This document summarizes the coevolution of plants and insect pollinators. It discusses how flowering plants and pollinators exert evolutionary pressure on each other over time, with examples like orchids evolving long nectar spurs that correspond to the long tongues of moths. It also describes different models of coevolution, noting Darwin's prediction of the long-tongued moth that pollinates the Madagascar star orchid. The summary concludes by presenting some general characteristics of common pollinator types and the plant traits that often coevolve with them.

1. COEVOLUTION OF PLANTS AND INSECT
POLLINATORS
Presented by:
Hemlata
Ph.D Previous
Dept. Of
Entomology
INDIRA GANDHI KRISHI
VISHWAVIDALAYA,RAIPUR

2. INTRODUCTION
• The term coevolution was coined by Paul R. Ehrlich and
Peter H. Raven in 1964, to describe the evolutionary
interactions of plants and butterflies.
• Coevolution occurs when two or more species reciprocally
affect each other's evolution.
• Coevolution is a term used to describe the mutual changes
in two or more species, usually one following the other, that
affect their interactions.
• Flowering plants and their pollinators are often used as the
classic example of this evolutionary phenomenon.
• The plant and the pollinator place evolutionary pressure on
each other for changes in morphology, physiology, or habits
that benefit both.

3. • The coevolution of flowering plants and their animal
pollinators presents one of nature's most striking examples
of adaption and specialization. It also demonstrates the
interaction between two groups of organisms can be a font
of biological diversity.

5. A long spur
• Charles Darwin described an
interesting case of pollinator-
flowering plant coevolution in
Madagascar: the star orchid,
Angraecum sesquipedale, has foot-
long spurs, with the nectary at the tip.
In 1862, when Darwin examined this
orchid, he predicted that a long-
tongued moth would be found that
pollinated it; no moth with that
extreme length of tongue was known
at the time.
• Then, in 1903, he was proven correct
when a long-tongued moth,
Xanthopan morganii praedicta was
discovered. It was so-named because
its occurrence had been predicted.

6. Bees
-Bees appear to be especially adapt at
perceiving bilateral symmetry and the colors
blue and yellow, and at manipulating flower
parts.
-So plants being pollinated by bees are subject
to a strong selective pressure favoring bilateral
symmetry and those colors.
-In turn, the flowers exert pressure on the bees,
favoring hairiness, body shape, and behavior
that effectively transfer pollen.
-The resulting specialization can favor a trend
toward an exclusive relationship, which may be
to the benefit of each participant.
-The plant gains the constancy of the bee,
which majors on the particular species and
facilitates pollination of widely spaced,
specialized flowers. The bee gains exclusive
access to the nectar.

7. Yucca moth
• The yucca, Yucca whipplei, is
pollinated exclusively by Tegeticula
maculata, a yucca moth that depends
on the yucca for survival.
• The moth eats the seeds of the plant,
while gathering pollen. The pollen has
evolved to become very sticky, and
remains on the mouth parts when the
moth moves to the next flower.The
yucca provides a place for the moth to
lay its eggs, deep within the flower
away from potential predators.

8. Darwin’s Mechanistic Model
• He noticed that the Angraecum, like the local British moth-
pollinated Platanthera orchids, had nectar at the very
bottom of the long spur and that moths would require a long
proboscis in order to claim this reward.
• The fittest moths in a population would then be those with
long tongues that could access the nectar in even the deepest
flowers, whereas the shorter-tongued moths would access
less nectar.

9. Darwin’s mechanistic model for plant–
pollinator coevolution

10. Alternative Mechanisms: The
Pollinator Shift Model
• The pollinator shift model was developed by Verne Grant (Grant and
Grant 1965) and Ledyard Stebbins (Stebbins 1970).
• In this model, pollinator shifts (utilization of different pollinators
through modification of floral traits) are induced by changes in the
local pollinator fauna, either because of expansion of a species range
or because of a change in pollinator composition over time
(Johnson 2006).
• In the shift model, plants adapt to pollinators with pre existing tongue
lengths (one-sided evolution), but the mechanism of selection on
corolla tube length is usually identical to that in the Darwin model.
• Studies of the African Disa draconis complex of orchids showed that
spur length evolution could be explained by shifts between pollinators
(Johnson and Steiner 1997).
• In his study of A.sesquipedale, Wasserthal (1997) concluded that the
pollinator shift model, rather than coevolution, could explain the
evolution of the very long spurs of this species.

