Asking 'Why?' Leads to Interesting Things - Makapee's Days #1852

This is Makapee.
Every morning, starting around 4:00 AM before dawn, the neighbor's roosters crow 'cock-a-doodle-doo' just like they do in Japan.

I usually wake up around 5:30 AM, thinking, 'It's so noisy, why do they keep crowing so loudly every single day without getting tired of it?'

Anyway, at Glory's house where I live, a hen hatched two chicks yesterday.

This hen belongs to Glory, and she had laid several eggs and incubated them after mating with a rooster from the house next door.

By the way, did you know that chicks hatch about 21 days after a hen starts incubating her eggs?

This is the general incubation period for chicken eggs, but I didn't know that, even though my family home in Gunma ran a poultry farm.

That's because in the poultry business my father started, we didn't hatch fertilized eggs at home, sex the chicks, and raise only the females to be laying hens.

We would quickly buy female chicks from a manufacturer known for good egg-laying, and raise them until they became adults, but they didn't have a 100% survival rate, as there were accidental deaths and losses to crows and foxes.

So, as the son of a poultry farmer, I grew up without ever having any interest in breeding or anything related to it.

Oh well.

Currently, I am living in the countryside of Ifugao Province in the Philippines, surrounded by dogs, cats, and chickens, and a thought suddenly occurred to me.

It was, 'Why do the eggs a hen incubates all hatch at the same time?'

Certainly, living in the countryside, I often come across scenes of roosters mounting hens, but I wonder if the rooster has to work that hard to fertilize seven eggs?

Since there was no one around to ask casually, I asked ChatGPT and a surprising fact came to light.

Having said that, people who know, know. Perhaps it's just that I, who should have learned these basic things while graduating from an agricultural school, simply don't remember them at all.

Answer: A single mating can result in multiple eggs laid over the following days to weeks being fertilized.

Once a hen mates, she can store the rooster's sperm in a place in her body called the 'sperm storage tubule.' Then, as the egg is being formed, the stored sperm is used to fertilize it.

• Sperm survival period: Inside a hen's body, sperm can survive for about one to two weeks.

• Continuous fertilization: Therefore, once mating occurs, in the case of a hen that lays eggs every day, more than 10 subsequent eggs can potentially be fertilized.

• Changes in fertilization rate: As time passes after mating, the vitality of the stored sperm decreases, so the probability of the eggs being fertilized gradually declines.

Therefore, it is said that there is no need to mate many times during the laying period; a single mating makes it possible to continue laying fertilized eggs for a while!

Wow, I really didn't expect to learn about the existence of the 'sperm storage tubule' at my age!

Furthermore, Macapee wondered, 'Well, can we assume that this kind of fertilization and egg-laying exists in other birds as well?'

The answer comes back immediately!

Surprisingly, the mechanism of 'storing sperm in the body' is not just for chickens, but is a very important feature commonly seen in many bird species.

Similar to the case of chickens, it turns out that females of other bird species also have special structures called 'sperm storage tubules' (or seminal receptacles) within their reproductive tracts (such as the uterovaginal junction of the oviduct).

So, many birds, once they mate, can store sperm in their internal storage glands for several days to several weeks, or evenseveral months (depending on the species) while maintaining their viability.

And continuous fertilization When an egg is ovulated and passes through the oviduct, the stored sperm is used to fertilize it, so multiple eggs laid consecutively after a single mating become fertilized eggs.

Location of fertilization In the uppermost part of the oviduct, a place called the infundibulum, the yolk meets the sperm as it passes through, and fertilization is completed. Daily/continuous egg-laying Birds that lay eggs daily or continuously, like chickens, can use this storage system to efficiently produce fertilized eggs without needing to find a male every time they mate.

If you think about this in terms of humans, there might be cases where a woman could potentially have multiple fertilizations if she uses ovulation stimulants to release many eggs, but there is no sperm storage function.

And so, my questions grew further. There was also an immediate answer to the question, 'By the way, are there any mammals that have this kind of long-term sperm storage function?'

Surprisingly, there are species among some mammals, such as bats, where the female has the ability to store sperm in her body for a long period, just like birds!

Oh, the world is truly a vast place, isn't it! Haha.

The most well-known example is many species of bats that inhabit temperate regions.

• Mechanism: Bats mate before hibernation in the autumn or during hibernation.

• Storage period: Females store the sperm received from males in their reproductive tracts for several weeks to several months (until spring when hibernation ends).

• Delayed fertilization: After waking from hibernation, body temperature rises, and food becomes abundant, they ovulate in the spring and fertilize with the stored sperm.

This 'delayed fertilization' is considered a unique reproductive strategy for bats to offset the optimal time for mating (autumn) from the optimal time for giving birth and raising young (summer, when food is abundant).

Furthermore, what I was told is slightly different from the 'sperm storage' seen in birds, but many mammals, including bats, have a mechanism to delay the development of the fertilized egg in order to align their reproductive timing with the environment.

• Embryonic diapause (Diapause/embryonic dormancy):

  • Bears🐻, kangaroos🦘, raccoons, weasels, and many other animals.

  • Fertilization occurs and a fertilized egg (embryo) is formed, but implantation (the start of pregnancy) into the uterus is intentionally delayed for several months.

  • This allows them to offset the timing of mating and birth, adjusting so that they can begin raising their young during a time when food is abundant.

The 'long-term sperm storage' of birds is unique to bats among mammals, and many other mammals control their reproductive timing through 'delayed development or implantation of the fertilized egg.'

I, Macapee, cannot help but be impressed by how well the natural world has developed its reproductive capabilities.

This was Macapee.
Thank you for reading until the end. What did you all think?