BYU diversification

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Convergent evolutionary divergence across environmental gradients DeWitt Lab Evolutionary Ecology Dept. Wildlife & Fisheries Sciences Texas A&M University


One question: From whence did organic diversity arise? Explanation 1: It arose spontaneously from the ashes as the mythical phoenix. Explanation 2: Stochastic and deterministic ecological factors drove (and are driving still) the evolution of alternative forms.


One constant in the universe: things change A consequence of environmental change is that organisms adapted to any one environment soon find themselves in another (and environmental change is the stuff of creation)


I. Predator gradients A. Gambusia affinis (Texas, USA) B. Gambusia hubbsi (Bahamas) C. Poecilia reticulata (Trinidad) D. Brachyrhaphis rhabdophora (Costa Rica) E. Pseudocrenilabrus multicolor (Uganda) II. Other (flow, diet and habitat structure gradients) A. Biotodoma wavrini (Venezuela) B. Bryconops caudomaculatus (Venezuela) C. Leiostomus xanthurus (Gulf of Mexico) D. Gambusia affinis (Texas, USA) Road Map to the Talk


I. Predator gradients A. Predator gradient in Gambusia affinis (Texas, USA) 6 populations - 3 with predators - 3 without predators 410 individuals Gambusia affinis (Mosquitofish) Bluegill Green Bass Longear

How we measured body shape: 

1 2 3 4 5 6 8 9 10 7 How we measured body shape Capture images of organism Digitize landmarks Use geometric morphometrics to analyze and visualise shape change across predator gradients


-3 -2 -1 0 1 2 3 1 2 Predator Effect Canonical Axis NP1 NP2 NP3 P1 NP1 NP2 NP3 P3 P2 P1 Females Males P2 P3 MANCOVA results: Predator regime, Population (Predator regime): P < 0.0001 95% confidence centroids Predator-associated divergence in G. affinis

New powers of visualization!: 

New powers of visualization! Exaggerated caudal region, smaller body/head, more elongate with predators Using canonical scores from MANCOVA magnified 3X. Predator-free Predators


Functional consequences? Do predator-assoc. shapes enhance escape ability? Increases escape scores Canonical scores & velocity × distance (R2 = 0.39, P = 0.023, N = 13) Do predator-assoc. shapes come with a cost? Higher endurance swimming. Canonical scores & endurance swimming (R2 = 0.38, P = 0.024, N = 13) Performance trials by David Gonzales and Mark Belk


2 populations Gambusia hubbsi Atlantic needlefish Great barracuda Tarpon I. Predator gradients B. Predator gradient in Gambusia hubbsi (Bahamas)


4 populations - 2 with predators - 2 without predators Poecilia reticulata (Guppy) Crenicichla Astyanax Hemibrycon I. Predator gradients C. Predator gradient in Poecilia reticulata (Trinidad)


Morphological Divergence G. affinis G. hubbsi P. reticulata Predator Effect Canonical Axis P P P NP NP NP (29% of shape variance) MANCOVA Predator regime, P < 0.0001 Pop (Pred regime), P < 0.0001 DFA: 72% correct 95% confidence centroids


Shared and unique partitioning MANCOVA Predator regime: P < 0.0001 Pop (Pred. regime): P < 0.0001 Using “species-free” residuals Submitted to American Naturalist Denied! 


But they liked the idea, so… We threw out all the data We collected new fish We changed our morphometric methods We changed our statistical model We changed guppies for Brachyraphis


I. Predator gradients D. Predator gradient in Brachyrhaphis rhabdophora (Costa Rica) Brachyrhaphis rhabdophora Parachromis dovii Rhamdia sp.


Shared predator response Shared predator-free response Shared and unique partitioning (all 3x)


I. Predator gradients E. Predator gradient in Pseudocrenilabrus multicolor (Uganda) Nile perch (Predatorius horribilis) P. multicolor


Predator-associated divergence in P. multicolor “Averaged” image: In collaboration with Lauren Chapman (U. Florida) Lakes without Nile perch Lakes with Nile perch (3×)


II. Other (flow, diet and habitat structure gradients) A. Flow gradient in B. caudomaculatus B. Flow gradient in B. wavrini Orinoco River (Venezuela) – Note the channel and lagoon structure


Flow-associated differentiation A. B. (3×) Submitted, Biol. J. Linn. Soc.


Images prepared by warping a single fish image with thin-plate-spline transformation grids (magnification of 3×) Shape of spot from structured habitat Shape of spot from barren habitat II. Other (flow, diet and habitat structure gradients) C. Alternative habitats in Leiostomus xanthurus (Gulf of Mexico)


II. Other (flow, diet and habitat structure gradients) D. Diet variation in Gambusia affinis (Texas, USA)


Trophic differentiation: CA1


Trophic differentiation: CA2 Neg Surface (T) Pos Benthic(B)


-0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 -0.5 0.0 0.5 1.0 C H Genetic differentiation MANCOVA: P < 0.03 Central Hensel Hensel Park predator free surface & midwater prey Central Park predators benthic prey Population CA


Genetic & phenotypic axes are very similar


Some thoughts on what it means… Predator induced indirect plasticity?

Future Directions: 

Future Directions Functional significance (performance trials, selection gradient analyses…) Plasticity vs. genetics (common garden rearing experiments, molecular genetics…) 3-D geometric morphometrics Financial support from Other organisms: red drum, annual killifish, haplochromines, characins, clupeids, tadpoles, turtles, snails, crayfish, Neurospora…

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