Olm Diary

Saturday, 30 January 2016

Cave guide Juan Pablo Maschio noticed the first olm egg and notified the management and the experts in charge of it.

At night, Primož and I took a close look at the egg attached to the wall of the aquarium (on the left-hand side viewed from where the cave tours pass by). The spot where the egg is located is the same spot where one of the female olms had spent a lot of time throughout summer. Judging by the scientific literature this is not the most suitable place for laying eggs, as there are, in fact, only two ideal egg-laying spots inside the aquarium. We removed all other olms, which could disturb the egg-laying process, or even eat the eggs, from the aquarium and moved them to the old olm pool in the Tartarus.


Wednesday, 3 February 2016

In the Concert Hall of Postojna Cave, we have noticed a new egg. It is attached to the bottom of a flat rock in the front part of the aquarium (viewed from where the cave tours pass by). In the last three days, the female olm has relocated its egg-laying territory to one of the two ideal spots. In the meantime, the chemical signals by means of which olms mark their territory might have disappeared. The olm is guarding its eggs.


Thursday, 4 February 2016

The third egg has appeared- on the reverse side of the stone which the second egg is attached to as well. The first egg has been left on its own. We have mounted a camera right above the egg. Ever since the egg laying started, three cave tours have been held on a daily basis, at 10:00, 12:00, 15:00.


Monday, 8 February 2016

The first egg has disappeared. Maybe the female has eaten it, or maybe she moved it somewhere else. Six eggs are visible on the egg-laying spot, guarded by the female.


Tuesday, 9 February 2016

The number of eggs has increased to 10. Seven of them are under the rock, and three behind it. The female is guarding them, never leaving their side.


Wednesday, 10 February 2016

Earlier today, at 11:30 am, there were 13 eggs in total. There might be even more of them now. In fact, the female olm was facing the bottom side of the rock with her belly turned towards it, so I did not want to disturb her in the middle of what might have been egg laying. An interesting detail: the olm wasn't climbing - it looked like she was using its tail to sort of fix herself between the bottom and the stone in order to reach the bottom of it.


Thursday, 11 February 2016

During the night, the olm has made us happy once again – today, there were 24 eggs in total, arranged on both sides of the flat stone.


Friday, 12 February

The olm's family to-be is still growing – earlier this afternoon there were 30 eggs in the aquarium.


Monday, 15 February

The female olm has laid two new eggs.


Tuesday, 16 February

At least forty-five. This is the number of eggs laid by the olm in two weeks. The eggs have made the stone under which they are hiding appear almost completely white.


Wednesday, 17 February

At some point during the night, the olm laid another egg. Now there are 48 eggs in total. We have installed an infrared camera. We have enclosed the aquarium with some black cloth and turned off all of the lights. There is nothing disturbing the female olm now. She is taking care of the eggs.


Thursday, 18 February

So far the olm has laid 50 eggs.


Friday, 19 February

The olm has laid egg number 52.

The camera allows us to watch cave amphipods getting nearer toindividual eggs. Small stream crustaceans used in our aquarium to feed the olms. At the moment, there are only few amphipods, but we could still see three of them trying to bite through the egg envelope while the female was away. As soon as the female returned, she immediately noticed them and attacked them. The amphipods hid between the egg and the rock. At the first opportunity, they got away to hide somewhere safe, behind the rocks.

The olms have a very well developed sense of smell and, more importantly, are able to detect even weak electric fields of other animals. Thus, they are able to get a sense of the world that surrounds them even without normally developed eyes, which they, in this eternal darkness of caves, actually do not even need.


Saturday, 20 February

The female has laid two more eggs, now there are 54 in total. The egg-laying period is slowly coming to an end and instead of adding up, we will start subtracting. All of the unfertilized eggs will decay and the number of eggs will thus start to decrease. But not right away. In a span of just over twenty days, olms lay up to seventy eggs.


Sunday, 21 February

The olm has laid egg number 55.


Monday, 22 February

We could observe our female olm gently sniffing the eggs, thus searching for those that had already decayed. While sniffing them, she gentle touched and cleaned them. This helps fine particles to fall from the egg envelope which would otherwise slowly cover and suffocate the eggs.


