Gastropod biodiversity at the 'Evolution Canyon' microsite, lower Nahal Oren, Mount Carmel, Israel

Twenty-six species of gastropods (terrestrial, shell-bearing snails and slugs) were recorded at the 'Evolution Canyon' microsite, lower Nahal Oren, Mount Carmel, Israel. Twenty-five species were recorded at the temperate, mesic north-facing slope (NFS) and 20 species at the xeric south-facing slope (SFS). Out of these species, six were NFS specific ( Pilorcula raymondi hebraica , Euchondrus septemdentatus , Monacha crispulata , Pyramidula rupestris hierosolymitana , Truncatellina haasi , and Vitrea contracta ) and one was SFS specific ( Prolimax eustrictus ). The interslope difference was probably partly due to missing forest species at the SFS in comparison with the NFS. Twenty-two species were Levantine endemics (84.6%) and four species were more widely distributed in the Palaearctic region (15.4%). The Levantine species are inhabitants of the mesic and mainly mountainous regions, but four species ( Granopupa granum , Calaxis hierosolymarum , Cecilioides acicula , and Helix engaddensis ) also penetrate the deserts. Seven species ( Buliminus labrosus , H. engaddensis , Levantina spiriplana caesareana , Metafruticicola fourousi , Monacha syriaca , Sphincterochila cariosa , and Xeropicta vestalis joppensis ) were significantly more abundant on the SFS than on the NFS. The local physical microclimatic sharp divergence leads to gastropod adaptive interslope biotic divergence caused by natural selection.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 147–155.     

Biodiversity and microclimatic divergence of chrysomelid beetles at 'Evolution Canyon', Lower Nahal Oren, Mt Carmel, Israel

Ninety species of leaf beetles (Chrysomelidae, Coleoptera, Insecta) were recorded from die 'Evolution Canyon' microsite (sample area 7000 m²), Lower Nahal Oren, Mt Carmel, Israel. Species richness was significandy ( P =0.018) higher on the drier, climatically more fluctuating savanna-like, soudi-facing slope (SFS, 60 species, sample area 3000 m²) than on the cooler, wetter and climatically less variable north-facing slope (NFS, 44 species, sample area 3000 m²), as in other terrestrial taxa. More species were found common to the local xeric SFS at die Canyon and the regional southern desert areas (Judean and Negev Deserts), than to the NFS and Galilee Mountains, respectively, suggesting that local patterns mirror regional patterns. Interslope differences in microclimate variability range indicate that this factor might be determinant of interslope species richness differences. Most species were collected in the spring (April; 47%) and least in the autumn (September; 3%) over the collecting period from March 1995 to June 1997.     

Adaptive microclimatic structural and expressional dehydrin 1 evolution in wild barley, Hordeum spontaneum, at 'Evolution Canyon', Mount Carmel, Israel

'Evolution Canyon' (ECI) at Lower Nahal Oren, Mount Carmel, Israel, is an optimal natural microscale model for unravelling evolution in action highlighting the twin evolutionary processes of adaptation and speciation. A major model organism in ECI is wild barley, Hordeum spontaneum , the progenitor of cultivated barley, which displays dramatic interslope adaptive and speciational divergence on the 'African' dry slope (AS) and the 'European' humid slope (ES), separated on average by 200 m. Here we examined interslope single nucleotide polymorphism (SNP) sequences and the expression diversity of the drought resistant dehydrin 1 gene ( Dhn1 ) between the opposite slopes. We analysed 47 plants (genotypes), 4–10 individuals in each of seven stations (populations) in an area of 7000 m², for Dhn1 sequence diversity located in the 5' upstream flanking region of the gene. We found significant levels of Dhn1 genic diversity represented by 29 haplotypes, derived from 45 SNPs in a total of 708 bp sites. Most of the haplotypes, 25 out of 29 (= 86.2%), were represented by one genotype; hence, unique to one population. Only a single haplotype was common to both slopes. Genetic divergence of sequence and haplotype diversity was generally and significantly different among the populations and slopes. Nucleotide diversity was higher on the AS, whereas haplotype diversity was higher on the ES. Interslope divergence was significantly higher than intraslope divergence. The applied Tajima D rejected neutrality of the SNP diversity. The Dhn1 expression under dehydration indicated interslope divergent expression between AS and ES genotypes, reinforcing Dhn1 associated with drought resistance of wild barley at 'Evolution Canyon'. These results are inexplicable by mutation, gene flow, or chance effects, and support adaptive natural microclimatic selection as the major evolutionary divergent driving force.     

