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Infections by maternally inherited bacterial endosymbionts, especially Wolbachia, are common in insects and other invertebrates but infection dynamics across species ranges are largely under studied. Specifically, we lack a broad... more
Infections by maternally inherited bacterial endosymbionts, especially Wolbachia, are common in insects and other invertebrates but infection dynamics across species ranges are largely under studied. Specifically, we lack a broad understanding of the origin of Wolbachia infections in novel hosts and the factors governing their spread. We used Genotype-by-Sequencing (GBS) data from previous population genomics studies for range-wide surveys of Wolbachia presence and genetic diversity in over 2,700 North American butterflies of the genus Lycaeides. As few as one sequence read identified by assembly to a Wolbachia pan-reference genome provided high accuracy in detecting infections as determined by confirmatory PCR tests. Using a conservative threshold of five reads, we detected Wolbachia in all but two of the 107 sampling localities spanning the continent, and with most localities having high infection frequencies (mean = 91\% infection rate). Three major lineages of Wolbachia were ide...
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Specialized plant-insect interactions are a defining feature of life on earth, yet we are only beginning to understand the factors that set limits on host ranges in herbivorous insects. To understand the colonization of alfalfa by the... more
Specialized plant-insect interactions are a defining feature of life on earth, yet we are only beginning to understand the factors that set limits on host ranges in herbivorous insects. To understand the colonization of alfalfa by the Melissa blue butterfly, we quantified arthropod assemblages and plant metabolites across a wide geographic region, while controlling for climate and dispersal inferred from population genomic variation. The presence of the butterfly is successfully predicted by direct and indirect effects of plant traits and interactions with other species. Results are consistent with the predictions of a theoretical model of parasite host range in which specialization is an epiphenomenon of the many barriers to be overcome rather than a consequence of trade-offs in developmental physiology.One sentence summaryThe formation of a novel plant-insect interaction can be predicted with a combination of biotic and abiotic factors, with comparable importance revealed for meta...
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Research Interests: Biology, Ecology, Special Relativity, Medicine, Biological Sciences, and 15 moreResource use, Case Study, Animals, Biological evolution, Sample Size, Individual variation, Frequency Dependence, Fitness Function, Genetic variation, Intraspecific Competition, Conservation of Natural Resources, Species Specificity, Population dynamic, Resource Partitioning, and The American
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Description Iterates through a phylogenetic tree to identify regions of rate variation using the parametric rate comparison test.
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Genomic outcomes of hybridization depend on selection and recombination in hybrids. Whether these processes have similar effects on hybrid genome composition in contemporary hybrid zones versus ancient, stabilized hybrid lineages is... more
Genomic outcomes of hybridization depend on selection and recombination in hybrids. Whether these processes have similar effects on hybrid genome composition in contemporary hybrid zones versus ancient, stabilized hybrid lineages is unknown. Here we show that patterns of introgression in a contemporary hybrid zone in Lycaeides butterflies predict patterns of ancestry in geographically adjacent, ancient hybrid populations. We find a particularly striking lack of ancestry from one of the hybridizing taxa, Lycaeides melissa, on the Z chromosome in both the ancient and contemporary hybrids. The same pattern of reduced L. melissa ancestry on the Z chromosome is seen in two other ancient hybrid lineages. More generally, we find that patterns of ancestry in ancient hybrids are remarkably predictable from contemporary hybrids, which suggests selection affects hybrid genomes in a similar way across disparate time scales and during distinct stages of speciation and species breakdown
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Recently there have been major theoretical advances in the quantification and partitioning of diversity within and among communities, regions, and ecosystems. However, applying those advances to real data remains a challenge. Ecologists... more
Recently there have been major theoretical advances in the quantification and partitioning of diversity within and among communities, regions, and ecosystems. However, applying those advances to real data remains a challenge. Ecologists often end up describing their samples rather than estimating the diversity components of an underlying study system, and existing approaches do not easily provide statistical frameworks for testing ecological questions. Here we offer one avenue to do all of the above using a hierarchical Bayesian approach. We estimate posterior distributions of the underlying "true" relative abundances of each species within each unit sampled. These posterior estimates of relative abundance can then be used with existing formulae to estimate and partition diversity. The result is a posterior distribution of diversity metrics describing our knowledge (or beliefs) about the study system. This approach intuitively leads to statistical inferences addressing bio...
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Among the greatest challenges facing the conservation of plants and animal species in protected areas are threats from a rapidly changing climate. An altered climate creates both challenges and opportunities for improving the management... more
Among the greatest challenges facing the conservation of plants and animal species in protected areas are threats from a rapidly changing climate. An altered climate creates both challenges and opportunities for improving the management of protected areas in networks. Increasingly, quantitative tools like species distribution modeling are used to assess the performance of protected areas and predict potential responses to changing climates for groups of species, within a predictive framework. At larger geographic domains and scales, protected area network units have spatial geoclimatic properties that can be described in the gap analysis typically used to measure or aggregate the geographic distributions of species (stacked species distribution models, or S-SDM). We extend the use of species distribution modeling techniques in order to model the climate envelope (or "footprint") of individual protected areas within a network of protected areas distributed across the 48 con...
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In their technical comment, Janz et al. take issue with our recent study examining the association between host breadth and diversification rates in the brush-footed butterflies (Lepidoptera: Nymphalidae) (Hamm and Fordyce 2015).... more
In their technical comment, Janz et al. take issue with our recent study examining the association between host breadth and diversification rates in the brush-footed butterflies (Lepidoptera: Nymphalidae) (Hamm and Fordyce 2015). Specifically, they are concerned that we misrepresent their "oscillation hypothesis" (OH) (Janz et al. 2006; Janz and Nylin 2008) and that one of our models was inadequate to test hypotheses regarding host breadth and diversification rate. Given our mutual interests in the macroevolutionary patterns of herbivorous insects, we appreciate the opportunity to respond to their concerns.
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Members of the plant genus Selaginella (de Beauvois 1805) have few known insect herbivores even though they are considered by some to be 'living fossils', with extant taxa virtually indistinguishable from 300 Mya fossils.... more
Members of the plant genus Selaginella (de Beauvois 1805) have few known insect herbivores even though they are considered by some to be 'living fossils', with extant taxa virtually indistinguishable from 300 Mya fossils. Butterflies are well-known herbivores, and the satyrs are among the most speciose of them despite having radiated ∼ 35 Mya ago. Nearly all satyrs feed on grass or sedges, but members of the Neotropical genus Euptychia Hübner 1818 feed on Selaginella; little is known about the degree to which this butterfly favors this ancient plant over those that its close relatives utilize. To advance our knowledge of Euptychia natural history, we conducted a series of experiments to examine oviposition preference and growth rates across a series of potential host plants on a Euptychia westwoodi population in Costa Rica. We found that Euptychia westwoodi Butler 1867 exhibit a strong preference to oviposit on Selaginella eurynota over the sympatric Selaginella arthritica, ...
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Migratory animals pose unique challenges for conservation biologists, and we have much to learn about how migratory species respond to drivers of global change. Research has cast doubt on the stability of the eastern monarch butterfly... more
Migratory animals pose unique challenges for conservation biologists, and we have much to learn about how migratory species respond to drivers of global change. Research has cast doubt on the stability of the eastern monarch butterfly (Danaus plexippus) population in North America, but the western monarchs have not been as intensively examined. Using a Bayesian hierarchical model, sightings of western monarchs over approximately 40 years were investigated using summer flight records from ten sites along an elevational transect in Northern California. Multiple weather variables were examined, including local and regional temperature and precipitation. Population trends from the ten focal sites and a subset of western overwintering sites were compared to summer and overwintering data from the eastern migration. Records showed western overwintering grounds and western breeding grounds had negative trends over time, with declines concentrated early in the breeding season, which were pot...
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Tropical fruit-feeding nymphalid butterflies generally restrict adult foraging exclusively to either the canopy or understory strata. We compared canopy and understory butterfly communities using data from four long-term studies in... more
Tropical fruit-feeding nymphalid butterflies generally restrict adult foraging exclusively to either the canopy or understory strata. We compared canopy and understory butterfly communities using data from four long-term studies in Central and South America. At all study sites we found little similarity in species composition between canopy and understory, with most species showing a strong affinity for one of the two habitats. There was a consistent phylogenetic signal for canopy and understory association, suggesting a substantial evolutionary history with these habitats. In addition to compositional differences, we found different patterns of beta diversity between canopy and understory communities. Across all study sites, the canopy had greater temporal and spatial beta diversity compared to the understory. Although these two communities are composed of the same feeding guild and separated only by a relatively small vertical space, each has its own stratum-specific species compo...
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ABSTRACT
Many hypotheses have been proposed to explain the adaptive significance of aggregative feeding in the Lepidoptera. One hypothesis that has received little attention is how induced plant responses may be influenced by aggregative feeding,... more
Many hypotheses have been proposed to explain the adaptive significance of aggregative feeding in the Lepidoptera. One hypothesis that has received little attention is how induced plant responses may be influenced by aggregative feeding, as compared to feeding by solitary larvae. This study investigated the role of aggregative feeding of the pipevine swallowtail, Battus philenor, in California with special emphasis on the induced responses to herbivory of its hostplant. Here, I show that first-instar larvae develop faster when feeding in a large aggregation compared to solitary or small groups of larvae. Furthermore, I show that this effect is mediated by a larval-density-dependent response in the plant and is independent of prior larval experience and direct interaction among larvae. These results indicate that large groups of larvae can effectively enhance hostplant suitability. A separate experiment showed that larvae feeding on previously damaged leaves had a reduced growth rate...
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Herbivorous insects represent one of the most successful animal radiations known. They occupy a wide range of niches, feed on a great variety of plants, and are species rich; yet the factors that influence their diversification are poorly... more
Herbivorous insects represent one of the most successful animal radiations known. They occupy a wide range of niches, feed on a great variety of plants, and are species rich; yet the factors that influence their diversification are poorly understood. Host breadth is often cited as a major factor influencing diversification, and, according to the Oscillation Hypothesis, shifts from generalist to specialist feeding states increase the diversification rate for a clade. We explored the relationship between host breadth and diversification within the Nymphalidae (Lepidoptera) and explicitly tested predictions of the Oscillation Hypothesis. We found strong evidence of diversification rate heterogeneity, but no difference in host breadth between clades with a higher diversification rate compared to their sisters. We also found some clades exhibited phylogenetic nonindependence in host breadth and these clades had lower host plant turnover than expected by chance, suggesting host breadth is evolutionarily constrained. Finally, we found that transitions among host breadth categories varied, but the likelihood of reductions in host breadth was greater than that of increases. Our results indicate host breadth is decoupled from diversification rate within the Nymphalidae, and that constraints on diet breadth might play an important role in the evolution of herbivorous insects.
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Ehrlich and Raven proposed a model of coevolution where major host plant shifts of butterflies facilitate a burst of diversification driven by their arrival to a new adaptive zone. One prediction of this model is that reconstructions of... more
Ehrlich and Raven proposed a model of coevolution where major host plant shifts of butterflies facilitate a burst of diversification driven by their arrival to a new adaptive zone. One prediction of this model is that reconstructions of historical diversification of butterflies should indicate an increase in diversification rate following major host shifts. Using reconstructed histories of 15 butterfly groups, I tested this prediction and found general agreement with Ehrlich and Raven's model. Butterfly lineages with an inferred major historical host shift showed evidence of diversification rate variation, with a significant acceleration following the host shift. Lineages without an inferred major host shift generally agreed with a constant-rate model of diversification. These results are consistent with the view that host plant associations have played a profound role in the evolutionary history of butterflies, and show that major shifts to chemically distinct plant groups leav...
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Despite accumulating evidence that evolution can be predictable, studies quantifying the predictability of evolution remain rare. Here, we measured the predictability of genome-wide evolutionary changes associated with a recent host shift... more
Despite accumulating evidence that evolution can be predictable, studies quantifying the predictability of evolution remain rare. Here, we measured the predictability of genome-wide evolutionary changes associated with a recent host shift in the Melissa blue butterfly (Lycaeides melissa). We asked whether and to what extent genome-wide patterns of evolutionary change in nature could be predicted (i) by comparisons among instances of repeated evolution and (ii) from SNP × performance associations in a laboratory experiment. We delineated the genetic loci (SNPs) most strongly associated with host use in two L. melissa lineages that colonized alfalfa. Whereas most SNPs were strongly associated with host use in none or one of these lineages, we detected a an approximately twofold excess of SNPs associated with host use in both lineages. Similarly, we found that host-associated SNPs in nature could also be partially predicted from SNP × performance (survival and weight) associations in a...
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Beta diversity is an important metric in ecology quantifying differentiation or disparity in composition among communities, ecosystems, or phenotypes. To compare systems with different sizes (N, number of units within a system), beta... more
Beta diversity is an important metric in ecology quantifying differentiation or disparity in composition among communities, ecosystems, or phenotypes. To compare systems with different sizes (N, number of units within a system), beta diversity is often converted to related indices such as turnover or local/regional differentiation. Here we use simulations to demonstrate that these naive measures of dissimilarity depend on sample size and design. We show that when N is the number of sampled units (e.g., quadrats) rather than the " true " number of communities in the system (if such exists), these differentiation measures are biased esti-mators. We propose using average pairwise dissimilarity as an intuitive solution. That is, instead of attempting to estimate an N-community measure, we advocate estimating the expected dissimilarity between any random pair of communities (or sampling units)— especially when the " true " N is unknown or undefined. Fortunately, measu...
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The slower-growth/higher-mortality hypothesis proposes that reduced her- bivore growth rates benefit plants because slower growing herbivores remain vulnerable to predator attack for an extended time period, resulting in a lower reduction... more
The slower-growth/higher-mortality hypothesis proposes that reduced her- bivore growth rates benefit plants because slower growing herbivores remain vulnerable to predator attack for an extended time period, resulting in a lower reduction in plant fitness attributed to herbivory. We propose cooling events as an alternative mechanism leading to higher mortality for slower growing larvae. We observed that, in the absence of predators, slower growing pipevine swallowtail (Battus philenor) larvae had higher mortality compared to faster growing larvae during the unseasonably cool spring temperatures of 1998. However, this was not true for the warmer spring of 1999. Laboratory experiments showed that the probability of surviving a chill coma increased with larval mass. We propose that smaller larvae are susceptible to chilling events because they have less energy reserved for me- tabolism during a chill coma, and that ''warm'' chill events near the activity threshold m...
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The slower-growth/higher-mortality hypothesis proposes that reduced her- bivore growth rates benefit plants because slower growing herbivores remain vulnerable to predator attack for an extended time period, resulting in a lower reduction... more
The slower-growth/higher-mortality hypothesis proposes that reduced her- bivore growth rates benefit plants because slower growing herbivores remain vulnerable to predator attack for an extended time period, resulting in a lower reduction in plant fitness attributed to herbivory. We propose cooling events as an alternative mechanism leading to higher mortality for slower growing larvae. We observed that, in the absence of predators, slower growing pipevine swallowtail (Battus philenor) larvae had higher mortality compared to faster growing larvae during the unseasonably cool spring temperatures of 1998. However, this was not true for the warmer spring of 1999. Laboratory experiments showed that the probability of surviving a chill coma increased with larval mass. We propose that smaller larvae are susceptible to chilling events because they have less energy reserved for me- tabolism during a chill coma, and that ''warm'' chill events near the activity threshold m...
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Rhyssomatus lineaticollis is a milkweed specialist whose larvae feed upon pith parenchyma in ramet stems of the common milkweed, Asclepias syriaca. Compared with other specialist insect herbivores on milkweeds, this curculionid beetle is... more
Rhyssomatus lineaticollis is a milkweed specialist whose larvae feed upon pith parenchyma in ramet stems of the common milkweed, Asclepias syriaca. Compared with other specialist insect herbivores on milkweeds, this curculionid beetle is unusual in that it is cryptically colored and does not sequester cardenolides characteristic of milkweed chemical defense. Based upon optimal defense theory, we predicted that pith tissue
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We investigated one causal explanation for geographic variation in clutch size and aggregative feeding of the pipevine swallowtail, Battus philenor. Populations in California lay larger clutches than those in Texas, and larger feeding... more
We investigated one causal explanation for geographic variation in clutch size and aggregative feeding of the pipevine swallowtail, Battus philenor. Populations in California lay larger clutches than those in Texas, and larger feeding aggregations grow at an accelerated rate on the California host plant. Using reciprocal transplant experiments with larvae from California and Texas populations, we found that the benefit
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We examined mitochondrial DNA (mtDNA) variation in pipevine swallowtail butterflies ( Battus philenor) from throughout its extant range to provide a historical, phylogeographical context for ecological studies of the disjunct population... more
We examined mitochondrial DNA (mtDNA) variation in pipevine swallowtail butterflies ( Battus philenor) from throughout its extant range to provide a historical, phylogeographical context for ecological studies of the disjunct population in California. We evaluate current hypotheses regarding host plant use, behavior, and mimetic relationships of B. philenor populations and generate alternative hypotheses. Compared to populations throughout the rest of
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The genetic and ecological factors that shape the evolution of animal diets remain poorly understood. For herbivorous insects, the expectation has been that tradeoffs exist, such that adaptation to one host plant reduces performance on... more
The genetic and ecological factors that shape the evolution of animal diets remain poorly understood. For herbivorous insects, the expectation has been that tradeoffs exist, such that adaptation to one host plant reduces performance on other potential hosts. We investigated the genetic architecture of alternative host use by rearing individual Lycaeides melissa butterflies from two wild populations in a crossed design on two hosts (one native and one introduced) and analyzing the genetic basis of differences in performance using genomic approaches. Survival during the experiment was highest when butterfly larvae were reared on their natal host plant, consistent with local adaptation. However, cross-host correlations in performance among families (within populations) were not different from zero. We found that L. melissa populations possess genetic variation for larval performance, and variation in performance had a polygenic basis. We documented very few genetic variants with tradeo...
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Cichlid fishes are classic examples of adaptive radiation because of their putative tendency to explosively diversify after invading novel environments. To examine whether ecological opportunity increased diversification (speciation minus... more
Cichlid fishes are classic examples of adaptive radiation because of their putative tendency to explosively diversify after invading novel environments. To examine whether ecological opportunity increased diversification (speciation minus extinction) early in a species-rich cichlid radiation, we determined if Heroine cichlids experienced a burst of diversification following their invasion of Central America. We first reconstructed the Heroine phylogeny and determined the basal node to use as the root of Central American Heroine diversification. We then examined the influence of incomplete taxon sampling on this group's diversification patterns. First, we added missing species randomly to the phylogeny and assessed deviations from a constant rate of lineage accumulation. Using a range of species numbers, we failed to recover significant deviations from a pure-birth process and found little support for an early burst of diversification. Then, we examined patterns of lineage accumu...