Tuesday, 23 February

An ordinary day. The female is guarding her eggs.


Wednesday, 24 February

We have received a visit by an expert on the biology of olms, Dr Lilijana Bizjak Mali, from the Biotechnical Faculty in Ljubljana, and Dr Stanley Sessions, an expert on integrative biology of amphibians from Hartwick College, New York, USA. They examined the eggs and found that some of them are showing signs of development. For the eggs laid only a few days ago it is perhaps still too early to show signs of embryonic development.

They measured the amount of oxygen in the aquarium water. There is more than enough of it for the olms. However, the two experts have nevertheless suggested aerating the aquarium water additionally.

In the USA, Dr Sessions, among other things, researches the closest olm's relative, i.e. a urodele amphibian from the genus Necturus. Necturi live in the surface waters of the eastern coast of North America. Ancestors and relatives of the olm hereabouts were also surface-dwelling animals. They died out during the ice age period.


Thursday, 25 February

Primož and I check on the other olms which had been living in our aquarium until they were moved elsewhere. In this dark space, most of them stay on the sinter wall of the pool. In the complete darkness of the cave, there is not a great amount of stimuli. In nature, the olms can stay motionless for hours on end.


Friday, 26 February

Primož and I have installed an air pump, which allows for better aeration of the aquarium water. We also regularly check the aquarium to make sure it is properly dimmed.


Saturday, 27 February

The olm has laid egg number 56. The camera shows a bulge, which gives us hope that there are some more eggs to follow.


Sunday, 28 February

The olm is guarding the eggs.       


Monday, 29 February

In the afternoon, the female laid egg number 57. In the Concert Hall, Primož and I have set up an additional aquarium. Visitors are able to see two of the olms from the Tartarus.


Tuesday, 1 March

The olm has laid another egg - now there are at least 58eggs in total. An air pump has been set up.


Wednesday, 2 March

Measurements in the aquarium have revealed the oxygen content to be 9'65 mg O2/l. Compared to the measurements before the air pump was installed, this was an increase by just over a milligram/litre. The saturation is 96%.


Friday, 3 March

The olm has laid two more eggs. She was rather restless and moved around a lot. We could see she was defending the eggs from the cave amphipods.


Monday, 7 March

Our female olm has laid two more eggs.


Thursday, 10 March

The long wait has started. The female has stopped laying eggs and is now behaving differently. She is much quieter. She spends a lot of time under the rock guarding the eggs. She is no longer looking for spots suitable for egg laying. Every now and then, she disappears from the screen for quite a long time. Since we are not filming the spot where the eggs are located (hence this particular spot is in complete darkness), we can assume that she is during this time near the eggs.


Tuesday, 15 March

Earlier today, Primož and I went to have a closer look at the subterranean River Pivka, the olms' natural habitat. The water level has risen. The Pivka was roaring and moving stones. These are the kind of conditions that allow the passages of Postojna Cave to expand. High water levels endanger the olms as the water may carry the olms out of the cave. Outside the cave, most of the olms die. The water may throw the olms against rocks. Therefore, olms tend to hide from high waters. In spots where usually up to thirty olm specimens can be seen, not a single olm was noticeable earlier today.


Thursday, 17 March

The female is guarding the eggs at all times.


Monday, 21 March

The eggs are photographed every fourteen days. Minimal lighting and exposure extended to few minutes produce good enough photographs for us to be able to keep track of what is going on in the semi-darkness. Some of the photographs show early stages of development. The fertilized eggs first undergo the process of cleavage, which lasts just over two weeks, followed by formation of the germ layers and axis formation, which takes up to a month after fertilization. During the neurulation process, the central nervous system is formed. The embryos slowly become visible.


Tuesday, 22 March

The water levels inside the cave are slowly decreasing. During a quick cave visit to the Tartarus, we saw four olm specimens. 


Monday, 28 March

In the last days of the week, we noticed some rather unusual behaviour. The female suddenly left the eggs where they were and moved to the other end of the aquarium. We thought she was having a rest, but when we had a closer look, we saw that she had laid another egg. Our two biologists are still wondering why she had withdrawn to this other spot; it was noticeable there were at least 3 more eggs left in the abdominal part of the olm’s body. Perhaps this was natural behaviour aiming to give the eggs divided into two different places a greater chance of survival, but it is impossible to say with certainty, as the olm has never before been exposed to being studied in such a way. 


