Trinity College Dublin, Ecology and Evolution
I recently returned from a short stint of fieldwork in Madagascar. The purpose of our trip was to run some behavioural tests of echolocation in tenrecs but things didn’t exactly go according to plan. Therefore we had plenty of time to explore and experience some of the wonders of the 8th continent.
Here’s a few of our wildlife highlights…
Author and Images: Sive Finlay, sfinlay[at]tcd.ie, @SiveFinlay
In a previous blog post I wrote about my work on “toxic nectar.” This paradoxical phenomenon occurs when potentially deterrent or toxic plant secondary compounds, usually associated with defense against herbivores, are found in floral nectar rewards. Throughout my PhD I’ve spent countless hours in the lab performing experiments on toxic nectar, discussed this work at Nerd Club, and presented it at conferences. After what seems like an awfully long time, our first article on nectar toxins has been published in the Journal of Experimental Biology. Here I want to describe what I think are the most exciting findings of the study, and also talk about how this work came to be part of my PhD.
When I first started my PhD I had what seemed like a never-ending list of questions about nectar toxins: do they impact plant fitness? What about pollinator survival? Are there sublethal costs to pollinators that ingest nectar toxins? But before we could tackle these bigger-picture concepts, we kept on coming back to a very simple question: are bees deterred by naturally occurring concentrations of secondary compounds in floral nectar?
We know that many plant secondary compounds, such as alkaloids, phenolics, and terpenes, play a role in deterring herbivores form consuming plant tissues, and that’s why toxic nectar is such a paradox. Why would plants have deterrent compounds in a tissue that is meant to act as a reward for pollinating flower-visitors? Nectar secondary compounds, however, tend to occur at much lower concentrations than those found in leaf or floral tissues. Previous work found that whether or not bees will forage on artificial nectar containing secondary compounds depends on ecological context, i.e. the availability of other food sources. However most work on this subject focuses on only one compound (gelsemine) and tests concentrations that are well above those found in floral nectar.
One might hypothesize that secondary compounds at nectar-relevant concentrations should not be deterrent to pollinators. If nectar toxins do deter legitimate pollinators, plant pollination and hence reproductive success could suffer, leading to selection for lower concentrations of nectar compounds. In addition, the direct impacts of nectar toxins on pollinators are still understudied; deterrence behavior might indicate a cost in terms of health or fitness for the pollinators. So we were convinced it was well worth determining deterrence thresholds for several of the most common/popular nectar toxins, and comparing these thresholds to nectar-relevant concentrations, but how did we do it?
The experimental design was very simple (my favorite kind!); we used an economically and ecologically important pollinator, Bombus terrestris, in a series of controlled, paired laboratory bioassays. In each assay, we offered bees two solutions of identical sugar content, one containing a secondary compound of interest and one without it. We repeated this 24-hour assay at a range of concentrations that included the nectar relevant dosage for each compound we tested. The deterrence threshold was determined when bumblebees significantly preferred the sucrose solution over the sucrose solution containing the compound. We also measured the total food consumed and bumblebee survival. I spent a lot of time in the laboratory and the bee room, weighing feeding tubes and counting dead bees; I’m not going to lie, I may have succumbed to talking to my bees now and again. It gets lonely in the lab! It was all worth it in the end though, because what we found was pretty interesting.
Our experiments showed that bumblebees are actually rather bad at detecting nectar toxins. The most deterrent compound was the alkaloid quinine, which was avoided at concentrations as low as 0.01 mM. All the other compounds we tested (caffeine, nicotine, amygdalin, and grayanotoxin) had deterrence thresholds 7-60 times greater than the concentration range naturally found in nectar. Previous work on the honeybee found that it too has poor acuity for the detection of nectar toxins, especially compared to insects in the orders Diptera and Lepidtopera. So why is it that social generalist bee species are relatively insensitive to the plant secondary compounds in their food? One hypothesis we highlighted in the discussion is that the relationship between bees and plants is largely mutualistic, as opposed to the antagonist interactions between plants and herbivores. There may not be strong enough selection pressure on bees to develop more sensitive gustatory receptors, especially because in eusocial bee species, individual bees are the consumers, but selection pressures act on the colony as the reproductive unit.
