Different Histories Of Exposure Research Articles

Widespread learned predator recognition to an alien predator across populations in an amphibian species

Alien predators are a major cause of decline and extinction of species worldwide, since native organisms are rarely equipped with specific antipredatory strategies to cope with them. However, phenotypic plasticity and learned predator recognition may help prey populations to survive novel predators. Here we examine geographical variation in the learning ability of larval spadefoot toads (Pelobates cultripes) to recognize invasive predatory crayfish (Procambarus clarkii). We compare the learning-mediated behavioural responses of tadpoles from six populations across two regions in Spain (central and southern), with different histories of exposure to the presence of the invasive species. Two of the populations showed innate recognition of chemical cues from the invasive crayfish, whereas three of them learned to recognize such cues as a threat after conditioning with conspecific alarm cues. Learning abilities did not differ among southern populations, but they did among central populations. We assessed patterns of genetic variation within and among these two regions through microsatellite markers and found low genetic divergence among the southern populations but greater differentiation among the central ones. We hypothesize that similar responses to the invasive crayfish in southern populations may have arisen from a combination of extended historical exposure to this introduced predator (~ 50 y) and higher levels of gene flow, as they inhabit a highly interconnected pond network. In contrast, populations from central Spain show lower connectivity, have been exposed to the invasive crayfish for a shorter period of time, and are more divergent in their plastic responses.

Alpine Newts (Ichthyosaura alpestris) Avoid Habitats Previously Used by Parasite-Exposed Conspecifics

Many organisms avoid habitats posing risks of parasitism. Parasites are not generally conspicuous, however, which raises the question of what cues individuals use to detect parasitism risk. Here, we provide evidence in alpine newts (Ichthyosaura alpestris) that non-visual cues from parasite-exposed conspecifics inform habitat avoidance. Alpine newts breed in aquatic habitats and occasionally move among adjacent terrestrial habitat during breeding seasons. We completed experiments with newts whereby individuals had access to both habitats, and the aquatic habitats varied in prior occupancy by conspecifics with different histories of exposure to the parasitic skin fungus, Batrachochytrium dendrobatidis (Bd). Continuous filming of newt activity for 2 days provided little evidence that prior use of aquatic habitats by conspecifics, regardless of their Bd exposure history, immediately influenced newt habitat use. However, newts that encountered aquatic habitats used specifically by Bd-exposed conspecifics on day 1 spent less time aquatic on day 2, whereas other newts did not alter habitat use. Responses could have been elicited by cues generated by Bd stages on the conspecifics or, perhaps more likely, cues emitted by the conspecifics themselves. In either case, these observations suggest that newts use non-visual cues sourced from exposed conspecifics to detect Bd risk and that those cues cause newts to avoid aquatic habitats. Bd may therefore influence host behavior in early phases of interactions, and possibly before any contact with infectious stages is made, creating potential for non-consumptive effects.

Vertical Distribution of Macrobenthos in Hypoxia-Affected Sediments of the Northern Gulf of Mexico: Applying Functional Metrics

Continuing trends of declining bottom-water dissolved oxygen (BWDO) in coastal oceans are a threat to marine organisms, especially the benthos, and in the northern Gulf of Mexico (nGOM), the hypoxic area is expected to expand. Within-sediment vertical functional metric responses of macrobenthos were examined in four depth strata at four sites with different histories of exposure to seasonal hypoxia. The sites H7, D5, E4, and A6 between 30 and 39-m water depth represented a historical oxygen stress gradient from 5.4 to 2.1 mg L−1 BWDO (mid-summer 11-year mean), from which macrobenthos were sampled in spring and late summer 2009 and in mid-summer in 2010. High abundance together with high biomass and production potential within upper strata under low BWDO stress supports the primacy of a numerically driven response in this system. Total abundance decreased along the BWDO stress gradient, and the lowest abundance coincided at the highest stress (MaxStress) site together with the highest proportion of opportunists, the smallest mean size, and the shortest turnover time. Accordingly, the relative abundance of opportunists within the upper two strata increased while surface deposit feeders decreased with greater hypoxic stress. Notwithstanding the proportion of opportunists, functional metrics generally decreased across the BWDO stress gradient within the upper strata, and metrics generally varied inversely between upper and lower strata. The findings underscore how vertical benthos distribution patterns reflect the BWDO exposure regime and how secondary production varies as an indicator of trophic transfer potential and organic matter processing within this system.

Response of bluebunch wheatgrass to invasion: Differences in competitive ability among invader‐experienced and invader‐naïve populations

Abstract Invasive species may alter selective pressures on native plant populations. Although there is some evidence that competition with invasive plants may lead to differences in competitive ability between populations that have experienced invasion and those that have not, previous results have varied among species but also among populations of the same species. We conducted a glasshouse experiment to determine whether there was variation in traits or in ability to tolerate or suppress an invasive species among populations of a common native grass that had different histories of exposure to competition from an invasive species. Specifically, we grew seeds of a native grass (Pseudoroegneria spicata) collected from 14 wild populations (six from invaded populations and eight from uninvaded populations) and a cultivar (Anatone) alone or in competition with the invasive aster (Centaurea stoebe) and measured traits of both species during and at the end of a 100‐day growing period. Pseudoroegneria spicata seedlings from invader‐experienced populations had more leaves than invader‐naïve populations, and juvenile plants from experienced populations were less affected by competition with C. stoebe than were plants from naïve populations. There were significant differences in traits among populations at the seedling and juvenile life stages, and at both life stages variation among populations was greater than variation among experience types. The most predictive traits of P. spicata tolerance to competition were number of leaves (seedling and juvenile stage) and total and root biomass (juvenile only). No traits significantly predicted suppression of C. stoebe. There was not a significant relationship between a population's suppression of C. stoebe and its tolerance of competition. Our results suggest that, in P. spicata, invasion selects for larger plants and traits that can influence tolerance of competition. If land managers are interested in identifying highly competitive seed sources for revegetation in invaded areas, both population and invader experience type should be considered. As tolerance and suppression do not appear to be related in P. spicata, seed source selection should be driven by the element of competitive ability (either tolerance or suppression) that is most important to project goals. A plain language summary is available for this article.

A Probabilistic Model of Meter Perception: Simulating Enculturation.

Enculturation is known to shape the perception of meter in music but this is not explicitly accounted for by current cognitive models of meter perception. We hypothesize that the induction of meter is a result of predictive coding: interpreting onsets in a rhythm relative to a periodic meter facilitates prediction of future onsets. Such prediction, we hypothesize, is based on previous exposure to rhythms. As such, predictive coding provides a possible explanation for the way meter perception is shaped by the cultural environment. Based on this hypothesis, we present a probabilistic model of meter perception that uses statistical properties of the relation between rhythm and meter to infer meter from quantized rhythms. We show that our model can successfully predict annotated time signatures from quantized rhythmic patterns derived from folk melodies. Furthermore, we show that by inferring meter, our model improves prediction of the onsets of future events compared to a similar probabilistic model that does not infer meter. Finally, as a proof of concept, we demonstrate how our model can be used in a simulation of enculturation. From the results of this simulation, we derive a class of rhythms that are likely to be interpreted differently by enculturated listeners with different histories of exposure to rhythms.

Pre-ingestive selection efficiency in two populations of the razor clam Tagelus dombeii with different histories of exposure to paralytic shellfish poisoning (PSP)

We studied toxic effects of the dinoflagellate Alexandrium catenella on filtration activity and pre-ingestive selection efficiency in Tagelus dombeii (razor clam). Samples came from two populations with different histories of exposure to paralytic shellfish poisoning (PSP): Melinka, Aysén (with frequent exposure to PSP) and Corral, Valdivia (without previous exposure to PSP). Feeding activity of T. dombeii was affected by a diet containing A. catenella, showing a reduction in individuals from Corral, Valdivia and Melinka, Aysén. Furthermore, pre-ingestive selection efficiency was significantly higher in specimens from the population of Melinka, than those from Corral. Significantly higher values of clearance rate and pre-ingestive selection efficiency from the Melinka samples may reflect adaptation to specific environmental conditions where PSP events frequently occur.

