Votan is the collective name for the alien species that invaded Earth in Arks.
Known species are:
In the town of Defiance, the highest proportion of Votan is Castithans. Relationships between the various Votan races differ greatly: Irathients and Castithans loathe each other, but Irathients get on well with Liberata and Sensoths, and have no strong opinion of Indogenes. Castithans get along with Liberata and Sensoths as long as they are respectful to them, while they have a bickering relationship with Indogenes. There is an almost universal fear and hatred of the Volge, who are known to wipe out all in front of them. Many Votans live under the auspices of the Votanis Collective, a government of Castithans, Indogenes, Irathients, Liberata, and Sensoths. What few Gulanee have survived are also members of the Collective, but their numbers are so low that they are rarely counted or considered. The Volge, of course, cooperate with no one and are not members.
Biologically, none of the Votans have independent mitochondria the way that animals on Earth do. Their equivalent cellular structures did not originate from an independent bacterial genome.
Humans, Castithans, and Irathients are similar enough biologically to allow for heterosexual coitus with no apparent difficulty. Datak Tarr, a Castithan, had a regular liasion with Kenya Rosewater, a Human. Eddie Braddock (a Human) was also shown copulating with an un-named Castithan prostitute at the NeedWant in "Brothers in Arms". In "The Serpent's Egg" Irisa (an Irathient) and Tommy Lasalle (a Human) begin a sexual relationship.
Some but not all of the Votan species can actually interbreed with humans to create hybrids. Both Castithans and Irathients can create hybrids with humans, though with a low success rate due to the health risks involved for both mother and fetus. Humans are diploid, receiving one set of chromosomes from the mother and one from the father. Irathients are triploid, receiving one from the father but two from the mother - meaning that the only possible human/Irathient hybrids are those with a Irathient mother and human father. Castithans are androploid - all chromosomes come from the father, not the mother, so male Castithans can have children with female humans.