Bats and viruses co-evolved!

Bats harbor many viruses and are a source of old and new emergent viral diseases in humans. Why? 

Two papers review the unique bat immunology summarize what we know thus far, as well as some as yet untested theories. In short, a bats' immune system is competent at confusing and tricking virus biology, and we don't quite fully understand all of it. 

Given their herculean immune system, viruses have to 'work hard' to fool and evade their immune system to actually cause disease, without, of course, killing them. (A virus that kills its host quickly is a dead end for a virus. It may be able to replicate a few times, but it can't transmit all those new virions to other hosts after it dies. So, dead end.)

One way for viruses to test the the bat immunity barriers is a random process of mutations and evolving behavior of the virus to successfully infect and replicate (fitness). I'll explain some of that in another post (information theory). One of those barriers is heat: viruses don't like heat. One immunity mechanism of mammals to fight virus infection is a fever. It may not kill all viruses, but it slows their biological trajectory to infect cells and replicate. Another component of that is it buys time for the rest of the immune system to respond and bring in the artilleries: antibodies, T-cells, etc. They attach to and disable or kill virus particles, and destroy already infected cells so that the little new virions inside the cells die, too. 

This was one of two approaches I used to rid very important plants (nuclear stock) of viruses before they went to certified nurseries for mass propagation and sale to industry growers and commercial nurseries (1980's-1990's). The approach was to expose a plant to high heat in a growth chamber, the hottest temperature it could stand, then take 1mm size pieces of the apical meristem (growing point) and grow them on tissue culture media containing an anti-viral, now known as Ribavirin. (Protocol developed by me and collaborator at university in CA.)

So now that I have established some credible evidence for the relationship of heat and viruses, albeit in plants, keep that in mind in this next part. 

Five scientists from US, UK and AUS methodically detailed over five pages a hypothesis of why bats and viruses co-evolved together(1). It actually makes sense, although not good for other mammals, especially humans. 

I recall from reading a review last year that viruses must be super-evolvers, aka go through many and numerous random mutations, in order to successfully infect and evade the bat immune system. By the time some of those viruses jump from bat to another animal, especially another mammal, they are super-duper viruses and often deadly to humans. 

Think about the first SARS-1 virus pandemic: a short-lived pandemic because it was less transmissible than the current SARS-2, but it was also more deadly. Short-lived because countries quickly contained and eliminated it. Also consider MERS, another bat coronavirus that emerged after SARS-1. Very deadly, and very poorly transmissible. It, too, was quickly controlled. That it was a deadly virus contributed to that. 

A decade later a new SARS-like virus emerges: it's highly transmissible, not as deadly, but it spreads like wildfire. It has, however, been able to also evade part of our immune system if the latter is in any way compromised, including obesity, diabetes, etc. Two other important factors helping it along is the relatively poor and/or belated human response in controlling spread, and its stealth: it can infect mammals, replicate and transmit to others while not inducing any or many symptoms. A caveat to the latter is we now know that some infected people of all ages may have had little to no symptoms but still developed some tissue damage (e.g. cardio myelitis, kidney, etc) that occurred slowly enough not to elicit recognizable symptoms. l can see this as a stealthy way to evade the bat immune system, too. 

Back to co-evolution of bats and viruses. This is a good summary from their abstract: 

 "We hypothesize that flight, a factor common to all bats but to no other mammals, provides an intensive selective force for coexistence with viral parasites through a daily cycle that elevates metabolism and body temperature analogous to the febrile response in other mammals. On an evolutionary scale, this host–virus interaction might have resulted in the large diversity of zoonotic viruses in bats, possibly through bat viruses adapting to be more tolerant of the fever response and less virulent to their natural hosts."

And, 

" We hypothesize that the increased metabolism and higher body temperatures of bats during flight might serve as an evolutionary adjuvant to their immune systems, providing a powerful selective force against virulence and promoting the diversity of viruses that infect bat populations. Perhaps counter-intuitively, this would enable bats to tolerate a greater diversity of viruses that have a high potential for virulence when transmitted to other mammals.

The hypothesis also might help explain why co-evolved bat viruses cause high pathogenicity when they spill over into other mammals because the bat-derived viruses might survive well under both febrile and cooler conditions."

Pretty respectable! Actually, it's brilliant. Don't blame the bats, or their viruses. It's just another biological ecosystem that we are not meant to get involved in. So leave the bats and their habitats alone. Many of those viruses become zoonotic because we tend to invade their habitats. 

