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Matt Johnson Lecture Notes

ORNITHOLOGY (Humboldt State Univ. WILDLIFE 365)

LECTURE 9 – SPECIES & SYSTEMATICS

I. Species A. Species number varies over time. For birds it probably has been as high as 50,000, but today it is a bit under 10,000 (close to 9,800). B. Species changes by three processes: 1. Phyletic evolution - the gradual change of a single lineage (does not alter species number but changes species identity) - probably rare. 2. Speciation - the splitting of a single phyletic line into two or more lineages (adds species) 3. Extinction - the elimination of species. C. What is a species? There are two conflicting views: 1. Biological Species Concept (BSC) - "groups of interbreeding natural populations that are reproductively isolated from other such groups" (Earnst Mayr - BSC champion and ornithologist from Harvard). Reproductive isolation (either real or inferred from geography) is the criterion used to distinguish closely related groups. E.g., Western vs. Florida Scrub Jay are different species due to morphological and range differences, but various forms of Fox sparrows are not because they are close enough to frequently interbreed. OVERHEAD 2. Phylogentic Species Concept (PSC) - "smallest diagnosable cluster of individuals within which there is a parental pattern of ancestry and descent" (Cracraft 1983). Here, species are judged based on behavioral, morphological, and molecular characters subjected to a "cladistic" analysis. II. Cladistics. A. Terms: 1. Homologous - characters shared in two or more taxa that are derived from a common ancestor. E.g., gull wing and penguin flipper. Homologous traits result from a common ancestry. 2. Analogous - characters shared in to two or taxa that are not derived from a common ancestor e.g., gull wing and butterfly wing. Analogous traits result from "convergence", or a common environment. 2

B. The mantra: "Shared derived characteristics reveal evolutionary relationships." This approach is called cladistic analysis. Figure 3-4 in Gill OVERHEAD 1. That is, homologous characteristics are the most useful in reconstructing evolutionary relationships. We are related to apes not because we have four limbs...turtles and frogs have four limbs too. We're related to apes because we have upright posture, opposable thumbs, large brain cases, binocular vision, etc. Its the derived (advanced) characteristics that we share that unites us. 2. To reconstruct evolutionary relationships, we adopt the assumption of parsimony, that is, the most likely evolutionary scenario is the one that provides the simplest progression from one taxa to another (fewest origins of new character states). 3. Convergence complicates our ability to reconstruct phylogenies. Convergence makes characters appear to be shared and derived that in fact are only analogous. 4. We assume that homology is more common than analogy in biology. (the reason parsimony works is because homology is more common than analogy; convergence is the exception and not the rule) 5. So, if we look at ENOUGH characters, and find lots of shared derived characters, we can assume they are shared due to a common ancestry, and not due to convergence. 6. But how many characters in enough?

Gray wolf Coyote Tasmanian wolf Kangaroo Long doggy snout Long doggy snout Long doggy snout Blunt snout Howls Howls Howls No howls Sharp canine teeth Sharp canine teeth Sharp canine teeth Chewing teeth Placental Placental Marsupial Marsupial

Now we know, the Tasmanian wolf is more closely related to a kangaroo than a gray wolf, despite multiple analogous similarities. If we looked at many more characters, the true homologous similarities between Tasmanian wolves and kangaroos would begin to outnumber (outweigh) the fewer analogous traits between gray and Tasmanian wolves. (also, we would recognize that some characters are better for reconstructing phylogenies than others, e.g., howls vs. no howls is not evolutionarily meaningful….but placental vs. marsupial is)

7. This is problem in bird evolution. Early birds have much in common with therapods, there's no doubt of that. But is that due to ancestry or convergence? 3

8. Similar questions are scattered about the relationships of extant birds as well. Vulture resemble raptors. But in some characters they also resemble storks. Which similarities are due to ancestry, and which are convergence? What about Flamingoes? Are they storks with duck-like bills, are they ducks with stork-like legs? 9. To try to solve questions like these, systematists employ an arsenal of information types to classify birds:

C. Systematic information: 1. Morphology. a. Oldest approach. Best when use is restricted to conservative characters, that is, characters that change slowly such as skeletal features rather than characters that change quickly, such as coloration. b. Trouble is that the environment can change an animal’s morphology, even some "conservative" characters. James (1983) transplanted red-wing blackbirds from Colorado to Minnesota and found that transplanted birds grew tarsi that resembled the Minnesota red-wings more than their Colorado parents. OVERHEAD 2. Behavior. Behavior is a character much like morphology. And it’s not as flexible as you might think. Examples of behavioral characters used to classify birds include nest building behaviors (related birds build similar nests), song types (e.g., flycatchers), scratching techniques. 3. Parasites. Feather parasites have co-evolved with their hosts. Their branching patterns should thus be parallel. 4. Molecular techniques. These techniques are becoming increasingly popular as new technologies make new approaches possible. Explosion of molecular analyses in the literature in the last 20 years. But remember that these are just more characters, which can be homologous and analogous just like others. a. Electrophoresis. Comparison of the composition of certain proteins (especially egg whites and special allozymes) have revealed some relationships. In these analyses, species with shared protein structures are suggested to share a common ancestry. b. This approach now widely replaced by DNA-DNA hybridization. OVERHEAD i. DNA of two species are isolated. ii. The paired strands are separated, then single strands from each species are brought together to "hybridize." iii. The more closely the two species are related, the more complementary their DNA stands will be, so the more tightly they will hybridize. 4

iv. The hybridized strands are heated until they disassociate. The higher the temp needed to disassociate them, the more tightly they were bound together, so the more closely related the species are to one another. OVERHEAD v. Recent findings published by Sibley and Alquist (1990) based on 25,000 DNA hybridizations of nearly all bird families of the world suggest some major re- classifications. These are still questioned. Only time will tell. D. What we’re looking for….. 1. Monophyletic groups. A monophyletic group is one that contains all the descendent taxa of a single common ancestor. Monophyletic groups are the only ones that reveal much about evolutionary relationships (history). Important to remember that monophyly is a relative term. Passeriformes are monophyletic (we’re pretty sure), and so are Corvids, and so are Acids, etc. If you go back far enough in time, big groups of taxa can be monophyletic. Indeed, life itself is probably monophyletic. 2. Polyphyletic groups are those that do not share a common ancestor. 3. Paraphyletic groups are those that share a common ancestor, but not all descendents are included in the group.