Inquiry Case 1 – Zebra Mussels
Zebra mussel = Dreissena polymorpha
Diversity - refers to the number of different species in a taxonomic group or a geographical
Byssal threads: ―silky‖ threads that are used by mussels to latch onto rocks, or submerged
Recruitment - production of the next generation
Morphology – changes/differences in physical traits. Can be due to either genetics, or
adaptations to the surrounding environment (―phenotypic plasticity‖)
Ex: differences in mussels of the same species inhabiting fast vs. slow running
Sometimes there can be very little morphological variation, but a significant amount
of genetic variation
Ex: mammals are not very diverse but they are very disparate — consider shrews
vs. bats vs. giraffes vs. blue whales. Bivalve mollusks, though much more diverse
than mammals, are not as disparate — on the whole, they all maintain a relatively
Convergent Evolution (AKA Homoplasy) - describes the acquisition of the same biological
trait in unrelated lineages.
Ex: The wing is a classic example of convergent evolution in action. Flying insects,
birds, and bats have all evolved the capacity of flight independently. They have
"converged" on this useful trait.
Traits arising through convergent evolution are termed analogous structures
Homology – similarities among species due to sharing a common ancestor
Traits arising through a common ancestor are termed homologous structures
Eyes of humans and eyes of cats. The ancestor of mammals had eyes, and we and cats
both inherited eyes from a shared ancestor. So, eyes are homologous among mammals.
Clade -A clade is a group of organisms that includes a common ancestor and all the
descendants of that ancestor. On a phylogenetic tree, you must be able to make only one ―cut‖
on the tree for it to be a cla.e
Disparity – Refers to how morphologically different species are from each other (for example,
mammals are very disparate -- think about a shrew vs. a blue whale). Variation - refers to differences among individual organisms within a population or species. It
might be genetic variation, or phenotypic variation.
Ontogeny - the origin and the development of an organism Ex: from the fertilized egg to
Conspecifics - Two or more individual organisms, populations, or taxa are conspecific