Morphometric and Osteological Methods

in Ichthyology

Brian SidlauskasNational Evolutionary Synthesis Center

Durham, NC

bls16@duke.edu

Three main types of morphological study

• Study of discrete character variation among species– Phylogenetics– Species delimitation

• Quantification of shape and size variation– Species delimitation– Age and growth studies

• Studies of character evolution– Phylogenetic comparative

methods

Systematics of Anostomidae (Characiformes)Systematics of Anostomidae (Characiformes)

Laemolyta taeniataLaemolyta taeniata

Sidlauskas and Vari 2008, Sidlauskas and Vari 2008, Zoological Journal of the Linnean SocietyZoological Journal of the Linnean Society

Phylogeny Reconstruction

Anostomidae & Chilodontidae (~140 spp.)

High Morphological Diversity

Image credits: B. Chernoff, T. Clark, J. Gery, M. Sabaj, B. SidlauskasImage credits: B. Chernoff, T. Clark, J. Gery, M. Sabaj, B. Sidlauskas

Rhytiodus argenteofuscusRhytiodus argenteofuscusSchizodon fasciatusSchizodon fasciatus

Anatomical differencesAnatomical differences

reveal evolutionary reveal evolutionary

patternspatterns

LeporinusLeporinus cf. cf. ecuadorensisecuadorensisFifth upper pharyngeal tooth plateFifth upper pharyngeal tooth plate

Leporinus mormyropsLeporinus mormyrops Leporinus fasciatusLeporinus fasciatus

Illustrations by Tamara ClarkIllustrations by Tamara Clark

123 morphological characters123 morphological charactersvariable among ingroup orvariable among ingroup or

informative as to anostomid monophylyinformative as to anostomid monophyly

Additional 35Additional 35

informative among outgroupsinformative among outgroups

29 multistate, all unordered29 multistate, all unordered

strict consensus strict consensus

of 1312 treesof 1312 trees

CI = 0.425 RI = 0.805CI = 0.425 RI = 0.805

From Sidlauskas and Vari, 2008From Sidlauskas and Vari, 2008

ParsimonyParsimony

From Sidlauskas and Vari, 2008From Sidlauskas and Vari, 2008

Leporellus most basal Leporinus paraphyletic

(and difficult to resolve

with morphology)

Hypomasticus (in Leporinus) monophyletic

Abramites within Leporinus Rhytiodus with Schizodon

Laemolyta monophyletic and sister to Anostominae sensu

Winterbottom (1980) Anostominae very strongly

supported Monophyly of Pseudanos

uncertain Anostomus paraphyletic New genus Petulanos

ParsimonyParsimony

11 22 33

44 44 55

66 77 88

Consensus Phylogeny from Supermatrix Analysis

Synthesis of 463 morphological characters from 14 studies

171 Species

Analyzed using Parsimony Ratchet via PaupRat (Sikes and Lewis, 2001) and PRAP (Müller 2004)

CU

RIM

AT

OID

EA

AN

OS

TO

MO

IDE

A

From Sidlauskas, in press, Evolution

Species Discovery and Delineation

From Sidlauskas et al. 2005, Copeia

A B

Schizodon isognathusSchizodon isognathus Schizodon kneriiSchizodon knerii Schizodon scotorhabdotusSchizodon scotorhabdotus

new speciesnew species

From Sidlauskas et al. From Sidlauskas et al. Copeia 2007Copeia 2007

Leporinus sp. nov. 1?(Brazil, Southern Amazon tributaries)

Leporinus sp. Nov. 2? (Suriname)

Leporinus cylindriformis, holotype (Brazil, Main Amazon channel)

ALLOMETRY

TraditionalLinear Morphometrics

Geometric Morphometrics

Traditional and Geometric Techniques Often Yield Complementary Answers

PCA for comparing individuals and testing group membershipCVA for recognizing difference between known groups

From Sidlauskas, Vari and Mol, in prep

PC 2 (snout)

PC

4 (

jaw

, do

rsa

l fin

)

-0.25

-0.05

0.15

0.35

-1.0 -0.6 -0.2 0.2 0.6

LOWLAND

HIGHLAND

Ln Centroid Size

RW

1 (

he

ad

, b

od

y d

ep

th)

-0.10

-0.06

-0.02

0.02

0.06

3.0 3.4 3.8 4.2 4.6

LOWLANDHIGHLAND

Highland fishes measurably Highland fishes measurably more streamlined than more streamlined than lowland fisheslowland fishes

Differing allometric Differing allometric trajectoriestrajectories

Consistent with induction by Consistent with induction by growth in fast watergrowth in fast water

Sidlauskas, Chernoff and Machado-Allison 2006, Sidlauskas, Chernoff and Machado-Allison 2006, Ichthyological ResearchIchthyological Research

21 skull landmarks21 skull landmarks 171 species, ca. 1200 specimens171 species, ca. 1200 specimens Analyzed with geometric morphometricsAnalyzed with geometric morphometrics

CurimatidaeCurimatidae

Curimatella alburnaCurimatella alburna

Measuring Measuring

MorphologicalMorphological

DiversityDiversity

From Sidlauskas, 2007, Evolution

Phylomorphospaces

• Relative Warp Analysis of skull shapes yields positions of species in morphospace

• Phylogeny links species

• Squared-change parsimony or likelihood infers position of internal nodes and morphometric distances (Euclidean) between them.

• Species sorted into diet classes based on literature accounts (Herbivore, Invertivore, Detritivore, etc.) and color coded

• Reconstruction of diet at internal nodes

Relative Warp 1

Rel

ativ

e W

arp

2

Sidlauskas, in press, Evolution

Sidlauskas in press, Evolution

Plotting phylogenies into a morphospace

ECOPHYLOMORPHOSPACE

Significance Testing via Simulation

• Simulate morphological evolution– Many possible phylogenies– constant tempo and mode (e.g.

single rate Brownian motion)

• Reconstruct distribution of possible phylomorphospaces

• Determine how often one generates two clades that differ as greatly as the observed

• If A/Cobserved > A/C simulated 95% of the time, then reject the null hypothesis of equal tempo or mode

• Otherwise, real world consistent with two random outcomes of the same process Unequal tempo?: P from 0.29 to 0.65

Unequal modes?: P from 0.01 to 0.05