Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73 (S2): e64541, mayo 2025 (Publicado May. 15, 2025)

Flowering time and pollinator abundance determine

the female reproductive success in the dioecious

palm Chamaedorea pinnatifrons (Arecaceae)

Alfredo Cascante-Marín1, 2*; https://orcid.org/0000-0001-6382-9316

Gilbert Barrantes1, 2; https://orcid.org/0000-0001-8402-1930

Luis D. Ríos2; https://orcid.org/0000-0002-8746-8401

Eric J. Fuchs1, 2; https://orcid.org/0000-0002-6645-9602

1. Centro de Investigaciones en Biodiversidad y Ecología Tropical (CIBET), Universidad de Costa Rica, 11501-2060 San

Pedro de Montes de Oca, San José, Costa Rica.

2. Escuela de Biología, Universidad de Costa Rica, 11501-2060 San Pedro de Montes de Oca, San José, Costa Rica.

(*correspondence) alfredo.cascante@ucr.ac.cr

Received 04-IX-2024. Corrected 07-III-2025. Accepted 14-III-2025.

ABSTRACT

Introduction: Female fecundity in dioecious plants is influenced by ecological factors that affect pollen and pol-

linator availability. A high flowering synchrony between sexes, an abundance of pollen donors and pollinators

are expected to increase female reproductive success.

Objective: To understand how fruit production is related to flowering phenology, sex ratio, abundance and

proximity of reproductive males to focal pistillate plants, and pollinator abundance in the dioecious understory

palm Chamaedorea pinnatifrons (Arecaceae).

Methods: We followed the population flowering of the study species in a montane forest in Costa Rica during

2012. We correlated the number of fruits and fruit set from 115 inflorescences (74 plants) with the size of male

and female neighborhoods surrounding focal plants, as well as with plant size and floral display (number of flow-

ers per inflorescence). We estimated pollinator abundance by sampling thrips (Thysanoptera) from staminate

inflorescences throughout the plant reproductive season.

Results: Flowering was seasonal, with a high degree of overlap between the sexes. The sex ratio of reproductive

plants did not significantly deviate from one (79 females and 88 males). Female reproductive success was not

related to the abundance or proximity of pollen donors but was instead associated with plants possessing shorter

stems, more leaves and flowers per inflorescence, and fewer female neighbors. Late-flowering inflorescences sig-

nificantly produced more fruits and had a higher fruit set, which coincided with an increase in thrips abundance.

Conclusions: We hypothesized that a higher floral display acts as a signal effect to attract pollinators, while larger

inflorescences with more flowers can attract more insects, resulting in greater pollination success. Moreover, late-

flowering inflorescences seem to benefit from the increase in pollinator abundance at the end of the flowering

season. Pollination of C. pinnatifrons and other Chamaedorea species is highly dependent on thrips; as a result,

the reproductive success of these palms is susceptible to fluctuations in pollinator population sizes.

Key words: flowering phenology; pollen limitation; fruit set; neighborhood effect; pollinator limitation; thrips

pollination.

RESUMEN

https://doi.org/10.15517/rev.biol.trop..v73iS2.64541

SUPPLEMENT

SECTION: REPRODUCTION

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73 (S1): e64541, mayo 2025 (Publicado May. 15, 2025)

INTRODUCTION

Dioecious flowering plants (i.e., with sepa-

rate sexes) require pollination vectors, mainly

insects, to accomplish their sexual reproduc-

tion (Bawa, 1994). Pollinator abundance, pollen

availability, competition for pollinators, and

resources for fruit development limit the repro-

ductive success of female plants (Lee, 1986).

Ecological factors that determine the avail-

ability of pollen include population density, sex

ratio (male:female ratio), and flowering time

(Knight et al., 2005; Larson & Barrett, 2000).

Tropical dioecious plants show high diversity of

life forms and pollination systems, but the rela-

tive importance of ecological factors on female

reproductive success is still poorly understood.

This is significant because the reproductive

success of female plants has a direct influence

on the demography of dioecious species.

