Dulce María Figueroa-Castro

Pollen:ovule ratio and its relationship with other floral traits in Papilionoideae (Leguminosae): an evaluation with Argentine species

The pollen:ovule ratio (P/O) has traditionally been used as a rough estimator of plant breeding systems. It has been shown that plant breeding systems are associated with particular floral traits. In this study, we determined the P/O in 21 Leguminosae species from Argentina and explored relationships between P/O and taxonomic position, flower size, floral rewards, pollen presentation and pollination mechanisms. According to the results, 15 out of the 21 species classified were obligate xenogamous, although some of them have been recorded as facultative xenogamous in previous studies. There was a significant effect of taxonomic position (genus), reward type and pollination mechanism on P/O. Species offering only nectar as a floral reward (which were species with a brush mechanism) had a significantly lower P/O than species offering pollen or pollen and nectar. Species with the brush pollination mechanism had the lowest P/O, while species with valvular and pump mechanism had the highest P/O. However, pollen presentation (primary and secondary) and flower size did not have a significant effect on P/O. Our results demonstrate that P/O variability is determined by taxonomic position and pollination mechanism in this plant group.

Pollen morphology of Pachycereus weberi (Cactaceae): an evaluation of variation in pollen size

Pollen morphology within a single plant species has been regarded as a relatively constant trait; it has, thus, been used as a taxonomic character. Numerous palynological studies have described the morphology of pollen from Cactaceae and from other families of plants. There have, however, been few studies of the variation of pollen traits, especially variation of pollen size. Here, we describe the morphology of pollen grains from Pachycereus weberi, paying particular attention to variation of the diameter of the grains. We found that pollen grains from P. weberi are spheroidal, isopolar, and tricolpate, with microperforate and spinulate tectum and visible perine. Pollen diameter is highly variable. Our results show that pollen size must be used carefully as a taxonomic character. Further, we discuss the importance of sample size in descriptive studies of pollen and diverse meiotic abnormalities that may be implied by the high variation of pollen grain size for P. weberi.

Spatial Variation in the Community of Insects Associated with the Flowers of Pachycereus weberi (Caryophyllales: Cactaceae)

ABSTRACT The positive relationship between productivity and species diversity is well-known. Insect communities associated with the flowers of Cactaceae species represent an interesting system to explore the productivity-diversity relationship because branches facing the equator receive more photosynthetically active radiation and have higher productivity. Thus, flowers with contrasting orientations within an individual, and even within a single branch, might differ in productivity. Therefore, higher abundance, species richness, and diversity are expected for the insect communities associated with south-facing flowers. This hypothesis was tested in Pachycereus weberi (J.M. Coulter) Backeberg (Cactaceae). Insects within flowers with contrasting orientations were collected and its abundance, richness, and diversity were estimated. We also asked if insects prefer big flowers. Thus, flower volume was estimated and regression analyses were conducted to test if there is a positive relationship between flower size and insect abundance. Flower orientation did not affect species richness. However, species abundance and diversity were different in flowers with contrasting orientations. In general, species abundance was higher in flowers facing southwards than in north-facing flowers. On the contrary, species diversity was higher in north-facing flowers. Abundance of Coleoptera was explained by flower volume in south-facing flowers. Contrary to our hypothesis, total diversity was greater in the less productive oriented flowers. Three possible explanations are discussed to explain the low diversity found in the highly productive, south-facing flowers. Our study provides evidence for the effects of productivity on the structure of insect communities at a very small-scale.

Insect Visitors to the Annual Plant Community in a Xeric Environment in Central Mexico

Abstract The interactions between the plant community and their floral visitors might vary through space, causing changes in the structure and composition of the communities of floral visitors. Although numerous studies have addressed the variation in the communities of floral visitors through space, none of them have analyzed how the structure of the community of floral visitors for all the co-flowering annual plant species changes between sites. We describe how the community of floral visitors to annual plants varies through space in a xeric community in central Mexico. We collected all the insects visiting the flowers of the annual plants growing in 2 sites with contrasting plant density (low vs. high). We determined species richness, abundance, and diversity for the insect communities in each site. We established the similarity in the composition of the insect communities and the importance of environmental variables on the dynamics of the communities of floral visitors. Abundance and diversity of floral visitors were significantly higher in the low plant density site. The composition of the insect communities differed between sites (similarity = 32%). Changes in abundance of a few groups of insects seem to be related to environmental factors such as disturbance (Myrmecocystus mexicanus Wesmael [Hymenoptera: Formicidae] and Tiphiidae sp. 1 [Hymenoptera]), humidity (Curculionidae sp. 1 [Coleoptera]), and temperature (Dorymyrmex grandulus (Forel) [Hymenoptera: Formicidae]). Our results indicate that vegetation density has a strong effect on the community of floral visitors of annual plants, which in turn, might affect their reproduction and their interactions with other organisms within the ecosystem.

Floral Visitors of Three Asteraceae Species in a Xeric Environment in Central Mexico

Abstract We describe the spatial variation in the structure and composition of the communities of insects visiting the inflorescences of Flaveria ramosissima Klatt, Florestina pedata (Cav.) Cass., and Parthenium bipinnatifidum (Ort.) Rollins (Asteraceae) in a xeric environment in Central Mexico. Inflorescences of the three Asteraceae were visited by a total of 96 species of Hymenoptera, Diptera, Lepidoptera, Coleoptera, and Hemiptera. Total species richness of floral visitors to the three Asteraceae and total abundance of insects of Fl. pedata and P. bipinnatifidum did not differ between low and high vegetation cover sites. Total abundance of insects visiting the inflorescences of F. ramosissima and abundance of Hymenoptera in all three Asteraceae were higher at the low vegetation coverage (LVC) site than at the high vegetation coverage (HVC) one. Diversity of insects of Fl. pedata and P. bipinnatifidum was higher at the HVC site. However, in F. ramosissima diversity was higher at the LVC site. The communities of insects of each Asteraceae were dissimilar between sites. These differences can be attributed to variation in the abundance of Lepidophora (Diptera: Bombyliidae), Miridae (Hemiptera), Melyridae (Coleoptera), Tiphiidae (Hymenoptera), Myrmecocystus mexicanus Wesmael, and Dorymyrmex grandulus (Forel) (Hymenoptera: Formicidae). The first three insect groups were sensitive to LVC, high temperature, and low humidity, whereas the last three tolerated those same environmental conditions. Changes in temperature, humidity, and resources associated with vegetation coverage seem to differentially affect each species of floral visitors of the three Asteraceae species studied.