Kiwi(fruit) power

I love bacon and eggs, but there's a downside, and it's a common household dilemma: a frypan that's encrusted with fried egg.

First I plunged it in a sinkful of hot soapy water, and took to it with a green plastic scourer.  It was pretty clear that was going to work, but only after a very long time and a lot of elbow grease.  Then I remembered: egg white is protein, and kiwifruit is rich in proteases (enzymes are named something-ase where "something" is the substrate they act upon.  Protease breaks down protein).  That's why kiwifruit is a good meat tenderiser.

So I cut a disk of kiwifruit (and ate the rest), and sat it in the frypan for a couple of hours (2h 20m, to be more precise, seeing I'm being scientific here).

Then wiped it quickly with a sponge and cold water.

So kiwifruit protease is pretty powerful at digesting protein.  But enzymes are proteins too, so why don't proteases self-destruct?

Disclaimer: this research was not funded by the Kiwifruit Marketing Board.

Wednesday wildflower: onion weed

I'm told a weed is a wildflower whose virtues have yet to be discovered.  But onion weed or three-cornered garlic (Allium triquetrum) has virtues and is still a detested weed.

The plants spread rapidly, either sexually by seeds or vegetatively by bulbs, to infest large areas.  The tiny black seeds germinate freely and get carried up on the tip of the first leaf as it grows.  The Flora of New Zealand Vol. 3 (Healy & Edgar 1980) says the first wild collection in New Zealand was made in 1928, and it was probably first introduced as a garden plant.

Allium triquetrum, onion weed.

The flowers are pretty and quite similar to those of a plant that everyone wants to grow: snowflake or Leucojum aestivum (below).  So what makes one desirable and the other an enemy of the gardener?  Well, the smell of onion weed for a start; it's garlic, but not really in a good way.  The fact it's hard to control makes it undesirable too, because it spreads and takes over wherever it lands.

Snowflake, Leucojum aestivum, a popular garden plant.

Onion weed is a close relative of those marvellous vegetables onion (Allium cepa), leek (Allium ampeloprasum var. porrum or A. porrum), garlic (Allium sativum), and chives (Allium schoenoprasum).  I understand it is edible, and at a pinch would be a substitute for garlic, but I haven't plucked up courage to try it yet.  There's enough in our garden to keep us going for a while!

Reference.

Healy, A.J., Edgar, E. 1980. Flora of New Zealand Vol. 3. Government Printer, Wellington.

Signs of Spring

Winter has just officially begun and I know there's a lot of wet and cold weather to come.  Last year we had 3 days of snow in August, almost unheard of in Wellington.  Yet in the Botanic Gardens this weekend I found unmistakeable signs of Spring:

This daffodiul, Narcissus, in the rock garden and others near the tree house were in flower.

Corydalis in the rock garden.  For a discussion on the shape of these flowers see my earlier blog.

Snowflake, Leucojum aestivum.

Wednesday wildflower: Tangier pea

Lathyrus tingitanus is a common legume throughout New Zealand.  Its compound leaves are modified so that the first pair of leaflets are normal, but the others are adapted as tendrils, which help the plant climb on other plants.  At the base of the leaf are a pair of stipules that clasp the stem.  Sweet pea is another common species of Lathyrus: L. odoratus.  

A leaf, buds, and flowers (seen from the front at left and the back at right) of Tangier pea, Lathyrus tingitanus.

Lathyrus sativus is grown as a food crop in South and South-west Asia and East Africa, known as grass pea or Indian pea.  Along with some other species of Lathyrus, it contains oxalyldiaminopropionic acid, which can lead to lathyrism if people are too reliant on these peas, or their flour, in their diet. Oxalyldiaminopropionic acid is a non-protein amino acid, which causes paralysis of the lower limbs and wasting of the buttocks, symptoms commonly seen in Africa during famines.

If this isn't Lathyrus tingitanus, it's a very similar species.  Roca Grosso, Catalonia.

Going through the motions: what did moa eat?

Moa were giant flightless birds found in New Zealand (the plural of moa is moa, because the Māori language doesn’t distinguish singular from plural nouns, with one exception).  There were 6 genera and 9 species of moa; the largest, Dinornis, stood well over 2m tall.  They’ve been extinct since shortly after Māori arrived here.  It’s thought they were an easily harvested source of protein and were quickly driven to extinction.  Although everywhere on earth where humans live has extinct megafauna (e.g., aurochs in Europe, giant sloths in South America, giant lizards and kangaroos in Australia), in most places the extinctions happened so long ago that they're very hard to study.  But in New Zealand, the extinction of moa is quite recent, dating from around the 13th century, and there are still traces to be found and studied.  Deposits of regurgitated gizzard stones are sometimes found, and subfossil birds can be recovered from caves.  It's thought that some large trees still alive today might have been dispersed as seeds by moa.  