Contrasting physiological responses of two populations of the razor clam Tagelus dombeii with different histories of exposure to paralytic shellfish poisoning (PSP).

This study describes the physiological performance of two populations of the razor clam Tagelus dombeii from two geographic areas with different histories of exposure to paralytic shellfish poisoning (PSP) linked to the toxic dinoflagellate Alexandrium catenella. Clams from Melinka-Aysén, which are frequently exposed to PSP, were not affected by the presence of toxins in the diet. However, clams from Corral-Valdivia, which have never been exposed to PSP, exhibited significantly reduced filtration activity and absorption, affecting the energy allocated to scope for growth (SFG). Ammonia excretion and oxygen uptake were not affected significantly by the presence of A. catenella in the diet. Measurements of energy acquisition and expenditure were performed during a 12-day intoxication period. According to three-way repeated measure ANOVAs, the origin of the clams had a highly significant effect on all physiological variables, and the interaction between diet and origin was significant for the clearance and absorption rates and for the scope for growth. The scope for growth index showed similar positive values for both the toxic and non-toxic individuals from the Melinka-Aysén population. However, it was significantly reduced in individuals from Corral-Valdivia when exposed to the diet containing A. catenella. The absence of differences between the physiological response of the toxic and non-toxic clams from Melinka-Aysén may be related to the frequent presence of A. catenella in the environment, indicating that this bivalve does not suffer negative consequences from PSP. By contrast, A. catenella has a negative effect on the physiological performance, primarily on the energy gained from the environment, on T. dombeii from Corral-Valdivia. This study supports the hypothesis that the history of PSP exposure plays an important role in the physiological performance and fitness of filter feeding bivalves.

Assessment of the impact of a pathogen, Bonamia ostreae, on Ostrea edulis oyster stocks with different histories of exposure to the parasite in Ireland

Abstract The protozoan parasite Bonamia ostreae has decimated Ostrea edulis stocks throughout Europe over the past four decades. A study of two stocks of O. edulis in Ireland with varying periods of exposure to B. ostreae , 5 years and 22 years, was undertaken. The objective of the study was to determine if varying lengths of exposure would translate into observations of differing susceptibilities to B. ostreae . A number of oyster beds within each area were screened. The study was carried out over 13 months to investigate seasonality and the role of environmental parameters, population density and size on disease development. Of particular interest was the fact that prevalence of infection in both stocks was very similar. The stock that had been exposed for 22 years had a similar prevalence, intensity and seasonality of infection as the stock infected for 5 years. B. ostreae was detected in both stocks throughout the year with the highest prevalence in spring, possibly related to the increase in water temperature and/or oysters directing their energy towards gametogenesis. The study indicated that oyster stocks can maintain themselves over extended periods of time in B. ostreae endemic areas. However, prevalence of B. ostreae will remain relatively stable within the stock without some intervention to improve resistance levels e.g. by breeding for resistance over a number of years. Some natural resistance to infection will build up in individual oysters but in natural populations this will continually be diluted by cross fertilisation with more susceptible oysters.

Feeding and intoxication–detoxification dynamics in two populations of the mussel Mytilus chilensis (Hupé, 1854) with different histories of exposure to paralytic shellfish poisoning (PSP)

Individuals of Mytilus chilensis with different histories of exposure to paralytic shellfish poisoning (PSP) were exposed to a diet containing the dinoflagellate Alexandrium catenella. Feeding and intoxication–detoxification dynamics were evaluated over a period of 12–16 days. Feeding activity was reduced during the first days of exposure, followed by a period of recovery from day 5 to the end of the experiment. Mussels from Corral population (no history of PSP exposure) exceeded the concentration of 80 μg STX eq. 100 g−1 tissue, although filtration activity was significantly lower compared with individuals from Melinka (frequent PSP exposure). The higher feeding activity and the lower degree of toxin accumulation in the Melinka population appear be associated with frequent exposure to PSP in the natural environment. The use of A. catenella as food resource and the capacity of a rapid intoxication of both populations showed that M. chilensis is an adequate indicator for early detection of PSP.

PYRENE EFFECTS ON RHIZOPLANE BACTERIAL COMMUNITIES

Certain plant species promote biodegradation of polycyclic aromatic hydrocarbons (PAHs), but few studies have examined the microbial populations that are associated with the rhizoplane of these plants. In this study, the bacterial composition of the rhizoplane were characterized for four plant species during in soils with different histories of exposure to PAH and in the presence or absence of a pyrene spike at 100 mg kg−1 pyrene. Three of the plant species including Andropogon gerrardii, Panicum coloratum and Melilotus officinalis were known to stimulate PAH degradation. Wheat (Triticum aestivum) was used as a reference species. Results showed that after 90 days, approximately 45% of the pyrene spike disappeared from soil without plants. In contrast, cultivation of plants resulted in 95% disappearance of pyrene. There were no significant differences in the extent of pyrene disappearance for different plants. In all cases, 16S rRNA gene profiles of the rhizoplane were less complex in the pyrene-spiked soils, suggesting that richness and evenness of the predominant bacteria were reduced. Our results show that pyrene contamination results in significant shifts in the composition of rhizosphere bacterial communities that are still further influenced by the plant species and prior exposure history to PAH contamination.

Ecological linkages between community and genetic diversity in zooplankton among boreal shield lakes

Ecological linkages between species diversity in communities and genetic diversity in populations have potential to influence the assembly of communities in habitats recovering from human disturbance, but few studies have attempted to synthesize relationships between these levels of biological organization, especially for locally adapted species. No such studies have been done in freshwater ecosystems despite the plethora of environmental stressors plaguing aquatic communities around the world. We present the first study to test (1) whether diversity and dissimilarity among communities and populations of a locally adapted species are correlated and (2) whether communities and population haplotypes respond differently to environmental selection and spatial structure of habitats. We used a fragment of mitochondrial DNA (mtDNA) belonging to the gene cytochrome oxidase subunit I (COI) as a neutral tag to discriminate among different population haplotype variants. In boreal lakes with different histories of exposure to anthropogenic acidification, diversity and dissimilarity metrics for crustacean zooplankton communities and locally adapted populations of an abundant and broadly distributed calanoid copepod species, Leptodiaptomus minutus, did not correlate. This discord was likely because zooplankton communities responded more strongly to acidity and acidity-related environmental variables than spatial structure of lakes, whereas the distribution of L. minutus haplotypes was more strongly governed by spatial structure of lakes than environmental selection. Although spatial structure was the dominant driver of haplotype structure among L. minutus lake populations, there were similarities in the types of environmental variables that influenced the distributions of species in communities and haplotypes in populations. How haplotype diversity among populations relates to community diversity depends on the relative influence of spatial structure of habitats and selection at each of these scales of biological organization.

Historic, Demographic, and Genetic Evidence for Increased Population Frequencies of CCR5Δ32 Mutation in Croatian Island Isolates after Lethal 15th Century Epidemics

