REPRODUCTIVE CHARACTERISTICS OF THE FLOWER BREEDING DROSOPHILA-HIBISCI BOCK (DROSOPHILIDAE) ALONG A LATITUDINAL GRADIENT IN EASTERN AUSTRALIA - RELATION TO FLOWER AND HABITAT FEATURES

For many insect species, egg and larval substrate characteristics are significantly correlated with interspecific differences in female repr oductive allocation and egg size-number tradeoffs. We tested the hypot hesis that a similar pattern occurred within the Australian drosophili d, Drosophila hibisci that is restricted throughout its life cycle to flowers of species in the genus Hibiscus. These plants occur as small, isolated, normally monospecific stands that should facilitate differe ntiation of the fly populations in relation to specific oviposition an d larval substrates. Data from 38 sites ranging from 20.8 degrees to 3 4.4 degrees S latitude in eastern Australia indicated no relationship between female body size, egg size, or ovariole numbers and floral siz e or mass among four species of Hibiscus. However, the flies did show a latitudinal dine in ovariole number that was independent of floral v ariation. Females averaged 15-20 ovarioles per female in the south (32 -34 degrees S latitude) and 10-12 ovarioles in the north (21-22 degree s S latitude). The increase in ovariole number with latitude was due t o divergence in the ovariole number of the largest females. In contras t, small females in the north and south had the same number of ovariol es. Reproductive allocation of female flies in the northern region was less than females in the southern region. The latitudinal divergence in ovariole number was not associated with habitat differences (densit y of trees, density of flies and beetles), nor with differences in flo ral characteristics (flower weight, petal length, yeast species presen t). Short term weather patterns in daily temperature and rainfall prec eding collections partly explain the variation in ovariole number. The se observations in conjunction with preliminary genetic results sugges t the cline is associated with genetic differences that interact with environmental determinants such as the temperature during larval devel opment. (C) 1997 The Linnean Society of London.