I apologize for the answer delay, but I haven’t been around this forum in a while. Even tough I am not a fish physiologist / endocrinologist per se, I will try to comment and contrast your post in a theoretical-practical way.
The role of the two major chemosensory channels, olfaction and taste (this last one mostly in anosmic fish) in every aspect of the fish reproductive process has been demonstrated in numerous experiments. Hormones and their metabolites commonly serve as reproductive pheromones in fish. Such pheromones and other related chemical substances have been found affecting directly matting behavior and parental care processes. It also has been demonstrated that, for example, exposure of males to water holding a gravid female, educes courtship behavior. Is perhaps one of the best ways to explain hybridization when (usually) in a closed system (aquarium) there is only one individual (or one gender) of several different species of more or less related cichlids, and then a gravid female arouses (ready to rumble) and a dominant male diminishes his aggressive mode towards her, and switches to pre-spawning mode. This is due in part because ovarian pheromones not only stimulate courtship behavior, but also inhibit the male aggression toward the female. These pheromones are used by both sexes to incite the opposite sex to engage in sexual behavior, being at the same time this sexual behavior a direct regulator of endocrine secretion. Androgen conjugates in males and oestradiol and testosterone glucuronides (typical ovarian pheromones) in females, (among other sex steroid hormones), are known to trigger courtship behavior by means of influencing olfactory mechanisms, probably mediated by steroid feedback on brain areas involved in control of the olfactory bulb. At the same time, courtship behavior and visual stimulus influences in the secretion of the aforementioned hormones/pheromones.
In my own experience, I have observed a similar scenario to yours. In an aquarium with various formed pairs of the same species, is not rare to observe reproductive behavior of two or more pairs of the same and closed related species at the approximate same time. In an 800gal (120’x48’x32’) containing various Archocentrus and Cryptoheros species, formed pairs -of the same species- defending territories tend to spawn almost at the same time. In this particular tank, water changes are seldom, due in part to an effective bio-denitrification system and a tight fitting cover. Thus, the chemical metabolites (hormones, pheromones, ovarian substances, egg substances, embryo substances, urine, and the like) must remain “actives” in the system until they either decay or are metabolized and decomposed by bacteria, adsorbed by filtering materials, or combined into other chemical structures. Obviously, temperature, photoperiod, water changes, food availability, etc., are the first to “ignite” the “first secretions” and visual displays; but after one couple has started, is not rare to watch, within a few days interval, other(s) pair(s) doing the same. To be able to observe these patterns I have had to wait some years in order to provide enough space (for multiple territories to occur) in the form of big aquaria, but in your case, a similar scenario has occurred with a 55gal and three egg-crate dividers.
I think that being your 2 pairs closed related, perhaps not even being a different species but just subspecies, races or a case of geographic variability…? (Oh taxonomy, taxonomy!)
, is not unusual that some substances produced by one pair were effective in triggering a particular behavior in the other couple.
Nevertheless, some particularities in your “experiment” have awaken some curiosity and by “domino effect”
, some other questions.
When you refer to the Herichtys sp ‘pantepec’ male, you mention that he will bite everything he can find, specially females of his own species. This is a fairly common conduct in anosmic males, who despite their visual capabilities are not able to channel aggression, even toward gravid females. Even though his inability to cope aggression toward the female, he manages to change his condition and develop a “fry guarding” behavior and color pattern. Perhaps the visual stimulus was the trigger. Maybe he is not anosmic and just has a non-adaptative particular behavior toward the females. As we get involved more and more in the study of fish behavior, individual variability is an area that will emerge powerfully. Not just fish from the same species differ morphologically, but without a doubt they present different ethograms given the same environment and choices.
In order to establish the hierarchical contribution of stimuli (visual vs. odor), it would be interesting to include variations in the experiment design. For instance: substituting the egg-crate dividers for other opaque surface that would allow water transfer, but would incapacitate any visual interaction to verify the “olfactory hypotheses”. The other variation would be, either to place 2 aquariums together and allow only visual cues to occur, or sealing 3 partitions of glass in the 55gal to verify the “visual hypotheses”. In both cases the fry would be placed manually in each compartment and the resulting behavior recorded.
The fact that the two ‘pantepec’ developed their fry guarding coloration and did neither show any other previous pattern (pair formation displays, egg incubation, etc.) nor sex physiological character (genital papillae, pre-spawning or courtship variations in coloration, gravid female, etc.), and being the “absent” male androgen secretion directly involved in the control of the pre-spawning and spawning behavior, as well as all secondary sex effects like the apparition of the genital papilla and the nuptial and breeding coloration (that you could not detect), lead us to think that, either there are perhaps some sort of postvitellogenic substance (pheromone) or some fry secreted chemical (pheromone) that could trigger the ‘pantepecs’ behavior, or the visual stimulus of the fry is triggering the fry-care conduct, or is perhaps a mix of both visual and odor stimuli. Also the presence, as you mentioned, of the biological H. carpintis parents (visually and chemically speaking) could have been participating in the ‘pantepecs’ response.
About your “pragmatic” approach to induce hard-to-breed” species with the presence of other easy-to-breed breeding species, I’m not sure to what extend olfactory pheromones are transferable inter-specifically. All I know about pragmatism, tangibility, and the like, (in this case) is that… after a good “bath” in MS222 and a proper injection, either with pituitary carp extract, human chorionic gonadotropic hormone… females of most fish species get gravid, and male testes get full.
On the mean time, experiments like yours could help to shape “other kind” of practical protocols with reasonable results for the aquaculture business based on pheromone activity instead the classic hormonal induction, as well as opening a door for the hobbyist that cannot get legal access to such hormones.
And now, after all this long “mess”, like most Sundays, it is time for me to take care of some major cleaning/water changes.
Talk to you soon.