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The wrinkled dove snail (Amphissa columbiana) is a columbellid gastropod common in marine waters along the west coast of North America. This species has long been anecdotally described as an opportunistic scavenger, but little is known about its diet or scavenging behaviors. A. columbiana were observed at subtidal sites within the San Juan Islands, Washington to document associations with potential food items. Laboratory experiments were done to determine what this species eats and how it finds food. In the field, A. columbiana were often found on dead or damaged organisms, frequently in aggregations. In the laboratory, the snails consumed a broad range of dead or damaged invertebrate prey, showing little discrimination. They appear to locate food resources primarily through chemosensory cues, often following conspecific mucus trails and sometimes congregating around actively feeding sea stars. The chemical cues that draw A. columbiana to food act as feeding stimulants; the addition of scent from a damaged animal induced the snails to feed on healthy prey. The ability to sense chemical cues from damaged animals, including those being consumed by feeding sea stars, creates scavenging opportunities other gastropods may be unable to exploit.

Associating with algal symbionts is considered largely beneficial for cnidarians such as corals and sea anemones, yet there are potential costs of hosting symbionts, such as the production of reactive oxygen species. We compared the photophysiology and H 2 O 2 production rates of Symbiodinium muscatinei and Elliptochloris marina , the dinoflagellate and chlorophyte symbionts, respectively, of the temperate sea anemone Anthopleura elegantissima. Analyses of photosystem II ( PSII ) function in the two symbionts, including maximum quantum yield and relative electron transport rates, were consistent with prior studies indicating that E. marina has lower photosynthetic performance than S. muscatinei at high temperature and irradiance. The efficiency of PSII in both symbionts was positively affected by the addition of exogenous catalase, suggesting that both symbionts experience H 2 O 2 -mediated declines in PSII efficiency. We found that S. muscatinei produced more H 2 O 2 than E. marina across all treatments, with the highest production under high light and temperature. Results were similar in experiments involving both isolated symbionts and symbionts residing within intact tentacles, indicating that the potential stress of symbiont isolation was not a significant factor biasing our results. Despite the lower typical densities of S. muscatinei relative to E. marina , extrapolations of cell-specific H 2 O 2 production rates to the intact symbiosis suggest that S. muscatinei imposes a greater H 2 O 2 burden on A. elegantissima. Even with this burden, however, the considerably higher productivity and fitness of S. muscatinei- bearing anemones documented in prior studies suggests that the net benefit of hosting S. muscatinei exceeds that of E. marina.

iv ACKNOWLEDGEMENTS vi TABLE OF CONTENTS vii LIST OF FIGURES viii LIST OF TABLES x INTRODUCTION 1 METHODS 4 Field sampling 4 Preparation of host and symbiont fractions 4 Lipid extraction 5 Lipid analysis 7 Statistical analyses 7 RESULTS 9 Fatty acid profiles of Symbiodinium muscatinei and Elliptochloris marina 9 Fatty acid profiles of zooxanthellate, zoochlorellate, and aposymbiotic hosts 15 Fatty acid profiles of hosts and their algal symbiont 20 DISCUSSION 24 Fatty acid profiles of Symbiodinium muscatinei and Elliptochloris marina 24 Fatty acid profiles of zooxanthellate, zoochlorellate, and aposymbiotic hosts 26 Fatty acid profiles of hosts and their algal symbiont 29 Conclusions and future research directions 30 REFERENCES 32

Accumulations of green macroalgae (green tides) are becoming increasingly common in many coastal habitats and substances released by these blooms may impact other organisms. In the northeastern Pacific, a dominant contributor to green tides is Ulvaria obscura, an alga that produces dopamine which affects a variety of physiological processes and can trigger metamorphosis in marine invertebrates. Eggs, embryos, and larvae of Pacific oysters (Crassostrea gigas) and sand dollars (Dendraster excentricus) were exposed to U. obscura exudates and dopamine to determine how exposure affects fertilization, development, and morphology. Exposing eggs to these compounds had no significant effect on fertilization of C. gigas and limited impact on D. excentricus, relative to unexposed controls. Early embryos exposed to the compounds developed successfully, but the resulting C. gigas veligers had larger shells and the D. excentricus gastrulae had shorter archenterons. When exposed to dopamine, C. gigas veligers had smaller shells, while larval arms of D. excentricus were significantly shorter relative to unexposed controls. Results indicate that compounds released by U. obscura affect development differently between invertebrate species and among developmental stages. The stage-specific responses likely result from changes in structure and metabolic activity at different life history stages, as well as changes in the localization and function of dopamine and dopamine receptors that occur during larval development. The changes in larval morphology and function induced by compounds released by marine macroalgae could ultimately impact the ability of larvae to feed and survive.

