BIO 425 Aquatic Zoology
Conservation, Phylogenetics, Taxonomy, Evolution
Conservation
We are currently witnessing the greatest period of extinction since the end of the Cretaceous Era (~65 mya)
Biodiversity of rivers especially imperiled
Some due to overexploitation
Passenger Pigeon
Dodo
Stellers Sea Cow
More of a problem for terrestrial & marine species
More recently, most are due to habitat destruction
Harelip Sucker
White-line Topminnow
What causes habitat destruction?
Logging
Mining
Oil and gas drilling
Dam construction
Agriculture
Urban sprawl
Species Endemism
Endemic = species found naturally in single geographic area
N.
North American Snails
601 native species
173 in need of protection
42 extinct (4 genera)
North American Mussels/Clams
297 species
native to
269 in SE
7% extinct
42% threatened or endangered
25% stable
Crayfish
338 species
2 extinct
110 threatened or endangered (3 listed)
176 stable
Fishes
~800 described
freshwater species in North America (north of
662 species in
187 in need of conservation (28%)
Factors Responsible For Extinction
Overexploitation
Introduced Species
Disruption of Ecological Relationships
Habitat Loss and Fragmentation
Loss of Genetic Variability
Why is biodiversity important?
Each species is adapted to function within ecosystem
Change in Biodiversity = change in ecosystem
Medicinal value (25%)
Agricultural value (100%)
Genetic diversity allows species to survive catastrophic events (natural and human)
Airplane metaphor
Is this really a big problem?
Yes, we depend on healthy aquatic ecosystems for drinking water, oxygen, pharmaceuticals, food
Ecosystems function because of their parts
What happens when parts disappear?
John Muir
When one tugs at a single thing in nature, he finds it attached to the rest of the world.
Theodore Roosevelt
The conservation of our natural resources and their proper use constitute the fundamental problem which underlies almost every other problem of our national life.
Baba Dioum
In the end, we will conserve only what we love, we will love only what we understand, and we will understand only what we have been taught.
Classification
Taxonomy = science of naming and classifying species
Linnaeus Systema Naturae. 1700s
Gave scientific name (binomen) to all known species (Genus species)
Identified higher taxa based on overall similarity
Had no thought of evolutionary relationships
Linnaeus Taxonomy
Kingdom
Phylum
Class
Order
Family
»Genus
»species
Descent with modification and speciation
Species are not immutable, they change over time (new characters evolve)
New species are derived from previous species = speciation
Some species are more closely related to one another than they are to other species
Closely related species often share many characteristics
Cladogram or Phylogenetic Tree
Hypothesis of how organisms are related to one another
Branches represent species
Nodes represent speciation events
Character evolution can be plotted on tree
Monophyly
State of being descended from a single common ancestor
Sister taxa - two taxa that are more closely related to each other than any other taxa (ie. descended from an immediate common ancestor)
Monophyletic group group of taxa that are more closely related to each other than any other taxa (all descended from a single common ancestor)
Phylogenetic Systematics (Cladistics)
Builds hypotheses of evolutionary relationships by using derived characters
Derived character (apomorphy) is recently evolved from ancestral character (pleisiomorphy)
Shared derived character = synapomorphy (only useful at one node)
Shared ancestral character = symplesiomorphy (not useful at all)
Whats the difference?
Synapomorphy evolves in a single species and the descendants of that species will inherit that character
Symplesiomorphy is a character that evolved previously and was passed along following multiple speciation events but replaced by an apomorphy in a descendant
Who cares?
Synapomorphy will identify an ancestor and all descendents of that ancestor (monophyletic group)
Symplesiomorphy will identify a group of organisms that share a particular character that evolved long ago and has not been lost or changed
Species are not necessarily closely related
Symplesiomorphies will identify an ancestor and some (but not all) of its descendants (non-monophyletic group)
Its all relative!
What is an apomorphic character on one part of a tree, is a plesiomorphic character at another part of a tree
An apomorphy can only be used to support a single node
How do you tell whether a character is an apomorphy or a plesiomorphy?
Outgroup comparison
Ingroup = group of organisms we are interested in studying
Outgroup = closest living relative of that group (should possess the plesiomorphic character)
Couldnt similar characters evolve more than once?
Yes, but like all sciences, we are interested in the most parsimonious solution to a problem
Trees with the fewer numbers of evolutionary changes to explain characters that we examine are more parsimonious than trees with greater numbers of changes
Parsimony has been modeled to best reflect known lineage splits
Is it perfect?
Of course not! But it is scientific, which means that addition of more taxa and more characters will likely provide us with a more accurate hypothesis of how organisms are related to one another
Taxonomy (like all sciences) works with hypotheses (we can never really know how things are related or even how many species exist on our planet)
Advantage of phylogenetic classifications
Recognizes only monophyletic groups
Scientific (testable!)
More accurately reflects evolutionary history
Can predict characteristics of extinct or extremely rare taxa
Helps distinguish between homology and homoplasy
Homology vs. Homoplasy
Characters derived from one another (ie. Apomorphies and plesiomorphies) have a common ancestry and are homologous
Characters that have different evolutionary histories but have evolved to be similar are homoplasous
Convergent Evolution (bird & bats)
Parallel Evolution (kangaroo rats & jerboa)
Reversal (sharks & dolphins)
Criteria of homology
Similarity of position (relative)
Ontogenetic similarity
Continuance through intermediate forms
Reciprocal Illumination
As we develop more thorough and stronger supported phylogenetic hypotheses, we can be more certain of homology of certain characters.
As we become more certain of homology of characters, we can generate stronger phylogenetic hypotheses
Resources
Wiley, E. O. 1981.
Phylogenetics. Wiley & Sons,
Inc.
Wiley, E. O., D.
Siegel-Causey, D. R. Brooks, and V. A. Funk.
1991. The Compleat Cladist. University of
Lipscomb, D. 1998.
Basics of Cladistic Analysis.