Website has moved!

26 01 2014

New URL: bioteaching.com. New RSS feed: http://bioteaching.com/feed/

Update your bookmarks and feeds as necessary. You can also get updates from Facebook and Twitter (latter still needs to be filled, I just activated it now). There will be no more updates on here!

So, why this change? This blog has basically outgrown the confines of the free, default WordPress. The archive is huge and ungainly to go through. While I may not be active anymore due to meatspace time constraints*, I do want all the information accumulated in here to be easily accessible. Moving to my own domain also opens up some monetisation options. Also, I get to have one more web design example to pad my CV with.

The new website does have a few ends to tie up, but is fully functional. The main page features the 6 latest big posts. The main menu on the left has the complete, sorted archive. Every category is clickable to get a listing of all the articles in that category. There is also a News section, the news being new books, papers, sales, etc. The top menu has the usual About sections, as well as a random post button for the bored reader. The bottom has subscription options and the donate button.

In the transition, all comments from here disappeared. I apologise to all commenters, it was a necessary sacrifice. The new comments sections run entirely on Facebook. It was an executive decision by me to have it that way. Those of you not on Facebook, I apologise… but I have had unsavoury commenters here before (read: creationists and associated stupids), so I’m hoping that a lack of anonymity will keep them away and save me from the trouble of moderating. It will also drive more traffic, and allow for a more personal experience.

Non-urgent things still to do:

  • Integrate an Amazon bookstore.
  • Make all articles downloadable as PDFs.
  • Change all internal links to the new site, instead of linking back to this one.
  • Edit lectures and long articles to make linkable sections, to save a reader the trouble of scrolling and skimming.

Please, if you find any bugs or would like to recommend changes to the look, let me know. Feedback from mobile users is appreciated – I’m too old-fashioned for web-surfing tablets and phones and other touchythingies, so I have no idea how it looks like on your tiny screens and deficient browsers.

*: My real life simply does not involve any science anymore, since the perpetual lack of funding and chronic unemployment has made me fed up with the whole enterprise, although my dream still is to become a tenured professor studying esoteric subjects nobody but me cares about. My future plans now involve the creation of some creative arts businesses. When they make me comfortably rich, I will get back to being a full-time scientist.

Regardless, I still do a lot of science communication and lecturing and mentoring whenever I am asked to do so – nothing will take away my passion for my subjects. More importantly, I will always constantly update the 30+ GBs of powerpoints I’ve prepared in my life and add to the 130000+ full-text papers in my database. So, while the blog is not very active at all, I will try to write stuff up whenever I have free time. It may well be that the new site will consist mostly of new book and paper announcements.





Selection of BioScience articles, open access for limited time

14 01 2014

The entire archive of the journal BioScience is going open access until the end of the February. This is one of my favourite journals, and I encourage you all to go through its archives. Here, I will link to several articles I like from 2008 to the latest issue. Keep in mind that I am not linking to the copious amounts of editorials, book reviews, and personal viewpoint articles that are one of the main attractions of the journal, so do go through the archives yourself.

Because there are a lot of articles, I have split them by rough topic. Use your browser’s search to jump to the section you’re interested in by searching for the number code. Links go to the HTML full text, PDFs available at the link. Apologies to authors for not including full citations, just the titles – I don’t have time to update my database to make new links to Oxford Journals insteads of BioOne or JStor (the open access is available only on Oxford Journals).

