Hi all,
My PhD research is in evolutionary biology, and I specifically use quantitative genetic (QG) approaches to answer questions concerning genetic variation in natural populations. This means that I develop large-scale experiments that involve breeding organisms, managing pedigrees, and tracking phenotypes (including fitness) over time.
I've been reading over this forum, and it's plainly obvious that there's major contention surrounding so-called "hybridizing" between morphs (I put this in quotation marks because these are within-species questions).
Before I go on, I'd like to state my intentions to make this a friendly conversation--I don't feel hostility toward any of you, the readers, and I'd like very much for this to remain a positive space in which we can all learn from one another.
With that out of the way, I'm having a little trouble wrapping my head around the major arguments against crossing morphs, because they seem to contradict much of what's in the scientific literature (and evolutionary biology in general). I'm hoping that someone or some of you might be willing to help me understand which arguments I'm missing, if any. Before anyone asks, I've been through other posts on the subject, but many/most of the arguments against the practice seem rooted in tradition/preference rather than science or empirical evidence suggesting it should be done.
Here are the arguments as I understand them and rebuttals from evolutionary biology (please feel free to speak up if I've missed any):
1) "Cross-morph breeding is bad for the frogs! Their natural within-species morphs will do better when bred together."
Evolutionary biology response: Overwhelmingly, populations of organisms do "better" (i.e. see their population-level average fitness increase) when maximizing heterozygosity at each locus--this reduces the probability of coupling deleterious recessive alleles together. Everybody's heard of the "hybrid vigor" that frequently applies when crossing species--this generally applies only to the F1 generation across species boundaries, but when outbreeding across populations (i.e. within species boundaries), we frequently see major improvements in fitness (i.e. an index of longevity and reproductive success) in the crossed offspring.
Comment on #1: An important implicit note, here, is that breeding strictly within a specific morph is very likely increasing the probability of inbreeding, which overwhelmingly moves populations in the opposite direction by increasing homozygosity among deleterious recessives (especially given the insulated populations being bred back and forth by hobbyists).
Yes, there are instances in which outbreeding depression occurs, but I can't find much evidence of this being studied in these frogs. The closest I come is here, in this publication by Wang and Summers from 2010 that mentions that reproductive isolation due to selection may be evident in "Dendrobates" [now Oophaga] pumilio. (This paper is also referenced in the Frankham et al 2011, which is the only other paper I can find that even mentions outbreeding depression in the same publication as anything Dendrobatid.) Note, though, that in the last ten years, numerous other frogs have been reclassified into different species and even genera (e.g. "Dendrobates pumilio" is now "Oophaga pumilio"), and so even the few existing concerns surrounding population divergence may be weaker arguments still with all the "splitting" that's occurred.
2) "Different morphs may show aggression toward one another due to imprinting on parents that occurs during development."
Evolutionary biology response: This is the argument that makes the most sense, but work by Yang et al in 2019 (again, on Oophaga pumilio) suggests that cross-fostering can effectively render this argument moot: the results suggest that offspring will behave "normally" toward anyone who resembles their "mother" (i.e. whichever morph of frog reared the offspring). In other words, it seems that you could rear frogs for the specific purpose of breeding with different morphs by raising multiple offspring with foster morphs.
Comment on #2: This is a little more effort than the average dart frog breeder might want to put in, and that I understand--I'm not suggesting that everyone should/must do this. I do, however, want to observe that it seems it would only take 1-2 generations of cross-fostering before you had new, "friendly-with-each-other" morphs. You could also potentially cross-foster individuals to make them more tolerant of other morphs in day-to-day life (e.g. cross-foster cobalt tinctorious with azureus tinctorious so that the cobalts could be comfortably/safely housed with reciprocally reared azureus*).
*(I know the study I mentioned above only explores Oophaga pumilio and not Dendrobates, and it may be that this doesn't apply to all species.)
3) "But why would you want to produce new morphs or cross-breed? There's so much natural variation in the wild--why can't we just enjoy what nature produces?"
Conservation response: My first thought, here, is that if you're only rearing frogs that can be found in the wild, you're encouraging more wild-catching because there's a larger/greater market for frogs that look like those in the wild. It seems like the community is (rightly) opposed to wild-collection, so this one's a bit of a head-scratcher for me.
General response to all of the above: I think it's fine if people are much more enchanted by the naturally-occuring variants than captive-bred morphs--they're really beautiful and display all kinds of cool behaviors (like biparental care sometimes-wow!), but given all of the above, I'm still a little confused about why people are so hostile toward the idea. There are countless populations of all of these naturally-occuring morphs out there, and some are bred to maintain genetic variation in case there's a need for selective "head-starting" in wild populations (if the practice is validated in the given context--it isn't always).
I know this was long, so thanks for reading all the way! Please let me know your thoughts--I'm eager to hear responses to these points and/or any arguments I might've missed (and I'll be happy to update this thread if someone makes a point that needs including, here).
