By request: My homework
There was some interest in my final paper for my Evolution and Biodiversity class, so what the heck, I've posted more embarassing things. I'm not in love with this paper--I think if I gave it a few more hours of research and general rigor it would be much better. But I did it for a grade, not to improve the quality of Oniscidean information available, so it succeeded on that level, if nothing else.
May 24th 2006
Jeffrey C.Taylor
Evolutionary Biology and Biodiversity
The Adaptations of Terrestrial Isopods (Oniscidea) to the Urban Environment
Oniscidea is a suborder of Isopoda, of the subphylum Crustacea, those arthropod animals that are distinguished from myriapods and hexapods by possession of a calcareous exoskeleton, two pairs of antennae, and branched (biramous) appendages. The vast majority of crustaceans are marine animals, with diverse taxa in both salt and fresh water habitats. The order Isopoda includes taxa living in salt water, fresh water, and the single suborder that includes fully terrestrial species, Oniscidea. Most species, though completely terrestrial, live in moist conditions: under leaf litter or in humid areas. They show a strong tendency toward a nocturnal existence, and avoid light. They generally consume vegetation, detritus, and fungi, and are considered important decomposers where they occur.
Oniscideans are also well-known urban animals. They can be found in a wide range of human-disturbed habitats, from the garden to the city. Urban organisms, and more generally, those that are successful in the habitats created and modified by human activity, are among the most important living things to study. Nearly half of the six billion people on earth live in urban areas, and with development, sprawl, human population growth, and mass extinctions as generally accepted realities for the future, those organisms that can live along side us deserve study. We will share the future earth with them. Understanding what has allowed certain groups of animals to survive the changes to the land that human use has caused will give allow us to be able to make changes that could result in more species surviving. Many people are already familiar with the “roly-poly,” or oniscidean, and these animals generally inspire the extreme negative reactions that other arthropods do. These facts are helpful, and can make us optimistic that studying why oniscideans are urban animals can potentially lead to changes in the way we use the land, and eventually to improved urban biodiversity.
There are over 3600 described species of Oniscidea as of 2004. Most of these species have been described in the past 120 years; in 1885 there were only 385 species described.1 This suggests that despite the biodiversity of Oniscidean species, only a few of these were commonly known until recently. In fact, the lay literature correlates with Schmalfuss’ recent comprehensive catalog of described species: three species comprise the most frequently encountered and studied, both by the scientific community, and by casual observers.
Casual observers of Oniscideans are often children and gardeners, as these people are the most likely to be in close contact with the soil. Common names such as woodlouse, sow bug, doodlebug, roly-poly, and potato bug all suggest an association with the garden or the playground. These common names are sometimes interchangeable between species, and often one name predominates in a geographic area. The most generally accepted common name is woodlouse (plural: woodlice) for all oniscideans except those belonging to families that can defend themselves by rolling into a ball (e.g. Armidillidae), which are usually called pill bugs.
Three frequently present oniscideans include Oniscus asellus, Porcellio scaber, and Armadillidium vulgare. When they are distinguished by common names they are usually called the common shiny woodlouse, the common rough woodlouse, and the common pill bug. It is worth noting that these represent three different families within the suborder. These three are also the most often used in studies of the effects of pollution, contaminants and heavy metals on terrestrial Isopods. These species are each native to a different region of Europe (northwest, northern, and Mediterranean, respectively) but have become common in and around cities worldwide. They are occasionally found as household pests, usually in concert with wet and rotting wood. In addition to the garden, home, and yard, these animals are also quite common in urban ecosystems. Any investigator who has not outgrown the habit of overturning logs and debris, to look for animals underneath, will almost invariably find these species, whether the log is in the woods, in the back yard, or in an urban vacant lot.
Before exploring those adaptations that have suited members of this suborder to survival in the sometimes harsh, often toxic urban environment, it will be useful to examine their history as animals associated with humans. It will also prove very illuminating to look at some of the specific adaptations that they developed in the course of transforming from aquatic to terrestrial animals. Both the historical and evolutionary perspectives are important for fully appreciating the oniscideans’ current place as a familiar and highly successful colonizer of the man-made landscape.
