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Archive 2010

Presence of observers prevents fur seal attacks Hilary Miller Dec 08

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Further to the recent attacks on fur seals in Kaikoura, comes a timely study just published in Conservation Biology.  Alejandro Acedevo-Gutierrez and Lisa Acedevo of Western Washington University, and Laura Boren, DoC’s national marine mammal coordinator, found that the presence of an official-looking volunteer stationed at a popular seal viewing areas was enough to deter tourists from harassing seals. 

The researchers carried out their study at Ohau stream waterfall, Kaikoura, near the location of the recent attacks that saw 23 animals bludgeoned to death.  Over a period of 9 months they recorded the behaviour of tourists in the presence or absence of a volunteer observer who was wearing a neon vest and made to look “official”.  Tourists were deemed to be harassing the seals when they approached the animals to within a few metres or threw an object at them.  They found that harassment dropped by two-thirds when the observer was present – from 38.4% down to 13% of groups with at least one person who harassed the seals  - even if the observer said nothing to the tourists. 

Viewing of fur seals is regulated by the Marine Mammals Protection Act 1992, but the researchers had previously found that simply having a sign up stating these regulations does nothing to ensure that tourists actually comply.  Having an actual person wearing a neon vest is far more effective at preventing harassment, even if this person is a volunteer with no authority to actually enforce compliance with the regulations. 

The researchers point out that using volunteers in this way is a cheap and effective way of managing tourist-wildlife interactions at popular wildlife viewing areas, and has the added bonus of observers being able to educate tourists about the animals. They found that approximately half the tourist groups approached the observer and asked questions about the behaviour of the seals, and all of them had misconceptions about how to behave around young seals.

Other posts on sciblogs about the fur seal attacks are here and here

Reference:

Acedevo-Gutierrez et al.  Effects of the Presence of Official-Looking Volunteers on Harassment of New Zealand Fur Seals.  Conservation Biology. Article first published online: 3 DEC 2010 | DOI: 10.1111/j.1523-1739.2010.01611.x

   

Great wildlife photography Hilary Miller Nov 18

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Some fantastic wildlife snaps from the winners of the GDT European Wildlife Photographer of the Year (the humingbird is my favourite)

http://www.guardian.co.uk/environment/gallery/2010/nov/17/gdt-wildlife-photography#/?picture=368699851&index=0

Tuatara tuesday – sex determination in a warming world Hilary Miller Nov 09

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Seeing as reptile reproduction seems to be a bit of a hot topic right now, I thought it was time to talk about sex determination in tuatara.

Tuatara do things a little differently to other reptiles when it comes to sex determination – not because they have temperature-dependent sex determination (thats common to lots of reptiles), but because their pattern of temperature-dependent sex determination (or TSD) is different from most other reptiles.  For tuatara, incubating eggs at higher temperatures (over 22°C) produces males, while lower temperatures (under 21°C) produce females.  In other reptiles with TSD, you generally either get a pattern of females being produced at high temperatures and males at low temperatures, or females being produced at both high and low temperatures, and males produced at intermediate temperatures.

Tuatara hatchling

Dr Nicola Nelson at Victoria University has experimented with switching tuatara eggs between male and female-producing temperatures in an effort to determine which part of the incubation period temperature is critical for sex determination.  She found that sex is set early on - by the time the incubation period is about one third of the way though.  However, incubating eggs in captivity at constant temperatures only tells part of the story, as of course temperatures are not constant in the wild, where eggs are laid in shallow burrows in the soil.  Nelson and colleagues have also collected temperature data from natural nests and found that warmer nests produce males and cooler nests produce females, but what isn’t known is how long eggs have to remain above or below the critical temperature in order to produce males vs females.  Its possible that the critical period for sex determination is actually quite short – for example an egg may actually only need to spend a few days above 22°C in order to turn out male.

A partially buried tuatara nest on Stephens Island

Having more males produced at warmer temperatures could be bad news for tuatara in the light of global warming.  Some tuatara populations, like the small, genetically distinct population on North Brother Island, already have more males than females.  A recent study by Nicola Mitchell of the University of Western Australia predicted that, under current “worst-case” global warming scenarios, populations like North Brother Island will produce all-male clutches by the mid 2080s.

Of course, tuatara have survived changes in climate in the past, but this time around the climate is changing faster than ever before – perhaps too fast for a species like tuatara with its long generation times and low levels of genetic variation to be able to evolve to compensate.   Tuatara may be able to adapt behaviourally to the higher temperatures by nesting earlier, digging deeper nests, or choosing cooler nest sites.  However, on many islands the choice of nest sites is limited, and as tuatara are now confined to offshore islands or ringed in by predator-proof fences on the mainland, they will be unable to simply move south to seek cooler temperatures. It seems likely that tuatara will need our help if they are to survive the threat of global warming.

