photo: Joop Brinkkemper
Click on birds to find out what they are doing!
Click here (1.4 MB, MP3 format) to hear an ancient CBC radio broadcast (Quirks and Quarks) describing my earier work on the ruff
Since 1984, I have studied the ruff, Philomachus pugnax, a sandpiper species which presents particular challenges for behavioral, population and evolutionary biologists because it has a stable genetic polymorphism in male mating behavior. While variation in male mating behavior is widespread among animals, maintenance of a genetic polymorphism - a stable set of competing strategies- is extremely unusual.
Three genetic morphs of males exist in all ruff populations. Darker-plumaged territorial males, comprising 84% of males, defend clustered 'lek' mating courts against other "residents". Lighter-plumaged, non-territorial "satellite" males, 14% of males, are recruited onto residents' courts, where the two form temporary, uneasy alliances, as shown above. Both kinds of males may mate with females that visit the court, and co-occupation appears to result in higher relative mating success for the participants. One percent of males are small female mimics, which lack ornamental breeding plumage (See Biology Letters 2:161-164 (2006)), do not engage in male display, and appear to obtain matings at lek by rapidly mounting crouching females. Males do not change plumage type or behavioral role during their lifetimes.
My co-workers and I have shown that these two morphs really are competing genetic types co-existing within all populations. Morph type inheritance is consistent with two single-locus two-allele autosomal genetic models (Nature 378:59-62, Lank et al. Proc. Roy Soc. Lond B 1999, and Biol. Lett. 9: 20130653. doi:10.1098/rsbl.2013.0653).
Click here to see a sample pedigree.
Since spring of 2006, working with Sue McRae, we bred female mimics, called 'faeders', with females of our captive flock, to test mechanisms of potential inheritance of this morph. The data support autosomal genetic inheritance of this morph, including an expression of the mimic allele in females, which shrinks their body size Lank et al 2013: Biol. Lett. 9: 20130653. doi:10.1098/rsbl.2013.0653 .
Watch three video clips, taken by Dr. McRae, of a resident, satellite,
and a cyptic male in action!
The cryptic male has dark blue bands on the lower parts of both legs, and is in the lower left corner of the first clip. In the third clip,it starts by standing on a brick. Stay tuned for more!!
The plumage variation of Ruffs, which is used for individual identification (see below) is also unique among birds.
Males on the TOP ROW are satellites. The REST are territorial "independents".
My research focuses on determining, at several levels, how and why genetic variation is maintained in a trait so closely associated with fitness. Major activities have included 6 field seasons on breeding grounds in Finland and breeding birds in captivity since 1985. Approaches in these collaborative studies include field observations, genomics, field experiments, hormonal measurement and manipulation, studies of sperm morphology, immunological function and life history, development of behaviour, functions of plumage variation, mate choice experiments, sex allocation strategies, and game theoretical modeling of evolutionary scenarios.
Having established a genetic model for the inheritance of behavior, I wish to analyze the more complex question of genetic models for the inheritance of plumage variation. This is of interest for its own sake, but also in the context of models of characteristics of traits that evolved for use in signalling individual recognition (Dale, Lank, and Reeve 2001: Am. Nat.118:75-86). My success in inducing expression of normally male-limited traits in females allows this analysis to go forward.
Our pedigree data also show that plumage variation is inherited, probably in a multi-allelic, multi-locus fashion. The variation in induced female plumages parallels that of their brothers, confirming that normally unexpressed autosomal genetic variation for plumage type occurs.
The hormone experiments raise issues in the control of behavioral variation. Measurement of circulating testosterone levels from captives, show that that the three male morphs differ in their androgen profiles during the breeding season (Tawna Morgan, M.Sc., Univ Alaska Fairbanks). [ Back to top]
In contrast to most other birds, male Ruffs are silent during their lek displays. The function of identifying themselves appears to have been transferred to a visual modality for which variation is transmitted genetically (Lank and Dale 2001, Auk 118:759-765), rather than by voice. Our pedigree data show that plumage variation is also inherited, although explicit models have not yet been developed.
