Yet another estimate of the number of species on earth

This week in PLoS Biology, paper was published that estimates the number of species on earth being around the 8 million mark (give or take 2 million). This study takes a rarefaction-type approach, seeing how the rate of discovery of higher taxa is decreasing, and extrapolating from that to the species level, resulting in the figure of 8.7 million with an error range of 1.3 million.

This study is nothing new—there's been a number of estimates published over the past two decades that attempt to give a number to the total diversity of life on earth. While this one does appear to be a bit more robust, all these studies are based on various assumptions, and have given some very different figures. There seems to be some sort of convergence on the 10 million mark, but at the end of the day, we just don't know.

I guess the value of these papers are that they make public how far we have to go before we know the most basic thing about the other organisms that share the world with us. I still surprise people when I tell them my tales of discovering new species, the general belief being that we know essentially all there is to know about biology. However, unless there are some useful outcomes (e.g. increased funding or employment) from them, I view these papers with a certain cynicism. We know the task ahead of us is huge. It'd be great to be able to dive into it whole-heartedly and without needing to worry about the finances.

The paper did alert me to the World Taxonomist Database, a register of taxonomists from around the world and encompassing all taxa. The register gives contact details for each of the researchers in the database, as well as their taxonomic and geographic interests. It's a very handy resource.

Pressing plants

Weevils feed on plants, with many species being very picky about the plants they eat. These host interactions are very important for understanding the ecology of both the weevils and the plants. When collecting therefore, it is important that the plants from which weevils have been collected are identified and noted. Therefore, as a weevil guy, it is important that I have a fair understanding of plant identification.

A key aspect of the process is knowing the proper way to collect, preserve and label plant specimens. Searching the internet has revealed good guides on the University of Florida Herbarium webpage and a PDF produced by the Herb Society of America.

It's not too arduous—pressing plant material can be done by placing the material under a few big books. Much more important is knowing what to put on the label. Plant specimens tend to be mounted on large (A3) sheets of paper, giving a lot of space to write pertinent information. Therefore, major additional categories from that on insect labels include its frequency (is it rare, common, or something in between?), and details of the plant's height, growth habit and description of aspects of the plant that disappear when pressed (e.g. colour of flowers, smell and sap). There's also the space and ability to provide exact locality data and more detailed habitat information than is possible with insect labels.

A mystery... scale insects on European manuka

Manuka (Leptospermum scoparium) is native to New Zealand and southeast Australia. It is common throughout New Zealand and is well known for being the source of manuka honey which is sought after for its healing properties, and for being a good source of firewood (particularly for smoking fish). Its trait of having numerous white flowers has also ensured that it is fairly commonly grown as a garden plant, and so has been exported around the world for this purpose.

So when a scale insect that apparently is specific to the plant is found in Italy and Corsica in 2004 and 2006, one would imagine that it came from New Zealand or Australia right?

Acanthococcus mariannae was described yesterday in a Zootaxa paper by Giuseppina Pellizzari and Jean-François Germain. The 30 or so specimens that went into the description were all collected from manuka from Italy and France. Surprisingly though, despite the author's (reasonable) assumption that the insect was introduced to these countries on the plants, this species has not (yet?) been found in either New Zealand or Australia. Moreover, specialists familiar with scale insects in these countries had not noticed it before. While it is likely that further searching will reveal it on manuka in NZ or Australia. However there is the lingering question: if it's not, where did it come from and how has it started attacking manuka?

Scale insects aren't glamorous. They are little more than a bag of fluid that get sap pumped into them. But they are important in a properly functioning ecosystem; and when they get out of control the consequences can be severe. This can be illustrated by an example that also involves manuka: the incidence of manuka blight in New Zealand in the 1940s and 1960s.

Manuka naturally harbours large numbers of the scale insect Coelostomidia wairoensis which produces a lot of honeydew. This in turn provides a food source for the sooty mould Capnodium walteri which covers the branches of manuka forming thick, black deposits.

In the late 1930s manuka in Canterbury (South Island of New Zealand) started to grow sick and die. By the late 1940s it was reported that it was hard to find living manuka in the region. Farmers assisted in the spread by moving infected manuka around the country to control what they viewed as a weed. The culprits were found to be two species of Eriococcus scale insect that presumably had been introduced from Australia. The effect on the plant appears to be due to nutrient stress from having large numbers of scale insects sucking on it as opposed to being a disease transmitted by the insects.

In 1957 it was discovered that a fungus was killing E. orariensis, the species that damaged manuka most severely. Subsequently, the numbers of this scale insect declined dramatically with a corresponding increase in manuka numbers. Manuka has also seen a rise in popularity and is no longer viewed as being as significant a weed.

References:

Epenjijsen CW, Henderson RC, Carpenter A, Burge GK. 2000. The rise and fall of manuka blight scale: a review of the distribution of Eriococcus orariensis (Hemiptera: Eriococcidae) in New Zealand. New Zealand Entomologist 23: 67-70.

Pellizzari G, Germain J-F. 2010. A new species of Acanthococcus (Hemiptera, Coccoidea, Eriococcidae) on Leptospermum scoparium (Myrtaceae) from Italy and France. Zootaxa 2543: 51-63

Molecular identification of New Guinea mammal poo

The use of environmental DNA samples for identification and monitoring of animals has been increasingly widely used over the past five years or so. This essentially involves extracting DNA from non-tissue materials and analysing it in such a way as to discover the creatures that produced/lived in/ate/passed by the material. For example, pond water has been analysed to discover what frog species were present in the area and faecal matter has been analysed to figure out both what was eaten and who was the eater.

