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Topic 5 ADAPTATION 1  Learning objectives Define adaptation in its different usages and distinguish it from acclimation Explain how exaptations are a form of adaptation and what characterizes them Outline what an adaptationist fairy tale is, why they are problematic, and how...

Topic 5 ADAPTATION 1  Learning objectives Define adaptation in its different usages and distinguish it from acclimation Explain how exaptations are a form of adaptation and what characterizes them Outline what an adaptationist fairy tale is, why they are problematic, and how they can be avoided List the criteria necessary to demonstrate that a trait is adaptative Explain the methods that can be used to demonstrate adaptation, including quantifying selection, reciprocal transplants, and the comparative method Discuss how adaptation and complexity are related (are adaptations necessarily complex?) Explain how complex adaptations can evolve via gradual, advantageous steps with reference to an example (e.g., the eye) Outline how exaptation may also contribution to the evolution of complex adaptations Summarize a Darwinian demon and describe the different factors that may constrain, or result in non-perfect, adaptation (i.e., explain why we don’t see Darwinian demons) 2 Outline 5.1 What is/isn’t adaptation 5.2 Detecting adaptation 5.3 Evolution of complex adaptations 5.4 Adaptation isn’t perfect/constraints on adaptation 3  Defining adaptation Two related meanings (a process and the thing the process produces): 1. A heritable phenotype that allows individuals to perform some function which enhances their survival and/or reproduction (i.e., their fitness) in their current environment; i.e., a trait maintained by natural selection for its current function e.g., the ability of succulents to store large amounts of water is an adaptation to life in arid deserts - Pay attention to what ISN’T included in this definition: it involves no requirement that the trait originally evolved by natural selection for this reason 2. The evolutionary process that produces adaptations. That is, the process by which a natural selection causes the evolution of traits that improve the fit between an organism and its environment (i.e., the process that produces phenotypes that enhance the survival and reproduction of an organism in its current environment) - this usage, as a process, is basically synonymous with natural selection 4 Example – the Jamaican bromeliad crab Entire life cycle takes place on bromeliads Females raise young in pools of water that collect at the base of the stems Females chemically engineer the pools for the benefit of their offspring Aechmea paniculigera: – they remove decaying organic matter from the pools to maintain oxygen levels By WereSpielChequers - Own work, CC BY-SA 3.0, Wikimedia commons – they add snail shells to raise the pH and calcium Experimental evidence demonstrates that these traits increase fitness for these reasons – i.e., they are adaptations Prof. Rudolf Diesel https://www.jstor.org/stable/51040 https://www.jstor.org/stable/4600778 5  Exaptations Structures that are currently adaptations but that originally evolved in a different context, for some other reason, and were later co-opted for their current, fitness-enhancing function Exaptations are adaptations that arose after a change in function (e.g., one example here concerning the jaws of trap-jaw ants: https://evolution.berkeley.edu/evo-news/quick-bites-and- quirky-adaptations) Exaptation does NOT imply that evolution is goal oriented, nor that it anticipates future needs or uses of a trait – natural selection can only improve a trait in the context of the current environment – have a look at the section on ‘Misconceptions about natural selection and adaptation” here: https://evolution.berkeley.edu/teach-evolution/misconceptions-about-evolution/#b2. It’s very good. 6 Exaptation example Feathers on birds did not evolve for flight! – birds evolved from theropods, bi-pedal meat-eating dinosaurs – feathers evolved long before flight – Read: Origin of birds, pp 787/795 (3rd/4th editions) Campbell (better: HHMI video at end of lecture) Archaeopteryx; Fig. 34.32 Campbell 3rd ed. 7 Fig. 4.31, Emlen & Zimmer (2020) Making Sense of Evolution; W.H. Freeman  Acclimation / acclimatization A process by which an individual organism adjusts to a change in its environment to minimize the effect of stressors and to maintain performance Generally, relatively rapid and reversible; changes are not heritable Contrast with the