In low-density populations, female repro-

ductive success (measured as fruit production

or fruit set) generally decreases due to limited

pollen availability (Knight et al., 2005). A low

density of reproductive individuals may also

increase the distance between male and female

plants, affecting the chances of effective pollen

transfer to female flowers and consequently

reducing their reproductive success (House,

1992; House, 1993; Steven & Waller, 2007).

The sex ratio in dioecious plant popula-

tions is frequently skewed toward an excess

of either males or females (Field et al., 2013).

These biased sex ratios can potentially affect

population fitness (Fisher, 1930). Some studies

suggest that pollen limitation increases in pop-

ulations with increasingly female-biased sex

ratios (Öster & Eriksson 2007; Shelton, 2008).

In contrast, female plants may experience

La época de floración y la abundancia de polinizadores determinan el éxito reproductivo femenino

en la palmera dioica Chamaedorea pinnatifrons (Arecaceae)

Introducción: La fecundidad femenina en plantas dioicas está influenciada por factores ecológicos que afectan la

disponibilidad de polen y polinizadores. Se espera que la alta sincronía de floración entre sexos, la abundancia de

donadores de polen y polinizadores aumente el éxito reproductivo femenino.

Objetivo: Entender cómo la producción de frutos se relaciona con la fenología de floración, la proporción sexual,

la abundancia y proximidad de machos reproductivos a plantas pistiladas focales y la abundancia de polinizadores

en la palma dioica del sotobosque Chamaedorea pinnatifrons (Arecaceae).

Métodos: Documentamos la floración poblacional de la especie de estudio en un bosque montano en Costa Rica

durante el 2012. Correlacionamos la cantidad y proporción de frutos desarrollados en 115 inflorescencias (74

plantas) con el tamaño de los vecindarios de machos y hembras alrededor de las plantas focales, así como con

el tamaño de la planta y el despliegue floral (número de flores por inflorescencia). Estimamos la abundancia de

insectos polinizadores mediante muestreos de trips (Thysanoptera) de inflorescencias estaminadas a lo largo de

la temporada de floración.

Resultados: La floración fue estacional, con un alto grado de traslape entre los sexos. La proporción de sexos de

las plantas reproductivas no se desvió significativamente de uno (79 hembras y 88 machos). El éxito reproductivo

femenino no estuvo relacionado con la abundancia y proximidad de donadores de polen, sino que se asoció a

plantas que poseían tallos más cortos, más hojas y flores por inflorescencia y menos hembras vecinas. Las inflores-

cencias de floración tardía produjeron significativamente más frutos y tuvieron una mayor proporción de frutos,

lo que coincidió con un aumento en la abundancia de trips.

Conclusiones: Planteamos la hipótesis de que un mayor despliegue floral actúa como un efecto señal para atraer

polinizadores, es decir, inflorescencias más grandes con más flores pueden atraer más insectos, lo que resulta en

un mayor éxito de polinización. Además, las inflorescencias de floración tardía parecen beneficiarse del aumento

en la abundancia de polinizadores al final de la temporada de floración. La polinización de C. pinnatifrons y otras

especies de Chamaedorea depende en gran medida de los trips; como resultado, el éxito reproductivo de estas

palmas es susceptible a fluctuaciones en el tamaño de la población de polinizadores.

Palabras clave: fenología de la floración; limitación del polen; cuajado del fruto; efecto de vecindad; limitación

de polinizadores; polinización por trips.

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greater pollen deposition in male-biased popu-

lations (Carlsson-Graner et al., 1998).

High flowering synchrony is expected

between conspecifics of both sexes in dioecious

plants (Bawa, 1980) to reduce competition

between females for pollen (e.g., Augspurger,

1983). Although selection generally appears

to favor early flowering individuals (Munguía-

Rosas et al., 2011), for obligatory outbreeding

plants (e.g., dioecious species), this may not

be the case when a high degree of flowering

synchrony is presumably necessary for effective

pollination (Pires et al., 2013). Concurrently,

individual phenology patterns may interact

with population density and sex ratios, exacer-

bating their effect on the reproductive success

of female plants. Early or late flowering plants

may experience a lower effective population

size and a highly skewed sex ratios, which in

turn will negatively affect the amount and qual-

ity of pollen deposition, thus impacting fruit

production (Fuchs et al., 2003). Again, this sug-

gests that selection should favor female plants

that are able to flower close to the flowering

peak of male plants (e.g., Augspurger, 1983).

