Agriculture and processed food-driven evolution of small mammals

Speculative evolution


Although the agricultural practice is an anthropogenic evolutional event by itself, by the selection and creation of new plant cultivars and animal breeds, is also a major factor in the evolution of non-targeted organisms. As it offers new sources of potential food, previously not available or in insufficient quantities, it laid to the emergence of new species, adapted to these new food sources. More or less, along with the abundance of processed food, a variety of behavioral, physiological and anatomical adaptations gradually caused the evolution of new species. The current paper represents the description of several such species, along with the major adaptive mechanisms, found in them.

General considerations

Agriculture and the environment

The basic effect of contemporary agriculture on the non-targeted organisms, e.g., that are not wanted to take advantage of the agricultural yield or are subject to breeding on their own, could be summarized in a few simple words – “new food”, “better food” and “more food”. Briefly explained, this means that a wild or feral animal will have access to new food sources, previously not available (e.g. potatoes, introduced to Europe). Most of these new, or old (but altered) food sources will be larger and richer in nutrients (e.g. the domesticated corn, which is far larger and resources richer than its wild ancestor). Finally, the agro-ecosystems offer a concentrated abundance of the said food and often, during most of the year. Considering this, many native or introduced animals do take advantage of this and gradually adapted to better suit the new conditions.

Processed food – more of a challenge than a gift

Unlike agricultural ecosystems, the abundance of processed food that is available to wild and feral animals (usually discarded or available in storage) is somehow more challenging. First of all, it usually contains more salt, sugar and other additives, not perfectly suitable for wild animals. It should be also highlighted that the packaging of processed food is often a challenge for animals, as they need to somehow open this package. Because of this, processed food is often considered less beneficial to wild animals and rarely leads to speciation (or the development of new species), but rather to slight physiological adaptations (because of additives) and newly acquired skills (to open packages). Despite that the expectation of populations of overly obese “junk-food rodents” was fully justified, this tendency remained limited and faded with time, due to the gradual adaptation to the high carbohydrate diet and the simple fact that an obese animal is less likely to escape enemies and reproduce.

New anthropogenic species

Not unexpectedly, the agriculture-driven speciation in mammals affected mostly the three biggest orders – Rodentia (rodents), Chiroptera (bats) and Soricomorpha (shrew-like), which account for nearly 70% of all known mammals and may be considered some with the highest ecological plasticity. As such, they have also benefited the most from the new food source opportunities, brought by human activity. In the simplest example, European mole rats did fully enjoy the delicious potato and mice and rats – corn, both American in origin, but introduced into the European agricultural practice relatively long ago. The following, however, are examples of highly specific adaptations that ultimately lead to the emergence of new species, and, most of these species in turn became agricultural pests.

Order Soricomorpha

Aquatic mole (Neotalpa aquatica)

It may remain a mystery when and where (on which continent) a typical fossorial (underground) animal decided to change to an aquatic lifestyle, but it arose as the most bitter enemy of freshwater aquacultures on every possible continent. This comparatively small animal, reaching about 15 cm and rarely more than 100 g (Fig. 1), completely blind, but equipped with the incredibly sensitive Eimer’s organ successfully combines its original subterranean lifestyle during the day with newly acquired aquatic hunting during the nights. Its ancestors were ready for the transition to aquatic habitat – with the digging paws similar to paddles and already adapted to a low oxygen environment. Their slightly different hemoglobin, with a higher oxygen affinity, enables unique underwater breathing, directly through specialized, blood-enriched skin formation that allows them to absorb water-dissolved oxygen. They further build a sophisticated system of both flooded and dry tunnels to keep predators (such as weasels) away. Its diet consists primarily of small fishes and crustaceans, thus, causing enormous losses to fish and prawn farming. A very similar species, Neotalpa clamilovora is highly specialized in eating freshwater mussels from aquacultures, by opening their shells with a modified thumb. In both species, the possible trigger for adaptation to aquatic life was the aquacultures, because they offered a higher concentration of possible prey, more or less isolated from larger predators and thus, a perfect niche for a killer, hiding underground during the days.

Figure 1. An aquatic mole (right) and egg-piercing shrew (left).