  • 01. Zoology
  • 02. Human Biology
  • 03. Evolution
  • 04. Historical Geology
  • 05. Ecology
  • 06. Environmental
  • 07. Botany
  • 08. Microbiology
  • 09. History
  • 10. Philosophy
  • 11. Pedagogy
  • 12. Science in the Media
  • 13. Scientific Culture

01. Zoology

02. Human Biology

03. Evolution

04. Historical Geology

05. Ecology

06. Environmental

07. Botany

08. Microbiology

09. History

10. Philosophy

11. Pedagogy

12. Science in the Media

13. Scientific Culture





The Twisted-Wing Parasites (Insecta: Strepsiptera)

3 01 2014

Source: Grimaldi & Engel (2005)

Morphology of adult male Strepsiptera. Source: Grimaldi & Engel (2005)

The Strepsiptera, commonly called twisted-wing parasites, are an enigmatic order of obligately parasitic insects discovered by the “founder of entomology”, William Kirby, and characterised by him in Kirby (1813). Unrelated, this paper also contains the first mention of another order of insect, the Trichoptera (caddisflies). There are over 600 Recent Strepsiptera species in 10 families, according to Kathirithamby’s database, and this is most likely a tremendous underestimation. Most strepsipterans are grouped together in the Stylopidia, which includes all strepsipterans besides fossil-only families and the basal Mengenellidae (Pohl & Beutel, 2005).

It’s very difficult to find them out and about in the field. Your best chance is to find an infected host and dissect the female out, or leave it in there and wait for the males to show up. Adult males range in size between 1-5 mm (largest up to 30 mm). They are recognisable by their possessing only one pair of hind wings; the male’s front wings are reduced to flight balancing organs, as seen in the detail above. Females tend to be paedogenic, resembling larvae: wingless and spending their entire lifespan as internal parasites of other insects, with the major exception being females of the Mengenellidae family, which are free-living as adults, presumably the state representative of the ancestor of the Strepsiptera (Pohl & Beutel, 2005).

Triungulin larva of Mengenilla chobauti. Source:

Triungulin larva of Mengenilla chobauti. Source: Osswald et al. (2010)

The larvae of strepsipterans count as among the smallest animals known, especially the first instar larvae, dubbed the triungulin larvae: they range between 80 – 850 µm (Beutel et al., 2005); for comparison, the typical Amoeba is around 600 µm. Everything in them is geared to allow them to enter their hosts: they have colour vision (Kirkpatrick, 1937), a jumping ability, and pads on their feet to stick to the host (Pohl & Beutel, 2004). With such a small size, you might think they have a tiny brain, but in fact, they invest so much in their brain that the 200 µm larva of Mengenilla chobauti has a brain that is larger than its head and extending into the prothorax – it takes up 5% of the body volume (Beutel et al., 2005). That’s a much better percentage than humans!

Host specificity of major Strepsiptera families. Source: Kathirithamby (2009)

Host specificity of major Strepsiptera families. Source: Kathirithamby (2009)

Hosts include silverfish, crickets, planthoppers, hymenopterans, cockroaches and mantises, flies, and caddisflies. As the diagram above shows, there is a degree of host specificity at the family level. Once the triungulin finds and enters the larval host, it will go through three more stages as a larva, staying inside the host through its entire life cycle (Kathirithamby, 2009). An infected host is referred to as being stylopised, and the main symptom is infertility, including by extreme reduction or disappearance of the host’s genitals. In remarkable cases of coevolution, some strepsipterans manage to avoid any reaction from the immune system of their hosts by making a house out of the tissue of their hosts (Kathirithamby et al., 2003). Interestingly, it could be that they also induce behavioural changes in their hosts: parasitised Polistes dominulus wasps leave their colonies and aggregate together, behaving more like gynes than workers (Hughes et al., 2004).

Exemplary developmental cycles of Strepsiptera. Source: Kathirithamby (2009)

Exemplary developmental cycles of Strepsiptera. Source: Kathirithamby (2009)

The developmental cycle of Strepsiptera is not very well known. Two summaries are presented above, and they show how variable their cycle can be. If you’re interested in this aspect of the strepsipterans, you need to get Kathirithamby (2009), the most comprehensive review of strepsipteran parasitism I know of, and the source of several stolen diagrams in this post. The general plan goes like this:

  • The larvae attack and grow in the hosts.

  • Females remain in the host. Upon reaching maturity, they extend their cephalothorax (fused head and thorax) to the outside.

Males emerge from the hosts and have to use their up to six hours of adult lifespan to find and mate with the females.