For decades, researchers of plant-animal interactions have been asking how and why toxic nectar evolved and is maintained in plant populations. Our work helps us to better understand the functional significance of toxic nectar. If legitimate pollinators fail to be deterred by nectar compounds at low concentrations, the plant is less likely to suffer from reduced pollination. This trait therefore may be maintained in plant populations, especially if it confers some sort of fitness advantage to the plant. What kind of fitness advantage could these compounds provide you ask? There are a plethora of possibilities, including antimicrobial resistance and selection against more sensitive nectar robbers or thieves. Possibly the presence of the compounds in nectar is simply a consequence of defense of other plant tissues. The results from our study, however, suggest that these other factors affecting nectar secretion and production are more likely to select for the production of toxins in nectar of bee pollinated plants, rather than pollinator preference.
Check the paper for more details and to read the whole story!
Author: Erin Jo Tiedeken, tiedekee[at]tcd.ie, @EJTiedeken
Images: Wikicommons and E.J. Tiedeken
There are many threats to our environmental security: climate change, habitat loss and degradation, pollution. All are damaging the environment and impacting on our long-term survival. One threat that seems to have been often overlooked by the public, however, is the effect of invasive species.
Invasive species are non-native species that adversely affect the invaded region. Not every non-native species becomes invasive: some fail to establish while others may establish but at sufficiently low population densities to have minimal impact on their new home. But a few species will find themselves so at home in their new land that their populations explode and, due to a lack of any predators adapted to deal with them, their populations remain unchecked.
There are many famous examples of invasive species: the Burmese python in Florida, rabbits and cane toads in Australia, the grey squirrel in the UK and Ireland. Attempts to control all these species have been made over the years, though none have successfully managed to completely eradicate them.
While much of the media is focused on local invasive species, the greatest impacts are often found not in large inhabited countries but on small, isolated islands. You may be wondering how invasive species can reach small, isolated islands but humankind’s reach has been vast and in the days of shipwrecks and long voyages sailors often found themselves on shores never-before touched by man. When they came ashore so too did stowaways in the form of rats. Some species were even purposefully introduced in order to provide food for victims of shipwrecks. In these ways species including rats, cats, rabbits, pigs, sheep and reindeer have found their way to islands all around the world, including those in the sub-Antarctic.
The impacts of these species have been great and varied. Many islands are home to ground-nesting seabirds and their eggs and chicks are extremely vulnerable to predation by rats and cats while their nesting sites can be damaged by rabbits and larger mammals. Grazing also impacts on the islands, leading to habitat loss and soil erosion. As seabird numbers have fallen due to interactions with fishing gear, harvesting for food and though the effects of invasive species on their breeding success, attempts have been made to rid islands of these now unwelcome interlopers.
The effects have been mixed. Some attempts have been hugely successful. The most successful is arguably that of Campbell Island, a sub-Antarctic island south of New Zealand. It had a succession of eradications starting in the 1980s that culminated in the early 2000s with the eradication of rats across the entirety of its 113 square kilometres. This was at the time the largest area ever cleared of rats. I remember being told by a lecturer, though this may be apocryphal, that there was a conference going on at the time where people were explaining why it was impossible to eradicate rats from large islands at the very same time that this eradication programme was coming to a successful close.
Some attempts have not been so successful and they highlight the importance of good management and understanding of food web interactions. I believe, or at least I certainly hope, that the following example is the most extreme case to date. Without further ado, I present to you the case of Macquarie Island.
Macquarie Island is a sub-Antarctic island between Australia and New Zealand. It is home to elephant seals, three species of fur seal and thirteen species of seabirds including penguins, petrels and albatrosses. Rats, mice and cats were introduced by sealers in the early 1800s and rabbits were introduced in the 1870s. Both the cats and the rabbits have had devastating impacts on the seabird colonies. Rabbits caused erosion through their burrowing and cropping of the vegetation while the rats ate young chicks. The combination of predation and habitat destruction are thought to be responsible for extinction of the two endemic species on the island, the Macquarie Island parakeet and the Macquarie Island rail.
By the 1980s the habitat destruction was becoming significant and a decision was made to control the rabbits through the introduction of myxomatosis which decimated the rabbit population. This had an unexpected impact on the cats: it turned out the cats had been predating on the rabbits and used them as their main food source so when the rabbits disappeared the cats turned their attention to seabird chicks. Once this was realised the need to control the cat population was quickly recognised.
