The Lanceheads

Introduction

Fer-de-lance! That is the name most people, whether herpetologists, herp-hobbyists or the average Animal Planet junkie watching "The Jeff Corwin Experience" would recognize.

Depending on what part of tropical America you interrogate, you may hear the names "Terciopelo", "Barba-Amarilla", "Jararaca", "Jararaca Pintada" just to name a few. No matter what the vernacular, they all refer to a genus of pit-vipers found throughout the Americas that strike fear in the minds of anyone who experiences the rainforest!! These are more commonly known to herpetologists (and more discerning herpetoculturists and private collectors) as the Lanceheaded pit-vipers or “Lanceheads”. I hesitate to say hobbyists here, as when dealing with any venomous snake, to characterize this as a hobby comparable to collecting baseball cards borders between naivete and idiocy. Additionally, these are not the average snakes for a herp enthusiast or even a herpetologist used to working with rattlesnakes. I would like to point out, prior to getting into the real nitty-gritty, that while these CAN BE dangerous customers to work around, like any reptile, they want to avoid humans at all cost and much like our native herpetofauna, they are in some areas of the tropics, so common as to be a plague but you won’t find them "all over the place."

Natural History

As I mentioned above, the genus Bothrops are commonly called "Lanceheads" due to the shape of their head. The natural history of these serpents is poorly understood despite numerous attempts over the past half century to sort it out. The name Bothrops comes from the Greek language for “pit face”. I will point out initially though, that the name “Fer-de-lance” more correctly is the name of one species, Bothrops lanceolatus, found on the island of Martinique.

Studies have shown that they are a recently evolved group having probably evolved from a common Agkistrodon basal species and later diverging morphologically from the rattlesnakes and bushmasters along the way to fill a broader ecologic niche. That may seem counter-intuitive as today, they are found in a variety of habitats, but some species have unique habitat and prey requirements. Bothrops are members of the family Viperidae, and of the sub-family Crotalinae, the pit-vipers, which also includes the Asian pit-vipers as well as the rattlesnakes, copperheads, cottonmouths and bushmasters [1]. There are currently about 40 recognized species in one genus, although classification revisions have included up to 5 genera and ~60 species depending upon the accepted taxonomic status.

Size

The Bothrops species come in a vast array of sizes, colors and patterns. They range in size from the tiny B. itapetiningae at under 0.4 meters up to reports of 3m long for Bothrops asper. For the latter species I have personally seen female specimens (from Manzanillo, Limon Province Costa Rica) up to 7.5 feet in length that weigh over 16lbs (pers observation, Dean Ripa collection). Other species, such as the Urutu (B. alternatus), while capable of reaching 2m, typically average about 1m in length (my pair of alternatus are all around 3.5 feet in length at 4 years of age and my estimation is that, based on their growth rate will not exceed 4 feet throughout their lives).

Color/Pattern

Males and females of most species within the genera tend to be quite dimorphic in size and color, but not so much the overall pattern. Female B. asper, generally exceed the length of the males two-fold and may weigh four to five times that of a male of equal age (and even of the same litter). This difference in size tends to only become apparent after a year or so of age, as juvenile males may start out larger and more brilliantly colored than females. At this stage, to determine the sex of juvenile males, it is necessary to determine the color of the tail: juvenile males possess a bright yellow/green tail tip, whereas the females are dark. While it is known both sexes use caudal luring to attract prey it has not been determined why one possesses a bright tip and one does not. To complicate matters, in other Bothrops species (e.g., B. jararacussu)[5], females also possess a brightly colored tail tip.

Lanceheads typically possess a series of dark hourglass or bow tie shaped X’s on their dorsal surface on a light gray or brown background. The X’s may or may not possess bright highlighted borders depending on the species. Some species are more brilliantly colored than others (See Figures 3, 5 and 7), but generally their patterns, unlike pythons and boas, typically become more brilliant with age. As an example, B. venezluensis females start out a light brown color. With each shed, their ground color lightens, and the bow ties become outlined with bright shades of pastel colors-quite distinct from the more somber B. atrox. B. neuweidi bolivianus also becomes a bright cream yellow and deep red rhomboids that become more contrasting with age. The Urutu, on the other hand, has a series of cross bands that take the shape more of a “C” rotated 90 degrees, i.e., they are like a horseshoe with round bulbs on the end. Some people have described them as inflated telephone receivers. Other species, such as the golden lancehead, tend to possess a more uniform color not unlike our Northern copperhead.

