tenrecs Archives - EcoEvo@TCD

08/05/201505/05/2015

Looks can be deceiving

We are all taught not to judge a book by its cover, it’s what inside that counts. Our new paper published in PeerJ shows that the same is true for tenrecs.

These cute Madagascar natives are often used as an example of a mammal family with high morphological diversity. It’s easy to see why: there are tenrecs which resemble shrews, moles, hedgehogs and even otters. These differences are even more remarkable when you consider that tenrecs are more closely related to elephants and aardvarks than they are to any of the small, “insectivore” mammals. One of only four native mammal clades in Madagascar, it appears that tenrecs have undergone an adaptive radiation to fill otherwise vacant, small mammal niches, evolving convergent similarities to other groups in the process.

Tenrecs are clearly very diverse in their appearance. However, prior to our study, no one had tested whether this apparently high diversity was more than skin deep. We tested whether tenrecs were more morphologically diverse than their closest relatives, the golden moles.

We measured the morphology of tenrec skulls and compared their diversity to the shape of golden mole skulls. This meant spending hours poking around the collections of natural history museums and many more hours placing landmarks on skull pictures for 2D geometric morphometrics analyses (Spotify was my friend!)

Pictures of an otter shrew tenrec (Potamogale velox) skull showing that landmarks (points) and semilandmarks (curves) that we used to summarise skull shape. See the paper for more information. — Pictures of an otter shrew tenrec (*Potamogale velox*) skull showing that landmarks (points) and semilandmarks (curves) that we used to summarise skull shape. See the paper for more information.

Tenrecs occupy a wider range of ecological niches (fossorial, arboreal, terrestrial and aquatic) than golden moles so we expected that tenrecs would be more morphologically diverse than their cousins. However, we found that tenrec skulls only have more diverse shapes than golden moles when we compared them in lateral (sideways) view but not dorsal or ventral views. These results show the importance of measuring morphology in many different views to gain a more complete understanding of overall morphological diversity.

The tenrec family includes species which convergently resemble many other, un-related small mammals. However, most tenrecs (19 out of the 31 tenrec species in our analysis) belong to the shrew-like Microgale tenrec genus. So, although many people tend to focus on the strange and unusual species (such as the otter shrew, hedgehog tenrec or the bizarre lowland streaked tenrec), most tenrecs are small, shrewy-type creatures that look very similar.

We tested whether the similarities among the Microgale tenrecs might be masking higher morphological diversity in the rest of the family. We repeated our analyses to compare the diversity of golden mole skulls to a sub-set of the tenrec family (including just 5 of the 19 Microgale species). In this case, tenrec skulls were more morphologically diverse than golden mole skulls in all comparisons (skulls in dorsal, ventral and lateral view).

Overall, our results indicate that, while there are clear physical differences among tenrec family members, the majority of tenrecs are quite morphologically similar to each other so morphological diversity in the family as a whole is not as big as it first appears. Of course comparing skull diversity is just one aspect of overall morphology – analysing the shape of other traits such as limbs could yield different results – but our study represents the first step towards a greater understanding of the ecological and evolutionary diversity of tenrecs.

It’s also testimony to the fact that you should never judge a tenrec by its cover.

Author: Sive Finlay, @SiveFinlay

29/10/2014

Say “the rise of the age of mammals” again, I double dare you!

In biology and among biologists, we like to use terms that we know are not correct but that still come in handy when you’re confident that your interlocutor understands them the way you do. I’m thinking of terms such as “key adaptations”, “living fossils”, etc… However, among them, there is one that particularly bugs me and makes me feel like Samuel L. Jackson in the iconic Pulp Fiction scene and that is: “the rise of the age of mammals”.

Recently, Barry Lovegrove and his students published a nice data driven paper in Proceedings of the Royal Society B on the hibernation of tenrecs. The team found that these amazing creatures (I refer you to Sive’s posts, our tenrec expert) do go into hibernation for 9 months straight even though they live in tropical latitudes. The paper first sparked my curiosity because of this new tenrec fact but also due to the spin that the authors put on the paper’s results. They create a broad significance for the implications of their research on hibernation in tenrecs by describing their potential applications for how we might biologically programme astronauts to hibernate on a journey to Mars.

