Finding the nearest relatives of Nasonia (Hymenoptera: Pteromalidae)

Roger Burks

University of California, Riverside

Department of Entomology

What is Nasonia?• Gregarious puparial parasitoids of

calyptrate flies in bird nests and refuse

• Model system, better known than any other species of Chalcidoidea—genome project ongoing

• Three species, each infected by two unique strains of Wolbachia

The three species of Nasonia• Females almost identical (Darling & Werren 1990)

• Males differ in degree of wing reduction

• Nasonia vitripennis worldwide, synanthropic

• N. giraulti in eastern North America, N. longicornis in western North America

– specialized on flies in bird nests

Wolbachia basic background• Bacteria infecting arthropods and filarial nematodes

• Transmitted vertically from mother to offspring (Binnington & Hoffmann 1989)

• Cause crossing incompatibility in Nasonia (Breeuwer & Werren 1990)

• Phylogenetic congruence between bacteria and host usually absent– horizontal transmission?

• May cause rapid speciation in arthropods (Laven 1959, 1967; Breeuwer &

Werren 1990)

How Wolbachia affects Nasonia• Cytoplasmic Incompatibility (Breeuwer & Werren 1990)

– Causes death of offspring of mothers that do not have same Wolbachia strains as the father

• Incompatible crosses:– Uninfected female x infected male– Infected female x male infected by at least one different

strain

• Infection rate near 100% in wild Nasonia– “Cured” colonies used to study Wolbachia effects in lab

Why Nasonia’s relationships still need studying

• Nasonia is a model system for evolutionary biology studies, yet…

• Ancestral states cannot be inferred with only three analyzed species!

• No agreement in classification of wasps in its family (Pteromalidae)

• Needed: means to reject some pteromalids as close Nasonia relatives

Pteromalidae is a scary taxon

• 587 genera in 31 subfamilies

• Pteromalinae with only 283 genera

• Parasitoids of various terrestrial arthropods

• No previous phylogenetic analysis using more than 10 pteromaline genera

• Previous analyses with either morphology only or 28S ribosomal sequences only

Pteromalinae molecular vs. morphological rates of evolution

• 283 genera of Pteromalinae, but...

• 28S D2 sequence divergence equal to that of the genus Aphelinus (Heraty 2004)

• Rapid morphological evolution or ribosomal constraints?

• Rapid evolution due to Wolbachia?

Tools for the search• Morphology

– 105 morphological characters (work in progress)

• 28S D2-D5 ribosomal DNA, Wingless – Secondary structure alignment for 28S (Gillespie et al. 2005) to be compared with POY

results

• Analysis with parsimony (PAUP, TNT, POY), maximum likelihood, Mr. Bayes

• Hypothesis testing with ML using CONSEL

Outgroup selection

• Based on Heraty lab matrix of Chalcidoidea– 28S D2-D5, 18S E17-E35 ribosomal DNA– 471 taxa (including outgroups)– All families, 84 total subfamilies represented

• Subfamilies Diparinae, Ormocerinae are legitimate outgroups for Pteromalinae

Combined 28S and Wingless molecular results, Parsimony (PAUP)

Numbers indicate bootstrap support (1000 replicates)

Agrees with simple POY run in topology

1176 steps in PAUPrci = 0.209ri = 0.403

black = Pteromalinaered = other Pteromalids* = Wolbachia positive

Combined 28S and Wingless molecular results, Mr. Bayes 3.1

Numbers indicate posterior probability

black = Pteromalinaered = other Pteromalids* = Wolbachia positive

6 parameters, 4 chains, partitioned by gene region, 1 million generations

Combined 28S and Wingless molecular results, Likelihood

black = Pteromalinaered = other Pteromalids* = Wolbachia positive

model: GTR+I+Gprogram: PAUP

Testing hypotheses not present in the optimum maximum likelihood tree (500 total sampled trees for test)

constraint tree with: au test p value sh test p value

Nasonia+ Urolepis clade 0.81 1.00

Nasonia + Trichmalopsis + Urolepis paraphyly

0.50 0.85

monophyletic Pteromalinae

0.38 0.80

Nasonia + Trichomalopsis clade

0.23 0.79

monophyletic Trichomalopsis

0.07 0.70

paraphyletic Nasonia 0.01** 0.50

au = approximately unbiased test (Shimodaira 2002)sh = Shimodaira-Hasegawa test (Shimodaira & Hasegawa 1999)

Problem: Not enough variation to have statistical power

Solution: Add a more rapidly evolving gene

Candidates: Long-wavelength Rhodopsin—multiple copies?Pten—contains intron, but shortCytochrome Oxidase I & II—AT richness

Perspective• Trichomalopsis sarcophagae 28S sequence

(>1100 base pairs) differs from that of Nasonia vitripennis by only 1 base pair

• Sampling remains incomplete– Nasonia not well-surveyed in Palearctic region– Trichomalopsis with 54 species!

Trichomalopsis microptera male

They differ by only one base pair in 28S??

Trichomalopsis sarcophagae

Nasonia vitripennis

Further goals• Sequence from more species of Trichomalopsis, other

genera near Nasonia (>120 specimens to be sequenced)

• Finish morphological analysis

• Wolbachia survey across Pteromalinae, comparing bacteria and wasp phylogenies

AcknowledgmentsAdvisory committee:

John Heraty

Richard Stouthamer

Bob Luck

Cheryl Hayashi

Jack Werren

Matt Yoder

Doug Yanega

Serguei Triapitsyn

Lara Baldo

James Russell

Genet Tulgetske

Danel Vickerman

Heraty lab:Dave HawksJohan LiljebladJames MunroJeremiah GeorgeJason MotternChrissy RomeroAdena Why

Jutta BurgerMatt Buffington

Funded by: NSF FIBR: 0328363