Domatia morphology and mite occupancy of Psychotria horizontalis (Rubiaceae) across the Isthmus of Panama

Abstract

Leaf domatia are small plant structures in vein axials on the undersides of leaves that are often inhabited by mites of several species. The mites are presumed to benefit the plant because they are predatory or fungivorous. The domatia are thought to provide the mites shelter from predators and changes in relative humidity, and in exchange, the mites protect the plant from small herbivores and fungal spores. Differences in relative humidity can affect food availability, changing the interaction between plants and mites. We examined domatium morphology of the shrub Psychotria horizontalis (Rubiaceae) and its associated mite diversity at three sites along the rainfall gradient of the Isthmus of Panama, during the dry and wet seasons. The dry forest had a domatium morphology consistent with providing greater desiccation protection, with trichomes and a smaller domatium opening relative to domatium size (size/opening ratio). Additionally, this size/ opening ratio was significantly higher in the dry season than in the wet season at all three sites. Mite diversity was highest at the intermediate rainfall site with a large degree of overlap with the other sites, whereas the dry site and wet site shared few mite species. More fungivorous mites were present in the moist forests and more facultative feeders on fungal spores and small mites in the dry forest. The average mite size at each site matched the average domatium size at each site. The dry forest had small mites in small domatia, whereas the moist forests had larger mites in larger domatia. While these data are primarily observational, the site and seasonal differences in domatium morphology and mite diversity are consistent with two main hypotheses: (1) that protection from changes in humidity would be particularly important when humidity was low, such as in the dry forest and during the dry season (2) more fungivorous mites would be found in domatia of the moist forests. The data presented here further highlight the close adaptive relationship between leaf domatia on plants and the mites that inhabit them.

Structural analysis and developmental stages of domatia of Schinus terebinthifolius Raddi (Anacardiaceae)

“…Studies aim at characterizing the morphology and anatomy of the different forms of domatia are rare, and most of them have been mainly dedicated to investigating the ecological relationships involving mites (O'Dowd 1989;Agrawal 1997;Norton et al 2001;Romero and Benson 2004). However, some authors have dedicated themselves to investigating morphoanatomical aspects and the development of the different forms of domatia (Tillberg 2004;Nishida et al 2006;Leroy et al 2008;Leroy et al 2010;Richards and Coley 2012). Solís and Ferrucci (2006) described morphoanatomical characteristics of the domatia of two species of Cardiospermum L. (Sapindaceae) in order to collect data that contribute to the systematic of the genus.…”

Mites on Plants

“…However, although the generalist predator Typhlodromus doreenae did best when domatia were present, an effect of humidity was apparently only at the highest relative humidities tested (70, 98 %) (Rowles and O'Dowd 2009 ). In the fi eld, though, the domatia of Psychotria horizontalis have been shown to vary in a manner that is consistent with providing better protection in dry environments (Richards and Coley 2012 ).…”

“…Across a rainfall gradient in Panama, the domatia of Psychotria horizontalis (Rubiaceae) have smaller openings and more hairs on drier sites and during the dry season at all sites. More fungivorous mites were present in humid sites and more scavenger-omnivores in drier sites (Richards and Coley 2012 ). Therefore, leaf domatia appear to elevate populations of fungivores but whether the plant gains from having herds of these mites roaming its leaves likely various with the fungal species, plant species, and weather.…”

LIMITED SEED DISPERSAL MAY SHAPE GENETIC STRUCTURE OF Hydnophytum formicarum JACK. POPULATIONS IN MANGROVE ECOSYSTEM

“…Once the plant is disturbed, the ants will swarm and fend off the threats. Many ant plant species have adapted their caudexes or tubers and provided shelter and protection for the ant colony associated with them (Heil 2010;Richards & Coley 2012;Gonzalez-Teuber et al 2014).…”