Isn't science beautiful? 😁

1. Bat Flight and Zoonotic Viruses, O’Shea, et. al. Emerging Infectious Diseases, Vol. 20, No. 5, May 2014.

Further reading on bat immunology:

Novel Insights Into Immune Systems of Bats, A. Banerje, et. al. Frontiers in Immunology, Vol. 11, No. 26, January 24, 2020.

The bat-virus detente, R. Ehrenberg, Knowable Magazine, June 19, 2020. 

Is life like Play-Doh?

On the tail of the silver fox.......

Despite that the field of epigenetics is often dismissed as a fad topic, that may come back to surprise us, just as the derision of ‘junk DNA’ did several decades ago. 

Similar to the silver fox domestication project, scientists in Sweden replicated domestication of red jungle fowl (ancestors of modern chickens) and selected for fear of humans tameness. After five generations, they examined changes in the genetic structure associated with certain phenotypic traits, especially behavior.

Behavioral traits are associated with many physiological and neural mechanisms. Signaling compounds in the body involved with these processes are dopamine, glucocorticoids, epinephrine, and many others. All of these signaling molecules are synthesized in tissues and organs, such as they hypothalamus. Based on prior studies, the research team examined changes in the hypothalamus of  their test subjects. They discovered that not only were DNA methylation patterns associated with cellular metabolism and neural signaling, but there were sex-specific changes.

In agreement with other similar studies of selection pressure during domestication, this study adds further evidence that changes in genetic structure are related to the driver(s) of selection for specific traits, such as egg size in a breed of domesticated chickens.

“This suggests that different selection pressures generate distinctive sets of epigenetic changes, which in turn are related to specific phenotypic traits.”

Epigenetics may have increasing importance now because of its suggestive role in phenotypic plasticity, which often precedes adaptation to environmental change. Understanding how organisms respond to selection pressure can help us better model and predict the fates of many species of concern in this age of rapid climate and anthropogenic changes. Including our own.

“Our results suggest that bidirectional selection for tameness involves epigenetic factors that can even differ in a sex-specific manner. Observation of divergent DNA methylation patterns in the hypothalamus after only five generations of artificial selection highlights the importance of epigenetic mechanisms, in addition to genetic composition, in evolutionary phenotypic variation that emerges in response to selection pressures.”

A researcher in Europe has been studying these association based on changes in gene expression in melanin, phenotype, and behavior adaptation in owls. Ironically, humans have unknowingly been experimenting in this for thousands of years by our own selection for domestication of many plant and animal species.

A-Z Clallenge. J is for Jaguarundi.

A mysterious small and elusive wild cat

A small wild cat, not much larger than the average house cat, the jaguarundi eludes us humans in many ways. Unbeknownst to this wild creature, our species can't seem to decide who and what it really is. So we have created many names for the animal, changing its label depending on place and time. All the while, the jaguarundi smiles and eludes us. 

This member of the feline family is one of the smallest and oddest looking. The size of a large house cat, it has the face of a miniature cougar (aka puma, panther, mountain lion) topped with little rounded nice-kitty ears. Its slender long body (22-31") and tail (14-24") is supported by short legs (stands at ~11" at the shoulder). Indeed, the mammal resembles an odd hybridized version of a house cat and dwarfed cougar whose ear and leg development was arrested within a  week after birth. In fact, the species has many times been mistaken for a large weasel. One wonders what circumstances selected for such odd paired combinations. Unless the other cats are the odd ones. 

The jaguarundi is a New World cat, native to forested and brushy regions, especially those near water, from South America to the southwestern United States. Rare north of Mexico, it is considered endangered in Texas, although sightings have been documented in SW Texas, Alabama and part of Florida. It is also known as the 'otter-cat' because of its otter-like appearance and swimming ability. In fact, early German zoologists mistook the animal for a cousin of the weasel, referring to it as the 'weasel cat'.

The name jaguarundi is interesting for several reasons. Many people recognize the root name, jaguar, which is one of the largest New World members of the feline family. This cat once roamed from the  U.S.-Mexican border southward to Patagonia, Argentina. It is now almost extinct in the northern part of its original range and survives in reduced numbers in remote areas of Central and South America. Similar to the jaguarundi, the largest known population exists in the Amazon rainforest.