Examplary life cycle of a strepsipteran species. Source: Kathirithamby (2009)

Examplary life cycle of a strepsipteran species. Source: Kathirithamby (2009)

As an example of how weird their parasitism can be, look at the diagram above, or consider the myrmecolacid Caenocholax fenyesi, in which males and females have different hosts: males infect ants, females infect crickets (Kathirithamby & Johnston, 2004).

Head of Mengenilla moldrzyki. Source:

Head of Mengenilla moldrzyki. Source: Pohl et al. (2012)

The life of the adult male is geared towards finding a female to mate with, which their well-developed sense organs can take care of (Beutel & Pohl, 2006). As can be seen above, their antennae are shaped rather like antlers, allowing them to sense more than simple antennae. The antennae are also covered in sensillae. Their compound eyes are relatively large, and have a unique structure. There are around 150 lenses in each. Each lens has its own independent retina that is sampled by a spate of photoreceptors (Buschbeck et al., 1999). Adult males also have microtrichia (small hairs) on the bottom of their legs to grab on to the host/female for mating (Pohl & Beutel, 2004)

The male’s quest is helped by the female releasing pheromones through Nassonow’s gland in the cephalothorax (Dallai et al., 2004).

Stylops melittae female parasitising an Andrena vaga bee. Source: Soon et al. (2011)

Stylops melittae female parasitising an Andrena vaga bee. Source: Soon et al. (2011)

The male strepsipteran genital apparatus is highly simplified. Unlike most holometabolans, strepsipteran males do not use spermatophores, instead having a sperm pump to transfer liquid sperm to the females (Kinzelbach, 1971). Only Diptera, Mecoptera, and Siphonaptera have the same condition, although it evolved separately in the Strepsiptera. The female is buried in the host, with her cephalothorax sticking out for the male to enjoy himself, as pointed out by the red arrow in the picture above. That’s right, they mate while the female is still in the host, like a sexually mature human male baby going into a delivery room and mating with a female baby as it’s coming out of the vagina.

In the Stylopidia there is a brood canal in the cephalothorax, but in the basal Mengenellidae, the female genitals are reduced to practical non-existence, so the male has to stab her and ejaculate, a mating method known as traumatic insemination. Sperm travels into the female, which has cells that engulfs it (Beani et al., 2005). Fertilisation occurs and several weeks later, the female gives birth to live young free to infect unparasitised hosts when they exit the host through the female’s brood canal.

Protoxenus janzeni (Protoxenidae). Source: Pohl et al. (2005)

Protoxenus janzeni (Protoxenidae). Source: Pohl et al. (2005)

Despite their tiny size and cryptic lifestyle, Strepsiptera do have a fossil record, including a parasitised halictid bee in Dominican amber (Poinar, 2004). The oldest specimen known comes from the Burmese amber (Grimaldi & Engel, 2005), and Pohl et al. (2005) describe a very basal Baltic amber strepsipteran, pictured above, that has both tell-tale strepsipteran features as well as more plesiomorphic characters, making it an important fossil for the study of the evolutionary history of strepsipterans.

Strepsipterans are mysterious for many reasons, but the most historically wild debate concerns their phylogenetic placement, so much so that we refer to it as the “Strepsiptera Problem” (Kristensen, 1981), and it was often used as a way to pit molecular phylogenetic methodologies against each other, especially in molecular phylogenetics where the variable substitution rates and shifts in base composition in the genes used for phylogenetic reconstruction provide great examples of long branch attraction (Huelsenbeck, 1997). The very first total evidence analysis combining morphological and molecular data conducted for elucidating insect phylogeny was done in order to solve the Problem (Whiting et al., 1997).

In his major reviews on insect classification, Kristensen even had doubts as to whether they could be placed in the Holometabola, the insects that undergo a complete metamorphosis in their life cycle (think caterpillar – butterfly, or maggot – fly) (Kristensen, 1981), but these doubts are now quelled. In his groundbreaking 1953 article, Willi Hennig left them floating free as holometabolans, not having any leads to associate them with any sister group (Hennig, 1953).

