Christopher T. Ivey

EFFECTS OF INBREEDING IN MIMULUS GUTTATUS ON TOLERANCE TO HERBIVORY IN NATURAL ENVIRONMENTS

Inbreeding, which is common in plants, may increase the vulnerability of populations to natural enemies. Similarly, natural enemies may increase the expression of inbreeding depression in their hosts, resulting in altered selection on host mating-system evolution. To examine effects of inbreeding on tolerance to herbivory, we transplanted experimentally self- and cross-fertilized plants into four field populations of Mimulus gut- tatus and applied single Philaenus spumarius (spittlebug) nymphs to half. At the end of the growing season, we scored plants for five fitness components (reproductive effort, biomass, survival, probability of producing flowers or buds, and probability of bolting). Inbreeding reduced population-level tolerance to spittlebug herbivory with respect to plant aboveground biomass. Inbreeding effects on tolerance varied significantly among plant families for three fitness traits, indicating the opportunity for selection by herbivores to improve tolerance in inbreeding populations. These results also indicate that herbivores can alter inbreeding depression in plants. Our results mirror earlier greenhouse studies of inbreeding effects on plant-herbivore interactions, and demonstrate that these effects can be manifested in natural settings as well. This study indicates that inbreeding in natural populations can affect fitness not only directly, but also indirectly through altered inter- actions with natural enemies.

Effects of herbivory and inbreeding on the pollinators and mating system of Mimulus guttatus (Phrymaceae)

Most models of mating system evolution predict mixed mating to be unstable, although it is commonly reported from nature. Ecological interactions with mutualistic pollinators can help account for this discrepancy, but antagonists such as herbivores are also likely to play a role. In addition, inbreeding can alter ecological interactions and directly affect selfing rates, which may also contribute to maintaining mating system variation. We explored herbivore and inbreeding effects on pollinator behavior and selfing rates in Mimulus guttatus. First, individual spittlebug (Philaenus spumarius) herbivores were applied to native plants in two populations. Spittlebugs reduced flower size, increased anther-stigma distance, and increased selfing rates. A second experiment factorially crossed spittlebug treatment with inbreeding history (self- vs. cross-fertilized), using potted plants in arrays. Spittlebugs did not affect pollinator behavior, but they reduced flower size and nearly doubled the selfing rate. Inbreeding reduced the frequency of pollinator visits and increased flower-handling time, and this may be the first report that inbreeding affects pollinator behavior. Selfing rates of inbred plants were reduced by one half, which may reflect early inbreeding depression or altered pollinator behavior. The contrasting effects of herbivory and inbreeding on selfing rates may help maintain mating system variation in M. guttatus.

Tests for the joint evolution of mating system and drought escape in Mimulus

BACKGROUND AND AIMS Self-fertilizing taxa are often found at the range margins of their progenitors, where sub-optimal habitats may select for alternative physiological strategies. The extent to which self-fertilization is favoured directly vs. arising indirectly through correlations with other adaptive life history traits is unclear. Trait responses to selection depend on genetic variation and covariation, as well as phenotypic and genetic responses to altered environmental conditions. We tested predictions of the hypothesis that self-fertilization in Mimulus arises through direct selection on physiological and developmental traits that allow seasonal drought escape. METHODS Phenotypic selection on mating system and drought escape traits was estimated in field populations of M. guttatus. In addition, trait phenotype and phenotypic selection were compared between experimental wet and dry soil in two greenhouse populations each of M. guttatus and M. nasutus. Finally, genetic variation and covariation for traits were compared between wet and dry soil treatments in a greenhouse population of M. guttatus. KEY RESULTS Consistent with predictions, selection for early flowering was generally stronger than for mating system traits, and selection for early flowering was stronger in dry soil. Inconsistent with predictions, selection for water-use efficiency was largely absent; selection for large flowers was stronger than for drought escape in the field; and most drought escape and mating system traits were not genetically correlated. A positive genetic correlation between flowering time and flower size, which opposed the adaptive contour, emerged only in wet soil, suggesting that variation in water availability may maintain variation in these traits. Plastic responses to soil moisture treatments supported the idea that taxonomic divergence could have been facilitated by plasticity in flowering time and selfing. CONCLUSIONS The hypothesis that plant mating systems may evolve indirectly via selection on correlated life history characteristics is plausible and warrants increased attention.

