Florivory and sex ratio in Annona dioica St. Hil. (Annonaceae) in the Pantanal at Nhecolândia, southwestern Brazil

Hipólito Ferreira Paulino Neto,Reinaldo Chaves Teixeira

doi:10.1590/s0102-33062006000200015

Hipólito Ferreira Paulino Neto, Reinaldo Chaves Teixeira

Open Access

https://doi.org/10.1590/s0102-33062006000200015

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Abstract

Annona dioica St. Hil. is a species that grows to approximately 2 m tall and is very widespread in the cerrados. Individual plants of this androdioecious species produce numerous hermaphroditic or male flowers, but few fruits. The aim of this study was to determine the sex ratio among the plants and to compare the frequency of herbivory between male and hermaphroditic flowers. The fieldwork was done by studying flowering plants in grasslands used as pasture for cattle at Fazenda Nhumirim. One hundred and forty-seven male plants and 71 hermaphroditic plants were examined and produced a total of 194 and 94 flowers, respectively, during the study period. The male:hermaphrodite sex ratio was 2.07:1, and was similar to the male:hermaphrodite flower ratio of 2.06:1. The frequency of florivory rate in hermaphrodites was significantly higher than in male flowers (33.0%, n = 31, and 25.7%, n = 50, respectively; G = 14.83; d.f. = 1; p < 0.001). The mean fresh weights of male and hermaphroditic flowers were significantly different (8.38 ± 2.40 g vs. 6.93 ± 2.68 g, respectively; 0 ± SEM; n = 50 each; t = 2.479; d.f. = 49; p = 0.017). These results indicate that the low fruit set in this species can be explained by the sex ratio, the greater herbivory of hermaphroditic flowers and the probable absence of pollinators.

Highlights

The Annonaceae (Magnoliales), the largest of the primitive families of flowering plants (Cronquist 1981), has a pan-tropical distribution and contains 122 genera and approximately 2300 species (Barroso 1992)
Annona dioica is an androdioecious plant in which some individuals have hermaphroditic flowers while
The 147 males produced 194 flowers, while the 71 hermaphrodites produced 94 flowers during the study period, which corresponded to a ratio of 2.06:1 that was very similar to the sex ratio of 2.07:1

Summary

Introduction

The Annonaceae (Magnoliales), the largest of the primitive families of flowering plants (Cronquist 1981), has a pan-tropical distribution and contains 122 genera and approximately 2300 species (Barroso 1992). The pollination system of this family is typically cantharophilous (Gottsberger 1970; 1974; 1990; Norman et al 1992), with flowers that are highly specialized for pollination by beetles. The flowers have massive, thick, nutritious petals (Gottsberger 1988; 1990; A.C. Webber, data not published) and use thermogenic respiration (Gottsberger 1989b; 1990; 1994; A.C. Webber, data not published) to guarantee an elevated temperature

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