Habitat

The Bothrops species have evolved into one of the most diverse and successful genera of snakes. This is due to the wide array of habitats in which they are found. Many species are found in rainforests as well as dry savannahs and agriculturally transformed lands. The terciopelo (Bothrops asper) is a prime example being found not only in primary rainforest but also thriving in and around crop fields and plantations. This may be due to it being the only species of lancehead found in Central America, not to mention one of the most dangerous and recognizable (more on that later). Terciopelos typically hunt along jungle trails, lying in wait to ambush a rodent as it scampers down a jungle trail, but will not hesitate to take up a hunting site near a coffee or banana plantation. In contrast to the mostly terrestrial terciopelo, the Golden Lancehead (Bothrops insularis) is essentially completely arboreal, endemic to Queimada Granda Island off the southern coast of Brazil. B. Insularis has developed over millennia, the most toxic venom of any pit-viper found in the Americas. This is possibly due to its affinity for birds and lizards that make up the majority of its diet as it hunts almost exclusively in trees. While the larger species, such as B. asper, jararaca, leucurus, atrox, etc. are primarily terrestrial, they even at 2m or more in length are still very agile climbers and can be found resting several meters off the ground. This agility also makes them a handful to deal with as while they are comparable in size to a large (and sometimes larger) Eastern diamondback rattlesnakes (Crotalus adamanteus), BUT the rattlesnake does NOT possess the speed, or agility to completely turn and crawl back up it’s own body with the gracefulness of a mamba (Dendroaspis). Not to make light of the dangerous nature of rattlesnakes, but in relation to the Bothrops, they are simply not in the same ballpark.

With most of the tropical species, whether it be pit-vipers or boids, one tends to think of them as dwellers of the lowland jungle, when in fact many are found at considerable altitude. This first became more apparent to me when I started keeping bushmasters (genus Lachesis) Several species are found at higher elevations and prefer cooler temperatures (low to mid-70’s) as opposed to higher temperatures (mid-80’s). Such is the case of Bothrops Venezuelensis as it is distributed along the coastal range of Venezuela at elevations in excess of 2000m. Bothrops andianus is distributed in a narrow patch of the Peruvian Andes Mountains and has been found above 3300m(9900ft). In contrast, Bothrops alternatus, the Urutu, is distributed throughout Northern Argentina, Uruguay and Paraguay and Southern Brazil. This species seems to prefer lowland swamps and marshy areas such as sugar cane plantations. It basically prefers humid, moist areas.


Diet

As juveniles, most Bothrops will accept either pinkies or anoles (depending on the species) as meals. For example, Bothrops asper, being a larger terrestrial species, will readily accept thawed pinkies right after their first shed. Occasionally a neonate that refuses pinks can easily get started on brown anole lizards (Anolis sagrei) since anoles are a common prey source in the wild. As stated above, many species start out preferring frogs or lizards as prey utilizing the bright tail tips for caudal luring (personal observation in captivity). In contrast to Bothrops asper, the Venezuelan lancehead generally only accepts lizards (anoles or other similar species) as prey. In captivity anoles are the choice as they can easily be shipped from the Southern states. A simple technique to switch them onto pinks is to pinch the head of the anole and allow the juices to drip onto the pinky, a trick told to me by Randal Berry, a reptile keeper at the Little Rock Zoo. The snakes will accept unscented pinkies after one or two “scented” meals. If this technique doesn’t work, I have found that the juveniles will eventually switch to pinkies naturally after at least 3 months of age due to the ability to swallow larger, bulkier prey. It may well be a physiological change related to changes in the components of their venom making it more toxic to mammals than reptiles or amphibians.

Bites and Venom

Bites from Bothrops species in general cause severe necrosis. Lesions at the bite site can result in extensive tissue damage. Complication by secondary infection with bacteria carried by the snake often occurs. This can be treated with penicillin, ampicillin and aminoglycoside drugs [4], though prophylactic use prior to envenomation does not appear indicated for persons working in close proximity to these species (i.e., venom researchers or agricultural workers). Studies in Brazil have shown that over 90% of the roughly 20,000 annual bites result from Bothrops species and of these only 100(0.5%) are fatal. Again this is due to the fact that the venom from the majority of the species, while potent and painful, causes more local damage rather than systemic reaction such as the primarily neurotoxic tropical rattlesnakes (Crotalus durissus) species or Bushmaster (genus Lachesis) species.