But what struck me the most (and I’m coming to main point of this blog post) is that the authors place their paper in the context of our understanding of the K-T boundary event which, they argue, was a key event in the evolutionary radiation of placental mammals (according to work by O’Leary and colleagues discussed here and here). And from there, the authors claim that tenrecs’ “predation-avoidance hibernation may be an ancient plesiomorphic characteristic in mammals and is a legacy, perhaps, of the 163 Myr of ecological suppression by the dinosaurs. It enabled the ancestral placentals, as well as the marsupials and monotremes […], to endure the short- and long-term devastations of the K-Pg asteroid impact, a capacity which is possibly the sole explanation for the existence of mammals today.”

This suggestion is based solely on their findings about hibernation in tenrecs. Their rather crude extrapolations to what these results tell us about the origin of placental mammals are mainly based on two erroneous assumptions:

-(1) they “report a plesiomorphic (ancestral) capacity for long-term hibernation that exists in an extant, phylogenetically basal, tropical placental mammal, the common tenrec”

– (2) “The long ca. 160 Myr stint of the nocturnal, small, insectivorous mammal was over, and gave way to the age of the mammals, the Cenozoic” because of the “Ecological release from the vice grip which the dinosaurs held over Mesozoic mammals”

(1) Tenrecs are Afrotherians. They are a sister group of golden moles and nested somewhere within the elephant shrews and aardvarks clade that is sister to the elephants, hyrax and sirenians (so, even within Afrotherians, tenrecs are not particularly basal). Afrotherians are a sister group to either Xenarthrans or Boreoeutherians (depending on the genomic region) but all three together form the extant eutherians. It is mistaken to interpret tenrecs as a “basal” mammal clade. The authors claim that their “hibernation data show some affinities to the ‘protoendothermy’ first noted in echidnas, suggesting retention of plesiomorphic characteristics of hibernation on Madagascar through phylogenetic inertia”. This implies that this hibernation characteristic has been lost in all other mammal groups .Using basic principles of parsimony, it would make more sense to attribute this hibernation characteristic to being yet another example of a convergent trait in tenrecs, not an ancestral state which was lost in most other mammals.

(2) I grew up reading a steady diet of books about the history of life. These presented a nicely summarized picture: around 65.5 Mya (now updated to 66 Mya, a small detail that can easily be fixed), all dinosaurs went extinct because they were too big and too stupid and the clever small mammals survived without any problem, liberated from their domination by the big stupid dinosaurs. This vision was awesome as a child; it had all the elements for a really anthropocentric/biblical view of the story (think about the Exodus) and clearly explained why mammals are the dominant species today. It even explains the success of humans: we used our cooperation and intelligence to reach our dominant position as head of all the mammals.

However, this romantic vision of the history of life (driven by paleontological data prior to the amazing discoveries of new Jurassic and Cretaceous mammals in the 90s and 2000s and the advent of molecular phylogenies) has, thankfully, been updated to integrate the last two decades of excellent work. This lead to a picture that is less romantic and more complex. The dinosaurs didn’t really disappear and are actually still more numerous (species richness-wise) than mammals nowadays. Similarly, the placental mammals and their ancestor didn’t just “bloom” after the K-T boundary event: they had their origin back in the late Jurassic, roughly at the same time as the dominant tetrapods of today (the birds), and they radiated multiple times: mainly due to global climatic changes during the Paleogene such as the “Grande Coupure” or the PETM…

I’m not sure why the authors chose to adopt an outdated vision of the evolution of mammals to introduce their work but it seems a pity to me that such a spin is necessary to present good work on unknown/understudied groups even if they’re as cool as tenrecs!

Author: Thomas Guillerme, guillert[at]tcd.ie, @TGuillerme

Photo credit: http://www.smbc-comics.com/?id=1535

02/05/201403/05/2014

Silence of the Tenrecs

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.

Just slightly excited to be holding a live tenrec!

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.

Ambohitantely forest surrounded by central plateau grassland — Looking down onto Ambohitantely forest; not a bad place to work…

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.

Our “experimental chamber”; the maze box (covered with material in the bottom right of the picture) set up in a shower cubicle!

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.