A cat eradication programme began in 1985 and by 1999 the last cat on the island was killed. You would be forgiven for thinking that this is the end of the story: rabbits controlled, cats switched their diet, the mistake is recognised, cats are controlled, and now the seabirds can live happily ever after. . . If only it were that simple.
The rabbit population began to re-establish itself. It increased rapidly and by 2006 was back to pre-control levels. The rabbits were devastating the island In 2006 a large landslip, caused by erosion by rabbits, partly destroyed a penguin colony.
It was clear that something had to be done and in 2007 the Australian Government announced their intention to eradicate Macquarie of invasive rabbits and rodents (rats and mice) at a cost of A$25 million. The need for this eradication was highlighted in a 2009 paper by Dana Bergstrom and colleagues from the Australian Antarctic Division. They showed the full effects of the cat eradication programme on the rabbit population and the terrible consequences to the vegetation of the island. Their report highlighted the need for integrated eradication programmes that examine the whole ecosystem and predict and plan for unintended consequences of the removal of invasive species.
The story could have ended there, a costly mistake both in ecological and economic terms. It is where the story ended for me until I started researching this piece. It turns out that there is a surprisingly happy ending as earlier this month the Australian and Tasmanian governments announced that Macquarie was officially pest free following the success of their eradication programme. This success means that Macquarie now beats Campbell Island as the largest island cleared of pests, an achievement that is of global significance. It’s an incredible feat, one I feared would be impossible. Though it will still take time for Macquarie to fully recover from the effects of more than 200 years of alien inhabitants, it now has that time. Finally Macquarie is home only to the birds and seals; a sub-Antarctic paradise has been restored.
Author: Sarah Hearne, hearnes[at]tcd.ie, @SarahVHearne
Images: Wikicommons
In centuries past, if you were to go into the hills of New Zealand on a summer’s night you may have heard a strange noise; a honking boom that resonated all around you. After 20 or 30 cycles of this boom you’d hear a high-pitched rasping ‘ching’ sound. This boom and rasp would come from all around you and would be heard all night, night after night for at least two months. This is the sound of kakapo males trying to attract a mate.
Kakapos, (Strigops habroptilus) are nocturnal, flightless parrots. They are found exclusively in New Zealand and while they were once common across all three main islands of New Zealand, they are now restricted a few small offshore islands. They are unique birds in a number of ways. They are the only flightless parrot and, probably as a result of this, are also the world’s heaviest parrot. They are also the only parrot to chose mates using the lek mating system.
Lek mating involves males displaying for the females and the female picking “the best” male. It’s a winner-take-all scenario as different females usually chose the same male. If you’re the chosen male then it’s a successful breeding season but if you’re not then you go home empty-handed. Males in lek systems typically take no part in the rearing of offspring and kakapo are no different.
Kakapo use an ‘exploded’ lek system, where males are generally out of sight of each other (the more traditional system has all males within eyeshot). During the summer months they go to hilltops and ridges and create a bowl in the earth in which they sit. These bowls are thought to help amplify their booms. They may have several bowls which are linked by tracks created by removing vegetation [1]. They then inflate a sac in their thorax and create the booms and chings. The booms are to attract a female and the ‘chings’ help her to find him as the booms can travel up to 5km while the ‘chings’ are more locatable due to their high frequency. Once a female has been attracted to a particular male and enters his view he performs a dance for her after which they mate
The female lays between one and four eggs in a makeshift burrow, either in cavities such as in those in trees or under vegetation. The eggs hatch within a month and she then has to look after the chicks for up to six months, though they leave the nest after about three months.
Kakapo only reach maturity after the age of about 5 and females only start breeding around the age of 10 [2]. Females reproduce every few years after a masting event. Masts are where plants, in this case the rimu tree, produce large amounts of fruit simultaneously, overwhelming the local wildlife with food. Even with the increased food not every female is able to get fit enough to exert the energetic costs associated with reproduction and so not all females will breed in a given year [3].
As I explained in a previous blogpost, New Zealand avifauna has been threatened by the introduction of predators. Given their slow reproductive rate and terrestrial lifestyle they are particularly vulnerable to predation and have been pushed to the edge of extinction. By the 1970s less than 20 were known to exist and all were males. It seemed that the kakapo were doomed. But in 1977 a female was found on Stewart Island and from that one female a miracle has occurred and the population currently stands at 130 birds.