Several facilities throughout the tropical Americas produce “geographically polyvalent” antivenoms. These are primarily equine derived from venoms of the locally significant snakebite culprits. For example, the Instituto Clodomiro Picado in San Jose, Costa Rica produces a polyvalent Anti-Botropico-Lacquetico-Crotalico* for treatment of the significant sources of snake bite throughout Central America. While this antivenom is effective against essentially all the pitviper species in Central America, it uses venom extracted from the “Big 3” species: Crotalus d. durissus (Neotropical rattlesnake), Terciopelo (Bothrops asper) and Central American Bushmaster (Lachesis stenophrys). This antivenom is not only much cheaper than US derived antivenoms ($25/vial for ICP versus $1000/vial for US) it is generally more effective on bites from these particular species as the US derived products are derived mainly from rattlesnake species. In addition, it has saved lives on several occasions [8 and pers comm, Dean Ripa]. Note: This is the antivenom I personally keep on hand in case of envenomation. On a recent trip to Costa Rica, I was bitten on the thumb by a neonate terciopelo(while investigating a paca burrow, where a 2m female Lachesis melanocephala had been killed several months earlier). The bite from the neonate (a snake of this size would’ve been born the previous April) produced only mild swelling, throbbing in the thumb and discoloration over an area the size of a pin-hole.

When describing the toxicity of venoms, a statistic termed the “LD50” value is generally used. This terms relates to the specific venom quantity in units of mg Venom per kilogram of prey body weight necessary to kill fifty-percent (50%) of a sample population of prey animals. To put the LD50 into perspective, the copperhead has an LD50 around 12 mg/kg; the timber rattlesnake around 2 mg/kg; the Asian cobra an LD50 around 0.40, and the Taipan around 0.01 mg/kg – note these are all approximate numbers). It is dependent on the route of introduction of the venom (e.g., intravenously, intramuscularly or subcutaneously). In it’s application to the Lanceheads, intravenously or intramuscularly would be most accurate as the fangs of Lanceheads are very long. At present the largest fang I have measured from an adult female Bothrops asper is 1 1/4”. Keep in mind, though that many factors influence the effects of a bite in humans, and LD50 is generally measured using mice. As an example, bushmasters have a very high LD50 (around 10 mg/kg), yet their venom causes severe systemic effects in humans, whereas few Bothrops bites are fatal, yet their bites are quite lethal to rodents. In fact, of all the species I have worked with, the only snake I have witnessed able to essentially kill a large rat instantaneously has been Bothrops asper!

Captive Experience and Care

Over the course of the past 4 years, I have had the opportunity to work with 6 different species of Bothrops, and currently maintain 4 different species comprising over 70+ individual specimens. These species include: 70 Bothrops asper (Terciopelo) from Central America; 4.4 Bothrops venezuelensis (Venezuelen Lancehead) indigenous to the coastal range of northern Venezuela; 1.1 Bothrops alternatus (Urutu) found in Paraguay, Uruaguay and northern Argentina; and 1.1 Bothrops neuwiedi bolivianus (Bolivian Neuweid’s Lancehead) of which there are 4 subspecies found in Southern Amazonia. In this section, I will describe the basic care and requirements in general for Lanceheads in captivity, as well as specific requirements and PRE-CAUTIONS between different species. As with any type of snake, there are differences among species in both care AND temperaments, and thus some species of Bothrops are “more difficult” to deal with than others.

Caging

Bothrops are rather easy to cage… make it big! As with any venomous species of reptile, you must make sure the caging is secure. That being said, the Neodesha cages were, in my opinion, the best design of the commercially available for housing venomous snakes. They employed a sliding glass or Plexiglas front, which afforded the keeper a complete view of the entire cage preventing any “hidden surprises”. The newer Vision cages, while conveniently stackable and durable, have two drawbacks in terms of housing venomous species: 1) They have a lip above and below the door tracks which allow snakes to hide (and they do!) and 2) They have poor venting which makes them dark requiring external illumination to see clearly into the cage.