For female plants, the resources available

for fruit and seed maturation will likely influ-

ence their reproductive success, even when

pollen is not limited. Resource allocation for

reproduction in perennial long-lived species

typically increases with a plant’s age or size

(Cheplick, 2005; Wenk & Falster, 2015). There-

fore, seed production is likely to positively cor-

relate with the size of female plants. However,

plant size (e.g., height or number of leaves)

can also affect other structural traits that affect

pollination success and seed production. Floral

display has been correlated to plant size (Oller-

ton & Lack, 1998), and bigger plants often

produce a higher number of flowers that may

promote pollinator attraction and visitation.

In this paper, we examine how flowering

phenology, mate availability, co-flowering with

other females, pollinator abundance, and plant

size affect the female reproductive success of

the understory palm Chamaedorea pinnatifrons

(Jacq.) Øerst. (Arecaceae) in a Costa Rican

montane forest. We estimated the flowering

synchrony between sexes, the male and female

pollination neighborhoods around focal plants,

plant vigor (height and number of leaves),

and changes in the abundance of pollinators

on fruit production and fruit set of female

plants. We expect a high flowering synchrony

between sexes and a greater reproductive suc-

cess of female plants that reproduce during

the population’s flowering peak, as well as a

positive correlation of fruit production and

pollinator abundance.

In the neotropics, palms (Arecaceae) are

a highly diverse, abundant, and representative

plant group of humid forests. Even though

most neotropical palms are monoecious, the

genus Chamaedorea stands out for its dioecious

condition and high diversity (ca. 100 spp.),

with several species of ornamental interest

(Hodel, 1992). Chamaedorea species inhabit

humid and wet forests of Central and South

America (Hodel, 1992). Pollination of Chamae-

dorea has been documented in several species

(Porter-Morgan, 2007; Ríos et al., 2014), and

it involves insects from a single species of

thrips (Brooksithrips chamaedorea, Thysanop-

tera) and wind in an ambophylous pollination

system (Ríos et al., 2014). Thrips use male

inflorescences as brood sites and apparently

pollinate female flowers by deception. Con-

sidering the prevalence of curculionid and sap

beetles (Nitidulidae) in most palm pollination

systems (Henderson, 2024), the pollination

system of Chamaedorea can be regarded as

highly specialized given the specificity of thrips

pollinators. Despite its ecological and economi-

cal importance, information on the factors that

influence seed production in natural conditions

in Chamaedorea plants is limited (see Berry &

Gorchov, 2004; Berry & Gorchov, 2007; Otero-

Arnaiz & Oyama 2001; Oyama, 1990).

MATERIALS AND METHODS

Study species and site: Chamaedorea

pinnatifrons has the widest geographic and

elevation range of the genus, from Bolivia to

southern Mexico and from near sea level to

2 600 m asl (Hodel, 1992). These long-lived

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palms develop a single stem up to 4 m high,

produce three to eight pinnate leaves (Grayum,

2003; Hodel, 1992; Fig. 1A-B), and may live up

to 61–66 years (Ataroff & Schwarzkopf, 1994).

The small flowers (<3.5 mm in diameter) are

greenish to yellow and are borne on branched,

racemose inflorescences with several rachillae;

pollen is dry and powdery (Hodel 1992; Fig.

1C-D). The petals of male flowers are apically

connate at anthesis and open by vertical slits

on their margins (Grayum, 2003; Fig. 1D).

Fruits are bird dispersed (Orozco-Segovia et al.,

2003) and develop a single seed. Upon ripen-

ing, the fruits turn yellow-orange and mature

to a purplish black color (Fig. 1F). A voucher

specimen was deposited at the Luis Fournier

O. Herbarium (USJ) at the University of Costa

Rica (Ríos 16, USJ102220).

Field work was conducted in a 2 400-

ha cloud montane forest in the Costa Rican

Talamanca Mountain range (9°53’ N; 83°58’

W; 1 750 m asl), within the La Carpintera

Protective Zone. The forest primarily consists

of old secondary forest (>50 years old), inter-

spersed with older remnant forest patches.

These patches include oaks (Quercus spp.), fig

trees (Ficus spp.), and several tree species in

the avocado family (Lauraceae), as reported by

Sanchez et al. (2008). The area has an annual

mean temperature of 16.1 °C and an average

annual precipitation of 1 839.2 mm, with a

seasonal decrease in precipitation (<60 mm

Fig. 1. Chamaedorea pinnatifrons (Arecaceae) at the studied population in a montane forest of Costa Rica: A. Reproductive

female plant, B. Reproductive male plant, C. Pistillate flowers at anthesis, D. Staminate flowers with pollen (arrow) shed

through lateral slits in the fused petals, E. Flowering phenology graph of pistillate (F) and staminate (M) plants during the

reproductive season of 2012. The data on y-axis represent the proportion of individuals with inflorescences in anthesis in a

sample of 79 female and 88 male plants, and F. Infructescence with maturing (orange) and ripen fruits (black).

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73 (S2): e64541, mayo 2025 (Publicado May. 15, 2025)

per month) from December to April (Instituto

Meteorológico Nacional, s. f.). Chamaedorea

pinnatifrons is the only palm species occurring

at the study site.

Study plot, population flowering phe-

nology and female reproductive success: We

established a 40 × 40 m plot in mature for-

est where we counted and tagged (aluminum

tags) all reproductive C. pinnatifrons individu-

als (i.e., palms with developing inflorescences).

We recorded 79 male and 88 female reproduc-

tive plants. For all individuals, we counted the

number of leaves, measured plant height as

a proxy of plant vigor and determined their

X-Y coordinate position in the plot (Fig. S1).

The spatial distribution of reproductive plants

allows us to determine the relative positions of

flowering males and females throughout the

reproductive season.

We monitored the flowering phenology

of all individuals every 3-4 days from Febru-

ary to July 2012, for a total of 39 visits. The

time between visits was determined based on

preliminary observations of the inflorescence’s

anthesis pattern, which lasts between 3 and 7

days. During each census, we examined inflo-

rescences for flowers in anthesis. For staminate

plants, we checked that anthers were releas-

ing pollen, and for pistillate plants, the stigma

receptivity by noting the light green color of

the stigma´s lobes and the presence of a bright,

transparent secretion. After the receptive peri-

od, the stigma turns dry and brown-colored.

We marked the pistillate inflorescences, record-

ed the flowering date, and monitored them

for fruit development. Female reproductive

success was estimated as the number of mature

fruits produced per inflorescence and as fruit

set (fruits/flowers ratio) per inflorescence from

115 inflorescences (n = 74 individuals).

Data analysis: We compared the flower-

ing patterns of pistillate and staminate plants

using the temporal overlap index proposed by

Schoener (1970):

This index graphically depicts the intersec-

tion area of two genders’ phenological curves;

where pik and pjk represent the proportion of

flowering individuals of genders i and j, respec-

tively, at census k. A value of zero implies no

overlap, while a value of one indicates complete

overlap in phenological patterns.

We evaluated the effect of predictor vari-

ables that describe the male neighborhood (i.e.,

distance to nearest synchronous male, number

of synchronous males at five and ten meters

around focal female plants), female neighbor-

hood (i.e., nearest synchronous female, number

of synchronous females at five and ten meters

around focal female plants), number of pistil-

late flowers per inflorescence, and variables

related to plant vigor (i.e., stem height, number

of leaves) on fruit number and fruit set per

inflorescence (response variables). We used

General Linear Mixed Models (GLMM) with

census and each individual inflorescence ID as

random factors (library lmerTest, Kuznetsova

et al., 2017), with a Gaussian distribution of

errors. For each response variable, we fitted

a set of possible models and then chose the

optimal model based on the Akaike informa-

tion criterium (AIC; Zuur et al., 2009). We

used the R statistical language (version 4.02;

R Core Team, 2020) for all statistical and

graphical analyses.

We also analyzed fruit production (i.e.,

number of mature fruits per inflorescence)

throughout the flowering season by dividing it

by terciles according to the number of female

inflorescences. Each tercile represented differ-

ent stages in the season: early flowering (n = 34

female inflorescences), flowering peak (n = 39),

and late flowering (n = 42). We used a Krus-

kal-Wallis test to compare the three terciles’

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number of fruits, and a Dunn test to look at

differences after a significant result using the

library FSA (Ogle et al., 2023) implemented on

the R platform.

Thrips abundance: As previously reported

(Ríos et al., 2014), the thrips Brooksithrips

chamaedorea (Thysanoptera, Thripidae) is the

main biotic pollinator of C. pinnatifrons in the

study site. That study found that thrips use

the male flowers for mating and feeding, thus

they are more abundant in male inflorescences.

Therefore, we estimated the abundance of polli-

nator insects by using staminate inflorescences

as sampling units. We randomly selected three

inflorescences per week, from early March to

mid-May (11 weeks) and from different male

plants outside the study plot (n = 33). We col-

lected the insects during the morning hours

(8:00–12:00 h) by placing the inflorescences

in a plastic bag and gently shaking it to detach

the insects. We then preserved them in 70 %

ethanol and counted adult thrips in the labora-

tory using a stereomicroscope. We corrected for

differences in inflorescence size by dividing the

number of thrips per inflorescence by the num-

ber of rachillae, as the size of the sampling unit

might influence the number of thrips caught

(Lewis, 1997). Data are presented as the mean

(± standard error) number of thrips/rachillae

for each week.

RESULTS

Phenology pattern: The flowering of C.

pinnatifrons lasted five months and showed a

seasonal pattern, beginning in early February,

peaking in late March and early April (at the

end of the dry season), and ending in early

July (Fig. 1E). The sex ratio of reproductive

plants was F:M ratio = 1.11 and did not sta-

tistically differ from a distribution with equal

sex frequencies (Goodness of Fit Test: Chi-

squared value = 0.48, P = 0.48). The flowering

of staminate and pistillate plants overlapped

significantly (Schoener index = 0.72; Fig. 1E).

Individuals from both genders developed 1–4

inflorescences (mean = 1.9 females and 1.8

males) throughout the reproductive season

and blooming in each inflorescence lasted

3–7 days. At the individual level, flowering

was highly variable, with inflorescences in the

same plant maturing either sequentially or

separated by intervals of several weeks, from

one to 5–6 weeks.

Reproductive success: The mean female

floral display was 697 flowers per inflorescence

(± 23.4 SE, min = 120, max = 1 662), while

mean fruit production was 99.7 fruits (± 12.1

SE, min = 0, max = 735) per inflorescence. In

general, nearly one-third of all inflorescences

(35 %, or 40 out of 115), developed more than

100 fruits. A similar number (30 %) produced

between 11 and 100 fruits, while the remain-

ing 35 % of the inflorescences had less than 10

fruits (29 out of these 40 inflorescences did not

produce fruits). The mean fruit set was rela-

tively low (0.144 ± 0.016 SE), although varia-

tion among inflorescences was quite high (min

= 0, max = 0.83, CV = 116 %).

The GLMM indicated that the number

of fruits produced was significantly higher in

plants with shorter stems and more leaves and

flowers per inflorescence (Table 1A; Fig. 2A-C),

but it was inversely correlated to the number of

female plants around each fruiting palm (Table

1A; Fig. 2D). Similarly, fruit set was signifi-

cantly higher in inflorescences from palms with

shorter stems and decreased with the presence

of co-flowering females in the neighborhood

(Table 1B).

