Peter A. Van Zandt

COMMUNITY‐WIDE IMPACTS OF HERBIVORE‐INDUCED PLANT RESPONSES IN MILKWEED (ASCLEPIAS SYRIACA)

The effects of early-season herbivory and subsequent induced plant responses have the potential to affect the diversity of herbivorous insect communities. We investigated the seasonal development of the herbivore fauna on common milkweed (Asclepias syriaca) to understand the effect of early-season herbivory by different species on insect growth, natural colonization, and community composition. First, we showed that damage by an early-season stem-feeding weevil (Rhyssomatus lineaticollis) reduced growth of monarch larvae (Danaus plexippus) and leaf beetle larvae (Labidomera clivicollis), suggesting that plant quality is reduced by weevil damage. To better understand the potential for initial herbivore damage to affect subsequent colonization by herbivores in the field, we compared undamaged controls to plants experimentally damaged with one of three herbivores: weevils, monarchs, or leaf beetles. We counted seven species of naturally colonizing herbivores on all plants for the next two months to assess colonization, damage, and insect community richness. Our results showed that initial herbivory by different species altered host plant use by herbivores in two years of experiments. Similarly, induced resistance and suscep- tibility occurred in both years, but due to different initial damaging species on individual plants. Treatment effects also scaled up to alter herbivore community richness. Initial treatments varied in their persistence through the season. For example, in 2001, the influence of initial monarch damage dissipated due to subsequent damage by colonizing herbivores, but the impacts of initial weevil treatment were unaffected. This result suggests that, al- though induced responses to weevil feeding persisted through the season, monarch herbivory was more likely to affect the herbivore community via a cascade of indirect effects. In 2002, plant and insect responses were more specific, depending on the identity of both initial and colonizing herbivore species. Despite year-to-year variation, considerable con- sistency in many responses to our treatments indicates that the identity of the initially colonizing herbivore can affect subsequent plant use and community structure. Given the preponderance of influential early-season herbivores, the effects of induced plant responses similar to those presented here may be widespread and may strongly contribute to the structure of phytophagous insect communities.

A Meta-Analysis of Adaptive Deme Formation in Phytophagous Insect Populations

The adaptive deme formation (ADF) hypothesis predicts that herbivorous insects become locally adapted to their host plants over time. Since its inception, approximately 17 independent studies have tested ADF, and they are divided in support and rejection of the hypothesis. This field of insect evolutionary ecology has a contentious history, and the contradictory studies obscure our understanding of the general evolutionary importance of adaptive deme formation in phytophagous insects. We conducted a meta‐analysis in an attempt to clarify this issue. Meta‐analysis is a statistical method for quantitatively comparing and synthesizing the results of different studies in a way that is more objective than a traditional literature review. Our analysis indicates that local adaptation is an important phenomenon in diverse insect systems. Contrary to predictions of the original hypothesis, there was no evidence that insect dispersal ability, and ostensibly gene flow, was associated with local adaptive differentiation. There was some indication that breeding (parthenogenetic, haplodiploid, diplodiploid) and feeding (exophagous, endophagous) modes may influence the evolution of locally adapted demes. Our analysis supports the theory of adaptive deme formation and provides guidance for future research directions.

SPATIOTEMPORAL VARIATION IN LEAFMINER POPULATION STRUCTURE AND ADAPTATION TO INDIVIDUAL OAK TREES

Stilbosis quadricustatella leafminers are microlepidopteran specialists of sand-live oak (Quercus geminata). These tiny moths produce one generation per year and have a parasitic life-cycle and long larval stage that develops entirely within a single oak leaf. Differences in host-plant age, phenotype, and phenology generate a coarse-grained, spatially heterogeneous environment for the leafminer population. Previous reciprocal trans- fers of leafminer eggs among mature oaks revealed that S. quadricustatella are locally adapted to individual oak trees. In this paper we use genetic markers and an extinction- recolonization experiment to explore further variation in leafminer population structure. Allozyme loci indicate significant interdemic genetic structure among recent colonists of new host trees, which weakens in the 10th generation and disappears by the 40th generation. In contrast, adaptive demic structure is evident by the 10th generation and is strong in the 40th generation, despite the potential for substantial intertree dispersal. We propose that host heterogeneity combined with leafminer fidelity to natal trees promotes divergent se- lection and rapid demic evolution on individual oaks, despite potentially high gene flow between the leafminers inhabiting them.

