Gregg Dieringer

BEETLE POLLINATION AND FLORAL THERMOGENICITY IN MAGNOLIA TAMAULIPANA (MAGNOLIACEAE)

The pollination biology involving floral thermogenicity of Magnolia tamaulipana was conducted at the El Cielo Reserve in Tamaulipas, Mexico, during May 1996. Our results indicate that M. tamaulipana possesses a highly specialized beetle pollination system involving Cyclocephala (Scarabaeidae: Dynastinae) and members of the Staphylinidae. Of the 366 insects visiting 213 flowers of M. tamaulipana, 364 were beetles. Cyclocephala caelestis accounted for 52% and Myrmecocephalus sp. for 46% of the visits. Breeding system experiments indicated that the flowers were self‐compatible but only 44% of the open‐pollinated stigmas were pollinated. Cyclocephala caelestis was frequently observed to feed on petals but never sepals. As a reward, flowers offered petals high in carbohydrate and low in fiber to Cyclocephala. The protogynous flowers of M. tamaulipana opened at night, were viable for a maximum of 24 h, and were thermogenic. Flowers were hottest when they first opened and female. Floral temperatures gradually declined with time and hence sexual phase and, 24 h after anthesis, were not different from ambient. Excess floral temperatures ranged from 1.0° to 9.3°C for female‐phase flowers and from 0.2° to 5.0°C for male‐phase flowers. The two species of beetles showed differential visitation to trees associated with floral thermogenicity. Our data indicate that large‐flowered trees dissipate more heat and, therefore, more floral odor from their petals than small‐flowered trees, thereby attracting a greater number of Cyclocephala.

Reproductive ecology of Magnolia schiedeana (Magnoliaceae), a threatened cloud forest tree species in Veracruz, Mexico

DIERINGER, G. AND J. E. ESPINOSA S. (Instituto de Ecologia, A.C., Apartado Postal No. 63, KM. 2.5 Antigua Carretera a Coatepec, 9 1000 Xalapa, Veracruz, Mexico). Reproductive ecology of Magnolia schiedeana (Magnoliaceae): a threatened cloud forest tree species in Veracruz, Mexico. Bull. Torrey Bot. Club 121: 154-159. 1994.-Flowering among three study populations of Magnolia schiedeana Schlecht. (Magnoliaceae) varied considerably, beginning in January or February and continuing for 2 to 4 months. The variability in time of flowering led to very low fruit production in some populations when not coincident with pollinator emergence. Flowers produced a strong fruity fragrance, were functional for one day, protogynous (opening in the morning and becoming male the same afternoon), and self-compatible. Pollinators were beetles, Stenagria sp. (Staphylinidae) and Cyclocephala jalapensis (Scarabaeidae), that entered flowers at night and remained throughout the next day engaged in a variety of behaviors (copulation and feeding on pollen and petal tissue). Cyclocephala jalapensis, a regional endemic, is closely associated with cloud forest habitat and appears dependent on M. schiedeana for adult nutrition. Magnolia schiedeana therefore seems to possess a more specialized pollination system than temperate Magnolia species. All three populations experienced some degree of previous disturbance (cutting) and exhibited very low fertility. The average tree produced 1 flower per day, 2-4 flowers during the season, and 1 fruit. Regeneration of populations was primarily by resprouting of roots and trunk bases and not seedling recruitment. Future existence of M. schiedeana within Veracruz is jeopardized by deforestation brought about by a large human population struggling for basic necessities.

Reproductive Biology of a Population of Acourtia runcinata (Asteraceae: Mutisieae: Mutisieae) at the Northeastern Limit of its Range

-Acourtia runcinata is a member of the tribe Mutisieae: subtribe Nassauviinae (Asteraceae). Breeding system studies showed the population to be primarily self-incompatible and pollinated by sporadic visits from various Lepidoptera. Typical for the tribe Mutisieae, the florets absorbed ultraviolet light and secreted a small amount of hexose-rich nectar and did not seem attractive to bees. Fruit production may have been limited by pollinator visitation since hand-pollinated florets set more fruit (92%) than did florets receiving natural pollination (51%). Twenty-seven percent of the capitula were lost to herbivory. Some self-compatibility was observed and seeds produced from self-pollination were equally viable as seed produced from xenogamous pollination. Seeds produced as a result of self-pollination may therefore be important for population growth or stability. Small populations may, nevertheless, be jeopardized given their restriction to an undisturbed habitat and frequent herbivory documented here.

Pollinator limitation in populations of Agalinis strictifolia (Scrophulariaceae)

DIERINGER, G. (Department of Botany, The University of Texas, Austin, TX 78713). Pollinator limitation in populations of Agalinis strictifolia (Scrophulariaceae). Bull. Torrey Bot. Club 119: 131-136. 1992.-Pollinator limitation of percent fruit production and mean seeds/ fruit was examined in two populations of Agalinis strictifolia during 1984, 1985, and 1987. Tests for a significant redistribution of resources caused by hand-pollination of a single flower per plant, that could produce a false, positive test for pollinator limitation, were negative. No portion of the flowering season was consistently limited by pollinators. Pollinator limitation in percent fruit production was never detected for either population. Limitation was detected for mean seeds/fruit in one population during one year. Seeds/fruit was limited four out of five times tested during the one flowering season and these periods of time accounted for 60 percent of the total flowers available. Agalinis strictifolia is a hemiparasitic annual and significant reductions in seed production, although rare, could affect future population size and persistence.

Ecological relationship between floral thermogenesis and pollination in Nelumbo lutea (Nelumbonaceae)

PREMISE OF STUDY Floral thermogenesis is an unusual floral trait with a well-documented physiological process, and yet, there is limited understanding of how this trait influences plant reproduction. The current study was undertaken to gain a better understanding of how floral thermogenesis in Nelumbo lutea impacts pollinator attraction and consequent plant reproduction. METHODS We conducted field studies on floral thermogenesis and thermoregulation, flower sexual development, floral visitation patterns, breeding system, pollen transfer dynamics, and floral scent production. KEY RESULTS The most abundant visitors to the thermoregulatory flowers included the Phoridae (Diptera), Chrysomelidae (Coleoptera), and Hymenoptera. Chrysomelid beetles, particularly Diabrotica, were frequent visitors to both first-day female- and second-day bisexual-phase flowers, while phorid flies were most common in bisexual-phase flowers. Pollen transfer experiments indicated that Diabrotica was equally effective in depositing pollen on stigmas, as were the less frequent, but pollen-loaded halictid bees. CONCLUSIONS Flowers received a taxonomically wide assemblage of floral visitors and appear adapted to attract beetles, primarily Chrysomelidae and medium-sized bees. This study is the first to provide strong support that beetles can comprise the dominant portion of floral visitors and are as effective in pollen transfer as bees. Thermogenesis aids in dispersing the main floral scent component-1,4-dimethoxybenzene-attracting both chrysomelids and bees, while thermoregulation causes chrysomelid beetles to actively seek out new flowers for evening residence. This search behavior likely results in chrysomelids affecting cross-pollination.

Pollen Structure of Acourtia (Asteraceae): New Findings and Some Taxonomic Considerations

The exine stratification of the pollen grains in Acourtia species was studied using scanning electron microscopy (SEM). Our results indicate that two patterns of exine stratification are found within the genus. The Trixis type, which is characterized by having an infratectum longer than the tectum, both separated from each other by a thick layer parallel to the nexine, was found in those Acourtia species with a well‐defined aerial caudex. Species of Acourtia with basal leaves forming a rosette were found to possess the Proustia type of exine stratification, in which the tectum and infratectum are about the same length. These results indicate that the caulescent and scapose groups represent different evolutionary lines. Additionally, the shape of the pollen grains was studied using light microscopy, rendering variable results.

Pollination and Reproductive Biology in a Hill Prairie Population of Nothocalais cuspidata (Asteraceae: Cichorieae)

Abstract Nothocalais cuspidata (Pursh) Greene (Asteraceae) is a plant species of conservation concern in Missouri; it typically occurs as isolated populations in hill and sand prairies which are themselves rare and fragmented habitats. The present study was undertaken to understand its reproductive biology as a hill prairie member and the possibility of reduced reproductive output in this isolated habitat. Nothocalais cuspidata is an early spring-flowering, nonclonal, primarily self-incompatible perennial that exhibits a 4 wk flowering phenology with most florets open to cross-pollination over a 2–3 wk period. The attractive UV reflective florets were visited by six species of halictid and solitary bees. The study population did experience depressed reproductive output in 2014 compared to 2004, with open-pollinated florets producing 19.1% fewer fruits than in 2004 along with a 37% decline in population size over a 13 y period. We suggest the depressed fruit production experienced is likely due to the unpredictable spring weather associated with early flowering and sporadic pollinator visitation in an isolated habitat leading to large variations in reproductive success over time or a reduction in compatible mating types as the population declines.