8/19/2013. What is convergence? Topic 11: Convergence. What is convergence? What is convergence? What is convergence? What is convergence?

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1 Topic 11: Convergence What are the classic herp examples? Have they been formally studied? Emerald Tree Boas and Green Tree Pythons show a remarkable level of convergence Photos KP Bergmann, Philadelphia Zoo (adult ETB) Several patterns are conflated into convergence: True All mean slightly different things Being clear on definitions is important Phylogenetic term Previously defined as the similarity of a character between taxa due to convergence However, it includes: True convergence Reversal Parallelism These have similar effects on phylogeny reconstruction Photos KP Bergmann, Philadelphia Zoo Snake-like Adults with gill slits Pough et al. 2004, Fig 3-1 When evolution switches A recently evolved character is lost A recently lost character is re-evolved Independent evolution of similar traits in related lineages whose common ancestor did not share that trait (Futuyma 1986) Lerista (Scincidae) Example: Bachia digit loss and reevolution Derived species tend to have 5 digits is ancestral Digit loss Digit gain Parallelism generally involves a homologous Generally closely related lineages (not always) This has not been tested in Lerista, but is likely Kohlsdorf & Wagner 2006; Photo E Alzate Greer

2 Independent evolution of similar traits in independent lineages, often by Difference from parallelism can be blurred when two taxa evolve to be more similar to one another than their ancestors were to each other (Stayton 2008) A B C Root D E F G H How is convergence viewed? Phylogeny Confounds ability to accurately reconstruct phylogeny A mistake in coding? Biology in general Adaptation by different taxa to similar situations A phylogenetic perspective is important to studying it A B A B C D E F G H C D E F G H Stayton 2008 Stayton 2008 What kinds of patterns does convergence result in? Pattern 1: Two different taxa converging What we typically think of as convergence Pattern 2: Two The two taxa may be quite different in some ways, similar in others Stayton, 2006; Photos KP Bergmann, Philadelphia Zoo Stayton, 2006; Photo Pattern 3: Two different taxa evolving Parallel evolution, but NOT necessarily parallelism The are convergent, even if the phenotype is not More typical of very unrelated taxa (?) What pattern of convergence are each of these examples? Why? Pufferfishes and horned lizards? Tail as a fat storage organ Suite of morphological & behavioral traits Stayton, 2006; Photos??, PJB Photos PJB, KP Bergmann, Philadelphia Zoo 2

3 8/19/2013 convergence? convergence? What are the herp examples? Snake-like body form (BE & LR) in squamates Fossoriality Has evolved independently Has occurred in two ways, but within each, we still have convergence Fusion of skull What pattern of convergence? Examples: Small relative head size Limited cranial kinesis Feed on smaller prey than non-fossorial relatives Gymnophiona Amphisbaenia Scolecophidia What pattern is this? Brandley et al. 2008; Bergmann Adhesive pads on digits Evolved 3 times in squamates Scales modified to have fine keratinous hairs called Same mechanism of action ( forces) Also seen in some inverts, like tarantulas Gekkonidae Clinging ability increases with & Skinks are poor clingers for their body mass pads are smaller, less effective Anolis Prasinohaema What pattern is this? Photos: KP Bergmann, USDA, Afco Zoo Supplies; Graph: Irschick et al Photos: KP Bergmann, USDA, Afco Zoo Supplies; SEMs: Williams and Peterson, Iguanidae and Agamidae New & Old World, respectively Ecological analogs look very similar Many instances of convergence Adaptation to Perhaps a lizard s shape can be modified in only certain ways Iguanidae and Agamidae More examples What pattern do we see here? e.g. a laterally flattened tail may be the easiest way for a lizard to adapt to swimming Photos K Bergmann, K Derby Photos: PJB, K Bergmann, Pough et al., E Rudolph 3

4 Iguanidae vs. Agamidae Most of these examples are relatively slight examples of convergence Phrynosoma & Moloch horridus is more complex Slow-moving Have micro-grooves that allow them to gather water in dry deserts Phrynosoma vs. Moloch Similar morphology Both eat ants Different from generalist lizards No body lunge Faster tongue protrusion Faster feeding cycle Don t process prey Photos: PJB, J Meyers Meyers and Herrel 2005 Reduction in shell defenses in insular giant tortoises Independent evolution of a saddle-backed shell in the Mascarine islands Similar patterns on Galapagos, Aldabra Herbivory in lizards Comparison of skull shape Comparing to non-herbivore sister group Herbivores tend to move towards a common area of morphospace, relative to sister groups Herbivores tend to evolve skulls with higher mechanical advantage What pattern is this? Austin and Arnold 2001 Stayton 2006 Unrelated rock-dwelling lizards have a flat body and long limbs Live on vertical rock surfaces Seen in: Petrosaurus (Phrynosomatinae) Platysaurus (Cordylidae) Pseudocordylus (Cordylidae) Anolis bartschi (Polychrotinae) Some tropidurines Convergence in saxicolous lizards In general, saxicolous taxa have evolved: Petrosaurus has evolved a shallower head, but not longer limbs PC-2: Head depth Has this body shape evolved along the branch on the phylogeny that also led to saxicoly? PC-1: Limb length Photos Branch, Kober Revell et al

5 Convergence? mtdna sequence phylogeny Ecomorphs evolved multiple times on different Greater Antillean islands Does this represent convergence? Need to look at the morphology Convergence? Anolis ecomorphs Morphometric data, distance clustering Each ecomorph clusters separately from others in morphospace Convergence is going on, but what pattern? From Losos et al., 1998 From Losos et al., 1998 Convergence? Anolis ecomorphs plays a role Same ecomorphs, but different sequence of evolution do not fall into ecomorphs Irschick et al. 1997; Losos et al.,