Within the Holometabola, the Strepsiptera are sometimes allied to the Diptera (flies). Lamarck (1816) placed them as such, a hypothesis later reprised by early molecular phylogenies (Whiting et al., 1997) and dubbed the “Halteria” hypothesis due to the major morphological commonality between Strepsiptera and Diptera being a reduced pair of wings. In Diptera, the hind wings are reduced to form the characteristic halteres, balancing organs for flight. The reduced forewings of male Strepsiptera have the same function (Pix et al., 1993). The fact that the Strepsiptera have reduced forewings and the Diptera reduced hindwings was trumpeted as a perfect example of a homeotic mutation in which master developmental control genes, Hox genes, got mutated, causing the second and third thoracic segments to be flipped around in the Strepsiptera – in effect saying that the halteres and reduced forewings are homologous, even though they are on different segments (Whiting & Wheeler, 1994). The precise mutation enabling this supposed reversal has not been found, and these molecular analyses are not very reliable anyway: they were done using ribosomal sequences, and a major problem for insect molecular phylogenetics is that these sequences evolve too fast to be useful (Hwang et al., 1998). Another feature is the presence of a sperm pump (Whiting, 1998), but the lack of structural homologies makes this unconvincing (Kristensen, 1999).

Another hypothesis states that the Strepsiptera are a weird cucujiform beetle group (Crowson, 1960), but this is highly unlikely since any traits they share also evolved convergently in other beetle groups, so the evidence for it is solid at all.

The general feeling for a long time was that the Strepsiptera are close to the Coleoptera, the beetles (Hinton, 1958), and the hypothesis that they are the sister group to the Coleoptera is currently the most supported (Niehuis et al., 2012). Crowson (1960) also suggested that the Strepsiptera are a beetle group, but this is not viewed as viable. The bulk of the morphological data supports a Strepsiptera+Coleoptera grouping, especially when it comes to hindwing venation (Kukalová-Peck & Lawrence, 2004). The main functional argument is that both use their hind wings for flight. Both of them have lost their dorsal pulsatile organs, as well as several muscles in the mesothorax (Beutel & Haas, 2000). As in beetles, the ventral segments of a strepsipteran are more sclerotised than the dorsal segments. There are several recent molecular phylogenies that also support this hypothesis, e.g. Ishiwata et al. (2011) or Longhorn et al. (2010).

Evolution of the Strepsiptera. Source:

Evolution of the Strepsiptera. Source: Pohl & Beutel (2008)

The main reason for all this confusion is the key trait of the Strepsiptera: their convoluted parasitism, with extreme sexual dimorphism. The unsteady molecular evolution rates make molecular phylogenetics tricky, and the parasitism makes morphological datasets difficult to assemble properly, since features are either reduced to oblivion (females) or possibly modified to an extent too large for reliable homologisation (males). What is clear is that the evolutionary success of the Strepsiptera was determined to a large part by the key novelty of having a completely endoparasitic female, as seen in the summary diagram above (Pohl & Beutel, 2008).

References:

Beani L, Giusti F, Mercati D, Lupetti P, Paccagnini E, Turillazi S & Dallai R. 2005. Mating of Xenos vesparum (Rossi) (Strepsiptera, Insecta) revisited. Journal of Morphology 265, 291-303.

Beutel RG & Haas F. 2000. Phylogenetic Relationships of the Suborders of Coleoptera (Insecta). Cladistics 16, 103-141.

Beutel RG & Pohl H. 2006. Head structures of males of Strepsiptera (Hexapoda) with emphasis on basal splitting events within the order. Journal of Morphology 267, 536-554.

Beutel RG, Pohl H & Hünefeld F. 2005. Strepsipteran brains and effects of miniaturization (Insecta). Arthropod Structure & Development 34, 301-313.

