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Dov Block

Primate Coevolution with Lice and the Impact of Human Lice (Pediculus humanus capitis, Pediculus humanus corporis, and Phthirus pubis) on Human Evolution

Lice are permanent parasitic insects dependent on their bird and mammal hosts for survival. While lice (Insecta: Phthiraptera) themselves appear to have ancient and intriguing origins, their coevolution with hosts can oftenbe used to shed light on the evolutionary history of birds and mammals^[1] Three species of lice parasitize humans: Pediculus humanus capitis (Head lice), Pediculus humanus corporis (Body lice), and Phthirus pubis (pubic lice) ^[2]. Following an overview of these three species of lice, we discuss their significance in studying human evolution, migration patterns, and cultural developments.

As members of the order Phthiraptera, lice can be further subdivided into four suborders: Amblycera, Ischnocera, Rhynchophthirina, and Anoplura. The first three suborders are typically grouped together as chewing lice, while members of the suborder Anoplura are known as sucking lice. Chewing lice parasitize a wide array of birds and mammals, using their chewing mouthparts to feed upon skin and sometimes blood. Sucking lice, On the other hand, exclusively parasitize eutherian mammals and feed directly from their hosts’ blood vessels. All three species of lice that parasitize humans are members od the Anoplura suborder^[3].

Sucking lice are physiologically adapted to life on their mammal hosts. It is hypothesized that sucking lice (Anoplura) evolved from free-living ancestors that contained simple feeding mouths. Nesting patterns became dependent on hosts and the ancestor transitioned from free-living to obligate parasitism (Light et al. 2010). Today, sucking lice lack wings, possess claws to cling to their host, and have modified mouths that allow direct feeding from host blood vessels ^[4].

The Anoplura suborder appears to have diversified around 77 million years ago. This date is in agreement with the suborder’s host’s evolution as mammalian suborders are thought to have diverged by about 75 million years ago. Anoplura divides further into 15 taxanomic families^[5].

Although mammalian coevolution with sucking lice can influence the study of all mammalian evolution, an attempt to synthesize all information regarding Anoplura and coevolution with mammals is beyond our scope. Now, we turn to the three species of sucking lice that parasitize human beings: head lice (Pediculus humanus capitis), body lice (Pediculus humanus corporis), and pubic lice (Phthirus pubis).

Pediculus humanus capitis (P.h. capitis) is a subspecies of Pediculus humanus commonly referred to as head lice. The most recent evolutionary ancestor of head lice is shared with sucking lice that parasitize chimpanzees ^[6]. Head lice exhibit strong sexual dimorphism; the females are significantly larger than their male counterparts. P.h. capitis have evolved several traits for life on their human hosts. Females are capable of secreting natural glue that fixes their eggs to human hair. Season and climate can impact position and number of eggs laid. In colder climates, only one egg per hair is laid close to the scalp^[7].

Pediculus humanus corporis (P.h. corporis) is commonly known as body louse. P.h. corporis diverged from P.h. capitis about 72,000 +/- 42,000 years ago. Despite this divergence event, head and body lice remain in the same clade indicating an ancestral polymorphism, or mutation that arose prior to divergence ^[8].

Phthirus pubis (P. pubis) is commonly known as pubic lice and is the final species of louse that parasitizes humans. While chimpanzees and humans share the genus Pediculus, humans share the genus Phtirus with gorillas (Reed et al. 2007). P. pubis is typically spread through sexual contact ^[9].

It is worth noting that the genus name Phtirus is sometimes spelled Pthirus in the scientific literature. Although Phthirus is the original nomenclature, a common misprint has led to the acceptance of Pthirus as legitimate spelling for the genus name ^[10]. Readers must be aware of these two spellings should they review the scientific literature on pubic lice themselves.

Although human lice are fascinating biological specimens in their own right, they also offer many hints and corroborating evidence for scholars concerned with human evolution. Many human evolutionary biologists and anthropologists seek to answer the question: When and how did humans become so human-like? It is difficult to characterize one trait that makes humans distinctly human, however, human lice can offer evidence about hominid divergence from other primate ancestors, pre-historic human migration patterns, and human cultural developments.

As noted above, human head and body lice (genus Pediculus) share a common ancestor with chimpanzee lice, while pubic lice (genus Phthirus) share a common ancestor with gorilla lice. This distribution of genera is noteworthy because chimpanzees cannot be parasitizes by Phthirus lice and gorillas cannot be parasitized by Pediculus lice. Why have humans maintained the ability to be parasitized by two genera of lice while chimpanzees and gorillas each only have one?

Using phylogenetic and cophylogenetic analysis, Reed et al. hypothesized that the lice genera Pediculus and Phthirus are sister taxa and monophyletic ^[11]. In other words, both genera descended from the same common ancestor. The age of divergence between Pediculus and its common ancestor is estimated to be 6-7 million years ago and matches the age predicted by chimpanzee-hominid divergence ^[12], Shao et al. 2012). Because parasites rely on their hosts, host-parasite cospeciation events are likely to occur. Gorilla lice and pubic lice last shared an ancestor approximately 3-4 million years ago. Unlike the genus Pediculus, the divergence in Phthirus does not match the age of host divergence that likely occurred 7 million years ago ^[13].