To assess the frequency of 32 base pair deletion in CCR5 (CCR5Delta32), which has been shown to confer resistance to HIV infection in a homozygous form, in 10 isolated island communities of Dalmatia, Croatia, with different histories of exposure to epidemics during and since the medieval period. In 2002, DNA analysis of 100 randomly selected individuals from each of the 10 isolated communities of 5 Croatian islands (Susak, Rab, Vis, Lastovo, and Mljet) showed high levels of 3-generational endogamy, indicating limited gene flow. Five of the communities were decimated by epidemics of unknown cause between 1449-1456, while the other 5 villages remained unaffected. Genotyping of the CCR5 gene was performed using the polymerase chain reaction method with primers flanking the region containing 32-bp deletion. The frequency of CCR5Delta32 in the 5 villages affected by the epidemic was 6.1-10.0%, and 1.0-3.8% in the 5 unaffected villages. The Delta32 mutation was found in 71 of 916 alleles among the individuals from the affected villages (7.5%), and in 24 of 968 alleles in unaffected villages (2.5%, chi(2)=27.3, P<10-6). A previous study in 303 random Croatian blood donors showed the frequency of the CCR5 Delta32 of 7.1% in the general population. The difference remained significant after correcting for population structure using both STRAT and STRUCTURE software and the genomic control test, to ensure results do not arise from the background genetic differences. Our results and historical evidence, suggest that the mid-15th century epidemic could have acted as a selection pressure for the CCR5Delta32 mutation.

Solar and cosmogenic argon in dated lunar impact spherules

We have studied lunar impact spherules from the Apollo 12 and Apollo 14 landing sites, examining the isotopic composition of argon released by stepwise heating. Elsewhere, we reported the formation ages of these spherules, determined by the 40Ar/ 39Ar isochron method. Here, we discuss solar and cosmogenic argon from the same spherules, separating these two components by correlating their partial releases with the releases of calcium-derived 37Ar on a “cosmochron” diagram. We use the abundances of cosmogenic argon to derive a cosmic ray exposure age for each spherule, and demonstrate that single scoops of lunar soil contain spherules which have experienced very different histories of exposure and burial. The solar argon is seen to be separated into isotopically lighter and heavier fractions, which presumably were implanted to different depths in the spherules. The abundance of the isotopically heavy solar argon is too great to explain as a minor constituent of the solar particle flux, such as the suprathermal tail of the solar wind. The fact that the spherules have been individually dated allows us to look for possible variations in the solar wind as a function of time, over the history of the Solar System. However, the isotopic composition and fluence of solar argon preserved in the lunar spherules appear to be independent of formation age. We believe that most of the spherules are saturated with solar argon, having reached a condition in which implantation by the solar wind is offset by losses from solar-wind sputtering and diffusion.

Intraspecific competition in populations of Helix aspersa with different histories of exposure to lead

A range of invertebrates have become adapted to certain toxic metals, such that, in the presence of the contaminant, some measure of their performance, typically growth or reproduction, is superior to that of an unexposed population. Under such a toxic stress, a population with a history of exposure might outperform a naı̈ve population in competition for limited resources. This study compared the shell growth of laboratory-bred juveniles from six populations of Helix aspersa with different histories of exposure to Pb. In 10 trials using various combinations of two populations, the snails competed for a limited supply of food that contained either no Pb or 500 μg/g−1 Pb, for 98 days. Each trial consisted of 10 juveniles, five from each population and was replicated four times. Nearly all of the food provided was consumed quickly after presentation. The total amount of shell growth within each replicate (the sum of the mean growth of the two populations) was highly consistent between trials so that the total amount of shell built was limited by food availability. The presence of Pb in the diet caused no measurable depression of shell growth and exposure history did not appear to confer any competitive advantage or disadvantage in any of the trials. One population consistently grew faster than its competitors in every trial of which it was a part. Shell growth tended to be greater in smaller juveniles. Snail activity is known to be inhibited at high densities and this may have contributed to the lower incremental growth in individuals kept at the higher densities. The competitive advantage enjoyed by one population may be primarily determined by their activity or perhaps their Ca metabolism.

