Color Variation in Venezuelan Guppies

Color variation amongst organisms in a species can prove advantageous or harmful – it can contribute to their survival or death, as seen in the 1970 study by John Endler on the drastic color differences between Venezuelan guppies in different pools. Some of these wild guppies sported vivid, bright colors, while others displayed more drab shades and only offered scattered specks of color. This tremendous contrast in coloration led to a question: “What caused these trends in the coloration of the guppies?” Upon analysis of the data provided, it is clear that many characteristics influenced this color change, including the location of the pools, the number of predators present in said pools, and the turbidity of the water.

As the data shows, more brightly-colored male guppies are populating the pools farther away from the main river, and they decrease in number with each closer pool. Pool 1, the closest pool, has the least amount of bright males – only 5 – while Pool 4, the farthest pool, has Pools 2 and 3 have 50 and 76 bright males, respectively, showing the increase of brightly colored guppies with each farther pool.

Meanwhile, the numbers of drab males remain scarce in farther pools and more predominant in pools closer to the river – Pool 1 holds 41 drab males, while Pool 2 holds 19, Pool 3 holds 10, and Pool 4 holds only 5. Predators also occupy the pools with the drabber guppies (which happen in the closer pools) and decrease in number as they move upstream, where the brighter guppies reside; Pool 1 has 28 predators, Pool 2 has 15, Pool 3 has 6, and Pool 4 has no predators at all.

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In addition, the turbidity of the water – the cloudiness or haziness of the water – is at its largest in Pool 1, from 27.50 to 36.25 NTU, and decreases with each further pool (Pool 2 is between 8.75 and 27.50 NTU, and Pool 3 and 4 are each between 3.00 and 8.75 NTU).

These patterns have a purpose; the drab guppies are shown to reside in areas closer to the main river with high turbidity and a large number of predators. The high turbidity prevents sunlight from reaching the guppies, making them their gray color, and grants the drab guppies a natural camouflage, as their gray color can blend in with the hazy, murky waters, providing them safety from the predators there. On the other hand, the bright guppies choose to inhabit the pools with low turbidity and little to no predators, as their brilliant colors, which are easily observable upon the clear water, are sure to attract the attention of unwanted predators; thus, areas with no such threats allow them to live freely and mate. As evidenced in the data collection, the guppies adapted to the environment; since they are the same species of guppy, this would mean the drab coloration was passed on through offspring since the original bright population could not survive the high predation levels – an example of natural selection, or descent with modification. One may argue that the location of the pool, amount of predators, and turbidity of the water had no conclusive correlation to the trends in the coloration of the guppies – perhaps that these guppies changed color purely by chance, with no explanation for the change – because of the numbers of the drab female guppies increasing with each further pool, an inverse pattern from the males; however, such a claim is false, as the females increase as they move upstream on because at there are no brightly-colored females present in any of the pools – this is an act of sexual selection. Brightly-colored male fish use their magnificent colors to attract females (referred to as intersexual selection), and because the greatest frequency of bright males is located in the farthest pools, the females tend to shift toward said pools to mate and produce more offspring with more desirable traits. Females lack bright colors as they have no use for them; such attractive characteristics are usually used by males to attract mates.

In conclusion, the coloration of the guppies was affected by the location and characteristics of the pools in which they inhabited. Some guppies were changed to a darker color to survive from the carnivorous predators sharing their pool, while others remained bright and moved to farther locations to avoid predatory creatures altogether and mate with the females. Natural selection and sexual selection were two collective concepts that helped identify why these trends in coloration changed and how they assisted in the survival of guppies in the pool locations. In general, the drab males were more likely to survive and reproduce, but reareleasethareaspredation bright colorations were found to be the more favorable.