Genome size microscale divergence of <Emphasis Type="Italic">Cyclamen persicum</Emphasis> in Evolution Canyon,Israel

Using DAPI flow cytometry, we examined genome size divergence of the Persian violet, Cyclamen persicum (Primulaceae) (2n=48) on close opposite slopes of Evolution Canyon (EC), Mt. Carmel, Israel. The range of genome size variation detected among measured cyclamens was 6.41% in relation to the smallest measured DNA content. Our data on C. persicum at EC showed that local variability in the 2C-value exists. Significantly less DNA was recorded in plants growing in one station of the African savannah-like south-facing slope (AS) but not in the remaining two stations of the same slope. We were not able to reject the null hypothesis that there are no significant interslope differences in the genome size between the temperate European garrigue-like north-facing slope (ES) and the drier AS. In spite of the nonsignificant interslope trend for the higher genome size in C. persicum, the data-fusion (meta-analysis) test using correlations between C-values in C. persicum, and earlier studied carob tree (Ceratonia siliqua), trifoil (Lotus peregrinus) and a beetle (Oryzaephilus surinamensis) and their distribution along the aridity gradient indicates a positive relationship between drought and genome size at the microsite.     

Soil microfungal communities of 'Evolution Canyons' in Israel – extreme differences on a regional scale

On a regional scale, we compared the local adaptive patterns of soil mycobiota revealed in four 'Evolution Canyons' located in the northern and southern parts of Israel. These microsites were chosen according to the framework of the Institute of Evolution, University of Haifa programme, focusing on the effect of interslope environmental divergence on biodiversity patterns. The comparative analysis demonstrated remarkable differences in spatiotemporal structure of the microfungal communities and their biodiversity level (species richness, heterogeneity and equitability). In the desert 'Evolution Canyon', stress-selected, slow-reproducing, dark-coloured species with large, multicelled conidia were dominant. At the same time, in the forest localities of the northern canyons, as well as in the agriculturally disturbed locality with soil degradation, ruderal-selected, fast-reproducing Penicillium species predominated. Environmental natural selection appeared to be the major factor affecting adaptive diversity patterns of soil microfungi in the studied area.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 157–163.     

Patterns of thermal adaptation of Bacillus simplex to the microclimatically contrasting slopes of 'Evolution Canyons' I and II, Israel

Identification of selective forces that drive evolution and speciation of bacteria in natural habitats is a central issue in bacterial ecology and evolution. Exploring the adaptive evolution of Bacillus simplex at 'Evolution Canyons' I and II, Israel, we report here on the impact of high heat stress on the speciation progress of individual evolutionary lineages. These canyons represent similar ecological replicates, separated by 40 km, in which the orientation of the sun yields a strong sun-exposed and hot 'African' south-facing slope (SFS) versus a rather cooler and mesic-lush 'European' north-facing slope (NFS) within a distance of only 50-100 m at the bottom and 400 m at the top. Among 131 strains studied, in Luria-Bertani broth, 'African' strains grow better than 'European' strains at a stressful high temperature (43.25 degrees C). The results suggest that adaptation to the hotter and more stressful SFS is continuously ongoing. The patterns of heat adaptation override the phylogenetic history of individual lineages. A positive correlation of growth rates at 43.25 degrees C and 20 degrees C, more markedly among 'African' strains, reflects probably the broader temperature range on the SFS. Summarizing, the hot temperature stress on the 'African' slope is a major environmental force driving the twin evolutionary processes of adaptation and speciation of B. simplex at 'Evolution Canyon'. Finally, we discuss the data in light of current controversies on species concepts.     

Population genetic response to microsite ecological stress in wild barley, Hordeum spontaneum

Genetic diversity was studied in six subpopulations (a total of 60 individuals) of wild barley, Hordeum spontaneum , the progenitor of cultivated barley, sampled from six stations located along a transect of 300 m across the two opposing slopes of 'Evolution Canyon', a Mediterranean microsite at Lower Nahal Oren, Mt Carmel. The two opposing slopes are separated by between 100 and 400 m and designated SFS (South-Facing Slope) and NFS (North-Facing Slope) with each having three equidistant test stations. The SFS, which receives up to 300% more solar radiation, is drier, ecologically more heterogeneous, fluctuating, and more stressful than the NFS. Analysis of 12 RAPD primers, representing a total of 51 putative loci, revealed a significant inter- and intraslope variation in RAPD band polymorphism. A significantly higher proportion of polymorphic RAPD loci was found amongst the subpopulations on the SFS (mean P = 0.909) than on the NFS (mean P = 0.682), on the basis of the presence and absence of 22 strong bands. Polymorphism generally increased upwards from the bottom to the top of the SFS (0.636, 0.773, 0.955) and NFS (0.409, 0.500, 0.545), respectively. Gametic phase disequilibria estimates, D, revealed SFS and NFS unique predominant combinations which sharply differentiated the two slopes and indicated that there is differential interslope selection favouring slope-specific multilocus combinations of alleles, or blocks of genes over tens to hundreds of meters. This suggests that selection overrides migration. RAPD polymorphism appears to parallel allozyme diversity which is climatically adaptive and driven by natural selection in the same subpopulations at the microsite.     

Carbon source utilization patterns of Bacillus simplex ecotypes do not reflect their adaptation to ecologically divergent slopes in 'Evolution Canyon', Israel

The 'Evolution Canyons' I and II in Israel are model habitats to study adaptation and speciation of bacteria in the environment. These canyons represent similar ecological replicates, separated by 40 km, with a strongly sun-exposed and hot 'African' south-facing slope (SFS) vs. a cooler and mesic-lush 'European' north-facing slope (NFS). Previously, among 131 Bacillus simplex isolates, distinct genetic lineages (ecotypes), each specific for either SFS or NFS, were identified, suggesting a temperature-driven slope-specific adaptation. Here, we asked whether the ecological heterogeneity of SFS vs. NFS also affected carbon utilization abilities, as determined using the Biolog assay. Contrary to expectation, a correlation between substrate utilization patterns and the ecological origin of strains was not found. Rather, the patterns split according to the two major phylogenetic lineages each of which contain SFS and NFS ecotypes. We conclude that traits related to the general energy metabolism, as far as assessed here, are neither shaped by the major abiotic features of 'Evolution Canyon', namely solar radiation, temperature, and drought, nor by the soil characteristics. We further conclude that some traits diverge rather neutrally from each other, whereas other, more environmentally related traits are shaped by natural selection and show evolutionary convergence.     

Adaptive spatiotemporal distribution of soil microfungi in 'Evolution Canyon' II, Lower Nahal Keziv, western Upper Galilee, Israel

We describe and interpret spatiotemporal micromycete community structure and adaptive complexes in contrasting xeric and mesic microclimates in the soils of 'Evolution Canyon' II, Lower Nahal Keziv, western Upper Galilee, Israel. A total of 192 species from 60 genera belonging to Zygomycota (nine species), Ascomycota (13 species), and mitosporic fungi (170 species) were isolated. The fungal communities on the south-facing, xeric, 'African' slope (AS) demonstrated significantly greater diversity than on the north-facing, mesic, 'European' slope (ES) and the valley bottom (VB). Seasonally, winter slope communities were less heterogeneous. Forest localities on the ES and the VB in all seasons and the shady localities on the AS in the winter were overwhelmingly dominated by mesophilic Penicillium species. The sunny locality on the AS was characterized by a dominance of melanin-containing micromycetes that was most pronounced in the summer and by high occurrence and abundance of thermotolerant and thermophilic Aspergillus and Fusarium species. Ascomycetes and zygomycetes were the minor components in all local mycobiota studied; sexual ascomycetes, being stress-selected fungi, were more than ten times more abundant in the soil of the AS than in that of the ES, with the peak of abundance in the sunny summer community. The results demonstrated a microscale adaptive spatiotemporal inter- and intraslope divergence in soil mycobiota structure. Microclimatic natural selection appears to be the major factor affecting soil fungus diversity patterns.  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78, 527–539.     

Microclimate,developmental plasticity and community structure in artificial temporary pools

Solar radiation, which influences temperature and hydroperiod, should strongly influence colonization, development rate, development strategies and survival in temporary pools. We assessed these hypotheses at two spatial microscales with varying microclimate. One scale, ca. 200 m, was opposing slopes of a canyon on MT Carmel, Israel, referred to as 'Evolution Canyon' (Nevo, 1995). Due primarily to differential solar radiation, the warmer and drier South-facing slope (SFS) supports a savanna-like open park forest while the cooler, moister North-facing slope (NFS) is heavily forested, primarily with live oak. Using artificial pools, we assessed how these close but contrasting environments may influence developmental plasticity in the frog, Hyla savignyi, and colonization of insects. As expected, hydroperiod was considerably longer on the NFS. Hyla tadpole development was significantly faster on the SFS, while size at metamorphosis was greater on the NFS. Insect species richness was higher in NFS pools. The most common species, Culex pipiens, oviposited significantly more in NFS pools than in SFS pools. In the second scale, we placed pools only meters apart, but varying in shade and thus maximum temperature at Haifa University Campus, MT Carmel. Species richness and maximum temperature among pools were not correlated during winter and early spring (cool to mild temperatures), but were strongly and negatively correlated during early summer (hot temperatures). Thermal tolerance in the laboratory of selected species matched their thermal spatial distribution in the field. These results indicate that temperature can play a strong role in affecting developmental strategies, species′ distributions and community structure in temporary pools over a very small spatial scale. This revised version was published online in July 2006 with corrections to the Cover Date.     

Desiccation resistance and mating behaviour in laboratory populations of Drosophila simulans originating from the opposing slopes of Lower Nahal Oren (Israel)

Lower Nahal Oren in Northern Israel, often referred to as 'Evolution Canyon', has been proposed as a microscale model site for ecological evolution. However, conflicting stress resistance and mating assay results contribute to controversy over the Nahal Oren model. In this study, we further tested the Nahal Oren model, while extending its focus from Drosophila melanogaster to its sister species, Drosophila simulans. Using fly populations derived from the opposing canyon slopes and acclimated to laboratory conditions for 11-22 generations, we did not find a significant slope effect on desiccation resistance (P = 0.96) or body metabolic fuel content (P > 0.43), which would indicate a genetic basis for adaptation to local resource limitation. Multiple-choice mating assays (47-48% homotypic couples in two replicate populations) did not indicate divergence from a random mating pattern between north- and south-facing slope flies. In conclusion, our findings do not support divergence of D. simulans populations across Lower Nahal Oren.     

Tree species distribution in canopy gaps and mature forest in an area of cloud forest of the Ibitipoca Range,south-eastern Brazil

The tree community of both canopy gaps and mature forest was surveyed in a 5 ha plot of cloud forest in the Ibitipoca Range, south-eastern Brazil, aiming at: (a) comparing the tree community structure of canopy gaps with that of three strata of the mature forest, and (b) relating the tree community structure of canopy gaps with environmental and biotic variables. All saplings of canopy trees with 1–5 m of height established in 31 canopy gaps found within the plot were identified and measured. Mature forest trees with dbh 3 cm were sampled in four 40×40 quadrats laid on the four soil sites recognised in the local soil catena. All surveyed trees were identified, measured and distributed into three forest strata: understorey (<5 m of height), sub-canopy (5.1–15 m) and canopy (15.1–30 m). The following variables were obtained for each gap: mode of formation, age, soil site, slope grade, size, canopy openness and abundance of bamboos and lianas. A detrended correspondence analysis indicated that the tree community structure of gaps in all soil sites was more similar to that of the mature forest understorey, suggesting that the bank of immatures plays an important role in rebuilding the forest canopy and that gap phases may be important for understorey shade-tolerant species. There was evidence of gap-dependence for establishment for only one canopy tree species. Both canonical correspondence analysis and correlation analysis demonstrated for a number of tree species that the distribution of their saplings in canopy gaps was significantly correlated with two variables: soil site and canopy openness. The future forest structure at each gap is probably highly influenced by both the present structure of the adjacent mature forest and the gap creation event.     

Sperm Size Evolution in Drosophila: Inter- and Intraspecific Analysis

Numerous reports were devoted to the variation of sperm length in relation to sperm competition amongst species. However, studies on intraspecific variations of sperm size are very scarce and the number of sperm measured, very limited. This paper investigates within-individual, between-individual and between-population variation of sperm length in the two cosmopolitan species, D. simulans and D. melanogaster. Sperm length distributions are completely discriminated against with these two species, with the mean values equal to 1.121 +/- 0.002 and 1.989 +/- 0.008 mm, respectively. Results of intraspecific variation show a contrasting pattern between the two species. The mode of sperm length distributions is much less variable in D. simulans than in D. melanogaster. The sperm size divergence is unaffected whenever the two species are in sympatry (tested at 'Evolution Canyon', Mount Carmel, Israel) or in allopatry, but the two species react differentially to abiotic local factors. D. melanogaster, in contrast to D. simulans, shows a clinal pattern in sperm size associated with drought. We discussed this pattern in relation to the potential role of sperm length in the ongoing process of non-random mating and incipient sympatric speciation observed in this locality in D. melanogaster.     

How the diversity,abundance, size and climbing mechanisms of woody lianas are related to biotic and abiotic factors in a subtropical secondary forest,Taiwan

Lianas are woody vines that play an important role in forest dynamics in tropical and subtropical areas. Their relationship to various biotic and abiotic conditions is, however, not yet wholly clear. We explored how the size, climbing mechanisms, diversity and abundance of woody lianas is related to host plant size, environmental factors and topography. Liana assemblages were examined in twenty 20 × 20 m plots in each of three topographic sites (valley, slope and ridge) in a subtropical secondary forest in southeastern Taiwan. The valley site had the highest abundance and species richness of lianas. The abiotic factors, soil pH and rock cover, were related to different topographic sites. Larger lianas were always found on larger host trees, while smaller lianas were found in smaller trees; no lianas with a DBH greater than 10 cm were found. Significantly more adhesive lianas were found on larger trees whereas twining and leaning-hook lianas were found in smaller trees. In conclusion, this study demonstrates that the species of liana is associated with the size and type of tree growing under different topographic conditions.     

Liana cover in the canopies of rainforest trees is not predicted by local ground‐based measures

Lianas (woody climbers) are structural parasites of trees that compete with them for light and below‐ground resources. Most studies of liana–tree interactions are based on ground‐level observations of liana stem density and size, with these assessments generally assumed to reflect the amount of liana canopy cover and overall burden to the tree. We tested this assumption in a 1‐ha plot of lowland rainforest in tropical Australia. We recorded 1072 liana stems (≥1 cm diameter at breast height {dbh}) ha^?1 across all trees (≥10 cm dbh) on the plot and selected 58 trees for detailed study. We estimated liana canopy cover on selected trees that hosted 0–15 liana individuals, using a 47‐m‐tall canopy crane. Notably, we found no significant correlations between liana canopy cover and three commonly used ground‐based measurements of liana abundance as follows: liana stem counts per tree, liana above‐ground biomass per tree and liana basal area per tree. We also explored the role of tree size and liana infestation and found that larger trees (≥20 cm dbh) were more likely to support lianas and to host more liana stems than smaller trees (≤20 cm dbh). This pattern of liana stem density, however, did not correlate with greater liana coverage in the canopy. Tree family was also found to have a significant effect on likelihood of hosting lianas, with trees in some families 3–4 times more likely to host a liana than other families. We suggest that local ground‐based measures of liana–tree infestation may not accurately reflect liana canopy cover for individual trees because they were frequently observed spreading through neighbouring trees at our site. We believe that future liana research will benefit from new technologies such as high‐quality aerial photography taken from drones when the aim is to detect the relative burden of lianas on individual trees.     

Detection and quantification of Paenibacillus polymyxa in the rhizosphere of wild barley (Hordeum spontaneum) with real-time PCR

Aim:  To detect and quantify the plant drought tolerance enhancing bacterium Paenibacillus polymyxa in a collection of 160 Hordeum spontaneum rhizosphere samples at the 'Evolution Canyon' ('EC'), Israel.
Methods and Results:  PCR primers and a FAM-TAMRA probe (6-carboxyfluorescein, 6-carboxy-tetramethyl-rhodamine) targeting 16S rRNA genes were designed and used to detect and quantify the target strain. Two commercial kits, Bio101 Fast Spin and Mo Bio Ultra Clean Soil DNA, were tested for DNA isolation from the rhizosphere and surrounding soil. Population densities of P. polymyxa were studied in the rhizosphere of wild barley and surrounding soil from the contrasting climatic slopes at the 'EC' using the real-time PCR and culture based methods.
Conclusion:  Paenibacillus polymyxa is one of the best established species in wild barley rhizosphere at the 'EC' slopes. With the real-time PCR assay we are able to detect 1 pg of DNA per PCR corresponding to 100 cells per ml. The results at the 'EC' correlate well to bacterial estimations by culture based methods.
Significance and Impact of the Study:  Significantly higher P. polymyxa cell number was detected in the rhizosphere of arid 'African' microclimate indicating possible role of adaptive co-evolution with plants.     

A metapopulation approach to the analysis of long‐term changes in the epiphyte vegetation on the host tree Annona glabra

Question: Do vascular epiphyte species have a metapopulation structure? What are the qualitative and quantitative long‐term changes of the complete vascular epiphyte vegetation in a particular host tree species? Location: Lowland forest on Barro Colorado Island (9° 10’ N, 79°51’ W), Republic of Panama. Methods: In 1994 and 2002 we conducted a census of all vascular epiphytes growing on more than 1000 Annona glabra trees (= patches). Epiphyte species abundances were recorded at the tree level in each census. Results: The number of epiphyte individuals increased from ca. 15 000 to ca. 23 700 individuals during the census interval while the species composition on Annona glabra as a whole was rather stable. There was a strong positive relationship between occurrence in patches and local abundance of the species, and between species richness and host tree stand size. The dynamics of local populations of a given species were uncorrelated to each other; small and large local populations of most species had the same probability to go extinct. The frequency distribution of species on all host trees was not bimodal, but on a subset of heavily colonized host tree stands it was. Numbers of species and individuals were correlated with tree size which was not due to a correlation of tree size and tree age. Conclusions: As far as the most abundant epiphyte species with metapopulation structures are concerned, these species belong to diverse families, e. g. Orchidaceae, Bromeliaceae and Polypodiaceae. Even ca. 80 years after the initial establishment of the host tree species in the study area epiphytes are still in the stage of initial colonization and have not reached a steady state as indicated by the strong increase in individuals and the ongoing colonization of empty trees.     

Disentangling multiple drivers of pollination in a landscape-scale experiment

Animal pollination is essential for the reproductive success of many wild and crop plants. Loss and isolation of (semi-)natural habitats in agricultural landscapes can cause declines of plants and pollinators and endanger pollination services. We investigated the independent effects of these drivers on pollination of young cherry trees in a landscape-scale experiment. We included (i) isolation of study trees from other cherry trees (up to 350 m), (ii) the amount of cherry trees in the landscape, (iii) the isolation from other woody habitats (up to 200 m) and (iv) the amount of woody habitats providing nesting and floral resources for pollinators. At the local scale, we considered effects of (v) cherry flower density and (vi) heterospecific flower density. Pollinators visited flowers more often in landscapes with high amount of woody habitat and at sites with lower isolation from the next cherry tree. Fruit set was reduced by isolation from the next cherry tree and by a high local density of heterospecific flowers but did not directly depend on pollinator visitation. These results reveal the importance of considering the plant''s need for conspecific pollen and its pollen competition with co-flowering species rather than focusing only on pollinators’ habitat requirements and flower visitation. It proved to be important to disentangle habitat isolation from habitat loss, local from landscape-scale effects, and direct effects of pollen availability on fruit set from indirect effects via pollinator visitation to understand the delivery of an agriculturally important ecosystem service.     

Adaptive differentiation of thermotolerance in Drosophila along a microclimatic gradient

We examined whether a remarkable occurrence - the physiological evolution of two Drosophila melanogaster populations, despite a spatial separation of only 100-400 m, was idiosyncratic and temporary, or persisted over multiple years. We ascertained the high-temperature tolerance of Drosophila descended from populations on the north-facing slope (NFS) and south-facing slope (SFS) of 'Evolution Canyon' (Lower Nahal Oren, Mt Carmel, Israel), which were collected in 1997, 1999, and 2000. Results for these Drosophila uniformly resembled other studies in many respects: an inverse relationship between survival and heat-shock temperature, male-female differences in thermotolerance, and inducible thermotolerance. Importantly, for all years of collection, SFS flies consistently exceeded NFS flies in basal and inducible thermotolerance after diverse heat shocks, with and without thermal pretreatment, and whether isofemale lines, synthetic populations, or inbred lines were compared. Inbred lines, however, had lower thermotolerance than outbred lines. Several nonexclusive processes may explain the evolution of such physiological differentiation.     

Composition and ecology of vascular epiphyte communities along an altitudinal gradient in central Veracruz,Mexico

Abstract. Vascular epiphytes were studied in forests at altitudes from 720 to 2370 m on the Atlantic slope of central Veracruz, Mexico. The biomass of all trees of each species > 10 cm diameter at breast height within plots between 625 and 1500 m² was estimated. The number of species per plot ranged between 22 and 53, and biomass between 9 and 249 g dry weight/m². The highest values, both of species and biomass, were found at an intermediate altitude (1430 m). Habitat diversity may contribute to epiphyte diversity in humid forests, but the importance of this effect could not be distinguished from the influence of climate. A remarkably high number of bromeliads and orchids grew in relatively dry forests at low altitudes. In wet upper montane forests, bromeliads were replaced by ferns, while orchids were numerous at all sites, except for a pine forest. The number of epiphytic species and their biomass on a tree of a given site were closely related to tree size. According to Canonical Correspondence Analysis, the factor determining the composition of the epiphytic vegetation of a tree was altitude and to some extent tree size, whereas tree species had practically no influence. The only trees which had an evidently negative effect on epiphytes were pines, which were particularly hostile to orchids and to a lesser degree to ferns, and Bursera simaruba, which generally had few epiphytes due to its smooth and defoliating bark.