Comparison between the anatomical and morphological structure of leaf blades and foliar domatia in the ant-plant Hirtella physophora (Chrysobalanaceae)

Background and Aims: Myrmecophytes, or ant-plants, are characterized by their abilityto shelter colonies of some ant species in hollow structures,or ant-domatia, that are often formed by hypertrophy of theinternal tissue at specific locations (i.e. trunk, branches,thorns and leaf pouches). In Hirtella physophora (Chrysobalanaceae),the focal species of this study, the ant-domatia consist ofleaf pouches formed when the leaf rolls over onto itself tocreate two spheres at the base of the blade. Methods: The morphological and anatomical changes through which foliarant-domatia developed from the laminas are studied for the firsttime by using fresh and fixed mature leaves from the same H.physophora individuals. Key results: Ant-domatia were characterized by larger extra-floral nectaries,longer stomatal apertures and lower stomatal density. The anatomicalstructure of the domatia differed in the parenchymatous tissuewhere palisade and spongy parenchyma were indistinct; chloroplastdensity was lower and lignified sclerenchymal fibres were morenumerous compared with the lamina. In addition, the domatiawere thicker than the lamina, largely because the parenchymatousand epidermal cells were enlarged. Conclusions: Herein, the morphological and anatomical changes that permitfoliar ant-domatia to be defined as a specialized leaf structureare highlighted. Similarities as well as structural modificationsin the foliar ant-domatia compared with the lamina are discussedfrom botanical, functional and mutualistic points of view. Theseresults are also important to understanding the reciprocal evolutionarychanges in traits and, thus, the coevolutionary processes occurringin insect–plant mutualisms.     

Pollination and Breeding System of two Co-Occurring Hirtella Species (Chrysobalanaceae) in Central Brazil

The phenology, major floral characteristics, breeding systems and fruiting success of two co-occurring species of Hirtella: H. glandulosa and H.gracilipes (Chrysobalanaceae) were studied in Central Brazil. The two species occur as trees in mesophyllous forests but H. glandulosa is frequent also in dense savanna areas. Both species flower at the end of the dry season (September) and have flowers with one-day longevity. In both species flowers produce nectar and are pollinated exclusively by butterflies. The number of visits recorded and pollination rate in each species were significantly different and indicate that pollinators prefer H. glandulosa flowers. Natural and controlled fruit sets were low in both species. The index of self-incompatibility (ISI) was 0.17 in H. glandulosa and 0.86 in H. gracilipes. Although ISI in H. glandulosa could denote an incompatibility system, the presence of fruits with aborted embryos at different degrees of development point to an inbreeding depression situation. Low pollen viability and fruit set in H. gracilipes suggested reproductive problems which may be linked to hybridization events.     

Mechanisms driving the specificity of a myrmecophyte–ant association

In the understory of pristine Guianese forests, the myrmecophyte Hirtella physophora almost exclusively shelters colonies of the plant-ant Allomerus decemarticulatus in its leaf pouches. We experimentally tested three non-mutually exclusive hypotheses concerning phenomena that can determine the species specificity of this association throughout the foundation stage of the colonies: (1) interspecific competition results in the overwhelming presence of A. decemarticulatus queens or incipient colonies; (2) exclusion filters prevent other ant species from entering the leaf pouches; and (3) host-recognition influences the choice of founding queens, especially A. decemarticulatus . Neither interspecific competition, nor the purported exclusion filters that we examined play a major role in maintaining the specificity of this association. Unexpectedly, the plant trichomes lining the domatia appear to serve as construction material during claustral foundation rather than as a filter. Finally, A. decemarticulatus queens are able to identify their host plant from a distance through chemical and/or visual cues, which is rarely demonstrated in studies on obligatory ant–plant associations. We discuss the possibility that this specific host-recognition ability could participate in shaping a compartmentalized plant-ant community where direct competition between ant symbionts is limited.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 90–97.     

The Weaver Wasp: Spinning Fungus into a Nest

Wasp nests range from simple to complex structures made of paper or mud. Here, we show that a Neotropical wasp of the genus Nitela builds its nest entirely by weaving endophytic fungal hyphae and spider silk harvested from the leaves growing in the understory of the rain forest in French Guiana.     

Specific, non-nutritional association between an ascomycete fungus and Allomerus plant-ants

Ant-fungus associations are well known from attine ants, whose nutrition is based on a symbiosis with basidiomycete fungi. Otherwise, only a few non-nutritional ant-fungus associations have been recorded to date. Here we focus on one of these associations involving Allomerus plant-ants that build galleried structures on their myrmecophytic hosts in order to ambush prey. We show that this association is not opportunistic because the ants select from a monophyletic group of closely related fungal haplotypes of an ascomycete species from the order Chaetothyriales that consistently grows on and has been isolated from the galleries. Both the ants' behaviour and an analysis of the genetic population structure of the ants and the fungus argue for host specificity in this interaction. The ants' behaviour reveals a major investment in manipulating, growing and cleaning the fungus. A molecular analysis of the fungus demonstrates the widespread occurrence of one haplotype and many other haplotypes with a lower occurrence, as well as significant variation in the presence of these fungal haplotypes between areas and ant species. Altogether, these results suggest that such an interaction might represent an as-yet undescribed type of specific association between ants and fungus in which the ants cultivate fungal mycelia to strengthen their hunting galleries.