Phenotypic plasticity in size of ant-domatia

Abstract

Ant-plants produce hollow structures called domatia to host protecting ants. Although size variation in domatia is well documented between related species, intraspecific variation is little explored. The central African ant-plant Barteria dewevrei exibits strong variation in domatium size, giving the opportunity to explore the mechanism underlying variation in a mutualistic trait. We showed that domatium size in Barteria dewevrei varies between sites. We transplanted individual plants between two sites in Gabon where plants have different domatium sizes. Domatium size of transplanted plants changed, revealing that variation in this mutualistic trait is driven by phenotypic plasticity. The two sites differed in their environmental conditions: highland open savanna on sandy soil vs lowland closed tropical rain forest on sandy-loam soil. However, as stomatal density and δ13C of leaves did not differ between sites or between branches produced before and after transplantation, we have no cue on the role of abiotic stress (such as light intensity and water availability) in domatium size variation. As the obligate Tetraponera ant symbionts are too large to fit in the small domatia, variation of the mutualistic trait in response to environmental change through phenotypic plasticity may impact this specialized mutualism.

Myrmecophytism as a driver of macroevolutionary patterns: perspectives from the Southeast AsianMacarangaant-plant symbiosis

“…However, cases of morphological distinctions can be observed within these sections as well (Supplementary material Table S3 ), and in the case of M. pruinosa , which is non-myrmecophytic on Borneo but myrmecophytic on Sumatra and Malay Peninsula (Davies, 2001), they occur within a single species. Cases of phenotypic plasticity in myrmecophytic traits, specifically domatia, have been reported in other genera such as Tococa where domatia production is influenced by water inundation of host plants (Izzo et al ., 2018), and Barteria (Kokolo et al ., 2020), which exhibits phenotypic plasticity in domatium size. Given these observations, it appears that myrmecophytic traits are generally plastic and the variation in traits among the Macaranga species could hence indicate divergent selection on plastic homologous traits by specific ecological factors and ant partners rather than independent acquisitions.…”

Mutualists construct the ecological conditions that trigger the transition from parasitism

“…Moreover, in the model some cost is paid even if the partner is parasitic or if the host is free of symbiont. For instance, domatia or extrafloral nectaries are unconditionally produced (Bronstein, 1998), even though domatia size can be plastic (Kokolo et al, 2020). Also, plants produce costly floral displays even in the absence of pollinators.…”

Fungi as mutualistic partners in ant-plant interactions

“…The first hypothesis suggests, that myrmecophytism may have existed much earlier than the recent plant lineages. The development of a domatium is most likely an evolutionarily labile trait that is easily acquired and lost for the following reasons: (i) it has been independently acquired at least 158 times and lost at least 43 times ( Chomicki and Renner, 2015 ), (ii) there are no known plant fossils with domatia, and (iii) in some species, this trait is highly variable ( Michelangeli, 2005 ; Shenoy and Borges, 2010 ;, Kokolo et al., 2020 ). Consequently, although the extant lineages of myrmecophytes are less than 20 Mya old, myrmecophytism may have existed much earlier but without leaving any detectable evidence.…”