New perspectives on the evolution of plant mating systems

BACKGROUND The remarkable diversity of mating patterns and sexual systems in flowering plants has fascinated evolutionary biologists for more than a century. Enduring questions about this topic include why sexual polymorphisms have evolved independently in over 100 plant families, and why proportions of self- and cross-fertilization often vary dramatically within and among populations. Important new insights concerning the evolutionary dynamics of plant mating systems have built upon a strong foundation of theoretical models and innovative field and laboratory experiments. However, as the pace of advancement in this field has accelerated, it has become increasingly difficult for researchers to follow developments outside their primary area of research expertise. SCOPE In this Viewpoint paper we highlight three important themes that span and integrate different subdisciplines: the changes in morphology, phenology, and physiology that accompany the transition to selfing; the evolutionary consequences of pollen pool diversity in flowering plants; and the evolutionary dynamics of sexual polymorphisms. We also highlight recent developments in molecular techniques that will facilitate more efficient and cost-effective study of mating patterns in large natural populations, research on the dynamics of pollen transport, and investigations on the genetic basis of sexual polymorphisms. This Viewpoint also serves as the introduction to a Special Issue on the Evolution of Plant Mating Systems. The 15 papers in this special issue provide inspiring examples of recent discoveries, and glimpses of exciting developments yet to come.

Genotypic Diversity and Clonal Structure of Everglades Sawgrass, Cladium jamaicense (Cyperaceae)

The extent of asexual reproduction and the spatial distribution of clones can influence ecological and evolutionary processes in populations. Sawgrass, Cladium jamaicense, which is the dominant ecosystem component in the Florida Everglades, can reproduce sexually and asexually. We examined patterns of genotypic diversity and evaluated the importance of clonal reproduction in Everglades populations of C. jamaicense, using allozymes as genetic markers. We sampled plants in a replicated grid along 11‐m transects in 18 populations of sawgrass distributed throughout the Everglades. Genotypic diversity was low in Everglades sawgrass populations, compared with other plants (mean [SE] number of multilocus genotypes per populatio \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Genetic variation and constraints on the evolution of defense against spittlebug ( Philaenus spumarius ) herbivory in Mimulus guttatus

\mathrm{n}\,=4.9

Support for the microenvironment hypothesis for adaptive value of gall induction in the California gall wasp, Andricus quercuscalifornicus

\end{document} [0.7]), but only one population was monomorphic. Diversity was present even at a small scale; 85 of 108 1‐m2 quadrats had more than one multilocus genotype. South Florida water management areas did not differ with respect to genotypic diversity, except for Everglades National Park, which had populations with a smaller proportion of polymorphic quadrats. Sawgrass clones were closer together than nonclones on average, although this varied among populations. Despite this observation, we found little evidence for spatial structuring of clones using the method of probability of clonal identity. This result reflected the broad interdigitation of clones along transects. Estimated mean (SE) minimum clone size was 46.2 (5.2) m2 and clones may reach over 200 m2. Our results indicate that asexual reproduction is common in C. jamaicense populations but that genotypic diversity is maintained throughout the ecosystem, even at relatively small scales.

The breeding system of desert milkweed, Asclepias subulata

Genetic diversity studies of wetland plants are scarce, but estimates of genetic diversity are useful for learning about plant biology or developing appropriate management strategies. We used allozymes to examine patterns of genetic diversity in Cladium jamaicense, the dominant plant species of the Florida Everglades. We sampled 18 populations (a total of 818 plants) in a replicated grid pattern. Because C. jamaicense can reproduce asexually, we compared estimates of genetic diversity calculated using all sampled ramets to those using only genets within populations. Fewer than half of the 13 loci studied were polymorphic ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape