Today in Science: GLV Daily Digest for August 21, 2014

Today in science, compelling evidence indicates that seals and sea lions spread tuberculosis to South America long before the Europeans did. A freeloading 'social parasite' ant species evolved from its own host, lending support to a model of speciation that has been the subject of a great deal of debate.

Cities provide new opportunities for a species of Australian spider, which grows larger and is more fertile in Sydney than it is in the surrounding countryside. Finally, a study of two early mammals from the Jurassic has found that they were dietary specialists, evolved to eat different kinds of insect prey. Welcome to the Guardian Liberty Voice Science Daily Digest for Aug. 21, 2014.

Seals and Sea Lions Spread Tuberculosis to South America Before Columbus

Tuberculosis spread to South America in pre-Columbian times, and samples taken from Peru indicate that seals and sea lions were responsible for bringing it across the seas. Three Peruvian samples of tuberculosis DNA from the period 750-1350 CE showed the clearest relationships to strains of the disease documented in seals and sea lions (pinnipeds). The disease may have even spread to North America before the Europeans arrived.

Parasitic Ant Species Evolved From Its Host

Contemporary strains of tuberculosis in the Americas are derived from European strains, and all evidence indicates that these European strains entirely replaced the strains indigenous to South America before Columbus. Tuberculosis appears to have originated in Africa, where the greatest diversity of the bacteria that cause the disease can still be found.

A species of parasitic ant that is new to science evolved from the same species that now serves as its host, lending support to a model of speciation that has long been the subject of debate. Mycocepurus castrator is a so-called 'social parasite,' because it lives in the nests of the related Mycocepurus goeldii and helps itself to the fungus that M. goeldii grows for its own food. To date the parasite is known from only one location on the campus of Brazil's São Paulo State University.

Genetic evidence from all 11 species in the genus Mycocepurus lends support to the remarkable conclusion that M. castrator evolved from M. goeldii, since the two are most closely related to each other. The parasite seems to have split off from its host a mere 37,000 years ago, a fairly recent speciation event.

The evolution of new species is usually thought to occur due to significant geographical barriers forming between populations, leading to a scenario known as allopatric speciation. However, M. castrator appears to have evolved from M. goeldii in the same colony and therefore without any geographical separation at all, a scenario known as sympatric speciation. The idea of sympatric speciation has been the subject of a great deal of controversy, and this new evidence helps to confirm that it is a valid model.

Australian Spiders Bigger and More Fertile in Cities

Queens of the parasitic M. castrator have evolved a smaller build than the queens of M. goeldii, something that is thought to help them pass themselves off as M. goeldii workers. If they were identified as parasites, the parasite queens would be killed by the host workers. M. castrator queens have also been documented riding on the larger M. goeldii queens, again for the purpose of masking the fact that they are not contributing members of the colony. The worker caste has not been documented at all in M. castrator, and is thought to have been lost entirely during the species' evolution to a parasitic lifestyle.

For one Australian species of spider, cities provide opportunities to become bigger and more fertile. A study of the humped golden orb-weaving spider ( Nephila plumipes) has found that these spiders are thriving in the city of Sydney, which is warmer than the surrounding countryside in southeastern Australia.

The scientists collected spiders from three different habitat types in and around Sydney, urban, semi-urban and semi-rural. The results indicated that female city-dwelling spiders were not only larger than their more rural cousins, but also had proportionally larger ovaries, indicating greater fertility. The ovaries were found to account for as much as 39 percent of the spiders' total body weight, the largest proportion documented in the study.

Cities tend to be warmer than the countryside around them, owing to the tendency of roads, structures and the like to absorb and retain heat. This so-called 'urban heat island effect' appears to be responsible for the spiders' increased size and fertility, since this species thrives in warmer conditions.

Jurassic Mammals Were Dietary Specialists

Although spiders often inspire trepidation and loathing, Nephila plumipes may actually be a net positive for the residents of Sydney. The spider preys on mosquitoes as well as other species of insects that tend to be an annoyance in urban areas. While the bite of Nephila plumipes can induce localized pain and numbness, the spider is far from aggressive and generally prefers to hide from humans.

A new study of two early species of mammals from the Jurassic (201-145 million years ago) has established that far from being indiscriminate insect-eaters, both Morganucodon and Kuehneotherium were dietary specialists. Using synchrotron X-rays and computed tomography (CT) scanning techniques, the team analyzed the jaws and dental wear patterns of the two tiny, shrew-like mammals, and determined that they held quite different ecological niches.

The fossil jaws of both Morganucodon and Kuehneotherium that were used in the study are only two centimeters (0.78 inch) long, but the scientists used highly sophisticated techniques to examine them in great detail, model them, and analyze their strength. What they found was that the two showed very different abilities for capturing and chewing their prey.

While Morganucodon was a specialist hunter of beetles and other harder-bodied insects, Kuehneotherium favored softer-bodied fare, such as scorpion flies. Both had specialized jaw joints and hearing apparatuses, characteristics held in common with later mammals.

Commentary by Michael Schultheiss, Science Editor

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Sources:

Seals and Sea Lions - Tuberculosis:Arizona State UniversityNatureSouthern Sea Lions image credit: Vince Smith

Spiders:Live ScienceGolden orb spider image credit: Andrew McMillan

Jurassic Mammals:University of SouthamptonNature Morganucodon image credit: Michael B.H.

Main image:Southern Sea Lions image credit: Reinhard Jahn

Entities 0 Name: Sydney Count: 4 1 Name: South America Count: 3 2 Name: goeldii Count: 3 3 Name: Kuehneotherium Count: 3 4 Name: Nephila Count: 3 5 Name: Morganucodon Count: 3 6 Name: European Count: 2 7 Name: Brazil Count: 1 8 Name: GLV Daily Digest Crime News GLV Daily Digest Health News GLV Daily Digest World News GLV Daily Digest Count: 1 9 Name: Southern Sea Lions Count: 1 10 Name: Peru Count: 1 11 Name: Sea Lions Spread Tuberculosis Count: 1 12 Name: Andrew McMillan Count: 1 13 Name: Columbus Count: 1 14 Name: Australia Count: 1 15 Name: Arizona State University Nature Southern Sea Lions Count: 1 16 Name: North America Count: 1 17 Name: São Paulo State University Count: 1 18 Name: Michael Schultheiss Count: 1 19 Name: Guardian Liberty Voice Science Daily Digest Count: 1 20 Name: Michael B.H. Main Count: 1 21 Name: Africa Count: 1 22 Name: South America Before Columbus Tuberculosis Count: 1 23 Name: University of Southampton Nature Morganucodon Count: 1 24 Name: Sea Lions Count: 1 Related 0 Url: http://ift.tt/1pj1yD5 Title: Even the Spiders Are Bigger in the City Description: Karora via Wikimedia Commons Most animals don't tend to thrive in big cities, and you could be forgiven for thinking that this might be true for spiders, especially given that many people are not fond of them. But a new study found that certain types of spiders grow bigger and more fertile in urban areas, compared with the countryside-arachnophobia be damned.

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