The names jaguarundi and jaguar have similar origins. Not surprisingly, because the two species inhabit the same region in South America. Before the arrival of the Portuguese to Brazil in the mid-1500's, the two principal indigenous groups were the Tupí and the Guaraní. The former mainly lived along the coast of Brazil and in the Amazon rainforest. The Guaraní lived further inland, inhabiting what is now Paraguay, southern Brazil, and parts of Uraguay, Bolivia and Argentina. The Tupi-Guaraní language is the most widely distributed traditional language of South America and is a hybrid of the older Guaraní and Old Tupí. In fact, it is the official language of Paraguay.

A fusion of the languages of the Spanish-speaking conquerors of South and Central America and of the indigenous peoples has given rise to an interesting evolutionary tree of name etymology. Many names of flora and fauna are often attributed to Spanish origin. However, the earlier conquerors merely adopted and adapted native names to their own language to try and make sense of them, and probably because they were easier to pronounce. For example,  words like jaguar, tapioca, jacaranda, anhinga, carioca, and capoeira are of Tupí–Guaraní origin. An exploration of plant name origins will commonly end up with root words of the Tupí and/or Guarní language.

The first known use of the name jaguar was 1604. It probably originated with the Portuguese and was derived from from Old Tupí, jawára. Similarly, jaguarundi is American Spanish, first used in 1885, and derived from from Old Guarani yaguarund-i and akin to the Tupi jawarund or Old Tupi, yawaum'di. The jaguarundi is commonly known in Spanish as leoncillo, gato colorado, gato moro, león brenero, onza, and yaguarundí. It is also called gato-mourisco, eirá, gato-preto, and maracajá-preto in Portuguese.

The jaguarundi wears coats of several colors, and several scientific names. With two color morphs, light (black and brownish gray) and light (reddish brown), they were thought to be two different species. Local villagers often refer to these cats based on their color: “jaguarundi” for the darker coat and “eyra” for the reddish coat. (The Tupi name was eirara or irara; 'eyra' is an American Spanish and Portuguese name.) Thus early taxonomists separated them, assigning Felis eyra (1814) or Herpailurus eyra (1858) to the reddish morphs. However, these are the same species and both color morphs may be found in the same litter.

Likewise, the taxonomical nomenclature assigned to this wildcat have gone through several renditions, some concurrently. Various authorities have placed the jaguarundi in their own genus (Herpailurus) or with the other cats (Felis). A French naturalist, Étienne Geoffroy Saint-Hilaire (1772-1844), assigned the small cat the genus and species names Puma yagouaroundi in 1803. A follower of Lamarckian evolutionary theory, Saint-Hilaire's assignment was based on comparative anatomy, paleontology, and embryology.

Use of Felis yagouaroundi has been attributed to two different authorities. However, the earliest attribution was given to Bernard Germain de Lacépède (1756-1825), a French naturalist, in 1809. Attributes to assigning the jauguarundi to the genus Herpailurus vary from Lacépède (again, 1809) to Nikolai Severtzov (1827-1885), a Russian explorer and naturalist (attributed to year 1858). Which of these men originally used this genus name might be lost to historical confusion, but this genus was still in use in 1919. Why Lacépède would use two genus names concurrently is beyond me.

Sometimes things come full circle, even if it takes a few centuries. Depending on the source of reference and information, anyone searching for the scientific name of the jaguarundi will  see all three genus names in use today. Interestingly, modern nomenclature again placed in the genus Puma by Johnson et al. (in 2006) and Eizirik et al. (in 2008). Recent genetic studies (mitochondrial DNA analysis) suggests that the puma (aka the cougar/mountain lion) and the jaguarundi are more closely related to each other and other felines in the genus Puma than the domestic cat, which shared the genus Felis. Additional research shows that the jaguarundi is closely related to the much larger and heavier cougar as evident by its similar genetic structure and chromosome count.

For those interested in the paleobiology of the New World felines, according to the 2006 genomic study of Felidae an ancestor(s) of today's leopard, lynx, puma, and Felis lineages migrated across the Bering land bridge into the Americas approximately 8-8.5 million years ago. It is proposed that those lineages subsequently diverged in that order. This and other recent studies have indicated that the cougar and jaguarundi are next most closely related to the modern cheetah of Africa and western Asia, but that relationship is still debated. It has been suggested that ancestors of the cheetah diverged from the Puma lineage in the Americas and migrated back to Asia and Africa, while other research suggests the cheetah diverged in the Old World itself. Consequently, feline migration to the Americas remains unclear.

