The influence of light, substrate and seed origin on the germination and establishment of an ant-garden bromeliad.

Plant germination and development depend upon a seed's successful dispersal into a suitable habitat and its ability to grow and survive within the surrounding biotic and abiotic environment. The seeds of Aechmea mertensii, a tank-bromeliad species, are dispersed by either Camponotus femoratus or Neoponera goeldii, two ant species that initiate ant gardens (AGs). These two mutualistic ant species influence the vegetative and reproductive traits of the bromeliad through their divergent ecological preferences (i.e. light and substrate). We hypothesised that the seeds dispersed by these two ant species have underlying genetic differences affecting germination, growth and survival of A. mertensii seedlings in different ways. To test this, we used an experimental approach consisting of sowing seeds of A. mertensii: (i) taken from the two AG-ant associations (i.e. seed origin), (ii) in two contrasting light conditions, and (iii) on three different substrates. Light and substrate had significant effects on germination, survival and on eight key leaf traits reflecting plant performance. Seed origin had a significant effect only on germination and on two leaf traits (total dry mass and relative growth rate). Overall, this bromeliad performs better (i.e. high growth and survival rates) when growing both in the shade and in the carton nest developed by C. femoratus ants. These results suggest that the plasticity of the tank bromeliad A. mertensii is mainly due to environment but also to genetic differences related to seed origin, as some traits are heritable. Thus, these two ant species may play contrasting roles in shaping plant evolution and speciation.

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.

The organization of artificial heterospecific ant colonies. The case of the Manica rubida/Formica selysi association: mixed colony or parallel colonies?

We studied the spatial and social organization of homospecific and heterospecific colonies of two ant species Manica rubida (Myrmicanae) and Formica selysi (Formicinae) reared without a queen in artificial nests. We used a method based on individual labelling and automated photographic recording of data. The two species, which are forced to live together in the same artificial mixed colony, show the same spatial organization as they do in control homospecific colonies. The Manica rubida were mostly clustered in one chamber while Formica selysi workers were spread throughout the nest. Formica selysi individual spatial profiles are very heterogeneous while in the other species they are very homogeneous. By using taxonomical techniques on behavioural data we show that the two species within the mixed colony are clearly distinguishable. An artificial association of these two species may therefore be considered to be a juxtaposition of two colonies functioning in parallel, rather than a "mixed colony".

An automated photographic technique for behavioural investigations of social insects.

We describe a technique based on automatic photography as an alternative to the visual scanning method for behavioural investigations of insect societies. This technique opens up the possibilities for studying poorly-populated colonies over prolonged periods. The reliability of this technique as compared to the direct observational method was demonstrated on the basis of an investigation of the social organization of a neotropical Ponerine ant (Ectatomma ruidum ). The results obtained by the two techniques were very comparable both in regards to the overall behavioural profiles for the colony and as concerns the description of functional groups and sub-castes.