Ruff Project (Philomachus pugnax)

Ruff Project

photo: Joop Brinkkemper

To hear a CBC radio broadcast describing some of my 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. Two kinds of males (OPPS! THREE KINDS OF MALES, SEE BELOW) exist in all ruff populations: darker-plumaged territorial males, which defend clustered mating courts against other "residents" (85%), and lighter-plumaged, non-territorial "satellite" males (15%), which are recruited onto residents' courts, where the two form temporary, uneasy alliances (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, although this conclusion, based on observational study, needs experimental verification. 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 a single-locus two-allele autosomal genetic model (Nature 378:59-62, Lank et al. Proc. Roy Soc. Lond B 1999). Click here to see a sample pedigree. While variation in male mating behavior is widespread among animals, maintenance of a genetic polymorphism - a stable set of competing strategies- is extremely unusual.

BULLETIN! Joop Jukema and Theunis Piersma report that 1/100 males are small "female mimics" that do not grow the usual male breeding plumage or do conventional male displays !!

See Biology Letters 2:161-164 (2006).

Since spring of 2006, working with Sue McRae, we bred these males with females in our captive flock, to test mechanisms of potential inheritance of this morph. The data support genetic inheritance of this morph. 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!!
This MPEG video. also posted on YouTube (search for "Philomachus"), shows a mating and courtship behaviour by a faeder. We had not previously seen courtship from the faeder.

Video showing male behavior by hormone implanted females are linked in the section on hormones, below.

The plumage variation itself, 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".

photos: D. Lank, montage: J. Dale

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 the establishment and maintenance of a breeding captive research flock. Approaches in these collaborative studies include field observations, DNA fingerprinting, field experiments, hormonal measurement and manipulation, studies of sperm morphology, immunological function , development of behaviour, functions of plumage variation, mate choice experiments, and game theoretical modeling of evolutionary scenarios.

Genetic mechanisms

On the genetic front, I wish now to determine whether the single "locus" determining behavioral morph differences also determines the development of the cryptic females. We have obtained ofspring from cryptic males since the spring of 2006, and data obtained thus far support a single locus two allele model, with a faeder domimant allele..

I also wish to determine whether the polymorphism is in fact a chromosomal inversion, as opposed to a single locus. Such karyotype differences occur in a sexually dimorphic case of plumage and behavioural polymorphism in white-throated sparrows, as well as better known cases in Drosophila and other organisms. I can use my pedigreed flock to verify the inheritance patterns of any polymorphisms found. Should a chromosomal polymorphism be found, a long term goal would be to identify the specific genes involved through microdissection and the rapidly improving tools available through molecular biology. Lindsay Farrell is starting as a Ph.D. student in 2007 to pursue molecular behaviour genetics.

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.

Hormonal manipulations and observational studies

We have used testosterone implants to induce normally sex-limited male behavior and plumage morphology in female ruffs, in collaboration with Kathy Wynne-Edwards (Lank et al. 1999: Proc. Roy Soc. Lond B, 266:2323-2330) . For videos showing female behavior first as a territorial resident, and then behaving with a real male like a satellite, click here Both Clips, windows media video format or, Resident - higher quality Quicktime (mov)format, or Satellite - higher quality Quicktime (mov) format, or Resident - higher quality mpg format, or Satellite -higher quality mpg format. The ability to assign phenotypes to females allowed stronger tests of our genetic model (Nature 378:59-62). As predicted, resident males, who are homozygous recessive, produce nearly all daughters that behave like residents, while satellite males, who are nearly all heterozygotes, produce an even mix of both types. Thus, the variation in testosterone-induced behavior of daughters parallels that of their brothers, as expected from our autosomal model.

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, suggest that territorial and non-territorial males differ in their hormonal profiles (Tawna Morgan and Sasha Kitaysky, Univ Alaska Fairbanks). Further studies of this are continuing. [ Back to top]

Development of behaviour

I plan to continue testing for some degree of developmental flexibility in behavioral morph. Having shown that chick growth pattern does not detectably influence morph development (Nature 378:59-62), my next step is to manipulate the first-year social experience of young captive males of known pedigree, looking for any indication of negative-frequency dependent development. [Back to top]

Communication Function of Plumage Variation

The breeding plumages of male ruffs are as variable in colours and patterns as the peltages of a population of domestic cats. Individual males are thus readily identifiable from plumage differences. What is the adaptive function of such extreme plumage variation?

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]

Mate choice studies

How does each morph obtain matings within the context of the lek? Analysis of video sequences of female solicitations in the wild has allowed me to delineate the social contexts resulting in matings by each type of male. A second result from these analyses is a strong inference that females chose at times to mate with particular satellite males. Finally, both the video sequences and behavioral observations of individually marked females show that individual females commonly mate with several males. DNA fingerprint analyses, using a set of 5 hypervariable minisatellite single-locus probes developed from the ruff genome by Terry Burke and co-workers at Leicester (Nature 378:59-62), confirmed that more than half of female ruffs have broods fathered by more than one male (Lank et al 2002: Behavioral Ecology 13:209-215). Such a high level of multiple paternity is an unusual finding for a lek breeding bird (but see Lanctot et al., 1996, Am. Nat. 149:1051-1070). The orginal thoughts about the probable frequency of multiple mating in birds, as proposed by Tim Birkhead and Anders Moller, suggested that copulation rates and multiple paternity should be low in lek breeding species, since females have a high degree of mate choice.

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]

Resident-satellite cooperation?

What is the nature of the relationship between territorial and satellite males? Why should residents recruit satellites? Field workers agree that the highest mating rates occur on courts co-occupied by satellites and territorial males. I am conducting mate choice experiments to establish whether the differences can be attributed to co-occupation per se. This is a crucial assumption of a game theory model of the invasion of satellite acceptance among territorial birds developed by Don Hugie and myself . (Hugie and Lank,1997 Behav Ecol 8:218-225) 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]

Alternative Life Histories?

Do the alternative behavioral strategies correlate with alternative life histories? 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 when food is limited, and quicker to retrieve treats (mealworms) when in competition with age-matched residents. 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 (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]

Evolutionary Ecology of Alternative Strategies versus Phenotypic Plasticity

Ultimately, I would like to understand what ecological context favored the evolution of such a system in ruffs but not in other species of shorebirds or in other lekking birds. Factors allowing for invasion of an alternative strategy have been considered in the game theoretic model with Don Hugie cited above. A second level of question is why alternative strategies, rather than conditional development, have been favored in this species. Unfortunately, the uniqueness of so many characteristics of the species offer little hope that a comparative approach can provide much insight in this respect. Promising applicable paradigms come from the sex determination mechanisms literature, and current theory about the evolutionary ecology of phenotypic plasticity in general. The most basic prediction is that male ruffs should have a high level of predictability in the competitive environment where they will eventually compete for mates. The mobility of males may produce a sufficiently fine grained environment to make this applicable. [Back to top] [ Back to top]