{"id":182206,"date":"2015-04-10T14:30:51","date_gmt":"2015-04-10T17:30:51","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/?p=182206"},"modified":"2015-09-02T12:01:43","modified_gmt":"2015-09-02T15:01:43","slug":"theory-under-construction","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/theory-under-construction\/","title":{"rendered":"Theory under construction"},"content":{"rendered":"

\"\"Marcelo Cipis<\/span><\/a>When a newspaper article depicts a newly discovered dinosaur hunting in the middle of a prehistoric forest, it’s hard to believe that the whole animal may have been reconstructed from a single tooth.\u00a0 But this is often the case.\u00a0 In part, this is possible because the proportions among body parts remain mostly unchanged across a wide range of organisms due to the concerted action of certain traits.\u00a0 \u201cEvolution plays with building blocks, remodeling living beings as if they were ‘Living Legos’,\u201d says biologist Gabriel Marroig from the Biosciences Institute of the University of S\u00e3o Paulo (IB-USP).<\/p>\n

His group at the Mammal Evolution Laboratory has been researching the workings of that game, by studying how different species of animals transmit these \u201cbuilding blocks\u201d from one generation to the next.\u00a0 But their most recent advance, which in some ways serves as a basis for other projects, did not focus on actual species: it came from theoretical simulations on a computer.\u00a0 The master’s research results of biologist Diogo Melo showed that the emergence of new evolutionary blocks of grouped traits requires a little push from natural selection \u2013 a push that evolutionists call directional evolution, as described in a paper published in January 2015 in the journal PNAS<\/i><\/em>.<\/p>\n

To exemplify, Marroig mentions the stable ratios of size and shape between mandible and maxilla, respectively the bones of the lower and upper jaw that anchor the teeth of most mammals.\u00a0 For an animal to obtain and chew food efficiently, these bones must be proportional.\u00a0 Because their function \u2013 namely, eating \u2013 is essential for survival, variations in the size of one part will necessarily trigger changes in the other.\u00a0 In other words, the lower and upper jaw bones make up a single building block, in terms of evolution.\u00a0 \u201cUnless it suddenly started raining baby food,\u201d the researcher conjectures.\u00a0 \u201cIn such case, it might be better for the animal to have a larger lower jaw in relation to its maxilla, which would allow it to effortlessly collect the food falling from the sky.\u201d\u00a0 Using the Lego analogy, evolution would have to create new blocks instead of reshaping existing ones.<\/p>\n

\"Genetica_Fapespgenetica2altaMarcelo Cipis<\/span>Whimsical as it may be, the example is not far from the truth.\u00a0 Like the shape of Lego blocks, which doesn’t vary much, the cranial structure of mammals is also extremely stable.\u00a0 The work of Marroig and Melo shows that a strong selective pressure \u2013 like a change in the type of food available and how it can be obtained \u2013 will cause the module to be broken down and a new one to be established within a few generations.<\/p>\n

This modularity exists because the relationship between genes and traits is rarely as simple as what is taught in school.\u00a0 There is usually a direct relationship between a specific gene and a given trait.\u00a0 But there can also be variations, in any direction, connecting groups of genes and blocks of traits \u2013 thus the modules.<\/p>\n

Complexity<\/b><\/strong>
\nBy running the simulations for weeks at a stretch, Melo managed an unprecedented feat in the search for understanding how these blocks appear: he created a scenario in which 10,000 generations of a population were subject either to different kinds of natural selection or to no selective pressure at all.\u00a0 More importantly, this theoretical evolution involved over a thousand genes, responsible for dozens of traits.\u00a0 \u201cAll studies published up to now were based on two-trait systems,\u201d says Melo.\u00a0 He and Marroig decided to invest in a multi-dimensional, more life-like scenario despite the immensely greater computational effort it would require.\u00a0 This was made possible by spending a quarter of the funding for Marroig’s project on a powerful server, whose use is shared with other researchers.<\/p>\n

\"Genetica_Fapespgenetica3altaMarcelo Cipis<\/span>By testing different types of natural selection, in addition to a selection-free scenario in which genes appear or disappear randomly within a population (a process known as genetic drift), the simulations showed that actual processes seen in nature can only be replicated by combining two types of natural selection: directional and stabilizing.\u00a0 Directional selection favors the survival of organisms whose traits are advantageous in a changing environment \u2013 such as a protruding lower jaw when food starts raining from the sky.\u00a0 The presence of this type of selection was a necessary condition for new blocks of traits to appear in the simulated populations.<\/p>\n

After a period of directional selection, stabilizing selection entered the scene.\u00a0 This second type of selection confers an advantage on organisms that preserve a given trait across generations.\u00a0 What was new becomes the norm.<\/p>\n

Although the experiment was based on simulated populations in a computer program, its conclusions mirror the empirical results Marroig obtained in previous studies, such as in his research on the evolution of body size in Neotropical monkeys (see Pesquisa FAPESP<\/i><\/em> Issue No. 141<\/a>), as well as current work conducted at the laboratory.<\/p>\n

Melo’s work emphasizes the importance of an idea that usually gets little attention in evolutionary biology: epistasis, or the influence that some genes have on others.\u00a0 \u201cEpistasis is the ugly duckling of genetics and evolution, but it has started to play a central role,\u201d says Marroig.\u00a0 The concept of epistasis has only been discussed for the past 20 years, which is not enough time to give it much space in the specialized textbooks.\u00a0 But according to Marroig, it explains most genetic variations found today in nature.\u00a0 This makes sense: when each of a thousand genes controls a single trait, their scope of action is limited.\u00a0 But if they operate through various combinations of the pieces available in the genetic repertoire, the possibilities increase considerably.\u00a0 This explains how evolution can react to environmental changes after just a few generations by breaking down old building blocks and creating better-suited ones.\u00a0 \u201cThings are not as linear as biologists usually imagine,\u201d concludes the researcher.<\/p>\n

Project<\/strong>
\nModularity and its evolutionary consequences (11\/14295-7<\/a>); Grant mechanism:<\/b><\/strong> Thematic Project; Principal investigator:<\/b><\/strong> Gabriel Marroig (USP); Investment:<\/b><\/strong> R$1,006,189.94 (FAPESP).<\/p>\n

Scientific article<\/em>
\nMELO, D. and MARROIG, G. Directional selection can drive the evolution of modularity in complex traits<\/a>.\u00a0 PNAS.\u00a0 <\/b><\/strong>V. 112, No. 2, pp. 470-75.\u00a0 Jan. 13, 2015.<\/p>\n","protected":false},"excerpt":{"rendered":"Natural selection creates groups of traits that vary in unison","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[209,231],"coauthors":[95],"class_list":["post-182206","post","type-post","status-publish","format-standard","hentry","category-science","tag-biology","tag-evolution"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/182206","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=182206"}],"version-history":[{"count":0,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/182206\/revisions"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=182206"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=182206"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=182206"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=182206"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}