Buschbeck E, Ehmer B & Hoy R. 1999. Chunk Versus Point Sampling: Visual Imaging in a Small Insect. Science 286, 1178-1180.

Crowson RA. 1960. The Phylogeny of Coleoptera. Annual Review of Entomology 5, 111-134.

Dallai R, Lupetti P, Giusti F, Mercati D, Paccagnini E, Turillazzi S, Beani L & Kathirithamby J. 2004. Fine structure of the Nassonow’s gland in the neotenic endoparasitic of female Xenos vesparum (Rossi) (Strepsiptera, Insecta). Tissue and Cell 36, 211-220.

Grimaldi D & Engel MS. 2005. Evolution of the Insects.

Hennig W. 1953. Kritische Bemerkungen zum phylogenetischen System der Insekten. Beiträge zur Entomologie 3, 1-85.

Hinton HE. 1958. The Phylogeny of the Panorpoid Orders. Annual Review of Entomology 3, 181-206.

Huelsenbeck JP. 1997. Is the Felsenstein Zone a Fly Trap? Systematic Biology 46, 69-74.

Hughes DP, Kathirithamby J, Turillazi S & Beani L. 2004. Social wasps desert the colony and aggregate outside if parasitized: parasite manipulation? Behavioral Ecology 15, 1037-1046.

Hwang UW, Kim W, Tautz D & Friedrich M. 1998. Molecular Phylogenetics at the Felsenstein Zone: Approaching the Strepsiptera Problem Using 5.8S and 28S rDNA Sequences. Molecular Phylogenetics and Evolution 9, 470-480.

Ishiwata K, Sasaki G, Ogawa J, Miyata T & Su Z-H. 2011. Phylogenetic relationships among insect orders based on three nuclear protein-coding gene sequences. Molecular Phylogenetics and Evolution 58, 169-180.

Kathirithamby J. 2009. Host-Parasitoid Associations in Strepsiptera. Annual Review of Entomology 54, 227-249.

Kathirithamby J & Johnston JS. 2004. The discovery after 94 years of the elusive female of a myrmecolacid (Strepsiptera), and the cryptic species of Caenocholax fenyesi Pierce sensu lato. Proc. R. Soc. B 271, Supp 3, S5-S8.

Kathirithamby J & Henderickx H. 2008. First record of the Strepsiptera genus Caenocholax in Baltic amber with the description of a new species. Phegea 36, 149-156.

Kathirithamby J, Ross LD & Johnston JS. 2003. Masquerading as self? Endoparasitic Strepsiptera (Insecta) enclose themselves in host-derived epidermal bag. PNAS 100, 7655-7659.

Kinzelbach RK. 1971. Morphologische Befunde an Fächerflüglern und ihre phylogenetische Bedeutung. Zoologica 41, 1-256.

Kinzelbach R & Pohl H. 1994. The Fossil Strepsiptera (Insecta: Strepsiptera). Annals of the Entomological Society of America 87, 59-70.

Kirby W. 1813. VI. Strepsiptera, a new Order of Insects proposed; and the Characters of the Order, with those of its Genera, laid down. Transactions of the Linnean Society of London 11, 86-122.

Kirkpatrick TW. 1937. Colour vision in the triungulin larva of a strepsipteron (Corioxenox antestiae Blair). Proceedings of the Royal Entomological Society of London A 12, 40-44.

Kristensen NP. 1981. Phylogeny of Insect Orders. Annual Review of Entomology 26, 135-157.

Kristensen NP. 1999. Phylogeny of endopterygote insects, the most successful lineage of living organisms. European Journal of Entomology 96, 237-253.

Kukalová-Peck J & Lawrence JF. 2004. Relationships among coleopteran suborders and major endoneopteran lineages: Evidence from hind wing characters. European Journal of Entomology 101, 95-144.

Lamarck JB. 1816. Histoire Naturelle Des Animaux Sans Vertèbres […], Vol. 2.

