Endler's Guppy Fish Selection Study PDF

Modelling of sexual and natural selection based on experimental control of selection pressures Endler’s Investigation of Selection in Guppy Fish Evolutionary biologist John Endler studied wild guppies (Poecilia wingei) in Trinidad where they live in small pools associated with mountain streams. ...

Modelling of sexual and natural selection based on experimental control of selection pressures Endler’s Investigation of Selection in Guppy Fish Evolutionary biologist John Endler studied wild guppies (Poecilia wingei) in Trinidad where they live in small pools associated with mountain streams.  Selection Pressures on Guppy Color Variation “Drab” “Average” “Flashy” Fish with only modest dots Fish with a few spots of color Fish with vivid blue and orange of color near their tails. along their body and tail. splotches along their sides. Endler observed wide variation between the male fish from different pools and even among male fish living in different parts of the same stream. Endler photographed hundreds of guppies and carefully measured their size, color, and the number and placement of their spots. He began to see a strong correlation between where guppies lived in a particular stream and whether the fish were flashy or drab. But what was responsible for these trends in coloration? Models of Endler’s Investigation of Selection in Guppy Fish Use this computer model to simulate John Endler's classic investigation of guppy fish. Manipulate the strength of female preference for flashy males, the number of predators, and the initial number of guppies. What is the impact of predators on the number of spots on male guppies? Use natural selection to explain the results. What is the impact of female preference on the number of spots on male guppies? Use sexual selection to explain the results. Endler’s Investigation of Selection in Guppy Fish Endler found that females prefer to mate with ‘flashier’ males, those with more orange spots on their tail. However, the flashier males may also be more conspicuous to predators and be more likely to be eaten. There are opposing selective pressures on the phenotype of male fish. The more “flashy” a male guppy is, the more likely he will eaten by a predator. Where predators are plentiful, male guppies become increasingly “drab” over generations, pushed by predation pressure toward greater camouflage. The "flashier" a male guppy is, the more likely a female guppy will choose him as a mate, giving him the opportunity to pass his genes along to the next generation. Flashy colors may be easier for female’s to locate and/or bright colors may indicate “good genes” (in the way the strong physique of a human athlete is a direct indicator of that individual's health and vitality). Predation Pressures on Guppy Color Variation Different parts of the streams in which the guppies live have different species of predators. Rivulus “killifish” are found at higher elevation near the beginning of guppy streams. Rivulus are the least voracious of all guppy predators. These predator fish generally eat only young guppies. Pike cichlids are found at lower elevations in the the largest, deepest stretches of guppy streams. Cichlids are the most voracious of all guppy predators; each may eat as many as four or five guppies per day. Models of Endler’s Investigation of Selection in Guppy Fish Use this computer model to simulate John Endler's classic investigation of guppy fish. Manipulate the number of rivulus and pike cichlids to assess how different predators affect the rate of evolutionary change over generations. Why do different predators affect the average number of spots on fish in the population? Predict what happened when Endler moved fish from a habitat with cichlid predators to a habitat in which there were none. Endler’s Investigation of Selection in Guppy Fish In higher sections of Trinidad streams and in experimental fish tanks with low predation, Endler found that strong sexual selection increased the number of the flashy males. Because the dull males were not selected for reproduction, the “dull” alleles were removed from the population. In lower sections of Trinidad streams and in experimental fish tanks he stocked with predators, Endler found that strong predator selection pressure reduced the number of the flashy males. Because the flashy males were preyed upon at a higher rate, they did not survive and reproduce and the “flashy” alleles were removed from the population. Endler’s Investigation of Selection in Guppy Fish Endler transplanted guppies from a source population with Cichlid predatory fish (he took dull-colored males) to a region with less dangerous predators and left them for about two years (~15 guppy generations). When he returned, the transplanted population had evolved into one with brightly colored males; more colored area and more spots. Without hungry predators eating fish, sexual selection favored “flashy” males. Variation within the population had provided the raw material for rapid evolution when the environmental conditions changes.  Scientific Models ◎ You explored two models of Endler’s experiments. Explain observations Models are conceptual representations used to explain and predict Predict future observations phenomena. ◎ Models are developed to explain processes that may Are realistic not be observable or when experimentation is not possible. Why are models used in science? ◎ Models can simplify complex structures and processes. ◎ Models can change the scale of objects that are too big or too small to see at all. ◎ Models can change the rate of a phenomenon; slow it down or speed it up. ◎ Models can help us communicate by simplifying difficult concepts and/or making concepts more tangible. ◎ Scientists use models (e.g. computer models) to make and test predictions and to understand processes that are not visible or easily observed. Types of Scientific Models There are many types of models used in science: ◎ Experimental Models: use of controlled experimental conditions to model processes occurring in complex natural conditions (such as a mesocosm.) ◎ Mathematical Models: the use of mathematical language to describe the behavior of a system. ◎ Computer Models: a computer program which attempts to simulate the behavior of a particular system. ◎ Physical Models: models of structures that can be carried, touched, or held. ◎ Images: pictures, graphs of diagrams developed in an effort to represent a phenomena. ◎ Analogies: a comparison between two things, typically on the basis of their structure and for the purpose of explanation or clarification. Limitations of Models Models have limitations. No model can possibly explain every detail of a phenomena. While a model is a similar substitute for what it represents, it can only relate to some properties of the target, as some aspects of the target must be excluded from the model. Therefore, models are not copies: they are similar to what they represent, but they are not the same as what they represent. A good model must be able to represent as many characteristics of reality as possible, but also be as simple as possible. Limitations of Models ◎ Like anything in science, models come under scrutiny and change over time. ◎ Models can only be as accurate as the current state of scientific knowledge about the phenomenon they describe. ◎ If models tested against experiments or data from observations prove inadequate, they may be modified or replaced by new models. Brooks, R. & J.A. Endler. 2001. Direct and indirect selection and quantitative genetics of male traits in guppies (Poecilia reticulata). Evolution 55:1002-1015. Endler, J.A. 1980. Natural selection on color patterns in Poecilia reticulata. Evolution 34:76- 91. Houde, A. E. 1993. Sex, Color and Mate Choice in Guppies. Princeton University Press.