Experimentally, Laurene Ratcliffe and I showed through plumage manipulations that males use this genetically-based variation to achieve "neighbor-stranger" discrimination, and presumably individual, identification. Many birds use variation in learned song types for this purpose. Future experimental work could test for similar discrimination of males by females.
Postdoc Jim Dale, Kern Reeve and myself developed a series of predictions contrasting the expected properties of signals which evolved to indicate individual identity rather than individual qualilty (Dale, Lank, and Reeve 2001: Am. Nat.118:75-86). Dale and I are currently testing assumptions and predictions of this model in Ruffs, including plumage genetics. Consistent with the model, we have shown that while certain aspects of a males breeding plumage phenotye change with a male's physiological condition, its coloration does not.
I have discovered that a complex plumage difference between territorial and satellites males occurs in non-breeding as well as breeding plumages. In each successive annual non-breeding plumage, satellites only grow more and more prominent white neck rings. The ontogeny of this plumage character is similar to that of "status signalling badges" in other bird species. The behavioral consequences of this are not yet clear, but in captivity, old satellites with such rings are unusually aggressive around food bowls. This suggests that they may have a different territorial or foraging strategy in the non-breeding season from young satellites and all residents. Winter field work in might confirm this speculation. As a direct approach to testing for life history differences, I am promoting tabulation of morph type by Europeans who band ruffs when such morph differences can be scored. However, it will take a long-term effort to generate sufficient data to make reasonable tests for survivorship differences between morphs. [Back to top]
Jim Briske et al. 1997 (Evolution 51:937-945) have shown that among passerine birds, species with higher levels of multiple paternity also have longer sperm. This finding motivated us to examine sperm length in ruff. We found that ruff sperm are ca. 125 microns long, the longest known for any shorebird. This suggests that the relationship found among passerines also applies to shorebirds (Johnson and Briskie 1999: Condor 101:848-854).
Our behavioural, genetic, and sperm morphological findings challenge the generalization that female monogamy will be associated with a high level mate choice, and suggest instead active genetic diversification by females. We found that greater than random cross-morph mating occurs testing against expected frequencies based on several assumptions about the bases of female mate choice with respect to morph (Lank et al 2002: Behavioral Ecology 13:209-215). We are also directly testing the mate preferences of females of known pedigree and/or previously hormone-induced known male phenotype for evidence of assortative mating. The results are relevant to more general theories in sexual selection for the co-evolution of male characteristics and female preferences. [Back to top]
The work stems from previous observations and field experiments showing that female preference for visiting and mating at leks is strong enough to maintain lekking in this species (Lank and Smith: Behav. Ecol. Sociobiol. 30:323-329; BES 20:137-145), despite competition among males favouring greater dispersion (e.g., Widemo and Owens: Nature 373:148- 151). The model explores the consequences of considering the resident-satellite relationship as a "lek within a lek", with territorial and satellite pairings favored by female choice. Remarkably, it is the first model within the alternative male mating behavior literature to ascribe a significant role to females in the evolution of such systems. [ Back to top]
As a direct approach to testing for life history differences, I am promoting tabulation of morph type by Europeans who band ruffs when such morph differences can be scored (J. Jukema, T. Piersma et al.). However, it will take a sustained long-term effort to generate sufficient data to make reasonable tests for survivorship differences between morphs.
As an alternative approach, George Lozono and I (Lozano and Lank 2003: Proceedings of the Royal Society B:27:1203-1208) have tested males of both morphs, and females, for evidence of immunosenescence. We found that a t-cell mediated response decreases between "middle-aged" and elderly birds, and does so more strongly during the breeding season than during the winter, implying a genuine phenotypic tradeoff between reproductive and immunological function. However we do not yet have sufficient data to demonstrate that the two male morphs have different slopes in immunological function with respect to age, as might be predicted if their life histories differ. [ Back to top]