The temperate sea anemone Anthopleura elegantissima is facultatively symbiotic with unicellular algae. Symbiotic A. elegantissima can supplement heterotrophic feeding with excess photosynthate from their algal partners, while asymbiotic individuals must rely solely on heterotrophy. A. elegantissima individuals were collected from Swirl Rocks, Washington (48°25′6″ N, 122°50′58″ W) in July 2010, and prey capture and feeding characteristics were measured to determine whether asymbiotic individuals are more efficient predators. Feeding abilities were then measured again after a 3-week exposure to full sunlight or shaded conditions. Freshly collected asymbiotic anemones had larger nematocysts, but symbiotic individuals showed greater nematocyte sensitivity. Sunlight enhanced digestion and reduced cnida density in all anemones regardless of symbiotic state. Results suggest that the phototropic potential of A. elegantissima, as influenced by symbiotic condition, has little effect on heterotrophic capacity. The anemones appear to maximize heterotrophic energy input independent of the presence or identity of their algal symbionts.

For small tube-building amphipods that live on the algae they consume, food and habitat are tightly linked. This study compared two closely related amphipods to determine whether the species’ algal preferences are based on the food value of the algae or on some other aspect of their algal habitat. Ampithoe lacertosa and Peramphithoe humeralis are both abundant on Shannon Point beach (Anacortes, Washington, USA; 48°30.542′ N, 122°41.070′ W) but specialize on different algae. In observations and laboratory experiments conducted July–September 1997, 2007, and 2008, the two species exhibited markedly different choices of food and habitat when offered six common macroalgae. Ampithoe lacertosa ate all algae offered, but preferentially built tubes on the green alga Ulva lactuca. Survival was relatively low among juveniles maintained on single species diets, except when they were fed Mazzaella splendens. Conversely, P. humeralis consumed primarily the brown kelp Saccharina latissima, Alaria marginata, and Desmarestia ligulata and preferred those species for tube building. Juvenile P. humeralis could not survive on a diet of U. lactuca or M. splendens. While A. lacertosa builds simple, temporary tubes and relocates frequently, P. humeralis is a highly thigmotactic species that builds long-term, complex tubes on the alga it prefers to eat. Feeding and habitat preferences of the two species were not clearly linked to nitrogen content of the algae, C:N ratio, or toughness of the algal tissue. Instead, preferences of the species may be related to their mobility and the permanence of the tubes they build. Ampithoe lacertosa and P. humeralis also use different feeding strategies; the former appears to mix algae to produce a high-quality diet, while the latter is more selective and has a capacity for compensatory feeding. The species are abundant on the same protected rocky shores, but specialize on different algae for habitat and food. Results suggest that the nutritional requirements of these sympatric mesograzers differ considerably and even closely related species can exhibit divergent behavioral strategies.

Because planktonic invertebrate larvae may be food-limited, anything that increases feeding and digestive efficiency should increase the chances of larval survival to metamorphosis. As light directly enhances both feeding and digestion in some planktonic heterotrophic protists, we hypothesize that similar processes might occur in the larvae of marine invertebrates. We studied the direct effects of light on feeding and development in sea urchin larvae (Strongylocentrotus droe- bachiensis, S. franciscanus and sand dollar Dendraster excentricus). Larvae were placed in 12:12 h light:dark cycles or in complete darkness and ingestion rates were measured. We monitored larval morphology during the first 2 to 3 wk of development and tested for light-related differences. Short- term changes in light regime had no effect on feeding rates. However, larvae of all 3 species showed longer-term diel feeding patterns with ingestion rates generally higher during daylight hours. These patterns persisted in S. franciscanus larvae even when larvae were held in complete darkness for 3 d. Larvae of D. excentricus exposed to natural light cycles developed longer arms usually associated with food limitation; those held in darkness had significantly shorter arms. The developing juvenile structures (i.e., rudiments) of S. droebachiensis larvae exposed to light were significantly smaller than those of larvae held in continuous darkness, suggesting that light may have negative effects on larval growth and development. Measuring the effects of light on feeding and growth may clarify the behaviors of invertebrate larvae during their critically important planktonic period.