Further reading:

Mitchell NJ, Kearney MR, Nelson NJ, Porter WP (2008) Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara? Proceedings of the Royal Society B-Biological Sciences 275: 2185-2193

Huey RB,Janzen FJ (2008) Climate warming and environmental sex determination in tuatara: the Last of the Sphenodontians? Proceedings of the Royal Society B: Biological Sciences 275: 2181-2183

Mitchell NJ, Nelson NJ, Cree A, Pledger S, Keall SN, Daugherty CH (2006) Support for a rare pattern of temperature-dependent sex determination in archaic reptiles: evidence from two species of tuatara (Sphenodon). Frontiers in Zoology 3: 9

 

The weird ways of reptile reproduction Hilary Miller Nov 04

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Two studies on reproduction in reptiles have made me go “wow, thats cool” this week.

Firstly, the report of a boa constrictor giving birth to two litters of offspring without the need for a father.  This sort of “virgin birth” is called parthenogenesis, and is not that uncommon in itself, having been previously observed in a few other reptile and fish species, and numerous invertebrates.  What separates this latest report from the others is the unusual complement of sex chromosomes observed in the offspring.

When vertebrates reproduce by parthenogenesis, the offspring are usually “half clones” of the mother.  Chromosomes come in pairs, and normally you get one half of the pair from your father and the other half from your mother.  But in parthenogenesis, both halves come from the mother – that is, two copies of one half of the mother’s chromosomes are inherited.   This means that when it comes to the sex chromosomes, the offspring end up with two of the copies of the same chromosome.  In all other recorded instances of pathenogenesis in vertebrates, species like snakes with the ZW sex chromosome system (where males have ZZ and females have ZW chromosomes) produce only male offspring, and species with XY chromosomes (males XY and females XX)  produce only female  offspring.   In other words, only the sex where the two sex chromosomes are the same is produced and the opposite scenario (WW females or YY males) was thought to result in non-viable offspring.  Until this boa constrictor came along, that is -  yep, her litters are made up entirely of WW female snakes, a finding which “up-ends decades of scientific theory on reptile reproduction”.

This study was published online this week in Biology Letters, and the BBC news has more on the story here

The second study, published online in Nature this week, is an great example of just how malleable sex determining systems can be.  For many reptiles, sex is determined not by sex chromosomes, but by what temperature the egg is incubated at.  In tuatara for example, incubating eggs at high temperatures produces males, while low temperatures produce females.  You might think that chromosomal and temperature-dependent sex determination are two fundamentally different, mutually exclusive ways of determining sex.  However, in some species the line between these two systems is blurred, suggesting that switching between systems is easier than you would think.  This study found that the Tasmanian snow skink (Niveoscincus ocellatus) has both types of sex determination, and all it has taken to switch between the two is a shift in climate. 

The snow skink lives in both the warm lowlands and cool highlands of Tasmania.  The study found that in the highlands, the skink uses chromosomal sex determination, producing an equal ratio of male and female offspring regardless of the temperature.  However, in the lowlands its sex determination is temperature-dependent - cool cloudy days produce males, and warm, sunny days produce females.  The researchers speculate that the divergence in sex determination mechanisms was caused by temperature differences, enabling the lizards to maximise their reproductive output in the differing climates. 

The paper is here, and ABC news has a report on this here.

A simple change determines male vs female organ development in flowers Hilary Miller Oct 30

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ResearchBlogging.org Gene duplication is a  major source of genomic novelty for evolution to work on.  When genes duplicate, the extra copy of the gene is often redundant – it might degrade and become a pseudogene or take on a completely new function.  Alternatively, the function of the original gene might become partitioned between the two duplicates in a process known as subfunctionalization.  An excellent example of this has recently been reported in the genes that control male and female organ development in the flower, and it’s (almost) all down to a single amino acid change between the duplicate genes.

Development of male and female reproductive organs in flowers is controlled largely by a group of genes called MADS-box transcription factors. Different versions of these transcription factors (known as A, B or C function genes) are expressed in different parts of the developing flower, acting either alone or together to produce sepals, petals, stamens (male) or carpels (female)*.

Much of what we know about flower development comes from studies on two “model” plants – Arabidopsis (rockcress) and Antirrhinum (snapdragon).  In these species, and in many other flowering plants, the MADs-box C-function gene that controls the production of carpels vs stamens has duplicated. In Arabidopsis, one of the copies (called AG) makes both male and female organs, but the other copy has taken on the completely new function of making seed pods shatter (and is appropriately called SHATTERPROOF).  However, in Antirrhinum both copies still play a role in sex organ development: one copy (called FAR) makes only male parts, while the other copy (PLE) makes mainly female parts but also has a small role in making male parts.