This success has been hard won. Part of the problem is that so little is known about the birds that trying to get them to breed successfully has been challenging. Added to that the long life-span (it’s not known how long the birds live but it appears to be decades) and the slow reproductive rate means that conservation efforts are going to take decades if not centuries before it is known whether or not they have been successful.
One stumbling block that was hit was an unintended consequence of trying to increase the number of breeding females. Females only breed when they reach a minimum weight. In order to increase the number of breeding females in a given year they were given additional, or supplementary, food. The unintended consequence was that this resulted in more males than females being reared.
The Trivers-Willard hypothesis predicts that females will produce more males when they are in good condition and more females when they are in poor condition. The idea is based on the costs and benefits of each offspring in terms of her ability to transmit her genes to future generations. In polygynous systems a female will be able to mate with a male regardless of her fitness: the males don’t care whether the females are only just fit enough to reproduce or are at peak condition. But in the same system only the fittest males can beat their rivals and gain access to females. The fitness of a female will affect the fitness of her offspring so if she’s not particularly fit it is in her interests to produce females whose future fitness will not significantly affect their reproductive potential. If she’s at peak fitness, however, it’s in her interests to produce males who are more likely to be the dominant male and be able to beat rivals to females.
You may be able to see the unintended consequences already. The supplementary food pushed all the females into top condition and they all produced males. Experimental supplementary feeding at different levels was used to confirm the hypothesis and found to be true [3]. As a result, the supplementary feeding program was adjusted so that females at fed to a level of fitness where they could successfully reproduce but are not so fit that they produce only males. It has been so successful that from the highly skewed sex ratio at the start of the programme it is now approaching parity with 70 males and 60 females.
The conservation program still has a long way to go before kakapo can be considered to be saved. It may be that disease (highly possible given the low genetic diversity) or a series of unfortunate events reduces the population to a level from which it cannot recover. In some sense the birds are living on borrowed time, but despite the uncertainty of success, the effort is well worth it. These birds are unique in the world and are worthy of our care and conservation. Long may their ‘borrowed time’ continue.
Author: Sarah Hearne, hearnes[at]tcd.ie, @SarahVHearne
Image Sources: Wikicommons
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Why are there no elephants in the mountains?
Well, mainly because it’s costly to climb when you’re an animal of that size. A previous study estimated that a 4 tonne elephant would have to eat for 30 minutes to compensate for a 100m climb. Ideas man Graeme Ruxton and his co-author David Wilkinson develop this further in their new paper. They ask whether avoidance of hilly areas is to be expected in general for animals of a large mass such as the sauropods. These are the long-necked dinosaurs that were the largest terrestrial animals that ever existed. Some of the upper mass estimates of, albeit poorly described, species are over 100 tonnes! Using simple scaling relationships relating to the energetics of movement, food intake etc. Ruxton and Wilkinson show that as a herbivore increases in size the fraction of time spent eating to balance the cost of climbing will increase. In the case of sauropods we can look to the fossil record for support and it does show the creatures preferred flat environments such as fluvial plains. Their footprints and nesting sites are often preserved in these areas. Of course, energetic concerns aren’t the only issue stopping these animals from populating the hills. The danger of falling would be much higher on a friable surface and the bigger you are…
Any thoughts of regaining your energy on the way down after a costly ascent can be dispensed with. An animal must expend energy to control the rate of descent especially to avoid falling. One benefit of being large is that you have energy reserves so it is possible to travel into the hills if absolutely necessary but these forays would be infrequent.
This result suggests steep areas should be depauperate with respect to larger herbivores. We could imagine highland islands of smaller herbivores alongside plants which are free from the pressures of huge plant-eaters. The conclusion of the paper asks us to explore extant ecosystems for such a pattern. This could be extended to Mesozoic ecosystems. Perhaps there would be an ontogenetic niche shift in the sauropods, moving from hilly areas to the flatlands as they developed.
Author: Adam Kane, kanead[at]tcd.ie, @P1ZPalu
Image Source: Wikicommons
I’ve been studying tenrecs for almost two years. I’ve read about them, watched video clips and handled hundreds of dead specimens. However, within that time I only met two live individuals, both of which were captive zoo animals. That’s all changed. I’m now well acquainted with a variety of tenrec critters. It turns out they’re a quiet bunch.