Nutritional provisioning that passes from a mother to her offspring can produce maternal carryover effects. Though the importance of maternal carryover effects on embryos and early juveniles is well established, it is less clear how long the effects persist and whether they can be detected in subsequent life stages of the offspring. Manipulating the amount of food available to a maternal organism is one way to manipulate maternal investment ability and thereby test maternal carryover. We collected adult brooding Leptasterias aequalis from three beaches with varying prey communities in the northern Puget Sound. When broods were released, we measured size and survival of the juveniles under starvation conditions. The maternal sea stars were then assigned to different feeding treatments and their diets were controlled for a full year until they spawned again. We measured size and growth of juveniles released from these second broods. Juvenile L. aequalis from the initial broods showed surprising resistance to starvation with 80% survival after 6 months and some juveniles living a full year with no food. Juvenile survival over time varied significantly among the mothers from the three study beaches, but we were unable to demonstrate a significant difference in the mean month of juvenile death. Juvenile size also varied significantly among mothers from the three study beaches, even when differences in female size by beach were accounted for. Adult female feeding treatments had no effect on the size of juveniles in the second broods. The patterns of juvenile performance mirrored those seen in the first year regardless of feeding treatment. The beach that a female came from seemed to have a stronger effect than a year of diet treatment. When looking at multiple generations of carryover in L. aequalis , it seems that genetic legacies, and possibly full female feeding history, have a greater effect on juvenile quality than a single year of maternal feeding.

In recent decades, the world has witnessed an array of harmful invasions by exotic marine organisms. To provide the public and policymakers with better information on the status of exotic species in southern California waters, and to assess differences between port and non-port areas, a Rapid Assessment Survey of selected habitat types in sheltered waters between San Diego and Oxnard was conducted in the summer of 2000. The objectives included comparing the prevalence of exotic species among habitats and regions and between recent and past surveys; obtaining reference data for future assessments of changes in invasion status and the effectiveness of prevention or control efforts; detecting new invasions; and documenting significant range extensions. Twenty-two sites were sampled to include the three major commercial port areas in southern California, non-port-area marinas and lagoon sites. Sampling included dock fouling and adjacent soft-bottom benthos, nearby intertidal sites, and selected subtidal lagoon habitats. Samples were collected by a variety of manual techniques. Sixty-nine of the species collected are exotic, including representatives from two algal divisions and six invertebrate phyla. Ascidians are especially well-represented (14 exotic species) and widely occurring, and some bivalves and bryozoans also occur very widely. The numbers and proportions of exotic taxa were not significantly greater in port areas than in non-port areas. Fil: Cohen, A. N.. San Francisco Estuary Institute; Estados Unidos Fil: Harris, L. H.. National Museum of Natural History; Estados Unidos Fil: Bingham, B. L.. University of Washington; Estados Unidos Fil: Carlton, J. T.. Williams College; Estados Unidos Fil: Chapman, J. W.. State University of Oregon; Estados Unidos Fil: Lambert, C. C.. University of Washington; Estados Unidos Fil: Lambert, G.. University of Washington; Estados Unidos Fil: Ljubenkov, J. C.. Dancing Coyote Ranch Environmental; Estados Unidos Fil: Murray, S. N.. California State University; Estados Unidos Fil: Rao, L. C.. San Francisco Regional Water Quality Control Board; Estados Unidos Fil: Reardon, K.. University of Maine; Estados Unidos Fil: Schwindt, Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina

Enormous variation exists in the reproductive output of marine invertebrates (e.g., in the numbers of embryos produced, the volumes of embryos, and the energy that they contain). It is not clear why there is such great variability or what the population-level consequences are. We sampled a population of the brooding seastar Leptasterias aequalis (Stimpson, 1862) to collect basic information on brood sizes, embryo volume, and embryo energy content with a goal to better understand the reproductive ecology of this species. We collected brooding females in February and again in April. We measured the size of their broods and sampled the broods to estimate volume and energy content of the embryos. There was great variability in the volume and energy content of embryos produced by individual females and among the embryos in a single female's brood. Larger adults produced larger embryos, which generally had greater energy content and may be of a higher quality. The average energy content of embryos appeared to increase during the brooding period. Larger females produced larger broods but lost a greater proportion of the embryos. The net result is that larger individuals may not produce any more juveniles than smaller individuals, but those that they do produce may be of a higher quality.

