Environment Versus Genetics

I have been doing some crosses between Full Red guppies and wild type feral guppies. I will report on these later. But an interesting observation fell out of the cross.

(A nice bonus of the cross.)

Here is a picture of three female guppies. The two grey females are closely related, coming from the same wild colony I maintain in a 75 gallon planted tank. 

Wild type females top and bottom, full red center.

The larger wild type female was raised with the Full Red female. The smaller wild type female was raised with the colony in the planted tank.

The smaller female was fed three times a day with New Life Spectrum small fish pellets, ground up. The entire colony was only fed as much as they could eat in 2 or 3 minutes. Parents and fry were raised together.

The larger females were fed three times a day with the same food. But they would have got more food than the wild colony. They were raised apart from their parents in a dedicated 5 gallon tank. They were also raised in the first three days with live brine fed exclusively. Between three days and a month they got two brine shrimp feedings a day and one dry. After that they got one brine shrimp feeding and two dry feedings.

Another point of difference. The planted tank only gets a 25% water change every three or four weeks. The fry tanks with the larger females got two 30% water changes a week.

The larger wild guppy is 126% longer than the smaller wild guppy. The Full Red guppy is 153% longer than the smaller wild guppy.

Stated another way, the larger wild female is 82% of the size of the Full Red female. The small wild female is only 65% percent of the size of the Full Red female.

This is an excellent demonstration of the relative influences of environment and genetics. The Full Red guppy is larger than the wild type female because of genetics. The larger wild type female is larger than the smaller one because of diet, competition for food and tank conditions. 

Here is another comparison between the larger wild type guppy and the Full Red female.

Wild type female and Full Red.

And now between the two wild type females.

The two wild type females

This thought strikes me.

"Why the hell am I feeding my guppies so much when all I gain is 25% increase in growth!"

I am changing the water twice a week in my fry tank because I feed heavily. If I cut way back I won't have to change as much water.

Another thought strikes me.

"Why the hell are we striving for large guppies?"

After forty years of selective breeding, the fancy guppy is only 20% larger than the wild guppy.

Large guppies, like large dogs, live shorter lives, have more health problems and are less fertile than their wild cousins. Is it really worth it?

What do you think?