Tuesday, 29 March

After a three days’ rest, the female returned to where the majority of eggs were, but now she is in a different position and seems much calmer. She is not checking on the eggs as often as during the first month, but is lying around most of the time. This is something new we have learnt about the olms, and most likely an indication of how exhausting laying eggs in a dark and cold environment and the constant scaring away of the amphipods are for olms, which, on average, only reproduce once in a decade. With everything she has been doing so far, the female olm is challenging our knowledge of olms, as previously it was believed that the egg-laying period lasts about 3 weeks, whereas in Postojna Cave it has this time been going on for almost two months.


Wednesday, 30 March

Some of the eggs that have been laid are unfertilised. The unfertilised eggs can be recognised by the lack of development, which is slowly followed by the first signs of decay. The decaying eggs become muddy and this is when they need to be removed, which is not an easy task to do inside the aquarium. Primož puts on a wetsuit and together we remove the four unfertilised eggs. The risk of fungi being transmitted onto the developing eggs has thus been reduced, however, the procedure will have to be repeated. There are still some unfertilised eggs left. Before repeating the procedure, we have consulted with Dr Olivier Guillaume, who is one of the greatest experts on dealing with the olms and is employed at the research laboratory in Moulis, France.


Friday, 1 April

Primož and I removed twenty decaying eggs. This one short sentence involves hours of debating what to do, observing, weighing different options and making decisions. We had prepared a base on which to place the stone with the eggs. Only then it became obvious how many eggs had been attacked by fungi. We first tried removing the eggs using tweezers and later a glass tube. We felt quite a relief after work was done.

The first embryos' movements coincided with the April Fools’ Day. Therefore, I was somewhat restrained listening to Branko telling me enthusiastically about how he had seen embryos moving in front of a group of tourists. But he was right, in some of the eggs, you could really see embryos coiling from one C-shape to another. The newly developed muscles were flexing.


Monday, 4 April

Three more eggs were showing signs of deterioration, so we removed them.


Thursday, 7 April

Primož, Dr Mali, Dr Sessions and I visited a speleobiological laboratory in Moulis, France. The day was full of confirmations and inspiration. Primož and I realized that what we had been doing so far does not differ much from the French practice. We also realized how unique everything that is going on in Postojna Cave is, when they told us they had been waiting for new offspring for ten years.


Sunday, 10 April

Some more embryos' movement took place, but today the natural, spontaneous movements were S-shaped. You can imagine the excitement of the Postojna Cave visitors who had the opportunity to watch a proper little dance performance on the screen inside the cave.


Monday, 18 April

We were getting ready to relocate the stone with the eggs to a smaller aquarium, which will make it easier for us to monitor the conditions in the water surrounding our offspring. Since the eggs are now two months old they are now somewhat less firmly attached to the surface. That is why we prepared a metal base on which the eggs will be able to keep on developing if they fall off.


Tuesday, 26 April

Observing the embryos under a stereoscopic magnifying glass revealed how well the gills foundation had developed so far. The rudiments of the front legs are visible. The back side of the embryo is studded with pigment cells. We hope the next time some heartbeat will be noticeable as well.


Wednesday, 27 April

The big relocation. We carefully moved the stone into the container that was used to move the stone to the aquarium, which had been set up some distance away from the main cave tour route. Some of the eggs fell off and we moved them onto the mesh-like metal construction. Thus, their development now continues close to the surface, where the amount of oxygen is large.


Saturday, 7 May

The gills of our embryos are slowly branching. The blood circulation and the first heartbeat are noticeable. Life is becoming more and more tangible. The embryos have become considerably calmer.


Tuesday, 17 May

Our offspring is lying on the back. We are about three periods of change away from the eggs hatching. Earlier today, we were happy to see an embryo turning around in the egg envelope rather vigorously for more than an hour. It won’t be long now until we will get to see it. 


Author: Sašo Weldt, biologist