process of adaptation: heritable phenotypic change in population across generations occurring via natural selection for improve performance in their environment Remember – individuals cannot evolve, only populations/species. Changes within an individual due to acclimation do not alter an individual’s genotype and so are not passed on to offspring 8  Acclimation / acclimatization example At ~2,100m the O2 partial pressure is insufficient for normal saturation of hemoglobin in human blood, leading to shortness of breath, altitude sickness, and other effects Acclimation – over several days to weeks, a range of physiological changes occur that improve performance; these are reversible at lower altitude Changes include elevated haemoglobin concentration, increased red blood cell count, and higher resting ventilation Mount Everest 9 By shrimpo1967derivative work: Papa Lima Whiskey 2. CC BY-SA 2.0 https://commons.wikimedia.org/w/index.php?curid=18262217  Acclimation / acclimatization example High altitude human populations have also adapted to these conditions Human populations vary in how they have adapted to high-altitude environments: – Tibetans: deeper breaths, faster breathing cycle, greater pulmonary capacity Sherpa family from Nepal. and increased blood flow; lower (not higher) hemoglobin concentration By: Gac at Italian Wikipedia, CC BY-SA 3.0 – Andeans: increased alveolar surface area in lungs, increased hemoglobin concentration and higher oxygen capacity in each red blood cell But there is also remarkable convergence across human populations and some domestic animals in some of the genes and biological pathways involved, although the alleles differ La Riconada, Peru (5,100m elev.) Hildegard Willer, CC BY-SA 4.0, via Wikimedia Commons Video correction : I should have said that adaptation of Tibetans was fast and evidence suggests it has occurred as fast as 3,000 years (not 10 generations)!  Practice Human skulls have several major bones and the junctions between them are called sutures. In human babies, sutures are flexible early in life, and this is thought to be an adaptation to allow the skull to be compressed for passage through a tight and convoluted birth canal. The birth canal in other species of vertebrates is wider and less convoluted and their skulls do not compress, yet all vertebrates have sutures. What does this suggest about the origins of this presumably adaptive trait in humans (i.e., identify and briefly explain the concept; 1-2 sentences; 2 marks). 11 Outline 5.1 What is/isn’t adaptation 5.2 Detecting adaptation 5.3 Evolution of complex adaptations 5.4 Adaptation isn’t perfect / constraints on adaptation 12 Adaptationist fairy tales Adaptationist fairy tale (‘just-so’ story) - an untested and unsupported ‘explanation’ for the adaptive value of a phenotype, arising from an assumption that most traits are adaptations that evolved via natural selection for their current function (the ‘adaptationist program’) A spandrel Radim Scholaster, CC BY-SA 3.0 Spandrels appear to have been designed to house fine paintings, but in fact are simply an architectural by-product Adaptationist fairy tales are not uncommon in science and are rampant in popular science and among the general public – E.g., the documentary video on land crabs says that their flat body is an adaptation to fitting between the closely spaces leaves of the bromeliads in which they live 13  Detecting adaptation Demonstrating that a trait is adaptive requires: – determining its function, and…. – showing that this function increases fitness in its current environment Red-billed oxpeckers Charles J. Sharp, CC BY-SA 4.0 Seemingly obvious explanations can be dangerously seductive; ‘conventional wisdom’ can be wrong. Recall topic 1 and the conditions for knowledge acquisition: scientists should be skeptical and need to be guided by the EVIDENCE. No explanation should be accepted in the absence of supporting evidence; in the absence of evidence, it is an (untested) hypothesis E.g., oxpeckers on large animals P. Weeks (1999) 14 https://doi.org/10.1093/beheco/11.2.154  Detecting adaptation A hypothesis concerning the adaptive value of a trait is saying that natural selection favours the trait due to fitness benefit it provides via some function More specifically, selection should be directional, favouring further Paedophryne amauensis ‘exaggeration’, or stabilizing to maintain current values Rittmeyer et al. 2012. PLoS ONE 7: e29797. CC BY 2.5; DOI: 10.1371/journal.pone.0029797 Previously discussed methods for detecting natural selection