A great leap forward

If research proves that New Zealand’s Maud Island frogs can coexist with mice, their future will be a lot brighter, say those who are trying to save the rare species from extinction.

A

New Zealand’s native frogs are among the most primitive on the planet--virtually unchanged since the late Jurassic period, 140--160 million years ago. Back then, New Zealand was part of the seabed and all the continents as we know them today were joined together as one land mass. However, New Zealand came to the surface just in time to provide a lifeboat for the prehistoric frogs to avoid the fate of the relatives they left behind. In other words, New Zealand’s native frogs did not disappear due to environmental conditions they could not survive. New Zealand’s primal forest floor was once crawling with them and tens of thousands of their bones, from at least seven different species, have been found all over the country.

B

Today, in the moonless dark of a frost night, Kerri Lukis, a postgraduate researcher from Victoria University, shines her torch into the undergrowth and quickly reaches towards a mouldy brown leaf. When she opens her hand, I see that this ‘leaf’--perhaps 40 millimetres long--has tiny, almost bird-like feet, a pair of onyx-black eyes and appears to have been sprinkled with glitter. These are not the kind of frogs that most New Zealanders have seen in their gardens. The glossy lime-green frogs that can be heard croaking to one another from farm ponds and rivers are in fact Australian imports; New Zealand native frogs are a very different creature. To begin with, people will certainly not hear one. They are silent, and consequently, in the evolutionary process, they have lost their eardrums as well, therefore making it easier for researchers like Lukis to trap them. Another behaviour that is unusual for frogs is that the Maud Island species avoid water, so their tiny feet have no webs between their toes, which would normally make swimming and movement in the water more effective.

C

Since a tadpole cannot move or survive on dry land, this stage is absent in Maud Island frogs and they go straight from gelatinous eggs (incubated by the males) to ‘froglets’, which spend their first few weeks of life as passengers on the back of a male. Before the first humans arrived, the frogs’ enemies were predators that hunted by sight--native birds such as weka, morepork and perhaps pukeko--so they developed a simple but effective defence: they kept very still. Unfortunately, freezing proved a pitifully inadequate defence against the keen-nosed pests that humans brought here. Rats, mice, and other four-legged enemies such as stoats and weasels all but wiped out the frogs.

D

Maud Island frogs or pakeha, one of just four surviving species of native New Zealand frog, once lived throughout New Zealand, but for the past 150 years have been confined to predator-free Maud Island, 900 metres from the rocky coast of the Marlborough Sounds. In 1997, however, the Department of Conservation moved 300 to Motuara Island, then another 100 to Long Island in 2005. Early this year the frogs were finally returned to the mainland, when 30 were brought back to the Karori Wildlife Sanctuary, just a short ride from the central business district in the capital city of Wellington.

E

The sanctuary is protected by a high-tech fence designed to keep rare native species in and hordes of introduced predators out--and mostly it does. But nobody counted on the dexterity--or determination--of baby mice, which, it turns out, can squeeze through a six-millimetre gap. Kerri Lukis is turning that setback into a golden opportunity: ‘It’s given us a chance to look at how mice impact on native frogs. There’s very little known about their effects on New Zealand wildlife,’ she says, but Karori Sanctuary--one of just a few protected places in the country where mice are the only introduced predators--provides the perfect study area.

F

A goal of frog conservation is to establish new populations as insurance against catastrophe: predators finally managing the swim to Maud Island, or fire raging through their forest stronghold. If Lukis can prove that the frogs can cope with mice, it would make more islands available to wildlife managers looking for extra homes for them. Lukis aims to answer some long-pondered questions: Do mice impact frogs directly through predation? If so, do they attack the adults, the juveniles or the eggs? Are males more vulnerable because they sit on the eggs? And if the males are unable to search freely for food, does their condition become weakened so that they won’t breed?

G

Back in the forest, Lukis weighs and measures the tiny frog, notes with satisfaction that it might be carrying eggs, then takes a photo of the animal’s flank and jaw. Her shot reveals patterns and colouration unique to each frog, so that she can identify them without resorting to invasive alternatives like toe-clipping. Then it’s gently returned to its special mouse-proof enclosure. There are enough tiny insects crawling about in the leaf litter to sustain 30 captive frogs, but sanctuary staff supplement the frogs’ diet with live moths. In early October, another 30 frogs were brought here from Maud Island and placed in a separate enclosure where they were tested for the lethal chytrid fungus, first found in New Zealand in two introduced Australian species, the green frog and the bell frog, in 1999. Once the scientists are sure they are free from disease and are not a danger to other frogs, the Maud Island frogs will be introduced to those already resident at Karori, then subdivided into two groups with roughly equal gender ratios.Tg:@originalexams. One group will go on living an isolated life in the enclosure; the other, left to see how they survive the intrusion of the sanctuary’s mice. This will hopefully give Lukis the answers she needs.