About 35 years ago, Michael Greenwood and Ian Atkinson (Greenwood & Atkinson 1977) proposed that moa could have been a major influence on growth forms of New Zealand plants.  In particular, they suggested the twiggy wiry tangled small-leaved growth forms that we call divaricating shrubs could have evolved as a defense against moa browsing.  That’s been a very popular and appealing idea, but one that’s had its critics.  While New Zealand botanists have been happy to attribute our unusual flowers to pollination by our depauperate and unspecialised pollinator fauna and our prevalence of small fleshy fruits to dispersal by frugivorous birds, many have been wary of accepting the moa browse hypothesis.

A divaricating shrub, Coprosma cuneata, Campbell Island.

Partly their objections have arisen from concern that these ideas can’t directly be tested, because moa are no longer with us.  Nevertheless, many other purely historical ideas in biology can be tested, by indirect methods at least.  Greenwood & Atkinson’s seminal paper has spawned an industry in New Zealand ecology largely driven by questions about the likely selection pressures of moa on New Zealand plants.  One recent test of moa browsing was a cafeteria experiment (Bond et al. 2004), where two other large ratite birds—emus and ostriches—were offered related pairs of divaricating and non-divaricating plants.  The birds stripped the non-divaricating plants in short order, but had trouble pulling the springy and wiry stems of the divaricates and manipulating the twigs and small leaves in their beaks. 

Another very successful research strategy is coproecology, the gleaning of evidence from fossil droppings, coprolites.  The most recent paper (Wood et al. 2012) by the moa coproecologists has received a lot of press attention because it showed for the first time that moa fed on flowers, as well as on fruits, leaves, and twigs.

The scientists found a pile of poo just inside the entrance of a cave in the Garibaldi Range, South Island mountains.  Dried in sunshine and breezes, but protected from rain, these droppings had lain undisturbed for hundreds to thousands of years.  Taking great pains to avoid contamination, the scientists sampled 35 of the coprolites, collecting DNA to identify the species of moa as well as plant species eaten, macrofossils (seeds, leaves, etc.), microfossils (pollen grains), and measuring organic content of the dung.  They also used radiocarbon dating to estimate when the droppings were dropped.

The dung was all from one moa species, the upland moa (Megalapteryx didinus), a stout bird that stood about 1m tall at the rump.  The oldest droppings were dated from about 6,300 years ago, and the youngest from a bit less than 700 years ago, so they span a good proportion of the time from the last ice retreat to the final extinction of moa.  Interestingly, several of the droppings had identical ages and plant contents and are thought to have been deposited in the same "defecation event". 

The three methods of sampling plant remains (the authors refer to these as proxies) in the droppings—pollen, macrofossils, and DNA— were complimentary.  Of these, pollen could be contamination from outside, especially when it comes from wind-pollinated trees that flower largely out of reach of moa, like Nothofagus (southern beech) or from plants that are highly poisonous, like wind-pollinated Coriaria.  The plot below, from the paper, relates pollen abundance in the coprolites to abundance in the environment; plants above the null distribution line are the ones likely to have been part of the moas' diet.

A range of montane and subalpine plants were found, some (southern beech, buttercups, sedges, grasses and Fuchsia) in all three proxies.  The results show moa were generalists, eating pretty much everything, and they ranged across all the available habitats, as the figure below demonstrates.  

But only a few of the eaten plants might be divaricating shrubs.  These include Myrsine and Coprosma, for which the DNA and pollen evidence can't distinguish if the plants eaten were divaricating or not, and Neomyrtus, which is divaricating.

A divaricating Myrsine, M. divaricata.

A non-divaricating Coprosma, C. foetidissima.

The finding of pollen from bird-pollinated flowers—Phormium and Fuchsia—is especially interesting.  These produce quite large amounts of sweet nectar and are pollinated by birds that are much smaller than moa, such as bellbirds and tūī.  Yet their pollen is not likely to have got into coprolites other than by passing through the gut of the moa.  The authors aren't suggesting moa were pollinating the flowers, rather that they were eating them.  The large fleshy flower stalks of Phormium are probably quite nutritious and the nectar from a single flower is a small but sweet treat for a human.  On the other hand, Fuchsia flowers are produced singly or in small clusters on the twigs or bare trunks of the trees, and it must be quite finicky work to pick these one at a time; they hardly look worth the effort for a large hungry bird.  If moa had a taste for sweet nectar such that they were a threat to flowers, could their grazing have driven the evolution of tall scapes in Phormium and the tree habit in Fuchsia excorticata?  The controversy lives on.

Flowers of tree fuchsia, Fuchsia excorticata.

Flowers and young fruits of mountain flax, Phormium cookianum.

I was surprised to find in this paper evidence that moa ate so many small alpine herbs and small fruits too.  They might have been significant seed dispersers.  This, like the Fuchsia flowers, suggests they might have been capable of choosing tasty morsels.

A previous study by some of the same scientists (Wood et al. 2008) showed the presence of a small buttercup, Ceratocephala pungens, in moa coprolites from Otago.  Ceratocephala is tiny and seasonal.  The plants are ground-hugging rosettes at most a couple of centimetres across, and they grow in bare ground, yet their seeds were found in coprolites from two species of moa.  The genus is otherwise known only from Europe and W. Asia, so when this new species was described from New Zealand, I entertained the possibility that it might not be a native (Garnock-Jones 1984).  Yet here it is, in coprolites produced before humans arrived in New Zealand.

