Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 May 2022 | 14(5): 21125–21126
ISSN 0974-7907
(Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.7915.14.5.21125-21126
#7915 | Received 09
March 2022 | Final received 16 April 2022 | Finally accepted 20 May 2022
Nectar robbing by sunbirds on the
flowers of Morinda pubescens
J.E. Smith (Rubiaceae)
A.J. Solomon Raju 1,
S. Sravan Kumar 2, G. Nagaraju 3,
C. Venkateswara Reddy 4,
Tebesi Peter Raliengoane
5, L. Kala Grace 6, K. Punny 7,
K. Prathyusha 8 & P. Srikanth 9
1, 3–9 Department of Environmental
Sciences, Andhra University, Visakhapatnam, Andhra Pradesh 530003, India.
2 Department of Basic Sciences
& Humanities, Baba Institute of Technology & Sciences, P.M. Palem, Visakhapatnam, Andhra Pradesh 530048, India.
1 solomonraju@gmail.com (corresponding
author), 2 sravankumarsamareddy@gmail.com, 3 nagaraju_gattu@gmail.com,
4 cvreddy1980@gmail.com, 5 traliengoane@gmail.com, 6
kalagracelankapalli@gmail.com, 7 punnykonapalli@gmail.com, 8
p.kodamala@gmail.com, 9 pallemsrikanth@gmail.com
Editor: Analinda C. Manila-Fajardo, University of the Philippines
Los Banos, Laguna, Philippines. Date of publication: 26 May 2022 (online
& print)
Citation: Raju, A.J.S., S.S. Kumar, G. Nagaraju, C.V. Reddy, T.P. Raliengoane,
L.K. Grace, K. Punny, K. Prathyusha
& P. Srikanth (2022). Nectar robbing by sunbirds on the
flowers of Morinda pubescens
J.E. Smith (Rubiaceae). Journal of Threatened Taxa 14(5): 21125–21126. https://doi.org/10.11609/jott.7915.14.5.21125-21126
Copyright: © Raju et al. 2022. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: Self-funded.
Competing interests: The authors
declare no competing interests.
Acknowledgements: We thank the Andhra University,
Visakhapatnam, for providing physical facilities to carry out this work.
The genus Morinda is represented by only eight species,
namely, M. angustifolia Roxb., M. persicaefolia Ham., M. villosa
Hook.f., M. umbellata
L., M. trimera Hillebr.,
M. elliptica (Hook.f.)
Ridl., M. citrifolia
L., and M. pubescens J.E. Smith, in India
(Arya et al. 2014). Recently, M. tinctoria Roxb. and M. tomentosa Heyene ex Roth. are treated as synonyms to M. pubescens and accordingly this is followed in this work
and the published work reported on these species is cited as related to M. pubescens. M. tomentosa
which is now known as M. pubescens is widely
distributed in India, Sri Lanka, China, central Myanmar, southern Thailand,
Vietnam, and Indonesia (Kesonbuaa & Chantaranothai 2013). It is a small evergreen tree adapted
to grow successfully in arid/semi-arid to mesophytic
conditions (Bermer & Manen
2000).
Morinda pubescens
distributed naturally with a few individuals in Kadiri
Reserve Forest with arid ecosystem (14.0667°N, 78.1967°E and
altitude 761 m) in Anantapur District, Andhra Pradesh, India, was used for the
study during February–June 2019. This tree grows here in cracks and crevices of
stony rocks and in partially weathered rocks accumulated with soil. Leaves are
petiolate, simple, opposite, decussate and broadly elliptic with acute
apex. Flowers are borne in leaf-opposed
solitary, terminal, globose heads. They are sessile, greenish-white, fragrant
and hermaphroditic with distyly. Calyx tube is
connate at base with denticulate lobes. Corolla is greenish-white and
salver-shaped with slender tube extended into five abruptly spreading flat
lobes exposing the sex organs. The stamens here are five attached to the
corolla throat and linearly extended beyond the rim of the corolla tube. The
ovary is bi-locular, 4-ovuled with linear style which is extended into a bi-lobed
stigma. The fruit is a green globose syncarp with four oblong pyrenes.
In Kadiri Reserve Forest, M. pubescens
blooms in foliate state during dry season from March to May (Image 1a). Mature buds open during early morning and
expose the sex organs out of the corolla tube (Image 1b–e). The flowers are nectariferous. However, the nectar is concealed at the base
of the corolla tube which is accessible only to legitimate foragers probing the
flower-opening side. Thrips use the floral buds for
breeding and open flowers for pollen and nectar. They move out during
flower-opening. Sunbirds, Nectarinia asiatica and N. zeylonica
were seen at the flowers of M. pubescens
foraging on thrips and nectar. These birds pick up thrips (Image 1f,g) from the flowers by probing the flowers
legitimately during which they occasionally effect pollination and collect
nectar illegitimately by making a puncture/slit at the base of corolla tube
from outside (Image 1h,i).
The flowers
with tubular corolla are vulnerable to nectar robbing. Maloof
& Inouye (2000) and Irwin et al. (2010) reported that nectar robbing is
very frequent in plant species producing flowers with long corollas and
abundant nectar production. Irwin & Maloof (2002) reported that nectar
robbing involves primary and secondary robbing with the first one as the most
common. In primary robbing, the flower forager makes a slit or hole or tear in
petal tissue to rob nectar bypassing the floral opening used by legitimate
pollinators. In secondary robbing, the flower forager acquires nectar via
slit/hole/tear made by primary robbers again bypassing the floral opening used
by legitimate pollinators. Specialization in floral architecture is vulnerable
to exploitation by flower visitors which remove or steal nectar without effecting
pollination (Navarro 2001). Nectar robbing by sunbirds on the flowers of M. pubescens is an indication of primary robbing which
does not effect pollination but this robbing
phenomenon reduces nectar reward and increases variability in nectar standing
crop. Such a situation is expected to promote pollination rate in general and
cross-pollination in particular when legitimate pollinators visit M. pubescens flowers for nectar. Therefore, M. pubescens is an important source of thrips
as insect food and nectar as instant drink for sunbirds during dry season in
the arid ecosystem.
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