Common Garden Environment Research Articles

Morphological variation and floral abnormalities in a trigger plant across a narrow altitudinal gradient

AbstractLocal adaptation in alpine plants has been demonstrated across wide altitudinal gradients, but has rarely been examined across the alpine‐to‐montane transition that often encompasses only a few hundred metres. Here we characterize morphological variation in leaf and floral characteristics of the trigger plant Stylidium armeria along a narrow altitudinal gradient in the Bogong High Plains in Victoria. Across this gradient, which encompasses the high‐elevation limit of this species, linear changes were found for floral scape height, leaf length and flower number. All these traits decreased with increasing altitude, whereas the frequency of abnormal flowers increased. When plants were grown in a common garden environment, an altitudinal pattern for flower abnormalities was no longer detected. However, altitudinal patterns for leaf length and scape height were maintained, albeit weaker than in the field. This indicates heritable variation for these morphological traits; the altitudinal patterns are likely to reflect the effects of selection by environmental factors that vary with altitude. Selection pressures remain to be identified but have generated both cogradient and countergradient patterns of variation.

Yolk hormones have sex-specific long-term effects on behavior in the pied flycatcher ( Ficedula hypoleuca)

The hormonal environment during early development, such as maternally derived androgens in bird eggs, shapes the development and phenotype of the offspring in ways that may have important long-term consequences for behaviour. We studied the effects of yolk androgens on multiple behavioural traits in female and male pied flycatchers ( Ficedula hypoleuca) by experimentally elevating androgen levels (testosterone and androstenedione) in the eggs. The birds were housed in a common-garden environment in captivity until full independence, after which their behaviour was tested. We found that androgen-treated males were more likely than control males to explore a novel environment and showed higher activity in the presence of a novel object. In response to a simulated predator attack, androgen-treated males mainly showed freezing behaviour, while control males showed escape behaviour. Females from the androgen treatment and control group showed no differences in these behaviours. Androgen treatment did not affect neophobia (latency to approach the novel object) or dominance behaviour in either sex. Behaviour in the novel environment and towards a novel object was repeatable, but behaviours in the different experiments were mostly not inter-correlated. These results indicate that yolk androgens have various long-lasting effects on behaviour, especially in males, but that they do not induce a distinct behavioural syndrome. As behaviour is strongly linked with fitness, our results suggest that yolk androgens may play a role in determining fitness, and thus play a potentially adaptive role.

Partitioning of genetic variation in the weedy clonal herb Aegopodium podagraria (Apiaceae) in Sweden

Although sexual reproduction appears to be rare in many clonal plant species, the majority of clonal species show similar levels of genetic variation to non‐clonal plant species. Aegopodium podagraria is a noxious garden weed and has become a successful invader in many natural habitats. Earlier studies have demonstrated population differentiation in life‐history traits between different A. podagraria populations in Sweden. In this study, we used three methods to assess genetic variation in this species. Using analyses of molecular markers (chloroplast DNA PCR‐RFLP and allozyme electrophoresis) we did not detect any variation between different A. podagraria clones. However, a multivariate analysis of leaflet shape in five populations from central Sweden revealed considerable variation both within and between populations. The variation found in leaflet shape is suggested to be genetically based because the leaves were collected from plants grown from seed under similar conditions in a common garden environment. These relatively high levels of variation within and between populations indicate that there is likely to be repeated seedling recruitment within established populations.1

Regional genetic variation in three native grasses in northern California

Germination, growth, and flowering traits varied widely in a common-garden nursery environment and expressed coarse-textured geographic patterns among Plumas National Forest seed sources of 3 native grasses (Poaceae): blue wildrye ( Elymus glaucus Buckley ssp. glaucus , California brome ( Bromus carinatus Hook. & Arn. var. carinatus ), and Orcutt's brome ( B. orcuttianus Vasey). Seed zones are justified to partition the geographic variation in grasses on the Plumas National Forest because: 1) adaptive traits varied significantly with geographic surrogates for climate and photoperiod; 2) a coarse-textured geographic and topographic pattern overshadowed microsite variation; and 3) paired (proximal) sources were more similar to one another than more distal sources, all of which indicated selection may have contributed to population differentiation. Each species displayed a different geographic pattern, but Bromus species were most similar. Low-elevation southwestern sources of B. carinatus had earlier and higher germination and slightly higher shoot dry weight, while high-elevation northern lots had later and lower germination and dry weight. S outhern sources of B. orcuttianus produced more flowers and germinated earlier than northern sources. Elymus glaucus from lower-elevation and more eastern sources, where summer drought is most pronounced, had higher dry weight and flowers. Kitzmiller JH. 2009. Regional genetic variation in three native grasses in northern California. Native Plants Journal 10(3):263–280. Kitzmiller JH. 2009. Regional genetic variation in three native grasses in northern California. Native Plants Journal 10(3):263–280.

Life history evolution in a globally invading tephritid: patterns of survival and reproduction in medflies from six world regions

Comparisons among populations from different localities represent an important tool in the study of evolution. Medflies have colonized many temperate and tropical areas all over the world during the last few centuries. In a common garden environment, we examined whether medfly populations obtained from six global regions [Africa (Kenya), Pacific (Hawaii), Central America (Guatemala), South America (Brazil), Extra-Mediterranean (Portugal) and Mediterranean (Greece)] have evolved different survival and reproductive schedules. Whereas females were either short-lived [life expectancy at eclosion (e0) 48–58 days; Kenya, Hawaii and Guatemala] or long-lived (e0 72–76 days; Greece, Portugal and Brazil], males with one exception (Guatemala) were generally long-lived (e0 106–122 days). Although males universally outlived females in all populations, the longevity gender gap was highly variable (20–58 days). Lifetime fecundity rates were similar among populations. However, large differences were observed in their age-specific reproductive patterns. Short-lived populations mature at earlier ages and allocate more of their resources to reproduction early in life compared with long-lived ones. In all populations, females experienced a post-reproductive lifespan, with this segment being significantly longer in Kenyan flies. Therefore, it seems plausible that medfly populations, inhabiting ecologically diverse habitats, have evolved different life history strategies to cope with local environmental conditions. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 106–117.

Morphological and physiological variation among seagrass (Zostera marina) genotypes

Intraspecific variation in habitat-forming species can have important ecological consequences at the population, community, and ecosystem level. However, the contribution of genetic variation among individuals to these effects is seldom documented. We quantified morphological and physiological variation among genotypes of a marine foundation species, the seagrass Zostera marina. We grew replicate shoots of eight genetically distinct Zostera individuals collected from Bodega Bay, California, in a common garden environment and then quantified shoot production and morphology, nutrient uptake, and key photosynthetic parameters. We found that genotypes differed in shoot production, biomass, and both root and shoot nutrient uptake rates, even when corrected for genotype-specific biomass differences. In addition, the rank order of uptake ability differed for ammonium and nitrate, indicating that genotypes may exhibit resource partitioning of different forms of nutrients. Our results suggest that both niche complementarity among genotypes and the sampling/selection effect could contribute to previously observed positive effects of seagrass clonal diversity on resource utilization and biomass production. Further, they highlight that genotypic variation in key traits of habitat-forming species could have measurable effects on community structure and function.

Physiological differences among twoPenstemonspecies and their hybrids in field and common garden environments

Hybrids can exhibit unique combinations of the physiological traits of their parents. These particular combinations may influence hybrid fitness and the evolutionary trajectory of a hybrid zone. Here, a hybrid zone between Penstemon newberryi and Penstemon davidsonii along an elevational gradient was examined, and physiological traits of parents and hybrids were measured in their native environment and a common garden. Gas exchange rates of nine different crosses were also measured. Alpine P. davidsonii had less negative pre-dawn water potential and lower water use efficiency (WUE) than its montane relative P. newberryi in a common garden and in field measurements. The species difference in WUE was attributable to lower conductance in P. newberryi in the field, but to a higher photosynthetic rate in this species in the common garden. The alpine species took less time to produce mature fruits and reached maximum photosynthetic rate at a lower temperature. Natural hybrids were intermediate for most characters. F(1) hybrids had lower conductance than progeny of natural hybrids. The intermediate WUE of natural hybrids may be one factor that allows them to persist in intermediate environments. Comparisons of different crosses suggest that the genotypic composition of hybrids influences their physiological performance.

