Cone Traits Research Articles

Cone selection by Eurasian red squirrels in mixed conifer forests in the Italian Alps

Abstract Tree squirrels are arboreal granivores that harvest and consume tree seeds both prior to and after seed-dispersal. Inter- and intraspecific patterns of seed predation suggest that squirrels may exert strong selective pressure on cone morphology and patterns of cone production, and suggest coevolutionary interactions between squirrels and conifers. In some pine species (genus Pinus ), mutualistic relationships have evolved between cone (seed) traits and seed-dispersal behaviour by birds and rodents. In other species, feeding by seed predators has selected for cone traits that decrease intensity of seed consumption. In mixed conifer forests, red squirrels ( Sciurus vulgaris ) feed intensively in some (target) trees but avoid others (nontarget trees). Here we explore defensive cone traits and seed traits correlated with tree selection for conifer species with different seed-dispersal strategies. No selection for cone traits existed in Pinus cembra , which has large wingless seeds, dispersed by birds and rodents. In Picea abies , the most favoured species, target trees had cones with more seeds per cone than nontarget trees, and number of seeds increased with cone length. Cone selection was most pronounced in Pinus sylvestris , where target trees had bigger cones with more seeds and higher total seed mass than nontarget trees. However, ratio of seed mass on cone mass did not differ among target and nontarget trees, suggesting that bigger cones also had more protective tissue, probably increasing difficulties for seed predators to gain access to seeds. Our results suggest that cone and seed traits of P. cembra facilitate seed consumption by squirrels, but that defensive cone traits of small-seeded conifers, in combination with annual differences in seed production (masting), might be the result of coevolution with seed-eating squirrels.

Effectiveness of neutral RAPD markers to detect genetic divergence between the subspecies uncinata and mugo of Pinus mugo Turra

Fifteen populations of Pinus mugo subsp. mugo (shrub) and Pinus mugo subsp. uncinata (erect), located in the Alps, were investigated through genetic variation scored at 64 polymorphic RAPD loci. In addition, morphological traits of the female cones were analysed. According to AMOVA most of the genetic variation was found within populations (83.39%), and only 1.25% of it between subspecies. Populations differed in terms of their internal genetic variation, with Nei’s gene diversity ranging from 0.227 to 0.397. Morphological data showed differences between subspecies, although none of the populations showed full accordance with expectations. Significant correlation was found between matrices for geographical and morphological distances, while genetic distances were not correlated with any other aspect. The efficacy of morphological and RAPD markers in discriminating between subspecies, and the contribution of the results in relation to the preservation of biodiversity, are discussed.

Elevated temperature during reproductive development affects cone traits and progeny performance in Picea glauca x engelmannii complex

Two temperature regimes were applied during reproductive development of seed and pollen cones of interior spruce (Picea glauca (Moench) Voss and Picea engelmannii (Parry) complex) to determine temperature effects on the adaptive traits of progeny. In Experiment 1, identical crosses were made on potted interior spruce using untreated pollen followed by exposure to a day/night temperature of 22/8 or 14/8 degrees C with a 12-h photoperiod during the stages of reproductive development from post-pollination to early embryo development. Frost hardiness and growth of progeny from seed produced in the two temperature treatments were measured over a 4-year period. Elevated temperature significantly affected both seed-cone development and the adaptive properties of the progeny. Seed cones exposed to the 22/8 degrees C treatment reached the early embryo stage in 53 days versus 92 days in the 14/8 degrees C treatment. Seed yields, cotyledon emergence and percent germination were also significantly enhanced by the 22/8 degrees C treatment. Progeny from seed produced in the higher temperature treatment showed significantly reduced spring and fall frost hardiness, but the elevated temperature treatment had no significant effects on time of bud burst, growth patterns or final heights. In Experiment 2, single ramets of the same clone were subjected to a day/night temperature of 20/8 or 10/8 degrees C during pollen cone development, starting from meiosis and ending at pollen shedding. The two populations of pollen were then crossed with untreated seed cones. Compared with pollen cones exposed to the 10/8 degrees C treatment, pollen cones exposed to the 20/8 degrees C treatment during development reached the shedding stage 2-4 weeks earlier, whereas pollen yields, in vitro viability and fertility (seed set) were significantly lower; however, the resulting progeny displayed no treatment differences in frost hardiness or growth after 1 year. Results suggest that seed orchard after-effects could be caused by temperature differences between orchard site and parent tree origin and that this effect acts on maternal development. Gametophytic (pollen or megagametophyte or both) and early embryo (sporophytic) selection are possible mechanisms that may explain the observed results. Although the effects are biologically significant, they are relatively small and do not justify changes in current deployment strategies for seed orchard seed.

