Animal News Roundup: Ancient Horse Genome Sequenced, Elephant Diet Choices Shape Evolution, & A Lizard Live Birth Mystery Solved

Przewalski's horse, wtih horse fossil
A genome sequence derived from a 700,000-year-old horse fossil (inset) confirms that Przewalski’s horse (pictured) is indeed genetically distinct from domesticated breeds.
Credit: Claudia Feh/Association pour le cheval de Przewalski, France; (inset) Ludovic Orlando

Three intriguing and exciting animal news stories to report…So, let’s get to it.

Genome from a 700,000 Year Old Horse Fossil Is Sequenced

Setting the record for the oldest animal (human or otherwise) to have its DNA sequenced, a team of evolutionary biologists has sequenced DNA found in a bone from an ancient horse-like species that once lived between 560,000 and 780,000 years ago.

The bone fragment was found jutting out of an exposed section of permafrost by evolutionary biologist Eske Willerslev of the University of Copenhagen while on expedition with a scientific team in the Canadian Yukon Territory. Based upon its location in the exposed strata, Willerslev estimated its age to be between 560,000 and 780,000 years old.

The previous age record for sequencing DNA from an animal bone fragment was 130,000 years (an ancient megafauna species of mammoth).

Using “next gen” sequencing technology, the scientists were able to reconstruct about 70% of the animal’s genome — enough to reveal many intriguing details. For example, genes associated with traits favorable for racing do not seem to be present yet.

The sequence data also suggests that all equids (a family of creatures that includes horses, donkeys and zebras) shared a common ancestor that lived  4 to 4.5 million years ago — 2 million years earlier than some previous estimates. The sequencing offers yet more validation for Darwin’s 19th Century notion of “descent with modification”.

The team compared their newly sequenced genome with that of a late Pleistocene era horse (dating back 43,000 years, and several modern species, including the famous Przewalski’s horse, believed to be the world’s only truly wild horse. Controversy had surrounded this animal (found only in the lowland regions of Mongolia) as many had believed it is not a distinct genus and species, but rather one descended from domesticated horses.

The sequence data showed that, in fact, Przewalski’s horse is genetically distinct from domesticated horses (unlike mustangs which are domesticated horses that escaped into the wild)

News Source: ‘700,000-Year-Old Horse Becomes Oldest Creature With Sequenced Genome’

Ancient Elephants’ Dietary Choices Shaped Their Teeth and Evolution

The switch from food browsing to grazing by the elephant’s ancestors helped shape their teeth to adapt to the grittier content of grass — though the tooth change would not become pervasive in elephants for almost 3 million years.

Evolution researcher Adrian M. Lister compared records of the carbon isotope 13 C in both soil (which reflects the isotope’s presence in the local vegetation) and elephant fossils dating back some 20 million years. He discovered that somewhere around 8 million years ago, the ancestors of modern elephants made the big switch to grass grazing. About 2 million years prior to this switch, the terrain in East Africa began to change from mostly woodlands to a mixture of wooded land and grasslands to, eventually, mostly drier grasslands.

As a result, the teeth of elephants also began to change; the crowns of their molars would grow up to three times higher, while they also added enamel ridges which served to help grind the grass with its higher silica content. However, these tooth changes would not fully emerge (and spread through the population) for another 3 million years after their “choice” to graze grass had begun, according to the researcher’s fossil data.

These intriguing findings — the “significantly offset chronology” of behavioral  change verses morphological change — suggests that the elephants, in their trying out of new food sources, were placing themselves in a better evolutionary position — one favoring better-adapted teeth. Thus notion seems to challenge the “passive” view of natural selection in which animals passively evolve in the face of environmental changes (i.e., that better-adapted teeth were positively selected due to environmental changes).

The study, published recently in Nature (‘The role of behaviour in adaptive morphological evolution of African proboscideans’), uses this fossil evidence to show that elephant behavior — their switch in dietary preferences — help shaped their evolutionary path.

News Source: ‘Elephants Shaped Their Own Evolution’

Solving the Puzzle of ‘Why Some Reptiles Give Birth to Live Young?’

While most lizards and snakes lay eggs, some are capable of giving birth to live young just like mammals. Why this is so has been a biological and evolutionary puzzle for some 30 years.

It was originally hypothesized that those species who give birth to live young (known as viviparity) did so to protect their off-spring from the dangers of colder temperatures (note: recall that reptiles are ectotherms). However, that theory did not explain why several species of tropical lizards and snakes give birth to live young (when presumably, this was not required due to the warmer temperatures in the tropics).

yarrow's spiny lizard
By studying the Yarrow’s spiny lizard , among others, researchers are understanding the evolution of live-bearing in reptiles. Credit: Carl R. Hutter

But a new study combining environmental and family tree data with GIS technology to pinpoint habitats, shows that a certain lizard group native to the tropics (the Phrynosomatidae — a wide-ranging group that includes horned lizards and fence lizards) originated in higher elevations — where the temperatures can get much colder. According to the study, this reproductive strategy originated first in creatures that evolved on tropical mountainsides. Only later did some species with the trait moved to the lowlands.

The study showed that this viviparity trait had evolved six separate times in this group. The study further showed exactly where on the lizard family tree this viviparity trait had evolved and showed that there are currently more than 40 live-bearing species of this group.

The study, conducted by graduate student Shea Lambert of the University of Arizona in Tucson (and colleague John J. Wiens), was presented on June 21 at Evolution 2013, an annual meeting of the American Society of Naturalists, the Society for the Study of Evolution, and the Society of Systematic Biologists.

According to Lambert, this strategy is quite efficient where temperatures get so low that eggs laid on cold ground might develop too slowly, if at all. A female lizard carrying live young inside her can move to warmer spots, allowing the young to develop faster and healthier.

Lambert’s study also proposes that a “lack of gene flow” between warm and cold-adapted, tropical lizards may account for why viviparity (verses oviparity) evolved and took hold in the tropics and not in temperate locales.

Many of the the world’s lizard species are endangered and facing extinction threats mostly from habitat loss and competition with other species; viviparous species adapted to colder locales are finding their habitats shrinking due to general global warming. Ironically, this adaptive trait may be inhibiting the ability of many of these species to survive in warmer areas.

News Source: ‘Lizard Family Tree Solves 30-Year-Old Mystery’






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