Living fossils

2011-05-02 00:00

MAMMALS and birds are the most successful vertebrates since the dinosaurs. From hedgehogs to humans, we’ve got Planet Earth buttoned-down. Put another way, looking back over evolutionary history, this means the warm-blooded creatures ultimately won out over the cold-blooded, with a little help from an asteroid.

“Scientists are looking at the whole topic of endothermy — warm-bloodedness in mammals — versus ectothermy or cold-bloodedness,” says Barry Lovegrove, senior professor and specialist in evolutionary physiology in the School of Biological and Conservation Sciences on the local campus of the University of KwaZulu-Natal. “From an evolutionary perspective, it doesn’t make sense that warm-blooded mammals are so successful because it’s a very expensive form of existence, five to 10 times more expensive than ectotherms. Considering this, raises the question of why they evolved.”

But how to answer that question when the fossil record is silent on matters of physiology?

The only way is to find mammals that are still in existence that are similar to mammals that lived at the beginning of the Cenozoic era, the ongoing age of the mammals that began after the extinction of the dinosaurs at the end of the Cretaceous era 65 million years ago.

The closest candidate is the tenrec, a hedgehog-like mammal, says Lovegrove. “They are proto-endothermic mammals and are only found on Madagascar.”

“At the end of the Cretaceous period an asteroid hit the Earth, creating global wildfires,” says Lovegrove.

“This wiped out the dinosaurs. But some mammals escaped the global inferno and thus gave birth to the Cenozoic Age, the age of the mammals. How? Because, like the tenrec, they probably hibernated through the worst of the apocalypse.”

Until a decade ago, tenrecs were thought to be related to hedgehogs and moles, but through DNA sequencing it was found that, like elephant shrews and golden moles, they are closer to hyraxes and elephants and belong to the group Afrotheria, which is endemic to Africa and includes elephants and manatees.

On Madagascar, the tenrec has lived unchanged for million of years, thanks to having been left in splendid isolation since it colonised Madagascar about 42 million years ago when the Earth was still tropical. A huge landmass, what would become Madagascar and India, broke away from the African landmass 120 million years ago and then in turn separated: India moved north and crashed into Asia, leaving the Himalayas as evidence of the massive collision.

Meanwhile, Madagascar stayed put and now it provides a glimpse of life when first the lemurs and later the tenrecs colonised Madagascar. “There was no need for change on such isolated tropical islands,” says Lovegrove. “In terms of their physiology, we may be looking at living Cretaceous fossils”.

So Madagascar provided the setting in which the answer to this evolutionary question could possibly be answered by an intense study of the tenrec. Lovegrove has spent six years setting up the project based in a six-square kilometre area of the Ankarafantsika National Park, which boasts an abundant population of tenrecs, or at least did. The project teamed three postgraduate students from UKZN with three graduate students from the University of Antananarivo.

One of the UKZN students was Kerileigh Lobban, who has just returned from nearly two years under canvas on Madagascar. She recalls the moment she decided that the project was for her. “Barry did a presentation on his work in Madagascar. The project, as well as life on the island, sounded fascinating. It tapped into my childhood dreams: working with animals, living in a tent, perfect. A few months later, at the end of 2009, I was on a plane to Madagascar.”

Lobban’s time on Madagascar coincided with a time of political upheaval, including the coup d’état in 2009. Following the coup, lawlessness increased and Chinese syndicates moved into the forests and began logging the valuable rosewood and mahogany, often with government collusion. Foreigners were not allowed into the forests at night. Not only would they be in danger, but there were also worries over what they might report to the outside world. This ban extended to the Ankarafantsika National Park and it took a month to negotiate the freedom of movement required to study tenrecs.

Despite all this, Lobban says she felt “very safe” and became involved with the everyday life of the local villagers. “I wanted to do more than just the project and give something back. I taught English and showed movies or documentaries every Sunday. I didn’t want to just pick up data, but memories. And I did that.”

Little is known about tenrecs, not least how they manage to have large litters — up to 30 — yet spend at least nine months of the year hibernating in shallow burrows. Lobban’s first task was to catch some. “We baited cage traps with bananas, peanut butter, cat food, even sardines. But nothing worked. Then we were told you could catch them by hand. Just pick them up. Animals on Madagascar are so chilled — snakes, mice, you can just pick them up.”

Simply picking them up is not without risk and Lobban got a badly bitten finger on one occasion.

Once the tenrecs were captured, radio transmitters and temperature data loggers were surgically implanted into them to enable the animals to be tracked when they were released.

Sixteen tenrecs were used in the project. “Most got eaten by boa constrictors, one was caught by a feral dog, others by fossa, a cat-like predator endemic to Madagascar, and some just disappeared,” says Lobban. “They were possibly poached for food. One tenrec can feed five or six people.”

Malagasies have many prohibitions and taboos known as fady. In many areas it is fady to eat or touch tenrecs. “Unfortunately, this did not apply in our study area,” says Lobban. ‘There were eight villages in the area and I visited them and explained the project. I wanted local people to buy into the project and so keep the tenrecs alive.”

Although Lobban had been able to gather data, with only two surviving tenrecs she did not have a big enough sample for the requirements of the study. So, in consultation with Lovegrove, she moved on to study the Long-tailed Big-footed mouse endemic to Madagascar and only found in the Ankarafantsika Forest.

Lobban followed a similar procedure as with the tenrecs. “Then I studied their oxygen consumption and metabolic rates at different temperatures.”

According to Lovegrove, nothing is known about this entire family (Nesomyidae) of mice. “Everything Keri recorded was a new contribution to science,” he says. “One thing she found was that at temperatures below 15 degrees centigrade they simply die, they do not exhibit what is called non-shivering thermogenesis (NST) which is a means of producing heat used by many mammals when they come out of hibernation.”

Such discoveries all feed into the information that could lead to discovering why warm-blooded mammals have been so successful. Currently, there are three possible models as to why: increased aerobic capacity, improved parental care and assimilation efficiency — the rate of energy transfer from food.

“We are the first to test these ideas in the field,” says Lovegrove. “To be able to test all three models with animals that are breeding, not breeding, hibernating, etc. So far, the evidence points to parental care being the most likely model.”

Right: Kerileigh Lobban (left) and Barry Lovegrove.

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