Reed et al. ^[14] present two explanations for the discrepancies observed in human lice. The first posits that both genera of lice had species that affected chimpanzees, gorillas, and hominids. The Phthirus louse species that used to parasitize chimpanzees and the Pediculus louse species that used to parasitize gorillas have both gone extinct while the hominid species line of both genera have not. The second explanation proposes a Phthirus species host-switch around 3-4 million years ago. While it is difficult to determine if a parasite-host switch occurred in evolutionary history, this explanation is the most parsimonious (contains the fewest number of evolutionary changes).

Aside from supporting evidence of hominid divergence from other primate ancestors, human lice can also shed light on human migratory patterns in pre-history. The dominating theory of anthropologists regarding human migration is known as the Out of Africa Hypothesis. Out of Africa posits that modern humans dispersed from Africa and populated the rest of the world around 80,000 years ago^[15]. Analysis of mitochondrial DNA in human body and hair lice revealed that greater genetic diversity existed in African than in non-African lice ^{[16] [17]}. Genetic diversity accumulates over time and mutations occur at a relatively constant rate. Because there is more genetic diversity in African lice, it can be assumed that lice (and their human) existed in Africa before anywhere else.

Finally, human lice can be informative in dating human cultural developments like the advent of clothing. Human head louse and body louse occupy distinct ecological zones. Head lice live and feed on the scalp, while body lice live on clothing and feed on the body. Kittler et al. (2003) performed dating analysis on mitochondrial DNA in human head and body lice and determined that the two species likely split 72,000 +/- 42,000 years ago. Because clothing lice require clothing to survive, it is thought that this date roughly estimates the introduction of clothing in human evolutionary history ^[18].

Despite the reputation of human lice as nuisances to society, these parasites can reveal incredible amounts about human evolutionary history. As a result of millions of years of coevolution, lice and humans have adapted to life with each other and within their environments. Human lice dependency on human hosts ensures that major evolutionary events in human history are recorded by these important parasites. Parasite coevolution can be a useful tool in deciphering the evolutionary history of their hosts.

References

Arrriaza B., V. Standen, H. Nunez, and K. Reinhard. 2013. Study of archaeological nits/eggs of Pediculus humanus capitis by scanning electron microscopy. Micron 45:145-149.

Burns D.A., and T.A. Sims. 1988. A closer look at Pthirus pubis. British Journal of Dermatology 118L497-503.

Kittler R., M. Kayser, and M. Stoneking. 2003. Molecular evolution of Pediculus humanus and the origin of clothing. Current Biology 13:1414-1417.

Light J.E., J.M. Allen, L.M. Long, T.E. Carter, L. Barrow , G. Suren, D. Raoult, and D.L Reed. 2008. Geographic distribution and origins of human head lice (Pediculus humanus capitis) based on mitochondrial data. Journal of Parasitology 94(6)1275-1281.

Light J.E., V.S. Smith, J.M. Allen, L.A. Durden, and D.L. Reed. 2010. Evolutionary history of mammalian sucking lice (Phthiraptera: Anoplura). BMC Evolutionary Biology 10(1):292-307.

Foster P. 2004. Ice ages and mitochondrial DNA chronology of human dispersals: A review. Philosphical Transactions of the Royal Society of London, Biological Sciences 359:255-264.

Reed D.L., J.E. Light, J.M. Allen, and J.J. Kirchman. 2007. Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice. BMC Biology 5(1):7-18.

Shao R., X.Q. Zhu, S.C. Barker and K. Herd. 2012. Evolution of Extensively Fragmented Mitochondrial Genomes in the Lice of Humans. Genome Biol. Evol. 4(11):1088-1101

Snodgrass R.E. 1944. The feeding apparatus of biting and sucking insects affecting man and animals. Smithsonian Miscellaneous Collections 104:1-113.

--Block.101 (talk) 08:37, 17 November 2014 (UTC)

Assignment II

Page URL: https://en.wikipedia.org/wiki/Louse

Suggestions:

These two sections seem to be lacking a lot of vital information and could use some restructuring. The three different species of lice that have coevolved with their human hosts have been used to uncover a lot of information about human evolution in recent years.

I propose the following changes:

Change the Subsection title from "Human lice and DNA discoveries" to something like: "Coevolution with Humans" or "Evolution of Lice and Humans." This will open up the section for contributions about the coevolution of human lice and humans as oppose to limiting the discussion to "DNA discoveries" alone. More details can be filled in at a later time regarding specific content.

Include phylogenetic tree of species of human lice (with closest lice relatives).