The Age of Exploration was a time when sailors from Europe traveled the world in huge ships, looking for trade routes and natural resources. During this period, animals and plants from Europe were brought to new lands. In many cases, such as those of livestock such as cattle, pigs, and goats, the introductions were quite intentional. In other cases, such as the black and Norway rats, and the house mouse, the introductions were accidental. In some cases (notably those already cited) these introductions were successful, and essentially permanent. In the case of European oniscideans (including the three important species cited above: Oniscus asellus, Porcellio scaber, and Armadillidium vulgare) the introduction was also accidental.
Ships heading to lands to acquire cargo need to be loaded with ballast, to make up weight and sail properly. In the present day, water is used as ballast, but in past centuries soil was used. When the ship was then to take on cargo, the ballast was dumped at port. Many European soil organisms, among them beetles, millipedes, and earthworms, were carried around the world this way, and several dozen species have become naturalized. 2 (The contemporary practice of using water as ballast has had its own consequences, in the introduction of noxious aquatic species.)
It is a safe assumption that the soil used as ship’s ballast was obtained from an area convenient to the European port of origin. It follows that the organisms living in this soil would have been those already adapted to the urban conditions of a port city. It is intuitive to nearly redundant, but bears emphasizing that “species that come into frequent contact with humans have more chance of being introduced to an alien continent than other species.” 3
Later, settled colonies would import European plants to use as crops and landscaping. Those organisms living in the plant nurseries in Europe would have been shipped along with the plants themselves. Again, since these were those organisms that had adapted to the conditions of commercial agriculture and gardening, they were pre-adapted to the conditions awaiting them in the gardens and fields of the New World continents that they found themselves in. The oniscideans transported this way were and are, significantly “common in within their source region,” and “able to colonize disturbed sites,” 3
Where they have been introduced, they invariably outcompete native Oniscideans. In one survey, which compared an area of high human impact to one less affected by human activity, Oniscidean abundance was found to be “much higher in the urban forests than in the relatively undisturbed reference site.” Eleven species were identified from the urban site, all introduced species, including the three covered here. These researchers concluded that “human impact is at least as important determining distribution and abundance of isopods as the abiotic and biotic environmental factors. “4
The fact that some European oniscideans were well situated to become successful organisms in new, human-disturbed ecosystems has been established. Now it is important to look at some specific adaptations that allow these terrestrial members of an otherwise aquatic taxon to live on land. Additionally, we can examine what these adaptations to a terrestrial existence contribute to the group’s collective success as a type of urban animal.
Oniscideans have a number of unique adaptations for living on land. These include abdominal appendages modified to become respiratory organs, known as pleopodal lungs, which vary in size and complexity between different species. More complex pleopodal lungs are present in those species that inhabit drier ecosystems; those Oniscideans occurring in more moist habitats tend to have reduced pleopodal lungs.5
An additional adaptation involves how wastes are dealt with. While in “most crustaceans the excretion of nitrogenous wastes requires that copious supplies of water be available for washing away the soluble end-products,” terrestrial Oniscideans, “are able to excrete ammonia as a gas, without being subject to toxic side-effects.”6 Certain amino acids, studied in Porcellio scaber, are thought to play a role in protecting these animals from the negative effects of ammonia exposure.7 A series of studies compiled by the World Health Organization found that isopods suffered far less from environmental ammonia pollution than a whole range of other organisms, including other arthropods such as insects. 8
Another important adaptation to living on land is the development of the embryo within a marsupium. While other crustaceans usually produce planktonic larvae, Oniscideans (and their relatives in the superorder Peracarida, which includes marine Isopods and the order Amphipoda) develop into manca, or subadult, resembling a miniature adult, but lacking one body segment and the appendages that segment would bear. Before emerging, the manca is protected from desiccation within the water-filled marsupium, or brood pouch. Presumably, in marine isopods, this breeding system is a trade-off that affords the manca some protection from predation, while limiting the ability for dispersal. In Oniscideans, the marsupium still provides protection for the young, increasing the likelihood that they will survive to adulthood, but more significantly it is clearly a critical adaptation for colonization of terrestrial habitats.
