Sterile & Producing Sterile Lines Explained
TL;DR Version:
- Females with the sterility gene are FERTILE.
- Males with the sterility gene are STERILE.
- A male cannot pass sterility onto his descendants.
- Producing sterile line gliders will not produce sterile joeys and are genetically no different than clean lines in this respect.
- A sterile line female has an unbroken maternal line to a sterile line founder and has the potential to give birth to sterile sons.
- While you can prove that a female does carry sterility when she bears a sterile son, you can never conclusively prove she does not carry sterility by her only bearing fertile sons.
- A producing sterile line glider will not pass on sterility, mate them to any mate that is an otherwise good match.
- A sterile line female’s mate does not influence her probability of having sterile sons.
- A sterile glider has the same quality of life as a neutered glider.
- There is no reason for a pet-only buyer to avoid a sterile, sterile line, or producing sterile line glider.
- The community response is completely disproportionate to the level of risk and the severity of the condition.
What is sterility in sugar gliders?
In sugar gliders, when we refer to sterility it is to a specific genetically inherited condition that causes certain male offspring to be sterile, often presenting as a lack of testicles or abnormally small testicles, but there is not always a visible indicator. There are many other ways that sterility can come about in an animal, but this specific genetic cause for sterility has been identified in several of our lineages, which are labeled sterile lines, or producing sterile lines.
How is it inherited?
Sterility is passed on like a dominant gene that doesn’t affect females. As a mental short cut, let’s think of it as a gene that codes for “no testicles.” When a female gets the no testicles gene, it doesn’t cause her any grief since she didn’t want those testicles anyway. But when a male gets the no testicles gene, he can’t have babies. So:
Females with the sterility gene are FERTILE.
Males with the sterility gene are STERILE.
Males with the sterility gene are STERILE.
Since the sterility gene only requires one copy to be inherited to cause sterility (in males), it is like a dominant gene, heterozygous males show the trait. This is similar to white face in sugar gliders, where only one parent needs to be white face in order to have white face joeys, it differs from white face in the fact that white face can affect females while sterility cannot. Much like how a standard grey glider from a white face parent will not have white face joeys because they do not carry the white face gene, a fertile male from sterile lines will not have sterile joeys because he does not carry the sterility gene.
If a male can have joeys, he is not sterile, does not carry the gene for sterility, cannot pass sterility onto his descendants, and will not produce sterile joeys. If a male cannot have joeys, he is sterile, and cannot pass on the gene for sterility because he cannot have joeys. Therefore:
A male cannot pass sterility onto his descendants.
A fertile male in a sterile line changes the line into a producing sterile line from him onward. A producing sterile line is a sterile line with a male anywhere in the direct lineage to the sterile line founder. If the joey you are looking at is a fertile male, or has a father, or grandfather, or great-grandfather, etc, that is on the path to the sterile line founder, that joey is in a producing sterile line.
Producing sterile line gliders will not have sterile joeys and are genetically no different than clean lines in this respect.
Lastly is the situation where the female joey you are interested in is in a sterile line. Not all females are in sterile lines, because a female who has a father or grandfather, etc. between her and the founder is in a producing sterile line. Only females and sterile males can be in a sterile line.
A sterile line female has an unbroken maternal line to a sterile line founder and has the potential to give birth to sterile sons.
A male cannot pass sterility onto his descendants.
A fertile male in a sterile line changes the line into a producing sterile line from him onward. A producing sterile line is a sterile line with a male anywhere in the direct lineage to the sterile line founder. If the joey you are looking at is a fertile male, or has a father, or grandfather, or great-grandfather, etc, that is on the path to the sterile line founder, that joey is in a producing sterile line.
Producing sterile line gliders will not have sterile joeys and are genetically no different than clean lines in this respect.
Lastly is the situation where the female joey you are interested in is in a sterile line. Not all females are in sterile lines, because a female who has a father or grandfather, etc. between her and the founder is in a producing sterile line. Only females and sterile males can be in a sterile line.
A sterile line female has an unbroken maternal line to a sterile line founder and has the potential to give birth to sterile sons.
Not all females in a sterile line can give birth to sterile sons, in fact the vast majority cannot. A female that can give birth to sterile males would be expected to have about half of her sons be sterile, and the other half to be fertile. Half of her daughters would be expected to be carriers (able to produce sterile joeys) while the other half would never produce sterile descendants. This is based on statistical probability, as it is an equal and random chance to inherit either sterility or not sterility. In practice you can flip a coin and get heads 5-6 times in a row before a tails. Small sample sizes do not always accurately reflect the underlying probabilities.
