Why Don’t More Animals Change Their Sex

Feb 02, 2009

(PhysOrg.com) -- Most animals, like humans, have separate sexes — they are born, live out their lives and reproduce as one sex or the other. However, some animals live as one sex in part of their lifetime and then switch to the other sex, a phenomenon called sequential hermaphroditism. What remains a puzzle, according to Yale scientists, is why the phenomenon is so rare, since their analysis shows the biological “costs” of changing sexes rarely outweigh the advantages.

A report by Yale scientists in the March issue of The American Naturalist says that while this process is evolutionarily favored, its rarity cannot be explained by an analysis of the biological costs vs benefits.

Sequential hermaphroditism naturally occurs in various organisms from plants to fishes. Following four decades of research that established why sex change is advantageous, the question remained why it is rare among animals. In this study, Yale graduate student Erem Kazancioglu and his advisor Suzanne Alonzo, assistant professor of ecology and evolutionary biology, demonstrate that sex change is surprisingly robust against costs.

While the adaptive advantage of sex change is well understood, it is not clear why relatively few animals change sex. According to Alonzo, “An intuitive, yet rarely studied, explanation is that the considerable time or energy it takes to change sex make hermaphroditism unfeasible for most animals.”

To test whether the biological costs of changing sex affect sex change actually occurs, the researchers built theoretical models of the hermaphrodite and separate-sex life histories. In their “game” models, sex change “players” vary the age of their sex change, while the separate-sex strategy responds by altering the number of male and female offspring it produces.

“We were surprised to see that a hermaphrodite could spend 30 percent of its lifetime in the process of change sex, and still persist in a population,” said Kazancioglu. “This suggests that only huge costs can disfavor sex change.”

So, why is sex change so rare? And, why does one species of fish reproduce strictly as separate sexes, while another very closely related species flexibly changes sex? A comparative study of hermaphroditic and separate-sex mating systems, which the authors are currently performing, may provide a clue, according to Kazancioglu, “Reproductive behaviors such as parental care seem to disfavor sex change in some species. We are investigating whether general patterns like these may explain the rarity of hermaphroditism.”

Citation: The American Naturalist (March 2008)

Provided by Yale University

Explore further: Study shows sharks have personalities

add to favorites email to friend print save as pdf

Related Stories

Scholar tracks the changing world of gay sexuality

Sep 19, 2014

With same-sex marriage now legalized in 19 states and laws making it impossible to ban homosexuals from serving in the military, gay, lesbian and bisexual people are now enjoying more freedoms and rights than ever before.

Taking the 'sting' out of reproduction

Sep 12, 2014

(Phys.org) —Female parasitic wasps have more reproductive success when working together with other females, which can also explain sex biased reproduction, according to new research.

Whale sex: It's all in the hips

Sep 08, 2014

(Phys.org) —Both whales and dolphins have pelvic (hip) bones, evolutionary remnants from when their ancestors walked on land more than 40 million years ago. Common wisdom has long held that those bones ...

We are all made of stars

Sep 02, 2014

Astronomers spend most of their time contemplating the universe, quite comfortable in the knowledge that we are just a speck among billions of planets, stars and galaxies. But last week, the Australian astronomical ...

Recommended for you

Study shows sharks have personalities

2 minutes ago

Some sharks are 'gregarious' and have strong social connections, whilst others are more solitary and prefer to remain inconspicuous, according to a new study which is the first to show that the notorious ...

Alaska refuge proposes killing invasive caribou

3 hours ago

Federal wildlife officials are considering deadly measures to keep an Alaska big game animal introduced more than 50 years ago to a remote island in the Aleutians from expanding its range.

Genetic secrets of the monarch butterfly revealed

6 hours ago

The monarch butterfly is one of the most iconic insects in the world, best known for its distinct orange and black wings and a spectacular annual mass migration across North America. However, little has been ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

LuckyBrandon
not rated yet Feb 02, 2009
they talk about asexual species as if they are hermaphodites, yet they are not, as they reproduce with themselves, which outside of plants, and I could be wrong here, as far as I know is unknown. Those plants which turn to hermaphs always have female or hermaph offspring, which depending on what you are growing, can be a good or bad thing. From an evolutionary point of view, it can either continue or kill a species.
BUT...a species turning FROM MALE TO FEMALE, OR VICE VERSA, is not a hermaphodite, since a herpmaphoite by defintion contains BOTH sexes within it. This makes at least the wording in this article contradictoary to its meaning.
In the end, we will likely end up an asexual species, and yes, hermies are probably a step in that direction...but so is the obvious weaknesses in past, current, and future generations...meaning, where a man (or woman) 100 yrs ago could tolerate a certain situation (such as no electricity or non-natural heat in a cold a*s winter), the future generations could not even contemplate it.
i guess i fail to see the usefulness in this experimentation/research until we could technically change our species to be asexual...
alot of tequila behind me though, so ill revisit this article tomorrrow :D
Ausjin
not rated yet Feb 03, 2009
a species turning FROM MALE TO FEMALE, OR VICE VERSA, is not a hermaphodite, since a herpmaphoite by defintion contains BOTH sexes within it.

That is simultaneous hermaphroditism. I believe you look up sequential hermaphroditism when you do revisit, though.
Mercury_01
not rated yet Feb 03, 2009
"Why Don%u2019t More Animals Change Their Sex"

Because its "tazoo"!