Microgale dobsoni; "I'm not going to produce any sound and you can't make me" — *Microgale dobsoni*; “I don’t want to produce any sound and you can’t make me”

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

28/03/201426/03/2014

Echolocating Tenrecs

I’m going to Madagascar tomorrow.

I have all the essentials; insect repellent, tent, flat pack wooden box, bat detector, three metres of blackout curtain material… Not the most usual of packing lists admittedly but all necessary items for the trip ahead.

I’m going to study tenrecs; cute mammals which are the subject of my PhD. I’m interested in convergent evolution between tenrecs and other small mammals. So far I’ve been focusing on morphological convergence – work which has involved trips to beautiful museums and taming the dark arts of morphometrics. The primary aim of my research is to assess the evidence for morphological and ecological convergences among tenrecs and the mammals they resemble. Technically I could complete these aspects of the project without ever seeing or dealing with the live animals. But where’s the fun in that?! I’m also interested in behavioural convergences among tenrecs and other mammals, particularly reports of the abilities of some tenrecs to echolocate.

Some shrews produce echolocation calls by clicking their tongues. More recent work indicates that shrews seem to use these clicking calls primarily for navigation within their habitat rather than communication. Intriguingly, there is evidence that at least three species of tenrec; the lesser hedgehog tenrec, lowland streaked tenrec and Dobson’s shrew tenrec, can also echolocate. The animals seem to use their tongue clicks for navigation. The stridulation sounds produced by specialised spines in lowland streaked tenrecs and juvenile tail-less tenrecs have also been linked to having an echolocatory function but immobilising the spines doesn’t seem to affect the animals’ abilities to navigate by sound.

These early experiments are tantalising evidence of intriguing behavioural convergences among shrews and tenrecs. However, limitations of 1960’s acoustic technology and the ever so slight changes in standards of experimental practice (blinding animals with cement doesn’t go down so well with modern ethics boards!) mean that the study of echolocation in tenrecs is ripe for further exploration.

Hence my unusual packing list. My plan is to place wild-caught tenrecs within a box that can be converted into a maze of various layout and complexity (I’m extremely grateful to our super technician, Peter Stafford for making an adjustable maze which can be flat-packed for travel to Madagascar!).

Using a bat detector, I’m going to record the sounds produced by the animals both when they’re “at rest” just in the empty box and when faced with the task of moving through the maze to reach food at the other end. I’m going to observe and film the animals moving through the maze, both in daylight and under red-light conditions in darkness (hence the blackout curtains) and record the sounds they produce as they move. The idea is to test whether the animals’ call patterns (structure/frequency of calls) changes as they navigate their way past an obstacle in the maze. Bats are known to modulate their call frequencies when they hone in on their prey or to navigate their way past obstacles. I want to test whether there’s similar call modification in tenrecs which would provide evidence that the animals are actually using their echolocation sounds for navigation. It would be fascinating to understand more of how tenrecs use echolocation and to test whether other tenrec species can also echolocate.

It all sounds quite straightforward but I’ve experienced some of the vagaries of fieldwork in the past and I’m anticipating many more problems to come. I’ve received advice and war tales from researchers who have tried to study echolocation in shrews only to be thwarted by problems of distinguishing the animals’ calls from background sounds or the noise of the animal’s claws on a wooden base. Similarly, the tenrecs may not want to cooperate with my idea of moving from one end of the maze to another. I’m hoping that a nice juicy earthworm at the other end will act as the metaphorical carrot but there’s no way to know until we actually try it out. Furthermore, it might be difficult to distinguish sounds that say “I’m scared of being in this box” from sounds that the animals are using for navigation. Similarly, since we have neither the option nor inclination to experimentally blind or deafen the animals we won’t be able to completely exclude the possibility that the animals are using other sensory cues aside from acoustic navigation.

Even still, I’m hoping to get results which demonstrate the range of calls produced by tenrecs and which provide clues into how the animals use their acoustic behaviour to their advantage. Echolocation has involved independently in different animal lineages. Most interestingly, there is even clear evidence for convergence at the level of genetic sequences. Hopefully the data I gather over the next few weeks will add to our understanding of this fascinating story of convergence among tenrecs and other mammals.