I currently use both of the above. My two (2) large female B. aspers are in a 72” standard Neodesha cage where I can see them clearly. In addition, I keep two pieces of driftwood in the cage for a sense of security (As if they needed it!) for the snakes and a hide box. I minimize the amount of cage furniture, as when having to handle these large animals, the less clutter the better! Keep in mind that both of these females are in excess of 6 feet. Same theory applies for my smaller four-foot long (4’) male B. asper. While smaller, you would think he’s easier to handle----Not true! The smaller males are faster and more agile and in my experience—NASTIER! Thus I also house him in a Neodesha, but this time it’s a 48” (standard) cage with a sliding glass front. The only cage furniture is a hollow piece of cork bark for him to hide in. I also have a 2 ½’ male B. asper that I keep in a 2’ Vision arboreal cage, as the snake is just the right size, and prefers to coil in the rear corner behind some fake vines, rather than hide under the lip of the sliding doors.
I also use Vision #211’s for housing my trio (1.2) of adult Urutus (B. alternatus). These are all approximately 3’ long and fit into the 28” #222 just nicely, though whether it’s sufficiently large enough for breeding remains to be seen. All of the Vision cages possess Jewelry case locks on the doors for security.

Feeding

Bothrops, like most large pit-vipers typically accept large pre-killed rodents as prey. During feeding, as with bushmasters, I tend to keep the lights in the herp room off, as they sometimes will become shy and bury their heads with the lights on. This poses another trick, as in order to feed, I will where a headlamp (PETZL ZOOM) to see what I am doing. One thing I’ve learned from feeding large Terciopelos and bushmasters—especially Lachesis muta - is that hungry snakes are attracted to bright light and they will sometimes ignore prey and go after the light! To minimize the risk of a feeding mishap, I open the cage door just enough to offer the prey, then close the sliding glass so that the opening is just a crack the width of the hemostats.

Feeding juveniles is quite another story. Since they are primarily lizard, frog and invertebrate feeders as babies, I have resorted to buying large quantities of small brown anoles. It has been my experience that juvenile Bothrops asper will accept pre-killed pinkies right away, with only a few stubborn feeders reluctant to feed. Even these few stubborn feeders will normally accept live anoles for the first few feedings and then switch to pinky mice. Of nearly 70 juvenile Terciopelos I have imported, all but 6 have eaten within a few days of arrival, and of the nearly 65 that have eaten, 64 have taken pinkies with 1 requiring an anole to get her going. Of the 42 neonates produced here through captive breeding, 30 of 42 either ate voluntarily or were “teased” into feeding. This still doesn’t guarantee a healthy captive, as the babies that are “coaxed or teased” into feeding through a defensive strike, not all of these necessarily live beyond 3-4 months. They will feed regularly and suddenly succumb to natural causes. Of the 30 that have eaten, 15 have lived to 5 months of age. This is due to natural selection and probably why Bothrops produce such large litters. Currently, there are 2 neonates that at 4.5 months of age have never eaten and even neonates will go for 4-8 weeks without eating. I do not believe in force-feeding them, simply because it is not nature’s way to have every one survive (nor am I desperate to make money off of them).

Bothrops venezuelensis, on the other hand, rarely take pinks (pers observation and communication with breeders in Central America) and usually always must be started on anoles or small frogs. I have found that after about 3-4 months of age, they suddenly “Snap out of it” and start taking pinky mice. I have had 3 (1 male, 2 females) venezuelensis all switch within 3 days to pinks, where 2 others (a ma1e and a female) still preferred anoles until about 6 months of age.

Temperature & humidity

This is where I have found the most difficulty. Unlike the bushmasters, which require a cool humid environment for complete health, the lanceheads can thrive in variety of conditions. Some will thrive in cooler montane climates with lower humidity, others will thrive in hot, humid conditions, and others can thrive in yet hot, dry conditions. Lanceheads tend to prefer temperatures in the low 80’s. I have observed a marked increase in desire to feed in simply boosting ambient room temperatures from 78-79F up a few degrees to the 80-82F range. Although this appears to be better for faster growth, I tend to prefer to keep them in the lower range. This is due to the fact that I feed them on a 2-3 week frequency and the “cooler” temps tend to prevent humidity drops. Bothrops require high humidity when it comes to shedding. If the relative humidity is low, they, as are many tropical species, are prone to bad sheds, many times coming off in pieces.

