Featured Research

from universities, journals, and other organizations

Genetic Conflict In Fish Led To Evolution Of New Sex Chromosomes

Date:
October 2, 2009
Source:
University of Maryland
Summary:
Biologists have genetically mapped the sex chromosomes of several species of cichlid fish from Lake Malawi, East Africa, and identified a mechanism by which new sex chromosomes may evolve.

The blotched color pattern is not beneficial for males, who must appear brightly colored to attract the greatest number of female mates (photo above shows normal male coloration at top and a fish expressing the blotched color pattern below).
Credit: Reade Roberts, University of Maryland

University of Maryland biologists have genetically mapped the sex chromosomes of several species of cichlid (pronounced "sick-lid") fish from Lake Malawi, East Africa, and identified a mechanism by which new sex chromosomes may evolve. In research published in the journal Science (October 1, 2009), Professor Thomas D. Kocher, Department of Biology, College of Chemical and Life Sciences; Reade Roberts, post-doctoral associate; and Jennifer Ser, research associate, describe the genetic basis for two co-existing systems of sexual determination in cichlid fish from Lake Malawi.

In nearly all mammals, the gene that determines the sex of offspring is located on the Y chromosome, which is much smaller than the X chromosome. But in many other animal groups, the genetic mechanism of sex determination evolves quite rapidly, and the differences between sex chromosomes are harder to observe. Even sister species of fish may have entirely different sex determination systems. How and why the genetic mechanisms for such an ancient developmental distinction continue to evolve has remained a mystery. The thousands of closely related cichlid fishes in the lakes of East Africa turn out to be an excellent model system for understanding how the mechanisms of how sex determination evolve.

The East African cichlid fishes that inhabit Lakes Malawi, Tanganyika, and Victoria are known for their sexually distinct appearance – the males are generally conspicuous and brightly colored, making them more attractive to females, while the females are drab and brown, making them inconspicuous to predators. One exception to the uniformly brown pigmentation among female cichlids is the "orange blotch" pattern, which appears in some female cichlids that live in rocky areas of Lake Malawi. "We believe that the orange blotch color pattern emerged as a new mutation in females and has a selective advantage in providing an alternative form of camouflage," says Dr. Kocher, who has been leading research to identify the genetic basis for phenotypic differences in cichlids for the past 20 years, and who made the first crosses to map the gene responsible for this color pattern in 1993.

Depending on the surrounding natural background, this color pattern can help disguise female fish and help them avoid predation. However males who express this phenotype lack the species-specific color patterns used by females to select their mates. "This phenotype creates a sexual conflict because the allele is favored in females but not favored in males," explains Dr. Roberts, who fine mapped the gene. "In 'survival of the fittest,' the genes underlying a beneficial trait will increase in frequency, but this is an odd case where the trait is really good for females but really bad for males."

Using genomic techniques, Roberts identified the gene (pax7) that is responsible for this difference in color pattern. He found that the orange blotch (OB) allele that produces the variable pigmentation in females was dominant over the "brown barred" (BB) allele (that produces the more common brown pigmentation) and that it was located very near a female sex determiner (W). The genetic conflict that started over color was resolved by a new mutation that took over the sex determining function, and ensured that nearly all orange blotch fish are female.

"This study marries two evolutionary mysteries: the incredible diversity of fish in the lakes of East Africa and the genetic basis of sex determination," says Sam Scheiner, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research. "This study shows how simple genetic changes can lead to enormous biological diversity."


Story Source:

The above story is based on materials provided by University of Maryland. Note: Materials may be edited for content and length.


Cite This Page:

University of Maryland. "Genetic Conflict In Fish Led To Evolution Of New Sex Chromosomes." ScienceDaily. ScienceDaily, 2 October 2009. <www.sciencedaily.com/releases/2009/10/091001164227.htm>.
University of Maryland. (2009, October 2). Genetic Conflict In Fish Led To Evolution Of New Sex Chromosomes. ScienceDaily. Retrieved September 21, 2014 from www.sciencedaily.com/releases/2009/10/091001164227.htm
University of Maryland. "Genetic Conflict In Fish Led To Evolution Of New Sex Chromosomes." ScienceDaily. www.sciencedaily.com/releases/2009/10/091001164227.htm (accessed September 21, 2014).

Share This



More Plants & Animals News

Sunday, September 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: San Diego Zoo Welcomes Cheetah Cubs

Raw: San Diego Zoo Welcomes Cheetah Cubs

AP (Sep. 20, 2014) The San Diego Zoo has welcomed two Cheetah cubs to its Safari Park. The nearly three-week-old female cubs are being hand fed and are receiving around the clock care. (Sept. 20) Video provided by AP
Powered by NewsLook.com
Chocolate Museum Opens in Brussels

Chocolate Museum Opens in Brussels

AFP (Sep. 19, 2014) Considered a "national heritage" in Belgium, chocolate now has a new museum in Brussels. In a former chocolate factory, visitors to the permanent exhibition spaces, workshops and tastings can discover derivatives of the cocoa bean. Duration: 01:00 Video provided by AFP
Powered by NewsLook.com
Could Grief Affect The Immune Systems Of Senior Citizens?

Could Grief Affect The Immune Systems Of Senior Citizens?

Newsy (Sep. 19, 2014) The study found elderly people are much more likely to become susceptible to infection than younger adults going though a similar situation. Video provided by Newsy
Powered by NewsLook.com
Jury Delivers Verdict in Salmonella Trial

Jury Delivers Verdict in Salmonella Trial

AP (Sep. 19, 2014) A federal jury has convicted three people in connection with an outbreak of salmonella poisoning five years ago that sickened hundreds of people and was linked to a number of deaths. (Sept. 19) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins