Closely related tree species support distinct communities of seed‐associated fungi in a lowland tropical forest

Abstract

Previous theoretical work has highlighted the potential for natural enemies to mediate the coexistence of species with similar life histories via density‐dependent effects on survivorship. For plant pathogens to play this role, they must differ in their ability to infect or induce disease in different host plant species. In tropical forests characterized by high diversity, these effects must extend to phylogenetically closely related species pairs. Mortality at the seed and seedling stage strongly influences the abundance and distribution of tropical tree species, but the host preferences and spatial distributions of fungi are rarely determined. We examined how host species identity, relatedness and seed viability influence the composition of fungal communities associated with seeds of four co‐occurring pioneer trees (Cecropia insignis, C. longipes, C. peltata and Jacaranda copaia). Seeds were buried in mesh bags in five common gardens in the understorey of a lowland tropical forest in Panama and retrieved at intervals from 1 to 30 months. A subset of the seeds in each bag was used to determine germination success. One half of each remaining seed was tested for viability; and the other half was used to culture and identify seed‐infecting fungi. Seeds were infected by fungi after burial. Although fungal communities differed in viable versus dead seeds, and across burial locations, community composition primarily varied as a function of plant species identity (30.7% of variation in community composition vs. 4.5% for viability and location together), even for congeneric Cecropia species. Phylogenetic reconstruction showed that relatedness of fungi mostly reflected differences between Jacaranda (Bignoniaceae) and Cecropia (Urticaceae). Although the proportion of germinable seeds decreased gradually over time for all species, intraspecific variation in survival was high at the same location (e.g. ranging from 0% to 100% for C. peltata) suggesting variable exposure or susceptibility to seed pathogens. Synthesis. Our study provides evidence under field conditions that congeneric tree species with similar life history traits differ markedly in seed‐associated fungal communities when exposed to the same soil‐borne fungi. This is a critical first step supporting pathogen‐mediated coexistence of closely related tree species.

Acrogenospora terricola sp. nov., a fungal species associated with seeds of pioneer trees in the soil seed bank of a lowland forest in Panama

“…Most seeds contained a single culturable microbe [14]. These isolates were deposited as living vouchers at MYCO-ARIZ under accessions PS001–PS5673 [14] with additional PS isolates accessioned later by [16]. The nuclear internal transcribed spacers (ITS) and 5.8S gene and an adjacent portion of the large subunit rRNA gene (ca.…”

“…All isolates examined in this work were derived from studies of seed-associated fungi in a lowland tropical forest at Barro Colorado Island, Panama [14][15][16]. In these studies, seeds were buried ca.…”

“… Accession numbers for sequences that contain both the ITS and ca. 600 bp of the LSU, which were extracted and analysed separately. †Data from: a , [44]; b , [40]; c , [45]; d , [41]; e , [38]; f , [14]; g , [9]; h , [31]; i , [3]; j , [16]. …”

“…The species was recorded from viable (rarely) and inviable seeds following surface-sterilization and plating on 2 % MEA. The studies that isolated the focal strains originally detected only 15 isolates among more than 5100 isolates from which the ITS was sequenced [14][15][16]. When queried against the GlobalFungi database of environmental sequences, SH1506827.08FU for this species returned 46 highly similar sequence variants from 13 samples.…”

Fruits, frugivores, and the evolution of phytochemical diversity

“…First, a major function of secondary metabolites in both abiotically and biotically‐dispersed fruits is defense against antagonistic consumers. Antagonists include vertebrate and invertebrate seed predators as well as pathogens, all of which can have large impacts on plant fitness and population dynamics (Hulme 1998, Kolb et al 2007, Tewksbury et al 2008b, Beckman and Muller‐Landau 2011, Mordecai 2011, Zalamea et al 2021). Secondary metabolites that defend against these diverse antagonists are likely ubiquitous in fruits (including seeds and surrounding appendages).…”