Lecture 14: Reconstructing Phylogenies 1) homoplasy (analogy) : character not present in RCA - convergent evolution - parallel evolution 2) homology : character inherited from CA a) ancestral (symplesiomorphy) - little change from distant ancestor b) derived (synapomorphy) - recent change Start with some terminology

Homology vs. Analogy Same fundamental structure Same relationship to surrounding characters Similarities in embryology humerus radius ulna carpals phalanges Human, dog, whale, bat.

Embryology Haeckel’s (1886) biogenetic “law” : “ontogeny recapitulates phylogeny” each embryonic stage = adult stage of ancestor WRONG! Von Baer’s (1828) law: among related spp., early stages are more similar than later stages examination of early dev’t can reveal close relationships What are these examples??

Examples Successive stages of vertebrate embryos: Cattle: metacarpals fish                                                                        chicken pig human Cattle: metacarpals start off separate; fuse during development Anteaters: teeth present early in development; resorbed

Von Baer’s Law Sometimes useful to distinguish b/w ancestral & derived traits, not always: e.g. fused cannon bone – derived toothlessness in Edentates – derived But, early stages may be special adaptations - “beak” of tadpole - milk teeth of bats - cotyledons in plants What do tadpoles use their beaks for?? Scrape food off rocks to filter Milk teeth are for? Because jaw too small Cotyledons are for? Contains food for early growth until seedling established

terminal stages of ancestor’s ontogeny may be lost e.g. paedomorphosis: (retention of juvenile characters in adult) - in salamanders is derived, not ancestral

Reconstruction continues… distinguish homologies from analogies distinguish ancestral homologies from derived homologies - need to determine polarity of change (ancestral → recent)

Strategies to Distinguish b/w Ancestral & Derived 1) morphocline or transformation series: e.g. chromosome inversions in Drosophila ABCDEFG ↔ AEDCBFG ↔ AEDFBCG - can infer sequence, but which is ancestral? a ↔ b

Outgroup Analysis outgroup = taxon that diverged from a group before they diverged from each other principle of parsimony: fewest changes consider: 3 spp + outgroup sp. - 1 character, 2 states sp. 1 : b sp. 2 : b sp. 3 : a sp. O: a A B C D Continued on next page…

the character state present in the outgroup is assumed to be ancestral 2 hypotheses: 1 : a → b (a = ancestral; b derived) 2 : b → a (b = ancestral; a derived) 1 2 3 O b a b → a a → b vs. the character state present in the outgroup is assumed to be ancestral

Butterflies brush-footed, monarchs → 2 reduced legs swallowtails, sulphurs → 6 functional legs which state is ancestral ? Moths diverged from butterflies before they diverged from each other (moths = outgroup) moths → 6 functional legs most parsimonious : 6 functional legs = ancestral

5 Characters Character 1: shared by A, B, C (synapomorphy) separates them from outgroup Synapomorphy – shared derived character.

Character 2: unique derived trait in taxon B no info about relationships Character 3: unique derived trait in taxon C

Character 4: synapomorphy unites B & C Character 5: unique derived trait in taxon A no info

Fused cannon bones in cattle; Toothlessness in adult anteaters: Derived traits b/c: unfused metacarpals & adult teeth are widespread in other mammals

Primitive characters primitive condition in an ingroup is that which is found in outgroups Common characters are not necessarily primitive! Often true: owl monkeys are only nocturnal primate; nocturnal habit is derived However…

Primitive vs. Derived Few vertebrates lack jaws, but jawlessness in lampreys is primitive, not derived Distribution, not number of spp. with the trait, is important

Complete Fossil Record Can aid in analysis e.g. Progressive reduction in # of digits in horses one-toed condition is derived same info from outgroup analysis : rhinos & tapirs But…

Litopterna Extinct horse-like mammals: 3 – toed observed later than Outgroup analysis necessary In fact, more detailed fossil record shows 3 – toed both before & after 1 – toed