Phenological patterns from two sympatric subspecies of the palm Geonoma cuneata (H. Wendl. ex Spruce) and their gall inductor Contarinia geonomae (Gagné)

Abstract

Geonoma cuneata is a variable species with eight subspecies and one of two palms worldwide with a gall record. In this species, staggered flowering has been suggested as a possible mechanism to explain its reproductive isolation from sympatric subspecies. In this study, we examined the phenology of two G. cunea­ta subspecies and their gall inductor, Contarinia geonomae, in the Caribbean lowlands of Costa Rica. For 207 consecutive weeks, we monitored the phenology of 79 G. cuneata individuals and recorded the outcomes of 434 inflorescences in terms of abortions, fruit, and gall success. We analyzed phenological patterns, checked for seasonality and synchrony, and evaluated the effects of precipitation and temperature on each phenophase. The reproductive outcomes of the two subspecies were compared in terms of abortions of the inflorescences and the development of fruits or galls in the infructescences. Both subspecies were mainly seasonal and showed a clear overlap in all phenophases during the four years of study. However, seasonality and synchrony were very well marked in G. cuneata subsp. cuneata whereas G. cuneata subsp. procumbens was characterized by lower synchrony and higher abortion rates. Emergent inflorescences were influenced by average temperature, while flowering was influenced by monthly rainfall and average temperature. More­over, the peak flowering occurred just after the end of the dry season, whereas ripe fruits peaked at the end of the rainy period. Ripe fruits showed higher levels of synchrony and were the only phenophase in which the mean date did not differ among subspecies. This was partly explained by the higher number of abortions and lower fruiting success of individuals flowering outside the peak period. Instead, such indi­viduals are more likely to have infructescences with galls and higher loads. Flowering convergence did not support phenology as a mechanism of reproductive isolation. However, an extended combination of time from flowering to fruiting in both subspecies benefits the gall inductor by providing an extended period of oviposition and adult emergence.