Presented by the Department of Zoology & the Graduate School, University
of Washington

All seminars take
place
4.30pm
132
Hitchcock
(refreshments 4.15)

*************
April 6, 1999

David B. Lank
Department of Biological Sciences
Simon Frasier University

Two sexes, three genders: maintenance of an evolutionarily stable
polymorphism in male mating strategy of ruffs, a European sandpiper.

Male Ruffs (Aves: Scolopacidae: Philomachus pugnax) have a well-known
behavioral dimorphism in territorial behaviour within their lek mating
system, which correlates strongly with the highly variable coloration of
their breeding plumages. Darker-plumaged "resident" males defend
mating courts against other residents, whereas lighter-plumaged,
non-territorial "satellites" insinuate themselves on residents' courts.
Both types of males attempt to mate on courts with visiting females.

Questions: 1) Do the behavioural and plumage variation reflect genetic
differences? 2) Do field data support equal per capita morph-specific
reproductive rates, as expected for a stable polymorphism? 3) How are
equilibrium morph ratios maintained?

Answers: 1) Individuals maintain the same plumage and behaviour type for
life. Pedigree data, including testosterone-induced expressions of male
phenotype in females, support a one-locus, two allele model for the
inheritance of a male's behavioural phenotype.

2) Males of both morphs have approximately equal annual per capita
mating success, but strong skews among males within each morph.
Paternity analyses confirm that mating rates correlate positively with
fertilization rates.

3) Male-male competition occurs both within and between morphs, through
contests for courts on leks (residents only), direct copulation
disruption (both morphs), and more subtle behavioural interactions. A
form of co-operation between morphs, apparently driven by female choice
of mating situations, stabilizes to the system, but frequency-dependant
mechanisms operating to maintain stable morph ratios are unclear.
Females mate unusually frequently for lekking species and most are
fertilized by more than one male. Sperm competition has lead to
production of exceptionally long sperm tails.

I consider four possible rules which might be used with respect to
female choice between morphs: 1) no morph preference, 2) positive or
negative assortment, 3) negative frequency-dependence, 4) mating with
both to bet-hedge. The data, surprisingly, favor bet-hedging. Females
seen mating with more than one male switched between morphs twice as
often as expected, suggesting active bet-hedging. On reflection, we
might have expected an unusual mate choice strategy in a species with
such unusually obviously diverse males.


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