My supervisor, Natalie, and I spent two weeks in Madagascar working with a research team from the Vahatra Association led by Steve Goodman. The purpose of their trip was to conduct a disease transmission study in bats and small terrestrial mammals study at Ambohitantely Special Reserve, a protected, upland native forest north west of Antananarivo.
We tagged along on the trip to run behavioural experiments to test whether there’s evidence for echolocation in the shrew-type (Microgale) tenrecs. Armed with a bat detector and an adjustable maze, my plan was to record the tenrecs’ calls as they move through their environment in search of a worm food reward at the end of the maze.
I had envisaged many potential problems with the experiment. How would we be able to filter out interesting noises from background sounds? Would the noise of the animals moving around mask out the true vocalisations? I didn’t, however, foresee the problem with which we were faced; they didn’t make any noise whatsoever, zilch, not a peep.
We tried multiple methods to coax some sound out of the furry creatures. The animals were kept warm in Natalie’s increasingly bulging coat pockets. We tried to entice the animals using juicy worms as proverbial carrots. We experimented with placing pairs of individuals in the box at the same time hoping to overhear some tenrec chat. We also eliminated technical faults as a possible cause by testing out my detector on the bats flying around camp at night. All to no avail.
I think they were holding out on us. The other, more experienced field researchers had heard tenrecs squeaking while foraging. The previous work on echolocation in tenrecs which inspired my experiments includes recordings of one species of Microgale so the animals are certainly not mute. I think our empty sound files are an unfortunate consequence of our experimental protocol. Existing research on possible echolocation in shrews and tenrecs used captive animals under highly controlled experimental conditions. We, however, were constrained by time and resources to an artificial experimental set up so it’s unfortunate but not entirely surprising that things didn’t go according to plan.
Still, the trip was far from wasted. Studying and observing living animals is just a tad more exciting than their museum counterparts and I now have enough pictures of tenrecs to last for a lifetime of presentations. We met some extremely interesting and knowledgeable researchers and we had the opportunity to work in a remote, beautiful and exotic place.
Furthermore, our failed experiments left time to go and explore other areas as tourists; expect our encounters with Indri, mouse lemurs, chameleons and enormous spiders to be coming soon…
Author and Images: Sive Finlay, sfinlay[at]tcd.ie, @SiveFinlay
Last week our newest EcoEvo@TCD paper came out in PRSB (it will be Open Access soon but currently it’s behind a pay wall – feel free to email me for a copy in the meantime. Code for the multiple PGLS models can be found here). This paper is exciting for me for two reasons – firstly because the science is really cool and secondly because of how it came about. In a previous post I explained the results of the paper. Today I want to focus on how it came about. Continue reading “Dying without wings: Part II”
Last week our newest EcoEvo@TCD paper came out in PRSB (it will be Open Access soon but currently it’s behind a pay wall – feel free to email me for a copy in the meantime. Also code to fit multiple PGLS models can be found here). This paper is exciting for me for two reasons – firstly because the science is really cool, and secondly because of how it came about. Today I want to focus on the paper itself, and in my next post I will explain how this collaborative project started. Continue reading “Dying without wings* Part I”
Are you interested in science?
From nano-materials to Martian landscapes, microbiology to neuroscience, immunology to ecology, chemistry to evolution, Soapbox Science Ireland has something for you.
On the 26th of April (this Saturday!), Soapbox Science will join efforts with Trinity College Dublin’s Equality Fund and WiSER to transform Trinity’s Front Square into a hub of scientific learning and discussion. Some of Ireland’s leading female scientists take to their soapboxes to showcase science to the general public. The aim is to dispel the myth that scientists conform to the “mad (male) scientist” stereotype and to promote the fascinating research led by women in Ireland. Continue reading “Soapbox Science Ireland”
The Easter Bunny apparently originated in German Lutherans’ traditions before 1682 when it was first mentioned in von Franckenau’s De ovis paschalibus. In France and Belgium however, it’s not a rabbit that hides eggs in the garden for Easter morning but flying bells coming back from Rome (they went there for their holidays since the Maundy Thursday). For many people this makes no sense at all (flying bells, come on!) but on the other hand I think that a bunny carrying coloured eggs and hiding them does not make much more sense… Continue reading “The Easter bunny’s origins are linked with climate change”