Species and Their Formation

In May and June, 1993, a previously unknown disease abruptly killed 10 people in the southwestern United States. The victims experienced flulike symptoms for several days, but then their condition deteriorated rapidly as their lungs filled with fluid. The disease agent was unknown; no cure was available, and initially 70 percent of infected people died.

Researchers from many disciplines focused on the outbreak. Within a few weeks, scientists at the U.S. Centers for Disease Control had identified the agent as a previously undescribed hantavirus—a type of virus known to be transmitted by rodents. Investigators initiated an intensive small mammal field trapping program. They quickly identified the deer mouse as the main host of the virus. The mouse sheds the virus in its feces, urine, and saliva. Humans become infected by inhaling microscopic particles of these substances that are present in the air.

Since the discovery of the hantavirus that caused the 1993 outbreak, about 25 additional hantaviruses have been described in the Western Hemisphere. People have been infected by some of these viruses in Florida, New York, Louisiana, and Texas. Other rodents, in addition to the deer mouse, harbor hantaviruses, and some of these viruses cause human diseases (Figure 24.1). Studies of the evolutionary relationships of hantaviruses and rodents indicate that rodents and hantaviruses have been evolving together for millions of years, and suggest that more kinds of hantaviruses, some of them likely to be human pathogens, have yet to be discovered.

Efforts to reduce risks to humans and develop effective cures will require an understanding of the distribution of hantavirus types among rodent species and measures of the rate at which the viruses appear to be evolving. The fact that so many new types of hantavirus have been discovered since 1993 suggests that hantaviruses may be evolving rapidly. If so, better knowledge about how new viruses form and how they have coe-volved with rodents will serve important human health objectives.

All species, living and extinct, are believed to be descendants of a single ancestral species that lived more than 3 billion years ago. If spe-ciation were a rare event, the biological world would be very different than it is today. How

A Source of Disease The deer mouse Peromyscus manicu-latus harbors a type of hantavirus that infects people.

A Source of Disease The deer mouse Peromyscus manicu-latus harbors a type of hantavirus that infects people.

Blue River Muleshoe

Isla Vista Sin Nombre

El Moro Canyon

Andes Hantavirus Images

New York Prospect Hill Monongahela Bloodland Lake Bayou

Black Creek Canal Caño Delgadito

Calabaso^^ Río Mamoré Laguna Negra Orán Bermejo Andes

Isla Vista Sin Nombre

El Moro Canyon

New York Prospect Hill Monongahela Bloodland Lake Bayou

Black Creek Canal Caño Delgadito

Calabaso^^ Río Mamoré Laguna Negra Orán Bermejo Andes

Rio Mamore

Juquitiba

Maciel HU39694 Lechiguanas Pergamino

Juquitiba

Maciel HU39694 Lechiguanas Pergamino

24.1 Hantaviruses in the New World The map shows the many different hantaviruses found in the Western Hemisphere. Those listed in red are known to be human pathogens.

did these millions of species form? How does one species become two? These questions are the focus of this chapter. We will examine the mechanisms by which a population splits into two or more new species, and we will see how such separations are maintained. We will look at the factors that can make speciation a rapid or a very slow process. Finally, we will look at the conditions that give rise to the great diversifications called evolutionary radiations.

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Essentials of Human Physiology

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  • duenna
    What is manicu rodents?
    8 years ago

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