Small-scale intraspecific life history variation in herbivorous spider mites (Tetranychus pacificus) is associated with host plant cultivar.

Life history variation is a general feature of arthropod systems, but is rarely included in models of field or laboratory data. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In this study, we tested whether field populations of Pacific spider mites (Tetranychus pacificus) on grapevines (Vitis vinifera) display significant intraspecific life history variation associated with host plant cultivar. To address this question we collected individuals from sympatric vineyard populations where either Zinfandel or Chardonnay were grown. We then conducted a "common garden experiment" of mites on bean plants (Phaseolus lunatus) in the laboratory. Assay populations were sampled non-destructively with digital photography to quantify development times, survival, and reproductive rates. Two classes of models were fit to the data: standard generalized linear mixed models and a time-to-event model, common in survival analysis, that allowed for interval-censored data and hierarchical random effects. We found a significant effect of cultivar on development time in both GLMM and time-to-event analyses, a slight cultivar effect on juvenile survival, and no effect on reproductive rate. There were shorter development times and a trend towards higher juvenile survival in populations from Zinfandel vineyards compared to those from Chardonnay vineyards. Lines of the same species, originating from field populations on different host plant cultivars, expressed different development times and slightly different survival rates when reared on a common host plant in a common environment

Individual heterogeneity in life history processes: Estimation and applications of demographic models to stage-structured arthropod populations

Life history variation is a general feature of natural populations. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In part, this is because a realistic treatment of individual heterogeneity results in very complex population models. Fitting models with individual heterogeneity to real data is further complicated by random effects in groups of the data, observations set at specific intervals, and the non-independence of data following a cohort of individuals through time. In this dissertation, I assume that individuals differ in the duration they spend in each developmental stage and also in the amount of time they live. Stage durations and survival times follow probability distributions with parameters specific to populations and stages. Parameters of these distributions may also include random effects when considering a subset of sampled populations and covariates such as temperature. In the first chapter I formulate a model and likelihood for variable development, using the time-to-event model framework. In the second chapter I use this model to ask whether field populations of herbivorous arthropods (Tetranychus pacificus) form host-associations on different cultivars of the same host species. In the third chapter I incorporate variable development with variable survival and ongoing reproduction in a stage-structured population model. I explore the ability of the approximate Bayesian computation framework to fit such a complex model to data, evaluating posterior distributions and model performance

Individual heterogeneity in life history processes: Estimation and applications of demographic models to stage-structured arthropod populations

Life history variation is a general feature of natural populations. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In part, this is because a realistic treatment of individual heterogeneity results in very complex population models. Fitting models with individual heterogeneity to real data is further complicated by random effects in groups of the data, observations set at specific intervals, and the non-independence of data following a cohort of individuals through time. In this dissertation, I assume that individuals differ in the duration they spend in each developmental stage and also in the amount of time they live. Stage durations and survival times follow probability distributions with parameters specific to populations and stages. Parameters of these distributions may also include random effects when considering a subset of sampled populations and covariates such as temperature. In the first chapter I formulate a model and likelihood for variable development, using the time-to-event model framework. In the second chapter I use this model to ask whether field populations of herbivorous arthropods (Tetranychus pacificus) form host-associations on different cultivars of the same host species. In the third chapter I incorporate variable development with variable survival and ongoing reproduction in a stage-structured population model. I explore the ability of the approximate Bayesian computation framework to fit such a complex model to data, evaluating posterior distributions and model performance

Small-scale intraspecific life history variation in herbivorous spider mites (Tetranychus pacificus) is associated with host plant cultivar.

Life history variation is a general feature of arthropod systems, but is rarely included in models of field or laboratory data. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In this study, we tested whether field populations of Pacific spider mites (Tetranychus pacificus) on grapevines (Vitis vinifera) display significant intraspecific life history variation associated with host plant cultivar. To address this question we collected individuals from sympatric vineyard populations where either Zinfandel or Chardonnay were grown. We then conducted a "common garden experiment" of mites on bean plants (Phaseolus lunatus) in the laboratory. Assay populations were sampled non-destructively with digital photography to quantify development times, survival, and reproductive rates. Two classes of models were fit to the data: standard generalized linear mixed models and a time-to-event model, common in survival analysis, that allowed for interval-censored data and hierarchical random effects. We found a significant effect of cultivar on development time in both GLMM and time-to-event analyses, a slight cultivar effect on juvenile survival, and no effect on reproductive rate. There were shorter development times and a trend towards higher juvenile survival in populations from Zinfandel vineyards compared to those from Chardonnay vineyards. Lines of the same species, originating from field populations on different host plant cultivars, expressed different development times and slightly different survival rates when reared on a common host plant in a common environment

Small-scale intraspecific life history variation in herbivorous spider mites (Tetranychus pacificus) is associated with host plant cultivar

Life history variation is a general feature of arthropod systems, but is rarely included in models of field or laboratory data. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In this study, we tested whether field populations of Pacific spider mites (Tetranychus pacificus) on grapevines (Vitis vinifera) display significant intraspecific life history variation associated with host plant cultivar. To address this question we collected individuals from sympatric vineyard populations where either Zinfandel or Chardonnay were grown. We then conducted a "common garden experiment" of mites on bean plants (Phaseolus lunatus) in the laboratory. Assay populations were sampled non-destructively with digital photography to quantify development times, survival, and reproductive rates. Two classes of models were fit to the data: standard generalized linear mixed models and a time-to-event model, common in survival analysis, that allowed for interval-censored data and hierarchical random effects. We found a significant effect of cultivar on development time in both GLMM and time-to-event analyses, a slight cultivar effect on juvenile survival, and no effect on reproductive rate. There were shorter development times and a trend towards higher juvenile survival in populations from Zinfandel vineyards compared to those from Chardonnay vineyards. Lines of the same species, originating from field populations on different host plant cultivars, expressed different development times and slightly different survival rates when reared on a common host plant in a common environment

Small-scale intraspecific life history variation in herbivorous spider mites (Tetranychus pacificus) is associated with host plant cultivar.

Life history variation is a general feature of arthropod systems, but is rarely included in models of field or laboratory data. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In this study, we tested whether field populations of Pacific spider mites (Tetranychus pacificus) on grapevines (Vitis vinifera) display significant intraspecific life history variation associated with host plant cultivar. To address this question we collected individuals from sympatric vineyard populations where either Zinfandel or Chardonnay were grown. We then conducted a "common garden experiment" of mites on bean plants (Phaseolus lunatus) in the laboratory. Assay populations were sampled non-destructively with digital photography to quantify development times, survival, and reproductive rates. Two classes of models were fit to the data: standard generalized linear mixed models and a time-to-event model, common in survival analysis, that allowed for interval-censored data and hierarchical random effects. We found a significant effect of cultivar on development time in both GLMM and time-to-event analyses, a slight cultivar effect on juvenile survival, and no effect on reproductive rate. There were shorter development times and a trend towards higher juvenile survival in populations from Zinfandel vineyards compared to those from Chardonnay vineyards. Lines of the same species, originating from field populations on different host plant cultivars, expressed different development times and slightly different survival rates when reared on a common host plant in a common environment

Appendix A. Summary statistics and distance metrics.

Summary statistics and distance metrics

Appendix B. Algorithm convergence.

Algorithm convergence

Appendix A. Four figures presenting within-year synchrony-vs.-distance patterns for both species in all years.

Four figures presenting within-year synchrony-vs.-distance patterns for both species in all years

Data from: Evaluating the potential for pre-zygotic isolation and hybridization between landlocked and anadromous alewife (Alosa pseudoharengus) following secondary contact

The recent increase of river restoration projects is altering habitat connectivity for many aquatic species, increasing the chance that previously isolated populations will come into secondary contact. Anadromous and landlocked alewife (Alosa pseudoharengus) are currently undergoing secondary contact as a result of a fishway installation at Rogers Lake in Old Lyme, Connecticut. To determine the degree of pre-zygotic isolation and potential for hybridization between alewife life history forms, we constructed spawning time distributions for two anadromous and three landlocked alewife populations using otolith derived age estimates. In addition, we analyzed long-term data from anadromous alewife migratory spawning runs to look for trends in arrival date and spawning time. Our results indicated that anadromous alewife spawned earlier and over a shorter duration than landlocked alewife, but 3% to 13% of landlocked alewife spawning overlapped with the anadromous alewife spawning period. The degree of spawning time overlap was primarily driven by annual and population level variation in the timing of spawning by landlocked alewife, whereas the timing and duration of spawning for anadromous alewife was found to be relatively invariant among years in our study system. For alewife and many other anadromous fish species, the increase in fish passage river restoration projects in the coming decades will re-establish habitat connectivity and may bring isolated populations into contact. Hybridization between life history forms may occur when pre-zygotic isolating mechanisms are minimal, leading to potentially rapid ecological and evolutionary changes in restored habitats