Matt Arnegard, Ph.D.

NIH Post-Doctoral Research Fellow

• Ph.D., Neurobiology & Behavior (2005)
  Cornell University
  

Research Interests | Publications 

Video of electric fish behavior 

Species radiations driven by natural and/or sexual selection are central to evolution of much of Earth's animal biodiversity.  My work aims to understand mechanisms by which new species arise during such radiations.  I am also interested in the diversification of animal communication and mating systems in terms of both proximate mechanisms (sensory and motor) and ultimate evolutionary mechanisms, particularly as they relate to species radiation.  I work on three different fish models:  rift lake cichlids in eastern Africa; weakly electric fishes of Africa and South America; and, most recently, parallel 'benthic' and 'limnetic' species pairs of threespine stickleback in British Columbia, Canada.

Radiographs of 'limnetics' (above) and 'benthics' (below) of the Gasterosteus aculeatus species complex. Reproductively-isolated benthics and limnetics have evolved independently in several isolated lakes of British Columbia. Photos by Matt Arnegard.

Currently, my main project with Katie Peichel and Dolph Schluter investigates the genetic basis of parallel speciation between benthic and limnetic sticklebacks.  Recently, I received postdoctoral NRSA funds from NIH to pursue this project with Katie at the Fred Hutchinson Cancer Research Center in Seattle.  In the Schluter lab, Gina Conte and I have created populations of F2 intercross hybrids between sympatric benthic and limnetic sticklebacks endemic to each of two lakes in British Columbia.  The hybrids have grown up under natural conditions in experimental ponds on the campus of the University of British Columbia (UBC).  We have begun measuring and genetically mapping several traits which have diverged under natural selection due to resource competition or are related to behaviors mediating pre-mating reproductive isolation between benthics and limnetics.  All traits are being measured under fully natural conditions in the ponds at UBC.  By conducting QTL mapping in the Peichel lab, we aim to identify the genomic regions that underlie parallel evolution of reproductive isolation between these species pairs.

Experimental pond facility at UBC. (Left) Nicole Bedford about to help me and Gina Conte make one of our regular collections of eggs from the nests of territorial males in pond #5 during the 2009 breeding season.  (Right) Territorial males guarding nests in their preferred habitats in the same pond, showing realistic, divergent nesting habitats we established in these ponds (Paxton benthic male above, Paxton limnetic male below). Photos by N. Bedford.

In addition to our investigation of the genetic architecture of parallel speciation in threespine sticklebacks, I have recently completed projects on a non-traditional model of vertebrate species radiation, weakly-electrogenic fishes.

In the first of these projects, I have led a collaborative effort to quantitatively compare the relative importance of natural selection on 'ecological traits' to sexual selection on 'signaling traits' during radiation of the Paramormyrops species flock.  In the first quantitative phylogenetic comparison of its kind, we show that sexual selection on electric organ discharges (EODs) - important courtship signals for which there are preferences in the context of mating - has played a key role in the radiation of mormyrid electric fishes.  Owing to well understood features of electrical communication, we also think 'opportunity' for divergence in signal space has contributed importantly to mormyrid radiation.  Mormyrids illustrate that greater opportunity for divergence in an under-exploited signaling landscape (here, the electrosensory communication modality) can promote rapid signal evolution, much like the effect that 'ecological opportunity' has on adaptive radiation.  Collaborators: Pete McIntyre, Luke Harmon, Miriam Zelditch, Will Crampton, Justin Davis, John Sullivan, Sébastien Lavoué, and Carl Hopkins.

One of many assemblages of the Paramormyrops species flock of mormyrids from Gabon, Central Africa. Shown here are the six sympatric species/morphs present in the Okano River at the abandoned Village 'Na'.  Oscilloscope tracings of their electric signals are shown to the right (time scale = 1 msec). Image by Matt Arnegard and Duncan Reid.

EODs result from summed currents of ion channels in the electric organ, which arose independently in mormyriforms in Africa and gymnotiforms in South America.  Recent work by Harold Zakon's group (UT, Austin) suggested that EOD diversification might have been specifically influenced by molecular evolution of a duplicated (skeletal muscle) sodium channel gene, yet relatively few taxa were available for the earlier investigation.  With both paralogs now cloned and sequenced from a much larger number of species, we (myself, Derrick Zwickl, Ying Lu, and Harold Zakon) now have a much clearer picture that the same paralog (Nav1.4a) independently experienced bursts of positive selection in mormyriforms and gymnotiforms immediately after this gene was lost from skeletal muscle and neofunctionalized for expression in electric organ.  This system provides a rare opportunity to ask questions about convergent evolution at the molecular level during independent origins (not loss) of a complex trait: muscle-derived electric organ.  Moreover, electric fish also provide a model for biomedical studies of sodium channel function: radical amino acid replacements caused by diversifying natural selection on Nav1.4a in electric fishes occur at the same residues where deleterious substitutions cause cardiac or neurological disease in humans (e.g., long QT syndrome).

