Harnessing ant defence at fruits reduces bruchid seed predation in a symbiotic ant–plant mutualism

Abstract

In horizontally transmitted mutualisms, mutualists disperse separately and reassemble in each generation with partners genetically unrelated to those in the previous generation. Because of this, there should be no selection on either partner to enhance the other's reproductive output directly. In symbiotic ant-plant mutualisms, myrmecophytic plants host defensive ant colonies, and ants defend the plants from herbivores. Plants and ants disperse separately, and, although ant defence can indirectly increase plant reproduction by reducing folivory, it is unclear whether ants can also directly increase plant reproduction by defending seeds. The neotropical tree Cordia alliodora hosts colonies of Azteca pittieri ants. The trees produce domatia where ants nest at stem nodes and also at the node between the peduncle and the rachides of the infloresence. Unlike the stem domatia, these reproductive domatia senesce after the tree fruits each year. In this study, I show that the tree's resident ant colony moves into these ephemeral reproductive domatia, where they tend honeydew-producing scale insects and patrol the nearby developing fruits. The presence of ants significantly reduced pre-dispersal seed predation by Amblycerus bruchid beetles, thereby directly increasing plant reproductive output.

Litter type and termites regulate root decomposition across contrasting savanna land‐uses

“…Perhaps this signifies the importance of other root traits delineating termite and microbial species differences. For instance, polyphagous wood‐litter termites’ preference for dung increases with higher carbon to nitrogen ratio, while microbe preference is for the opposite (Freymann et al 2008, Sitters et al ). Meanwhile for bamboo stems, both termite and microbial decomposition are negatively related to increasing woody density with termites even consuming thicker bark to obtain less dense stems (Liu et al 2015).…”

“…grazing regime) (Anderson et al 2007; see root traits in Supplementary material Appendix 1 Table A2) and finally pooled across provenances. Living and dead roots were collected from soil–vegetation turfs 20 cm deep, washed free of adhering soil, air‐dried, pooled and then coarsely chopped before being packed into litterbags (Smith et al ). A sub‐set of pooled root material was retained to determine morphological and physiochemical traits and nutrient contents.…”

“…A double layer of 1 mm stainless steel mesh was used to exclude larger Macrotermitinae species from half of all litterbags. Unfortunately, on collection this metal mesh had partly or completely disintegrated in almost all locations, so the presence or absence of termites was determined by visual observation of holes in litterbags and sheeting (and sheeting fragments) surrounding root material, the soil cast made by termites during foraging (Sileshi et al 2010, Sitters et al , Veldhuis et al 2017). Termite presence was further quantified by scanning all litterbags to estimate percentage area of holes.…”

Seed predation food web, nutrient availability, and impact on the seed germination of Senegalia tenuifolia (Fabaceae)

“…Frequently, Crematogaster species are observed forming small satellite colonies on plants to keep themselves close to ephemeral food sources, such as extrafloral nectaries (Lanan et al, 2011), organs that are present on the studied plant species. Some studies have detected a positive effect of ants on plants (Rosumek et al, 2009), frequently because ants play an indirect defense role, driving off organisms that could feed on the host plant's seeds (Perry et al, 2004;Pringle, 2014). Thus, M. ruszkii and Crematogaster sp.…”

“…We determined these relationships between Bruchinae and parasitoids based on the comparison of Bruchinae larvae remaining mouthparts between those that successfully developed and those that were parasitized. We also used literature data to help us determining these relationships (Janzen, 1969;Southgate, 1979;Johnson & Siemens, 1997;Graham, 1987;Macêdo & Monteiro, 1989;Hanson & Gauld, 1995 Triana & Ravelo, 2007;Bonet, 2008;Chavarría, Hanson, Marsh, & Shaw, 2009;Rosumek et al, 2009;Perry et al, 2004;Fusu, 2009;Lanan, Dornhaus, & Bronstein, 2011;Rossi, Rodrigues, Ishino, & Kestring, 2011;Pringle, 2014). In order to estimate nutrient availability and C:N balance of S. tenuifolia seeds and fruits we grounded fruits and seeds and sent them to the Laboratory of Leaf Analysis at the Federal University of Lavras for chemical analysis (NPK-nitrogen, phosphorus, and potassium).…”