This last scenario has been played out on the Huon Peninsula in Papua New Guinea. Research has begun on the endangered Matschie's tree kangaroo (Dendrolagus matschiei) looking into its population structure and genetics. This research has applications to help direct the future conservation of the species by giving an indication as to how many individuals there are and how much they move around. However, the capture and collection of tissues from a rare, endangered animal that spends the majority of its time in montane rainforest canopies present both logistic and ethical concerns which are alleviated by the collection of DNA from their faeces. Finding poo is sometimes a lot easier than the beast itself!

Unfortunately, poo from one marsupial often looks the same as poo from another and so faeces were mistakenly collected from an additional two species the New Guinea pademelon (Thylogale browni) and the small dorcopsis (Dorcopsulus vanheurni). A recent paper published in Molecular Ecology Resources by Thomas McGreevy and coauthors give a method for determining which species of marsupial produced the poo of interest. The primer set they've developed amplifies a portion of DNA that is a different length in each species---making it easy to distinguish which came from what and making sure that time is not spent looking at the wrong ones.

References:
McGreevy TJ Jr, Dabek L, Husband TP. (2010). A multiplex PCR assay to distinguish among three sympatric marsupial taxa from Huon Peninsula, Papua New Guinea, using the mitochondrial control region. Molecular Ecology Resources. 10(2): 397-400.

Marshall Islands Biodiversity report

It would appear that the UN Development Program has looked at the biodiversity of Kiribati and the Marshall Islands. At least, they've got a report to that effect. After a lot of fluffing around when I stumbled across the appendices of the report, I finally managed to find the contents page with actual links:
http://www.undp.org/bpsp/nbsap_links/nbsap_Kiribati.htm

It's worth a look, particularly because it has the brilliant Marshallese phrase "Eruj in jebarbar" - Excited like a reef crab. Use that in your next conversation....

Another project of the UNDP has completed was the "South Pacific Biodiversity Conservation Programme" - its writeup is found here.

Belligerent newcomers and shrinking wings - Carabid Ecology on Maui

To make use of an allusion from literature, things are rotten in the Hawaiian Islands. Like many places, they are being overrun by Argentine ant (Linepithema humile) (Hymenoptera: Formicidae). Coupled with this, they also have a carabid beetle, Trechus obtusus that is running amok over the island of Maui. Stuck in the middle are a number of endemic carabids in the genus Mecyclothorax.

James Liebherr and Paul Krushelnycky have published a paper detailing the plight of the Mecyclothorax over the past seven years, and it makes for interesting reading. In a nutshell: Trechus obtusus was first found on the island of Maui in 1999 (sounds familiar…) and increased dramatically, such that a 4m2 collection of leaf litter in 2001 had 77 beetles in it. The numbers of Mecyclothorax since that time have had a statistically significant decline since then, while T. obtusus numbers remain approximately the same. The presence of ants is also an important predictor in whether or not Mecyclothorax is present in an area or not. The numbers of Mecyclothorax are significantly lower in ant-infested areas, while the abundance T. obtusus is not significantly affected by Argentine ants. It looks grim for Mecyclothorax, but the authors do not seem to express any pessimism about the future of the beetles.

Another interesting aspect about the system is how Trechus obtusus is losing its wings. T. obtusus has two forms - a fully winged (macropterous) form that can fly around, and a short winged (brachypterous) form whose wings reach halfway down the abdomen and is flightless. There has been a very rapid change in the proportion of wing forms in populations of T. obtusus on Maui. In one site, 0% of beetles collected in 2001 had short wings. Four years later, in 2005 15% of beetles collected were brachypterous. At another site the proportions have increased from 0% brachyptery to 18% in three years. This change has a number of possible consequences. It is hoped that the decrease in numbers of flighted individuals will help prevent T. obtusus from spreading to other Hawaiian Islands. However, this does not prevent it from invading through human transportation, which is the most likely way it got to Maui in the first place. Second, the dimorphism of T. obtusus will no doubt help it spread around Maui to a much greater extent, and form more stable populations, than the endemic Mecyclothorax which are exclusively brachypterous.


Wing dimorphism is considered to be determined by a single allele. Individuals with full wings are thought to be homozygous recessive, while shorter wings can be heterozygous or homozygous dominant. While the authors suggest that all of the first beetles to arrive were macropterous (i.e. homozygous recessive), this would seem to indicate that there would be no alleles for brachyptery in the population. The situation here probably suggests that wing size in carabids is slightly more complicated than classical Mendelian genetics, and that more than one allele influences the size of wings in Trechus obtusus.

The influence of Argentine ant on the populations of carabid beetles is also pretty scary. Argentine ant is one of the world's worst invasive ant species and it is established in Hawaii, New Zealand and Australia. It is not found elsewhere in the Pacific. It is one of the species on the Pacific Ant Prevention Plan and it is hoped that it doesn't get established. The carabids elsewhere in the Pacific are not well known, and their response to Argentine ant invasion would probably be similar to the situation in Hawaii.


The globalisation of biodiversity has had a huge impact on native ecosystems. It looks set to continue, despite advances in biosecurity policy and techniques. It looks gloomy, and to an extent it is. However, nature has survived this long, and will continue to get by, though in a slightly more impoverished state. Another aspect of invasions that I haven't looked up yet is the beneficial side, where new organisms enrich and add to the indigenous ecosystem. Does it happen? I don't know, and it's not something you hear about. Maybe an idea for someone?

Liebherr, JK; Krushelnycky PD. 2007.
Unfortunate encounters? Novel interactions of native Mecyclothorax, alien Trechus obtusus (Coleoptera: Carabidae), and Argentine ant (Linepithema humile, Hymenoptera: Formicidae) acress a Hawaiian landscape.
Journal of Insect Conservation 11:61-73