In particular, I have one rather large female Bothrops asper (approximately 7’ in length) which has a problem initially splitting the rostral scale, which initiates the shed process. As a result if the humidity is not high enough, she will simply not try to shed and become ‘Stuck’ in the old skin. Most of the skin can be removed by soaking her in 2-3” of water for a few hours and letting her crawl back around the cage rubbing against driftwood and manzanita branches. The problem lies in her removal of the spectacles (eye-caps). The skin on the top of the head and supraocular scales tends to not come off, nor will the pre-ocular scales. Therefore, the eyecaps remain stuck as well. The only method for removal is by manually picking them off. This results in having to restrain the snake by pinning and using either a small pair of tweezers to lightly pull the dead skin off. I normally will not perform this if it’s only one shed, but if she goes through a second shed and this happens, then I must resort to manually removing them.

One method I have had success with is anesthetizing the snake with Isoflorane prior to eyecap removal. While large Bothrops aren’t difficult to pin, they do not cooperate. Several unshed eyecaps will eventually build up pressure in the conjunctuval cavity and lead to a pressure buildup. This tends to close the oro-pharyngeal duct and bacteria within cause an infection known as Panopthalmitis. If this is not treated, the eye becomes cloudy and eventually the infection will become necrotic and the snake will go blind, have a ruptured cornea, or require the eye to be removed. I have also seen this happen with juvenile terciopelos being kept on too wet a substrate. A similar bacteria infection occurs (not sure how), but juvenile snakes develop an eye infection and eventually stop eating and die.

Breeding

I was successful in my first attempt last year to reproduce Bothrops asper in captivity. My two female aspers, from Manzanillo, Limon province, Costa Rica were paired with a smaller 4’ male from the vicinity of Siquirres, in Limon Province on the Caribbean side of Costa Rica. The Caribbean animals tend to breed between January – May and rear their litters in September to December. Pacific animals (of which I have a few from the Central Valley Northwest of San Jose) tend to have their litters from May-July. This is basically due to differences in the rainy seasons on the Pacific and Atlantic slopes of Central America.

I introduced the male to the females on Friday, January 24, 2003 at 8AM. At 11PM, the male was copulating with female #1(the smaller of the two females). At 6AM on January 25th, the two snakes were still joined. The male made several attempts to breed with female #2 over the next several weeks but was not successful. Female #1 continued to feed normally until early April, at which time she ceased feeding. On August 27th, I woke and entered the reptile room and found 42 live babies and 5 slugs in the cage. Female 1 was in a large Neodesha hide box, while the larger (and more high strung) female #2 was coiled in the far corner of the cage. It took approximately 30 minutes to delicately remove all of the neonates from the cage, while not spooking female #2, who was very alert and was anticipating a rodent. Fortunately, female #2 didn’t spook until all the neonates from the far end of the enclosure were removed, which was convenient as it revealed another dozen hiding behind her.

Handling/Medication

Handling Bothrops species requires constant attention, not that rattlesnakes do not, but Lanceheads are much faster and more apt to change directions. It is not uncommon for a 7-foot female B. asper to dart off in one direction, and after being pursued with a hook, stop on dime, and do a complete 180! Generally two hooks are the rule for handling these large serpents. Generally I prefer a large python size hook to give me at least five feet (5’) of reach. These snakes are quite capable of striking over half of their body length. In general, they will remain perfectly calm in a coil, until they are TOUCHED! Then they explode like a coil and go helter-skelter every which way.

Typically, tubing is not that difficult. I use 24” Plexiglas tubing. Because Bothrops will move quickly, they tend to dart right up a tube and the body can be grabbed at the tube opening and the snake is safely restrained. This is unlock snakes, such as timber rattlesnakes, which are much calmer in captivity, and will slowly, methodically investigate the tube opening—often preferring to climb around the tube, instead of inside it.

If the situation presents itself that the snake needs to be pinned, for example to remove eyecaps, this is a so-so process. On one hand, they are easy to pin using the 3-finger technique with the thumb and middle finger to secure the mandibles, and the index finger as a brace on the top of the head. Lanceheads have such large venom glands and triangular heads; the grip is not the problem. The real problem comes with the snake squirming. These snakes do not cooperate, as say, rattlesnakes do. Most Bothrops struggle and large ones are quite powerful enough to wiggle loose. EXTREME CAUTION MUST BE TAKEN when pinning any Bothrops species.

