CHAPTER 2. EVOLUTIONARY ECOLOGY Evolutionary ecology studies the evolution in populations of organisms. It is questioned if different phenotypes lead to differences in biological efficacy and how that affects the distribution of phenotypes in the following generations. 1) CONCEPT OF ADAPTATION AND ACCLIMATION Adaptation: the process of change by which an organism or species becomes better suited to its environment. This is an evolutionary process so it is permanent and takes long time. Acclimation: is a form of adaptation that an organism undergoes when transferred to a different habitat. It doesn’t take as long as evolutionary adaptation and it doesn’t affect the body composition of the entire species. Adjustment is made by modifying physical reactions to environmental changes, like shivering when exposed to cold weather. This process is temporary. High altitude plants are better adapted to frost days than tropical plants. Correct High altitude plants reduce their adaptation to cold during summer and re adapt again over winter. It’s incorrect because and adaption can not be changed in a short period of time After treating corn plants with heavy shade for 1 month, these adapted to the lack of light increasing their chlorophyll concentration. Incorrect, it isn’t an adaptation, it’s an acclimation. Since antibiotics are used in medicine, a number of bacteria have antibiotics that have acclimated, gaining resistances. Incorrect Humans are adapted to summer’s high UV-B radiation. They acclimate by increasing the melanine concentration in the epidermis after exposition to UV-B. Correct. 2) CONCEPT OF FITNESS The fitness of an individual animal is a measure of its ability, relative to others, to leave viable offspring. The fittest individual is not necessarily the strongest, fastest, or biggest. A genotype's fitness includes its ability to survive, find a mate, produce offspring and ultimately leave its genes in the next generation. Biologists have long worked in evolutionary processes and they have been able to demostrate the adaptation of a big poblation. In 1976, before the drought the birds had small beaks, some had medium sized beaks, and others had large beaks In 1978, after the extremely drought, smaller and larger beaks being more common. The ecological explanation for this outcome was that the drought resulted in a less food for the finches, which led to a large proportion of the population dying of starvation. However, proportionally more large hard seeds were produced than small soft seeds, and birds with larger beaks were better able to crack these open than birds with smaller beaks. Thus, birds with larger beaks had a selective advantage, even if a large proportion of these still died. So, the size of the beaks got bigger, there was a increase in the average size of the trait. Evolution can act on behaviour traits, morphological traits, physiological traits, anatomical traits, etc. 3) WHAT IS BIOLOGICAL EVOLUTION? Evolution is the change on the genetic composition of populations (proportion of genotypes). The evolution of a population entails the diversification of organisms with time. Microevolution: Change of populations of a given species throughout time (shorter time scales) Macroevolution: Change of species throughout time (longer time scales). Don’t confuse with speciation! Speciation is the fact that two isolated populations of a same species transform to two different species. Microevolution is all about how it does people differs from each others. The speciation can be considered as the link between microevolution and macroevolution. 4) DRIVERS OF EVOLUTION If we exclude dispersion and mutation, the main drivers of population evolution are: Natural selection: some genotypes get selected over others due to differences in survival, growth and reproduction (the phenotypes expressed are selected) (individuals show differences in FITNESS in any given environment). Sexual selection: some genotypes get selected over others due to differences in ACCESS to reproduction (the phenotypes expressed are selected). The consequences of the two processes is that individuals in a population vary in the number of viable offspring they produce from one population to the next. Both types of selection (natural and sexual) affect the phenotype of individuals but the consequences affect the proportion of genotypes in the population. Genetic drift: is a mechanism of evolution in which allele frequencies of a population change over generations due to chance (randomly). The three drivers of evolution can act at the same time. 5) REQUIREMENTS FOR EVOLUTION BY NATURAL SELECTION There must be genetic variation in the population for that trait Can you have evolution in clonal populations? Variation is a precondition to selection: without genetic variation there can be neither selection nor evolution. The population must produce more descendents that can survive (leads to competition) (Difficult to see evolution by natural selection in a decreasing population) The best adapted individuals (a given trait value) leave proportionally more offspring alive and with reproductive capacity than the rest (we say that the “selected individuals” have “higher fitness”) Genetic variation for a given trait must be heritable: How do we measure heritability? Traits with high heritability: body size, cream content in milk, egg weight, start date egg laying Traits with low heritability: fecundity: nº offspring 6) UNITS OVER WHICH NATURAL SELECTION ACTS (DIFFERENT TO INDIVIDUAL) Gametes: Gametic selection Ej: sperm, pollen grain Family groups: altruistic behaviour is driven by kin selection (suggested to explain altruistic behaviours in family groups) It’s contradictory with theory evolution because it was not focusing on an individual competing with others to have more offspring. The actor (giver) increases its fitness significatively The actor (giver) incurs low costs The actor (giver) and receptor (benefited) are kin: I will help who can help me in the future Fitness = direct fitness + indirect fitness (The organism's genetic success is believed to be derived from cooperation and altruistic behaviour) Group selection: no close family ties The population “uncountiously” maintains a consesus not to reach maximum reproductive potential and hence avoid competition for resources. 7) SEXUAL SELECTION Selective process (deterministic), responsable for the evolution of some traits, given the advantage of some individuals exclusively in relation to their access to reproduction (mating). - In dioecious species females tend to invest more in reproduction than males. - Thus, female reproductive success (offspring alive for the next generation) is limited by their capacity to produce eggs (and care for the offspring) - Male reproductive success is determined by the total number of eggs they can fertilize, given that male gametes are much cheaper to produce: CONFLICT OF INTERESTS, sexes have different strategies (priorities) to maximize their reproductive success. Consequence: females tend to be more selective when mating to get the maximum quality possible for their offspring mating with and “adequate” male, whilst males compete for mating with as many females as possible. Sometimes the roles are inverted and it is the males the ones that are selective, and the females the ones that compete for males: IT ALL DEPENDS ON WHO MAKES THE HIGHEST REPRODUCTIVE EFFORT. Intersexual: males compete selection to attract the female’s attention: she actively chooses her mate Intrasexual selection: the female allows the winner of a combat or contest mate with her or the male that is a better resource provider. In some species, intrasexual selection happens not just before copulation: SPERM (competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction) and INFANTICIDE (killing of young offspring by a mature animal of the same species so that the female can be able to reproduce faster with the winner) There can be conflicts between sexual and natural selection… However, often sexual selection entails selection for individuals of higher genetic quality / higher overall fitness. 