Association patterns of swollen‐thorn acacias with three ant species and other organisms in a dry forest of Panama

Host Plant Specificity in Web-Building Spiders

Spiders are ubiquitous generalist predators playing an important role in regulating insect populations in many ecosystems. Traditionally they have not been thought to have strong influences on, or interactions with plants. However, this is slowly changing as several species of cursorial spiders have been reported engaging in either herbivory or inhabiting only one, or a handful of related plant species. In this review paper, we focus on web-building spiders on which very little information is available. We only find well-documented evidence from studies of host plant specificity in orb spiders in the genus Eustala, which are associated with specific species of swollen thorn acacias. We review what little is known of this group in the context of spider-plant interactions generally, and focus on how these interactions are established and maintained while providing suggestions on how spiders may locate and identify specific species of plants. Finally, we suggest ideas for future fruitful research aimed at understanding how web-building spiders find and utilise specific plant hosts.

Scaling of indirect defences in Central American swollen-thorn acacias

Myrmecophytes may adjust the investment on ant rewards, depending on tree size and ant defence level. In swollen-thorn acacias (Vachellia collinsii), we tested whether the level of protection provided by the resident ants (defending vs. non-defending) influenced the relation between tree size and ant rewards, or between types of ant rewards (housing and food). We quantified ant rewards in trees occupied by defending and by non-defending ants. We predicted: (1) a positive relation between plant diameter and ant reward investment, with a steeper slope for defending than for non-defending ant species; and (2) that if there is any tradeoff between ant rewards, it should be aggravated (steeper slope) when inhabited by non-defending ants. We found that most structures for ants grew according to plant diameter, but contrary to our first prediction it was independent of the level of ant defence. Most ant rewards did not show a tradeoff between them, besides a weak negative relation between spine length and number of pinnules, which contrary to the prediction occurred when occupied by defending ants. The evidence shows that the interacting ants had a weaker influence on the scaling of defence structures in myrmecophytes than the habitat (location).

Short-term plasticity and variation in acacia ant-rewards under different conditions of ant occupancy and herbivory

In ant-plant defense mutualisms, plants known as myrmecophytes provide food and shelter to ant partners in exchange for defense against herbivores and pathogens. To ensure interaction pay-off, myrmecophytes must regulate their investment in ant-rewards depending on local conditions and herbivore pressure. We investigated how myrmecophyte investment in multiple ant-rewards relates to herbivory, ant defense, and ant occupancy over time. Specifically, we examined the plasticity of ant-rewards produced by swollen-thorn acacias (Vachellia collinsii) under different ant occupancy and herbivory conditions. We compared food rewards (number of extrafloral nectaries and pinnules as a proxy for food bodies) and housing rewards (domatia dimensions) of V. collinsii for three conditions: (1) occupied (defended by the obligate mutualist Pseudomyrmex spinicola) versus unoccupied trees, (2) occupied trees subject to an experimental herbivory manipulation versus control trees, and (3) trees occupied by different ant species varying in their level of defense (P. spinicola, P. simulans, Crematogaster crinosa). We found that food rewards were more likely to vary in time depending on ant occupancy and resident species. Conversely, housing rewards varied with the condition (occupancy or species of partner) and less through time. A one-time herbivory manipulation did not cause any changes to the ant-rewards produced. Our results reveal short-term plasticity in V. collinsii ant-rewards and demonstrate that myrmecophytes with constitutive rewards can adjust their investment in ant-rewards depending on the presence and identity of ant partners.