Sexual selection and mating systems

Over a century ago, Charles Darwin provided a robust explanation for behavioral and morphological differences between the sexes, the theory of sexual selection. But how can we explain variation, and even discrete morphs, within a single sex of a single species? A major focus of our lab is to explore how variation in social and ecological environment drive flexible mating strategies and phenotypic evolution, using Malurus fairy-wrens in Australia and Papua New Guinea as a study system. This group of birds is ideally suited to this line of inquiry because it is found in a wide range of habitats and exhibits exceptional intra- and inter-specific variability in mating behavior and sexual signals.
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Much of our work to date has been on the Red-backed Fairywren (Malurus melanocephalus) in northern Australia. Males of this highly promiscuous species breed in either dull female-like plumage or in bright nuptial plumage, with very few intermediate types. Bright males are more successful in obtaining extra-pair copulations and have increased reproductive success relative to dull males. Dull plumage reduces aggression from conspecifics, but this does not translate into increased survival. Instead, it appears that dull breeding males are making the best of a bad situation. Male phenotype is not a fixed trait in Red-backed Fairywrens. Rather, most males switch from dull to bright plumage at some point in their lives. This phenotypic switch is triggered by changes in breeding status (from subordinate helper to bright breeder), and appears to be proximately mediated by testosterone production. A core goal of our current research is understanding how hormones, such as testosterone, influence both behavioral and morphological variation in this system. Recent research by recent graduate Dr. Samantha Lantz has expanded on this work by assessing the interaction between habitat quality (as mediated by fire), social organization, hormones, mating system, and sexual signals in Red-backed Fairywrens. Ongoing work by Ph.D. student Sarah Khalil is digging deeper into contribution of the underlying mechanisms behind carotenoid-based signal variation both between individuals and populations.

 

Since 2011, we have worked in New Guinea to study the White-shouldered Fairywren, a close relative of the Red-backed Fairywren that shows remarkable variation in female coloration between populations. This unusual pattern of variation in females (and not males) presents an opportunity to examine the adaptive significance and underlying mechanisms of female ornamentation. In many populations of this species both males and females are ornamented with similar bright plumage (i.e., both sexes are boldly sexes in coloration, though females are less bright than males), whereas in other WSFW populations males are ornamented but females are cryptic brown. Through field-based study, manipulative experimentation, and molecular analyses of different populations with differing degrees of female ornamentation, we hope to resolve the environmental and social correlates, proximate mechanisms, and fitness consequences of variable female plumage in this species. Current Ph.D. candidate Erik Enbody focuses his dissertation research on the behavioral correlates of female ornamentation and the underlying genetic and hormonal mechanisms that influence female ornamentation and dimorphism in this group. Ph.D. student John Anthony Jones is focusing on the influence of testosterone sensitivity in the brain and periphery on the variation in behavioural and phenotypes between and within populations of fairywrens.
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Related Publications

2017

Enbody E.D., S.M. Lantz, and J. Karubian. 2017. Production of plumage ornaments among males and females of two closely related tropical passerine bird species. Ecology and Evolution. 00:1-11 doi 10.1002/ece3.3000 PDF

2017

Iverson, E.N.K., and J. Karubian. 2017. The role of bare parts in avian signaling. Auk 134: doi 10.1642/AUK-16-136.1 PDF

2017

Lantz, S.M., J. Boersma, H. Schwabl, and J. Karubian. 2017. Early-moulting red-backed fairywrens males acquire ornamented plumage in the absence of elevated androgens. Emu. doi 10.1080/01584197.2017.1297206 PDF

2016

Lantz, S.M. and J. Karubian. 2016. Male red-backed fairywrens enhance a plumage-based signal via adventitious molt. Auk 133:338-346. PDF

2014

A. Rose, S. Lantz, J. Swaddle, and J. Karubian. 2014. Habitat and Arthropod Relationships Supporting the Red-Backed Fairy-Wren in the Australian Tropical Savanna Dry Season. Tulane Undergraduate Research Journal – Volume 1. PDF

2014

Baldassarre, D. T., T. A. White, J. Karubian,, and M. S. Webster. 2014. Genomic and morphological analysis of a semipermeable avian hybrid zone suggests asymmetrical introgression of a sexual signal. Evolution. doi: 10.1111/evo.12457. PDF

