Meet the micromammals

Felines, wolves, elephants, apes… We all know big mammals, but what about the smaller ones? Do you know what is a desman or a solenodon? Read on to find out more about small mammals and their importance.

WHAT IS A MICROMAMMAL?

The word “micromammal” has no taxonomical value: it is not a word that biology uses in the classification of mammals. However, this colloquial term, like the word “dinosaur” sometimes it is used in scientific publications to group together several orders of small mammals, although in the same taxonomic group some species can have a large size.

European hedgehog (Erinaceus europaeus), a micromammal. Source

In general, we consider micromammals animals of the following groups:

• Bats
• Rodents (rats, mice, squirrels, marmots, beavers, prairie dogs, hamsters, lemmings, gerbils, voles, chinchillas…)
• Lagomorphs (rabbits, hares and pikas)
• Insectivores (shrews, hedgehogs, moles, desmans …)

BATS

As we learnt in a previous post, bats are essential animals for ecosystems, they also have unique characteristics that make them worthy of several records: they are the only mammals able to fly actively, they are distributed to nearly every continent, they don’t get sick… to find out more about bats, visit What is a bat for?

Flying fox cubs rescued by the Australian Bat Clinic after the floods of 2010. Source

In the Iberian Peninsula live eight species of bats. Learn more about them in the website Fauna Ibérica.

RODENTS

Rodents are the largest order of mammals, accounting for over 40% of the total and inhabit all continents except Antarctica. Some rodents are not considered micromammals for its large size, such as capybaras or porcupines. Most rodents are quadrupeds with long tail, claws, whiskers and continuously-growing large incisors. This fact forces them to constantly gnaw through its specialized jaws, to wear away the incisors and always keep them sharp. They have a great sense of smell and hearing, and the sense of touch in his whiskers. They communicate by scent and various vocalizations.

Common vole (Microtus duodecimcostatus). Photo: Herminio M. Muñiz

Most species are social and form large communities. Their anatomy is not so specialized than other mammals, allowing them to adapt to different habitats. Added to the high birth rate, they can keep populations stable in adverse conditions. The black rat, for example, can have litters every month of more than 10 babys.

Gray dormouse (Glis glis). Photo: Miguel Ángel Castaño Ortega

Some rodents, especially rats and mice, occupy the same habitats that humans and are considered a plague. In addition to eating human food, they can contaminate it with their urine and feces and they are transmitters of more than 20 diseases, including the typhus and plague.

Common squirrel (Sciurus vulgaris). Photo: Peter Trimming

In the Iberian Peninsula inhabit about 23 species, divided into five categories:

• Cricetidae: voles (8 species), water vole and southern muskrat (non-native).
• Gliridae: Gray dormouse
• Sciuridae: common squirrel
• Muridae: mice and rats
• Myocastoride: Coypu (non-native)

Coypu (Myocastor coypus). Photo: http://www.simbiosisactiva.org

RABBITS, HARES AND PIKAS (LAGOMORPHS)

Ili pika. It is an endangered species, it was seen again after 10 years disappeared. Pic: Li Weidong

Contrary to what a lot of people believe, rabbits and hares are not rodents but they belong to the order of lagomorphs. Unlike rodents, lagomorphs have a small, round tail, paws with thick fur and hair in  their foot sole that helps grip while running.

All species are terrestrial and are distributed almost worldwide. They are among the most hunted animals, so its body has adapted to elude predators:

• Long ears for good hearing
• Eyes on top of the head with a vision of almost 360º
• Elongated hind legs to reach 56 km/h

Like rodents, the incisors are also continuously-growing, but behind them there is another smaller pair. They have high reproductive rates (some species can conceive a second litter before the first is born), sexual maturity within a few months of life and short gestations.

Comparison between the skull of lagomorphs (above) and rodents (below). Source

Lagomorphs are herbivores and practice cecotrophy: substances that can not be diggested, are evacuated through the anus in the shape of soft balls. They eat this balls in order to do a second digestion. If you have a rabbit as a pet ¡this behavior is completely normal!