My PhD research is in evolutionary biology, and I specifically use quantitative genetic (QG) approaches to answer questions concerning genetic variation in natural populations. This means that I develop large-scale experiments that involve breeding organisms, managing pedigrees, and tracking phenotypes (including fitness) over time.
I've been reading over this forum, and it's plainly obvious that there's major contention surrounding so-called "hybridizing" between morphs (I put this in quotation marks because these are within-species questions).
Before I go on, I'd like to state my intentions to make this a friendly conversation--I don't feel hostility toward any of you, the readers, and I'd like very much for this to remain a positive space in which we can all learn from one another.
With that out of the way, I'm having a little trouble wrapping my head around the major arguments against crossing morphs, because they seem to contradict much of what's in the scientific literature (and evolutionary biology in general). I'm hoping that someone or some of you might be willing to help me understand which arguments I'm missing, if any. Before anyone asks, I've been through other posts on the subject, but many/most of the arguments against the practice seem rooted in tradition/preference rather than science or empirical evidence suggesting it should be done.
Here are the arguments as I understand them and rebuttals from evolutionary biology (please feel free to speak up if I've missed any):
1) "Cross-morph breeding is bad for the frogs! Their natural within-species morphs will do better when bred together."
Evolutionary biology response: Overwhelmingly, populations of organisms do "better" (i.e. see their population-level average fitness increase) when maximizing heterozygosity at each locus--this reduces the probability of coupling deleterious recessive alleles together. Everybody's heard of the "hybrid vigor" that frequently applies when crossing species--this generally applies only to the F1 generation across species boundaries, but when outbreeding across populations (i.e. within species boundaries), we frequently see major improvements in fitness (i.e. an index of longevity and reproductive success) in the crossed offspring.
Comment on #1: An important implicit note, here, is that breeding strictly within a specific morph is very likely increasing the probability of inbreeding, which overwhelmingly moves populations in the opposite direction by increasing homozygosity among deleterious recessives (especially given the insulated populations being bred back and forth by hobbyists).
Yes, there are instances in which outbreeding depression occurs, but I can't find much evidence of this being studied in these frogs. The closest I come is here, in this publication by Wang and Summers from 2010 that mentions that reproductive isolation due to selection may be evident in "Dendrobates" [now Oophaga] pumilio. (This paper is also referenced in the Frankham et al 2011, which is the only other paper I can find that even mentions outbreeding depression in the same publication as anything Dendrobatid.) Note, though, that in the last ten years, numerous other frogs have been reclassified into different species and even genera (e.g. "Dendrobates pumilio" is now "Oophaga pumilio"), and so even the few existing concerns surrounding population divergence may be weaker arguments still with all the "splitting" that's occurred.
2) "Different morphs may show aggression toward one another due to imprinting on parents that occurs during development."
Evolutionary biology response: This is the argument that makes the most sense, but work by Yang et al in 2019 (again, on Oophaga pumilio) suggests that cross-fostering can effectively render this argument moot: the results suggest that offspring will behave "normally" toward anyone who resembles their "mother" (i.e. whichever morph of frog reared the offspring). In other words, it seems that you could rear frogs for the specific purpose of breeding with different morphs by raising multiple offspring with foster morphs.
Comment on #2: This is a little more effort than the average dart frog breeder might want to put in, and that I understand--I'm not suggesting that everyone should/must do this. I do, however, want to observe that it seems it would only take 1-2 generations of cross-fostering before you had new, "friendly-with-each-other" morphs. You could also potentially cross-foster individuals to make them more tolerant of other morphs in day-to-day life (e.g. cross-foster cobalt tinctorious with azureus tinctorious so that the cobalts could be comfortably/safely housed with reciprocally reared azureus*).
*(I know the study I mentioned above only explores Oophaga pumilio and not Dendrobates, and it may be that this doesn't apply to all species.)
3) "But why would you want to produce new morphs or cross-breed? There's so much natural variation in the wild--why can't we just enjoy what nature produces?"
Conservation response: My first thought, here, is that if you're only rearing frogs that can be found in the wild, you're encouraging more wild-catching because there's a larger/greater market for frogs that look like those in the wild. It seems like the community is (rightly) opposed to wild-collection, so this one's a bit of a head-scratcher for me.
General response to all of the above: I think it's fine if people are much more enchanted by the naturally-occuring variants than captive-bred morphs--they're really beautiful and display all kinds of cool behaviors (like biparental care sometimes-wow!), but given all of the above, I'm still a little confused about why people are so hostile toward the idea. There are countless populations of all of these naturally-occuring morphs out there, and some are bred to maintain genetic variation in case there's a need for selective "head-starting" in wild populations (if the practice is validated in the given context--it isn't always).
I know this was long, so thanks for reading all the way! Please let me know your thoughts--I'm eager to hear responses to these points and/or any arguments I might've missed (and I'll be happy to update this thread if someone makes a point that needs including, here).