When inflorescences were grouped by their

flowering phenology, they showed significant

differences in the number of developed fruits

(H2 = 51.72, df = 2, P < 0.001). Early flowering

inflorescences were less successful, producing

less than 10 fruits each (65 %), and only 6 %

(2/34) ripened more than 100 fruits. In contrast,

59 % (23/39) of the inflorescences that flowered

during the flowering peak produced more than

10 fruits (Dunn test; P-value < 0.001). However,

late flowering plants produced significantly

more fruits per inflorescence (Fig. 3A). Of these

late-flowering inflorescences, 74 % (31/42) set

more than 100 fruits each; meanwhile, only

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Fig. 2. Predictor variables with a significant effect on the number of fruits developed in Chamaedorea pinnatifrons

(Arecaceae) at a Costa Rican montane forest. Results from GLMM analysis. Number of fruits per inflorescence decreases

with height of the stem (a), increases with number of leaves (b), and number of flowers (c), and decreases with the number

of conspecific females in the neighborhood (d).

7 % (3/42) produced less than 10 fruits (Fig.

3A). Furthermore, when fruit-set was com-

pared based on the plants’ flowering phenology,

those inflorescences that flowered late had a

greater fruit set (mean 0.296 ± 0.027 SE) than

those that flowered early (0.030 ± 0.009 SE) or

at the population´s peak (0.079 ± 0.013 SE).

Thrips abundance: Thrips were the most

abundant and frequent visitors to flowers

of staminate and pistillate inflorescences of

C. pinnatifrons. The mean number of thrips

per staminate inflorescence was 1 044 ± 145

SE (min = 35, max = 2 893). From early March

to mid-May, the abundance of adult thrips

increased 13-fold, from 20.8 (± 10.6) individu-

als per rachilla in the first week of March (early

flowering period) to 282.0 (± 74.4) in the third

week of May (late flowering period) (Fig. 3B).

Additional floral visitors, albeit less fre-

quent or occasional, comprised an unidentified

beetle species from the family Cryptophagi-

dae (Coleoptera) on both inflorescence types

and the stingless bee Partamona orizabaensis

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(Strand, 1919) (Apidae, Meliponini). These

insects were predominantly observed gathering

pollen on staminate inflorescences. Two other

leaf beetles (Chrysomelidae) from the genera

Tretagonotes and Demotispa were exclusively

observed on staminate flowers.

DISCUSSION

Our analysis revealed that traits related

to plant size, floral display, and the number of

co-flowering female plants near focal plants

best predicted female reproductive success in

C. pinnatifrons. Plants with shorter stems, more

leaves and flowers, and fewer female neighbors

produced more fruits and had a higher fruit

set. Contrary to our predictions, reproductive

success was significantly higher for inflores-

cences that developed during the later part of

the flowering season, which was correlated with

increased abundance of pollinators. Moreover,

the male neighborhood (i.e., proximity and

Table 1

GLMM results of the effect of stem height, number of leaves, number of flowers, and nearby co-flowering females in a 10-m

radius (Fem-10) on (A) the number of fruits and (B) fruit set (fruits/flowers) per inflorescence of Chamaedorea pinnatifrons

(Arecaceae) in a montane forest, Costa Rica. P-values in bold letters indicate significant effects (P < 0.05).

Factor Estimate SE df T P

A. Number of fruits

Intercept -10.67 69.60 97.24 -0.153 0.878

Height -0.32 0.15 84.94 -2.09 0.040

Leaves 21.52 11.60 95.13 1.86 0.067

Flowers 0.19 0.03 92.57 5.53 <0.001

Fem-10 -14.60 6.20 107.72 -2.35 0.020

B. Fruit set

Intercept 2.20 e-01 8.11 e-02 102 2.71 0.008

Height -4.50 e-04 1.84 e-04 85 -2.44 0.017

Leaves 2.05 e-02 1.42 e-02 94 1.44 0.153

Fem-10 -2.10 e-02 7.67 e-03 103 -2.74 0.007

Fig. 3. Data from the understory palm Chamaedorea pinnatifrons during the reproductive season of 2012 in a montane forest,

Costa Rica: A. Frequency of female inflorescences according to the number of developed fruits and ordered by flowering time

(early, peak, and late). B. Mean number (± SE) of adult thrips (Brooksithrips chamaedorea, Thysanoptera) per rachillae caught

on staminate inflorescences (n = 33) from 11 sampling census carried out on a weekly basis.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73 (S2): e64541, mayo 2025 (Publicado May. 15, 2025)

number of staminate plants) as a proxy for pol-

len availability had no effect on female success.

