Dr. Mark Gardener

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Nectar Chemistry | Plant-Animal Interactions | Tropical Research | Publications


My research is broadly in the field of plant-animal interactions. The main focus of my investigations has been on pollination but I have also looked at defence mutualisms in wild cotton (defended by ants). My PhD research was conducted on the role of amino acids in floral nectar. I studied a range of plant species in the UK and abroad and used analytical chemistry (HPLC) to determine the composition of the nectar. I also examined the response of some insects to different 'flavours' of nectar. Stingless bees in Queensland and ants in the UK were my study species. I have also examined the extrafloral nectar of wild cotton in Arizona. Ant species visit these nectaries and defend the plants from herbivores. After my PhD I looked at the nectar composition (amino acids and carbohydrates) in two contrasting plant hybrid zones. The first was a woody plant in Georgia, USA and the other a herb in Colorado. In 2003 I worked at the University of Hawaii where I studied the pollination of some endangered plant species. Since returning to the UK in 2004 I have been teaching Ecology and Environmental Science for the Open University whilst continuing research.
Nectar is more than just sugar. It contains a variety of amino acids, the building blocks of proteins.

Nectar Chemistry:

Nectar is an important resource. Many animals use it as a food, for some it is a welcome bonus but for others it is a mainstay. Lots of insects eat nectar, bees, flies and butterflies for example. Many birds will try it and the hummingbirds eat almost nothing else. Nectar is composed of various sugars: mainly sucrose, glucose and fructose in varying proportions. Amino acids are also present in small concentrations. Many plants produce over a dozen different amino acids in the nectar of their flowers. Nectar is important for the animals that eat it but it is also important for the plants; the nectar acts as a reward to visiting animals and the cross-pollination of the plant is the ultimate 'goal' of the plant. Some plants produce nectar not in flowers but in other structures on stems or leaves for example. This nectar attracts other insects, wasps and ants for example, and the plant benefits from reduced herbivory: an example of a defence mutualism.

Some of the equipment used in the chemical analysis of nectar.

Link to: the Open University Science pages.

Corncockle growing at the Open University field site.

Fertilizer and Nectar:

I grew the cornfield annual plant Agrostemma githago, corncockle, at the Open University field site. Three fertilizer treatments were used in one metre plots; no added nitrogen, 75g of nitrogen and 175g. The nectar was analyzed for amino acids and it was found that the treatments affected the composition. The main finding was that extra nitrogen in the soil finds its way into nectar as an increased concentration of amino acids.

Corncockle, Agrostemma githago.

Link to Highlands Research Station, NC.

Link to RMBL: Rocky Mountain Biological Laboratory, Crested Butte, CO.

A buckeye hybrid in Georgia, USA.

Sugar concentration in buckeye hybrids is not intermediate to its parents.


Nectar in Plant Hybrids:

I have studied the nectar composition in two plant hybrid zones. In Georgia, USA I examined two buckeyes (Aesculus, small trees) and their hybrid. In Colorado I studied two sky-rockets (Ipomopsis, a forb) and their hybrid. In both systems the hybrid appears intermediate in size and colour to its parents. The nectar composition however is not intermediate. Both hybrids showed lower sucrose and higher levels of hexoses (glucose and fructose).


Plant-Animal Interactions:

The majority of plant species rely on animals to transfer their pollen. Many insects perform this task but a variety of other animals also visit flowers; birds, bats and monkeys for example. I have studied pollination by looking at nectar. This is produced by many species and the animals that come to drink it also carry pollen with them. I have also looked at the pollination of some plants in Hawaii.

Some plants produce nectar in nectaries located not in flowers but on stems or leaves. These attract insects such as wasps and especially ants. These animals act like bodyguards and defend the plant against herbivores that wish to eat leaves, seeds or fruit. Some of my research examined the nectar of wild cotton in Arizona. These plants produce nectar and are visited by several species of ant.

A gatekeeper butterfly
pollinates a buddleja.

Not all nectar is inside flowers. Some plants produce it on stems. This nectar attracts a variety of insects.

Link to Santa Rita Experimental Range, AZ.