And maybe we’ll spot a few lemurs on the way…

Author: Sive Finlay, sfinlay[at]tcd.ie, @SiveFinlay

Image Source: S. Finlay

05/03/201424/02/2014

School of Natural Sciences Postgraduate Symposium 2014: Part 4/4

On the 20th and 21st of February we had our annual School of Natural Sciences Postgraduate Symposium. Over the course of two days many of our PhD students presented their work to the School. We also had two interesting plenary talks from Dr Sophie Arnaud-Haond (Ifremer) and Dr Lesley Morrell (University of Hull). Unfortunately our third speaker, Dr Fiona Jordan (University of Bristol) had to cancel due to illness.

For those of you who are interested in exactly what we work on here at EcoEvo@TCD, here are the abstracts from the PhD student presentations. Check out the TCD website for more details!

Ruby Prickett*: Geographical, ecological and genetic characterisation of perennial biomass grasses

*Unfortunately Ruby was unable to attend but we still have her abstract

Evidence suggests that increasing CO2 concentration from fossil fuels in the atmosphere is contributing to global climate change. There is great interest in producing energy from biological sources such as willow (Salix spp.), and the grass Miscanthus. This project aims to contribute to the development of grasses of the C4 genus Miscanthus and several C3 species (Dactylis glomerata, Festuca arundinacea and Phalaris arundinacea) for use as biomass crops, particularly on marginal land. This project aims to produce maps and species distribution models for each of the four species, to identify potential areas for production and their impact on biodiversity; to collect new accessions of Dactylis and Phalaris in the Northwest Europe and Miscanthus in Asia; and to assess the genetic diversity within each species.

Rebecca Rolfe: Identification of Mechanosensitive Genes during Skeletal Development: Functional evidence associated with the Wnt Signalling Pathway

Mechanical stimulation is important for the correct formation of the skeleton. Mutant embryos that develop with an altered mechanical environment result in defects in ossification and joint formation in the limb. We tested the hypothesis that mechanical stimuli influence the regulation of genes important in skeletal development by analysing the transcriptome of muscle-less and control skeletal tissue. We found 1,132 independent genes are differentially expressed with significant enrichment of genes associated with development and differentiation and cell signalling. In particular, multiple components of the Wnt signalling pathway are affected. An investigation of the functional effects of over/ectopically expressing Wnt pathway components in the developing chick will be tested using in ovo and ex ovo electroporation. It will be used to assess whether manipulation of the Wnt pathway in the developing joint mimics the phenotype that is seen when mechanical stimulation is removed, to identify whether or not disturbing the pathway alone causes the phenotypic disturbance seen when mechanical stimulation is removed.

Anurati Saha: The Influence of Mechanical Forces for the Definition of Articular Cartilage

Articular cartilage covers the terminal ends of bones at synovial joints. It allows pain-free movement with injury or degeneration leading to diseases such as osteoarthritis. Current treatment is whole joint replacement but stem cell regenerative therapies would offer a more sustainable solution. Previous research in the lab has shown that appropriate mechanical stimulation from movement of the embryo is required for normal joint formation; joints fuse when movement is absent. My project aims to increase our knowledge of mechanical regulation of joint development in a number of respects and to explore application of such findings to achieve stable differentiation of cartilage for alternative regenerative therapies.

In the first year of my PhD, I investigated the potential of embryonic limb bud cells to form cartilage in micromass culture. This allowed me to establish a protocol to achieve chondrogenesis and revealed the stage of maximum chondrogenic potential. This part of my work will be developed to compare the response of embryonic limb bud cells and adult progenitor cells from different sources (bone marrow and joint derived) to mechanical stimuli in 3D scaffolds, potentially valuable in the refinement of protocols for regenerative therapies

Claire Shea: Mechanotransduction in Skeletal Development: From Embryonic Development to Regenerative Therapies*