Some aspects of oniscidean natural history are easy to overlook, but are important for understanding their success in urban environments. Oniscideans “have a relatively high surface area to volume ratio and are therefore likely to lose water by diffusion more quickly than many other species. They also lack a waxy, waterproof cuticle and so water will readily diffuse through their exoskeleton more rapidly than in other arthropods.” 9 As a result of this, oniscidean behavior includes a strong response to lack of humidity, and these animals are commonly known to prefer moist areas as habitat. A related behavior is their tendency to move away from light, or “negative phototaxis.”9 Taken together, these behaviors mean that oniscideans prefer habitat that is both dark and moist. Apart from the obvious locations like leaf litter and other debris, there is a range of man-made habitats that fit these requirements. The arthropod most associated with the urban ecosystem, the cockroach (family Blattidae) has similar behavioral reactions to light and (to a lesser extent) moisture. Urban cockroaches found in temperate zones exclusively live in buildings, because they are tropical animals that rely on artificial heat sources to survive temperate winters. Urban woodlice, on the other hand, are from temperate or Mediterranean climates, and so while they may make use of dark and damp building spaces such as basements and around plumbing, they are not confined to them. Indeed, often the advice is given, that if you wish to exclude oniscideans from your home, you must limit the humidity in your house. This will, of course, mean that these animals will instead live in the margins of the buildings, in soil, under debris, and in the lawn and garden.
One of the obstacles to survival in a post-industrial urban ecosystem is contamination of the soil by heavy metals. The negative effect to soil-dwelling organisms, of the presence of toxic substances in the soil, should be obvious.
Oniscideans exposed to “concentrations of metals can suffer early mortality and reduced body size,” as well as limited reproductive success. It was found that populations of Porcellio scaber and Oniscus asellus that were collected from a metal-contaminated site had a different level of tolerance to metal toxicity than those of the same species raised in a non-contaminated laboratory setting. It was found that those Oniscidean populations that were collected from the most contaminated sites had a greater tolerance to metal toxicity. These populations showed greater reproductive success compared to the control animals. This suggests that natural selection has provided these two species with an ability to adapt to a particularly hostile man-made environmental condition.10
In another study, it was shown that Porcellio scaber was able to distinguish between food contaminated with a non-lethal dose of the metal cadmium and uncontaminated food. Over the three week period of the experiment, the woodlice became better at avoiding the cadmium-dosed food.11 In a wild, urban environment, the ability to discern between metal-contaminated food and uncontaminated food would reduce individual mortality, and increase reproductive success. The ability of isopods to recognize and avoid a contaminated site was even suggested as a possible method for soil quality and risk assessment. 12
Another study involved collecting oniscideans from sites near metal-smelting industry in Great Britain. The only species found was Porcellio scaber. Unsurprisingly, high levels of zinc, cadmium, lead, and copper were detected in these animals. What was surprising was that high levels of zinc and cadmium were found to occur in control animals collected from uncontaminated areas. The researchers noted that Porcellio scaber has a “high affinity” for these elements. They also point out that there are very few invertebrate predators of oniscideans, and suggest these are the few that have evolved some way to deal with the high levels of metals in their prey.13 (Presumably the effect on larger, vertebrate, predators is less important.) Here we see a two-sided adaptation: P. scaber not only can survive exposure to certain toxic metals, but in at least some cases seeks them out, and these metals confer a defense against some predators.
Evolution has provided this interesting group of animals with a whole host of unexpected and fascinating adaptations. Each developed through natural selection to make oniscideans successful colonizers of the land, and participants in their soil and detritus ecosystems. Through many accidents of history, they became heir to a geologically new set of ecosystems: those that are dramatically disturbed by human action. The garden, crop field, yard, and even the city are new habitats that oniscideans have not only managed to survive in, but thrive. Some groups at least, from different families in the suborder, have expanded their original range to include everywhere on earth that humans have caused great changes to the landscape. All the animals and plants of the world are faced with a future where the adaptations that natural selection has given them will determine whether they can live alongside humanity. We understand now that because of a variety of different adaptations, oniscideans are one group that can, and will, share the future with us.