Unexpectedly, the stem height of C. pin-

natifrons females was not a positive predictor

of a plant’s reproductive success. Otero-Arnaiz

& Oyama (2001) reported similar results in

the related C. alternans, and Berry & Gor-

chov (2004) in C. radicalis. Additionally, female

plants with taller stems did not produce more

leaves (r = -0.22, p = 0.021), but there was a

marginal correlation between the number of

leaves and a higher number of fruits. Neither

of these plant size parameters were associated

with floral display traits, including the number

of inflorescences and flowers per inflorescence.

These findings suggest that the development of

reproductive structures and the reproductive

success of pistillate plants of C. pinnatifrons are

not exclusively limited by the plant´s resources.

However, research suggests that higher repro-

ductive costs, i.e., females allocating more

resources to reproduction than males, may

reduce the vegetative growth of female dioe-

cious plants (Obeso, 2002). Our findings indi-

cate that using the number of leaves and plant

height as proxies for the availability of resources

for sexual reproduction in C. pinnatifrons may

be misleading.

Among the variables examined, the num-

ber of flowers showed a positive correlation

with the number of fruits, but no correlation

with fruit-set. If pollen or resources are not

limited, plants that produce a greater number

of flowers are not constrained by the avail-

ability of ovules and may produce more fruits

(Wyatt, 1982). Moreover, the number of flowers

may be related to pollinator attraction (Fuchs

et al., 2010). According to Hodel (1992), the

majority of Chamaedorea species produce floral

fragrances, which are believed to attract their

thrips pollinators (Porter-Morgan, 2007). Flo-

ral visitors rely on floral scents to locate plants

and estimate the amount of reward available

in flowers (Schiestl, 2015). Thus, we hypoth-

esize that an increase in the number of flow-

ers per inflorescence in C. pinnatifrons would

attract more pollinators to a more rewarding

inflorescence, leading to higher rates of suc-

cessful pollination and fruit production.

Although inflorescences with more flowers

tend to produce more fruits in C. pinnatifrons,

the proportion of flowers that developed into

fruits was low and highly variable, as indicated

by the fruit-set ratio per inflorescence (mean =

0.144, CV = 116%). This may be the result of

pollen or pollinator limitation which can con-

strain fruit and seed set (Ashman et al., 2004;

Burd, 1994; Fuchs et al., 2010). While similar

fruit set results have been reported for other

Chamaedorea species, ranging from 0.13 to

0.47 (Berry & Gorchov, 2007; Listabarth, 1992;

Otero-Arnaiz & Oyama, 2001; Porter-Morgan,

2007; Ríos et al., 2014), pollen or pollinator

limitation has not been experimentally tested

in this group. Evidence from hand pollina-

tions in a dioecious tree suggested the occur-

rence of pollen limitation (Voigt et al., 2005)

and given that most tropical dioecious plants

rely on specialized pollinators for reproduc-

tion (Renner & Feil, 1993), pollen limitation

could be a widespread phenomenon among

tropical species with separate genders. In C.

pinnatifrons, contrary to our expectations, we

found that the abundance of males (pollen

donors) in the vicinity of female plants had

little to no effect on the number of fruits per

inflorescence or fruit set. Additionally, the

unbiased sex ratio of reproductive individuals

and the strong synchrony of flowering between

pistillate and staminate individuals suggests

that female reproductive success is not limited

by the availability of pollen donors. Instead, it

could be related to the abundance of pollinators

that determines the degree of pollen transfer,

as suggested by an increase in fruit production

and thrips abundance at the end of the repro-

ductive season.

Therefore, the alternative explanation for

the low female reproductive success in general,

but increased success in late-flowering plants of

C. pinnatifrons is likely related to a combination

of the time of flowering and pollinator abun-

dance. Many research studies that looked at

how phenology affects fruit production found

that plants that flower early experience less

10 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73 (S1): e64541, mayo 2025 (Publicado May. 15, 2025)

competition for pollinators or give their seeds

more time to mature (Munguía-Rosas et al.,

2011). However, C. pinnatifrons showed an

opposite trend, since late-flowering females had

the highest reproductive success. This result

seems counterintuitive since, in general, late-

flowering female plants likely experience low

pollen availability due to decreasing number

of mates at the end of the flowering season.

