Geographic variation of reproductive traits and competition for pollinators in a bird-pollinated plant

Mycotoxin tolerance affects larval competitive ability in Drosophila recens (Diptera: Drosophilidae)

Certain mycophagous Drosophila species are the only known eukaryotes that can tolerate some highly potent mycotoxins. This association between mycophagy and mycotoxin tolerance is well established because Drosophila species that switch hosts from mushrooms to other food sources lose their mycotoxin tolerance trait without any evolutionary lag. These findings suggest that mycotoxin tolerance may be a costly trait to maintain. In this study, we attempted to identify whether mycotoxin tolerance has a fitness cost. Larval competitive ability is a vital fitness trait, especially in holometabolous insects, where the larvae cannot move to a new host. Furthermore, larval competitive ability is known to be associated with many critical life-history traits. Here we studied whether mycotoxin tolerance adversely affects larval competitive ability on isofemale lines from 2 distinct locations. We observed that the extent of mycotoxin tolerance affected larval competitive ability, but only in isofemale lines from one location. Additionally, we observed that the high mycotoxin-tolerant isofemale lines from the same location showed poor survival to eclosion. This study shows that mycotoxin tolerance is associated with fitness costs and provides preliminary evidence of an association between local adaptation and mycotoxin tolerance.

Geographic variation of reproductive traits and competition for pollinators in a bird-pollinated plant

Geographic variation in the reproductive traits of animal-pollinated plants can be shaped by spatially variable selection imposed by differences in the local pollination environment. We investigated this process in Babiana ringens (Iridaceae), an enigmatic species from the Western Cape region of South Africa. B. ringens has evolved a specialized perch facilitating cross-pollination by sunbirds and displays striking geographic variation in perch size and floral traits. Here, we investigate whether this variation can be explained by geographic differences in the pollinator communities. We measured floral and inflorescence traits, and abiotic variables (N, P, C, and rainfall) and made observations of sunbirds in populations spanning the range of B. ringens. In each population, we recorded sunbird species identity and measured visitation rates, interfloral pollen transfer, and whether the seed set of flowers was pollen limited. To evaluate whether competition from co-occurring sunbird-pollinated species might reduce visitation, we quantified nectar rewards in B. ringens and of other co-flowering bird-pollinated species in local communities in which populations occurred. Variation in abiotic variables was not associated with geographical variation of traits in B. ringens. Malachite sunbirds were the dominant visitor (97% of visits) and populations with larger-sized traits exhibited higher visitation rates, more between-flower pollen transfer and set more seed. No sunbirds were observed in four populations, all with smaller-sized traits. Sunbird visitation to B. ringens was not associated with local sunbird activity in communities, but sunbird visitation was negatively associated with the amount of B. ringens sugar relative to the availability of alternative nectar sources. Our study provides evidence that B. ringens populations with larger floral traits are visited more frequently by sunbirds, and we propose that visitation rates to B. ringens may be influenced, in part, by competition with other sunbird-pollinated species.