LITMIR.BIZ

1 General Biology and Evolution

       Kanyon McLean1 and Andrew J. Niehaus2

       1 Montgomery Zoo and Mann Wildlife Learning Museum, Montgomery, AL, USA

       2 Department of Veterinary Clinical Sciences, Farm Animal Medicine and Surgery, College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA

      The domesticated camelids of the world have had a significant impact on civilizations throughout recorded history. Populations of camels, referred to as Old World Camelids (OWCs), are indigenous to Africa and Asia, while South American camelids (SACs), also called New World Camelids (NWCs), have evolved in the countries along the western mountains of South America. OWCs include the one‐humped (dromedary) camel, the two‐humped (Bactrian) camel and, more recently, the wild Bactrian camel of Mongolia. NWCs include alpacas, llamas, guanacos, and vicuñas. Alpacas and llamas exist only as domestic species, while guanacos and vicuñas are undomesticated. The vast majority of camels alive today are domesticated dromedary camels in Africa and the Middle East and domestic Bactrian camels in Asia. Wild Bactrian camels are considered critically endangered with an estimated population of about 1000 individuals inhabiting a few select geographic areas in Asia [1, 2].

Taxonomy

Though the classification of OWCs has remained consistent, the classification of NWCs has changed frequently over time, and controversy continues regarding their classification. Carl Linnaeus placed the llama, alpaca, and Old World camels in a single genus, Camelus, in 1758. The scientific name for the dromedary camel is Camelus dromedarius (Figure 1.1) and that for the Bactrian camel is Camelus bactrianus (Figure 1.2). The more recently classified wild Bactrian camel of Mongolia is named C. bactrianus ferus (Figure 1.3) [3–6]. More recent taxonomic classifications place SACs into the genera Vicugna and Lama. The most widely accepted nomenclature for SACs is the following: alpacas are classified as Vicugna pacos, vicuñas are classified as Vicugna vicugna, llamas are classified as Lama glama, and guanacos are classified as Lama glama guanicoe . (Table 1.1) More detailed information on taxonomic history is found in earlier editions of this text.

General Biology and Genetics

      The karyotype of all camelids is 2n = 74. All SACs have produced fertile hybrids. Dromedary and Bactrian camels also produce fertile crosses. Though less common, it is possible to produce camel – SAC hybrids, however, most experimentation with this hybridization has resulted in non‐viable offspring. Llama – camel crosses are known as camas [7], and alpaca – llama hybrids are known as wari or wakayu [8]. In Israel, a cross between an alpaca male and a dromedary female by artificial insemination produced a stillborn full‐term fetus. One report of a guanaco inseminated with camel semen produced a viable calf [9].

      Significant size differences exist among camelid species, though they maintain similar anatomic relationships. Domesticated camelids tend to have a larger body size than their wild ancestors. Though there is overlap, vicuñas tend to have the smallest body size, followed by alpacas, guanacos, and llamas are the largest [10]. Environmental pressures influenced different adaptations of camels from the SACs. The camels completed Pleistocene evolution in a semidesert environment in southern Asia, the Middle East, and North Africa and developed sophisticated adaptations for dealing with heat and dehydration. The SACs became adapted to South American habitats, especially the high‐altitude lands of the Andes.

Figure 1.1 Dromedary camel cow nursing her calf (

      Source: Photo courtesy of Dr. Sharon Deem at the Saint Louis Zoo Institute for Conservation Medicine

      ).

Figure 1.2 Bactrian camel.

Camelids are often compared to true ruminants, though distinct differences in gastrointestinal (GI) anatomy and physiology place them in separate phylogenic suborders. Geologic evidence suggests that camelids and ruminants began to diverge near the beginning of the tertiary period from primordial, monogastric species. Camelids have a complex, three‐compartmented stomach. Similar to ruminants, camelids consume fibrous forage and have developed similar foregut fermentation systems by parallel evolution (Chapters 3 and 12). Camelids regurgitate and rechew ingested forage, as do ruminants, however, camelids have more efficient mechanisms than ruminants for extracting protein and energy from poor quality forages [11]. More detail on the differences between camelids and ruminants are found in earlier editions of this text

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