Biogeographic differences in cone, needle and seed morphology among natural Picea asperata populations in Western China

This study represents a geographical approach to morphological variation of cones, needles and seeds in natural dragon spruce (Picea asperata Mast.) populations across western China and the relationship between morphological traits and weather variation for the origins of populations. Significant differences were found for all cone, needle and seed traits among populations and trees within populations. The coefficients of variation in 2 higher latitude populations were higher than those in other populations in all traits except for needle width and seed width. Fairly high within-population variability was also detected for cone dry weight, seed dry weight and needle traits in this study. Cone length, cone width, cone dry weight, seed scale length, seed scale width and seed wing length were strongly positively intercorrelated. Seed length and seed dry weight showed a significantly positive correlation with seed wing length. And needle width showed a significant negative correlation with cone traits, seed scale length, seed wing length and seed length. The higher the annual mean temperature, the higher the average cone length. This study also revealed a negative linear dependence on latitude: the higher the latitude, the lower the population average seed length. Seed dry weight was positively and linearly related with altitude.

Variación morfológica y anatómica en poblaciones mexicanas de Pseudotsuga (Pinaceae)

Con base en características morfológicas y anatómicas de conos, hojas y ramillas se evaluó el patrón geográfico de variación en poblaciones naturales del género Pseudotsuga en México. Las muestras de órganos vegetativos y reproductivos se colectaron en un total de 293 árboles procedentes de 19 localidades de las diferentes regiones geográficas en las cuales se distribuye el género en nuestro país. Se analizaron los caracteres considerados como importantes desde el punto de vista de la sistemática, de tal forma que fueran útiles para tratar de esclarecer los límites de los taxa de este género en México. El análisis de varianza mostró que existe una fuerte diferenciación entre las poblaciones en la mayoría de las variables consideradas, con 22 a 92% de la varianza total a este nivel. La región geográfica de procedencia tuvo un papel importante en la separación de las muestras, lo que implica la existencia de ecotipos diferentes de Pseudotsuga en el territorio de la República. Debido a que la variabilidad atribuible a los taxa putativos fue menor que la correlacionada con las regiones geográficas, se concluye que no existen bases morfológicas suficientes para separar las especies de Pseudotsuga propuestas para México con anterioridad.

Association of cone thermogenesis and volatiles with pollinator specificity in Macrozamia cycads

Cone traits (volatile components and thermogenesis) of three cycad species in the genus Macrozamia were examined for differences related to their specific insect pollinators, the weevil, Tranes spp., or the thrips, Cycadothrips chadwicki. Linalool (>80% of emissions) dominated cone volatile components of M. machinii (Tranes-pollinated) and beta-myrcene was a minor component (<9% of emissions). Volatiles of M. lucida and M. macleayi cones (Cycadothrips-pollinated) were dominated by beta-myrcene (up to 97% of emissions), but no linalool was detected. Pollinator movement into and out of cones coincided with cone thermogenesis and peak odor emission: around sunset for Tranes, and at mid-day for Cycadothrips. Female cone traits were similar to those of their conspecific male cones. Differences in cone traits between Macrozamia species may thus be responsible for conferring pollinator specificity in areas of sympatry.

INTERACTIONS AMONG MOTHS, CROSSBILLS, SQUIRRELS, AND LODGEPOLE PINE IN A GEOGRAPHIC SELECTION MOSAIC

Repeated patterns among biological communities suggest similar evolutionary and ecological forces are acting on the communities. Conversely, the lack of such patterns suggests that similar forces are absent or additional ones are present. Coevolution between a seed predator, the red crossbill (Loxia curvirostra complex), and lodgepole pine (Pinus contorta var. latifolia) exemplifies the ecological and evolutionary predictions for coevolving systems. In the absence of another seed predator and preemptive competitor (pine squirrels Tamiasciurus hudsonicus), natural selection by crossbills results in the evolution of larger cones with thicker distal scales, while relaxation of selection by squirrels results in the evolution of cones with more seeds and a greater ratio of seed mass to cone mass. However, in one range, the Little Rocky Mountains, distal scale thickness has diverged as expected but cone size has not. In these mountains seed predation by lodgepole pine cone borer moths (Eucosma recissoriana) was about 10 times greater than in other ranges lacking squirrels. We quantified moth predation and cone traits and found that moths select for smaller cones with fewer seeds. Thus, selection by moths in the Little Rocky Mountains counters both selection by crossbills for large cone size and relaxation of selection by squirrels favoring more seeds per cone and accounts for the relatively small and few-seeded cones in these mountains. It is also apparent that selection by crossbills changes seed defenses in a manner that favors seed predation by moths, whereas selection by squirrels likely reduces such predation. These results demonstrate the importance of considering the evolutionary consequences of community context in locally evolved (coevolved) traits and interactions.

