So I think many of the regular readers of the Lightning Project know I have an outspoken stance on breeding. Specifically, that preservation of natural biodiversity trumps the creation of captive-originated ornamental forms and the intentional and unintentional hybridization of wild forms. Not going to get on that soapbox today (I’m busy doing that on the MBI), but in doing my “homework” I came across an interesting publication. More on that in a moment.
The concept I was trying to find some documentation on relates to what we’d call “foundation stock”. Foundation stock being the individuals used to create a new population of a species. In the case of species survival programs, foundation stock would be the wild collected specimens used in zoo breeding programs to maintain the captive population with the goal of arking the species and hopefully one day reestablishing wild populations. In the case of aquarium breeding, it’s no different..i.e. the 4 breeding pairs of Mccullochi Clownfish (Amphiprion mccullochi) owned by Ryan Dwyer are the 8 specimens that will be the ancestors of all future Mcc’s (unless the unlikely happens and more wild fish are brought into captivity).
There’s another way of looking at this question, a darker viewpoint. Functional extinction. This is a term I came across first when reviewing IUCN Red Lists (Banggai Cardinalfish anyone…still on that list as endangered). What “Functionally Extinct” means is that while the species still exists, the population is so small that from a breeding and genetics standpoint, it fails to have sufficient genetic diversity to prevent a total genetic meltdown (and ultimately, extinction). For example, you probably could not bring back a species of bird if there were only a single pair left – it would be termed functionally extinct. In such dire circumstances, actual intentional hybridization might be thrown out as a last-resort mechanism in the hopes that you could one day breed back to some approximation of the ancestral species, although in truth, you’ll never get back to the actual species.
At any rate, the document published by FAO (The Food and Agriculture Organization of the United Nations) is part of the Fisheries and Aquaculture Department. Conservation of the genetic resources of fish: problems and recommendations provides general guidelines on minimum population sizes for short and long term captive maintenance, and actually explains, quite clearly, some very interesting talking points on inbreeding and genetic integrity.  While this is all generalizations, here’s some interesting talking points:

  • A minimal captive population size of 50, in equal sex ratios, randomly mating, will keep inbreeding at roughly 1%.   At this population size, the total population will lose 1/4 of it’s genetic variations in 20 to 30 generations.
  • An interesting aside to the first point, the number of individuals in a small population (let’s say 25) is roughly equivalent to the number of generations that population can exist while maintaining a reasonable level of “fitness” (so 25 generations if the total population is limited to 25 individuals in each generation, as well as the other stipulations of equal sex ratios and random matings).
  • It is argued that 500 individuals is the minimum necessary to maintain a long term captive population that loses variations to genetic drift at a rate compensated for by new variations gained through mutation.
  • The most interesting one I’ll quote verbatim – “the number of founders in a colony, so long as it is greater than about five individuals, is not nearly as important as the long-term maintenance size of the colony (Nei et al., 1975; Denniston, 1978). That is, a single bottleneck event followed by rapid growth to a large size, say 2Ne greater than 500, does relatively little damage, compared, that is, to a chronically small Ne.”.  Or to try to paraphrase – a captive population started with only 5 individuals can still be enough (in a fish) to potentially establish a stable captive population, so long as that population is brought up to at least 500 breeding individuals in short order.

So what does that all mean?  Well, for starters, it means that even with only 8 founding individuals, the captive population of Amphiprion mccullochi could be very stable and with us for a long time so long as the fish is actively bred by many people and it’s done in as few generations as possible.  Pile on intentional avoidance of any inbreeding in the first generation or two, and the future could be very bright.  And on the flipside, even if the population of breeding individuals was kept well below 500 (and it’s entirely possible that could happen), the generation time for that to be a problem, as measured in years, could be centuries or more (given that you can spread out the generation time to be 10-20 years in a clownfish if you plan for that).
How does that all relate to the Lightning Maroon and it’s PNG mate (and neighboring pair)?  Well, if nothing else, it means I really should get one more PNG white stripe maroon pair into the mix if I ever can, just to get above that foundation minimum of 5 😉