Longhorn SJ, Pohl HW & Vogler AP. 2010. Ribosomal protein genes of holometabolan insects reject the Halteria, instead revealing a close affinity of Strepsiptera with Coleoptera. Molecular Phylogenetics and Evolution 55, 846-859.

Niehuis O, Hartig G, Grath S, Pohl H, Lehmann J, Tafer H, Donath A, Krauss V, Eisenhardt C, Hertel J, Petersen M, Mayer C, Meusemann K, Peters RS, Stadler PF, Beutel RG, Bornberg-Bauer E, McKenna DD & Misof B. 2012. Genomic and Morphological Evidence Converge to Resolve the Enigma of Strepsiptera. Current Biology 22, 1309-1313.

Osswald J, Pohl H & Beutel RG. 2010. Extremely miniaturised and highly complex: The thoracic morphology of the first instar larva of Mengenilla chobauti (Insecta, Strepsiptera). Arthropod Structure & Development 39, 287-304.

Pix W, Nalbach G & Zeil J. 1993. Strepsipteran forewings are haltere-like organs of equilibrium. Naturwissenschaften 80, 371-374.

Pohl H & Beutel RG. 2004. Fine structure of adhesive devices of Strepsiptera (Insecta). Arthropod Structure & Development 33, 31-43.

Pohl H & Beutel RG. 2005. The phylogeny of Strepsiptera (Hexapoda). Cladistics 21, 328-374.

Pohl H & Beutel RG. 2008. The evolution of Strepsiptera (Hexapoda). Zoology 111, 318-338.

Pohl H, Beutel RG & Kinzelbach R. 2005. Protoxenidae fam. nov. (Insecta, Strepsiptera) from Baltic amber — a ‘missing link’ in strepsipteran phylogeny. Zoologica Scripta 34, 57-69.

Poinar G. 2004. Evidence of parasitism by Strepsiptera in Dominican amber. BioControl 49, 239-244.

Proffitt F. 2005. Twisted Parasites From “Outer Space” Perplex Biologists. Science 307, 343.

Soon V, Kesküla T & Kurina O. 2011. Strepsiptera species in Estonia. Entomologica Fennica 22, 213-218.

Whiting MF. 1998. Phylogenetic position of the Strepsiptera: Review of molecular and morphological evidence. International Journal of Insect Morphology and Embryology 27, 53-60.

Whiting MF & Wheeler WC. 1994. Insect homeotic transformation. Nature 368, 696.

Whiting MF, Carpenter JC, Wheeler QD & Wheeler WC. 1997. The Strepsiptera Problem: Phylogeny of the Holometabolous Insect Orders Inferred from 18S and 28S Ribosomal DNA Sequences and Morphology. Systematic Biology 46, 1-68.





How I Teach Biology

5 12 2013

The trickiest challenge a biology teacher faces is having to balance the need to develop an intuitive, integrative understanding of biology in the student with the sheer amount of foundational rote memorisation needed in biology. A student who can memorise everything but can’t solve an unknown will not be a good biologist, but neither will the student who “gets it” but can’t memorise the basic information.

I often struggle with getting this across – I’m not good at memorisation, so I do tend to overemphasise the intuition aspect of biology. Nevertheless, I’ve converged on a set of teaching methodologies that I feel innoculate my students with the best of both worlds. I’m sure these are old hat for those of you with official pedagogical training, but most biologists who teach at university level don’t get that, and school teachers are often too burdened with the need to teach for standardised exams. Hopefully these will give you some ideas to improve your students’ knowledge and understanding of biology.

My most common method is to give my students problems to solve, either as open-ended essay questions or as mathematical ones. This tends to catch many students off guard, and they will often be lost, especially at the start of the course when they’re not used to you. The usual way of doing it is to give them the problem in the middle of the lesson time, after the lecturing is done. I solve it in front of them, so the solving of the problem constitutes half the lesson, and I will pepper every step of the way with explanations based on the previous lecturing I was doing. The students are encouraged to chime in and help me out. Eventually, you will find that student participation will outweigh yours. When that point in the lesson/course is reached, you can rest assured that the students feel very comfortable with the material you’re teaching. Accounting for shyness and other such psychological factors, this will also allow you to identify students who have problems with the material, so you can approach them after class.

