Comparative and Experimental Studies of Morphology and Development

点击翻译按钮获取中文摘要

How the great diversity of animal forms arose remains an enduring challenge. Two major questions still puzzle evolutionary biologists: 1) To what degree do the effects of genes and environment contribute to the new variation upon which natural selection acts to yield novel forms of organisms? 2) In what order did these novel forms arise evolutionary among early lineages of diverse animal groups? Our past work has yielded strong evidence for a ‘genes as followers’ mode of evolution, where observable variation arises first by developmentally plastic changes in form and where genetic variants (mutations) that influence development arise later. This work has contributed significantly to a growing appreciation that, in terms of evolution, development may be as important a source of novel forms as genetics. Using lab and field experiments, and comparative studies, we will continue to explore this crucial interplay between development and evolution. 1) Using our easily studied barnacle system — where large differences in leg form can be induced predictably — we will: a) test which cues they are responding to (food supply or mechanical action of moving water), and b) tease apart the cellular and molecular mechanisms that give rise to such big differences in leg length and leg segment number. Usually, leg segment number is fixed in arthropods, so this great variation in barnacle legs offers a superb tool for studying how leg segment number may increase — or decrease — in arthropods, the most diverse animal group on Earth. 2) We will test whether feeding leg form in filter-feeding porcelain crabs, which live in huge numbers on wave-swept shores, varies as in barnacle legs. This study tests for convergent evolution of developmental plasticity in two co-occurring yet evolutionarily distant groups — barnacles and crabs. It will also help us understand how the form of sieve-like feeding structures is constrained by flow across a wide range of water velocities. 3) We will study how snails control shell form. The great beauty and diversity of snail shells has intrigued biologists and non-biologists alike for centuries. But surprisingly little is known about how snails grow particular shell features. We will study two types of shell sculpture: frilly blades and spiral ribs. By manipulating food supply and position of past blades we will test how these affect placement of new blades (internal ‘clock’ or external cues?). We will also use modern microscopy techniques to study how mantle tissue, which produces the new shell, differs between two genetically different forms (smooth or spiral ribs) in a polymorphic species. 4) Using new data from fossils, and careful anatomical studies of ‘primitive’ living animals, we will revisit two puzzling regions of the Tree of Life: the basal branches of the true crabs (Brachyura) and the vertebrates. In crabs we will focus on eye, limb and abdomen form. In jawless fishes we will study features of head anatomy (cartilages, muscles, nerves, feeding structures). 5) We will test an intriguing hypothesis about the evolutionary origin of conspicuous right-left asymmetries: does handed behavior induce asymmetries in limb form via developmental plasticity? We will a) grow juvenile shell-breaking Cancer crabs on hard-shelled diets to study the development of handed behavior and claw asymmetry over time, and b) test whether differential use is the trigger that induces the spectacular large signaling claw to grow on only one side in male fiddler crabs, and c) do surveys of evolutionary relations among taxa that show random and fixed asymmetry. Most work will be done at Canada’s top marine field-research facility: Bamfield Marine Sciences Centre, Vancouver Island.