In the past, the deer-hunting lobby in New Zealand has argued that introduced mammals were good for the environment because they replace these extinct giant herbivorous birds.  This study suggests otherwise.  Two very palatable plants that were common in moa diet—Fuchsia and wineberry—are no longer found on the Garibaldi Range, and many others are now confined to inaccessible cliffs and edges of sink-holes.

References.

Bond WJ, Lee WG, Craine JM (2004). Plant structural defences against browsing birds: a legacy of New Zealand's extinct moas. Oikos 104: 500–508.

Garnock-Jones PJ (1984). Ceratocephalus pungens (Ranunculaceae): a new species from New Zealand.  New Zealand Journal of Botany 22: 135–137 (Note the different spelling in this paper; the original spelling Ceratocephala is now preferred)

Greenwood RM, Atkinson IAE (1977). Evolution of divaricating plants in New Zealand in relation to moa browsing. Proceedings of the New Zealand Ecological Society 24: 21–33.

Wood JR, Rawlence NJ, Rogers GM, Austin JJ, Worthy TH, Cooper A (2008). Coprolite deposits reveal the diet and ecology of the extinct New Zealand megaherbivore moa (Aves, Dinornithiformes).  Quaternary Science Reviews 27: 2593–2602.

Wood JR, Wilmshurst JM, Wagstaff SJ, Worthy TH, Rawlence NJ, & Cooper A (2012). High-Resolution Coproecology: Using Coprolites to Reconstruct the Habits and Habitats of New Zealand's Extinct Upland Moa (Megalapteryx didinus). PloS one, 7 (6) PMID: 22768206

Wednesday wildflower: ivy

The name ivy conjures up evocative images of established gentry in the northern hemisphere: old buildings covered in ivy, the Ivy-League colleges in the US, and the holly and the ivy at Christmas.  In New Zealand, the reality is not so pretty.  Ivy is an aggressive and unwelcome weed, partly because many people still plant it, or at least tolerate it until it's too late.

Ivy, Hedera helix.  A, juvenile leaves; B, adult leaves; C, an umbel at flowering; D, an immature fruit; E, flower stalk to show the stellate hairs; F, flower, side view; G, young shoot to show the adventitious roots that the plant uses for attachment; H, flower from above.

The familiar lobed ivy leaf is the juvenile form (A above).  When the plant climbs into the sunlight and flowers, its leaves are generally simple (B above).

Ivy flowers and mature leaves, Kelburn, Wellington.

Ivy flowers are in globular clusters—umbels—where all the stalks originate from a single point.  This kind of inflorescence is common in the ivy family Araliaceae, and its related family Apiaceae.  It's also found in some unrelated plants, like onions and garlic (Alliaceae) and Agapanthus (Agapanthaceae).

The flowers have an unpleasant smell, and are visited by flies, bees, and wasps, and also some moths and butterflies.  Of these, Jacobs et al. (2009) concluded that wasps would likely be the most effective pollinators in England.

Ivy is an effective treatment for graffiti on this old wall in Kelburn, Wellingtom.

Ivy fruits are dispersed by birds, and they germinate freely.  The plants spread across the ground or climb up trees and buildings, attaching the stems by clusters of roots (G above).  These can weaken mortar on stonework and brickwork.  Fortunately, unwanted ivy on a tree or building is quite easy to deal with: cutting the stems at ground level will quickly kill them, but getting rid of the plant altogether isn't so easy.

References.

Jacobs, J.H.; Clark, S.J.; Denholm, I.; Goulson, D.; Stoate, C.; Osborne, J.L. 2009. Pollinator effectiveness and fruit set in common ivy, Hedera helix (Araliaceae). Arthropod-Plant Interactions DOI 10.1007/s11829-009-9080-9

Wednesday wildflower: red escallonia

Only about 10% of New Zealand's dicotyledon weeds come from Central and South America, and of those that do, many are cultivation escapes.  Red escallonia, Escallonia rubra, is in that category.  Plants from the Americas with red hanging flowers are often hummingbird pollinated (including E. rubra: Aizen & Rovere 2010).

Red escallonia, Escallonia rubra.  The branch at left is shown from the underside.

Red escallonia is often grown as a hardy hedge plant, especially in coastal sites.  I've never seen it being a nuisance; in my experience it just establishes sporadically nearby to cultivation sites, but some serious weeds have started out that way.

References

Aizen M.A.; Rovere, A.E. 2010. Reproductive interactions mediated by flowering overlap in a temperate hummingbird–plant assemblage.  Oikos 119: 696–706.  doi: 10.1111/j.1600–0706.2009.17762.x

Webb, C.J., Sykes, W.R.; Garnock-Jones, P.J. 1988.  Flora of New Zealand Vol. 4.  DSIR, Christchurch.