Thus in Antirrhinum, the function of the original gene (making both male and female parts) has almost been split between the two duplicate copies.  In a study published online in PNAS last week, researchers at the University of Leeds, led by Professor Brendan Davies,  found a surprisingly simple difference in the two copies has led to their profoundly different roles.

Davies and colleagues created chimeric versions of PLE and FAR, swapping domains between the proteins to determine exactly what parts of the different proteins are responsible for their differing function.  They narrowed down the difference between the two genes to a single amino acid that is present in FAR but not in PLE. When this amino acid was removed from FAR, the gene switched to making both female and male parts.  FAR and PLE are estimated to have duplicated around 120 million years ago, and the researchers estimate that the mutation responsible for inserting the extra amino acid into FAR happened around 20 million years after the duplication.

Duplicated genes often take on new functions because changes in their regulatory regions change how and where they are expressed.  Thus, finding an example such as this one, where a simple change in the protein coding sequence causes a profound change in function is somewhat unusual.  However, these proteins don’t act in isolation – they are just one part of a network of genes that must work together to control sex organ development.  Davies and colleagues found that the single amino acid change alters the ability of the protein to interact with other proteins in this network.

The additional amino acid in FAR is found in the part of the protein that interacts with other types of MADs-box proteins called SEP proteins.  C-function genes without the additional amino acid (like PLE) can interact with 3 different SEP proteins (SEP1, SEP2 and SEP3), but proteins with the additional amino acid (like FAR) can only interact with SEP3.  The SEP3 gene is not expressed in the first whorl of the flower, where female parts are produced, so FAR doesn’t have anything to interact with in this whorl and therefore doesn’t produce female parts.

Davies describes this as “an excellent example of how a chance imperfection sparks evolutionary change”.  It is also a nice example of subfunctionalization in action, where a simple amino acid change provides a means of separating the functions of the duplicate copies by causing a change in how the protein operates in a larger regulatory network.

Reference: Airoldi CA, Bergonzi S, & Davies B (2010). Single amino acid change alters the ability to specify male or female organ identity. Proceedings of the National Academy of Sciences of the United States of America PMID: 20956314

*For more on the ABC model of plant development, see here or here.

Tuatara tuesday – an iconic parasite for an iconic species Hilary Miller Oct 26

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As you might expect from an animal that is so evolutionarily distant from its nearest relatives, the tuatara also has some unique parasites to call its own.  One of these is the tick Amblyomma sphenodonti (sometimes also called Aponomma sphenodonti), pictured here.

Tuatara ticks Amblyomma sphenodonti

Like many ticks, A. sphenodonti are host-specific, spending all three of their life stages feeding on tuatara but dropping off into the soil in between stages.

So why should you care about tuatara ticks?  Well, these ticks are evolutionarily distinct in their own right, and are actually quite rare – far rarer than the tuatara themselves.

The taxonomic history of the tuatara tick is a little complicated, so bear with me for a minute.  The tuatara tick is “hard” tick in the family Ixodidae, and was originally named in the genus Aponomma, a group of ticks that predominately parasitise reptiles.  However, a revision of the Aponomma genus placed some of the these species into a new genus Bothriocroton, and moved the rest, including the tuatara tick, into the existing genus Amblyomma. A few years ago, with the help of a keen undergraduate student, I did a small genetics study comparing the tuatara tick with both Bothriocroton and Amblyomma ticks and found that it’s actually not particularly closely related to either group (see the tree below – click on it to enlarge).   The tuatara tick should probably actually be in its own genus, highlighting the fact that it has likely had a long evolutionary relationship with its evolutionarily distinctive host.

Phylogeny of hard ticks, based on 18S rRNA sequences. A. sphenodonti is shown in bold. Other members of the Amblyomma genus group in the top part of the tree, while Bothriocroton ticks form a group in the lower half of the tree.

Surveys carried out in the late 80s-early 90s found A. sphenodonti on only 8 out of 28 natural tuatara populations, and the Department of Conservation lists it as “Range Restricted” in its Threat Classification System. They are also virtually absent from populations established by translocations.  This is partly because up until recently, the ticks were removed when animals were translocated.  However for recent translocations, such as into the  Zealandia wildlife sanctuary in Wellington, the ticks have been left on, but disappeared naturally within the months after the translocation.  The most likely cause of the disappearance is the low density of tuatara in the new location, meaning that when a tick drops off a tuatara at the end of one of its life stages, finding a new host for the next life stage is difficult.  This inability to find new hosts when they are at low densities may have also contributed to the demise of tick populations in the wild.