can therefore be used: – Direct measurement: i.e., observational studies of the association between variation in phenotypes and variation in fitness – Manipulative studies can also be used 15  Hosken (1998) https://doi.org/10.1007/s002650050529 Comparative method Seeks to correlate trait differences among populations or species with variation in a presumed selective agent (e.g., differences in biotic or abiotic environments) Pattern: testes size (relative to body size) varies among bat species Hypothesis: larger relative testes size is an adaptation to sperm competition And because sperm competition is more likely in species that live in larger groups… Prediction: a positive association among species between group size and relative testes size Test: observational study exploring quantifying any association between testes size and group size across bat species Inference: hypothesis is supported 16 Little red flying foxes; Mdk572, CC BY-SA 3.0,via Wikimedia Commons  Reciprocal transplant Recall: local adaptation occurs when populations diverge due to natural selection adapting them to differences in their local environments Can be tested via a reciprocal transplant experiment in which fitness of individuals is quantified in each of the two environments; local adaptation makes a clear prediction: population 2 population 1 fitness Site 1 Site 2 17 Reciprocal transplant example – oldfield mice Light colour in gulf coast beach mice is largely due to two mutations: single amino acid change in melanocortin-1 receptor (Mc1r) that causes it to produce less pigmentation mutation in Agouti that causes increased interference with Mc1r expression Hypothesis: different coat colours are adaptations to reducing predation in their different habitats Prof. Hopi Hoekstra Harvard Univ. Modified in part from “Evolution by Natural Selection in Oldfeld Mice”. 2019. National Center for Case Study Teaching in Science, Univ. at Buffalo, State Univ. of New York. 18 Images: Bedford & Hoekstra, eLife 2015;4:e06813 doi: 10.7554/eLife.06813 Reciprocal transplant example – oldfield mice Hundreds of life-sized clay models, half dark and half light, placed in each habitat Wait for predators to attack (models are quickly discarded once predators realize they aren’t real) Gather all models and tally attack rates by model colour and habitat type: Vignieri et al. (2010) https://doi.org/10.1111/j.1558-5646.2010.00976.x 19 Outline 5.1 What is/isn’t adaptation 5.2 Detecting adaptation 5.3 Evolution of complex adaptations 5.4 Adaptation isn’t perfect / constraints on adaptation 20  Complex adaptations Adaptations do not have to be complex; e.g., internal parasites often have extremely simple body structures but are nevertheless very well adapted to their environment Liver fluke But natural selection can and does also produce very complex structures I, Flukeman, CC BY-SA 3.0, via Wikimedia Commons Complex adaptations often consist of interdependent parts that cannot work their own, leading to the suggestion of divine creation (i.e., Paley’s watchmaker) We now understand these to have been built, bit by bit, over (sometimes long) periods of time, with various intermediate yet adaptive steps along the way – Exaptation can also contribute (e.g., feathers in birds) 21 Complex adaptation example – the eye Various intermediate stages in the development of a complex eyes can be seen among extant organisms Limpets Planaria 1Alejandro Sánchez Alvarado, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=2748648 Nautilus ©Hans Hillewaert See excellent videos in Additional resources 22 Fig. 25.29, Campbell Biology, 3rd Canadian Edition. 2021. Pearson  Complex adaptations - exaptations Complex structures can be co-opted from existing structures or molecular/developmental pathways – E.g., treehoppers are a group of insects characterized by bizarre helmet-like structure – helmet structure resembles wings in certain keys ways and key genes that affect wing development impact helmet formation in treehoppers – wings were originally found on T1 in insects, were later suppressed, and at some point treehoppers co- opted this developmental pathway for helmet production 23 Research: Prud’homme et al. 2011. Nature 473:83-86 Images: Moczek 2011. Nature 34-35 https://doi.org/10.1038/nature09977 https://doi.org/10.1038/473034a  Practice Hyperlink (click here), or: Q60: Detecting adaptation. 