Two coexisting tank bromeliads host distinct algal communities on a tropical inselberg

The tank bromeliads Aechmea aquilega (Salisb.) and Catopsis berteroniana (Schultes f.) coexist on a sun-exposed Neotropical inselberg in French Guiana, where they permit conspicuous freshwater pools to form that differ in size, complexity and detritus content. We sampled the algal communities (both eukaryotic and cyanobacterial taxa, including colourless forms) inhabiting either A. aquilega (n = 31) or C. berteroniana (n = 30) and examined differences in community composition and biomass patterns in relation to several biotic and abiotic variables. Chlorella sp. and Bumilleriopsis sp. were the most common taxa and dominated the algal biomass in A. aquilega and C. berteroniana, respectively. Using a redundancy analysis, we found that water volume, habitat complexity and the density of phagotrophic protozoa and collector-gatherer invertebrates were the main factors explaining the distribution of the algal taxa among the samples. Hierarchical clustering procedures based on abundance and presence/absence data clearly segregated the samples according to bromeliad species, revealing that the algal communities in the smaller bromeliad species were not a subset of the communities found in the larger bromeliad species. We conclude that, even though two coexisting tank bromeliad populations create adjacent aquatic habitats, each population hosts a distinct algal community. Hence, bromeliad diversity is thought to promote the local diversity of freshwater algae in the Neotropics.

Genetic isolation between two sympatric host plant races of the European corn borer, Ostrinia nubilalis Hubner. II: assortative mating and host-plant preferences for oviposition

The European corn borer, Ostrinia nubilalis Hubner, colonized maize (Zea mays L.) after its introduction into Europe about 500 years ago and is now considered one of the main pests of this crop. In northern France, two sympatric host races have been described: one feeding on maize and the other on mugwort (Artemisia vulgaris L.) and hop (Humulus lupulus L.). In a previous study, we showed that mating between the two races may be impeded by differences in the timing of moth emergence and in the composition of the sex pheromone produced by the females. In this study, we further investigated the genetic isolation of these two races using strains from the maize (Z strain) and mugwort (E strain) races selected for diagnostic alleles at two allozyme loci. In a cage containing maize and mugwort plants and located in natural conditions, mating between individuals of the same strain occurred more often than mating between males and females of the E and Z strains. In particular, we obtained no evidence for crosses between Z females and E males. We also found that females of the Z strain laid their eggs almost exclusively on maize, whereas females of the E strain laid their eggs preferentially, but not exclusively, on mugwort. These results suggest that the genetic differentiation between the two host races may also be favored by host-plant preference, one of the first steps toward sympatric speciation.

Carbon stable isotopes: a tool for studying the mating, oviposition, and spatial distribution of races of European corn borer, Ostrinia nubilalis, among host plants in the field

The European corn borer, Ostrinia nubilalis (Hübner, 1796) (Lepidoptera: Crambidae), is a polyphagous corn pest species that includes two host races: one feeding on corn (Zea mays L.) and one feeding on mugwort (Artemisia vulgaris L.) and hop (Humulus lupulus L.). Being able to determine the type of host plant on which field-caught moths fed as larvae would allow for the quantification of mating rates within and between races, as well as the quantification of the spatial distribution and oviposition of both races in the field. We found that stable carbon isotopes (δ;13C) are a reliable indicator of host-plant photosynthetic type (C3 or C4) regardless of adult food and intensity of metabolism; so even when food or metabolism had a significant effect on wing δ13C values, the magnitude of this effect was too small to obscure the signal characterizing host-plant type. Egg and spermatophore δ13C values similarly reflect female and male host-plant type, respectively, regardless of adult feeding. We found 224 host-plant species of O. nubilalis in the literature, including 19 species with C4-type photosynthesis. However, in temperate areas, corn is probably the only significant C4 source of adult moths. Accordingly, wing δ13C values were more variable in field-caught moths showing a typical C3-type δ13C value than in those showing a typical C4-type δ13C value.