Once the unfortunate animal is firmly attached and appropriately subdued, shrikes then tear their prey apart. These researchers were interested in one particular species that the shrikes prey upon, the flat-tailed horned lizard, which is found in the Sonoran desert. This lizard has a distinctive crown of large horns on its head. Biologists had previously assumed these horns served a defensive purpose against predators.
The rationale was that it would be too energetically costly to lizards to grow and carry the heavy horns for no reason, so the horns were probably useful somehow; ergo, the horns likely helped the lizards avoid being eaten. It is often impractical or even impossible to prove that a particular trait has evolved for a specific purpose, no matter how appealing the idea is. As shrikes leave distinctive records of their kills—dangling lizard corpses are unique to shrike predation, since no other animal hunts in the same way—the biologists could simply find shrike-killed lizards and measure their horns.
The scientists then compared those measurements to ones taken from horned lizards that were still alive to see whether shrike-killed lizards had differently sized horns. While these results may seem obvious of course longer horns will make it harder for a predator to get close enough to attack an animal!
How the horned lizard got its horns. Science 2 : View all posts by Catherine Chen. I am blown away! Desert horned lizard, Phrynosoma platyrhinos. Phrynosoma platyrhinos : Desert horned lizard Diagnostic Characters: One row of lateral abdominal fringe scales Two moderately elongated occipital horns, not in contact at base Enlarged chin shields Nostrils inside the canthus rostralis Blunt snout Geographic Range: Lowland deserts in southeastern Oregon, southwestern Idaho through Nevada, western Utah, California, Arizona, south barely into northern Baja California and northern Sonora, Mexico.
Phrynosoma solare : Regal horned lizard Diagnostic Characters: One row of lateral abdominal fringe scales Four large occipital horns, in contact at base and continuous with six temporal horns forming a large crown of ten horns. Nostrils inside the canthus rostralis Ventral scales keeled Geographic Range: The species is restricted to Sonoran desert in south-central Arizona, east to extreme southwestern New Mexico, south through most of Sonora including Isla Tiburon and into northern Sinaloa, Mexico.
Phrynosoma taurus : Diagnostic Characters: One row of lateral abdominal fringe scales Occipital spines reduced and separated by a notch Temporal area greatly enlarged posterolaterally, ending with two heavy, moderately long spines All ventral scales keeled Nostrils inside the canthus rostralis Geographic Range: Little is known about this species. It is found in montane chaparral-oak forest and desert areas of the Sierra Madre del Sur, south and southeast of Mexico City, in Guerrero and Puebla, Mexico.
Geographic distributions of egg laying species. Geographic distributions of live-bearing species. Phylogeny and Natural History Phylogeny allows us to trace evolutionary history and relationships of organisms. Much like humans draw their genealogies, or family trees, to discover where their blue eyes or baldness came from, or perhaps whether they are genetically predisposed for cancer -- systematists construct such trees to show how different species have evolved.
Ecologists use phylogenetic relationships to learn how characteristics of species evolved, or how different species acquired traits and evolved to occupy their current niche. Principles of parsimony are used to identify the simplest explanations for how a trait evolved. There are two major lineages of horned lizards, one of which lay eggs oviparous while members of the other group give birth to living young viviparous.
Although the ancestral state is oviparity, one lineage of horned lizards, all high altitude species, has evolved live bearing braconnieri, boucardi, ditmarsi, douglasi, hernandezi, orbiculare , and probably taurus. Viviparity appears to have arisen only once in the genus, rather than independently 5 times.
Interestingly, all species are montane which provides support for the idea that drier and colder mountain climates demand that montane lizards retain their progeny internally until birth rather than laying eggs.
Two hypothetical phylogenies for horned lizards. Horned lizards are a rather fecund group, and lay or give birth to many offspring compared to other lizards. The median clutch size for P. Reproductive effort measures the resources given to producing offspring and is often measured by comparing the weight or volume of the offspring to female volume or body weight relative clutch mass, or RCM.
Females can have a few large versus many small progeny. Some species also reproduce twice in a season. This large investment in offspring throughout the active season weighs down females and makes them vulnerable to predators. Because babies are tiny and easy prey for a multitude of predators, horned lizards would go extinct without such high fecundities. An interesting more recent analysis of horn lengths among horned lizards is shown in the above figure from Leache and Maguire Preferred phylogeny for Phrynosoma based on combined mtDNA and nuclear data.
The most parsimonious reconstruction of antipredator blood-squirting ABS is mapped on the phylogeny black bars. Blood squirting behavior was ancestral and has been lost 4 times.
Silhouettes of Phrynosoma heads are shown to illustrate the variation in cranial horn anatomy, color coded to correspond to relative horn length ancestral state reconstructions mapped on each node. The asterisk adjacent to P. Share Tweet Email. Go Further. Animals Climate change is shrinking many Amazonian birds.
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