Therefore: |
While you can prove that a female does carry sterility when she bears a sterile son, you can never conclusively prove she does not carry sterility by her only bearing fertile sons.

If you know how many generations back the last sterile male was born, you can determine the probability that a sterile line female inherited the gene from the last known sterile producing female. 0.5 to the power of the number of generations times 100%. If a female’s mother had sterile sons, she has a 50% chance of being a carrier. If her grandmother had sterile sons, she would have a 25% chance of inheriting it, great-grandmother 12.5% chance, and so on.
Additionally, it can be informative to know how many joeys each generation produced without producing a sterile. If a pair was only allowed to have 3-4 joeys before being retired and some of them were girls, that wouldn’t tell you much. But if the pair had 20 joeys, 10 of them males, none of them sterile, and none of their sisters produced sterile sons, then that can be informative, even though it is not conclusive.
The more generations you have between your girl and the last known sterile, and the more joeys each generation has had without producing a sterile, the lower the chances your girl is a carrier. You will have to decide for yourself at what point you consider it an acceptable risk.
Additionally, it can be informative to know how many joeys each generation produced without producing a sterile. If a pair was only allowed to have 3-4 joeys before being retired and some of them were girls, that wouldn’t tell you much. But if the pair had 20 joeys, 10 of them males, none of them sterile, and none of their sisters produced sterile sons, then that can be informative, even though it is not conclusive.
The more generations you have between your girl and the last known sterile, and the more joeys each generation has had without producing a sterile, the lower the chances your girl is a carrier. You will have to decide for yourself at what point you consider it an acceptable risk.
This is where generation counting would be helpful if the community used it wisely, which they don’t. Sadly, most generation counting does not refer to the last known sterile but rather the first. In one lineage the white face blonde generational count was hijacked into a sterility generation count around generation 6.
How do I chose a mate for my producing sterile line?
A producing sterile line glider will not pass on sterility, mate them to any mate that is an otherwise good match.
As of yet, there is not a reason to believe there is additional risk mating a producing sterile line to another producing sterile line, but some breeders caution against it “just in case”. I see this as wrong as thinking crossing a grey to a grey could produce a white face, in other words, neither parent has the gene so the kid is not getting it either. The same logic applies when mating a producing sterile to a “clean line”, neither have the gene, so the kid is not getting it either. Mating a producing sterile line
male to a sterile line female has the same chance of resulting in sterile sons as mating a clean line male to a sterile line female, since it is the sterile line female that determines it.
male to a sterile line female has the same chance of resulting in sterile sons as mating a clean line male to a sterile line female, since it is the sterile line female that determines it.
How do I choose a mate for my sterile line female?
A sterile line female’s mate does not influence her probability of having sterile sons.
You can’t mate a sterile line to a sterile line since by definition any male capable of mating is a producing line, and as a producing sterile line he can’t pass on sterility so he is functionally the same as a clean line male in that regard. Once again, “just in case”, you might avoid mating to another sterile lineage, especially if she and her intended producing sterile mate are both close to their founders.
Some breeders say that mating sterile line to clean line makes the clean line a sterile line, and will refuse to sell their joeys as mates. This is absolute prejudicial nonsense. It's equivalent to saying that if a black person and a white person have a baby, then the white person's siblings and parents will turn black. A glider would not be considered sterile line just because one of their siblings was mated into one. The seller stands to lose nothing, and none of their other joeys are affected. These sellers are simply discriminating against breeders of sterile lines.
What if my pair produces a sterile joey?
A sterile glider has the same quality of life as a neutered glider.
...Minus the horrific experience of having his testicles cut off. Please mark in the Pet Glider database that he is sterile and that his mother produced sterile sons. Sell him as a pet-only and save $50-$250 on a neuter, then decide if you want to spend that savings on his dad’s procedure instead, or re-mate the father and retire the mother, or continue to breed and sell the joeys as pet-only. Also, please track me down, as I am interested in knowing which lines are still actively producing sterile sons.
There is no reason for a pet-only buyer to avoid a sterile, sterile line, or producing sterile line glider.
What about the $tigma?
The community response to sterile lines is completely disproportionate to the level of risk and the severity of the condition.
The taboo against sterile lines is a real market force, reducing the selling value of joeys in these lines and increasing the difficulty of finding homes for them. It can be frustrating to experience the methods of peer pressure used in the community to discourage breeders and buyers.
Many Facebook groups have rules that require producing sterile and sterile lines to be labeled in their ad, and failure to do so will get you banned and reviewed in a beware group. Meanwhile, the rules specify that serious problems like wiggle, infections, or hand-raised simply need to say "TLC" in the ad. |
My personal experiences include ruthless name calling, insinuations against my character and motivations, suggestions to neuter and even put down my producing sterile male, lost customers, lower prices, and - my personal favorite - I had a woman forbid another driver from allowing my joey in the same car as her gliders.
