“To expect the unexpected shows a thoroughly modern intellect”

I spoke before of how to use mathematics to convey an idea in biology. Here, I’ll take a different tack and discuss a paper in which the author makes his argument with naked English. The author in question is Nicholas Humphrey who in his famous paper ‘The social function of the intellect’ draws a wonderful metaphor of Mother Nature as an economist,

“It is not her habit to tolerate needless extravagance in the animals on her production lines: superfluous capacity is trimmed back, new capacity added only as and when it is needed”.

His metaphor serves as an introduction to the puzzle of the seemingly unnecessarily inflated intellects of some animals, notably humans.

Humphrey questions if such a highly developed intellect is really necessary for invention. The ability to produce tools is generally not a result of deductive reasoning or creative thought but rather follows from aping other individuals or pure trial and error learning. The intellect must have some other function in his estimation and in the end, he proposes that it is as a social glue. The complex interactions that arise out of the social milieu require some serious intellectual horsepower,

“[S]ocial primates are required by the very nature of the system they create and maintain to be calculating beings; they must be able to calculate the consequences of their own behaviour, to calculate the likely behaviour of others, to calculate the balance of advantage and loss – and all this in a context where the evidence on which their calculations are based is ephemeral, ambiguous and liable to change, not least as a consequence of their own actions.”
 

Calculating the consequences of your own behaviour is one thing but understanding that others around you have motivations of their own is a huge leap in understanding. All of this is done without ever having direct access to the subjective thoughts, motives, and desires of another person. Understanding the reasons for understanding is even more impressive and Humphrey’s paper has rightly influenced the theories of scientists since its publication. Most recently a study in the school that mechanistically linked sociality and selection for intelligence.

Author

Adam Kane: kanead[at]tcd.ie

Photo credit

Wikimedia commons

Is island life easier?

Lemon-bellied White-eye (Zosterops chloris)

For over 10 years we have been making regular visits to islands in the Sulawesi region of Indonesia. We trap birds on these islands, collecting morphometric data. Each bird we trap is measured, marked with a plastic ring and released. As our dataset grows we gain more insight into the lives of the birds on these islands.

In 2007 and 2010 we visited the island of Kaledupa in the Wakatobi archipelago. In 2010 we made a point of revisiting all of the sites we had trapped at in 2007. This gave us an opportunity to look for the birds we had originally caught in 2007.

The Wakatobi islands

In 2010 we caught four of the birds we had marked in 2007. These birds were all lemon-bellied white-eyes (Zosterops chloris). Using an equation for survival (the Lincoln–Petersen method), we calculated the average lifespan of the lemon-bellied white-eyes on Kaledupa. Our birds had a similar lifespan to white-eyes from an Australian island, but lived much longer than white-eyes from the African mainland.

While the number of studies is still small, there is a suggestion that island populations of white-eyes have longer lifespans. Smaller islands generally have lower biodiversity. This can lead to reduced competition and predation, so “prey” species are likely to experience reduced environmental stress. Recent work on the fossils of island cattle species supports this idea (Jordana et al. 2012).

References

1. Kelly, DJ and Marples NM (2012) Annual survival rate and mean life-span of Lemon-bellied White-eyes Zosterops chloris flavissimus on Kaledupa island, Wakatobi, south-east Sulawesi, Indonesia. Forktail 28, 148-149.

2. Jordana, X Marin-Moratalla, N DeMiguel, D Kaiser, TM, Kohler, M (2012). Evidence of correlated evolution of hypsodonty and exceptional longevity in endemic insular mammals. Proceedings of the Royal Society B: Biological Sciences; DOI: 10.1098/rspb.2012.0689

Authors

David Kelly djkelly[at]tcd.ie

Nicola Marples nmarples[at]tcd.ie

Photo Credit

David Kelly

The plight of the bumble bee; diapause, immunity and parasitic attack

Sphaerularia bombi with an everted uterus.

Bee populations are in severe decline, an alarming and worrying trend when you consider their vital importance as commercial and ecological pollinators. Research and media attention often focuses on afflictions of honeybees such as the Varroa mite and colony collapse disorder. However, parasites are also major contributors to the plight of the bumble bee.

Bumble bee queens spend 6-9 months in diapause, a hibernation-like state which allows them to survive harsh winter weather. My research demonstrated that queens have reduced immune function during this time, leaving them vulnerable to infections and parasitic attack.

Sphaerularia bombi is a common yet poorly studied nematode which is found primarily in the Northern hemisphere, infecting up to 50% of queen bumble bees in some areas. Adult female Sphaerularia present in the soil infect diapausing queens. My project showed that, with their immunological guards down, the queens cannot mount an effective response to invading parasites.

Sphaerularia exerts significant influence on its host after the queens emerge from diapause. The nematodes evert their uterus to a structure 300 times the volume of the rest of their body (see picture above). This enormous uterus releases numerous eggs into the host and also extracts nutrients from the bees.

Sphaerularia castrate the queens so they don’t form new colonies. The parasite also changes queens’ behaviour so they go to sites suitable for diapause even though it’s the wrong time of year. Having released larval stage nematodes into the soil, parasitised queens die while the nematodes are then poised to infect new queens entering diapause.