In the Iberian Peninsula lives a species of rabbit and 4 species of hares (Iberian, European and Cabo del Piornal (non-native).

Rabbit (left) and hare (right). Source

INSECTIVOROUS MICROMAMMALS

Currently the order Insectivora is no longer used and micromammals that feed on insects (and other animals) can be classified into five Orders:

• Hedgehogs, moonrats or gimnurs (Erinaceomorpha)
• Shrews, moles and  solenodons (Soricomorpha).
• Tenrecs and golden moles (Afrosoricida)
• Elephant shrews (Macroscelidea)
• Treeshrews (Scandentia)

Hispaniolan solenodon (Solenodon paradoxus). Photo by M. Eladio Fernandez.

They are considered to be the most primitive mammals. Many species are characterized by:

• Elongated, thin and mobile snout. They have a good sense of smell
• Ears and small eyes in some species, like moles
• Five clawed toes on each paw
• They are plantigrades
• Some species, such as hedhehogs and tenrecs have spikes
• The solenodonts, water shrews and shrews are among the few poisonous mammals in the world. Read this post to learn more.

Mediterranean water shrew (Neomys anomalus). Photo by Rollin Verlinde

Most of them are nocturnal and their diet is based on insects, spiders and worms, but they also eat plants and other animals. Besides, they are not the only mammals that eat insects.

Lowland streaked tenrec (Hemicentetes semispinosus). Photo by Robert Siegel

In the Iberian Peninsula lives the Pyrenean desman, two species of hedgehog, about five species of shrews, two species of water shrews, and the Spanish mole. To learn more about the Pyrenean desman, in the website El Bichólogo you can find more information.

Pyrenean desman (Galemys pyrenaicus). Photo: David Perez

IMPORTANCE OF MICROMAMMALS

• In Paleozoology, the fossils of micromammal provide a lot of information as they tend to be found more often in deposits than other mammals. In addition, many times their bones are accumulated due to the eating habits of their predators. They provide valuable information on the climate of the past (paleoclimatology) and the classification of rocks in layers (biostratigraphy).
• Despite its bad reputation, some rodent species are beneficial, controlling insect populations and destroying weeds, contributing to the health of forests spreading fungus… and  are still used in scientific research.
• Many species are responsible for the spread of pollen or seeds.
• They are vital for the conservation and maintenance of their predatory species in decline, as the Pyrenean owl or Iberian Lynx.
• Since some of them live in burrows (rabbits) or they are burrowers (moles), they contribute to the ventilation of the soil and its fertility.

REFERENCES

• Clutton-Brock, Juliet et al. 2002. Animal. Pearson Education
• Diversidad con los micromamíferos de la Sima del Elefante (Atapuerca, Burgos)
• fauna ibérica
• Botanical-online
• Por qué es tan importante el conejo?
• Source of cover image (star-nosed mole)

Danger, poisonous mammals!

We usually associate snakes, spiders, jellyfish, etc. as venomous animals par excellence, but did you know that there are poisonous mammals? In this article we will discover who are they and the nature and use of their poisons.

THE PLATYPUS

The platypus (Ornithorhynchus anatinus) is the most famous among the poisonous mammals, and not just for this feature. With a peak like a duck and oviparous (laying eggs), when it was discovered some scientists thought it was a fraud.

Platypus (Ornithorhynchus anatinus). Photo by Jonathan Munro

They belong to the order monotremes, which means “one hole” in reference to the cloaca, the end of the digestive and reproductive systems. Some evolutionary biologists refer to them as the “missing link” between reptiles and mammals, as they have characteristics of both groups. Monotremes are the only mammals that lay eggs, but his body is covered with hair and the young are fed with breast milk. They are distributed by Australia, Tasmania and New Guinea.

