A topic that frequently comes up among isopod hobbyists is the increasingly large available amount of isopod mutations throughout separate species. Many people struggle with understanding the concept of mutations, so today we're going to discuss what exactly is a mutation, when does it become a morph, and how does it become that way?
Oniscus asellus "Maple orange, B.C. Canada" is both a recessive trait, and a locale.
An incorrect assumption that is commonly made about mutations throughout isopods is that they are a separate species. After all, they do make the animals look drastically different. The truth is, a mutation doesn't affect the species, only the appearance of the animal. So what exactly changes? The answer lies in what is not visible: the genetic components of the animal. Mutations can occur over 3 methods: recessive, co-dominant (shortened to co-dom), and line bred.
Typically in sexually producing species (male and female reproduction), offspring receive one half of their genes from each parent. For recessive mutations, each parent needs to carry the gene in order for the offspring to express the trait. For co-dom, only one parent needs to carry the gene (and will visually express it) in order for offspring to also express the trait. In the world of isopods, the only known co-dom gene is "lava" in P. scaber, so this article will focus on the other two.
A well known example of recessive genetics that most people already know about is albinism. Albino animals rarely, but naturally occur, in populations. These genes are quickly weeded out of wild populations, because the animals are more evident in their environment and either preyed on quickly or, in the case of predators, starve because they are not as successful hunters. In a captive environment, animals thrive under the care of human intervention and so we are able to culture and see all kinds of genetic diversity.
Porcellio scaber "Spanish orange" is probably the most well known recessive trait in the isopod trade.
The easiest way to explain recessive genetics with with Punnet squares. A Punnet square is 4 lines crossing each other, on the outside the genes of the parents are written, on the inside the potential combinations are written. In the following graphics, the orange gene in isopods will be discussed. A capital, black O is a non carrier gene, and represents a dominant trait. A small orange o is a carrier gene, and represents a recessive trait. If an animal has the genes Oo, it means that it is what's called a "carrier" for the trait. If an animal is a carrier, its has the possibility to produce offspring that visually display the trait, but due to the dominant O gene it does not express it. Animals like this are called "heterozygous" for genetic traits, the root word "hetero" coming from Greek, which means "different". Animals with the same gene are called "homozygous", "homo" coming from Greek meaning "same". In the following examples homozygous will refer to animals with 2 recessive genes. A homozygous animal with two recessive genes, in the following examples this is illustrated by oo, the animal will visually express the genetic traits.
This first example is two heterozygous parents, each a carrier for the orange gene. When breeding together, 25% of their offspring are expected to not carry the gene, 50% are expected to carry the gene but not express it, and 25% will be visually orange and homozygous for the trait.
In this next example, one parent is not a carrier while the other is heterozygous. No offspring will present the trait visually, but 50% will be carriers.
Lastly, an example of a visual homozygous parent crossed to a non visual heterozygous parent. 50% of offspring will be heterozygous carriers, and the other 50% will be homozygous and visually express the trait.
If neither parents carry a gene, all offspring will be noncarrier normals. If both parents are homozygous expressing, all offspring should be homozygous and visually express as well.
Now, here is where it gets tricky: most isopods are quite promiscuous little minxes. One study on genetic diversity cited that up to 80% of offspring in the same brood of P. scaber can have separate fathers. In a litter of 30 mancae, that's twenty four separate males she bred with! To further complicate matters, isopods are sexually mature when they are only 25% grown. Their litters are smaller, but they are already breeding and reproducing at that size.
So, how does a random mutation become an established morph? First, the visually presenting animals must be separated from the main population. To ensure that there is reproduction, the animals should be sexed. Usually, if all the animals are female, there is no need to add additional animals from the main population, because once they are visible they have reached a size large enough to be fertilized. If they are male, 2-3 females per male should be added to the culture to encourage genetic diversity and pass on the genes.
The first generation is called "F1", and typically will be all heterozygous and not have any animals expressing the trait. At this point, adult non visual animals should be removed from the isolated culture. Now the next generation, or the offspring of F1, is called the "F2", or second generation. In this set of offspring, there should be some animals expressing the trait. Offspring expressing the trait in the F2 generation should be isolated from F1. This method of producing and isolating the animals should continue, the number after F growing with each additional generation. Once the trait breeds true, meaning that all offspring visually present the trait with no normals occurring, for three generations, the trait is considered a proven morph and whoever isolated it may name it!
Recessive genes don't just affect color, they affect the pattern distribution on the animal too! Piebald and dalmatian traits are two such examples of recessive genes than affect the pattern of the animal. Recessive traits can also be further combined for more possibilities, for example orange and dalmatian have been combined to produce orange dalmatian animals.
The dalmatian trait in P. scaber affects patterning in the animal.
Orange dalmatian is a combination of orange and dalmatian traits.
The line breeding method of developing mutations is not quite so clear; it is a multifactoral gene with many separate influences. Over time and many generations, animals are selected for particular traits breeding towards a certain goal. Sometimes it is color, pattern, and has even been done to increase the size of an animal in captivity! The line breeding method is a bit more time consuming, because the animals do not express clear genetic traits. The same concept of several generations breeding true offspring to the desired standard applies; however the downside of this method is that animals may regress to previous traits and need constant monitoring and intervention to ensure that the traits expressed are the desired animals. Most keepers will routinely remove non-visual animals from these populations. Locales of different species are visually different, but the same species so sexually compatible and produce viable offspring. Locales are isopods that have been separated by either distance or geologic formations, causing the animals to develop differently over time. Some animals have absolutely stunning visual differences.
Two locales of Porcellio hoffmannseggi: "classic" and "black", collected from different areas of Spain.
The line breeding method is also applied to recessive genetics. Orange animals are bred to produce brighter oranges, or sometimes lighter, muted color. The genes that cause patterning are bred to produce animals with high contrast - because a low contrast animal (very little or a lot of pattern) will not be as visually appealing.
Mutations may be the single most exciting aspect of isopods. Many visually stunning animals have been produced with these methods, affecting color and patterning. The possibilities are endless!
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