8) CONCEPT OF GENETIC DRIFT OR SAMPLING ERROR AND THE FOUNDER EFFECT Topics to prepare for the scientific poster in the seminar session o What is genetic drift? o When does it happen and when is relevant for populations? o What is the founder effect? o Consequences for conservation and population viability 9) CONCEPT OF ECOTYPE Population within a species which is genotypically adapted to specific environmental conditions. 10) APPLICATIONS OF EVOLUTIONARY ECOLOGY Manage populations for increased reproductive success Manage populations for desired sex ratios Manage populations for desired trophy sizes To understand the consequences of invasive species RESUMEN: What are the requirements for a population to evolve? - Genetic variation: we need mutations, without mutation there wouldn’t be genetic variation, and without variation there would be no evolution. Natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation, and environment can act on this. - Selection: after genetic variation, selection can act on this population. It’s a competition between individuals leading to a better performance of some groups and worst performance from others. - Migration or gene flow is a very important source of genetic variation because gene comes to a population where those gene previously didn’t exist. - Genetic drift: it’s the other main force. In each generation, some individuals, just by chance, leave behind a few more descendents (and genes, of course) than other individuals. The genes of the next generation will be the genes of the "lucky" individuals, not necessarily the healthier or "better" individuals. There is a lack of understanding of what evolution is. People in general think that evolutionary time scales are long and ecological time scales are short. People thought that if you look at species in the environment we can no see them change. There was a dichotomy between genetics and ecologists that disappeared when they realized that evolution takes place in short time scales as well. The Breeder’s ecuation is a good way to see what evolution works but it’s not ideal for predicting evolutionary changes in natural populations, it goes generation by generation which is very limiting because when we think about evolution, we think about hundreds or thousands generations. If we study evolution or we study cuantitative genetics we need to know what the ecological pressure is. The R is the response to selection. It can refer a response in a morphological trait, in a physiological trait, etc. When response is 0 (heritability or selection is 0) means that after many generations the trait does not change. The breeders select two parents that have beneficial traits to reproduce (artificial selection). They can select: - Morphological traits heavier individuals - Physiological traits number of eggs, milk production - Life-history traits the time they start to breed, when they die, when they stop growing… - Behaviour traits loud call in birds A physiological trait, like the total number of eggs or the total offspring of an individual, involve behavior because that individual must found a mate. h is heritability: the ability to transmit the information of your phenotype to your offspring. You need to have heritability in that trait. The proportion of the phenotypic variation in a quantitative trait in a population that is attributable to genetic variation (differences in genotype). If we have heritability for a trait there is a positive relationship between the value of the trait in the parents and the value of the trait in the offspring. S is selection, that can be measured in many ways but here it’s focus in the measure of the phenotype. Selection can be the selection of the breeder, the natural selection (to survive) or the sexual selection (compete with others of the same specie in order to reproduce). Now we know how evolution works through natural selection. You know that natural selection in reality, at the end of the day, is about the total number of copies that individuals leave. The number of copies that individuals leave must be stronger related with survival, the time they live. Evolution occurs in direction of response the trait when there is heritability and selection. If selection is positive, after negative and so on we don’t have evolution. Traits may be linked with treads-off. A trade-off exists when one trait cannot increase without a decrease in another. One trait increase performance (fitness) while decreasing performance in another. For example, being big gives you some advantages in life but being big means you need more food and present a bigger target to predators. Being small means that you don't need much food and can hide easily but it makes it easier for another animal to eat you. Genetic correlations can be either positive or negative, which reflects the direction of the relationship between the two traits. A negative genetic correlation indicates that as one trait increases, the other trait tends to decrease. For example, individuals that in general invest more in reproduction tends to invest less on somatic grotwh or immune defense. A trade-off occurs when an organism wants to do two different things, but has a limited amount of some important resource. The resource could be time, calories, vital nutrients, or many other things. A simple example from everyday life would be trying to buy both a television and a bike with a limited amount of money. You can’t afford an expensive television AND an expensive bike. You would ideally want both an expensive bike and an expensive television, but you are limited by a resource: money. Trade-offs in biology work similarly, but often the mechanism or the resource are not fully understood. To biologists, this often takes the form of the observation that species rarely exhibit ‘perfect’ combinations of traits that are evolutionarily important, such as lifespan and reproductive rate. Some species, such as elephants, are very long lived, but reproduce very slowly. Other species, such as mice, reproduce extremely rapidly, but are also short-lived. An ideal combination from an evolutionary perspective would be to live a very long time and also have lots of kids really fast. Nevertheless, this is rarely seen in nature. There are many examples of traits that are similar involved in trade-offs, such as brain size, muscle strength, and growth rate. Essentially, any trait that is important in fitness but requires some limited resource will likely exhibit trade-offs.