Platypuses have a spur on the hind legs, which only in the case of males, release poison produced by femoral glands (located in the leg). The male uses it mainly to defend their territory and establish their dominance during the mating season, although if it is bothered also uses it as a defense. This poison can kill small animals, including dogs, and cause severe pain and swelling in humans. This pain can last days or months.

Spur on the hind leg of a platypus. Photo by E. Lonnon

Toxins are four proteins, three of which are unique to the platypus. They are like the defensins (DLP, defensin-like proteins). These are globular proteins, small and compacted, involved in the activation of pain receptors. Understanding how these toxins act it has special interest because they cause a lasting and severe pain; it may open new chances in the synthesis of analgesic drugs.

Short-beake echidna (Tachyglossus aculeatus). Photo de Tony Britt-Lewis

Echidnas (family Tachyglossidae) complete the order of monotremes with the platypus; consequently they are also oviparous. The family consists of four species, with the common characteristic of having the body covered with dense hair and spines. They are mainly insectivores specializing in ants and termites.

Like the platypus, they also have spurs behind the knees, but their secretions are not poisonous. The substances are used to mark their territory, according to the recent studies.

SLOW LORIS

As we saw in a previous post, lorises are primates in the prosimians suborder. They are nocturnal, arboreal and feed primarily on insects, vegetables and fruits. The slow lorises (Nycticebus) living in Southeast Asia, are the only poisonous primate. They possess poison glands on the elbows (brachial gland), and poison their body with arms and tongue, which can also join saliva and be transmitted by bitting.

Pygmy slow loris (Nycticebus pigmaeus). Photo by Ch’ien C. Lee

In this case the poison is used as a defense against predators, causing them pain, inflammation, necrosis (cell death) in the area of the bite, hematuria (blood in urine) or in some cases anaphylactic shock (allergic reaction) which can lead to death, even in humans (some are threatened by the illegal pet trade and traditional Chinese medicine). The poison also serves as protection for the young, they are licked by their parents and the poisonous secretion is distributed throughout the coat. Being poisonous, unusual among primates, can help counteract the disadvantages of its slow movements. Exudate from glands, as in echidnas, can also give olfactory information of range and territory between individuals of loris (Hagey et al., 2007).

Kayan loris (Nycticebus kayan). Photo by Ch’ien C. Lee

Toxins are polypeptides (generated when glandular secretion is mixed with saliva) and an unidentified steroid. Secretion is similar to the allergen Fel d 1 which is in the domestic cat and cause allergies in humans (Hagey et al., 2006; Krane et al., 2003).

It is believed that slow lorises even have converged evolutionarily with cobras, for his defensive behavior when threatened, whistling and raising his arms around his head. (Nekaris et. al, 2003).

Mimicry between loris and cobras. 1. Javan slow loris, 2 y 3. Spectacled cobra, 4. Bengal slow loris. Photo by Nekaris et. al.

In the following video a lazy lori is disturbed and hisses like a snake while trying to bite:

SOLENODON OR ALMIQUI

They are small and nocturnal mammals, basically insectivores, that live in the West Indies. The Hispaniolan solenodon (Solenodon paradoxus), also known as the Dominican solenodon, Haitian solenodon or agouta, lives on the island de La Española (Dominican Republic and Haiti) while The Cuban solenodon or almiqui (Solenodon cubanus) is distributed throughout Cuba. They are considered living fossils because they have similar characteristics to primitive mammals of the end of the Mesozoic Era (kingdom of the dinosaurs).

Hispaniolan solenodon (Solenodon paradoxus). Photo by Eladio M. Fernández.

Unlike other poisonous mammals, toxic saliva is produced under the jaw (submandibular glands), which is transported by pipes to the front of the mouth. The second incisor teeth have a groove where toxic saliva accumulates to promote their entry into the wounds. They are the only mammals that inject venom through its teeth, similar to the way snakes do.

