The species diversity and ultimate survival of amphibians, one of the major groupings of vertebrate animals, face tremendous challenges today for reasons that are still not entirely understood. Since the 1980s, the pace of amphibian extinction has been alarming, and almost 200 identified species have become extinct. About one-third of all amphibian species have seen dramatic declines in populations, and are now considered to be endangered or threatened with extinction. See also: Biodiversity; Endangered species; Extinction (biology); Extinction of species

Collectively, members of the class Amphibia are facing massive reductions in total numbers, and the overall biodiversity of amphibians across the globe is under threat. Scientists have determined that global climate change and habitat destruction are two chief factors responsible for some of the decreases observed in amphibian populations. However, another prime culprit has been discovered—specifically, chytridiomycosis. Chytridiomycosis is a disease caused by the waterborne fungal pathogen Batrachochytrium dendrobatidis (abbreviated as Bd). Since the 1980s, scientists have linked the chytrid fungus to the significant loss of much amphibian biodiversity in many locations around the world. More than 500 amphibian species have suffered total number losses as a result of chytridiomycosis, with at least 90 of these species becoming extinct. In addition, 124 species have suffered a 90% reduction in their populations, endangering their continued existence. Although all amphibian species are thought to be susceptible to chytridiomycosis, frogs and toads (order Anura) have been affected to the greatest degree. See also: Amphibia; Anura; Biodiversity; Endangered species; Extinction; Fungi; Global climate change; Mycology; Origins of modern amphibians

The Asian longhorned tick (Haemaphysalis longicornis), also known as the bush tick, is a troublesome parasitic species and is an important vector of disease agents. (Note that vectors are capable of biologically transferring a pathogen from one organism to another.) It also is becoming a problematic invasive species. Specifically, it is invading areas located far from its native region in East and Central Asia and is spreading within the United States. In particular, this arachnid is remarkable because female members can reproduce asexually without mating. Thus, scientists fear that the species will spread rapidly in locations where it has already invaded, thereby transmitting numerous diseases that are potentially harmful to humans and other animals. See also: Acari; Disease; Invasive species; Ixodides; Parasitology; Pathogen; Tick virus diseases; Zoonoses

Wildfires, also termed bushfires or forest fires, are currently devastating large swaths of land in Australia. Detrimental ecologic consequences of these uncontrolled combustions of forest fuels and vegetation are numerous. One of the most serious issues pertains to the survival of the koala, which is a small marsupial (pouch-bearing mammal) found only on that continent. Conservationists and scientists are concerned that the hundreds of fires presently raging in Australia, which were brought about by hotter and drier conditions exacerbated by anthropogenic climate change, may cause significant enough reductions in the population of koalas to threaten the continued existence of this species. See also: Australia; Forest fire; Global climate change; Global warming; Koala; Marsupialia

Bats are members of the order Chiroptera, which is the second-largest order of living mammals. The geographic distribution of these flying mammals is tremendous as well, ranging from the limit of trees in the Northern Hemisphere to the southern tips of Africa, South America, and New Zealand. Within such a wide distribution, bats frequently encounter human populations. However, close contact between bats and humans is problematic with regard to disease ecology and epidemiology because bats are natural reservoirs (primary hosts) or intermediate hosts for numerous zoonotic pathogens—that is, infectious disease agents that are transmitted from animals to humans. Specifically, bats harbor more than 60 pathogenic viruses that can infect humans, including Ebola, Marburg, Nipah, Hendra, and rabies viruses. Bats also harbor various coronaviruses, including those responsible for severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and coronavirus disease 2019 (COVID-19). See also: Chiroptera; Coronavirus; Disease ecology; Epidemiology; Exotic viral diseases; Infectious disease; Mammalia; Pathogen; Rabies; Virus; Zoonoses