Seed cone traits and insect damage in Tsuga canadensis (Pinaceae)

We measured seed cones of Tsuga canadensis (L.) Carrière, assessed seed potential (number of fertile scales × 2) and seed efficiency (number of filled seeds/seed potential), and estimated the impact of Eupithecia mutata Pearsall (Lepidoptera: Geometridae) and Megastigmus hoffmeyeri Walley (Hymenoptera: Torymidae) on seed production. Mean length, width, and volume of healthy cones varied little among sites from Ontario. Cones had about 28 scales; 13 were sterile. Seed potential and seed efficiency differed among sites, ranging from 25 to 31 ovules and 24% to 72%, respectively. The number of scales (both sterile and fertile) increased with cone volume, but the proportion of fertile scales was independent of cone size. The maximum proportion of cones infested by E. mutata was 21%. On average, each larva destroyed &gt;90% of the filled seeds from each cone, thus from a practical perspective, the proportion of T. canadensis seeds destroyed per site was equivalent to the proportion of seed cones infested. The proportion of cones infested by M. hoffmeyeri ranged from 9% to 40%, but the proportion of seeds destroyed per site (range: 1.1%–6.1%) was much lower than that of E. mutata. The maximum number of M. hoffmeyeri-infested seeds per cone was seven. To our knowledge, this is the first report documenting cone traits of T. canadensis and the impact of E. mutata and M. hoffmeyeri.

Diversifying coevolution between crossbills and black spruce on Newfoundland.

Coevolution is increasingly recognized as an important process structuring geographic variation in the form of selection for many populations. Here we consider the importance of a geographic mosaic of coevolution to patterns of crossbill (Loxia) diversity in the northern boreal forests of North America. We examine the relationships between geographic variation in cone morphology, bill morphology, and feeding performance to test the hypothesis that, in the absence of red squirrels (Tamiasciurus hudsonicus), black spruce (Picea mariana) has lost seed defenses directed at Tamiasciurus and that red crossbills (L curvirostra) and black spruce have coevolved in an evolutionary arms race. Comparisons of cone morphology and several indirect lines of evidence suggest that black spruce has evolved defenses in response to Tamiasciurus on mainland North America but has lost these defenses on Newfoundland. Cone traits that deter crossbills, including thicker scales that require larger forces to separate, are elevated in black spruce on Newfoundland, and larger billed crossbills have higher feeding performances than smaller billed crossbills on black spruce cones from Newfoundland. These results imply that the large bill of the Newfoundland crossbill (L. c. percna) evolved as an adaptation to the elevated cone defenses on Newfoundland and that crossbills and black spruce coevolved in an evolutionary arms race on Newfoundland during the last 9000 years since glaciers retreated. On the mainland where black spruce is not as well defended against crossbills, the small-billed white-winged crossbill (L leucoptera leucoptera) is more efficient and specializes on seeds in the partially closed cones. Finally, reciprocal adaptations between crossbills and conifers are replicated in black spruce and Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia), with coevolution most pronounced in isolated populations where Tamiasciurus are absent as a competitor. This study further supports the role of Tamiasciurus in determining the selection mosaic for crossbills and suggests that a geographic mosaic of coevolution has been a prominent factor underlying the diversification of North American crossbills.

Quantifying the geographic range ofPinus patulavarlongipedunculatain Southern Mexico using morphologic and RAPD marker data

Synopsis Pinus patula var. longipedunculata occurs in southern Mexico, but the extent of its geographic range is poorly defined. Trees from some populations are morphologically similar to P. tecunumanii, which adds to the confusion over the variety's geographic range. Recent field explorations have identified six new populations of supposed P. patula var. longipedunculata in the Sierra Madre del Sur of Oaxaca and Guerrero. In an effort to determine the validity of these sightings, botanical samples were collected from 79 trees in these six populations and were assessed for ten cone and needle morphology traits. Random Amplified Polymorphic DNA (RAPD) analyses were conducted on 73 trees from the six populations, 38 of which were in common to 79 trees used in the botanical study. Species control lots for both the botanical and RAPD studies were P. herrerae, P. oocarpa, P. patula, P. pringlei and P. tecunumanii. Morphologic assessment indicated trees in the Manzanal population were predominantly patula-relat...

The influence of a competitor on the geographic mosaic of coevolution between crossbills and lodgepole pine.

The geographic mosaic theory of coevolution posits that the form of selection between interacting species varies across a landscape with coevolution important and active in some locations (i.e., coevolutionary hotspots) but not in others (i.e., coevolutionary coldspots). We tested the hypothesis that the presence of red squirrels (Tamiasciurus hudsonicus) affects the occurrence of coevolution between red crossbills (Loxia curvirostra complex) and Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia) and thereby provides a mechanism giving rise to a geographic mosaic of selection. Red squirrels are the predominant predispersal seed predator and selective agent on lodgepole pine cones. However, in four isolated mountain ranges east and west of the Rocky Mountains, red squirrels are absent and red crossbills are the main predispersal seed predator. These isolated populations of pine have apparently evolved without Tamiasciurus for about 10,000 to 12,000 years. Based on published morphological, genetic, and paleobotanical studies, we infer that cone traits in these isolated populations that show parallel differences from cones in the Rocky Mountains have changed in parallel. We used data on crossbill and conifer cone morphology and feeding preferences and efficiency to detect whether red crossbills and lodgepole pine exhibit reciprocal adaptations, which would imply coevolution. Cone traits that act to deter Tamiasciurus and result in high ratios of cone mass to seed mass were less developed in the isolated populations. Cone traits that act to deter crossbills include larger and thicker scales and perhaps increased overlap between successive scales and were enhanced in the isolated populations. In the larger, isolated mountain ranges crossbills have evolved deeper, shorter, and therefore more decurved bills to exploit these cones. This provides crossbills with higher feeding rates, and the change in bill shape has improved efficiency by reducing the concomitant increases in body mass and daily energy expenditures that would have resulted if only bill size had increased. These parallel adaptations and counter adaptations in red crossbills and lodgepole pine are interpreted as reciprocal adaptations and imply that these crossbills and pine are in coevolutionary arms races where red squirrels are absent (i.e., coevolutionary hotspots) but not where red squirrels are present (i.e., coevolutionary cold-spots).

THE INFLUENCE OF A COMPETITOR ON THE GEOGRAPHIC MOSAIC OF COEVOLUTION BETWEEN CROSSBILLS AND LODGEPOLE PINE

The geographic mosaic theory of coevolution posits that the form of selection between interacting species varies across a landscape with coevolution important and active in some locations (i.e., coevolutionary hotspots) but not in others (i.e., coevolutionary coldspots). We tested the hypothesis that the presence of red squirrels (Tamiasciurus hudsonicus) affects the occurrence of coevolution between red crossbills (Loxia curvirostra complex) and Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia) and thereby provides a mechanism giving rise to a geographic mosaic of selection. Red squirrels are the predominant predispersal seed predator and selective agent on lodgepole pine cones. However, in four isolated mountain ranges east and west of the Rocky Mountains, red squirrels are absent and red crossbills are the main predispersal seed predator. These isolated populations of pine have apparently evolved without Tamiasciurus for about 10,000 to 12,000 years. Based on published morphological, genetic, and paleobotanical studies, we infer that cone traits in these isolated populations that show parallel differences from cones in the Rocky Mountains have changed in parallel. We used data on crossbill and conifer cone morphology and feeding preferences and efficiency to detect whether red crossbills and lodgepole pine exhibit reciprocal adaptations, which would imply coevolution. Cone traits that act to deter Tamiasciurus and result in high ratios of cone mass to seed mass were less developed in the isolated populations. Cone traits that act to deter crossbills include larger and thicker scales and perhaps increased overlap between successive scales and were enhanced in the isolated populations. In the larger, isolated mountain ranges crossbills have evolved deeper, shorter, and therefore more decurved bills to exploit these cones. This provides crossbills with higher feeding rates, and the change in bill shape has improved efficiency by reducing the concomitant increases in body mass and daily energy expenditures that would have resulted if only bill size had increased. These parallel adaptations and counter adaptations in red crossbills and lodgepole pine are interpreted as reciprocal adaptations and imply that these crossbills and pine are in coevolutionary arms races where red squirrels are absent (i.e., coevolutionary hotspots) but not where red squirrels are present (i.e., coevolutionary coldspots).

Cone traits of jack pine and black spruce in young seedling seed orchards

The number of fertile and infertile scales, filled and empty seeds, cone volume, seed efficiency and the incidence of insect and disease damage to seed were evaluated for seven jack pine (Pinus banksiana Lamb) and six black spruce (Picea mariana [Mill.] B.S.P.) seedling seed orchards in northern Ontario, Canada. On average, the seed potential of jack pine and black spruce cones was 50 and 82 seeds, respectively. Cone volume and the number of fertile scales were under strong genetic control and well correlated with one another for both species. Seed efficiency values were high for jack pine (60%) but poor for black spruce (24%). The incidence of seed insect damage was less than 2.5% for both species and nil for seed diseases.

Phenotypic variation in cone and needle characters of Pinus banksiana (jack pine) in northwestern Ontario

To investigate the pattern of natural variation of jack pine (Pinus banksiana Lamb.), 64 natural stands from northwestern Ontario were compared based on phenotypic variation of cone and needle morphology. Cone and needle traits were determined for 10 trees from each stand. Vegetation and soil data for the stands were determined following the procedures established by the Ontario Ministry of Natural Resources Forest Ecosystem Classification program. Climatic data for each stand were interpolated using a geographic information system based on 1951 to 1980 data for Ontario and Minnesota weather stations. Nested analyses of variance indicated that most of the variation was expressed between trees and within trees, with relatively little (1.6 – 18.9% depending on the trait) expressed between sampled populations. Discriminant analysis of cone and needle data indicated that the 64 populations generally varied longitudinally with a steep cline in the Nipigon area (ca. 88°15′W) apparent for cone data. A corresponding irregularity in the pattern of needle variation suggested that the modern pattern may be the result of separate lineages, i.e., descendents from two migration routes along eastern and western shores of Lake Superior or from two refugia. However, temperature data follows a similar pattern in this area of Ontario, and multiple regression of the discriminant analysis score means for the 64 sampled populations against elevation, climatic, and soil data indicated that much of the cone and needle variation expressed between populations could be accounted for by the regressions. Thus, the observed patterns of phenotypic variation may simply be the result of local adaptations to a variable environment. Key words: jack pine, Pinus banksiana, phenotypic variation, cone traits, needle traits, northwestern Ontario.

Range-wide morphological and anatomical variation in Larix laricina

To investigate the nature of infraspecific variation in Larix laricina (Du Roi) K. Koch, 60 naturally established stands constituting 44 provenances were sampled from throughout the species' range. Cones were scored for nine traits and short-shoot needle transverse sections were scored for seven traits and 20 radial distances. Variation in all traits was minimal, with the greatest components expressed between trees within stands and within trees. Canonical variates analysis of needle traits demonstrated that provenances were differentiated according to location, whereas canonical variates analysis of cone traits showed a much weaker geographic trend. These results are consistent with the hypothesis that Alaska and northern Yukon provenances resulted from geographically separate migratory waves originating from different locations in the south following glacial recession. While Alaska provenances were distinguished from other provenances based on canonical variates analysis of needle data, but not of cone data, this distinction is insufficient to recognize Alaska tamaracks separately at either the species or varietal level.

Cone and Seed Weight Relationships in Douglas‐Fir From Western and Central Oregon

Cone sizes and weights and seed weights were determined for 89 trees in 9 stands in the Oregon Coast Ranges, Cascade Ranges, and central Oregon. From west to east this represented a transition from mesic to xeric sites and from longer to shorter growing seasons. Differences among regions for all cone traits, and regression coefficients for change in cone and seed weights with distance from the ocean, were significant. Cone size and weight decreased, seed weight increased, and the regression coefficient of seed weight on cone weight, based on trees within regions, increased with distance from the ocean. Geographic variation in cone and seed weights was compared with variation in the phenology of cone and seed development as reported in the literature. This comparison indicated that where relatively large seeds were important to regeneration success and the growing season was short, Douglas—fir showed at least 3 changes in the timing of development as compared with milder sites. (1) The cone growth period was reduced more than the seed growth period. (2) The overlap in time of the developmental cycles of cone and seed was increased. (3) Cones and seeds grew during an increased portion of the growing season.