Delayed and carryover effects of salinity on flowering in Iris hexagona (Iridaceae)

Saltwater intrusion into wetland ecosystems has destroyed or damaged many native plant populations. Iris hexagona is a salt-sensitive species that exhibits intraspecific variation in salinity tolerance. To investigate the effect of salinity on flowering, we exposed I. hexagona collected from natural populations to salt treatments in a common garden. Experimental salinity additions strongly delayed flowering phenology, but the effect was not apparent until the second year, when less than 4 g/L NaCl delayed flowering up to 3 d. In the field, soil salinity and flowering phenology varied substantially within I. hexagona populations. Iris flowers are receptive to pollinators for 2 d or less, therefore a 3-d delay could affect outcrossing dynamics, and ultimately, the evolutionary ecology of iris populations. Salinity also had a carryover effect; prior salinity exposure delayed flowering in irises that had been replanted in freshwater conditions for 6 mo. This is an important result because it suggests that episodic stress (such as tropical storms) can influence performance well after the stress has disappeared. Our research further underscores the importance of long-term studies because a 1-yr experiment would have failed to reveal the strong effects of salinity that emerged in the second year.

Growth and Reproduction of a Clonal Plant in Response to Salinity and Florivory

Salinity is increasing in wetland ecosystems, but the consequences for ecological communities are poorly understood. Iris hexagona is the only North American iris that survives in brackish marsh. Environmental salinity affects the physiology, growth, and reproduction of this glycophytic perennial, as well as plant-herbivore interactions. In brackish wetlands, 80% of iris flowers are consumed by whitetailed deer (Odocoileus virginianus), which rarely browse flowers in freshwater habitats. We investigated the effects of florivory and salinity on I. hexagona sexual and clonal reproduction. Irises that were protected from deer produced 20 times more mature seed capsules than unprotected plants. Experimental floral browsing increased both belowground clonal growth by 30% (P = 0.0003) and flower production the following year by 16% (P = 0.112). Iris populations differed significantly in clonal reproduction (P = 0.004), and interactions between salinity and population affected clonal (P = 0.005) and sexual (P = 0.054) output, suggesting that populations may be differentially adapted to environmental salinity. Brackish conditions can promote floral browsing and loss of sexual reproduction, but plants such as I. hexagona can compensate by allocating more resources to belowground clonal growth.

Diversity and Habitat Use of Neotropical Harvestmen (Arachnida: Opiliones) in a Costa Rican Rainforest

In tropical rain forests, harvestmen assemblages are extremely diverse, with richness often exceeding 25 species. In the neotropics, there are published accounts of harvestmen faunas in South America rainforests (especially Amazonia), but relatively little is known about the community ecology of harvestmen in tropical forests of Central America. In this paper, we provide the first insights into the diverse assemblage of harvestmen inhabiting a wet forest at La Selva Biological Station, Costa Rica. Over five field seasons, we recorded 38 species. During our 2009 field season, we examined variation in species abundance, richness, and composition between adjacent successional forests (young secondary, mature secondary, and primary forests) as well as between distinct habitats (ground/litter layer and shrub/tree layer). Based on night samples (but not day), our results indicate that there are only minor differences in species composition and relative abundance between the forest ages, but no differences in richness. The ground/litter layer and shrub/tree layer habitats differed markedly in species composition, species richness, and relative abundance of several species. Our analysis of covariance supports the hypothesis that leg length is related to climbing behavior for several species belonging to Eupnoi and Laniatores.

Loberus Impressus (LeConte) (Coleoptera: Erotylidae) Fungal Associations and Presence in the Seed Capsules of Iris Hexagona

Abstract Adults and larvae of the loberine erotylid beetle Loberus impressus (LeConte) were found associated with fungi growing on corolla and seed capsule tissue of the blue flag iris, Iris hexagona. We examined adult beetle specimens using light and scanning electron microscopy to determine if specialized structures (mycangia) may function in transporting fungi. Two pairs of deep pits on the ventral aspect of the gena between the eyes and the maxillae of both sexes contained fungal spores and hyphae, suggesting a possible role as mycangia in addition to their role as glandular outlets. Inoculation from the surface of cleaned beetle specimens produced colonies of Cladosporium and Fusarium. These genera are widespread, usually air-dispersed conidial fungi that sometimes are associated with insects.

Description of the Larva of Loberus impressus (Coleoptera: Languriidae: Xenoscelinae) with Notes on its Natural History

Abstract The larva of Loberus impressus LeConte is described based on adult-associated and reared specimens collected from corollas and seed pods of Iris hexagona on the gulf coast of Louisiana. The larva of L. impressus is similar to larvae of Zavaljus brunneus (Gyllenhal) Hapalips prolixus Sharp, Pharaxonotha spp., and Bolerus angulosus (Arrow), the other described larvae within the Xenoscelinae. Larval characters typical for the Loberini that are found in L. impressus include arrangement of integumental granules into rows, frayed and aciculate setae borne on spiny tubercles, and urogomphi spiny or tuberculate and recurved. The tarsungular setae of L. impressus and B. angulosus are single, in contrast to the dual setae present in other described larvae of Languriidae. Larva and adults of L. impressus were common in dried corollas and seed pods of I. hexagona that had begun to split open or had been invaded by Crematogaster ants. Fusarium and Cladosporium fungi were potential sources of food for L. impressus and other fungivorous beetles in the iris seed pods and on corollas.