It’s a nice gesture to tidy up your home before a date comes over, but the male cichlid takes this move to a whole new level, building potential mates an elaborate sand structure in an effort to woo them. Down on the sandy bed of Lake Malawi in East Africa, one of the cichlid’s many habitats around the world, these structures known as “bowers” can take two main forms: castles or pits. New research on these fish explores the genetic basis for which kind of bowers a cichlid builds.

In a paper in the Proceedings of the National Academy of Sciences published online on November 5 ahead of print, an international team of researchers found that certain cichlids only build castles, while others only build pits. This was not particularly surprising, but what came next was strange indeed. When castle-builders and pit-builders have babies together, each of those offspring alternated between building pits and castles, always in the same order.

As shown in the video above, castle-builders scoop sand and spit it into a pile, forming a volcano-like structure. Pit-builders, on the other hand, scoop sand from the center of an area and spit it around the edges to form a bowl.

By breeding fish that are hybrids of castle-builders and pit-builders, the researchers moved a step toward a fuller understanding of the influence of genetics on behavior.

Todd Streelman stands among tanks of cichlids.
Todd Streelman stands among tanks of cichlids.

“We’re not there yet, but we’re beginning to get a handle on gene regulation patterns that drive the neuronal patterns,” Todd Streelman, Ph.D., chair of the School of Biological Sciences at Georgia Tech and the study’s co-principal investigator, said on Tuesday. “We were able to see that there’s a clear connection between gene expression and behavior.”

And an analysis of gene expression in the fish’s brains revealed even more details about the genetic roots of hybrid cichlids’ behavior. Streelman and his team found that when the hybrids were building castles, the gene alleles for castle-building were expressed, whereas the pit-building alleles were expressed when the hybrids were building pits. The changes in which genes were turned on and which were turned off, the researchers write, was gradual — less like a light switch and more like a volume knob.

The study was conducted on fish in a lab to prevent concerns about hybrid fish disrupting wild populations.

The whole process of building a bower, which the tiny fish accomplish with machine-like efficiency and dedication, is oriented toward finding a mate. If a male’s pit or castle looks nice, a female will mate with him. But usually a female is only looking for a pit or a castle, not just whatever bower looks the best since the type of structure a male builds gives an indication of what species he is. With the hybrid fish, the picture gets more complicated, since a fish may be able to attract two different species of females.

And while this study may sound like it proves that genes directly create behaviors, the researchers aren’t quite able to draw that conclusion yet. What it does show is a complex interplay between the genes we’re born with and the gene expression that turns them off and on. Future research will give a more accurate impression of just how much our genes dictate our behavior.