Desert pupfish live in springs of the american southwest. today there are about 30 species of pupfish, but they all evolved from a common pleistocene ancestor. the southwestern united states was once much wetter than it is now, and the pleistocene pupfish flourished over a wide geographic area. over thousands of years, however, the sierra nevada mountain range was pushed upward by geological forces, blocking rainfall from the pacific ocean. as the large lakes dried up, small groups of pupfish remained in springs and pools fed by groundwater seepage. now, although many of these small springs still have pupfish, each population, through evolution, has become very different from populations of pupfish in other springs. the variation in gene pools among the 30 pupfish populations occurred through an evolutionary mechanism called:

not the best question format lol but what i think might as scale color is controlled by a single gene with two alleles, the green allele and the yellow allele. when moths that are homozygous for green scales are mated with moths that are homozygous for yellow scales, 100% of the offspring have green scales.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c