THE LOCATION OF LANDMARK LEKS IN THE SMALL HEATH BUTTERFLY, COENONYMPHA-PAMPHILUS - EVIDENCE AGAINST THE HOT-SPOT MODEL

Two major theories have been developed to explain the location and evo lution of leks. According to the hot-spot model leks are male initiate d and occur because males aggregate at locations of maximum female hom e range overlap. The alternative female preference model, on the other hand, assumes that leks are female initiated, and that females prefer to mate with males that aggregate. Small heath butterfly leks are sit uated close to landmarks such as trees and bushes in open grassland. C ensuses of wild populations and experiments with artificial landmarks showed that their attractiveness increased with height and width measu red at the middle of tree height. Landmark width at field layer height was negatively correlated with attractiveness, which suggests that a comet shape is preferred to a pyramid shape. Together these landmark s ize variables explained 60% of variation in lek size. Release experime nts showed that landmarks were approached by receptive virgin females, but mated females were indifferent to them. Landmark use was correlat ed to microclimatic conditions. Males preferred wider landmarks during cooler weather. They also competed for the lee side of landmarks. The re was no correlation between the location of landmarks and the disper sion of mated females or emergence sites of females. Hence, receptive female dispersion was largely determined by their mate-locating behavi or, which in turn appeared to result from male dispersion. Leks may in itially have developed around easily detected visual cues that offered a more suitable microclimate for male activity. Females visiting thes e locations would find a suitable mate more rapidly and save valuable time for oviposition. Although nonadaptive evolution cannot be exclude d, taken together the results support the female preference model for lek evolution.