Small-male advantage in the territorial tropical butterfly Heliconius sara (Nymphalidae): a paradoxical strategy?

Large size is often decisive to victory in territorial disputes. Here we report for the first time a natural territorial advantage associated with small size, possibly exemplifying a 'paradoxical strategy' (Maynard Smith & Parker 1976, Animal Behaviour, 24, 159-175) in which small individuals with inferior resource holding power win war-of-attrition contests against superior adversaries because resource value/rate of cost accrual (V/K) is greater for small contestants. Males of the aposematic nymphalid butterfly Heliconius sara that defend scattered mating arenas in subtropical Brazilian forest have wings that are on average 3% shorter than males caught away from territories during any part of the year. Smaller residents tend to return to territories over longer periods, and field experiments show that intruders retreat faster when confronting smaller than average territory owners. Heliconius sara has a second, seemingly much more important mating system in which female pupae attract males pheromonally, and in which large males may be more successful in winning mates. Because it is unlikely that small H. sara have intrinsically superior resource holding power, and because territories should be about equally valuable to all males, we propose that large males, supposedly favoured in pupal mating, may risk losing more in terms of future reproductive success through chance injury in territorial fights (large K) and thus avoid combats with small opponents which risk little from injury because of their diminished mating prospects (small K). Copyright 1998 The Association for the Study of Animal Behaviour