Insect Evolution Lecture 3 PDF

Insect Evolution Ent 104 Johnson Outline Darwin Evolution by natural selection Basic concepts Applications Mendel Some basic patterns in insect evolution Wallace Behavior and evolution Behavioral ecology and Animal Behavior is: Application of evolutionary theory to animal behavior Behaviorists study...

Insect Evolution Ent 104 Johnson Outline Darwin Evolution by natural selection Basic concepts Applications Mendel Some basic patterns in insect evolution Wallace Behavior and evolution Behavioral ecology and Animal Behavior is: Application of evolutionary theory to animal behavior Behaviorists study phenotypic adaptation Hence evolution is central to our field What do evolutionary biologists do? Speciation, systematics, evolutionary genetics, drift, etc Evolutionary biology Evolution: change in biological systems over time Natural selection is one mechanism of evolutionary change Most important one of several From Deretsky Natural selection 3 big forces in Evolution: Natural selection adaptation Drift Random change Major random events Asteroids, major geological events Natural Selection Natural selection leads to adaptation Form and function An adaptation is a trait shaped by natural selection Natural Selection depends on 1. Variation 2. Heritability 3. Differential reproductive success Variation Organisms vary in many ways Continuous variation Normal curves for traits like height and weight Discrete variation Flower colors in Mendel’s peas Major sources of variation Mutation Sexual reproduction Meiosis / recombination Heritability Heritability refers to offspring resembling their parents more than a random selection of individuals from the same species Heritability, leading to evolutionary change, is caused by genetic inheritance In many simple and complex ways Differential reproductive success Some individuals leave more offspring than others They outcompete them in some way When the form of competition is not in the context of mating we refer to it as natural selection When the competition is for obtaining mates we call it sexual selection Male male competition Female choice Evolution by natural selection Put all three factors together and you get gene frequency change A higher fraction of some allele in the next generation due to differential reproductive success, variation in a trait, and heritability of that trait Evolution in action Convergent evolution Animals can either be similar due to shared decent or via exposure to a common selective force When animal are similar by descent we call it homologous similarity When animals are similar due to shared selective pressure we call it convergence Powerful force in nature Systematics Building evolutionary trees is called systematics A tree shows the pattern of divergence in a group of organisms Who is most closely related (evolutionarily) to whom Tree building Trees are built by comparing animals to one another and determining which are the most similar Older methods used morphology New methods use DNA The two closest species have the most similar DNA Very complex models for figuring out how similar two sequences are Not all bases in DNA are equal Some much more likely to change then others Evolutionary theory Evolution is not always a useful theory for understanding behavior Adaptation is simple Maladaptive and neutral is hard Not evolutionarily grounded Behavior can be biologically based, but not evolutionarily explainable Adaptation Herding is adaptive because: Safety in numbers Why do we still see some outside the herd? Evolutionary answer: Insufficient selection pressure, recessive alleles, etc Is that an explanation? Tell us why it hasn’t gone away Not why the behavior occurs Levels of Analysis Tinbergen pioneered the levels of analysis concept Sherman picked it up Many answers to the same question Not mutually exclusive Both are true Avoid pointless arguments Levels of analysis Why do crickets sing? Origin Current utility Developmental origin Physiological genetic mechanisms Evolutionary theory The lone wildebeest Probably has an answer based on a mechanistic understanding of: Genetics Development / environment Broad patterns in insect systematics Early phylogenies were mostly wrong with respect to major divisions What is the nearest relative of all insects? What orders are closest to what other orders? Morphology alone Morphology leads to bad trees for distant relationships Convergent evolution is a major problem Radical shifts in morphology that don’t track evolutionary divergence Rapid change, then long periods of stasis What are the insects closest relatives? Many arthropods Major groups Chelicerates (spiders, scorpions) Myriapoda (centipedes, millipedes Crustaceans Crustaceans are nearest relatives Insects are terrestrial crustaceans! Then comes Myriapods Chelicerates Arachnids, scorpions, etc Insects are terrestrial crustaceans Water fleas are closer to insects than to other Crustacea Remipedia are closest to insects Solution Add insects to crustaceans or Add insects + branchiopods + Remipedia together into new group Close insect relatives in the Crustaceans Remipedia Found in salty aquifers Small venomous predators Branchiopoda Water fleas and fairy shrimp Mostly eat detritus Algae, bacteria, protists Brine shrimp are commonly used as fish food Their eggs survive drying and come to life after immersion in water Evolution of insects Earliest fossils from 412 Million years ago Likely origin 450-509 million years ago What was going on at that time? Land plants originate at the same time Insects and plants probably coevolved right from the start Scavengers first Herbivores second Predators third Radiations Hymenoptera, Diptera, and Lepidoptera all diverged in the early cretaceous with the evolution of flowering plants