Why Good Food Tastes Good

*A review of Taste What You’re Missing: the passionate eater’s guide to why good food tastes good

As a professional food developer, Barbara Stuckey has to understand the how and why of taste in order to create new palate-pleasing food products. Her book, Taste What You’re Missing, is the latest release in a recent spate of books on the multisensory perception of flavor. This new volume, though, is certainly targeted at a somewhat different audience from the others. It is part memoir, detailing the author’s many years working in a major North American company focused on developing novel food and beverage products, and part self-help book, offering advice on how we could all improve our ability to taste.

The author lays out her position at the start of the book when she states that she longed to read a straightforward book written for a lay person that could teach how to taste food without first having to teach the science. Consistent with this objective, complex terms that might prove difficult for a lay audience to understand, such as orthonasal and retronasal olfaction, are cleverly simplified as ‘nose-smelling’ and ‘mouth-smelling’, respectively. Stuckey also strenuously objects to the label ‘supertaster’. This is the term used to describe those individuals (approximately one quarter to one third of the population) who exhibit an increased sensitivity to certain tastes (especially bitter tastes) and textures of food.

The thorough research Stuckey conducted for this book also deserves commendation. The text includes numerous quotes from the interviews that she conducted with many of the best-known international figures from the world of flavor research. But Stuckey also does a great job of extending beyond what most academics are normally willing to say in print, but which may well turn out, ultimately, to be true. For example, she puts forward the provocative suggestion that there may be as many as 25 different basic tastes. While most researchers who are happy with the notion of a basic taste would agree with the inclusion of sweet, sour, salty, bitter, and nowadays probably also umami* as basic tastes, it is interesting to realize that there are many other substances for which receptor sensitivity on the tongue has now been demonstrated.

Stuckey includes a number of case studies in her book, including some fascinating material on the preparation, and consumption, of food and drink by those who have lost one of their senses, such as vision or hearing. Also, when she realized that there was a lack of relevant research regarding the question whether those who are deaf suffer from reduced flavor perception, she collected relevant data herself.

*umami: a taste sensation that is meaty or savoury

Stuckey’s book is strongest in the numerous industry examples she provides from her work with a large food product development company in North America. Many of the cases she describes seem to hinge on trying to find the right balance of the basic tastes, and the right ‘mouth-feel’ for a particular food or beverage product. Indeed, one of the major themes that came out throughout the book was the importance of food consistency, and the temporal dynamics of changes in mouth-feel as we eat and drink. However, it is certainly an area of food science that is tricky to work on in an academic research setting. It is just much easier to change the color or aroma of a foodstuff, for example. However, on numerous occasions we see just how important the tactile attributes of various foods and beverages are to their success amongst consumers.

In Taste What You’re Missing, one certainly gets a real sense of the kinds of problems that she and her colleagues are faced with on a daily basis in a commercial setting. Many of the cases that are described in the book involve the use of one taste to mask, or unmask, another; for example, adding salt to a grapefruit or tonic water can, paradoxically, make it taste sweeter. However, where I thought that Stuckey was on weaker ground was when it came to the neuroscience of tasting. For example, in the brief section on ‘The expert eater brain’ she confidently asserts that, ‘Not only do tasting experts use more areas of the brain, they can enjoy the process of tasting better than novices.’ While the second part of the claim may be true, the former statement fails to do justice to the complexity of much of the widely acknowledged published data available.

There were a number of other claims in the book that, intuitively at least, seem hard to swallow. For example, Stuckey contends that the human ear is so sensitive that people can tell the difference between hot and cold coffee simply by listening to the two being poured. Although not performed under strict laboratory conditions, Stuckey tested this on more than 500 people and 99% of them found it easy to distinguish between hot and cold water poured from the same tea kettle, from the same height, into the same teacup.

What is striking about the quotes on the cover of Stuckey’s book praising the contents is that they all come from people working in the food industry; that is, from chefs and those placed in cookery schools.Tg:@originalexams. Ultimately, I suspect this volume will have a much more enthusiastic reception there, and, as per the subtitle to her book, amongst ‘passionate eaters’ everywhere, than necessarily among those academics who conduct research on flavor perception and may be more critical.