This phylogenetic tree depicts the evolutionary relationships of eight major vertebrate classes.  Tiktaalik is an intermediate fossil that represents an early ancestor of all tetrapods. Specifically, Tiktaalik is known for its wrist, a key feature of the tetrapod limb that made it possible for which major evolutionary transition in animals? If you were to add Tiktaalik to this phylogeny, where would the Tiktaalik branch extend from?

Which statement is true about sexual selection?

Australian Marsupials have been geographically isolated from Placental mammals for ~50 million years. In that time, many species in both groups have independently evolved the same adaptations via convergent evolution. The analogous adaptations observed in Placental mammals and Marsupials are best explained by…

The presence of altruistic behavior in some animals can be explained by kin selection, a theory that maintains that…

Prior to European colonization, tens of thousands of whooping cranes lived in North America. By 1938, due to overexploitation and habitat loss, whooping cranes were virtually extinct, with a total population of only 15 individuals. Since then, careful conservation efforts have increased the North American whooping crane population to over 800 today. From a genetic standpoint, as a result of this catastrophe, whooping cranes experienced a “population bottleneck”, which is a severe form of . The current population of whooping cranes should be expected to have , relative to the pre-colonial population.

You perform an experiment to test for the evolution of resistance in Salmonella bacteria to the antibiotic amoxicillin. To quantify the evolution of resistance in the population, you measure the “zone of inhibition” (i.e., how close the bacteria can grow to the antibiotic on the paper disk in the center of the Petri dish). After several generations, you find that the “zone of inhibition” has decreased in size—the bacteria are able to grow closer to the antibiotic paper disk. Based on these results, you can conclude…  

The graph below shows the change in the frequency of allele A1 over 100 generations in four populations of fish. All four populations are found in separate, remote lakes and are completely isolated from each other, as well as, other populations.  The allele A1 does not affect the fitness of individuals who carry the allele, all changes in the frequency of allele A1, therefore, can be attributed to genetic drift. Given this information, which of the four populations is most likely the smallest?

The Müller’s ratchet hypothesis to explain sex suggests that…

A study on blood sharing among vampire bats has shown that a hungry bat is more likely to receive a blood meal from another unrelated individual if the hungry bat has fed that same individual in the recent past. This observation supports the hypothesis that sharing of blood meals could have evolved by way of…

A scientist might use the “molecular clock” technique to…