Biology subjects

Simha, A.

Publications and source records attributed to Simha, A..

4 recordsLinked to original sources

bioRxiv2026

Heritable variation in root bacterial microbiomes alters natural selection on host plants

Heritable variation in microbiome composition could theoretically evolve in response to selection acting on hosts, but empirical evidence of this is scarce. We tested for effects of allelic variation in Boechera stricta on microbiome composition and downstream consequences for host fitness. In the greenhouse, near-isogenic lines with contrasting phytochemistry alleles differentially conditioned soil microbiota in ways that changed the relative fecundity of host genotypes. In the field, root microbiome differences mediated allelic effects on host fitness. Selection gradients on individual taxa and multivariate axes of root microbiome composition suggest that independent components of the bacterial community favor each allele, especially under drought. These results show that microbiota contribute to natural selection on a major-effect phytochemistry gene, empirically closing the loop between microbiome heritability and host trait evolution.

evolutionary biology↗

bioRxiv2026

Urban Environments Reshape Reproductive Phenology in Plants Across the Tropics

Plant phenological responses to global change phenomena like urbanization remain understudied in the tropics, hindering predictions regarding the dynamics of tropical ecosystems amid rapid land use changes. Studies of tropical phenology are limited by complexities, like the limited availability of phenological data, especially in urbanized landscapes. Observations recorded on citizen science platforms can overcome this limitation by providing vast, spatially distributed data. In this study, we utilize iNaturalist data to evaluate plant reproductive phenology in tropical urban vs. rural habitats. We first compare iNaturalist data (111533 records) to herbarium collections (217991 records) in order to validate their use, and we then investigate urban-rural phenology differences within 25-km spatial grids for 238 species. Data from iNaturalist and herbaria yield complementary insights, with the former being uniformly distributed between urban and rural settings, and the latter biased towards rural observations. On average, we found species to have significantly longer reproductive duration ({beta} = 11.79 {+/-} 2.83 SE, t = 4.16, p < 10^4), and correspondingly weaker strength of seasonality in urban settings than in nearby rural localities. We also find trait-mediated variation, with seasonal, annual, and herbaceous plants showing more pronounced differences in reproductive duration and seasonality strength. These results suggest that urbanization in tropical landscapes might have important implications for plant demography, with potential consequences for community and ecosystem dynamics. Our work also points to the value of integrating insights from natural history collections with data from citizen science platforms for enabling broad-scale insights into ecological dynamics in tropical urban landscapes.

ecology↗

bioRxiv2025

Spring ephemeral Erythronium umbilicatum may not be vulnerable to phenological mismatch with overstory trees

PremiseThe defining life history strategy of spring ephemeral wildflowers is their avoidance of shading by trees during the brief, high-light period before canopy leaf-out. Studies suggest that spring ephemerals will experience increased light competition because canopy leaf-out is more sensitive to warming than is the phenology of spring ephemerals. However, it remains unclear how longer durations of shade will alter the population dynamics of spring ephemerals and whether all populations are at risk. MethodsWe experimentally shaded Erythronium umbilicatum for one to six additional weeks prior to canopy leaf-out to test for immediate and lagged effects of early shading on the timing of senescence and the probability of survival and flowering. To predict the potential for earlier shading, we combined long-term time series of spring air temperature, remotely-sensed tree leaf-out, and E. umbilicatum flowering phenology in North Carolina, USA. Key resultsEarly shading did not alter E. umbilicatum until the following year, when more-shaded plants senesced later. We found no change in year-to-year survival, and a reduction in the probability of flowering only when plants experienced extremely early shading. Moreover, E. umbilicatum phenology was more sensitive than tree leaf-out to warming temperatures. Under climate warming, we project that E. umbilicatum is unlikely to experience shortened periods of high light. ConclusionsOur findings show that a plant species defining life history strategy does not necessarily predict their sensitivity to phenological mismatches. This complicates, but also underscores the importance of identifying the most vulnerable species and directing our research efforts accordingly.

ecology↗

bioRxiv2021

Higher-order interactions among coinfecting parasites and a microbial mutualist impact disease progression

Interactions among parasites and other microbes within hosts can impact disease progression, yet study of such interactions has been mostly limited to pairwise combinations of microbes. Given the diversity of microbes within hosts, higher-order interactions among more than two microbial species may also impact disease. To test this hypothesis, we performed inoculation experiments that investigated interactions among two fungal parasites, Rhizoctonia solani and Colletotrichum cereale, and a systemic fungal endophyte, Epichloe coenophiala, within a grass host. Both pairwise and higher-order interactions impacted disease progression. While the endophyte did not directly influence R. solani growth or C. cereale symptom development, the endophyte modified the interaction between the two parasites. The magnitude of the facilitative effect of C. cereale on the growth of R. solani tended to be greater when the endophyte was present. Moreover, this interaction modification strongly affected leaf mortality. For plants lacking the endophyte, parasite co-inoculation did not increase leaf mortality compared to single-parasite inoculations. In contrast, for endophyte-infected plants, parasite co-inoculation increased leaf mortality compared to inoculation with R. solani or C. cereale alone by 1.9 or 4.9 times, respectively. Together, these results show that disease progression can be strongly impacted by higher-order interactions among microbial symbionts.

ecology↗