Hybrid Inviability Sperm and egg from the two species may combine, but the genetic information

is insufficient to carry the organism through normal development.

The embryo dies after a few cleavages, or some time before birth/hatching. Example 1: Drosophila spp. Despite their superficially similar appearance, D. melanogaster

x and D. simulans have incompatible alleles

x for nuclear pore proteins.

and have incompatible alleles for nuclear pore proteins. Dysfunction of this vital gene results in inviable hybrids. Example 2: Tigers (Panthera tigris) and Leopards (Panthera pardus) Tigers and Lions are sister taxa.

Their hybrid offspring are viable and robust, but sterile.

A mating between a lion and leopard will produce sterile hybrids.

A mating between a tiger and leopard will produce inviable hybrids.

Zygotes divide, but embryo miscarries or is stillborn. Example 2: Rana draytonii and Rana catesbeiana Although members of the same genus, they have been geographically

x separated for tens of thousands of years.

separated for tens of thousands of years. If zygotes form, they are inviable.

This has created a conservation problem in areas where Bullfrogs

x have been introduced in Red-legged Frog habitat.

have been introduced in Red-legged Frog habitat. Adding insult to injury, Bullfrogs will voraciously eat juvenile frogs. x =