Fire lizards are one species, not two, because of "sneak-mating" browns.
- As presented, there's no evolutionarily-sound reason for three different male color/size morphs to exist in a single species or be part of the same social groups, as genetic self-interest would encourage bronzes which don't win a gold's favor to drive off the smaller males, allowing the bronzes to at least breed with green females instead. Nor is there much reason for gold and green females to coexist, as queens should chase off any greens that dare to breed competitors for their own ravenous hatchlings' food. Between genetic drive and their existing differences in size, it'd make more evolutionary sense for fire lizards to speciate into two lineages: a strength-focused, territorial species with gold females, bronze males, and large well-defended clutches, and a speed-focused, nomadic species with green females, blue males, and small hidden clutches that hatch without need for parental care. Each species' eggs would hatch only their own type, and the green/blue sort would routinely be chased off the gold/bronze variety's turf, like foxes dodging hostile wolves.
- So why aren't Pern's fire lizards divided into two species? Because brown males bridge the gap via "sneak mating". Browns - possibly the original color of ancestral fire lizards, before they'd diverged into multiple phenotypes - are males which are almost large enough to compete with bronzes, and definitely strong enough to out-muscle blue rivals. Browns can hang around near queens, acting subordinate enough to placate the dominant bronzes, waiting for the gold to return from a mating flight. When she sends her bronze paramours out to gather food, the browns sneak back and mate with her on the ground, seizing the opportunity to fertilize any leftover ova the lead bronze might have missed. Their drab coloration is camouflage so the bronzes won't spot them sneaking around; the queen tolerates their attention, because she's too tired from her flight to mate on the wing again, but adding a few more eggs to the clutch is worth it, and mating with a brown instead of a second bronze ensures her equally-tired primary mate won't get injured fighting her second one. When the queen isn't breeding, the browns compete with blues for green mates instead, both pitting their endurance against the blues' agility in the air and sneaking off with the equally-camouflaged greens for seconds.
- It's this regular interchange via browns' multiple breeding strategies that's maintained a shared gene pool between the gold/bronze and green/blue phenotypes of fire lizard, ensuring that queens continue to produce offspring other than bronze and golds. If a brown mates with a green, her clutch will include browns as well as greens and blues; if one of those browns grows up to sneak-mate with a gold, she'll produce offspring of all colors. The reverse, where a brown with gold/bronze ancestry mates with a green, doesn't produce golds or bronzes, but only because the greens' smaller body and clutch size doesn't allow for eggs big enough to hatch out those phenotypes.
