iHerp_Australia_-_November_-_December_2018

conveyed away from the parent plants, and may be

deposited in favourable or protected microclimates

(crevices or burrows, for example), or it may be that

successful dispersal is effected through sheer weight of

numbers. For example, of 160 scats collected from

Galapagos Land Iguanas (Conolophus subcristatus),

93% contained undamaged seeds, with a total of 5,

seeds from 32 plant species. Although trials resulted in

only 4% of these seeds germinating, C. subcristatus’

large body size and long gut retention times means

that it is able to ingest large quantities of seed and

carry them considerable distances. This coupled with

its high local density means that C. subcristatus is an

effective, legitimate agent of seed dispersal. It is, in

fact, the sole disperser of endemic Jasminocereus

thouarsii, Scalesia affinis, Stylosanthes sympodialis and

Tephrosia cinerea, and appears to be important in

revegetating areas denuded following volcanic activity.

In another instance of a lizard species assuming the

dual roles of both saurophily and saurochory, the

Striped Lava Lizard (Tropidurus semitaeniatus) is both

the most important pollinator and seed dispersal agent

of the cactus Melocactus ernestii. Lizard pollination has

been found to result in a significant increase in fruit

set, and seeds that had passed through the lizards’

digestive tracts exhibited a significantly enhanced

germination rate. Lizard-plant mutualisms involving

pollination and seed dispersal are all the more incredi-

ble because in general there are very few instances in

which plants rely on the same agent to perform both

functions. Like most other cases of double-mutualisms,

the above relationship has evolved between two

endemic species in an ‘extreme’ habitat containing

with low animal diversity.

Highly Unusual Mutualists.

Returning for a moment to the Green Iguana (Iguana

iguana), this species has recently been shown to

practice a highly novel form of seed dispersal. All other

known seed dispersal by reptiles is via endozoochory:

fruits are ingested, and the seed is subsequently

dispersed when it is eventually deposited in scats.

Epizoochory involves dispersal in which seeds adhere

to the external surfaces of animals, and is common

amongst mammals and birds, whose fur and feathers,

respectively, provide ideal surfaces to which seeds can

adhere. Reptiles’ smooth, scaly skin would seem to

preclude this method of dispersal, however Green

Iguanas have been documented to effectively disperse

seeds of Melocactus curvispinus which adhere to their

snouts when they consume the fleshy fruits. Moreover,

seeds stuck to the lizards’ snouts germinated in higher

numbers and at faster rates than ingested seed and

those collected from fruits.

Mexican Spiny-tailed Iguana (Ctenosaura pectinata)
eating leaves in a herb garden in Puerto Vallarta,
Mexico. Image by Jeremy Christensen.

Australia is home to another most unusual case of

lizards facilitating plant reproduction. In this instance

however, the lizard is neither a pollinator nor a seed

disperser. In the alpine regions of Tasmania, the Snow

Skink (Niveoscincus microlepidotus) enables pollen and

seed transport for the Honey Bush (Richea scoparis)

without acting as a vector. It does this whilst feeding

on the fused petals of flowers - the calyptras - by

exposing the plant’s reproductive organs, which are

otherwise inaccessible to pollinating agents and

prevent any seeds

from being released.

Researchers found

that the skink is

essential for repro-

duction of R. scoparis:

when lizards were

excluded, only 16% of

inflorescences had the

calyptra removed,

compared with 96% of inflorescences that lizards had

access to. Outcrossing was only possible when the

calyptra was removed, allowing access for insect

pollinators, and any seeds produced through selfing

were small and mouldy. Moreover, with the calyptra

intact, no seeds were released, whereas 87% of

flowers which had their calyptra torn by foraging

skinks released their seeds. How did this mutualism

evolve? Well, it appears that in an ecosystem which is

characterised by often extreme, cold, blustery

conditions, relying on insects alone - the diet that

characterises other lizards in this lineage - would be

insufficient to fulfil N. microlepidotus’s energy

requirements. In return for the energy resources

provided by consuming the nectar of R. scoparis, the

plant benefits because its reproductive organs are only

exposed during times of optimal insect activity: both

lizards and insects are ectotherms, and so the lizard’s

activity will coincide with periods favourable for

pollinating agents.

On the small island of Alegranza, part of the Canary

Island archipelago, another highly unusual set of inter-

actions involves birds

as indirect seed

dispersers mediated by

lizards, but in this

instance, one of the

interactions is far from

mutualistic. Great Grey

Shrikes (Lanius

excubitor) are major

predators of the

Noronha Skink (Gallotia atlantica), which in turn

consumes fruits of the plant Lycium intricatum.

Although the birds themselves do not consume the

fruits, by eating the lizards they indirectly disperse the

seeds. A study published in 1998 found that seeds

from shrike faecal pellets exhibited higher germination

rates than those collected from lizard scats. Similarly,

on Lanzarote, another island in the group, not only is

G. atlantica directly responsible for dispersing the seed

of L. intricatum, Rubia fruticosa and Asparagus nesiotes,

but these plants’ seeds were also present and germi-

nated from scats of the lizard’s avian predators, in this

instance both the Iberian Grey Shrike (Lanius

‘Australia’s SNOW SKINK is

ESSENTIAL for the reproduction of

the HONEY BUSH, but is neither

pollinator nor seed dispersal agent.’

Galapagos Land Iguana (Conolophus subcristatus).

The species’ large body size and long gut retention

times enable it to ingest large quantities of seed

and carry them considerable distances. Image by

buteo.