Include description of human lice species origins with estimate origin dates. The Reed et al. article cited in this section posits three potential phylogenetic trees (A, B, and C) and concludes that C is the most likely tree given molecular dating of species divergence. Of the three species of human lice, two are related to chimpanzees (genera Pediculus) and one is related to gorillas (genera Pthirus). Pediculus and Pthirus genera likely split around 7 million years ago. The Pediculus humanus capitis (human head lice) and Pediculus humanus corporis (human body lice) likely diverged from a chimps 6 million years ago. Interestingly, pubic lice (Pthirus Pubis) only dates back 3-4 million years. Reed et al. interpret this to mean that a host species switch occurred when the louse species "jumped" to hominid hosts.^[19]

Correct the following sentence which is incorrect as it stands:

Additionally, the DNA differences between head lice and body lice provide corroborating evidence that humans started losing body hair about 2 million years ago.[18)

The Travis news article listed as the source as well as the original publication (Kittler et al.) clearly state that divergence between head lice (Pediculus humanus capitis) and body lice (Pediculus humanus corporis) occured 72,000 years ago +/- 42,000 years. The authors argue this is a potential explanation for the origin of clothing not the loss of body hair 2 million years ago.^[20]

Proposed Edit to Page: Mitochondrial analysis of Head lice (Pediculus humanus capitis) and body lice (Pediculus humanus corporis) diverged approximately 72,000 years ago +/- 42,000 years. This divergence date may coincide with the origins of clothing use in humans as clothing would have created two distinct ecological zones for speciation to occur on the human body.Kittler, Ralf; Kayser, Manfred; Stoneking, Mark (19 Aug 2003). "Molecular Evolution of Pediculus humanus and the Origin of Clothing". Current Biology. 13: 1414-1417.</ref>

--Block.101 (talk) 22:54, 30 September 2014 (UTC) --Block.101 (talk) 22:41, 30 September 2014 (UTC) Block.101 9/30/14

Dov Block TA – Yue Zhang, Thursday – 3 pm EEOB 3310 – Evolution 15 September 2014

Wikipedia Project Topic and Annotated Bibliography

Research Question: How does the evolutionary history of human lice (Perdiculus humanus capitis, Perdiculus humanus corporis, and Pthirus pubis) inform and expand our understanding of human evolution?

References:

Kittler R, Kayser M, Stoneking M. 2003. Molecular evolution of Pediculus humanus and the origin of clothing. Current Biology 13:1414-1417.

Kittler et al. studied the divergence of human head louse (P. h. capitis) and human body louse (P. h. corporis). Using analysis of mitochondrial DNA, Kittler et al. conclude that there is greater diversity in African over non-African lice suggesting that the origin of human lice occurred in Africa. Additionally, Kittler et al. postulate that the divergence of the two species of lice occurred as a result of ecological separation (i.e. the use of clothing created distinct geographical regions on the human body). Given the estimated time of divergence of the two species of human lice, Kittler et al. extrapolate a rough estimate for the advent of clothing in human history. This article helps explain the divergence of two species of head lice and the possible human evolutionary explanation for such a divergence.

Light JE, Allen JM, Long LM, Carter TE, Barrow L, Suren G, Raoult D, Reed DL. 2008. Geographic distribution and origins of human head lice (Pediculus humanus capitis) based on mitochondrial data. Journal of Parasitology 94(6)1275-1281.

In this study, Light et al. three divergent clades (A, B, and C) of human head lice (P. h. capitis) and their geographic distributions. Analysis of mitochondrial DNA and geographic distribution reveal that clade B likely originated in North America (not Asia, as previously thought). The authors postulate a migration route for the B clade of human head lice out of North America and suggest that the beginning of European colonization was responsible for the spread of clade B human head lice out of North America.

Light JE, Smith VS, Allen JM, Durden LA, Reed DL. 2010. Evolutionary history of mammalian sucking lice (Phthiraptera: Anoplura). BMC Evolutionary Biology 10(1):292-307.

Light et al. examined the evolutionary history of 65 sucking lice taxa. Using molecular data, the authors constructed the phylogenetic relationships of the lice taxa and compare to morphological data available. Finally, the authors compare the phylogenetic relationships of lice to host relationships. Results from phylogenetic analyses suggest that sucking lice and mammals diverged at similar times in history. This article will be helpful for my research question by providing essential background information on the evolution of many species of lice and their coevolution with mammals.

Reed DL, Light JE, Allen JM, Kirchman JJ. 2007. Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice. BMC Biology 5(1):7-18.

Reed et al. studied the 25 million year history of lice coevolution with their mammalian hosts. The results indicate that the current distribution of anthropoid primate lice is a result of many evolutionary events (e.g. cospeciation, parasite duplication, host switching, etc.) and the coevolutionary history of primates and their lice has not been parsimonious. This article provides details on the coevolutionary history of lice and their primate hosts and provides plausible explanations for the distribution of primate lice seen today.

Rick FM, Rocha GC, Dittmar K, Coimbra CEA, Reinhard K, Bouchet F, Ferreira LF, Araujo A. 2002. Crab Louse Infestation in Pre-Columbian America Journal of Parasitology 88(6)1266-1267.

Reed et al. examined evidence of Pthirus pubis (pubic lice) on South American mummified bodies. Using molecular dating, Reed et al. conclude that pubic lice were present before Columbus made contact with the New World. This finding suggests P. pubis arose around the time of human migration to the New World (well before the Columbian era).