How sperm evolved into storage for years can survive

we had an article in March, "Don't want to go to work on Monday?" Ants' sperm work harder than yours, telling the story of the leaf-cutting ants' efforts to pass on generations. Leaf-cutting ants mate only once in their lives, during which they mate with several male ants and then store sperm that will be used to fertilized millions of eggs over their lifetimes.
today's paper is the author's blog for us, and Liberti and his colleagues explain more about the ant's unique mating biology and how sperm evolved to survive years of storage.photo shoot: Pixabay
often encountered countless ants transporting long processes of large plants while visiting forests in Central and South America. These are leaf-cutting ants, the main herbivores in the new tropics, which are collecting leaves and flowers to feed their bacterial crops in underground chambers.
this symbiosis is similar in many ways to our agriculture: ants rely exclusively on bacteria for food, fertilize them with collected materials, and even use antibiotics to treat bacterial garden diseases.
has long attracted the attention of scientists trying to understand the evolutionary dynamics of collaboration between organisms in the biological world. However, the unique mating biology of these ants and the extra long life span of the ants are also of great interest.ant queen can live for twenty or thirty years, during which time she will not re-mate, but she will carefully use sperm from male ants to fertilized millions of eggs.
leaf ant queens mate in a single mating activity in early adulthood. When the queen begins the mating flight, she mates with multiple male ants and then returns to the ground to shed her wings and look for a suitable place to dig a hole.
Although male ants die almost immediately after delivering sperm to the queen, the queen can live for twenty or thirty years, during which time she will no longer mate, but will carefully use the sperm from the male ant , which is stored in a specialized organ called a sperm sac , to fertilized millions of eggs.
This prolonged sperm storage is a record in the animal kingdom and creates a rare lifelong commitment between partners - similar to a female vertebrate that uses sperm from several males to conceive continuously, and sperm needs to remain active and protected from aging mechanisms years after the male's death, at ambient temperatures.
because multiple male ants inseminate a leaf-cutting ant in one afternoon, sperm from different male ants compete for storage in the sperm sacs of the queen. This interaction between competing storage and the need to survive years of storage has created a unique evolutionary adaptation in ant sperm.reproductive studies of vertebrates have determined that sperm can respond to subtle changes in their surroundings, allowing them to reach female eggs more efficiently and inseminate. These changes may be pH, ion concentration, or changes in reproductive system temperature and gland secretions, or the appearance of specific molecules that attract sperm to insemination.
By drawing on an experimental method commonly used in vertebrate research to quantify sperm vitality, we found that ant sperm do the same thing: when exposed to male secretions and the reproductive organs of queens, not only do larger proportions of sperm become active and swim faster, but sperm react very differently depending on whether the secretions come from themselves or from queen and competing males."
first noticed that when semen from different males was mixed, sperm movement increased compared to swimming alone with the same shot. To determine what causes these increases, we conducted additional experiments to collect sperm from concerned males and let the sperm swim through semen from the same male, semen from competing males, or secretions from different chambers of the queen reproductive organs, and a mixture of these fluids.
We found that semen ejacuited with sperm increased movement compared to control groups using physiological saline, and this movement increased further once the sperm came into contact with fluids from competing male semen or queen sacs.
Since the fluids in the semen and queen sacs of competing males are non-auto-tissue secretions from the sperm point of view of concern, we infer that sperm must respond to molecules present in non-self-secretions and regulate movement accordingly - a meaningful response when competitor ejaculation exists, i.e. competition for storage increases a chance of male reproduction success."Once sperm are insemination in the queen, their activity may immediately become maximum, irrelevant to the presence of competing sperm, so why do sperm swim more slowly in their own semen? Expressing an identification mechanism that distinguishes between self and non-self can be costly, so our observations need to be explained from an evolutionary perspective.
we assume that this cognitive evolution is due to the high energy consumption of continuous sperm movement and the production of reactive oxygen (ROS). Sperm are particularly sensitive to structural damage caused by ROS because they lack a rich damage repair mechanism, which means that any increase in ROS could lead to irreversible loss of sperm fertilization capacity
so there may be a trade-off between the increased movement that sperm needs to gain storage competition and the long-term survival of sperm once stored - which is important because it can take many years for the eggs to fertilized.
data from several studies suggest that ROS damage control is a key factor in maintaining sperm viability - a variety of ants and bees are increased in antioxidant enzymes after sperm storage, and these enzymes are abundant in their semen.
Refore, to further illustrate the evolutionary dilemma of how ants ensure long-term sperm survival at the cost of sperm competition, future studies should attempt to measure more directly the amount of ROS produced in connection with sperm movement. (Source: Science.com)