Seasonal Shifts in Reproductive Investment of Female Northern Grass Lizards (Takydromus septentrionalis) from a Field Population on Beiji Island, China

Understanding seasonal variation in reproductive investment is crucial to explore life-history strategies of a given species. We measured the timing of reproduction and the reproductive output of recently captured females to test whether the conclusions on seasonal shifts of reproductive investment made in the laboratory can apply to field populations in a lacertid lizard Takydromus septentrionalis. Female T. septentrionalis started producing eggs in April and ceased reproduction in August. During the midreproductive season (May to July), more than 60% of field-captured females were gravid. The females produced more eggs and thus had heavier total egg mass in May than in July, although egg mass and hatchling size did not vary seasonally. The seasonal variation in clutch size did not induce seasonal shifts in trade-offs between clutch size and egg size. In general, these results are largely consistent with data collected in the laboratory and support the conclusion of previous studies in this species that seasonal shifts in reproductive output are determined ultimately by natural selection. However, Relative Clutch Mass (RCM) of recently captured females was greater than that of females in captivity, which suggests that RCMs could be affected noticeably by proximate factors. Therefore, when explaining the evolutionary strategies of an organism based on intraspecific comparisons of RCMs, investigators should measure them in a common-garden environment so as to control the potential influence of environmental factors.

Moving beyond Common‐Garden and Transplant Designs: Insight into the Causes of Local Adaptation in Species Interactions

Theoretical and empirical studies of local adaptation in species interactions have increased greatly over the past decade, yielding new insights into the conditions that favor local adaptation or maladaptation. Generalizing the results of these studies is difficult, however, because of the different experimental designs that have been used to infer local adaptation. Particularly challenging is comparing results across empirical studies conducted in a common laboratory or garden environment with results of those conducted using transplants in natural environments. Here we develop simple and easily interpretable mathematical expressions for the quantities measured by these two different types of studies. Our results reveal that common-garden designs measure only a single component of local adaptation-the spatial covariance between the genotype frequencies of the interacting species-and thus provide only a partial description of local adaptation. In contrast, reciprocal-transplant designs incorporate additional terms that measure the contribution of spatial variability in the ecological environment. Consequently, the two types of studies should yield identical results only when local adaptation is caused by spatial variability in the genotype frequencies of the interacting species alone. In order to unify these disparate approaches, we develop a new methodology that can be used to estimate the individual components of local adaptation. When implemented in an appropriate experimental system, this partitioning allows the examination of fundamental questions such as the relative proportion of local adaptation attributable to interactions between species or to the abiotic environment.

Variation in horizontal and vertical transmission of the endophyte Epichloë elymi infecting the grass Elymus hystrix

Systemic fungal endophytes (Clavicipitaceae) of grasses reproduce sexually when the fungus forms stromata and contagious ascospores, or asexually by vertical transmission of hyphae into seeds and seedlings. Vertical transmission is predicted to favor reduced virulence compared with horizontal transmission in systems with both types of transmission. Here, variation in vertical and horizontal transmission and its potential heritability in a host grass-endophyte interaction, Elymus hystrix infected with Epichloë elymi, were examined in natural populations and two common garden experiments using field-collected host tillers and seed progeny of maternal plants with known infection phenotypes. Transmission mode exhibited year-to-year variation in field and common garden environments. In the common garden there were consistent differences among maternal plant families in stroma production and significant correlations between stroma production in the common garden and in natural populations. Transmission mode differed among maternal families, spanning a continuum from pure vertical transmission to a high proportion of stroma production and horizontal transmission potential. Vertical transmission to seeds occurred at high rates in all maternal families regardless of their stroma production. Observed patterns of variation indicate that endophyte transmission mode and correlated changes in virulence can respond to selection by biotic and abiotic factors.

A latitudinal cline in flowering time in Arabidopsis thaliana modulated by the flowering time gene FRIGIDA

A latitudinal cline in flowering time in accessions of Arabidopsis thaliana has been widely predicted because the environmental cues that promote flowering vary systematically with latitude, but evidence for such clines has been lacking. Here, we report evidence of a significant latitudinal cline in flowering time among 70 Northern European and Mediterranean ecotypes when grown under ecologically realistic conditions in a common garden environment. The detected cline, however, is found only in ecotypes with alleles of the flowering time gene FRIGIDA (FRI) that lack major deletions that would disrupt protein function, whereas there is no relationship between flowering time and latitude of origin among accessions with FRI alleles containing such deletions. Analysis of climatological data suggests that late flowering in accessions with putatively functional FRI was associated with reduced January precipitation at the site of origin, consistent with previous reports of a positive genetic correlation between water use efficiency and flowering time in Arabidopsis, and the pleiotropic effects of FRI of increasing water use efficiency. In accessions collected from Southern latitudes, we detected that putatively functional FRI alleles were associated with accelerated flowering relative to accessions with nonfunctional FRI under the winter conditions of our experiment. These results suggest that the ecological function of the vernalization requirement conferred by FRI differs across latitudes. More generally, our results indicate that by combining ecological and molecular genetic data, it is possible to understand the forces acting on life history transitions at the level of specific loci.

Evolution of intrinsic growth and energy acquisition rates. II. Trade-offs with vulnerability to predation in Menidia menidia.

The Atlantic silverside (Menidia menidia) exhibits countergradient latitudinal variation in somatic growth rate along the East Coast of North America. Larvae and juveniles from high-latitude populations display higher intrinsic rates of energy consumption and growth than genotypes from low-latitude populations. The existence of submaximal growth in some environments suggests that trade-offs must counter the oft-cited theoretical benefits of energy and growth maximization (e.g., "bigger is better,'' ''faster is better'') in the immature life stages. We hypothesized that energy and growth maximization trades off against investment in defense from predators. We conducted laboratory selection experiments to compare vulnerability to predation of silversides from: (1) fast-growing northern (Nova Scotia, NS) versus slow-growing southern (South Carolina, SC) source populations; (2) phenotypically manipulated fast-growing versus moderately-growing NS fish; and (3) recently fed versus unfed NS and SC fish. Tests involved fish drawn from common-garden environments and were conducted by subjecting mixed-treatment schools of size-matched silversides to natural, common piscine predators. NS silversides suffered significantly higher predation mortality than SC silversides. Parallel results were found in phenotypic manipulation of growth: NS silversides reared on a fast-growth trajectory (approximately 1.0 mm/day) were significantly more vulnerable to predation than those growing at a moderate rate (approximately 0.5 mm/day). Food consumption also affected vulnerability to predators: Silversides with large meals in their stomachs suffered significantly higher predation mortality than unfed silversides. Differences in predation vulnerability were likely due to swimming performance, not attractiveness to predators. Our findings demonstrate that maximization of energy intake and growth rate engenders fitness costs in the form of increased vulnerability to predation.

EVOLUTION OF INTRINSIC GROWTH AND ENERGY ACQUISITION RATES. II. TRADE-OFFS WITH VULNERABILITY TO PREDATION IN MENIDIA MENIDIA

The Atlantic silverside (Menidia menidia) exhibits countergradient latitudinal variation in somatic growth rate along the East Coast of North America. Larvae and juveniles from high-latitude populations display higher intrinsic rates of energy consumption and growth than genotypes from low-latitude populations. The existence of submaximal growth in some environments suggests that trade-offs must counter the oft-cited theoretical benefits of energy and growth maximization (e.g., “bigger is better,” “faster is better”) in the immature life stages. We hypothesized that energy and growth maximization trades off against investment in defense from predators. We conducted laboratory selection experiments to compare vulnerability to predation of silversides from: (1) fast-growing northern (Nova Scotia, NS) versus slow-growing southern (South Carolina, SC) source populations; (2) phenotypically manipulated fast-growing versus moderately-growing NS fish; and (3) recently fed versus unfed NS and SC fish. Tests involved fish drawn from common-garden environments and were conducted by subjecting mixed-treatment schools of size-matched silversides to natural, common piscine predators. NS silversides suffered significantly higher predation mortality than SC silversides. Parallel results were found in phenotypic manipulation of growth: NS silversides reared on a fast-growth trajectory (∼1.0 mm/day) were significantly more vulnerable to predation than those growing at a moderate rate (∼0.5 mm/day). Food consumption also affected vulnerability to predators: Silversides with large meals in their stomachs suffered significantly higher predation mortality than unfed silversides. Differences in predation vulnerability were likely due to swimming performance, not attractiveness to predators. Our findings demonstrate that maximization of energy intake and growth rate engenders fitness costs in the form of increased vulnerability to predation.Corresponding Editor: D. Roff