An increase in reproductive success when the

number of flowering plants decreases suggests

that changes in the abundance of pollinators

occur during the flowering season of C. pin-

natifrons. If pollinators are highly specific and

their population grows as the flowering season

progresses, then early flowering plants would

receive fewer visits by pollinators in compari-

son to late-flowering plants (Augspurger, 1983).

In this study, we found that the abundance of

thrips increased during the flowering season of

C. pinnatifrons, which coincided with a higher

number of fruits in late-flowering plants. Por-

ter-Morgan (2007) reported a similar pattern

for other Chamaedorea species from Belize,

noting that female plants that flowered early in

the reproductive season had a lower seed set

compared to those that flowered late.

Pollination in Chamaedorea is highly spe-

cialized, involving a mutualism with thrips

(Thysanoptera) and this interaction has been

observed in species from Belize (Porter-Mor-

gan 2007) and Costa Rica (Ríos et al., 2014).

According to these studies, thrips use male

flowers to feed and oviposit and then visit

female flowers for mating opportunities while

depositing pollen on the stigmas, which resem-

bles a nursery pollination system (Dufaÿ &

Anstett, 2003). Both studies mentioned the

same thrips species: Brooksithrips chamaedorea

which was described from specimens obtained

from Chamaedorea inflorescences (Retana-

Salazar & Mound, 2005). According to Porter-

Morgan (2007), thrips pupate in the topsoil

during the rainy season, and the emergence

of adult thrips coincides with the reduction of

rains and increasing soil temperatures during

the dry season, the period when C. pinnatifrons

produces flowers.

Thrips are also effective pollinators of

other dioecious tropical woody plants (Moog

et al., 2002; Sakai, 2001; Zerega et al., 2004).

These insects typically have a life cycle from egg

to adult that lasts around two weeks (Bethke et

al., 2014); thus, it is likely that several genera-

tions can occur during the flowering period of

C. pinnatifrons. The growing number of male

C. pinnatifrons inflorescences throughout the

reproductive season increases the availabil-

ity of food resources and breeding sites for

thrips. This enables the thrips population to

rapidly grow, potentially contributing to the

high fruit production of late-flowering plants

through an increase in the insects’ population

and subsequently higher visitation rates to

pistillate inflorescences.

In conclusion, the female reproductive

success of the dioecious palm C. pinnatifrons

appears to primarily depend on the floral dis-

play or number of flowers per inflorescence,

rather than the plant size, the abundance, or the

proximity of pollen donors. We hypothesized

that a signal effect, where larger inflorescences

with more flowers can attract more pollinators,

could be partially responsible for fruit produc-

tion. As expected, in our study site, the flower-

ing of pistillate and staminate plants overlapped

significantly; however, the flowering phenology

of individual inflorescences seems to play a

major role in female reproductive success. Late-

flowering individuals had a higher fecundity,

most likely due to an increase in pollinator

abundance as the flowering season advances.

These results contrast with previous research

(Munguía-Rosas et al., 2011) in which early,

rather than late, flowering plants had a higher

reproduction. Because C. pinnatifrons and other

Chamaedorea species rely on a single species of

thrips for pollination, the reproductive success

of these palms is susceptible to fluctuations in

their pollinator populations.

Ethical statement: The authors declare

that they all agree with this publication and

made significant contributions; that there is no

conflict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73 (S2): e64541, mayo 2025 (Publicado May. 15, 2025)

and requirements. All financial sources are fully

and clearly stated in the acknowledgments sec-

tion. A signed document has been filed in the

journal archives.

ACKNOWLEDGMENTS

We thank the Asociación de Guías y Scouts

de Costa Rica for their permission to conduct

this research at Campo Escuela Iztarú at Cerros

La Carpintera. To all field assistants for valu-

able help. The Vicerrectoría de Investigación

from the Universidad de Costa Rica provided

funds (project B0223). This manuscript was

completed during EJF sabbatical leave. To two

anonymous reviewers for their comments and

suggestions.

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