1. Schmalfuss HaW-S, K. A bibliography of terrestrial isopods (Crustacea, Isopoda, Oniscidea). Stuttgarter Beitrage zur Naturkunde. 2002;A:120
2. Sailer RI. Our immigrant insect fauna. Bulletin of the Entomological Society of America. 1978:3-11
3. Andreas Prinzing WD, Stefan Klotz, Roland Brandl. Which species become aliens. Evolutionary Ecology Research. 2002:385-405
4. Hornung KSaE. Diversity and dynamics of terrestrial isopods in urban forests. 5th International Symposium on the Biology of Terestrial Isopods. Natural History Museum of Crete; 2001
5. Paoli P, Ferrara, Franco and Taiti, Stefano. Morphology and evolution of the respiratory apparatus in the family Eubelidae (Crustacea, Isopoda, Oniscidea). Journal of Morphology. 2002;253:272-289
6. Mantel DEBaLH. Adaptations of Crustaceans to Land: A Summary and Analysis of New Findings. American Zoologist. 1968;8:673-685
7. Wright J DM, Reichert J. Effects of ammonia loading on Porcellio scaber: Glutamine and Glutamine Sythesis, ammonia excretion and toxicity. Journal of Experimental Biology. 1994;188:143-157
8. E.A. Bababunmi ea. Environmental Health Criteria. Geneva: World Health Organization; 1986
9. Mckenzie GJ. Woodlice Homepage. Vol. 2006; 1997
10. Jones DTaSPH. Reproductive Allocationin the Terrestrial Isopods Porcellio scaber and Oniscus asellus in a metal-polluted environment. Functional Ecology. 1996;10:741-750
11. Zidar P BJ, Strus J. Behavioral response in the terrestrial isopod Porcellio scaber (Crustacea) offered a choice of uncontaminated and cadmium-contaminated food. Ecotoxicology. 2005;14:493-502
12. Loureriro S, Soares, AM, Nogueira, AJ. Terrestrial avoidance behaviour tests as screening tool to assess soil contamination. Environmental Pollution. 2005;138:121-131
13. Hopkin S, Hardisty, GN, Martin, MH. The Woodlouse Porcellio scaber as a 'Biological Indicator' of Zinc, Cadmium, Lead and Copper Pollution. Environmental Pollution (Series B). 1986;11:271-290
May 24th 2006
Jeffrey C.Taylor
Evolutionary Biology and Biodiversity
The Adaptations of Terrestrial Isopods (Oniscidea) to the Urban Environment
Oniscidea is a suborder of Isopoda, of the subphylum Crustacea, those arthropod animals that are distinguished from myriapods and hexapods by possession of a calcareous exoskeleton, two pairs of antennae, and branched (biramous) appendages. The vast majority of crustaceans are marine animals, with diverse taxa in both salt and fresh water habitats. The order Isopoda includes taxa living in salt water, fresh water, and the single suborder that includes fully terrestrial species, Oniscidea. Most species, though completely terrestrial, live in moist conditions: under leaf litter or in humid areas. They show a strong tendency toward a nocturnal existence, and avoid light. They generally consume vegetation, detritus, and fungi, and are considered important decomposers where they occur.
Oniscideans are also well-known urban animals. They can be found in a wide range of human-disturbed habitats, from the garden to the city. Urban organisms, and more generally, those that are successful in the habitats created and modified by human activity, are among the most important living things to study. Nearly half of the six billion people on earth live in urban areas, and with development, sprawl, human population growth, and mass extinctions as generally accepted realities for the future, those organisms that can live along side us deserve study. We will share the future earth with them. Understanding what has allowed certain groups of animals to survive the changes to the land that human use has caused will give allow us to be able to make changes that could result in more species surviving. Many people are already familiar with the “roly-poly,” or oniscidean, and these animals generally inspire the extreme negative reactions that other arthropods do. These facts are helpful, and can make us optimistic that studying why oniscideans are urban animals can potentially lead to changes in the way we use the land, and eventually to improved urban biodiversity.
There are over 3600 described species of Oniscidea as of 2004. Most of these species have been described in the past 120 years; in 1885 there were only 385 species described.1 This suggests that despite the biodiversity of Oniscidean species, only a few of these were commonly known until recently. In fact, the lay literature correlates with Schmalfuss’ recent comprehensive catalog of described species: three species comprise the most frequently encountered and studied, both by the scientific community, and by casual observers.
Casual observers of Oniscideans are often children and gardeners, as these people are the most likely to be in close contact with the soil. Common names such as woodlouse, sow bug, doodlebug, roly-poly, and potato bug all suggest an association with the garden or the playground. These common names are sometimes interchangeable between species, and often one name predominates in a geographic area. The most generally accepted common name is woodlouse (plural: woodlice) for all oniscideans except those belonging to families that can defend themselves by rolling into a ball (e.g. Armidillidae), which are usually called pill bugs.
Three frequently present oniscideans include Oniscus asellus, Porcellio scaber, and Armadillidium vulgare. When they are distinguished by common names they are usually called the common shiny woodlouse, the common rough woodlouse, and the common pill bug. It is worth noting that these represent three different families within the suborder. These three are also the most often used in studies of the effects of pollution, contaminants and heavy metals on terrestrial Isopods. These species are each native to a different region of Europe (northwest, northern, and Mediterranean, respectively) but have become common in and around cities worldwide. They are occasionally found as household pests, usually in concert with wet and rotting wood. In addition to the garden, home, and yard, these animals are also quite common in urban ecosystems. Any investigator who has not outgrown the habit of overturning logs and debris, to look for animals underneath, will almost invariably find these species, whether the log is in the woods, in the back yard, or in an urban vacant lot.
Before exploring those adaptations that have suited members of this suborder to survival in the sometimes harsh, often toxic urban environment, it will be useful to examine their history as animals associated with humans. It will also prove very illuminating to look at some of the specific adaptations that they developed in the course of transforming from aquatic to terrestrial animals. Both the historical and evolutionary perspectives are important for fully appreciating the oniscideans’ current place as a familiar and highly successful colonizer of the man-made landscape.
The Age of Exploration was a time when sailors from Europe traveled the world in huge ships, looking for trade routes and natural resources. During this period, animals and plants from Europe were brought to new lands. In many cases, such as those of livestock such as cattle, pigs, and goats, the introductions were quite intentional. In other cases, such as the black and Norway rats, and the house mouse, the introductions were accidental. In some cases (notably those already cited) these introductions were successful, and essentially permanent. In the case of European oniscideans (including the three important species cited above: Oniscus asellus, Porcellio scaber, and Armadillidium vulgare) the introduction was also accidental.
Ships heading to lands to acquire cargo need to be loaded with ballast, to make up weight and sail properly. In the present day, water is used as ballast, but in past centuries soil was used. When the ship was then to take on cargo, the ballast was dumped at port. Many European soil organisms, among them beetles, millipedes, and earthworms, were carried around the world this way, and several dozen species have become naturalized. 2 (The contemporary practice of using water as ballast has had its own consequences, in the introduction of noxious aquatic species.)
It is a safe assumption that the soil used as ship’s ballast was obtained from an area convenient to the European port of origin. It follows that the organisms living in this soil would have been those already adapted to the urban conditions of a port city. It is intuitive to nearly redundant, but bears emphasizing that “species that come into frequent contact with humans have more chance of being introduced to an alien continent than other species.” 3
Later, settled colonies would import European plants to use as crops and landscaping. Those organisms living in the plant nurseries in Europe would have been shipped along with the plants themselves. Again, since these were those organisms that had adapted to the conditions of commercial agriculture and gardening, they were pre-adapted to the conditions awaiting them in the gardens and fields of the New World continents that they found themselves in. The oniscideans transported this way were and are, significantly “common in within their source region,” and “able to colonize disturbed sites,” 3
Where they have been introduced, they invariably outcompete native Oniscideans. In one survey, which compared an area of high human impact to one less affected by human activity, Oniscidean abundance was found to be “much higher in the urban forests than in the relatively undisturbed reference site.” Eleven species were identified from the urban site, all introduced species, including the three covered here. These researchers concluded that “human impact is at least as important determining distribution and abundance of isopods as the abiotic and biotic environmental factors. “4
The fact that some European oniscideans were well situated to become successful organisms in new, human-disturbed ecosystems has been established. Now it is important to look at some specific adaptations that allow these terrestrial members of an otherwise aquatic taxon to live on land. Additionally, we can examine what these adaptations to a terrestrial existence contribute to the group’s collective success as a type of urban animal.