Wild Cotton:

Cotton plants, Gossypium thurberi, in Arizona produce nectar. Flowers produce one kind and there are two types of extrafloral, on bracts and leaf stems. Several species of ant visit the extrafloral nectar. Large bees visit the flowers for both nectar and pollen. I looked at nectar composition with a colleague, Jenn Rudgers. We found that local populations of cotton produce slightly different compositions of nectar.

Wild cotton, Gossypium thurberi,
in Arizona.


This garden ant, Lasius niger, has a taste for amino acids in its nectar.

Ants and Nectar:

I looked at the preferences of the black garden ant, Lasius niger, for nectar with or without added amino acids. Foraging ants were presented with a number of feeding stations, each provided a sugar-only solution or one with added amino acids. The ants preferred the solution with both sugars and amino acids.

Foraging garden ants get a choice of food.


Tropical Research:

The tropics are important for many reasons. They are places where plants and animals exist in abundance. The tropics provide researchers the opportunity to study organisms that have very narrow ecological niches. Tropical regions also allow researchers to conduct field work at times when it is not possible back home in more temperate zones.

My work in the tropics so far has two strands: I collected nectar from a variety of plants in Queensland as part of my PhD study into the ecological role of amino acids in floral nectar. I also studied the response of a native stingless bee, Trigona hockingsi, to artificial nectar with and without amino acids. In 2003 I worked at the University of Hawaii on Oahu. I examined the pollination of two groups of endemic plants. The first group, lobeliads, have probably lost most of their pollinators (birds) and are in serious decline. The second group, Cyrtandra, are not endangered but are highly diverse and their pollination has never been observed.

A tropical forest in Hawaii.

A lobeliad, Clermontia kakeana in Hawaii.

Link to James Cook University.

Tropical stingless bees, Trigona hockingsi, in Queensland.

Bees in Queensland:

I made an artificial nectar solution using sucrose. To half I added amino acids in a mixture designed to mimic natural flowers. A feeding experiment was set-up at a hive of stingless bees, Trigona hockingsi, at James Cook University in Townsville, Queensland. Bees were presented with a choice of feeders and their activity recorded. They seemed to show no preference for either solution.

Link to The University of Hawaii at Manoa, Oahu.

Pollination in Hawaii:

I studied two groups of plants. Many lobeliads are endangered and I did not observe any visits to Clermontia kakeana. They probably rely on self-pollination. A native bee visited Cyanea superba and it is possible that these bees may provide a limited pollination service. The genus Cyrtandra has many representatives in Hawaii. Their pollination strategy was unknown. I discovered that they are visited by night-flying moths.

The pollination system of Cyrtandra was unknown.
You can click on the links to open PDF versions of these papers, an approximate file size is shown.


Elnagdy S., Majerus M.E.N., Gardener M., and Lawson Handley L-J. 2013. The direct effects of male killer infection on fitness of ladybird hosts (Coleoptera: Coccinellidae). Journal of Evolutionary Biology, 26, 1816-1825. [pdf 300k]

Kaczorowski R.L., Gardener M.C., and Holtsford T.P. 2005. Nectar traits in Nicotiana section Alatae (Solanaceae) in relation to floral traits, pollinators, and mating system. American Journal of Botany, 92, 1270-1283. [pdf 800k]

Rudgers, J. A. & Gardener, M. C. 2004. Extrafloral nectar as a resource mediating multispecies interactions. Ecology, 85, 1495-1502. [pdf 90k]

Gardener, M. C., Rowe, R. J. & Gillman, M. P. 2003. Tropical bees (Trigona hockingsi) show no preference for nectar with amino acids. Biotropica, 35, 119-125. [pdf 275k]

Gardener, M. C. & Gillman, M. P. 2002. The taste of nectar - a neglected area of pollination ecology. Oikos, 98, 552-557. [pdf 150k]

Gardener, M. C. & Gillman, M. P. 2001. Analyzing variability in nectar amino acids: composition is significantly less variable than concentration. Journal of Chemical Ecology, 27, 2545-2558. [pdf 245k]

Gardener, M. C. & Gillman, M. P. 2001. The effects of soil fertilizer on amino acids in the floral nectar of corncockle, Agrostemma githago L. (Caryophyllaceae). Oikos, 92, 101-106. [pdf 200k]

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