Paradoxus Solenodon lower jaw incisor showing the groove. Photo by Phil Myers

The main function of this venom is to immobilize prey, as well as insects they can hunt small vertebrates such as reptiles, amphibians and birds.

Cuban solenodon (Solenodon cubanus). Photo by Julio Genaro.

This poison may have been developed to keep alive but immobilized prey during times of shortage, to aid in digestion, minimize energy expenditure in the struggle for hunting and face prey even twice as big as them. This venom is not deadly to humans.

SHREWS

The northern short-tailed shrew (Blarina brevicauda), the Eurasian water shrew (Neomys fodiens) and the Mediterranean water shrew (Neomys anomalus) also have submandibular glands similar to solenodons. They are distributed by North America (northern short-tailed shrew) and Europe and Asia (water shrews), including the Iberian Peninsula.

The northern short-tailed shrew (Blarina brevicauda). Photo by Gilles Gonthier.

The short-tailed shrew can consume up to three times its weight in food per day. Their saliva is the most poisonous and uses it to paralyze their prey, to eat them or keep them alive in times of shortage. The water shrews also store its immobilized prey under rocks.

Mediterranean water shrew (Neomys anomalus). Photo by Rollin Verlinde.

These animals attack from behind and bite the neck of its prey so that the poison acts more quickly, affecting the central nervous system (neurotoxins). The respiratory and vascular system is also affected and causes seizures, incoordination, paralysis and even death of small vertebrates.

Eurasian water shrew (Neomys fodiens). Photo by R. Altenkamp.

Its teeth don’t have grooves as the solenodons do, but a concave surface to store the toxic saliva.

Lower jaw of Neomys anomalus. Photo by António Pena.

It is suspected that other mammals also produce toxic saliva similarly, as the European mole (Talpa europaea) and other species of shrew, but there are no conclusive studies.

MANED RAT

The maned rat or crested rat (Lophiomys imhausi), lives in Africa and  uses his poisoned hair to protect themself from predators.

Maned rat (Lophiomys imhausi). Photo by Kevin Deacon

Unlike other mammals that produce their own poison, the crested rat gets toxin (called ouabain) from the bark and roots of a tree (Acokanthera schimperi). Chews the bark and the mixture of saliva and toxins are distributed on the body. Their hairs are cylindrical whith a perforated microscopic structure, which favors the absorption of venom. In case of danger, it bristles and shows his brown coat with white stripes, warning of its potential danger. This strategy of persuasion based on brightly colored warning is known as aposematism present in many animals, such as bees.

In this BBC video you can see a crested rat and a hair under the microscope absorbing ink, showing its porous structure:

It is unknown how it is immune to the toxin, since it is the same substance used by some African tribes for hunting such large animals like elephants.

Ouabain is a glycoside which controls the heartbeat, causing infarcts if absorbed in large quantities. The study of the mechanisms that protect the crested rat of a substance that regulates the heartbeat, can help develop treatments for heart problems.

European hedgehogs (Erinaceus europaeus) have similar behavior (smearing the body with foreign poison), but it is not established whether the objective is defensive because it does not scare away predators.

In conclusion, strategies, practices and nature of the poison in mammals are varied and their study may have important medical implications for drug development and increase awareness of the evolutionary relationships between different groups of living animals (reptiles-mammals) and their ancestors.

REFERENCIAS

• Platypus poison
• Scientists discover the function of the echidna’s spur
• Los primates venenosos existen
• El único primate venenoso del mundo ya no está solo
• “Venom” of the slow loris: sequence similarity
  of prosimian skin gland protein and Fel d 1 cat allergen
• Venomous Slow Loris May Have Evolved To Mimic Cobras
• La rata que se unta con veneno para defenderse
• ¿Es cierto que los erizos se embadurnan de veneno?
• Pequeños pero feroces: mamíferos venenosos
• Are slow lorises really venomous?
• Encuentro con un “fósil viviente” en R. Dominicana
• Imagen de portada de Dave Watts