Biology subjects

Miller, T. E. X.

Publications and source records attributed to Miller, T. E. X..

5 recordsLinked to original sources

bioRxiv2026

Atmospheric nitrogen deposition and anthropogenic land use linked to changing fungal endophyte prevalence in cool-season grasses

Background and AimsAnthropogenic global change is altering the environmental stressors facing plants and their microbial symbionts. Changes in drought and temperature have received wide attention, but how other pervasive human impacts - land conversion for agricultural development and urbanization, and changes in nutrient conditions and pollutants - impact plant- microbe symbioses is relatively unknown. Here, we investigated how these anthropogenic global change drivers influence historic changes in the prevalence of widespread symbionts of grasses, Epichloe fungal endophytes. MethodsWe examined 8,739 seeds from 1,951 herbarium specimens collected between 1895 and 2019 for the presence of seed-transmitted Epichloe fungal endophytes in three grass host species (Agrostis hyemalis, Agrostis perennans, and Elymus virginicus). We hypothesized that the symbiosis provides fitness benefits under anthropogenic stresses (i.e. increased nitrogen deposition and land use change) that should translate to increased prevalence of the interaction among specimens exposed to those stresses. Key ResultsAnthropogenic stresses had contrasting effects on endophyte prevalence. Notably, among Agrostis host species, high nitrogen deposition was associated with high endophyte prevalence and with increasing trends in prevalence through time. We also found that highly urbanized landscapes were associated with reduced prevalence and negative temporal trends in endophyte prevalence across species. We also identified a weak positive relationship between agricultural land cover and average endophyte prevalence for Elymus virginicus, though temporal trends in prevalence did not differ between high and low levels of agricultural land cover. ConclusionsAnthropogenic stressors influenced endophyte prevalence in diverse ways. While we found increasing prevalence in the face of nitrogen deposition, a sign of the potential resilience of the symbiosis, urban land cover was associated with declining endophyte prevalence, a sign that anthropogenic activity may contribute to a breakdown of the symbiosis.

ecology↗

bioRxiv2024

Forecasting range shifts of a dioecious plant species under climate change

Global warming has triggered an urgent need for predicting the reorganization of Earths biodiversity. Currently, the vast majority of models used to forecast population viability and range shifts in response to climate change ignore the complication of sex structure, and thus the potential for females and males to differ in their sensitivity to climate drivers. We developed demographic models of range limitation, parameterized from geographically distributed common garden experiments, with females and males of a dioecious grass species (Poa arachnifera) throughout and beyond its range in the south-central U.S. Female-dominant and two-sex model versions both predict that climate change will alter population viability and will induce a poleward niche shift beyond current northern limits. However, the magnitude of niche shift was underestimated by the female-dominant model, because females have broader temperature tolerance than males and become mate-limited under female-biased sex ratios. Our result illustrate how explicit accounting for both sexes could enhance population viability forecasts and conservation planning for dioecious species in response to climate change.

ecology↗

bioRxiv2024

Increasing prevalence of plant-fungal symbiosis across two centuries of environmental change

Species distributions and abundances are shifting in response to ongoing global climate change. Mutualistic microbial symbionts can provide hosts with protection from environmental stress that may promote resilience under environmental change, however this change may also disrupt species interactions and lead to declines in hosts and/or symbionts. Symbionts preserved within natural history specimens offer a unique opportunity to quantify changes in microbial symbiosis across broad temporal and spatial scales. We asked how the prevalence of seed-transmitted fungal symbionts of grasses (Epichloe endophytes) has changed over time in response to climate change, and how these changes vary across host species distributions. Specifically, we examined 2,346 herbarium specimens of three grass host species (Agrostis hyemalis, Agrostis perennans, Elymus virginicus ) collected over the past two centuries (1824 - 2019) for the presence or absence of Epichloe symbiosis. Analysis of an approximate Bayesian spatially-varying coefficients model revealed that endophytes increased in prevalence over the last two centuries from ca. 25% to ca. 75% prevalence, on average, across three host species. Changes in seasonal climate drivers were associated with increasing endophyte prevalence. Notably, increasing precipitation during the peak growing season for Agrostis species and decreasing precipitation for E. virginicus were associated with increasing endophyte prevalence. Changes in the variability of precipitation and temperature during off-peak seasons were also important predictors of increasing endophyte prevalence. Our model performed favorably in an out-of-sample predictive test with contemporary survey data from across 63 populations, a rare extra step in collections-based research. However, there was greater local-scale variability in endophyte prevalence in contemporary data compared to model predictions, suggesting new directions that could improve predictive accuracy. Our results provide novel evidence for a cryptic biological response to climate change that may contribute to the resilience of host-microbe symbiosis through fitness benefits to symbiotic hosts.

ecology↗

bioRxiv2017

Demographic causes of adult sex ratio variation and their consequences for parental cooperation

The adult sex ratio (ASR) is a fundamental concept in population biology, sexual selection, and social evolution. However, it remains unclear which demographic processes generate ASR variation and how biases in ASR in turn affect social behaviour. Here, we evaluate the demographic mechanisms shaping ASR and their consequences for parental cooperation using detailed survival, fecundity, and behavioural data on 6,119 individuals from six wild shorebird populations exhibiting flexible parental strategies. We show that these closely related populations express strikingly different ASRs, despite having similar ecologies and life histories, and that ASR variation is largely driven by sex differences in the apparent survival of juveniles. Furthermore, families in populations with biased ASRs were predominantly tended by a single parent, suggesting that parental cooperation breaks down with unbalanced sex ratios. Taken together, our results indicate that sex biases emerging during early life have profound consequences for social behaviour.

ecology↗

bioRxiv2017

Adult sex ratio bias in snowy plovers is driven by sex-specific early survival: implications for mating systems and population growth

Adult sex ratio (ASR) is a central concept in population biology and a key factor in sexual selection, yet why do most demographic models ignore sex-biases? Vital rates often vary between the sexes and across life history, but their relative contributions to ASR variation remain poorly understood--an essential step to evaluate sex ratio theories in the wild and inform conservation. Here we combine structured two-sex population models with individual-based mark-recapture data from an intensively monitored polygamous population of snowy plovers. We show that a strongly male-biased ASR is primarily driven by sex-specific survival of juveniles, rather than adults or dependent offspring. This provides empirical support for theories of unbiased sex allocation when sex-differences in survival arise after the period of parental investment. Importantly, a conventional model ignoring sex-biases significantly overestimated population viability. We suggest that sex-specific population models are essential to understand the population dynamics of sexual organisms: reproduction and population growth is most sensitive to perturbations in survival of the limiting sex. Overall, our study suggests that sex-biased early survival may contribute towards mating system evolution and population persistence, with implications for both sexual selection theory and biodiversity conservation.\n\nSIGNIFICANCE STATEMENTSex biases are widespread in nature and represent a fundamental component of sexual selection and population biology--but at which point in life history do these biases emerge? Here we report a detailed individual-based demographic analysis of an intensively studied wild bird population to evaluate the origins of sex biases and their consequences on mating strategies and population dynamics. We document a strongly male-biased adult sex ratio, which is consistent with behavioral observations of female-biased polygamy. Notably, sex-biased juvenile, rather than adult survival, contributed most to the adult sex ratio. Sex-biases also strongly influenced population viability, which was significantly overestimated when sex ratio and mating system were ignored. Our study therefore has implications for both sexual selection theory and biodiversity conservation.

ecology↗