The dance language of honeybees (Apis mellifera) is a unique form of animal behavior and communication that was discovered by the zoologist Karl von Frisch (1886–1982) in the 1920s, which he continued to study through the 1960s and for which he was awarded a Nobel Prize in 1973. When foraging worker honeybees return to the hive with pollen or nectar, they perform dance movements to recruit other bees (follower bees) to visit a food source. The specifics of these movements convey information about the distance and direction from the hive to the food. This type of communication is highly unusual: Nonhuman animal communication typically concerns conditions and events immediately surrounding the instigator, whereas the honeybee dance language transmits information about remote events [scientists have documented bee dances about food sources up to 15 kilometers (9.3 miles) away from hives]. See also: Animal communication; Beekeeping; Ethology; Hymenoptera; Pollen; Pollination; Social insects

Although cats are the number one lethal threat to birds, collisions with building glass are not far behind. The number of birds killed each year by glass collisions worldwide is estimated to be in the billons. In the United States, the U.S. Fish & Wildlife Service estimates that between 400 million and one billion birds die each year from collisions with buildings. In contrast, an annual average of only 250,000 bird deaths result from collisions with land-based wind turbines. See also: Aves; Building; Glass; Wind power

Caenorhabditis elegans is a small, unsegmented, transparent member of the order Rhabditida in the phylum Nematoda (Nemata). Measuring approximately 1 millimeter in length in its adult form, this roundworm is typically found in soil, often feeding on bacteria among rotting vegetation and decaying organic matter, and is nonparasitic (free living) and nonpathogenic. Despite being a primitive invertebrate, C. elegans possesses many of the anatomical features and organs found in higher-level animals, such as those pertaining to its nervous, reproductive, muscular, and digestive systems; however, it lacks a circulatory system and a respiratory system. Because C. elegans is transparent, easily observed and manipulated, has a relatively short life cycle (2–3 weeks), and can be cultivated in large numbers under laboratory conditions (with 10,000 nematodes per petri dish), researchers frequently use it to study questions that would be difficult to explore directly in humans and other animals. In particular, because the cells of C. elegans hold steady in number and position in the body throughout its life, it is a popular model organism in developmental biology, embryology, genetics, and neuroscience. See also: Developmental biology; Developmental genetics; Embryology; Genetics; Invertebrate embryology; Nemata (Nematoda); Nervous system (invertebrate); Rhabditida

Neonicotinoid insecticides are the most used insecticide worldwide and have been linked to the decline of pollinator insects. In 2018, the European Union banned the outdoor use of three neonicotinoid insecticides: clothianidin, imidacloprid, and thiamethoxam. A new sulfoximine-based insecticide, called sulfoxaflor, is coming to market worldwide as a neonicotinoid replacement. Sulfoxaflor acts on the central nervous system of insects, just as neonicotinoids do, and, surprisingly (or not), it has similar harmful effects on wild bumble bees, researchers reported in Nature (August 2018). See also: Die-off of bees; Hymenoptera; Insecta; Insecticide; Neonicotinoid insecticides banned in Europe; Pesticide; Pollination

It has been a long-held belief that, as a result of hunting habits, early humans were partly or even primarily responsible for the decline and eventual extinction of most of the largest mammalian species that inhabited ancient Africa. These large plant-eating mammals, called megaherbivores and weighing more than 1000 kg (2200 lb) each, displayed an incredible biodiversity and numbered more than 30 species in the past, but only a handful remain today: the hippopotamus, the black rhinoceros and white rhinoceros, four species of giraffe, and two species of African elephants (the larger African bush elephant and the smaller African forest elephant). However, more detailed analyses of the parameters and factors involved in the demise of ancient African megaherbivores suggest that humans did not cause the extinction of these mammals. Instead, changes in the ancient climate of Africa, in addition to the concomitant changes in African ecosystems and food sources, led to the extinction of the majority of these creatures. See also: Africa; African mammals; Animal evolution; Biodiversity; Elephant; Extinction; Giraffe; Global climate change; Hippopotamus; Proboscidea; Rhinoceros