Vampire shrew (Neoblarina sanguisuga)

A relatively large North American shrew, the vampire shrew is highly specialized in consuming blood from larger mammals. Its saliva contains several enzymes, such as kallikrein-like protease, with the action to cause local paralysis at the site of the bite and to dilate blood vessels and bioactive peptides such as the paralytic soricidin. It usually attacks livestock and prefers to feed at night, in cowsheds and barns when domestic animals are gathered to sleep. The venom is not powerful enough to kill a larger animal, but numerous bites in continuous days, along with the blood loss could eventually render the target animal (in most cases cattle) sick. The evolution of the vampire shrew is believed to be very similar to that of the vampire bats but triggered by the mass breeding of cattle. Unlike bats, shrews are not so mobile and their evolution into hematophages was possible only when sufficient food was available in the same place over the year. Wild ungulates tend to be migratory animals, while livestock suits much better as potential prey.

Egg-piercing shrew (Neosorex gallinarium)

Another member of the shrews, but this time a European one, the egg-piercing shrew (Fig. 1) evolved due to the abundance of eggs, produced by the poultry industry. Such a strict diet and the corresponding puncture tooth would not be possible in the wild, because bird eggs are relatively rare, hard to reach, and usually a well-defended delicacy. On a hen farm, however, chicken eggs are abundant and easy to feed on. Very similar to the vampire shrew, who developed additional teeth to puncture ungulates’ skin, the egg-piercing shrew developed a single, left lower incisor, tooth to puncture eggs and suck up their content.

Order Chiroptera

Honey bat (Lonchophylla meliphaga)

This species is a unique example of a South American species, evolved from nectar-feeding bats that spread worldwide and became the most hated by beekeepers pest. This relatively small bat, about 4 cm in length, successfully enters beehives and sucks up the honey in a unique manner, by using its tongue like a straw. It is also equipped with very thick fur, thus avoiding bee stings, and possesses a certain degree of bee venom insensitivity.

Milking bat (Neodesmodus parasitus-pecus)

Another South American species with worldwide distribution, this unique creature (Fig. 2) is specialized in sucking up milk from the udder of milking cows. Much like the honey bat, it is a nocturnal parasite, entering barns and feeding on the cattle milk. Its negative effect is considered insignificant for the dairy industry although in some cases it might cause injuries and bacterial infections by scratching the udder. It is a species, descending from the vampire bat, which, at some point found that the constantly milking cows in farms offer more nutritious and accessible food.

Figure 2. A milking bat (up) and seal rat (down).

Order Rodentia

Wandering ground squirrel (Neomarmota latro)

These highly social rodents represent also highly specialized robbers of root vegetables, spread throughout Europe. Very similar to prairie dogs, they live in social groups of thirty to over one hundred individuals with a very strict hierarchy. They build complex underground towns, made of tunnels and chambers, which they frequently abandon and move to a new area. The term “wandering”, however, comes from the specialized system of food gathering. Firstly the scouts, usually young males, search for a potential food source – a garden or field, preferably planted with potatoes, carrots, turnip, or beetroot and sometimes a few kilometers from the town. Then, at nightfall about 2/3 of the colony undertakes an expedition to the designated field and digs out as much as possible of the available food. During this activity three classes of squirrels execute specialized tasks – diggers virtually plow up the entire field, carriers collect food and store it in a specialized pouch (similar, but not related to the marsupial one) and guards take care of the safety by looking for potential danger and alarming the rest of the squirrels. The biggest problem with wandering squirrels is the fact they never gather food near their town and they never come back to the same place, so it is very difficult to predict their next hit and locate their colony. Undoubtedly, their most specialized feature is the poach, which evolved from overgrown skin on the belly.

Seal rat (Neorattus aquaticus)

Although many rats and other related rodents are semi-aquatic, adapted and to a large extent dependent on water, the Asian seal rat (Fig. 2) is the first example of a fully aquatic rodent. It is called seal rat because it resembles a seal in many ways but still is way too different. Among important adaptations to life underwater is the beaver-like tail, the back limbs turned into flippers and the shutting nostrils. Still, the seal rat kept its fur and, most importantly, the anatomy of the forelimbs perfectly adapted to manipulate various objects. Their main evolutional trigger, habitat and food source are the deep-water rice paddles, where they swim and feed on rice seeds. Besides this, however, their ecological plasticity allows them to live also in various swamps and rivers and feed on crustaceans, small fishes, or whatever is available.

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