24 Outline 5.1 What is/isn’t adaptation 5.2 Detecting adaptation 5.3 Evolution of complex adaptations 5.4 Adaptation isn’t perfect / constraints on adaptation 25  Darwinian demons An ‘ideal’ organism that would simultaneously maximize all aspects of fitness; it would begin breeding immediately after birth, produce many large offspring, and continue to do so indefinitely with no decline in performance. Why don’t we see Darwinian demons? I.e., why do we see imperfections in adaptation (or maladaptation)? 1. Selection on acts on existing variation – variation may be lacking for some certain phenotypes/adaptations – this suggests simply a waiting game 26  2. Historical constraints Natural selection modifies phenotypes that are the product of past evolution; an organism’s evolutionary history can impact future evolution E.g., mammalian laryngeal nerve – tetrapods evolved from lob-finned fish which grow a series of nerve branches that run from their brain, over certain blood vessels, to their gill Recurrent laryngeal nerve arches within their gill pouch (a direct, efficient route) Wedel. 2011 https://doi.org/10.4202/app.2011.0019 – in adapting to life on land, tetrapods lost functional gills and the gill pouch evolved new functions, but remained innervated by the same nerve that loops around those blood vessels – As tetrapod morphology evolved, this resulted in cases of monumental inefficiency of design that only make sense when examined in the evolutionary context of their ancestors 27  3. Functional trade-offs Traits can serve multiple functions and the optimal design for one function may differ from that for another function Also Fig. 41.10 in Campbell 28 Modified from DOI: 10.1126/science.282.5393.1455  3. Trade-offs in investment Traits can also be costly to produce and maintain, but organisms have only finite energy budgets; resources invested in one are therefore unavailable for another # inflorescenses/plant in 2nd season Meadow grass Two different James Lindsey at Ecology of Commanster, CC BY-SA 2.5, via populations of Wikimedia Commons meadow grass R. Law. 1979 https://doi.org/10.1086/283361 29 # inflorescenses/plant in 1st season  4. Environments change Natural selection lacks foresight; it arises from variation in survival and reproduction in an organism’s current environment and previously adaptative traits may no longer be so in a different environment An organism's environment includes other organisms with which it interacts (e.g., predators vs. prey, herbivores vs. plants, parasite vs. host, host vs. pathogen) Natural selection acts on these organisms as well, often favouring traits that allow them to ‘win’ interactions and hence diminishing adaptation in the other species Robertson et al. 2013. 30 http://dx.doi.org/10.1016/j.tree.2013.04.004  5. Other evolutionary processes may matter Genetic drift (including bottlenecks & founder events), gene flow, and recurrent mutation are also evolutionary processes These are not linked to variation in fitness (i.e., they do not produce adaptation), and they can cause some maladaptation. For example: – recurrent gene flow into a population from surrounding populations may reduce or prevent local adaptation – a founder event may cause the loss of genetic variation, hampering adaptation; or it may cause a deleterious mutation to increase in frequency or even fix – genetic drift may cause the increase in frequency of a deleterious allele, or a decrease in frequency of a beneficial one 31  Practice Hyperlink (click here), or: Q61 on maladaptation. 32  Topic 5: Additional resources Readings in Campbell Biology: – 25.6 - ‘Evolution is not goal oriented’ & ‘Evolutionary novelties’, pp 578-579 – ‘Origin of birds’ within 34.5 (pp 787) – Mouse coat colour: Fig. 1.24 and accompanying ‘A Case Study in Scientific Inquiry: Investigating Coat Colouration in Mouse Populations’ (pp. 18-20) Documentary on Jamaican land crabs (section about the bromeliad crab starts at 29:20): https://www.youtube.com/watch?v=un9jpbKuZi4&t=1830s Excellent HHMI video on the origin of birds and feathers: https://www.youtube.com/watch?v=z4nuWLd2ivc Coat colour in mice: – Prof Hoekstra explains her work: https://www.youtube.com/watch?v=5UkxNkuc_OY – HMMI video about a near identical example in another species, the rock pocket mouse: https://www.biointeractive.org/classroom-resources/making-fittest-natural-selection-and-adaptation A great video on complex adaptations: the evolution of the eye (featuring Richard Dawkins): https://www.bbc.co.uk/programmes/p00cdlsj A fabulous online resource about misconceptions concerning natural selection and adaptation (and lots of other material as well): https://evolution.berkeley.edu/teach-evolution/misconceptions-about-evolution/#b2 33