Kathleen H. Keeler

The phylogenetic distribution of extrafloral nectaries in plants

BACKGROUND AND AIMS Understanding the evolutionary patterns of ecologically relevant traits is a central goal in plant biology. However, for most important traits, we lack the comprehensive understanding of their taxonomic distribution needed to evaluate their evolutionary mode and tempo across the tree of life. Here we evaluate the broad phylogenetic patterns of a common plant-defence trait found across vascular plants: extrafloral nectaries (EFNs), plant glands that secrete nectar and are located outside the flower. EFNs typically defend plants indirectly by attracting invertebrate predators who reduce herbivory. METHODS Records of EFNs published over the last 135 years were compiled. After accounting for changes in taxonomy, phylogenetic comparative methods were used to evaluate patterns of EFN evolution, using a phylogeny of over 55 000 species of vascular plants. Using comparisons of parametric and non-parametric models, the true number of species with EFNs likely to exist beyond the current list was estimated. KEY RESULTS To date, EFNs have been reported in 3941 species representing 745 genera in 108 families, about 1-2 % of vascular plant species and approx. 21 % of families. They are found in 33 of 65 angiosperm orders. Foliar nectaries are known in four of 36 fern families. Extrafloral nectaries are unknown in early angiosperms, magnoliids and gymnosperms. They occur throughout monocotyledons, yet most EFNs are found within eudicots, with the bulk of species with EFNs being rosids. Phylogenetic analyses strongly support the repeated gain and loss of EFNs across plant clades, especially in more derived dicot families, and suggest that EFNs are found in a minimum of 457 independent lineages. However, model selection methods estimate that the number of unreported cases of EFNs may be as high as the number of species already reported. CONCLUSIONS EFNs are widespread and evolutionarily labile traits that have repeatedly evolved a remarkable number of times in vascular plants. Our current understanding of the phylogenetic patterns of EFNs makes them powerful candidates for future work exploring the drivers of their evolutionary origins, shifts, and losses.

Are there trade-offs among antiherbivore defenses in Ipomoea (Convolvulaceae)?

The concept that the cost of antiherbivore defenses leads to trade-offs where species will have one but not both of a set of alternative defenses was tested in the genus Ipomoea (Convolvulaceae). Indole alkaloids were analysed in 19 species and compared with the number of other antiherbivore defenses in the same species (defense nectaries, hairy leaves or woody stems). Within the Ipomoea species tested, there was no tendency for species having one defense to lack others, i.e. indole alkaloids were no less numerous in species with defense nectaries than those without. This evidence is therefore inconsistent with the idea that allocation of resources to one defense will favor reduction of other defenses. The most likely explanation of the results presented here is that most traits involved in defense have multiple uses so that they do not form simple alternatives leading to trade-offs.

Evolutionary implications of meiotic chromosome behavior, reproductive biology, and hybridization in 6x and 9x cytotypes of Andropogon gerardii (Poaceae).

Andropogon gerardii, big bluestem, has 60 and 90 chromosome cytotypes. Meiosis in the hexaploid was shown to be regular, although some secondary associations of bivalents form. Meiosis in the enneaploid (2n = 9z = 90) is irregular, leading to most gametes having unbalanced chromosome complements. Both cytotypes show considerable self-incompatibility. Cytotypes crossed freely, forming a variety of fertile euploids and aneuploids. Indistinguishable exomorphology, intermixing in natural populations, and compatibility suggest that A. gerardii is best understood as a cytotypically complex single species.

Comparison of common cytotypesof Andropogon gerardii(Andropogoneae, Poaceae).

Many plant species contain populations with more than one polyploid cytotype, but little is known of the mechanisms maintaining several cytotypes in a population. Andropogon gerardii cytotypes were compared to evaluate different models of autopolyploid cytotype coexistence. The enneaploid (90 chromosome, 9x) cytotype was found to be larger and taller than the hexaploid (60 chromosome, 6x) cytotype. Seed production is significantly more efficient in hexaploids, but seed production per area was not significantly different. The two cytotypes are not exomorphologically separable in the field because of great plasticity in response to environmental variation and wide variation within each cytotype. These data suggest cytotypic variation is maintained by natural selection.

Impact of Intraspecific Polyploidy in Andropogon gerardii (Poaceae) Populations

Abstract Andropogon gerardii populations are comprised of two (or more) polyploid forms over much of the range of the species. To understand the impact of intraspecific polyploidy, polyploid cytotypes were compared over 4 y in native grasslands in Boulder, Colorado. Boulder A. gerardii populations averaged 59.6% hexaploids (60 chromosomes), 35.3% enneaploids (90 chromosomes) and 5.1% intermediate (aneuploid) chromosome numbers using flow cytometry to infer chromosome numbers. Neither mean clone area nor mean annual change in clone area differed significantly between ploidy levels. Hexaploid clones produced significantly more viable seeds than enneaploids. Enneaploids are not replacing themselves, whether that is measured absolutely or relative to hexaploids. Enneaploid reproductive effort was greater than hexaploid reproductive effort in some years and they produce substantial numbers of good seeds, but those seeds rarely have enneaploid cytotypes. The populations should eventually become entirely hexaploid. In the current populations, however, enneaploids are big, vigorous and fertile individuals.

Extrafloral nectaries on plants in communities without ants: Hawaii

Since the Hawaiian Islands lack native ants, it was hypothesized that extrafloral nectaries, an ant-related mutualistic trait, should be lacking on native species. Presence of extrafloral nectaries (EFNs) on plants was determined by direct observation and related to vegetation structure and floral composition. Frequency of plants with EFNs was low by all possible comparisons. However, several endemic species had functional EFNs. The hypotheses to explain these anomalies are (1) phylogenetic inertia or (2) mutualism with some other organism than ants.

Distribution of Plants with Extrafloral Nectaries and Ants at Two Elevations in Jamaica

Frequencies of plants with extrafloral nectaries were determined for two elevations in Jamaica. Extrafloral nectaries were found on 0.28 of the plants at sea level (Happy Grove, Portland) and 0.00 of the plants at 1310 m (Whitfield Hall, St. Thomas). Ant abundance, as indicated by discovery of and recruitment to baits, was greater at the lower elevation site. However, despite the apparent absence of plants with extrafloral nectaries, there were abundant ants at 1310 m. MUCH EVIDENCE suggests that extrafloral nectaries attract insects which defend plants against herbivores and/or seed predators (Elias and Gelband 1975; Bentley 1976, 1977a, b; Keeler 1977). Extrafloral nectaries are glands which are located anywhere on a plant except those sites involved in pollination. These glands produce an aqueous solution containing sugars and other compounds (Baker and Baker 1975, Bentley 1977a, Keeler 1977). At present, only Bentley (1976) has studied the distribution of extrafloral nectaries in a natural habitat. She reported a positive correlation between frequency of plants with extrafloral nectaries and ant abundance in tropical dry forest in Guanacaste, Costa Rica. I report extrafloral nectary frequency and ant abundance from two sites in Jamaica. Two sites were compared: Happy Grove, Portland, Jamaica (sea level, approximately 1700 mm annual rainfall, mean annual temperature 260C, mean monthly temperatures 24-28?), and Whitfield Hall, near Hagley Gap, St. Thomas (1310 m up Blue Mountain, 3500 mm annual rainfall, mean annual temperature 220 C, mean monthly temperatures 16-32?). Since there are no weather records for the specific sites, values are extrapolated from U.S. Weather Bureau (1966) and Clarke (1974). Significant human disturbance was seen at both sites. Studies were conducted close to trails used daily by local people. The transects at both sites ran from under the forest canopy (presumably second growth) out into partially open areas (early second growth at Happy Grove, coffee fields at Whitfield Hall). Frequency of plants with extrafloral nectaries was determined in four transects at each site. At approximately every meter along each transect, plants were scored as having or lacking extrafloral nectaries and ants. The presence of extrafloral nectaries was determined by observing ants feeding in a stereotyped manner, and then locating the nectary. Once a species was determined to have extrafloral nectaries, it was scored as such on subsequent encounters. Ants were present at most extrafloral nectaries; of the 70 plants with extrafloral nectaries observed, only 10 (14%) did not have ants on them. The frequency of plants with extrafloral nectaries determined by this method is an underestimate, since some species may produce extrafloral nectar at other times of the year (e.g., fruit nectaries). Ant abundances were estimated by using baits of canned corned beef and local commercial jelly. A pile of each food about 1 cm in diameter was placed on a separate piece of plastic, 25 cm2, in the litter at each station. Time until arrival of the first ant, type of ant, peak number of ants responding and number of ant species attracted were recorded at each bait. Representative ants from baits at both sites and from foliar nectaries of plants at Happy Grove were collected. The experiments were carried out for three hours each, from 09.00-12.00 hrs in December 1977. Results from the extrafloral nectary transects are given in table 1. No species with extrafloral nectaries was observed at Whitfield Hall. At Happy Grove, 28 percent of the observed plants had extrafloral nectaries. These differences are statistically significant (T-test; p p> 0.01 and p-0.005, respectively). Ants collected from baits at Hatpy Grove included Paratrechina longicornis (Latreille), Solenopsis sp. 152 BIOTROPICA 11 (2): 152-154 1979 This content downloaded from 207.46.13.75 on Fri, 08 Jul 2016 05:47:31 UTC All use subject to http://about.jstor.org/terms (not S. geminata) , and Tetramorium guineense (F.); ants collected at Whitfield Hall were P. longicornis, Crematogaster brevispinosa Mayr., and Monomorium floricola (Jerdon). Ants collected from extrafloral nectaries at Happy Grove were P. longicornis, Solenopsis sp. (same as above), and Wassmannia auro-

Fifteen Years of Colony Dynamics in Pogonomyrmex occidentalis , the Western Harvester Ant, in Western Nebraska

AusTIN, T. L., AND J. A. KITCHENS. 1986. Expansion of Baiomys taylori into Hardeman County, Texas. Southwestern Nat., 31:547. CAIRE, W. 1991. A breeding population of the northern pygmy mouse, Baiomys taylori, in southwestern Oklahoma. Southwestern Nat., 36:364-365. CAIRE, W., J. D. TYLER, B. P. GLASS, AND M. A. MARES. 1989. Mammals of Oklahoma. Univ. Oklahoma Press, Norman. CLEVELAND, A. G. 1986. First record of Baiomys taylori north of the Red River. Southwestern Nat., 31:547. DIERSING, V. E., AND J. E. DIERSING. 1979. Additional records of Baiomys taylori (Thomas) in Texas. Southwestern Nat., 24:707-708. HOLLANDER, R. R., J. K. JONES, JR., R. W. MANNING, AND C. JONES. 1987. Noteworthy records of mammals from the Texas panhandle. Texas J. Sci., 39:97-102.

Distribution of plants with extrafloral nectaries in temperate communities.

The abundance of plants with extrafloral nectaries was determined for a series of temperate habitats in Nebraska. Mean cover of plants with extrafloral nectaries was 1.3% in riparian forest understory, 1.8% in virgin deciduous forest understory, 0.0% in tall-grass prairie, and 8.3% in sandhill prairie. Sandhills prairie contained distinct communities with different mean cover of plants with extrafloral nectaries and showed seasonal changes in nectary activity. Cover of plants with extrafloral nectaries was compared to ant abundance, plant species diversity, rainfall and frost-free season: the first two showed highly significant correlations with mean cover of extrafloral nectaries.

Clone Size of Andropogon gerardii Vitman (Big Bluestem) at Konza Prairie, Kansas

Abstract Clone size of plants of Andropogon gerardii from Konza Prairie Biological Station, Manhattan, Kansas was estimated from spatial patterns of genetic variation, using proteins detected by starch gel electrophoresis and DNA content (ploidy) measured by flow cytometry. Unique multi-locus protein banding patterns and differences in ploidy were used to exclude plants as members of the same clone. Individual clones averaged about 2 m in diameter and areas of prairie of 100 m2 were calculated to contain an average of 31.8 genetic individuals.