Developmental instability in hybrids between Lychnis viscaria and Lychnis alpina (Caryophyllaceae)

Developmental instability shown by increased fluctuating asymmetry can be caused by either genetic or environmental stress. Genomic coadaptation and heterozygosity are the genetic factors that are commonly assumed to increase the level of developmental stability. Therefore, in hybrid populations the level of fluctuating asymmetry (FA) can be lower due to higher heterozygosity or higher due to disruption of coadapted gene complexes, depending on the degree of divergence between hybridizing taxa. Here I present data on FA in petals from hybrids between Lychnis viscaria (Caryophyllaceae) and Lychnis alpina and from parental species grown in a common garden environment. Petal asymmetry of hybrids was clearly higher than that of either parental species grown in common environment. Between the two parental species petal asymmetry did not differ. The mean size of the petals in hybrids was about the same as in L. viscaria, thus indicating no heterotic effect. Therefore, it seems that hybrids between L. viscaria and L. alpina do suffer from the disruption of coadapted gene complexes as indicated by higher developmental instability.

Gas Exchange of Idaho Fescue in Response to Defoliation and Grazing History

We tested the hypothesis that prior grazing history would influence the defoliation responses of Idaho fescue (Festuca idahoensis) growing in a common garden environment. Plants were taken from a grazed pasture and adjacent exclosure which had not been grazed since 1937, and established in a common garden at 1 m spacings during spring of 1989. Plants from defoliated and nondefoliated treatments within the 2 populations were sampled during 1992 and 1993. Photosynthesis, conductance to H2O, and xylem potentials were measured during the 2 growing seasons, and carbon isotope ratio (delta 13C) was measured for senescent leaf tissue. Both within exclosure and outside exclosure defoliated plants exhibited compensatory photosynthesis that averaged a 12% increase the first year, and a 52% increase during the second year, compared with nondefoliated plants. No differences in photosynthesis occurred between the 2 collections. However, outside exclosure plants had higher stomatal conductance than did exclosure plants for the dry year 1992. Also, outside exclosure plants exhibited more negative delta 13C (thus lower water use efficiency) than exclosure plants for 1992 and 1993. We suggest that the higher conductance of previously-grazed plants relative to nongrazed plant populations may be an adaptive response to greater soil moisture often found in grazed sites.

Intraspecific variation of leaf pubescence and drought response in Encelia farinosa associated with contrasting desert environments

SUMMARYTraits associated with leaf energy balance are especially important for desert plants because decoupling leaf and ambient temperatures can be critical for maximizing productivity and survival in these hot, dry regions. Deserts are also one of the most climatically unpredictable and heterogeneous biomes; thus, variation of energy balance characters due either to plasticity or genetic differentiation might also be crucial to the success of desert plant species. In a common garden environment we examined variation in the traits associated with energy balance and productivity in Encelia farinosa A. Gray (brittlebush) plants. Comparing two populations from contrasting rainfall and drought climates, we found that plants from the wetter site (Superior, Arizona) always maintained higher leaf absorptances than plants from the more xeric region (Oatman, Arizona) when at similar water potentials. Superior plants also increased stomatal conductance and photosynthesis in response to mid‐spring rainfall, whereas Oatman plants did not. Oatman plants, however, tended to have greater leaf areas and continuous spring growth, which made them larger than Superior plants, yet both populations produced the same number of flower heads. The differences for these traits, and the associations among them, agree with predictions based on the contrasting drought and rainfall environments of these two populations. Our results suggest that the differences might represent alternative suites of characters of selective importance for maximizing carbon gain over the climatically variable range of this widespread species. Furthermore, these differences, detected in common environment conditions, might have a genetic basis, which might contribute to a greater potential for local adaptation in this species.