Bibliography:
[1] Campbell, J. A. and William W. Lamar, Venomous Reptiles of Latin America, Cornell University Press, Ithaca, 1989.
[2] Campbell, J. A., Amphibians and Reptiles of Guatemala, Yucatan and Belize,
[3] Greene, Harry W., Snakes: The Evolution of Mystery in Nature, University of California Press; Los Angeles, 1997.
[4] Jorge, M.T. and L.A. Ribeiro, “Infections at the Bite Site after Envenoming by Snakes of the Bothrops Genus”, The Journal of Venomous Animals and Toxins, 3(2), Review Article.
[5] Pinheiro, H.P., A.S. Pinheiro, A.S. Abe, and S. F. Reis, “Phylogenetic Relationships and DNA Sequence Evolution Among Species of Pitvipers“, www.ime.unicamp.br/~hildete/versao1.pdf .
[6] Werman, S., “Phylogenetic Relationships of Central and South American Pitvipers of the Genus Bothrops (Sensu Lato): Cladistic Analyses of Biochemical and Anatomical Characters”, in Biology of the Pitvipers, J.A. Campbell and E.D. Brodie Jr., Selva Publishing, Tyler, TX, 1992.
[7] Sazima, I, “Natural History of the Jararaca Pitviper, Bothrops jararaca, in Southeastern Brazil”, Biology of the Pitvipers, J.A. Campbell and E.D. Brodie Jr., Selva Publishing, Tyler, TX, 1992.
[8] Oscar, Francisco, Thesis Summary presented to the College of Medicine, University of Sao Paolo, SP, Brazil: “Association of Venom Antigenaemia and Severity of Bothrops Accidents”, Magazine of the Brazilian Society of Tropical Medicince; 31(5): 495-496,1998.
[9] Ripa, Dean, The Bushmasters (Genus Lachesis, Daudin 1803): Morhphology in Evolution and Behavior, Ripa Ecologica; Wilmington, NC, 2002.
[10] Waster, W. M. Da Graca Salamao, J. A. Quijada-Mascarenas, R.S. Thorpe and BBBSP, “Origins and Evolution of the South American Pitviper Fauna: Evidence from Mitochondrial DNA Sequence Analysis”
[11] Wuster W., R.S. Thorpe, G. Puorto, and BBBSP, “Systematics of the Bothrops atrox Complex (Reptilia: Serpentes: Viperidae) in Brazil: A Multivariate Analysis”, Herpetologica, 52(2): 263-271; 1996.
[12] Wuster, W., M. Da Graca Salamao, G. J. Duckett, R.S. Thorpe and BBBSP, “Mitochondrial DNA Phylogeny of the Bothrops atrox Species Complex (Squamata: Serpentes: Viperidae)”,
[13] Da Graca Salamao, M., W. Wuster, R.S. Thorpe and BBBSP, “MtDNA Phylogeny of Neotropical Pitvipers of the Genus Bothrops (Squamata: Serpentes: Viperidae)”,
[14] Theakston, R.D.G., G.D. Laing, C.M. Fielding, A.F. Lascano, J.M. Touzet, F. Vallejo, R.H. Guderian, S.J. Nelson, W. Wuster, A.M. Richards, J. Rumbea Guzman, and D.A. Warrell, “Treatment of snake bites by Bothrops species and Lachesis muta in Ecuador: laboratory screening of candidate antivenoms”, Transactions of the Royal Society of Tropical Medicine and Hygiene, 89:550-554; 1995.
[15] Werman, S.D., B.I. Crother, and M.E. White, “Phylogeny of some Middle American Pitvipers based on a Cladistic Analysis of Mitochondrial 12S and 16S DNA Sequence Information”, Contemporary Herpetology:1999(3), 8 June 1999.
[16] Puroto, G., M. Da Graca Salamao, R.D.G. Theakston, R.S. Thorpe, D.A. Warrell, and W. Wuster “Combining Mitochondrial DNA Sequences and Morphological Data to Infer Species Boundaries: Phylogeography of Lanceheaded Pitvipers in the Brazilian Atlantic Forest, and the Status of Bothrops pradoi (Squamata: Serpentes: Viperidae)”, Journal of Evolutionary Biology, 14:527-538, 2001.


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