New frogs, who dis? | Greater Vancouver Zoo News

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New frogs, who dis?

Well, the breeding season for Oregon Spotted frogs has proven to be exciting, busy, and abundant. We tried a few different husbandry changes in our breeding program this year. Some changes were planned and some were based on our real-time observations as we watched egg-laying season progress. So here is a run-down on the complexities, secrets, and successes of the OSF breeding program this spring!


It all starts with communication! Shouldn’t it always? We knew from previous years that we wanted to keep males and females separate overwinter. In years past our overzealous males had moved into amplexus position (where the male tightly grasps the female) very early. This early amplexus was resulting in what is effectively frog bed sores on the females, which can lead to infection and death. To avoid this we kept the males and females in separate tubs over winter, so they wouldn’t have access to each other. Our plan was to communicate closely with the field crews and only introduce the captive frogs once field crews were seeing the movement of frogs in the wild. Also since last year, we were talking with the field crews about what they were observing in the field. They noted that they often see a lot of movement by males right before they start to see eggs being laid. That got us to thinking, maybe the males are moving more and aren’t “hibernating” around the females, and thus more likely to get caught in traps we place around the traditional egg-laying sites. We knew that we wanted to keep males and females separate overwinter, so this fits right into our plan.


Once the traps were in the water and the frogs were moving in the wild we prepped our tanks for introductions. One of the main things we do to put frogs in the mood to breed is dropping the water in the tanks really low, so low that there isn’t more than one inch of standing water above the submerged vegetation and debris layer at the bottom of the tank. This is to mimic the shallow water that frogs lay in the wild that corresponds to the natural drop of water levels which occurs right around breeding time. We also make sure there are plenty of emergent plants and less open water as these features most resemble wild laying sites.


And then we wait.


And in a few days, we started to see egg masses, lots of them. One thing we noticed right away is how closely the egg-laying pattern was matching the wild. In previous years the females in the captive program laid their eggs gradually, over the course of a few weeks. One or two egg masses a night, and scattered around the tank and not clustered together. This is in contrast to wild egg masses which tend to be laid in a relatively tight time frame and are laid clustered together in a large group.


We also noticed out of the first 14 egg masses…all were laid in one tub, the tub the females were overwintered in. Interesting. With that many masses being laid we would expect to have at least some in the other tubs, which had held males over winter. So to satisfy our curiosity we transferred some pairs, who were already in breeding position back into the tub that held females overwinter.


BOOM!


Within 20 hours of being transferred all the females had laid their eggs, again in a tight group and right where the females had laid previously. Must be a nice spot!


So we tried again. We removed the laid egg masses to their hatching tubs (to avoid them being trampled by the adults), we moved the frogs that had laid into a holding tank, and moved in more pairs. These pairs didn’t even wait a day, they laid within 5 hours of being transferred into the female overwinter tank.


That got us thinking…is there actually “something in the water”?


Well, we don’t know, but we suspect so! Since we have one shot per year to observe anything related to frog breeding we have to wait till 2021 to develop and test any further hypothesis, but as of now, we have great success! Not only did we get 41 of our 43 females to breed, but 19 of those females were also only 2 years old, which is young for an OSF. As a result of getting so many females to lay we also had no female death due to egg binding. Egg binding has been a problem in previous years, where females just seemed to not be able to release their eggs. This causes infection and ultimately death.


Now to see how many eggs develop and hatch…stay tuned!


Photo Credit: Pourya Sardari

Categories: WPCNewsOSF

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