Labeling and disclosure
There was much controversy in the past over sterile lines because they were not labeled or disclosed and people bought gliders to breed and ended up with sterile males unexpectedly. Pressure was put on breeders to label the lines to protect buyers that were not fluent in the sterile line lineages. The labels helped to reinforce a very negative and disproportionate stigma. The stigma has grown to be more of an issue than the actual genetic problem, which fades out as sterile producing breeders are retired. Now there is a push from some breeders to remove these labels on ads, especially on pet only ads where sterile lines are irrelevant anyway, and especially for producing sterile lines which have been unfairly stigmatized as equivalently risky to sterile lines.
As someone who bought expensive, colored gliders for breeding from breeders that claimed their lines were clean, I fully disclose my gliders' sterile lineage to anyone planning to breed and mention it to pet-only buyers as well. I understand this keeps the stigma alive, but until it is dead, I feel obligated to inform new breeders.
How did sterility originate?
In short no one knows.
Expanded answer. Our current best guess is a cross between caramel subspecies and our normal subspecies. Such a cross has been shown to produce sterile males, and there is some resemblance between caramels and champaigns (an old descriptor not commonly seen these days). One sterile line founder is a champaign herself, Sterling. And several other mosaic lines were paired with champaigns. However, one would then expect that any champaign would have produced sterile sons with any of our other gliders and that there would be many more sterile lines around, so who really knows?
For a long time it was assumed that inbreeding was the cause of the sterility, but this is not actually possible since the sterility is not recessive. Yes sterility and lowered fertility can be a consequence of inbreeding, but when it is, it is because the individual is inheriting recessive mutations in reproductive genes from both parents. Reduced fertility cause by inbreeding would be completely reversed after a single generation of mating with an unrelated glider. Obviously, full sterility would be harder to prove that with, since they can’t breed. The sterility we see in gliders gets passed on no matter who the father is, related or otherwise, because it is not recessive, so inbreeding doesn’t matter at all. Inbreeding does not create mutations, or new traits, it simply pairs up matching copies of a gene. Sterility in gliders does not require matching copies of the gene to cause sterility because it is not recessive. In fact, since the males that have it cannot give it, it is not possible for two copies of the sterility gene to be inherited in the offspring.
Expanded answer. Our current best guess is a cross between caramel subspecies and our normal subspecies. Such a cross has been shown to produce sterile males, and there is some resemblance between caramels and champaigns (an old descriptor not commonly seen these days). One sterile line founder is a champaign herself, Sterling. And several other mosaic lines were paired with champaigns. However, one would then expect that any champaign would have produced sterile sons with any of our other gliders and that there would be many more sterile lines around, so who really knows?
For a long time it was assumed that inbreeding was the cause of the sterility, but this is not actually possible since the sterility is not recessive. Yes sterility and lowered fertility can be a consequence of inbreeding, but when it is, it is because the individual is inheriting recessive mutations in reproductive genes from both parents. Reduced fertility cause by inbreeding would be completely reversed after a single generation of mating with an unrelated glider. Obviously, full sterility would be harder to prove that with, since they can’t breed. The sterility we see in gliders gets passed on no matter who the father is, related or otherwise, because it is not recessive, so inbreeding doesn’t matter at all. Inbreeding does not create mutations, or new traits, it simply pairs up matching copies of a gene. Sterility in gliders does not require matching copies of the gene to cause sterility because it is not recessive. In fact, since the males that have it cannot give it, it is not possible for two copies of the sterility gene to be inherited in the offspring.
As an analogy, mating together gray siblings won’t get you white face offspring, and you wouldn’t expect white face to be caused by inbreeding, whereas mating together gray siblings could get leucistic offspring because leucistic is recessive and is thus required on both sides of the offspring's lineage.
Many people call for genetic testing on this to be certain before accepting the sterile lines. I wholeheartedly disagree. Science is amazing and wonderful and cruel and heartless. I read a paper studying the effects of subspecies mating on male sterility in mice. They bred lots of mice, cut their testicles off and weighed them, then euthanized the mice. I have a friend that works in a mouse lab, and even though they take great pains to be humane there, those mice live in conditions I would never ever permit for a glider. So, instead of torturing hundreds of gliders to satisfy our curiosity, how about we just act like reasonable human beings that realize it is not appropriate to kill/neuter someone because their great, great, great, great uncle couldn’t have children?
|