Sex Determination in Parasitic Fish Species Surprises Scientists

Fagjun | Published 2017-04-01 06:57

Scientists have found that the availability of resources is what drives sex determination in lampreys, an eel-like fish.

In mammals, chromosomes determine sex. In reptiles, meanwhile, the temperature eggs are in determines sex. The new discovery about lampreys is thus surprising. For now, they are the only known species whose sex is determined by the availability of resources and their growth rate at the larval stage.

For a long time, scientists have wondered why adult lamprey populations are either mostly male or mostly female. Now, they may have their answer.

Sex Determination at Its Most Practical

A lamprey's mouth and teeth
[Photo by Drow_male]

Lampreys are jawless, eel-like fish with a funnel-like mouth that contains circling rows of sharp teeth. They feed by sucking blood out of other fish. People have long considered them weird at best and terrifying at worst, with good reason. They are a parasitic species that can become quite invasive. In fact, they've decimated native fish populations in the areas they've invaded.

Now, a new study has discovered more about the biological characteristics of lampreys. As larvae, lampreys have undifferentiated sex organs, and sex determination begins when they are about a year old. When the lamprey larvae have access to a lot of nutrients, they grow bigger at a faster rate. Larvae with access to abundant nutrients develop into females. However, when the larvae have access to less or insufficient nutrients, they don't grow as large or as quickly. These larvae develop into males.

A team of scientists discovered these findings when they conducted an experiment in streams near the Great Lakes in the US. Some of the study areas had a lot of nutrient sources, while other areas had little. The team released between 1,500 to 3,000 lamprey larvae into these areas.

When the larvae matured into adult lamprey, the scientists recaptured them to study their development. The scientists found that the lamprey that had access to a lot of nutrients were larger and matured earlier. These lampreys were also more likely to be female. Meanwhile, in the areas with fewer sources of nutrients, the lampreys were smaller and predominantly male.

Controlling Lamprey Invasions

Sea lamprey feeding on another fish
[Photo via]

The researchers say that one reason for this may be because females need more nutrients to produce eggs. A nutrient-rich environment is of course better for breeding. Thus, larvae are more likely to become female if they are surrounded by sources of nutrients.

This information on the sex determination of lampreys may be beneficial to efforts to control lamprey populations. The findings can help save money by directing control efforts to focus on female-dominated areas. This way, authorities can stop lamprey invasions from happening.

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