Leptasterias hexactis, a sea star common in rocky intertidal areas of Puget Sound, Washington, often has damaged or missing arms. We measured the frequency of arm damage in 5 populations and examined the causes and costs of the damage. Between 30 and 46% of L. hexactis found at the study sites were missing arms or parts of arms. Some of the damage, particularly when only parts of arms were missing, may result from physical disturbance (e.g., crushing). Most arm damage, however, appears to result from predation by the crab Cancer oregonensis. The ability to lose, or autotomize, arms has adaptive significance if it saves a sea star from death. However, it also carries costs. The greatest cost was a decrease in reproduction. Leptasterias hexactis missing arms showed a 44-69% drop in egg production 7 months after arm loss. The effect was still evident during the next reproductive season (19 months after arm loss). We estimate that natural levels of arm damage could decrease the reproductive output of a population of L. hexactis by 7-10%.

Dense populations of the holothurian Cucumaria lubrica (Clark) occur subtidally within the San Juan Archipelago, Washington, USA. These animals occur in a discrete subtidal zone, but the pattern has not been thoroughly studied. The objectives of this study were to document the distribution of C. lubrica, determine if the pattern was stable, and experimentally determine what factors produce it. Ten months of sampling showed that the C. lubrica population exists in a stable band between 7 and 17 m; maximum densities of 400 individuals · m−2 occurred at 12–13 m. The water column at the study site was well mixed, and seawater features (temperature, salinity, turbidity, Chl a, water flow, siltation) were not sufficiently variable to produce the zonation. Light was the only factor that varied significantly with depth. Cucumaria lubrica showed no phototaxis in the laboratory, but did show a strong photokinetic response; the animals were more active at high and low light intensities than they were at intermediate intensities. We propose that photokinetic behavior, particularly of young C. lubrica which are the most active, may contribute to their subtidal zonation. The resulting aggregation is adaptive given the reproductive behaviors of the more sedentary adults.

Submerged roots of red mangroves (Rhizophora mangle) in the Florida Keys were photographed at 1– or 2-month intervals for 38 months to measure population dynamics of the epifaunal invertebrate species. Photographs were analysed for species composition and abundance and information on life spans, persistence, mortality, and seasonality. Larval recruitment to artificial surfaces was used to assess reproductive seasonality. As a measure of stability, populations were tested for narrow stochastic boundedness. In contrast to reports for a tropical mangrove root community, the Florida Keys root community showed enormous variability despite being dominated by long-lived species with low, largely non-seasonal recruitment. Species composition on individual roots changed dramatically on short time scales. Populations of the major species were not narrowly bounded on most roots and there was little evidence for a closely regulated community. Variability of this community related to the frequency and intensity of stochastic perturbations. Physical disturbance due to strong tidal Rows appeared to be the most important structuring process. Species-specific predation and fragmentation of sponges were also important. These features contribute to the instability of the community by producing dramatic fluctuations in species abundances and preventing competitive processes from producing a more stable, equilibrium community. Temporal measurement scale was an additional important consideration in this habitat. Structuring processes occurred on very short time scales (1–2 months) and analysis on longer time scales gave inaccurate impressions of community dynamics.

SUMMARY The susceptibility of algal–cnidarian holobionts to environmental stress is dependent on attributes of both host and symbiont, but the role of the host is often unclear. We examined the influence of the host on symbiont light stress, comparing the photophysiology of the chlorophyte symbiont Elliptochloris marina in two species of sea anemones in the genus Anthopleura. After 3 months of acclimation in outdoor tanks, polyp photoprotective contraction behavior was similar between the two host species, but photochemical efficiency was 1.5 times higher in A. xanthogrammica than in A. elegantissima. Maximum relative electron transport rates, derived from rapid light curves, were 1.5 times higher in A. xanthogrammica than in A. elegantissima when symbionts were inside intact tissues, but were not significantly different between host species upon removal of outer (epidermis and mesoglea) tissue layers from symbiont-containing gastrodermal cells. Tissues of A. xanthogrammica were 1.8 times thicker than those of A. elegantissima, with outer tissue layers attenuating 1.6 times more light. We found no significant differences in light absorption properties per unit volume of tissue, confirming the direct effect of tissue thickness on light attenuation. The thicker tissues of A. xanthogrammica thus provide a favorable environment for E. marina – a relatively stress-susceptible symbiont – and may explain its higher prevalence and expanded range in A. xanthogrammica along the Pacific coast of North America. Our findings also support a photoprotective role for thicker host tissues in reef corals that has long been thought to influence variability in bleaching susceptibility among coral taxa.