Oniscideans have a number of unique adaptations for living on land. These include abdominal appendages modified to become respiratory organs, known as pleopodal lungs, which vary in size and complexity between different species. More complex pleopodal lungs are present in those species that inhabit drier ecosystems; those Oniscideans occurring in more moist habitats tend to have reduced pleopodal lungs.5
An additional adaptation involves how wastes are dealt with. While in “most crustaceans the excretion of nitrogenous wastes requires that copious supplies of water be available for washing away the soluble end-products,” terrestrial Oniscideans, “are able to excrete ammonia as a gas, without being subject to toxic side-effects.”6 Certain amino acids, studied in Porcellio scaber, are thought to play a role in protecting these animals from the negative effects of ammonia exposure.7 A series of studies compiled by the World Health Organization found that isopods suffered far less from environmental ammonia pollution than a whole range of other organisms, including other arthropods such as insects. 8
Another important adaptation to living on land is the development of the embryo within a marsupium. While other crustaceans usually produce planktonic larvae, Oniscideans (and their relatives in the superorder Peracarida, which includes marine Isopods and the order Amphipoda) develop into manca, or subadult, resembling a miniature adult, but lacking one body segment and the appendages that segment would bear. Before emerging, the manca is protected from desiccation within the water-filled marsupium, or brood pouch. Presumably, in marine isopods, this breeding system is a trade-off that affords the manca some protection from predation, while limiting the ability for dispersal. In Oniscideans, the marsupium still provides protection for the young, increasing the likelihood that they will survive to adulthood, but more significantly it is clearly a critical adaptation for colonization of terrestrial habitats.
Some aspects of oniscidean natural history are easy to overlook, but are important for understanding their success in urban environments. Oniscideans “have a relatively high surface area to volume ratio and are therefore likely to lose water by diffusion more quickly than many other species. They also lack a waxy, waterproof cuticle and so water will readily diffuse through their exoskeleton more rapidly than in other arthropods.” 9 As a result of this, oniscidean behavior includes a strong response to lack of humidity, and these animals are commonly known to prefer moist areas as habitat. A related behavior is their tendency to move away from light, or “negative phototaxis.”9 Taken together, these behaviors mean that oniscideans prefer habitat that is both dark and moist. Apart from the obvious locations like leaf litter and other debris, there is a range of man-made habitats that fit these requirements. The arthropod most associated with the urban ecosystem, the cockroach (family Blattidae) has similar behavioral reactions to light and (to a lesser extent) moisture. Urban cockroaches found in temperate zones exclusively live in buildings, because they are tropical animals that rely on artificial heat sources to survive temperate winters. Urban woodlice, on the other hand, are from temperate or Mediterranean climates, and so while they may make use of dark and damp building spaces such as basements and around plumbing, they are not confined to them. Indeed, often the advice is given, that if you wish to exclude oniscideans from your home, you must limit the humidity in your house. This will, of course, mean that these animals will instead live in the margins of the buildings, in soil, under debris, and in the lawn and garden.
One of the obstacles to survival in a post-industrial urban ecosystem is contamination of the soil by heavy metals. The negative effect to soil-dwelling organisms, of the presence of toxic substances in the soil, should be obvious.