11. Selection on Flower Tube Length
• Alexandersson and Johnson (2002) later demonstrated a
positive relationship between fitness (measured by the
number of seeds produced) and naturally varying corolla
tube length in the hawkmoth-pollinated Iris Gladiolus
longicollis.
• Plants with shorter tubes were not effectively pollinated
because of their mismatch with the tongue lengths of the
majority of individuals of the hawkmoth pollinator Agrius
convolvuli (range in tongue length: 85–135 millimeters).
• For example, mismatches in the length of the proboscis of
the fly Moegistorhynchus longirostris and the tube length of
its nectar host plant Lapeirousia anceps lead to lowered
pollination success (Pauw et al. 2009).

12. Nemestrinid flies M. longirostris with a tongue length of approximately 50 millimeters probe flowers of
two morphs of Lapeirousia anceps that differ in tube length. a Long-tubed flowers (53 millimeters) that
match the length of a fly which has not yet fully inserted its proboscis. b Short-tubed flowers
(28 millimeters) that are mismatched to the proboscis of a fly and thus receive less pollen on stigmas
(Pauw et al. 2009).

13. Selection on Pollinator Tongue
Length
• Long tongues have evolved in many groups of flower-
visiting animals.
• hummingbirds (bills up to 10 centimeters)
• hawkmoths (tongues up to 25 centimeters)
• nemestrinid flies (tongues up to 8 centimeters)the
elongation of these tongues represents adaptation for
feeding on nectar.
• Pauw et al. (2009) presented flowers singly to foraging
nemestrinid flies (M. longirostris) and found that
individuals with longer tongue lengths were able to drink
more nectar in a single visit to the deep-tubed flowers of the
iris Lapeirousia anceps.

14. Geographical Patterns of Coevolution
• Selective pressures on pollinator tongues and tubes are not uniform
across geographic landscapes because interacting organisms seldom
have precisely overlapping distribution ranges (Grant and
Grant 1965).
• As a result, plants may have different floral visitors in different
populations, and floral visitors may forage from different plant
communities in different parts of their range.
• For example, Gomez et al. (2009) found that the mustard Erysimum
mediohispanicum has very different pollinator communities in
different populations and that this accounted for differences among
the populations in selection on traits such as corolla width and shape.
• Although not an example of coevolution, the results of this study
predict that coevolutionary relationships should also have
geographically variable outcomes when community structure differs.
This is an important idea which has been developed over the last few
decades by John Thompson and his colleagues
(Thompson 1994, 2005).

15. Pollinators and flower types
The table below presents some of the general characteristics of the most common
pollinators and the plant characteristics that have coevolved with them.
​Pollinator ​​Pollinator characteristics ​​Typical flower types ​​Example plants
Bees, including
bumblebees, honey bees,
and solitary bees
​Perception of bilateral
symmetry, blue and yellow
colors and ultraviolet light;
dexterity at manipulating
plant parts, ability to
strongly vibrate by
buzzing, need for both
nectar and pollen.
​Flowers with bilateral
symmetry, often in shades
of blue or yellow,
nectar guides in the
ultraviolet spectrum,
flowers that require
dexterity to open,
sometimes bell-shaped
flowers.
​Lupines, clovers, orchids,
penstemons, ericads (buzz
pollination).
​Butterflies
​High nectar needs, require
sunlight for flying, long
tongues
​Bright colors, often tubular
flowers, nectar rewards.
​Phlox, milkweed,
sunflower family.
​Moths
​Often fly at night, sensitive
to fragrance, ability to
hover.
​White or pale flowers
which may open at night
and close during the day,
releasing fragrances,
pendant or horizontal
​Catchfly, stickseed, wild
tobacco.

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