Marine invertebrates growing epifaunally on red mangrove (Rhizophora mangle) prop roots in the Indian River, Florida, USA, were studied in a small mangrove island (Jim Island) through which a number of channels had been cut. Roots hanging down into the water supported diverse epifaunal communities including sponges, oysters, barnacles, bryozoans, and acidians. To determine what factors control species' population dynamics and contribute to the high degree of spatial heterogeneity characteristic of communities in the unique habitat, two hypotheses were tested: (1) Distributions of species on the roots are controlled by differential growth and mortality due to physical features; and (2) Recruitment, as influenced by larval supply, structures the community. Four channels of the island were chosen for comparison and experimentation. Distributions of abundances of epifauna in the channels were determined and physical parameters (i.e., temperature, pH, salinity, flow, turbidity) were measured over a 13—mo perio...

Swimming and nonswimming tadpole larvae of the ascidian Ecteinascidia turbinata Herdman were followed in situ by divers to determine whether swimming affects larval dispersal. Swimming affected neither dispersal direction nor time spent in the water column. However, the dispersal rates and distances of swimming larvae were significantly lower than those of nonswimming larvae. Potential paths of larval dispersal were modeled with subsurface drogues. Movements of both swimming and nonswimming larvae differed consistently from surface flo w direction in these shallow (1.0–1.5 m) waters, indicating that caution should be used in modeling larval dispersal with drogues, particularly when larvae do not consistently remain in surface waters. In our south Florida study site, E. turbinata colonies were present only on unanchored mangrove prop roots and survival of colonies transplanted into surroundings habitats was very low. Drogue paths demonstrated that currents could potentially carry E. turbinata between mangrove islands, but behavior of the larvae suggests that dispersal is generally very localized with larvae settling near colonies from which they were released. This behavior differs dramatically from that reported for E. turbinata larvae in a more homogeneous habitat in the northern Gulf of Mexico. The short-distance dispersal of swimming tadpole larvae inthis study may represnt a local adaptation to favor recruitment near parental habitats and to prevent advection to inappropriate sites. Long-distance exchange between isolated islands probably occurs through rafting of adult colonies on fragmented mangrove roots rather than through larval dispersal.

We manipulated live sponges in Belize, Central America, Big Pine Key, Florida (USA), and Indian River lagoon, Florida (USA) in summer/autumn, 1988. At each location, live sponges of three species were placed within 0.5 cm of ceramic tiles. Tiles with synthetic sponges positioned in the same manner and tiles with no sponges served as controls. Of 26 recruiting species analyzed, only one (Sponge sp. 6 — Indian River) was inhibited by living sponges. Four species (Perophora regina — Belize;Aiptasia pallida — Big Pine Key; andCrassostrea virginica andAscidia nigra — Indian River) recruited in greater numbers in the presence of sponges, suggesting that some larvae may be attracted rather than repelled by sponge allelochemicals. Allelopathic effects were less important than small-scale flow effects and patchy larval supply in determining recruitment patterns on surfaces adjacent to sponges.

