Tuatara’s speedy sperm may provide conservation clue, say study authors

PhD candidate Sarah Lamar has discovered that tuatara sperm are the speediest so far discovered in the reptile world.

image of a tuatara which is a lizard with spines along back and wise eyes
Tuatara, Aotearoa New Zealand’s surviving remnant from the age of dinosaurs, are not noted for their speed. But new Te Herenga Waka—Victoria University of Wellington-led research has turned up one surprisingly swift aspect of their anatomy—their sperm.

“While this is a pilot project and more work is ongoing, initial results indicate tuatara sperm may be the fastest reptile sperm ever analysed—two to four times faster than any previously studied reptile,” says Sarah Lamar, a PhD candidate in the University’s Te Tumu Whakaoho Mauri o te Ao Koiora—Centre for Biodiversity and Restoration Ecology (CBRE) and lead author of a PLOS One journal article about the findings.

Despite massive conservation efforts, much about tuatara reproduction remains unknown,

“Our pilot project was the first time we had had live, mature sperm from a tuatara,” says Ms Lamar. “There has been a huge focus on their conservation, but large gaps in our knowledge of male reproduction remain, which is rather surprising.”

Gathering the sperm was the initial challenge. Unlike other reptiles, male tuatara do not have a penis. Instead they mate in a similar way to birds, by lining up their cloaca with that of the female.

“Tuatara are the only living reptiles to mate in this way,” says Ms Lamar. “We conjectured that the speed of the sperm may be because it has a limited time outside the reproductive tract before it becomes non motile (or stops moving), so the faster they can get into the cloaca and female reproductive tract, the more likely they are to be successful at fertilising the egg.”

The researchers found the best way of getting a sample was to wait until the tuatara were actually mating. Although this meant breaking up mating pairs of the reptiles, they do mate multiple times within a season. “It took luck and chance and being at the right place at the right time,” says Ms Lamar. “You can miss it easily but the actual samples are concentrated—a tiny drop has millions of cells.”

Tuatara today occupy less than 10 percent of their historic range. The sex of tuatara hatchlings depends on the temperatures they are exposed to, with more males hatching at warmer temperatures. Projected temperature rises because of climate change are likely to mean many more males being born, and skewed sex ratios in the population can lead to eventual extinction.

“Developing breeding programmes by storing tuatara eggs and sperm cryogenically is a form of insurance,” says Ms Lamar. “We want to develop methods of cryopreservation ahead of time. Storing at extremely low temperatures preserves the integrity of the cells for a significant amount of time—in theory indefinitely—as long as they are stored in the correct chemical.

“Our first study showed quite a bit of variation between individuals and a lot of variation depending on the storage treatment. We are looking at finding the right combination of chemicals that retain cell integrity, with no ice damage, and the correct freezing regime.”

During a recent field season, the team took more samples.

“Using the chemicals that we found worked in the pilot study, and some new chemicals that work in a similar way, we will continue to investigate the best cryopreservative for storing tuatara sperm,” says Ms Lamar.

“We are also looking at more samples to confirm the sperm motility rates and to investigate whether motility relates to the physical aspects of a good male. We have found in other studies that larger males are more successful in fighting off others and being chosen by females. We are yet to find if that is related to sperm motility, and are working on that now.”

Ms Lamar’s fellow researchers included colleagues from the CBRE, which is part of the University’s Te Kura Mātauranga Koiora—School of Biological Sciences, and collaborators at the University of Otago and Grand Valley State University in the United States.

She and they have written an article about the project for The Conversation and it is available for free republication under Creative Commons.