Vertebrate Adaptations
Important Vocabulary
Adaptation - A modification in structure or routine, often hereditary, by which a species enhances its survival in relationship to its environment.
Sexual Dimorphism - the apparent differences between sexes of the same species
Convergent Evolution - The adaptive evolution of superficially similar structures, such as the wings of birds and bats, in unrelated species subjected to similar environments.
Homologous Evolution - Similar in structure and evolutionary origin, though not necessarily in function, as the flippers of a seal and the hands of a human.
Adaptations develop over time and generations as a response to the ever changing environment. One of the best models of vertebrate adaptation is the evolution of the "abstract thinker" (Homo sapiens), from the filter feeder (Hemichordates). There are a number of specific vertebrate adaptations of interest, but this lab focuses on three of the most well understood: Locomotion, Feeding and Reproduction.
Adaptations for Locomotion:
One locomotion adaptation is flight. Only three groups of vertebrates have developed adaptations for powered flight: pterosaurs, birds, and bats.
Pterosaurs
Birds
Bat (© Photo
courtesy J. Scott Altenbach)
The Pterosaurs or "winged reptiles" ruled the skies during the Jurassic and Cretaceous periods - about 150 million years. With wing spans ranging from 0.5m - 12m, these ancestral vertebrates were the first to develop the ability to fly. As they are now extinct, scientists study Pterosaurs fossils along-side the bird and the bat as they provide key information about the evolution of flight.
Despite the obvious similarities between pterosaurs and birds, it is important to realize that they are very different animals, that followed different evolutionary pathways. This is known as convergent evolution. Pterosaurs, birds, and bats each solved the problem of flight in a different way. This is apparent when wings and the supporting bones that attach to the powerful flight muscles are compared. Another obvious difference is wing covering; bird wings are covered with feathers, while bats have thin wing membranes which are probably very different from the flexible, fibrous membranes of pterosaurs. Other wing bones in the bat and bird also show adaptive variation:
Reduced digits, fused arm bones
Elongated digits
The fish in the lab show many different adaptations for different swimming styles. One of the more obvious adaptations has to do with tail shape. Forked or indented tails (like that of the red shiner) assist fast, sustained swimming (think of a tuna) – if you notice, the red shiners are always swimming in the tanks. Square or rounded tails (like that of the pupfish) are better for acceleration and stopping – the pupfish tend to stop – then move quickly – then stop. This is good for territorial defense.
Red Shiner (Cyprinella
lutrensis)
Pupfish (Cyprinodon
pecosensis)
Adaptations for Feeding:
Fish have also developed adaptations to help them compete for food. Our tanks focus on three water regions: bottom, middle and top. The guppies and mosquito fish have superior mouths for top-feeding (mosquito fish eat mosquito larvae). The pupfish and red shiners are generalists and have terminal mouths (see images above). The loaches and catfish have inferior mouths for bottom feeding.
Mosquito fish (Gambusia
affinis)
Catfish (Plecostomus)
A second feeding adaptation is different types of teeth. In mammals, four basic kinds of teeth are recognized: incisors, canines, premolars and molars.
Incisors are the front most teeth. They are generally chisel shaped and used for cutting or grasping. There are also several alternative types of incisors. Rodents have very stout incisors, used for gnawing, which must grow continually as they are worn down by constant use. The incisors found in vampire bats resemble small scalpels that help to open the blood vessels of other animals and allow the bat to feed. Elephant tusks and the shovel-like lower front teeth of hippos are also incisor modifications.
Canines, the single, sharp, longer teeth right behind the incisors are used to catch, hold and kill prey. In many herbivores this tooth is either greatly reduced or completely absent. In some mammals, like the baboon or musk deer, the canine is rather exaggerated and used for fighting or social displays. Often in these cases the canines of the male of the species are larger then those of the female.
Premolars lie right behind the canines. They are often smaller then the molars, but range in size and shape depending on the diet of the animal. For some mammals, these anterior, molariform teeth are adapted to crushing or grinding vegetation, insects, meat, or plankton. In others, they are more suited to shearing and slicing. Premolars are different from molars because there is a "baby molar set" that is eventually replaced by and adult set. Molars, however are not replaced; they only exist as adult teeth.
Molars are the most posterior teeth in the jaws of most mammals. Like premolars they vary in size, shape and function. Molars do not usually develop until the animal has reached the adult stage of life.
Another important adaptation related to feeding is placement of the eye sockets. In terrestrial environments, vertebrate prey species tend to have lateral placement of the eyes, allowing them to have panoramic vision. Terrestrial predators, on the other hand, have frontally placed eyes, allowing for binocular vision and better depth perception. In marine environments, both aquatic predator and prey species have laterally placed eyes. It is theorized that in an aquatic environment, it is much more difficult for the eye to rotate laterally because of the fluid density. Frontal eye placement would require greater rotation to keep the prey (or predator) in view as the hunter (or quarry) darts to one side or the other.
Terrestrial prey (pronghorn)
Terrestrial predator (lynx)
Aquatic prey and predator
*Click here to view more skulls*
Adaptations for Reproduction:
In this lab we focused on 2 main types of dimorphism present in the fish found in the lab tank:
Color dimorphism
- Red shiners: Males have blue body and red fins during breeding season, females are drab.
- Pupfish: Males have iridescent blue patch on top of head and orange fins with black edges during breeding season. Males can instantly change the amount of blue coloration by opening and closing melanophores (glands that release the pigment melanin)– they become more blue when mating is imminent, and become drab when nervous. Females always remain drab.
- Guppies: Males have many brightly colored spots on their sides and caudal fins. Females are drab. (Many experiments have shown that while female choice of mates increases the brightness and number of spots in male guppies through sexual selection, natural selection acts to reduce male coloration due to greater predation on bright males.)
Size dimorphism
- Pupfish: Males tend to grow larger than females. Males will fight each other constantly for mating opportunities.
- Guppies and Gambusia: Females are generally much larger than males. This should lead to a fecundity advantage for females (remember, they are live-bearing).
One other thing, which is harder to notice, is that the anal fin (the lower
fin behind stomach) is rounded in female guppies and Gambusia, but is
much flatter and rectangular in the males – this is because it is used to
transfer sperm into the females for internal fertilization. All of the other
fish in this lab are external fertilizers – females lay eggs and males release
sperm into the water or substrate.
Cool Information about Adaptations in Rattlesnakes
Review Questions
- Define adaptation and provide a specific example.
- What is a phylogenetic tree and why is it useful?
- What is the similar adaptation for locomotion that is shared by frogs and
bats?
- Define and give an example of convergent evolution.
- Which structures are found in species with convergent adaptations? (homologous
or analogous)
- What is the difference between homologous and analogous structures?
- Looking at a skull, how can you tell if the animal is an herbivore, an
omnivore, or a carnivore?
- Define the different types of teeth and their uses.
- What is special about a snake's skull?
- Why does the skull of a grazer have an elongated rostrum?
- Give an example of a feeding adaptation.
- Give an example of sexual dimorphism.
- What does sexual dimorphism among species represent?
- Give two examples of adaptations that help carnivorous animals.
- Give two examples of adaptations that help herbivorous animals.
- What are the benefits for having a keel in birds?