The case of the tuatara tick highlights how, when populations become endangered, their natural “flora and fauna” are also at risk.  Parasites are the most diverse and species-rich metazoan group on earth, and form a highly important part of host ecosystems, so they deserve our conservation efforts just as much as their hosts.

Further reading:   Miller HC, Conrad AM, Barker SC, and Daugherty CH (2007) Distribution and phylogenetic analyses of an endangered tick, Amblyomma sphenodonti. New Zealand Journal of Zoology, 34: 97-105.

Tuatara tuesday — Spring fever Hilary Miller Oct 12

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I haven’t had much time for writing this week, so instead I thought I’d share this photo as a reminder to my New Zealand readers that it is actually spring, even though it doesn’t feel like it!

 

Tuatara basking in the daisies on Stephens Island

 

Don’t forget to vote! Hilary Miller Oct 10

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No, not for your local government (you’re too late for that).  For New Zealand’s Bird of the Year, of course! Apparently the pukeko is out in front. Come on people, can’t we at least chose something endemic? A species that we don’t share with Australia and numerous other countries??  There’s plenty to chose from – the kakariki is giving the pukeko a run for its money (only 2 votes in it at 10am this morning!), and the old favorites kiwi, kakapo and weka might get up with a late run of voting.  You can vote here.

Tuatara tuesday — how cold is too cold for a tuatara? Hilary Miller Oct 05

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ResearchBlogging.org Tuatara like it cold.  Unusually so, for a reptile.  While reptiles in most other countries are happiest with temperatures over 25 degrees celcius, here in New Zealand our reptiles prefer much lower temperatures.  Alison Cree’s group at the University of Otago has been investigating exactly which temperatures tuatara prefer, with a view to determining whether new populations of tuatara could be established in the southern South Island.

Research just published in Animal Conservation by PhD student Anne Besson examined the effects of cool temperature on juvenile tuatara sourced from Stephens Island, the southern-most natural population.  Sub-fossil remains tell us that tuatara were once present in Otago and Southland, but they have been extinct in this region for possibly hundreds of years.  Temperatures on Stephens Island are on average 3-4 degrees warmer than those at proposed translocation sites in Otago, and it is possible that tuatara originally living in the deep south had special adaptations to enable them to withstand the cold that are absent in animals from more northerly present-day populations.  To test whether Stephens Island tuatara are likely to be able to survive in the deep south, Besson compared tuatara behaviour at low temperatures with that of three lizard species found in the wild in Otago (common geckos, jewelled geckos and McCann’s skinks), hypothesizing that if tuatara have the same responses as these lizard species, then its likely they will be able to survive similar temperatures.

Besson investigated feeding behaviour at 20, 12 and 5 degrees, measuring the time it took an animal to catch, handle and digest prey at the three different temperatures.  She found few differences between tuatara and the lizards.  For all species, feeding performance dropped off significantly at 5 degrees as animals became very sluggish at catching and handling their food, and neither skinks or tuatara could digest food at this temperature.  However, one important difference between tuatara and lizards was seen at 12 degrees.  At this temperature lizards were able to digest food, albiet more slowly than at warmer temperatures, but tuatara were not.  Besson also measured preferred body temperature and critical thermal minimum (i.e. the temperature at which animals can effectively no longer function) across the four species and again found little difference between tuatara and the lizard species.

Besson’s results suggest that Stephens Island tuatara would survive a move south, but their inability to digest food at temperatures of 12 degrees or lower has important implications for choosing translocation sites in Otago, given that ambient temperatures rarely rise above 12 degrees in winter in this region.  As tuatara do not hibernate and still feed throughout the winter, Besson and Cree recommend that proposed translocation sites for tuatara should provide plenty of opportunities for animals to bask in the sun in order to digest their food.

Testing physiological and behavioural responses to investigate whether animals are likely to be survive in new environments is something that is rarely done in conservation studies, but is likely to become increasingly important in the face of climate change.  Tuatara are particularly vulnerable to warming temperatures, as sex determination in tuatara is temperature-dependent and warming temperatures are likely to produce an excess of males.  Establishing new populations further south may be one way of countering future temperature rises.  Besson’s research shows that this is likely to be a viable strategy for conservation management of tuatara, but whether they can produce self-sustaining populations at cooler temperatures still needs to be tested.

Besson, A., & Cree, A. (2010). Integrating physiology into conservation: an approach to help guide translocations of a rare reptile in a warming environment Animal Conservation DOI: 10.1111/j.1469-1795.2010.00386.x

A falcon’s eye view of flight Hilary Miller Sep 27

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This video has been doing the rounds, and its so cool I just have to post it here.  The video shows the amazing maneuverability and speed of birds of prey in flight, thanks to “on bird” cameras mounted on a peregrine falcon and a goshawk.

hat-tip: Ars technica

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