2013

Karubian, J. 2013. Female ornamentation in Malurus fairy-wrens: a hidden evolutionary gem for understanding female perspectives on social and sexual selection. Emu 113: 248-258. doi: 10.1071/MU12093 PDF

2013

Baldassarre, D. T., H. A. Thomassen, J. Karubian, and M. S. Webster. 2013. The role of ecological variation in driving divergence of sexual and non-sexual traits in the red-backed fairy-wren (Malurus melanocephalus). BMC Evolutionary Biology 13: 75. doi: 10.1186/1471-2148-13-75. PDF

2012

Varian-Ramos, C.W., W.R. Lindsay, J. Karubian, and M.S. Webster. 2012. Female red-backed fairy-wrens do not appear to pay a price for high rates of sexual promiscuity. Auk. 129: 529-536. PDF  *Editor’s pick: July issue of Auk

2011

Karubian, J., W.R. Lindsay, H. Schwabl, and M.S. Webster. 2011. Bill coloration, a flexible signal in a tropical passerine bird, is regulated by social environment and androgens. Animal Behaviour 81: 795-800. PDF

2010

Webster, M.S, J. Karubian, and H. Schwabl. 2010. Dealing with uncertainty: flexible reproductive strategies by a tropical passerine bird in an unstable ecological and social environment. Advances in The Study of Behavior 42: 123-153. PDF

2010

Varian-Ramos, C.W., J. Karubian, V. Talbott, I. Tapia, and M.S. Webster. 2010. Offspring sex ratios reflect lack of repayment by auxiliary males in a cooperatively breeding passerine. Behavioral Ecology and Sociobiology 64: 967-977. PDF

2009

Karubian, J., J.P. Swaddle, C.W. Varian, and M.S. Webster. 2009. The relative importance of male tail length and nuptial plumage on social dominance and mate choice in the red-backed fairy-wren: evidence for the multiple receiver hypothesis. Journal of Avian Biology. Journal of Avian Biology. 40: 559-568. PDF

2008

Karubian, J., T.S. Sillett, and M.S. Webster. 2008. The effects of plumage color on aggression and survival in male red-backed fairy-wrens. Behavioral Ecology 19(3): 507-516. PDF

2008

Karubian, J. 2008. Changes in breeding status are associated with rapid bill darkening in male red-backed fairy-wrens Malurus melanocephalus. Journal of Avian Biology 39(1):81-86. PDF

2008

Macedo R.H., J. Karubian, and M.S. Webster. 2008. Extra-pair paternity and sexual selection in socially monogamous birds: are tropical birds different? Auk. 125(4):769-777. PDF

2008

Webster, M.S., C.W. Varian, and J. Karubian. 2008. Plumage color and reproduction in the red-backed fairy-wren: Why be a dull breeder? Behavioral Ecology 19(3): 517-524. PDF

2008

Tori, W.P., R. Durães, T.B. Ryder, M. Anciães, J. Karubian, R.H. Macedo, J.A.C. Uy, P.G. Parker, T.B. Smith, A.C. Stein, M.S. Webster, J.G. Blake, and B.A. Loiselle. 2008. Advances in sexual selection theory: insights from tropical avifauna. Neotropical Ornithology 19:151-163. PDF

2003

Karubian, J. and A. Alvarado. 2003. Testing the function of petal displays in the red-backed fairy-wren. Emu 103:87-92. PDF

2002

Karubian, J. 2002. Costs and benefits of variable breeding plumage in the red-backed fairy-wren. Evolution 56(8): 1673-1682. PDF

2001

Karubian, J. and J.P. Swaddle. 2001. Selection on females can lead to ‘larger males’. Proceedings of the Royal Society of London (B) 268:725-728. PDF

2001

Karubian, J. 2001. Social organization and mating system of the Striated Grasswren. Condor 103:412-418. PDF

2000

Swaddle, J.P., J. Karubian, and S. Pruett-Jones. 2000. A novel pattern of reversed sexual dimorphism in fairy-wrens: implications for sexual selection. Behavioral Ecology 11:345-349. PDF