Reproductive Methods

Parthenogenesis

Development from unfertilized eggs, producing offspring without male contribution
12 Animals
Overview

Understanding This Category

Parthenogenesis is a form of asexual reproduction in which an embryo develops from an unfertilized egg, producing offspring without genetic contribution from sperm. It can occur as an obligate life-history strategy or facultatively when mates are absent.

Parthenogenesis is when females make eggs that develop without fertilization. Types include arrhenotoky (haploid eggs in many Hymenoptera), automixis, and apomixis, which keep different amounts of genetic variation. It helps rapid growth, colonizing by one female, or surviving when mates are rare. It occurs in aphids, stick insects, some bees/wasps/ants, Daphnia, rotifers, and some lizards, snakes, sharks, and birds.

Key Characteristics

Embryos develop from unfertilized eggs; no sperm contribution to initiating development
Can be obligate (exclusive) or facultative (used when mates are unavailable)
Multiple cytological routes (e.g., haploid development, automixis, apomixis) that differ in genetic outcomes
Often enables rapid population increase and reproduction in low-density or newly colonized habitats
May alternate with sexual reproduction in some species (cyclical parthenogenesis)
Typically reduces recombination and can lower genetic diversity relative to sexual reproduction (depending on mechanism)
Examples

Animal Examples

Iconic Examples

Whiptail lizards (e.g., New Mexico whiptail) A classic, textbook example of obligate parthenogenesis in a vertebrate-entire lineages reproduce without males.
Komodo dragon A widely publicized case showing that large, charismatic reptiles can reproduce by facultative parthenogenesis.
Aphids Among the best-known examples of cyclical parthenogenesis, especially in agricultural contexts.
Honey bee A famous case of parthenogenesis in a major model of social insects: males arise from unfertilized eggs.
Water fleas (Daphnia) A well-known freshwater model organism that alternates between clonal (parthenogenetic) and sexual reproduction depending on conditions.

Surprising Examples

Bonnethead shark
Boa constrictor
California condor
American crocodile

Extreme Examples

Bdelloid rotifers
Marbled crayfish
Aphids

Found across: Insects (e.g., aphids, bees/wasps/ants, stick insects), Arachnids (some mites, ticks, and spiders), Crustaceans (e.g., Daphnia; some crayfish), Rotifers (notably bdelloids), Nematodes (some lineages), Reptiles (many lizards; documented in snakes and monitor lizards), Fishes (including some sharks and rays; some bony fish lineages), Amphibians (some salamanders and frogs via hybrid/complex systems), Birds (rare, but documented in a few species)

Fun Facts

Did You Know?

Parthenogenesis isn't always "all-female": in species with ZW sex chromosomes (like Komodo dragons), unfertilized eggs can produce ZZ offspring-males-so a lone female can found a new population by first producing sons and later breeding sexually.

"Virgin birth" doesn't necessarily mean cloning. Many vertebrate cases use automixis (the egg fuses with one of its own products), which restores diploidy but often makes offspring much more genetically uniform (increased homozygosity) rather than identical copies.

Some animals treat sex like a seasonal "mode switch." Aphids and water fleas (Daphnia) can crank out multiple generations of parthenogenetic daughters when conditions are good, then switch back to sexual reproduction to make tougher, genetically mixed resting eggs for hard times.

Parthenogenetic lizard species still perform courtship and mating-like behavior. Female whiptail lizards often "pseudocopulate," and the behavior is linked to higher egg output-sex-like behavior can boost reproduction even when sperm are irrelevant.

Parthenogenesis can be an emergency exit rather than a lifestyle. In sharks, snakes, and some birds, facultative parthenogenesis can occur when females are isolated from males-producing rare offspring without fertilization, but not necessarily creating a thriving long-term lineage.

Parthenogenesis Animals