Morphological and Phenological Variation in Barnyardgrass (Echinochloa crus-galli) in California

Individual barnyardgrass plants were grown in the absence of competition in a common garden environment. Cohorts were initiated in mid-March, late April, early June, mid-July, mid-August, and mid-September. Plants within a cohort varied from prostrate to upright. Early and late cohorts required slightly longer to achieve flowering and seed shatter than those initiated in late spring and early summer. The onset and development of senescence varied by as much as 5 wk between individuals within a cohort, and senescence progressed more rapidly for plants in later cohorts. Longest tiller length per plant averaged 150 cm and did not differ by cohort, but within cohort variation was approximately 33%. The number of tillers per plant declined with increasing delay in cohort initiation; within cohort variation exceeded 40%. Leaf numbers decreased from more than 10,000 per plant to less than 400 per plant with increasing delay in cohort initiation date. Individuals within a cohort had more than two-fold variation in leaf numbers. The number of inflorescences decreased from more than 4500 per plant to less than 100 with increasing delay in cohort initiation. Mean inflorescence length and frequency of different inflorescence lengths per plant varied between plants within a cohort. Vegetative biomass exceeded 3000 g for many plants in the early cohorts, and decreased to less than 25 g per plant for some individuals in the September cohort. More than two-fold variation in biomass occurred between plants within a cohort. Plasticity in morphology and phenology may contribute to the success of barnyardgrass as a weed.

Genetic variation in red alder (Alnusrubra) in relation to native climate and geography

Genetic variation was examined within and among populations of red alder (Alnusrubra Bong.) from elevational gradients in four river drainages of the Pacific Northwest. Wind-pollinated progenies of 120 trees were grown for 3 years in a common garden environment and measured for growth and shoot phenology. Variation in top weight, bud flush, and leaf abscission was analyzed in relation to native climate and elevation and compared with sympatric species. Strong geographic patterns of variation were observed for all measured traits, apparently reflecting adaptations to highly variable climates within the region studied. Growth traits were correlated with temperature amplitude and length of growing season. Growth rhythm in bud flushing and growth cessation was related to two important environmental cues, spring thermal sums and fall frost dates. Overall levels of variation in red alder appeared to be similar to several sympatric conifers, although variation within populations of red alder was lower. The latter finding may be due to the demography of the riparian populations sampled, or perhaps a characteristic of the species and its colonizing life history.

Microgeographic genetic variation of Sitka spruce in southeastern Alaska

Microgeographic genetic variation among populations of Sitka spruce on Mitkof Island in southeastern Alaska is described. In two common-garden environments, we evaluated genotypes of 208 parent trees from 114 locations in a 17 000-ha area. Two principal components accounted for most of the variation among locations in 11 traits measured to evaluate growth vigor and rhythm of 2-year-old seedlings. Regression analyses of factor scores derived from principal components revealed genetic gradients associated with elevation, slope, aspect, and west–east and north–south direction. Large amounts of additive genetic variation in factor scores occurred among trees within locations. When this variation within locations was used as a scale, variation among locations was also large. In an extreme case, locations differed in factor scores of the first principal component by about 3.0 units of the standard deviation of additive genetic variation in factor scores. Of the total differentiation in this case, elevational range (600 m) contributed 0.7 units of standard deviation, aspect contributed 0.9 units, and distance (16 km) from north central to southeastern parts of the island contributed 1.4 units.

COMPETITIVE RELATIONSHIPS OF OENOTHERA SPECIES WITH DIFFERENT RECOMBINATION SYSTEMS

The hypothesis that outcrossers are competitively superior to close relatives with specialized genetic systems was tested. Interspecific competition between three closely related Oenothera species was examined in common garden environments. Oenothera grandis, an obligate outcrosser, is competitively superior to its derivative, O. laciniata, an obligate chromosomal heterozygote. Both of these species are superior to O. mexicana, a closely related facultative selfer. These relationships were consistent over two levels of density stress. Therefore, in this species triad, the outcrosser has a competitive advantage over its close relatives with derived breeding systems.