CALCIUM PROVISION TO EGGS IN TWO POPULATIONS OF HELIX ASPERSA BY PARENTS FED A DIET HIGH IN LEAD

The reproductive performance of two populations of Helix aspersa with different histories of exposure to lead was assessed by their egg production, hatching success and the metal content of the eggs. By using laboratory-bred parents raised in a Pb-free environment, the possibility of an inherited response to a high Pb exposure was assessed. Following a period of dormancy, six individuals in each population were paired for copulation and allowed to oviposit. During this time they were fed a diet with 500 pg.g-' Pb, for a total of 14 days. After oviposition, the egg mass from each pairing was weighed, counted and samples analysed. Metal concentrations in four tissue fractions of the parents (shell, hepatopancreas, reproductive system and 'rest') were also analysed. There was no significant transfer of Pb to the eggs in either population. There were differences in their egg masses-the population from an uncontaminated site, Rottingdean (RD), laid, on average, twice the number of eggs of the snails from Minera (MI), a contaminated site in North Wales. However the latter had a higher average percentage emergence (90% compared to 55% for RD). There was also considerable hatching asynchrony in the RD offspring, while hatching within each MI egg mass was completed within two days. This is discussed in relation to the Ca status of the parent and possible differences in reproductive strategy between the two populations.

Sensitivity to acidic pH in benthic invertebrate assemblages with different histories of exposure to metals

A number of studies have documented tolerance in aquatic communities exposed to contaminants, but few have examined costs of tolerance and potential community-level consequences. We assessed the effects of metals and acidic pH, a novel stressor, on communities from streams with different histories of metal pollution. Acidic pH was a novel stressor to communities in streams that are consistently circumneutral. Intact benthic invertebrate assemblages collected from metal-polluted sites on the Arkansas River (AR1, low levels of pollution, and AR5, greater levels of pollution) and a reference site on the Cache la Poudre River (PR), Colorado, were exposed to either metals (Zn, Cu, Cd) or pH 4.5 in stream microcosms. Multivariate analyses on a subset of taxa showed different patterns of response to metals and acidic pH among the 3 sites, which corresponded to exposure histories of the communities: PR assemblages were more sensitive to metals, whereas AR assemblages were more sensitive to acidic pH. These patterns were supported by analyses on specific characteristics of community structure. Exposure to metals significantly reduced abundance of mayfly taxa in PR (p = 0.0041, ANOVA, linear contrast), AR1 (p = 0.0108), and AR5 (p = 0.0329) assemblages and taxa abundance in PR (p = 0.0225) and AR1 (p = 0.0469) assemblages. Total invertebrate abundance also decreased in PR assemblages exposed to metals (p = 0.0274). The results suggested that greater metal tolerance within the Arkansas River communities was a result of assemblage-level differences in community structure and population-level differences in sensitivity among sites. In contrast, Arkansas River assemblages, especially those from AR5, were sensitive to acidic pH, which reduced invertebrate abundance in PR (p = 0.0339), AR1 (p = 0.0284), and AR5 (p = 0.0062) assemblages. Abundances of mayflies and mayfly taxa also were significantly lower in AR1 (p = 0.0247, p = 0.0042, respectively) and AR5 (p < 0.0001, p = 0.0006, respectively) assemblages exposed to acidic pH but were not significantly altered in PR assemblages. These differences among sites in response to acidic pH resulted primarily from differences in community composition. For instance, the AR5 mayfly assemblage was dominated by Baetis spp., which were eliminated from all treatment streams. In contrast, less sensitive mayfly taxa (Rhithrogena hageni and Ephemerella infrequens) were abundant at stations AR1 and PR. Our results suggested that chronic metal pollution may have produced communities tolerant of metals but more sensitive to acidic pH.

Metal-binding capacity of arbuscular mycorrhizal mycelium.

