The Laboratory Primate

• Publisher: Academic Press
• Year: 2005
• ISBN:
  9780080454160
• Topic: Medicine
• Subtopic: Veterinary Medicine

A volume in the Handbook of Experimental Animals series, The Laboratory Primate details the past and present use of primates in biomedical research, and the husbandry, nutritional requirements, behaviour, and breeding of each of the commonly used species. Practical information on regulatory requirements, not available in other texts, is covered. Sections on experimental models cover the major areas of biomedical research, including AIDS, cancer, neurobiology and gene therapy. Assisted reproductive technology, tissue typing, and minimum group sizes for infectious disease/vaccine studies are also included.

• Two-color, user-friendly format, with copious illustrations and color plates
• Includes detailed, well-illustrated sections on gross & microscopic anatomy, common diseases, and special procedures, including surgical techniques

Part 1

Definition of the Primate Model

CHAPTER 1

The Taxonomy of Primates in the Laboratory Context

Groves Colin, School of Archaeology and Anthropology, Australian National University, Canberra, ACT 0200, Australia

Taxonomy: Organizing nature

Taxonomy means classifying organisms. It is nowadays commonly used as a synonym for systematics, though strictly speaking systematics is a much broader sphere of interest – interrelationships, and biodiversity. At the basis of taxonomy lies that much-debated concept, the species.

Because there is so much misunderstanding about what a species is, it is necessary to give some space to discussion of the concept. The importance of what we mean by the word “species” goes way beyond taxonomy as such: it affects such diverse fields as genetics, biogeography, population biology, ecology, ethology, and biodiversity; in an era in which threats to the natural world and its biodiversity are accelerating, it affects conservation strategies (Rojas, 1992). In the present context, it is of crucial importance for understanding laboratory primates and their husbandry.

What are species? The biological species concept

Disagreement as to what precisely constitutes a species is to be expected, given that the concept serves so many functions (Vane-Wright, 1992). We may be interested in classification as such, or in the evolutionary implications of species; in the theory of species, or in simply how to recognize them; or in their reproductive, physiological, or husbandry status.

Most non-specialists probably have some vague idea that species are defined by not interbreeding with each other; usually, that hybrids between different species are sterile, or that they are incapable of hybridizing at all. Such an impression ultimately derives from the definition by Mayr (1940), whereby species are “groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups” (the Biological Species Concept). Mayr never actually said that species can’t breed with each other, indeed he denied that that this was in any way a necessary part of reproductive isolation; he merely said that, under natural conditions, they don’t.

Reproductive isolation, in some form, stands at the basis of what a species is. Having said this, it must be admitted that it is no longer possible to follow Mayr’s concept as definitive. In a recent book (Groves, 2001, see especially Chapter 3) I sketched the main reasons why this is so:

• It offers no guidance for the allocation of allopatric populations.

• Many distinct species actually do breed with each other under natural conditions, but manage to remain distinct.

• The interrelationships of organisms under natural conditions are often (usually?) unknown.

• Many species do not reproduce sexually anyway.

Allopatry

To say that two populations are allopatric means that their geographic distributions do not overlap – they are entirely separate. This means that they do not have the chance to breed with each other, even if they wanted to. There is, for example, no way of testing whether Macaca fuscata (of Japan), M.cyclopis (of Taiwan) and M.mulatta (the Rhesus Macaque, of the East Asian mainland) are actually different species or not; they are classified as distinct species in all major checklists, but there is no objective way of testing this classification under the Biological Species Concept.

Indeed, this is the usual situation: populations that differ, in some respect, from one another and are, by relevant criteria, closely related are usually allopatric. To take demonstrable reproductive isolation, the requisite criterion under the Biological Species Concept, as the sine qua non of species status would be to leave the majority of living organisms unclassifiable except by some arbitrary fiat.

Natural interbreeding

The two common species of North American deer (Odocoileus virginanus, the Whitetail, and O.hemionus, the Blacktail) are found together over a wide geographic area, and are always readily distinguishable; yet molecular studies have found evidence that there has been hybridization. For example, in Pecos Country, west Texas, four out of the nine whitetails examined had mitochondrial DNA characteristic of the blacktails with which they share their range (Carr and Hughes, 1993). Evidently in the not-too-distant past blacktail females joined whitetail breeding herds and, while the whitetail phenotype was strongly selected for, the blacktail mtDNA has remained in the population, fossil documentation of the hybridization event.

In Primates, also, there are examples of hybridization in the wild. A good example of the first case, Cercopithecus ascanius (Redtail monkey) and C.mitis (Blue monkey) in Uganda, has been described in detail by Struhsaker et al. (1988). The two monkeys, which are widely sympatric, meaning that they live in the same areas over a wide range, interbreed at quite noticeable levels, yet remain separate and clearly distinguishable and no one has ever proposed to regard them as anything but distinct species. This case is not unlike that of the North American deer, mentioned above.

These are two examples – one non-Primate, one Primate – of pairs of distinct species which manage to remain distinct over wide areas even though there is gene-flow between them. Much more common (or, better, more readily documented) are cases where pairs of species occupy ranges that are largely separate but meet along their margins (parapatric), and interbreed where they do so. Interbreeding varies from occasional to full hybrid zones, and such cases have, unlike the hybridization-in-sympatry cases, been regarded as evidence that reproductive isolation does not exist, so the two species should be merged into one. But there is no difference, in principle, from the hybridization-in-sympatry cases.

The classic study of a hybrid zone is that of two mice, Mus musculus and Mus domesticus, across the Jutland peninsula, Denmark (see summary in Wilson et al., 1985). The hybrid zone, as measured by morphology and protein alleles, is very narrow; yet the mtDNA of the southern species, M.domesticus, introgresses well across the boundary, and across the seaway (the Skagerrak) into Sweden. This suggests both that hybridization has been occurring, and that M.musculus has been expanding its range, and the hybrid zone has been moving south since before the sea broke through separating Denmark and Sweden in the early Holocene. There has b...