In order for this to be effective though, you need to make sure that your lesson is planned out thoughtfully, and that the students can follow what you’re trying to say. I don’t just mean speech-wise, but also logic-wise. The transition to the problem solving part of the lesson should not be sudden, it should follow on organically from what you were saying before. A great way to do this is to incorporate some history in your lesson – talk about the topic and what we know of it, but leave out one critical component. Explain that critical component by going through the experiment and data from that one super-important analysis done several decades ago with your students, and then integrating it with what you said before. Ask them to fill the gaps in the reasoning and logic – it’s what we’re supposed to be doing as scientists.

Implicit in this approach is the need to deconstruct the topics that you’re teaching. Your students know how to read, they can get the textbook from the library, and if you just plagiarise the textbook, they will just not bother with you. As a teacher, you need to distill the textbook material down to the fundamental ideas, and work off of them. Use the textbook as a springboard, but don’t parrot it.

One thing I have tried with success is to tell the students to do this process themselves. This is what they usually have to do when they have to prepare a presentation for a seminar, but there’s no reason why they can’t be given a textbook chapter or a paper to read and summarise. However, the only way this works is if you provide copious amounts of feedback. Of course, this should go without saying, but I’ve known several teachers who don’t give any feedback to their students. Needless to say, these are horrible people who should be banned from teaching – feedback is extremely important to students, and I’m very steadfast in my commitment to it. I spend 20 minutes discussing exams after the students have finished writing them (better to do it when everything is still fresh in their minds), I annotate all answers, I keep my door open for personal discussion at all times (I once spent 4 hours with one student in my office, even ordered pizza for dinner to get through it all).

One thing I have learned through my giving of feedback is that sometimes, my approach of doing things open-endedly and with student participation backfires. In these cases, the solution isn’t to force-feed them a ton of facts in a meaty lecture. What I do instead is take the content and make it more digestible. Instead of presenting the entire table of facts, or go through it all with them, I throw away the table and show them a pretty, simplified chart. Instead of having a list of points, I’ll do a flowchart. If the students are not responding, that means what you’re telling them is flying too far above their heads for them to even be puzzled by it, so you will need to break everything down to smaller and more presentable pieces – highlight the title of your topic, show high-quality pictures and diagrams, use arrows, do practical demonstrations. Remember, they can always get the details from a textbook; your job is to put everything in the proper context.

In other words, put some extra effort into making your lesson appealing to everyone. Remember that while students come in many forms, there are some universal facts: they can all read, they know how to take initiative, they know where the library is. If you don’t make your lesson worth coming to either for extra knowledge or for more easily-accessible knowledge, you stand absolutely no chance against an “X For Dummies” book, or a Wikipedia page. Provide them with something they can get nowhere else – practical experience, a unique perspective, customised training – and you will have achieved all the goals your course should have, mainly creating students that love biology and whatever subfield you’re teaching.





Christmas book sales!

4 12 2013

I have done a monumental amount of book recommendations this year, but many of those books have obscene price tags. So I will also share any good publisher book sales I come across and give recommendations from them. This time, we have Columbia University Press, John Hopkins University Press, and Bloomsbury Publishing. Prices listed here are the discounted prices.

Use this code when checking out: GIFT

Use checkout code BRIPRO for: Bringing Fossils to Life: An Introduction to Paleobiology (Prothero; 2013; $67.50)

Use checkout code WHEMCG for: When the Invasion of Land Failed: The Legacy of the Devonian Extinctions (McGhee Jr.; 2013; $31.50)

Use this code when checking out: HDPD

Automatically discounted:





Carnival of Evolution #66 now up

3 12 2013

Hopefully looking at this Carnival edition will not have the same effect as looking at a Silent, because there’s some truly good stuff to read and you don’t want to forget them. Go!