*Highly commended

Why do babies kick? Why do astronauts in zero-gravity lose bone mass? What are the causes of osteoporosis and osteoarthritis? The human skeleton allows us to move, but also requires movement for its own development and maintenance. Mechanical forces impact developing tissues, making embryonic movement (kicking and stretching) necessary for normal skeletal development. Understanding how a healthy skeleton forms is also important for skeletal disease therapies which seek to generate replacement tissues by recapitulating the normal developmental pathway with cell cultures. Wnt is a cell-signalling system known to be vital to many aspects of embryonic patterning, and has been implicated in mechanotransduction by our lab. My work focuses on identification of Wnt component genes responsible for transducing mechanical signals such as tension, hydrostatic pressure, or shear into a genetic response in developing joints and bones. To characterise gene expression patterns in normal vs. mechanically-altered environments, and to assess the role of Wnt, I use genetic mutants (mouse) and gene electroporation (chick). My goal is to apply this in vivo information to in vitro efforts, where stem cells embedded in 3-D scaffolds will be treated with an optimal genetic and physical environment to form functional, stable adult bone or cartilage tissue.

Sive Finlay: Tremendous tenrecs: curious convergence and distinctive disparity*

*Best talk 1/2

Understanding patterns of variation in morphological diversity, such as convergence and disparity, remains a challenge in evolutionary biology. In particular, questions of convergence and the predictability of evolution are central to the long-standing debate about the relative influences of historical contingency and determinism in evolutionary processes. Theoretical models indicate that some degree of convergence is expected by chance in most phylogenies. Therefore, quantitative analysis and explicit tests of superficial patterns are essential if we are to identify and understand significant cases of evolutionary convergence. However, most quantitative methods of identifying convergence were developed using relatively few groups for which detailed morphological and ecological data were already known. I want to test the wider applicability and usefulness of such quantitative methods by applying them to a new study group.

Malagasy tenrecs appear to be both disparate from each other and convergent with other “insectivore” mammal species. I’m assessing the evidence for significant morphological disparity within tenrecs and convergences among tenrecs and other mammals using a combination of geometric morphometric techniques and phylogenetic comparative methods. Subsequently, I will establish whether there are correlations between morphologically similar species occupying convergent ecological niches.

Kevin Healy: The evolution of potent venom in snakes*

*Highly commended

The ability of a predator to capture its prey is a fundamental element of ecological interactions. Such interactions can broadly be described as following general scaling laws underpinned by factors such as predator-prey body size difference’s, or habitat complexity. Unlike many predators, the ability of snakes to subdue and capture prey is mediated not by physical size but by their highly evolved venoms. Based on general predator prey scaling predictions I explore the hypothesis that venom potency is affected by ecological factors relating to the ability to quickly subdue prey. The factors I predict to increase venom potency include large prey size and low prey metabolic rate, as they reduce the speed of the venom affects, and habitat complexity, as more complex habitats would allow prey more opportunity to escape. Understanding the general drivers of venom evolution can lead to insights into the evolution of snakes and other venomous species and point to perhaps other untapped venom derived bio-resources.

Erin Jo Tiedeken: The impacts of Rhododendron nectar toxins on Ireland’s bees: deadly meal or valuable forage?*

*Best talk 2/2

Bees provide the valuable ecosystem service of pollination while visiting flowers and collecting nectar. We are currently experiencing a “pollinator crisis,” as pollinating species decline in response to anthropogenic pressures. Moreover, bees may exhibit species-specific responses to drivers of decline.

Rhododendron ponticum is an invasive flowering shrub that causes ecological and economic damage in Ireland. R. ponticum produces floral nectar in order to attract pollinators, but paradoxically this nectar contains neurotoxins called grayanotoxins. Our study investigated the impact of grayanotoxins on three bee species; Apis mellifera, Bombus terrestris, and a solitary Andrena species. For each species we tested whether consumption of nectar grayanotoxins had an impact on (1) survival, (2) consumption rate, and (3) behavior. Our results demonstrate that bees have critically different responses to grayanotoxins. Grayanotoxins are acutely toxic to honeybees, however, bumblebees exhibited no lethal or sublethal effects. Solitary bee survival was not affected, however bees exhibited temporary neurological symptoms after eating grayanotoxins. Rhododendron reduces available forage for honeybees and some solitary bees but could provide an important food resource for certain bumblebees. Our results demonstrate that studies of pollinator decline should include multiple species and should not extrapolate to species other than those included in the study.