Experiments with excised mycelium of several Glomus spp. with different histories of exposure to heavy metals were carried out to measure their capacities to bind Cd and Zn. Cd sorption was followed for up to 6 h of incubation to determine its time course relationships. Controls treated with a metabolic inhibitor were included to evaluate whether sorption was due to active uptake or passive adsorption. The effect of ion competition (effects of Ca or Zn on Cd sorption) and general measurements of cation exchange capacity (CEC) of roots and hyphae were also performed. The results showed that AM mycelium has a high metal sorption capacity relative to other microorganisms, and a CEC comparable to other fungi. Metal sorption was rapid (<30 min) and appeared mainly to be due to passive adsorption. Adsorption was highest in a metal-tolerant G. mosseae isolate and intermediate for a fungus isolated from a soil treated with metal-contaminated sludge. The former adsorbed up to 0.5 mg Cd per mg dry biomass, which was three times the binding capacity of non-tolerant fungi, and more than 10 times higher than reported values for, e.g., the commonly used biosorption organism Rhizopus arrhizus. The implications of these results for AM involvement in plant protection against excess heavy metal uptake are discussed.

Response to fenbutatin oxide in populations of Tetranychus urticae Koch (Acari: Tetranychidae) in UK protected crops

Control of spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), in protected edible crops in the UK has depended on the combined use of the predatory mite, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae), and the selective acaricide, fenbutatin oxide. However, in recent seasons there has been concern that the chemical has not performed well against all T. urticae populations. This paper reports the results of laboratory-based tests to determine the response to fenbutatin oxide of five populations of T. urticae collected from various sources with different histories of exposure to the acaricide. There were significant differences in the response of the mite populations; one appeared to be resistant, one partially resistant and three susceptible to fenbutatin oxide. Three of the mite populations became significantly more resistant following a single exposure to fenbutatin oxide but there was evidence that they reverted to being more susceptible when the selection pressure was relaxed. The results explain why many growers have experienced intermittent difficulties controlling T. urticae with fenbutatin oxide for several years without the widespread development of complete resistance.

Variation in response to defoliation between populations of Bouteloua curtipendula var. caespitosa (Poaceae) with different livestock grazing histories

Distinctive plant growth and development have been associated with resistance to defoliation by herbivores. Descriptions of resistance (tolerance/avoidance) strategies are common, although little is known about genetic variation affecting their expression in natural plant communities. This research compared response to three frequencies of defoliation in populations of Bouteloua curtipendula var. caespitosa from Arizona with different histories of exposure to domestic herbivores. One population occurs on a site that has likely been unaffected by large herbivores including cattle, while the other has been regularly grazed by cattle. Mixed-model analysis of variance was used to examine variation in traits associated with defoliation resistance. Data were collected in a 168-d greenhouse experiment using ramets of 15 genets from each population. Mortality was lower in the cattle-impacted population, suggesting improved defoliation resistance. This was associated with increased production of tillers with lower mass following defoliation. Plasticity was observed for all traits in response to different defoliation frequencies. The cattle-free population exhibited significant genetic variation for plasticity affecting leaf blade angle, while little variation was noted for this trait in the cattle-impacted population. Evidence of reduced genetic variation within the cattle-impacted population was noted for traits associated with defoliation resistance. In general, these observations are consistent with expectations following selection for resistance to defoliation.

Mothers' and Fathers' Reports of Children's Reactions to Naturalistic Marital Conflict

To examine how children, aged 8 to 11 years, react to observing their parents' naturally occurring marital conflict in their own homes and to compare reactions among children raised in homes characterized by different types of marital conflict. For 5 1/2 weeks, mothers and fathers of 110 children used daily home diaries to record independently their children's reactions to marital conflict. Logistic regression compared the likelihood of exhibiting specific reactions to conflict among children from marriages characterized by low conflict (LOWCON; n = 37), nonphysical conflict (NOPHYCON; n = 35), and physical conflict (PHYCON; n = 38). Mothers' and fathers' reports indicate that children from PHYCON homes were more likely than children from LOWCON and NOPHYCON homes to leave the room, misbehave or appear angry, and appear sad or frightened. These results support the notion that different histories of exposure to marital conflict may contribute to the way in which children react to their parents' marital conflict.