Living in the Footsteps of Elephants

The first pattern that we identified after analyzing these haplotype networks was a pattern shared by all rainforest dwelling species that we sequenced. You might think that the six species of fish living in the Congo River basin would inhabit pretty similar environments; however, that actually isn’t the case at all. Take New York City. When people from elsewhere in the world think about living here, they imagine tall skyscrapers and bustling streets near Times Square. Sure, some city residents might live here, but some might live in apartment buildings in Brooklyn, others in houses in Queens. Therefore, although some fish in the Congo River basin live in the margins of rivers, others reside in the rainforest. To name a few, Hylopanchax Moke, Epiplatys multifasciatus, and Aphyosemion elegans, while inhabiting specific microhabitats, all reside under dense rainforest canopy. The others live in river margins.

This would consist of small, shallow pools and forest streams tucked under thick rainforest canopy. Some fish even live in the rainwater that fills up the footprint of an elephant! These habitats aren’t as connected as rivers, which flow much more continuously. Rather, these  scattered puddles and streams only link up briefly during heavy rains, if at all. That means (hate to break it to any rainforest dwelling fish reading this) a fish born in a small forest pool has very little chance of ever reaching the next one over.

The ability for these fish to move and disperse is called vagility. Therefore, these three fish species experience a limited vagility due to their ecological constraint. This directly affects their genetic variation and what their haplotype networks look like. You can see this visually for yourself. When we compare the haplotype networks of these forest fish to those of river-dwelling species, the difference is obvious. Can you figure it out?

Were you able to? Unlike the networks of the river fish, which show colors overlapping frequently in the circles from locations far apart on the map, the networks of forest fish split into separate, tightly clustered branches, with each branch tied to a specific color, or location. Each of these branches are also set apart by a high magnitude of nucleotidic differences, which you can see by looking at the numbers on the lines. This immediately implied to us that populations living scattered under rainforest canopy are much more prone to being cut off from other pools or streams and are likely to begin drifting further and further apart from other populations genetically. It’s like how we consider people living in Staten Island to not actually be New Yorkers—like, where even are you? 

Anyway, now we’re at the most exciting part. Epiplatys multifasciatus is the fish species that demonstrates genetic difference most dramatically. Its populations from different areas don't just look slightly different genetically, they’re separated by nucleotide differences of up to 36 base pairs. The network is extremely geographically structured as well, with each branch maintaining a location and no overlap of color in any circle. So here’s what’s cool. Usually, you can’t rely just on haplotype networks to identify the presence of new species. However, my mentor has also looked at the morphology (physical features) of these populations and they exhibit coloration differences. This confirms our hypothesis that this pattern for this specific fish indicates that these populations have diverged enough genetically from one another to be classified as new species!!! If I had any input on this, I would name one of the new species Epiplatys anushkus, but I’m not sure the big research folks up there would listen to a highschooler without a fully developed prefrontal cortex. Oh well.