Image Source: Wikicommons

08/11/201307/11/2013

Trophy Hunters

Antler collection at Harvard's Museum of Comparative Zoology — Antler collection at Harvard’s Museum of Comparative Zoology

It may be an inconvenient truth in these conservation-focused times but we owe a debt of gratitude to the trophy hunters; the army officers and colonial-types who killed animals for sport and prestige. Without their considerable efforts, the vaults of natural history museums would be devoid of the skeletons and skins which form the bases of both exhibitions and many PhD and MSc. theses. Of course, were it not for the over-zealous efforts of hunters perhaps many charismatic animal species wouldn’t be so endangered now but let’s focus on the positives here…

Naturally, if you’re a hunter looking for a prize, bigger is usually better. It’s far more impressive to have a stag or bear’s head mounted on your wall than a hedgehog or shrew – although I would like to hear the embellished stories which might arise from tales of killing your first hedgehog! Similarly, if you are a taxidermist or museum collections manager in many ways it is easier to prepare and preserve large rather than small mammal specimens.

These collection trends are all well and good if you’re interested in the charismatic species. I, however, am studying the little shrewy-type things; hedgehogs, moles, shrews, golden moles and tenrecs – fascinating species but not prized possessions for your trophy case. Even in some of the world’s largest natural history museums it’s difficult to find intact skulls and skeletons of some of these creatures. Combined with the inherent delicate nature of these animals (some tenrecs’ limbs are tiny!) compiling a complete morphometric data set of the groups remains challenging.

Tenrec limbs with a pen for scale; teeny tiny tenrecs!

For the museum collections of these little critters that do exist; I am eternally grateful to the progenitors of carefully handwritten labels accompanying the skulls and skeletons on which my PhD research depends. Adventurers such as Major Forsyth, G.K., Creighton, and C.J., Raxworthy who donated specimens from their tropical voyages deserve special thanks in any research which arises from their collective efforts. However, I am also grateful to the back-yard naturalists, the people who collected and preserved the seemingly ordinary, every-day species of common shrews and hedgehogs which are no less important to ecological and evolutionary research than their exotic counterparts. I benefitted greatly from their collective efforts during my recent trip to Chicago’s Field Museum.

Whether naturalists or trophy hunters, the individuals immortalised by museum specimen labels couldn’t possibly have envisaged all of the diverse future research which would be based on their prized collections. It’s an important reminder that, despite the inherent appeal of flagship species, the lesser-spotted or common-something-or-others are just as deserving of our attention and study. Even if you don’t have the equipment or inclination to start posting skeletal remains of common species to your local natural history museum, there are still plenty of ways of contributing to the study of “ordinary” wildlife. Don’t be dazzled by the allure of large-animal trophy hunting and remember that, when it comes to understanding the natural world, bigger is not always better.

Author:

Sive Finlay: sfinlay[at]tcd.ie

@SiveFinlay

Photo Credits

Sive Finlay

22/03/201322/03/2013

Morphological convergence and disparity in Malagasy tenrecs

“I wish to register a complaint…” the first six months of my PhD have passed by far too quickly. As the date of departure for my first major data collection trip looms, I’m navigating the exciting but unnerving transition from the planning to action stages of my project. Fortunately the members of NERD club were on hand to very kindly listen to my ramblings and provide excellent ideas to add to and modify my research.

Here’s the plan so far…

Evolutionary studies have long-been concerned with understanding patterns of variation in morphological diversity. Two aspects of morphological variation which attract particular interest are convergence – the independent evolution of similar morphologies in phylogenetically distant species – and disparity –the range or significance of morphology in a given sample of organisms.

Morphological variation among tenrecs is particularly interesting – they appear to be both disparate from each other and convergent with other species such as hedgehogs, shrews, moles and otters. However, previous studies have neither quantified the degree of convergence or disparity among tenrecs nor attempted to identify reasons for the occurrence of these patterns. My aim is to fill these significant gaps in our understanding of the evolution of such a fascinating mammalian group.

I work with morphometric data compiled from museum collections of tenrecs and the mammals which they convergently resemble (my data collection involves traveling to museums in London, Washington DC, New York and Boston – oh the trials of PhD life!) I use calipers to take linear measurements and also photograph the species’ skulls and limbs. I use geometric morphometric techniques (this article is a great introduction to the murky world of morphometrics) to statistically analyse the degree of morphological (dis)similarity among tenrecs and other species.