I would describe my graduate career in ecol ogy as "serendipitous". As a daughter of Latino parents who grew up in challenging environments with limited access to education, I was lucky to graduate from college, let alone pursue a PhD. I was also fortunate to meet a men tor who introduced me to ecology and graduate school. Unfortunately, many students from underrepresented groups lack adequate opportunities and mentorship as they head through the "pipeline" to graduate school. Despite the need for unique perspectives in collaborative scientific research, ethnic minority students continue to "leak" from the system. According to demographic projec tions, over 50% of the US population will be composed of individuals from underrepresented groups by the year 2050 (US Department of Commerce 1996). At present, how ever, these groups constitute only 6.5% of students enrolled in higher degree programs in ecology (NSF 2007). What can we do to remedy this? Exposure, oppor tunity, and access appear to be key. Here, I present some points for consideration for academic professionals (including educators, administrators, and program man agers), based on the first-hand experiences of successful minority scientists I have interviewed or who have pub lished on the subject. Introduce ecology early and supply access to research and career opportunities. It is important to publicize research, internship, and graduate program opportunities and pro vide financial support. The Ecological Society of America's (ESAs) Strategies for Ecology Education, Development, and Sustainability (SEEDS) program has effectively intro duced minority scientists to ecology by providing fellow ships and field trips, as well as travel awards to ESA's annual meetings (www.esa.org/seeds/). Create "bridge" programs that facilitate the transition of minority students from one level of academia to the next. Summer courses, orientation programs, intemships, research experiences, and cultural events all teach stu dents about the academic and social expectations of uni versities. For example, the Meyerhoff Scholars Program at the University of Maryland (UMD) has offered scholar ships, summer bridge programs, and intemships, as well as engaged students' families, and provided faculty and peer mentoring in an effort to recruit and retain minorities in science. As a result, minority participation in the sciences at UMD has increased 18%; in addition, UMD has recently introduced a graduate fellows program (Summers and Hrabowski 2006; WebTables 1 and 2). Build a sense of community through the creation of outreach

In the coastal waters of Florida (USA) tadpole larvae of the colonial ascidian Ecteinascidia turbinata contain chemicals which make them unpalatable to planktivorous juvenile pinfish Lagodon rhomboides. Experiments demonstrate that the bright organe color of E. turbinata tadpoles is aposematic. Fish that have recently tasted larvae of E. turbinata will not attack the palatable tadpoles of Clavelina oblonga when the latter are dyed organe to resemble larvae of E. turbinata. Tadpoles of E. turbinata that have been mouthed and rejected by fish generally survive to complete a normal metamorphosis. Individual selection explains the evolution of aposematic coloration in E. turbinata better than kin selection. The identity of the defensive chemical is unknown. The unpalatable substance in larvae of E. turbinata is removed by dialysis, indicating that it has a molecular weight less than 14000 d. Larvae are not acidic, nor is the active substance denatured by doiling.

Many potentially predatory species of gastropods, decapods, asteroids, and fishes were tested to determine their responses to Psolus chitonoides Clark. Asteroids, particularly Dermasterias imbricata (Grube), were found to be the only important predators. Psolus chitonoides was not found in guts of any field-collected fishes, though other sea cucumbers were. Psolus chitonoides had the highest saponin content of four species of Greater Puget Sound holothurians tested. Homogenates of P. chitonoides were highly unpalatable to the tidepool sculpin, Oligocottus maculosus Girard and tissues were toxic when force-fed to O. maculosus. Toxicity of Psolus chitonoides tissue was due to the high saponin content whereas unpalatability appears to be unrelated to the saponins. Toxicity of saponins from Puget Sound holothurians to Oligocottus maculosus depends on whether the toxin is respired or ingested.

Gut analyses of five ascidian species from the San Juan Islands, Washington, Chelyosoma productum Stimpson, Pyura haustor (Stimpson), Ascidia callosa Stimpson, Boltenia villosa (Stimpson) and Styela gibbsii (Stimpson) and five species from the Atlantic coast of Florida, Herdmania momus (Savigny), Ascidia curvata (Traustedt), Ascidia nigra (Savigny), Molgula occidentals Traustedt and Styela plicata (Lesueur), indicate that solitary ascidians consume a variety of invertebrate larvae. Analysis of plankton samples collected near aggregations of live ascidians and near mimic aggregations, however, indicate that the ascidians are not significantly depleting the local supplies of larvae. Temporal and spatial patchiness in larval supply combined with selective feeding by the ascidians and escape responses of larvae are invoked to explain the lack of small scale depletion effects.

The direct developmental mode and sedentary habit of Leptosynapta clarki (Heding), an infaunal, brooding holothuroid, suggest that this species has limited dispersal capabilities. Using starch gel electrophoresis, we estimated allele frequencies at two polymorphic enzyme loci in three populations to look for consequences of limited dispersal on genetic structure of populations. Genetic composition within populations was characterized by linkage equilibrium and heterozygote frequencies which equalled or exceeded Hardy-Weinberg expectations, indicating that inbreeding does not occur and self-fertilization is not a common reproductive mode in this species. Comparisons among populations separated by 11–24 km showed significant differences in allele frequencies at both loci, indicating that populations are genetically differentiated. These differences are probably due to genetic drift or local adaptation occurring in the absence of high levels of gene flow.