Population size, sex-ratio and sexual dimorphism in <em>Fuchsia parviflora</em> (Onagraceae) an endemic dioecious shrub

Abstract

Background: In small dioecious populations stochastic events may increase biased sex ratios decreasing the viability of populations. Moreover, pollinators may promote pollen limitation if sexual dimorphism related to pollinator attraction, such as flower size and number of flowers are present. Questions: 1) In order to estimate the viability of natural populations of Fuchsia parviflora, population size, sex ratio and fruit production were estimated in natural populations. In addition, number of flowers and floral traits were compared between genders as a way to predict pollinator preferences to particular gender. Studied species: Fuchsia parviflora is an endemic Mexican dioecious, animal-pollinated shrub. Methods: In 2012 and 2013 population sizes and sex ratios were estimated in 12 populations in the states of Michoacan and Jalisco. In addition, the number of flowers and floral traits were estimated between genders. Results: Population sizes varied widely from 14 to 550 individuals and an overall significant male-bias was found. Male frequency varied from 50 to 78 % among populations and some male-biased populations were also the small populations. A significant negative correlation between population size and male frequency was found, but no relationship was found between population size and number of flowers or fruit production. Reproductive plant height varied among populations but not between genders within populations. Male plants had larger number of flowers but floral longevity did not differ between genders. Consistently in all evaluated populations, staminate flowers had longer floral tubes and wider corolla diameter than pistillate flowers. Conclusions: In accordance to stochastic sex ratio fluctuations by small population sizes, it was expected to find populations with male and female-biased sex ratios. However, the absence of female-biased sex ratio suggests that male plants may have a higher survival chance but this hypothesis has to be tested. Although populations seem not to be seed-limited, some populations were cut during this study to plant avocado trees, suggesting the need to implement conservation efforts to preserve populations of F. parviflora. Keywords: biotic pollination, dioecy, floral dimorphism, population size. ResumenAntecedentes: En poblaciones dioicas pequeñas, eventos estocásticos pueden incrementar los sesgos en las proporciones sexuales lo que puede afectar la viabilidad de las poblaciones. Además, los polinizadores pueden promover la limitación de polen si existe un fuerte dimorfismo sexual en el tamaño y número de flores. Preguntas: Con la finalidad de estimar la viabilidad de las poblaciones de Fuchsia parviflora se estimaron los tamaños poblacionales, las proporciones sexuales y la producción de frutos en poblaciones naturales. Además, se comparó el despliegue floral y los caracteres florales entre géneros como una forma de predecir posibles sesgos de los polinizadores hacia algún género en particular. Especie de estudio: Fuchsia parviflora es un arbusto dioico de ...

Unraveling the development behind unisexual flowers in Cylindropuntia wolfii (Cactaceae)

“…Plants that are dioecious can deviate from the 1:1 sex ratio, especially those restricted to small populations, thereby decreasing their viability [ 28 , 29 ]. Among them, male biased ratios are at least twice as frequent as the female biased ones [ 28 ].…”

Effects of sexual dimorphism on pollinator behaviour in a dioecious species

“…One common feature in plants with separate sexes is sexual dimorphism, both in terms of vegetative and reproductive traits (reviewed by Barrett and Hough 2013). In insect-pollinated dioecious species, male plants often display more conspicuous floral phenotypes than females, at least species from temperate ecosystems, with males typically producing larger floral displays and/or larger flowers (Guitián 1995, Delph et al 1996, Pailler et al 1998, Eckhart 1999, Costich and Meagher 2001, Ramsey and Vaughton 2001, Kriebel 2014, Matsuhisa and Ushimaru 2015, Cuevas et al 2017.…”

“…One common feature in plants with separate sexes is sexual dimorphism, both in terms of vegetative and reproductive traits (reviewed by Barrett and Hough 2013). In insect‐pollinated dioecious species, male plants often display more conspicuous floral phenotypes than females, at least species from temperate ecosystems, with males typically producing larger floral displays and/or larger flowers (Guitián 1995, Delph et al 1996, Pailler et al 1998, Eckhart 1999, Costich and Meagher 2001, Ramsey and Vaughton 2001, Kriebel 2014, Matsuhisa and Ushimaru 2015, Cuevas et al 2017). One common explanation for this pattern is sexual selection: if male's reproductive success is more limited by mate acquisition than female's reproductive success (as predicted by Bateman principles: Bateman 1948), any trait involved in pollinator attraction should be under stronger selection in males than in females (Delph and Ashman 2006, Moore and Pannell 2011).…”

Effects of sexual dimorphism on pollinator behaviour in a dioecious species

“…One common feature in plants with separate sexes is sexual dimorphism, both in terms of vegetative and reproductive traits (reviewed in Barrett and Hough 2013). In insect-pollinated dioecious species, male plants often display more conspicuous floral phenotypes than females, at least in temperate species, with males typically producing larger floral displays and/or larger flowers (Guitián 1995, Delph et al 1996, Pailler et al 1998, Eckhart 1999, Costich and Meagher 2001, Ramsey and Vaughton 2001, Kriebel 2014, Matsuhisa and Ushimaru 2015, Cuevas et al 2017. One common explanation for this pattern is sexual selection: if male's reproductive success is more limited by mate acquisition than female's reproductive success (as predicted by Bateman principles, Bateman 1948), any trait involved in pollinator attraction should be under stronger selection in males than in females (Delph andAshman 2006, Moore andPannell 2011).…”