Sphaerularia clearly has a significant impact on a host species with high ecological and commercial value yet it remains very poorly studied.  In collaboration with research currently being performed by PhD student Joe Colgan (Trinity College Dublin: Supervisor Dr. Mark Brown) and Dr. Jim Carolan (National University of Ireland, Maynooth), my project filled some of the gaps in our understanding of the molecular interactions between host and parasite. One particularly interesting finding was that S.bombi infection seems to change the protein expression in bees, indicating a complex interaction between host and parasite at the molecular level in parallel to the dramatic physiological and behavioural changes in the bees.

Continuation of this research on a fascinating host-parasite system will bring us closer to understanding and hopefully eventually combatting the plight of the bumble bee.

References

1. Society of Biology News Page http://www.societyofbiology.org/newsandevents/news/view/469

Author

Sive Finlay: sfinlay[at]tcd.ie

Sive is a PhD student from Trinity College Dublin, who recently won Best Biology student at the 2012 SET awards for her undergraduate project detailed here

Photo credit

Mike Kelly

Thunder lizards + methane = climate change

Mathematics is the language of science and when it comes to biology this is no exception. It’s only when you start researching for yourself that you realise how useful a skill it is. Consider, for example, the mathematical approach that Graeme Ruxton and collaborators bring to their research in ecology and evolution. Ruxton has addressed questions ranging from the foraging radius of vultures to a hypothesis proposing that sauropod dinosaurs produced enough methane, a la modern cows, to affect the climate of the time. The latter paper does seem to ask an intractable question on first inspection given that the animals have been extinct for at least 65 million years. So how do the authors even begin to tackle their question?

Mathematically of course. To begin, they estimate the population density of sauropods during the Jurassic Period from fossil data. Then they take a medium sized sauropod like Apatosaurus louise, which weighed around 20,000kg, as a representative animal. Finally they apply a relationship which gives an indication of methane production per animal, while being careful to note the relatively shorter Mesozoic day:

Methane (litres per day) = 0.18 (body mass in kg) 0.97

Multiplying it all out and the bottom line is that these beasts could put out 520 million tonnes of methane per year into the atmosphere. Incredibly, this is comparable to modern day emissions when the effects of this are apparent to all.The upshot the authors draw is that sauropods were drivers of climate change during the Mesozoic Era. There are some uncertainties in the paper to be sure. For one, the metabolism of dinosaurs is still an unknown and this has implications for their output. But the argument seems to be a sound one and this was all achieved with some fairly basic maths.

References

1. Ruxton, GD, Houston, DC (2002). Modelling the energy budget of a colonial bird of prey, the Ruppell’s griffon vulture, and consequences for its breeding ecology. African Journal of Ecology. 40 (3) p. 260–266.

2. Wilkinson DM, Nisbet EG, Ruxton GD (2012) Could methane produced by sauropod dinosaurs have helped drive Mesozoic climate warmth? Current Biology 22: R292-R293. DOI: http://www.cell.com/current-biology/retrieve/pii/S0960982212003296

Author

Adam Kane: kanead[at]tcd.ie

Photo credit

Todd Marshall

 

Hot heads lead to hot flashes: the evolution of menopause

A new study has been published online in Ecology Letters by Mirkka Lahdenperä and colleagues, which suggests that competition between grandmothers and their daughters-in-law may explain the evolution of menopause. The study used a 200-year dataset of births, deaths and residency patterns in pre-industrial Finland to show that competition between unrelated females of different generations was a key component of selection for menopause.

Humans are among only four species known to lose their ability to reproduce long before they die; the others being killer whales, pilot whales and one aphid species. This phenomenon of menopause poses somewhat of an evolutionary conundrum: how could the loss of the ability to reproduce increase an individual’s fitness?

One possible answer was suggested by Cant & Johnstone, based on differences in how related a mother and daughter-in-law are to each other’s offspring. Historically, females of reproductive age usually leave their family to co-habit with their spouse’s family in most human societies, while males stay near their parents. This means that elder females are typically unrelated to next generation of reproductive females in their locale. Thus, it is expected that young females should invest in competition with their mother-in-law, while the elder mothers-in-law may be selected to cease investing in reproduction and instead invest in helping to raise their related grandchildren.

The new study by Lahdenperä et al. showed that when a mother and daughter-in-law reproduce at the same time offspring survivorship is reduced by up to 66%, while simultaneous reproduction by a mother and daughter had no effect. These patterns suggest that a daughter and mother-in-law compete strongly for resources for their children, as predicted by Cant & Johnstone.

The authors also used their data to parameterise a kin selection model to show that selection should favour menopause around the age of 50 in order to reduce this conflict. This study provides an excellent example of how theory and data can be combined to tackle evolutionary problems, and provides insight into one of the great peculiarities of the human species.

References

1. Lahdenperä M, Gillespie DOS, Lummaa V, Russell AF (2012) Severe intergenerational reproductive conflict and the evolution of menopause. Ecology Letters. (http://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2012.01851.x/abstract)

2. Uematsu K, Kutsukake M, Fukatsu T, Shimada M, Shibao H (2010) Altruistic colony defense by menopausal female insects. Current Biology 20: 1182-1186. (http://www.sciencedirect.com/science/article/pii/S0960982210006391)

3. Cant MA, Johnstone RA (2008) Reproductive conflict and the separation of reproductive generations in humans. Proceedings of the National Academy of Sciences 105: 5332-5336. (http://www.pnas.org/content/105/14/5332)

4. http://en.wikipedia.org/wiki/Kin_selection

Author

Luke McNally: mcnalll[at]tcd.ie

Photo credit

Wikimedia Commons