Question

Hermaphrodites are individual organisms containing both male and female sex organs. Discuss how sexual selection might operate on hermaphrodites, and explain which different aspects of sexual selection are likely to be stronger or weaker in hermaphrodites than in separate-sexed organisms.

Answer 1

In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the "female" or "male".

For example,

the great majority of tunicates, pulmonate snails, opisthobranch snails, earthworms, and slugs are hermaphrodites.

Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates.

Most plants are also hermaphrodites.

with help of an example hermaphrodite sexual selection will be explained as below.

Organisms is Earthworm.

One of the most interesting aspects of earthworms is their sexuality.

Earthworms are simultaneous hermaphrodites, meaning worms have both male and female reproductive organs.

During sexual intercourse among earthworms, both sets of sex organs are used by both worms. If all goes well, the eggs of both of the mates become fertilized.

You can imagine this is a highly efficient way of ensuring the survival of the species. Vermicomposters, people who raise worms and other organisms to compost, report that their earthworm populations typically double every 60 to 90 days

To copulate, two worms line up against one another facing opposite directions.

In this position, both worms excrete so much mucous, that what is called a slime tube forms around their bodies.

Each worm ejaculates sperm from its sex organs into this slime tube and it is then deposited in the other worm's sperm receptacle.

The act of mating is completed, but the process of reproduction still continues as each worm goes its separate way

You know the wide band near the front of any earthworm?

That band is called the clitellum and it's responsible for producing another tube of mucus.

This band is passed forward toward the mouth end of the worm.

As it travels forward, the mucus passes over the sacs containing the worm's own eggs, which stick to the slime.

Attached to the slime tube, the eggs then pass over the seminal receptacle, where the other worm's sperm is kept.

The eggs and sperm come in contact in the slime tube and if all goes well, the eggs are then fertilized.

The band of slime is wriggled off the head of the worm and forms a cocoon in the shape of a lemon for the anywhere from four to 20 worm eggs that the common European earthworm typically lays. In about two to three weeks, the newborn worms will hatch and emerge from the cocoon into the soil. This cycle of reproduction can happen every week to 10 days, another reason earthworm populations can grow so quickly

Sexually selected traits are predicted to show condition dependence by capturing the genetic quality of its bearer. In separate‐sexed organisms, this will ultimately translate into condition dependence of reproductive success of the sex that experiences sexual selection, which is typically the male.

Such condition dependence of reproductive success is predicted to be higher in males than females under conditions promoting intense sexual selection.

For simultaneous hermaphrodites, however, sex allocation theory predicts that individuals in poor condition channel relatively more resources into the male sex function at the expense of the female function.

Thus, male reproductive success is expected to be less condition dependent than female reproductive success. We subjected individuals of the simultaneously hermaphroditic snail Physa acuta to two feeding treatments to test for condition dependence of male and female reproductive success under varying levels of male–male competition.

Condition dependence was found for female, but not for male, reproductive success, meaning that selection on condition is relatively stronger through the female sex function.

This effect was consistent over both male–male competition treatments. Decomposition of male and female reproductive performance revealed that individuals in poor condition copulated more in their male role, indicating an increased male allocation to mate acquisition.

These findings suggest that sex‐specific condition dependence of reproductive success is at least partially driven by condition‐dependent sex allocation.

We discuss the implications of condition‐dependent sex allocation for the evolution of sexually selected traits in simultaneous hermaphrodites