I will plot the morphometric data from my species in a “morphospace”, something similar to Brusatte et al.’s 2008 paper on dinosaur morphology. This graphical interpretation will be useful for measuring both convergence among tenrecs and other species and disparity within tenrecs.

In morphospace plots, morphologically similar species sit closer together than dissimilar species. However, from a convergent evolution perspective these patterns are only interesting if morphologically close species are also phylogenetically distant. I will combine and modify existing approaches (e.g. Stayton 2008 and Muschick et al., 2012) to quantify the amount of convergence among tenrecs and other species and also determine whether tenrecs have evolved a higher degree of convergence than expected by random chance. Similarly, if tenrecs are significantly disparate from each other I expect that the range and variance of their morphological variation will be both greater than random evolution models and also significantly different from their nearest sister taxa, the Golden Moles (e.g. Harmon et al., 2003).

Many texts claim that convergent phenotypes evolve in animals that fill similar ecological niches. However, morphological and ecological convergences don’t necessarily go hand in hand so, while this idea is certainly very plausible in tenrecs, it is important to test the assumption. Fortunately relevant data on physical habitat characteristics, species range maps, life history traits and overlaps with potential competitors and predators are readily available from a range of sources (e.g. PanTheria, LANDSAT and the IUCN) so I can model the ecological similarities among tenrecs and other species. It will be very interesting to determine whether morphological convergence and ecological similarities truly correlate.

So that’s my plan for at least the next six months or so. Interspersed with working in major museum collections while taking a break to tap dance in a parade down Constitution Avenue in Washington DC, I think there are interesting times ahead.

Author

Sive Finlay: sfinlay[at]tcd.ie

Photo credits

http://www.digimorph.org/specimens/Hemicentetes_semispinosus/body/

21/11/2012

Tenrec tales

Tenrecs are one of the most interesting and fascinating mammal groups yet many people have never heard of them. They are one of only four mammalian groups to have colonised Madagascar, a land filled with evolutionary curiosities.

Tenrecs are a striking example of convergent evolution. From a single colonising ancestor, tenrecs have evolved into incredibly diverse species which resemble moles, shrews, hedgehogs and even otters! Contrary to appearances, tenrecs’ closest relatives are actually the golden moles and elephant shrews (Chrysochloridae). However, physical convergences are so strong that early taxonomists didn’t recognise tenrecs as being closely related to each other, an easy mistake to make when you look at this picture from Richard Dawkin’s 1996 book “Climbing Mount Improbable”.

Convergent evolution in tenrecs. The Algerian hedgehog, Erinaceus algirus (a), is a close cousin of the shrew hedgehog, Neotetracus sinensis (b). The greater hedgehog tenrec, Setifer setosus (c), is a close cousin of the long-tailed tenrec, Microgale melanorrhachis (d)

In addition to being great species for studying convergent evolution, the tenrec family includes a whole host of quirky traits. For example, the common tenrec (Tenrec ecaudatus), an animal which is only around 30 cm and 2kg, holds the record for the largest litter size of any mammal at an astounding 32 babies!

My personal favourite tenrec oddity is the unusual means of communication found in the lowland streaked tenrecs (Hemicentetes semispinosus). These cute critters are covered in spiny quills, a special set of which are used as a stridulating organ. Reminiscent of grasshoppers or crickets and uniquely among mammals, these tenrecs rub the quills together to produce sound which then allows them to keep in contact with their family group. This clip from the David Attenborough BBC series on Madagascar shows the stridulating tenrecs in action.

In short, tenrecs are an awesome family filled with evolutionary oddities yet they remain relatively understudied and poorly understood.

In my PhD work, I’m particularly interested in measuring the extent of convergent evolution in tenrecs and figuring out the reasons why they have evolved to be so similar to unrelated species. I’m also intrigued by early behavioural experiments which showed that 3 species of tenrec use echolocation. I want to test whether other tenrec species also echolocate and hopefully link this behavioural convergence to genetic similarities in “echolocating genes” which are conserved in whales and bats.

In the meantime, a charming children’s book gives the perfect excuse for some light, PhD-related extra reading!

Author

Sive Finlay: sfinlay[at]tcd.ie

Photo credits

wikimedia commons

Richard Dawkins