So, what's in a Name? Well, that is the subject for another post. As readers can infer, names can be very complex and more confusing than not. Regardless, the jaguarundi, or the leoncillo - the little lion- remains elusive in name and reality. Perhaps that is best for it's survival.

A-Z Challenge: B is for Bobcat

I'm cheating today for this letter. I write weekly posts for the FaceBook page of Terlingua Ranch (Terlingua, Texas), and today's post happened to be about the bobcat. This secretive animal deserves some special attention, so it will be the subject for today's letter 'B'.

The Bobcat (Lynx rufus) is found throughout the North American continent and their habitat ranges from forests to deserts. This wild cat is closely related to the larger Canadian lynx (Lynx canadensis). Both of these wild cats evolved from a common ancestor, the Eurasian lynx, which crossed the Bering Land Bridge into northern Canada from Asia approximately 2.6 million years ago. The first wave of the Eurasian lynx migrated into southern North America, which was soon cut off from the north by glaciers. This population evolved into modern bobcats around 20,000 years ago. Later migrations from Asia settled in the northern areas and developed into the Canadian lynx.

Most taxonomists do not readily accept the proposed 12 subspecies of the bobcat because their division is roughly based on geographical regions that do not have clear breaks. The only cited differences between the subspecies are general size and coloration, and even these features have blurred boundaries. The larger species members range in eastern Canada and New England, and the smaller are often found in the southeast states, such as Florida. Bobcats inhabiting the forests tend to be darker than those found in the deserts. Then again, a wide divergence exists between sizes of the sexes depending on their location. So it appears that the bobcat is readily adaptable to their immediate environment and habitat.

The bobcat is roughly twice as big as the average housecat. The adult varies from 19 to 49 inch long from the head to the base of the tail, averaging 33 in.  The stubby ‘bobbed’ tail, from which the animal derives its name, adds another 3.5 to 8 inches. An adult measures about 12 to 24 inches tall at the shoulders. The male weighs an average of 21 lbs, but have been reported up to 40 lb. The female averages about 15 lbs with a few weighing in at 34 lb.

Movement of the bobcat depends on the habits of their prey. Typically they hunt during dusk until midnight and dawn hours. An animal’s range size can vary from 8-126 square miles, dictated by season, food and mate availability. They tend to follow alongside roads and in trails, moving 2-7 miles within their habitual route and are usually secretive.

Bobcats are solitary hunters. In southern regions, rabbits, hares and small rodents are the primary food source. Like the coyote, the bobcat is an opportunistic predator that, unlike the more specialized Canadian lynx, will readily vary its prey selection. They will also scavenge kill from other animals. Coyotes also compete with bobcats for food, since they both eat the same prey species.

Here in Texas, bobcat breeding season usually begins in February and the young are born about fifty days later in dens located in caves and crevices. Litter size varies from two to seven, but two is most common. Kittens are weaned when they are about two months old and remain with their mother until early fall, when they move out on their own.

Tracks of the bobcat resemble the cougar, but can easily be extinguished based on size. Like all felines, bobcat tracks show four toes without claw marks. They range in size from 1 to 3 inches wide with the average about 1.8 inches. Additionally, their tracks are larger (by ½ to 1”) than those of house and feral cats. Like most wild cats, the bobcat 'directly registers', meaning its hind tracks usually fall exactly on top of its fore tracks. Also, their front feet are larger than their hind feet.

If you see a bobcat, they are probably more scared of you than you of it. Regardless, leave them alone and feel lucky that you spotted one.

Bears in wolf clothing

Reported in May 23' 2013' issue of Nature journal:

Hot topic, scalding hot, is the observed decrease in elk population in Yellowstone Nation Park. "It's those damned wolves!!!" Wolves, the ancient scapegoat for everything. Let's look underneath the wolf clothing.

In an attempt to 'reclaim' the trout population in the park lakes, 'humans' (clarification of which humans are not mentioned in the report) restocked the lakes with lake trout. Instead of the native trout. A detail missing from the original ecological assessment was that the lake trout spawn on the bottom of the lakes, unlike the natives, which do not. The introduced non-native fish are unable to be harvested by grizzly bears. Since fish are a major dietary source for grizzlies, the bears look for alternative food sources. Elk calves.

A research team in Wyoming estimated that this dietary shift accounts for as much as 11 percent reduction in the elk population, even elk that winter outside the park. "The decline of these elk is often blamed, perhaps erroneously, on the reintroduction of wolves."

But we do so love our scapegoats, don't we?