at the height of 25 meter in the air and temperature exceeding 20°C.
- Queen bee’s reproductive system consists of Spermatheca that can store millions of spermatozoa and nourish them. Hence Queen bee controls the fertilization of the oocyte or egg.
- Fertilized egg will determine to become female worker bee or queen bee.
- Unfertilized egg will determine to become Drone or male. Thus, Drones are produced by Arrhenotoky or Haplo-diploidy parthenogenesis.
- Note*- Queen lays eggs singly in the comb which will take care by female worker bee. Larva of queen bee is solely fed royal jelly throughout development. Larvae of worker bee and Drone are fed royal jelly for first three days and later by pollen and honey.
