Lecture 20 Morphological Changes in Macroevolution Microevolution evolution

Lecture 20: Morphological Changes in Macroevolution • Microevolution = evolution w/i species • Macroevolution = evolution at or above sp. level Macroevolution: often major morph changes How do they occur? • Saltation: new features arise by major reorgan’n not progression through intermediates Punctuated equilibrium ( no specific mech. ) Darwin was an anti-Saltationist

Morphological Changes Completely new features rare: • usually modification of ancestral feature • e. g. branchial basket (agnathans) gill arch (bony fish) jaw (reptile) ear bones (mammal) (N. B. not direct descendants, C. A. )

Transformation Changes in elements: number size shape position association with other parts differentiation (complexity)

Examples • Enlargement of Cerebral Hemispheres (reptile mammal) • Complexity of Lung ( amphib rept mamm) • Reduction of skull bones ( fish mamm)

Serially Homologous Features: e. g. petals, scales, stamens, digits etc. • May increase in number: (vertebrae in snakes; body segments in millipedes) • More frequently reduced: (teeth, vertebrae, digits in most vertebrate lineages)

Serially Homologous Structures • change more likely when indeterminate (large #, variable) • e. g. stamens ( magnolias vs. legumes)

• Differentiation of structures from ancestor: e. g. leaves tendrils; spines etc. e. g. appendages of trilobites mouthparts, reproductive, locomotary • Structures may become homogeneous e. g. toothed whales

Allometry : • differential rates of growth of body parts • comparisons may be inter- or intraspecific • intraspecific : w/i inds (ontogenetic - different ages) among inds (static - same age)

Allometry Equation: y = b xa Linearized: log y = log b + a log x • e. g. ontogenetic allometry Humans Black-headed Godwits

Adaptiveness of Allometry • e. g. intestine scales 3/2 body size i. e. intestine length = body size 1. 5 • b/c surface area : volume ratio

Interspecific Allometry of brain: body weight: • Homeotherms: Brw = 0. 07 (Bw)0. 67 • Poikilotherms: Brw = 0. 007 (Bw)0. 67

Heterochrony brain wt Evolutionary changes in timing of dev’t of feature e. g. compare ontogeny of 2 spp. : sp 2 sp 1 body wt Brain size changes faster (rel. to body) in sp. 2 vs. sp. 1 Brain cell lines in sp. 2 develop faster than in sp. 1

Types of Heterochrony 1) Peramorphosis: add’n of extra stages beyond adult stage of ancestor a) Hypermorphosis: more stages, longer time b) Acceleration: more stages, same time c) Predisplacement: starts earlier

Types of Heterochrony 2) Paedomorphosis : retention of juvenile features in adult (opposite of peramorphosis) a) Progenesis : development stops early b) Neoteny : development slowed c) Postdisplacement : starts late

Growth curves line of equal growth (m=1) log y ancestral trajectory: = starts growing = stops growing log x slope > 1 y grows fast relative to x

Hypermorphosis • Type of peramorphosis: • growth of structure lasts longer during dev’t • greater y/x ratio at maturity rel. to ancestor 1 extended dev’t log y m= 1 log x = ancestral cond’n 1 = descendant cond’n

Irish Elk • e. g. of Hypermorphosis • extinct ~ 10, 000 years ago • antlers: 13 ft span ~ 100 lb! • metabolic costs of antler prod’n • implicated in extinction: • to grow 40 kg antlers in 150 days : 60 g calcium; 30 g phosphorus per day!