Thursday, May 9, 2024

The Effects of Inbreeding on Captive Invertebrate Colonies (My Opinion)

Time and time again, when an invertebrate keeper's colony crashes for reasons not immediately made clear, inbreeding is the first thing we in the hobby tend to blame. This has only become more and more prevalent over the last several years, however in truth the cause of colony crashes in captivity are rarely due to inbreeding, and this is due to several reasons. 

Firstly, insects can take much more genetic bottlenecking than vertebrates in general, and if they have defective copies of genes, they will often die relatively early in life, usually before making it to adulthood and mating. They cannot hide deleterious traits in their genome as well as vertebrates can. I would assume the same is true in isopods and other Crustaceans, considering recent phylogenetic evidence nestles Insecta within the Crustaceans (and I would even go so far as to say the same is likely true for most other arthropods).
Inbreeding is therefore safer than in mammals, where deleterious recessive traits can more frequently combine with inbreeding to form homozygous expressed phenotypes. Effectively, colonies will usually rid themselves of fatal genes before said genes can be passed onto future offspring. So while severe inbreeding may possibly increase the amount of offspring that receive fatal genes, they will almost always be a vast minority, and the chances of those genes being passed on is also minimal.

Of course, culling unhealthy or deformed individuals when spotted in a colony is still advised, because sometimes if those genes aren't outright fatal, said individuals can survive to mate and pass those genes on. However, that is not really an inbreeding issue per say, because even a genetically diverse population can have those kinds of genetic flukes and deformities pop up. Using common sense and culling deformed and unhealthy looking individuals as they show up will prevent that from becoming an issue in a colony, regardless of the genetic diversity within.

Pystalla horrida, a species in culture started from a single WC female back in 2008.
Now, if you do a simple Google search "inbreeding effects in insects" for example, you're going to come across a lot of articles, with findings leaning towards reduced vigor, fertility, and higher rates of deformity in insects and other invertebrates after multiple generations of consistent inbreeding. These findings are valid, but not necessarily applicable to the pet invert hobby, for the reason that these papers focus mainly on multi-generational, exclusively sibling to sibling or child to parent inbreeding... Which is something that would almost NEVER happen exclusively in a normal, captive colony setting. 
Notable exceptions would be mantids, arachnids, and other predatory/cannibalistic inverts we tend to keep singly and only hold back a few from each generation, in which case if one's not very careful, multi-generational sibling to sibling mating could become a reality and real problem in terms of genetic stabilty.

In reality, consistent sibling to sibling or child to parent inbreeding is only going to happen for the first one to two two generations in a typical breeding colony of any roach, beetle, isopod, etc.. After that, it becomes cousin to cousin, second cousin to third cousin, etc., until eventually they are distantly related enough that the genetic bottlenecking is no longer that extreme, and not so problematic.
There are many species in culture started from SINGLE WC females (Elliptorhina davidi, Pystalla horrida, Thorax porcellana, to name a few), that have been going strong in captivity for years, decades even, with little to no issues in captive culture that could be attributed to "inbreeding". If that were actually an issue for these inverts, they would have died out from culture long ago. 

Keeping in mind the fact that many long term captive stocks in the hobby were started from a very few individuals, from single imports with no more wild individuals ever added to captive culture, if one were to add "new blood" to say, their failing Pystalla horrida colony, from a different breeder, they would NOT actually be increasing the genetic diversity of their colony much at all. They are, after all, from the same parent stock, and while individuals from two different colonies from two different breeders may be less closely related to each other than they are to individuals within their respective colonies, the genetic diversity will not have increased enough within captivity for that to make much of a difference when it comes to "outbreeding" them to each other or increasing genetic fitness. So, when seeking to increase genetic diversity in your invert colonies, unless you are getting freshly wild caught stock to add to your colony, the chances of actually increasing the genetic diversity of your colony by any significant amount are slim... and constantly having to introduce wild specimens to culture in order to keep our colonies going would be unsustainable and defeat the purpose of captive breeding these invertebrates IMO.

Eustegasta buprestoides. All hobby stock is descended from a single WC female, collected circa 2017.
Now, there are plenty of anecdotal reports of people failing with their invert colonies, only to add "new blood" (which may be not so "new" after all) and suddenly having the colony revive itself. While this can appear to support the theory that inbreeding was to blame, one must consider a couple of things first.

