Life of the Meridian Islands: The Flagbearer Tribbat

The Meridian Islands are notable during the Ultimocene for being home to a clade of endemic, flightless dividopteran tribbats. More specifically, they are volanvenators, an ancestrally carnivorous group of which the aerocuda is the best known example. They reached this isolated island twenty million years ago, and as they gradually adapted to feed more frequently on the ground in a habitat with few large predators to flee from, they gradually developed smaller and less functional wings, until in the modern day most of their descendants have lost their wing digits virtually completely and returned to a fully terrestrial existence. In an ironic twist, the flightless tribbats which evolved because of a lack of predators have since given rise to the island's dominant predator guild, the ferocious flesh-eating terracudas, of which the man-sized shadowstalker - the apex predator of the Meridians - is the most formidable.

But the shadowstalker is only one of a wide and varied assortment of flightless tribbats which all share a common ancestor, and not all of them are carnivorous, even though their common ancestor likely was. A wide variety of food occurs on the islands in addition to animal prey, including abundant seeds, nectar, fungus, fruit, and of course leaves and stems. While tribbats are poorly suited overall to digest tough plant matter, particularly in comparison to native birds, they evolved to make use of all of these other food resources in the absence of any other tribbethere competitors, such as molodonts, which would normally out-compete them. Though molodonts have recently rafted to the islands, they remain small and currently restricted from expanding into the niches still filled by these unusual tribbats, who only here have evolved into small, flightless herbivores, with uniquely specialized incisor and molar teeth adapted to chew seeds, berries, soft shoots, and mushrooms.

Most of these tribbats live in the wet and musty forests of the island, lurking in the shadows to stay out of sight of their cannibalistic cousins and staying along narrow trails where bigger threats cannot follow. They are often cryptic creatures, shy and nervous, and traces of any flying ancestry in most of them are limited to small remnants of once wide wing membranes. Yet for some, known as flagbearers, a single wing digit remains in only the male. It is often extraordinarily, apparently harmfully elongated, formed wholly of cartilage and so very flexible while serving no practical function at all. Most species of flagbearer have a characteristic flag at the end of this hypertrophied finger, varying in color and shape, which always drags behind the male, hitting against bushes and certainly sometimes drawing attention to him from predators. Why would this extreme and seemingly deleterious finger have evolved? The answer, it seems, is because it is sexy.

The ancestor of flagbearer tribbats, of which there are now about ten species, developed its special finger as an honest signal of fitness to potential mates; carrying around a brightly colored wing structure despite being unable to fly demonstrated that a male was strong enough to have energy to spare, and would pass on very good genes to his offspring. But now, the different flagbearers have found themselves in a remarkable competition of sexual selection, with females of each species having come to prefer very different traits in her partner and so the closely related species all developing radically unique flags, which continue to grow more elaborate and absurd as female's choices become increasingly particular. In addition to their flags, males of some species also now sport additional display structures - tufts of hair, colorful ears, or in the case of the candescent flagbearer, two large, extensible lip flanges which reflect dappled forest sunlight into a prismatic display of color.

The male of this rabbit-sized tribbat resembles the female very little, for he is nearly jet black in most lighting while she is a mottled brown ( though in bright light, the male's coat reveals red and rusty hues.) His dark pelage serves to effectively let him disappear in the shade of the forest and let his flags and his flange steal the show. Males form leks, each clearing a space on the mossy substrate as his own arena, which groups of the drab-colored females periodically visit to peruse. Whenever a potential mate stops by, each male immediately jumps up into an elaborate dance performance involving waving each flag around, first slowly and at wide angles but gradually becoming quicker and leading the female's eyes toward his face. At the climax of the dance, with the female mesmerized by the show, he flashes his lip flanges and jerks his head back and forth, flashing violet, blue, green and gold in an ever changing spectrum. If she is impressed, they will then mate and he will play no further role in her life or that of her offspring. Were male flagbearers to help raise their young, they would likely only put them in danger; because of their extreme decoration, males are predated more than four times as often as females, and few live more than one to two breeding seasons. But this high generational turnover likely does benefit the next generation by freeing resources for the young to use which would otherwise be used by the older males.

The flagbearer tribbat and their out of control sexual selection is yet another strange and remarkable example of evolution that can often only occur on such isolated islands, be they literal islands like the Meridians, or metaphorical ones like Serina itself. A world where plant and animal life has produced countless incredible forms which, without it, would never have been able to exist, Serina continues to demonstrate the remarkable, beautiful, and sometimes downright ridiculous adaptations lifeforms acquire to better perpetuate their genes.