Oniscideans exposed to “concentrations of metals can suffer early mortality and reduced body size,” as well as limited reproductive success. It was found that populations of Porcellio scaber and Oniscus asellus that were collected from a metal-contaminated site had a different level of tolerance to metal toxicity than those of the same species raised in a non-contaminated laboratory setting. It was found that those Oniscidean populations that were collected from the most contaminated sites had a greater tolerance to metal toxicity. These populations showed greater reproductive success compared to the control animals. This suggests that natural selection has provided these two species with an ability to adapt to a particularly hostile man-made environmental condition.10
In another study, it was shown that Porcellio scaber was able to distinguish between food contaminated with a non-lethal dose of the metal cadmium and uncontaminated food. Over the three week period of the experiment, the woodlice became better at avoiding the cadmium-dosed food.11 In a wild, urban environment, the ability to discern between metal-contaminated food and uncontaminated food would reduce individual mortality, and increase reproductive success. The ability of isopods to recognize and avoid a contaminated site was even suggested as a possible method for soil quality and risk assessment. 12
Another study involved collecting oniscideans from sites near metal-smelting industry in Great Britain. The only species found was Porcellio scaber. Unsurprisingly, high levels of zinc, cadmium, lead, and copper were detected in these animals. What was surprising was that high levels of zinc and cadmium were found to occur in control animals collected from uncontaminated areas. The researchers noted that Porcellio scaber has a “high affinity” for these elements. They also point out that there are very few invertebrate predators of oniscideans, and suggest these are the few that have evolved some way to deal with the high levels of metals in their prey.13 (Presumably the effect on larger, vertebrate, predators is less important.) Here we see a two-sided adaptation: P. scaber not only can survive exposure to certain toxic metals, but in at least some cases seeks them out, and these metals confer a defense against some predators.
Evolution has provided this interesting group of animals with a whole host of unexpected and fascinating adaptations. Each developed through natural selection to make oniscideans successful colonizers of the land, and participants in their soil and detritus ecosystems. Through many accidents of history, they became heir to a geologically new set of ecosystems: those that are dramatically disturbed by human action. The garden, crop field, yard, and even the city are new habitats that oniscideans have not only managed to survive in, but thrive. Some groups at least, from different families in the suborder, have expanded their original range to include everywhere on earth that humans have caused great changes to the landscape. All the animals and plants of the world are faced with a future where the adaptations that natural selection has given them will determine whether they can live alongside humanity. We understand now that because of a variety of different adaptations, oniscideans are one group that can, and will, share the future with us.
1. Schmalfuss HaW-S, K. A bibliography of terrestrial isopods (Crustacea, Isopoda, Oniscidea). Stuttgarter Beitrage zur Naturkunde. 2002;A:120
2. Sailer RI. Our immigrant insect fauna. Bulletin of the Entomological Society of America. 1978:3-11
3. Andreas Prinzing WD, Stefan Klotz, Roland Brandl. Which species become aliens. Evolutionary Ecology Research. 2002:385-405
4. Hornung KSaE. Diversity and dynamics of terrestrial isopods in urban forests. 5th International Symposium on the Biology of Terestrial Isopods. Natural History Museum of Crete; 2001
5. Paoli P, Ferrara, Franco and Taiti, Stefano. Morphology and evolution of the respiratory apparatus in the family Eubelidae (Crustacea, Isopoda, Oniscidea). Journal of Morphology. 2002;253:272-289
6. Mantel DEBaLH. Adaptations of Crustaceans to Land: A Summary and Analysis of New Findings. American Zoologist. 1968;8:673-685
7. Wright J DM, Reichert J. Effects of ammonia loading on Porcellio scaber: Glutamine and Glutamine Sythesis, ammonia excretion and toxicity. Journal of Experimental Biology. 1994;188:143-157
8. E.A. Bababunmi ea. Environmental Health Criteria. Geneva: World Health Organization; 1986
9. Mckenzie GJ. Woodlice Homepage. Vol. 2006; 1997
10. Jones DTaSPH. Reproductive Allocationin the Terrestrial Isopods Porcellio scaber and Oniscus asellus in a metal-polluted environment. Functional Ecology. 1996;10:741-750
11. Zidar P BJ, Strus J. Behavioral response in the terrestrial isopod Porcellio scaber (Crustacea) offered a choice of uncontaminated and cadmium-contaminated food. Ecotoxicology. 2005;14:493-502
12. Loureriro S, Soares, AM, Nogueira, AJ. Terrestrial avoidance behaviour tests as screening tool to assess soil contamination. Environmental Pollution. 2005;138:121-131
13. Hopkin S, Hardisty, GN, Martin, MH. The Woodlouse Porcellio scaber as a 'Biological Indicator' of Zinc, Cadmium, Lead and Copper Pollution. Environmental Pollution (Series B). 1986;11:271-290