If suboptimal husbandry was to blame (which it almost certainly was, even if it's something as small as less than optimal ventilation, improper air humidity, etc.), and you add new individuals to your failing colony, then of course you're going to see improvements, since you just bulked up your population with healthy, un-stressed individuals. However, that success may be short lived, because if you haven't corrected the husbandry issues, those new individuals will also start to fail, even if it takes a generation or two (the lasting effects of substandard husbandry can take a generation or two to take it's toll, and may take multiple generations to recover from). This can also give the illusion of inbreeding being the issue, as the colony will keep crashing after awhile until you add "new blood"... when really you're just dumping healthy, breeding individuals into a suboptimal environment, after which they will eventually start dying out or refuse to breed.  

Now, what happens if after adding "new blood", the state of the colony actually does improve indefinitely? Well, one has to assume that in addition to adding new individuals to a failing colony, many a keeper will also double check their husbandry parameters, ask others for better care advice, and may change a few things about their setup, even if it's something as small and as simple as adding more ventilation, slightly increasing or decreasing humidity, offering a new food type, etc.. So, if the problem was husbandry related, and they happen to fix the problem, then of course they're going to see improvements in the culture, especially after bumping their numbers up with "new blood". However, as is often the case when the changes made to husbandry were small, keepers will often attribute their failures to inbreeding, and their more recent successes to adding new blood to their colonies, despite the issue merely being some small husbandry parameter that needed tweaking. Surely this must be the case when others are having consistent success with the same species, without ever having added new blood to their colonies.

Elliptorhina davidi, yet another species in culture started from a single WC female, circa 2014.
Now, as for the detriments of adding new blood to a colony... Not only can adding new individuals to a colony introduce new pathogens or pests that come in with said stock, but most importantly you may be adding mislabeled hybrid stock or incorrectly labeled stock of a completely different species or locality/morph, which will in turn lead to species hybridization or bastardization of a specific locality/morph. Hybridization is of particular concern when it comes to roaches and beetles (many have been proven to interbreed within the same genera or even closely related genera), and locality/morph mixing and destruction of those strain specific traits is of particular concern when it comes to isopods.

So not only does adding new blood not do much for a culture 99% of the time, but you can completely compromise the purity and even health of your line as a result. If a complete culture restart is necessary due to colony collapse (which can be due to lasting effects of poor husbandry, loss of gut flora, or ending up with poor sex ratios after a crash), then just get new stock and set them up in a completely different enclosure from your old stock, to avoid any issues with mixing lines/species. Hybridization due to mixing stocks has been plauging the cockroach hobby in particular, and it seems every year there's some new hobby staple genus that suddenly has hybrids being sold of in the hobby. 😑

Porcellio hoffmannseggi "White-Out", a leucistic morph isolated through inbreeding, from a probably already inbred wild type colony.
Another thing I find interesting is that people seem to oddly ignore the potential risks of inbreeding when it comes to morphs, whether they be simple recessive or line bred. This is ironic considering isolating morphs requires much more severe inbreeding and sometimes even multi-generational sibling to sibling or offspring to parent mating to restrict genetic diversity further and select for the specific genetic traits that are desired for the morph. Even then though, other than sometimes breeding slower than their wild type ancestors, I've yet to see any documented evidence of pet hobby invertebrate morphs suffering any significant ill effects of inbreeding.
And most reasonable people know not to mix different lines/localities of morphs together unless creating a "Gem/Lotto Mix", since that will ruin the selective process and completely change the appearance of the morph you started with. So I just find it kinda funny that no one seems to make a fuss about the hyper inbreeding that is involved in creating morphs, yet random colony crashes of wild type inverts? Must be inbreeding! 🙃

All in all, I consider the notion of inbreeding being the be all end all excuse for culture crashes or cultures doing poorly long term to be ridiculous, and unsubstantiated by any relevant evidence. Whereas there's plenty of evidence to the contrary, as supported by the fact there are many species in culture that we seldom, if ever see secondary WC imports of that continue to thrive in captivity even decades after their original introduction to the hobby, with no new genetics ever introduced.
All the "inbreeding" excuse does most of the time is take the conversation away from potential husbandry issues, and in the complacency of "knowing" the issues were out of our hands from a genetic standpoint, we learn less about how to care for our invertebrates properly as a result. Dooming ourselves and others to repeat the same mistakes over again as a result.

And with that, I rest my case. Thanks for reading, I hope some found this informative, and I'll see you all next time! 😉 


  1. The bit about males having only one copy of each chromosome only applies to hymenopterans, with their haplodiploidy! Males of other orders still have the usual chromosome count. Butterflies tend to have a ZW system, roaches and mantises have an XY system like us, etc.

    1. Well that's good to know, thanks for the correction!