Investing less in their beaks shorter and sturdier

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Investing less in their beaks Shorter and sturdier works better -could be an adjustment of the organism in the presence of the new host -the difference persisted in the lab, and when the bugs were reared on fpgrt or on bv fruit Not caused by phenotypic plasticity Trinidad and Tobago -rivers and streams in northern range are relatively pristine and undisturbed by humans upper reaches and lower reaches are separated by barrier water falls so the cascade down Some fished are found throughout the streams, like the guppies And some are only found in the lower reaches Ecological difference in predation regime from top to bottom -guppies living upstream have small predators that only prey on young guppies -guppies living downstream into oceans encounter larger fishes like the pike cichlid, crenicichla that “eat guppies like popcorn” -this caught the attention of John endler Natural laboratory Started looking at streams and realized high and low predation of the streams Male guppies vary in colour intensity from upper reaches to lower reaches of the river Males from the upper reaches grow to large size and colourful spots Down below males grow to smaller sizes, with smaller spots, and less colourful Females are uniformly cryptic
In the face of big predators, it pays to be hidden, unless you're a male that has to take the chance to show off to a female is this because of predation or are other factors at work? Potential of more corotonoid pigments in foods available to the gupper upstream o Diet has the capacity to make them more colourful Streams change in energy level and canopy cover (amount of shading) John Endlers classic study Field cause (Aripo river) fishes were brought into artificial streams in the greenhouse and created 3 different predator treatments (no predators, rivulus- low effects of predation, crenicichla) Measured male spots (number, size, colour) according to experiment treatment o Over 6 generations male spot number increased in control and rivulus treatments; decreased in crenicichla treatment o Most visible colours (blue & iridescent) went down sharply in the control treatment o Spot size and colour also shifted towards matching gravel under high predation Endler found a part of a tributary (A2) where guppies were absent above a barrier waterfall General conditions were similar to a lower location containing C. alta and other predators (A1) He caught and moved sample of 200 guppies upstream A third location (A3) with the rivulus and guppies was used as a control o After 21 months (15 generations) the introduced fished came to resemble fish at A3 Endler’s transplantation experiments have been repeated by researchers many times not and with a variety of twists Bilateral movement of fishes between predation regimes Communities of predators differ on N and S slopes of the range Studies have shifted to understand how life history strategies change (how their living, how they’re growing, aging, investing in reproduction)

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