Ants: genes make queens

The environment is not only responsible for the role in the colony

Red and black male of the harvest ants Ohio State University
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Social insects such as bees or ants live in a strict caste system - a precise division of duties between the members of the insect state. In most cases, environmental conditions determine whether a larva develops into a queen or a barren worker. But scientists have now discovered ant colonies where genes, not the environment, determine the later stages of individual animals.

A colony of harvest ants usually consists of one queen and hundreds or thousands of sterile workers. Male harvest ants, made from unfertilized eggs, typically serve only one purpose: to mate with a queen. Similarly, a queen lays eggs for males and fertile females only if new colonies are to be established.

Crucial gene differences discovered

Steve Rissing, a biology professor at Ohio State University, Columbus, and colleagues have studied harvest ants in southern Arizona and New Mexico, and found that some of the males in those colonies looked unusual. They collected several dozen pairs of queens and males and analyzed their genes in the lab - with surprising results.

"The DNA from some of these ants was just weird - we did not expect to get such results, " explains Rissing. "It appears that the queens in these colonies mate with males of two distinct genetic lineages. From mating with a line usually fertile females emerged - new queens. But when they mated with the other genetic lineage, their offspring became overwhelmingly infertile workers. "

"This type of reproductive behavior is very different from what we know in ant colonies, " the researcher continues. "We expected to find the same DNA sequence in all animals in the colony. But that was not the case here. "Both males and queens each had two gene lines. According to traditional interpretations, the need for female workers in a colony dictates the fate of their offspring, regardless of their genetic predisposition. But this study now seems to refute these assumptions. display

Targeted mating ensures balance

In order for the desired parity to be achieved, the researchers conclude that the queen must mate with males of the two different lineages during their single mating season. Only then can she store a supply of both types of sperm and fertilize her eggs. However, this presupposes that she also recognizes the different males. But how?

Here, too, the collected ants brought to light: The males of both gene lines were colored differently. If the queen orients herself to this color, she can ensure that she pairs with both types frequently enough to create a supply of both sperm that will ensure the survival of the colony.

Conversely, the males apparently have no chance of distinguishing the queen's lineages fortunately: If males could do this, this could be the end mean the colony, "explains Rissing. Because theoretically every male wants to pass on his genes to future generations. However, if it is paired with a female of the other lineage, the offspring are infertile workers and its genes die out. If, however, it would only mate with females of its own line, the colony will later lack the workers.

This population of crop ants needs the two-line system to survive. The hybrid workers' caste is the link between the otherwise independent gene lines H1 and H2, according to the researchers. This is a pretty unusual result. But with access to better and better analytical tools to explore such phenomena at the molecular level, we will most likely find that a whole range of social insects deviate from our ideas and theories.

(Ohio State University, 27.01.2005 - NPO)