Surprise catch during field work in Odzala National Park, Congo (2006). To the dismay of local fishermen we released the python unharmed. Photo by Pete McIntyre.

Holotype of Otopharynx pachycheilus, another cichlid fish with enlarged, fleshy lips (Arnegard and Snoeks, 2001).  The lips of this fish contain high densities of taste buds. Photo by Matt Arnegard.

   Publications

• Arnegard, M. E., D. J. Zwickl, Y. Lu, and H. H. Zakon. In Prep. Gene duplication underlies origin and diversification of a new communication system, twice.
• Arnegard, M. E., P. B. McIntyre, L. J. Harmon, M. L. Zelditch, W. G. R. Crampton, J. K. Davis, J. P. Sullivan, S. Lavoué, and C. D. Hopkins. In Prep. Sexual signal evolution outpaces ecomorphological and trophic divergence during electric fish species radiation.
• Oliver, M. K. and M. E. Arnegard. In Review. New genus for Melanochromis labrosus Trewavas, a problematic Lake Malawi cichlid with hypertrophied lips (Teleostei: Cichlidae).
• Arnegard, M. E. 2009. Ongoing ecological divergence in an emerging genomic model. Mol. Ecol. 18: 2926-2929.
• Lavoué*, S., M. E. Arnegard*, J. P. Sullivan, and C. D. Hopkins. 2008. Petrocephalus of Odzala offer insights into evolutionary patterns of signal diversification in the Mormyridae, a family of weakly electrogenic fishes from Africa. J. Physiol. - Paris 102: 322-339.
• Lavoué, S., J. P. Sullivan, M. E. Arnegard, and C. D. Hopkins. 2008. Differentiation of morphology, genetics and electric signals in a region of sympatry between sister species of African electric fish (Mormyridae). J. Evol. Biol. 21: 1030-1045.
• Markert*, J. A. and M. E. Arnegard*. 2007. Size-dependent use of territorial space by a rock-dwelling cichlid fish. Oecologia 154: 611-621.
• Arnegard, M. E., B. S. Jackson, and C. D. Hopkins. 2006. Time-domain signal divergence and discrimination without receptor modification in sympatric morphs of electric fishes. J. Exp. Biol. 209: 2182-2198.
• Arnegard, M. E. and B. A. Carlson. 2005. Electric organ discharge patterns during group hunting by a mormyrid fish. Proc. R. Soc. B 272: 1305-1314.
• Arnegard, M. E., S. M. Bogdanowicz, and C. D. Hopkins. 2005. Multiple cases of striking genetic similarity between alternate electric fish signal morphs in sympatry. Evolution 59: 324-343.
• Sullivan, J. P., S. Lavoué, M. E. Arnegard, and C. D. Hopkins. 2004. AFLPs resolve phylogeny and reveal mitochondrial introgression within a species flock of African electric fish (Mormyroidea: Teleostei). Evolution 58: 825-841.
• Arnegard, M. E. and A. S. Kondrashov. 2004. Sympatric speciation by sexual selection alone is unlikely. Evolution 58: 222-237.
• Arnegard, M. E. and C. D. Hopkins. 2003. Electric signal variation among seven blunt-snouted Brienomyrus species (Teleostei: Mormyridae) from a riverine species flock in Gabon, Central Africa. Environ. Biol. Fishes 67: 321-339.
• Arnegard, M. E. and J. Snoeks. 2001. New three-spotted cichlid species with hypertrophied lips (Teleostei: Cichlidae) from the deep waters of Lake Malawi/Nyasa, Africa. Copeia 2001: 705-717.
• Markert, J. A., P. D. Danley, and M. E. Arnegard. 2001. New markers for new species: microsatellite loci and the East African cichlids. Trends Ecol. Evol. 16: 100-107.
• Danley, P. D., J. A. Markert, M. E. Arnegard, and T. D. Kocher. 2000. Divergence with gene flow in the rock-dwelling cichlids of Lake Malawi. Evolution 54: 1725-1737.
• Markert, J. A., M. E. Arnegard, P. D. Danley, and T. D. Kocher. 1999. Biogeography and population genetics of the Lake Malawi cichlid Melanochromis auratus: habitat transience, philopatry and speciation. Mol. Ecol. 8: 1013-1026.
• Arnegard, M. E., J. A. Markert, P. D. Danley, J. R. Stauffer, Jr., A. J. Ambali, and T. D. Kocher. 1999. Population structure and colour variation of the cichlid fish Labeotropheus fuelleborni Ahl along a recently formed archipelago of rocky habitat patches in southern Lake Malawi. Proc. R. Soc. Lond. B 266: 119-130.

*The first two authors contributed equally to these studies.