Two from one: new research maps out evolution of genders from hermaphroditic ancestors

Nov 20, 2008

Research from the University of Pittsburgh published in the Nov. 20 edition of Heredity could finally provide evidence of the first stages of the evolution of separate sexes, a theory that holds that males and females developed from hermaphroditic ancestors. These early stages are not completely understood because the majority of animal species developed into the arguably less titillating separate-sex state too long ago for scientists to observe the transition.

However, Tia-Lynn Ashman, a plant evolutionary ecologist in the Department of Biological Sciences in Pitt's School of Arts and Sciences, documented early separate-sex evolution in a wild strawberry species still transitioning from hermaphroditism. These findings also apply to animals (via the unified theory) and provide the first evidence in support of the theory that the establishment of separate sexes stemmed from a genetic mutation in hermaphroditic genes that led to male and female sex chromosomes. With the ability to breed but spared the inbred defects of hermaphrodites, the separate sexes flourished.

"This is an important test of the theory of the early stages of sex chromosome evolution and part of the process of understanding the way we are today," Ashman said. She added that the study also shows that plants can lend insight into animal and human evolution. "We have the opportunity to observe the evolution of sex chromosomes in plants because that development is more recent. We wouldn't see this in animals because the sex chromosomes developed so long ago. Instead, we can study a species that is in that early stage now and apply it to animals based on the unified theory that animal and plant biology often overlaps."

Ashman reported in Science in 2004 that animals and flowering plants employ similar reproductive strategies to increase reproductive success and genetic diversity. These methods include large numbers of sperm cells in males, mate competition and attraction through fighting or natural ornamentation, aversion to inbreeding, and the male inclination to sire as many offspring as possible.

For the current study, Ashman and Pitt postdoctoral research associate Rachel Spigler worked with a wild strawberry species in which the evolution of separate sexes is not complete, so hermaphrodites exist among male and female plants. Sex chromosomes in these plants have two loci—or positions of genes on a chromosome—one that controls sterility and fertility in males and the other in females. Offspring that inherit both fertility versions are hemaphrodites capable of self-breeding. Plants that possess one fertility and one sterility version become either male or female. Those with both sterility versions are completely sterile, cannot reproduce, and, thus, die out.

The single-sex plants breed not only with one another but also with hermaphroditic plants and pass on the mutation, which can result in single-sex offspring. (Sterile plants also can result, but plants with genes that favor the production of fertile offspring will be more successful.) When inbreeding depression in hermaphrodites is also considered, Ashman said, a gradual decline in the number of hermaphroditic plants is to be expected. Consequently, fewer chromosomes with both fertility versions of the loci will be passed on and the frequency of single-sex individuals will increase.

Access this paper on the Heredity Web site at www.nature.com/hdy/journal/vaop/ncurrent/full/hdy2008100a.html

Source: University of Pittsburgh

Explore further: Lemurs match scent of a friend to sound of her voice

add to favorites email to friend print save as pdf

Related Stories

The search for seeds of black holes

Mar 27, 2014

(Phys.org) —How do you grow a supermassive black hole that is a million to a billion times the mass of our sun? Astronomers do not know the answer, but a new study using data from NASA's Wide-field Infrared ...

Sucker-footed fossils broaden the bat map

Feb 04, 2014

Today, Madagascar sucker-footed bats live nowhere outside their island home, but new research shows that hasn't always been the case. The discovery of two extinct relatives in northern Egypt suggests the ...

Recommended for you

Gene removal could have implications beyond plant science

1 minute ago

(Phys.org) —For thousands of years humans have been tinkering with plant genetics, even when they didn't realize that is what they were doing, in an effort to make stronger, healthier crops that endured climates better, ...

Lemurs match scent of a friend to sound of her voice

12 hours ago

Humans aren't alone in their ability to match a voice to a face—animals such as dogs, horses, crows and monkeys are able to recognize familiar individuals this way too, a growing body of research shows.

Chrono, the last piece of the circadian clock puzzle?

14 hours ago

All organisms, from mammals to fungi, have daily cycles controlled by a tightly regulated internal clock, called the circadian clock. The whole-body circadian clock, influenced by the exposure to light, dictates the wake-sleep ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Stratford
not rated yet Nov 25, 2008
A submersed aquatic macrophyte, Hydrilla verticillata, has both monoecious and dioecious forms. Is this another example of incomplete evolution from monoecious to the dioecious state?

More news stories

ESO image: A study in scarlet

This new image from ESO's La Silla Observatory in Chile reveals a cloud of hydrogen called Gum 41. In the middle of this little-known nebula, brilliant hot young stars are giving off energetic radiation that ...

First direct observations of excitons in motion achieved

A quasiparticle called an exciton—responsible for the transfer of energy within devices such as solar cells, LEDs, and semiconductor circuits—has been understood theoretically for decades. But exciton movement within ...

Patent talk: Google sharpens contact lens vision

(Phys.org) —A report from Patent Bolt brings us one step closer to what Google may have in mind in developing smart contact lenses. According to the discussion Google is interested in the concept of contact ...

Warm US West, cold East: A 4,000-year pattern

Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, ...