Lecture 14 Reconstructing Phylogenies 1 homoplasy analogy character

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

Homology vs. Analogy 1. Same fundamental structure humerus 2. Same relationship radius to surrounding ulna characters carpals phalanges 3. Similarities in embryology

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

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

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

• 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… 1. distinguish homologies from analogies 2. 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. A B C D - 1 character, 2 states sp. 1 : b sp. 2 : b sp. 3 : a sp. O: a

2 hypotheses: 1 : a → b (a = ancestral; b derived) 2 : b → a (b = ancestral; a derived) 1 b 2 b 3 O a a 1 b vs. 2 3 b a O a b→a a→b b→a b a 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

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

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 1 – toed • Outgroup analysis necessary • In fact, more detailed fossil record shows 3 – toed both before & after 1 – toed