Endocasts: A Superficial Look At Ancient Brains

1 12 2013

PhrenologyPixBack in the 19th century, a very popular neurological research program developed: phrenology. Its proponents posited that the brain is a collection of many organs, each organ leading to a specific personality trait. The diagram above is a phrenological one, and the phrenologist would feel up and measure the bumps on a person’s skulls. The logic was simple: if a person has a bump, then the brain region beneath the skull must be larger, and therefore whatever that region represented would be highly-manifested in that person. So, according to the chart above, the skull around my ear would be a great cavity because I’m not active, destructive, or very hungry. But I would have bumps around my eye because of my serial multilinguality and my obsession with order.

Needless to say, this is all pseudoscientific poppycock. Most importantly, the brain does not work that way – rarely are personality traits mappable to individual sections. The outside of the skull can be modified by muscular attachments (e.g. the jaw muscles) and by mechanical damage, but it does not reflect the state of the brain underneath it.

human-brain_1001_600x450

However, the brain can influence the inside of a skull. You all know what the outside of a human brain looks like: it’s a dense maze of grey matter grooves and ridges (sulci and gyri, respectively). This is the cerebral cortex.

If you look at the inside of a human braincase, you will see that the cerebral cortex’s torturous pattern is etched onto it. The reason why this happens is because the skull is made of bone, and bone is a living tissue that responds to local mechanical stimuli, such as the brain pushing up into it. The skull is too thick for these effects to be seen on its outside, but they are clear enough on the inside that they are even fossilised.

Vertebrate palaeontologists can take a fossil skull and fill it with latex rubber to make a mould. This is called an endocast, short for endocranial cast. Nowadays not even that is needed, you can just shove a skull in a CT scanner to get digital reconstructions. Very rarely, an endocast can be formed naturally when the corpse’s skull gets filled with mud or other fine sediment. Regardless of how you get an endocast, because the animal to whom it belonged had a brain in its skull, the mould might show the pattern of the outside of the brain, and palaeontologists can then use this to study palaeoneurology, a field founded by Ralph Holloway, a household name for anyone even remotely interested in the evolution of human brains.

endocast

Human endocast. Source: Holloway (2010)

The type and amount of information that can be gleaned is limited, even if one gets a perfect endocast. Compare the endocast up there with the brain picture a few paragraphs ago – you don’t really get that much of the cerebral cortex preserved, and nothing at all from the inside of the brain. Nonetheless, endocasts provide invaluable glimpses into the evolution and development of brains, and thus indirectly into the behavioural biology of animals, and they remain the only direct evidence for how ancient brains looked like. The foundational logic behind palaeoneurology is that the amount fo neural tissue present ina certain area correlates positively with the importance of that area’s fuinction. So if an animal’s endocast shows a very large visual lobe, then vision must have been highly-sophisticated in that animal.

The study of endocasts began with fossil humans, and so endocasts are critical in palaeoanthropology. One of the most important fossils ever discovered, the Taung Child, is notable both for its facial features and for the impeccably preserved endocast, painstakingly recovered from rock by Raymond Dart using his wife’s knitting needles in 1924. Topics ranging as varied as the evolution of language and the taxonomic status of Homo floresiensis are informed by endocast studies. For example, H. floresiensis, the “hobbit” human found on the Flores Island, had long been at the center of a controversy about whether it’s a true insular dwarf species derived from Homo erectus, or whether it’s a regular H. erectus suffering from microcephaly. Endocasts were used in the elucidation of its true status; see the exchange between Martin et al. (2006) and Falk et al. (2006).

As for the evolution of human language, endocasts are valuable in revealing the taxonomic distribution of Broca’s area, a region of the cerebral cortex involved in facial coordnation and in language processing. It appears to have been rudimentarily present in all Homo species, and some have even argued for it being found in australopithecines. In either case, what that tells us is that the potential capacity for language has long been present in humans, not something that appeared out of thin air in Homo sapiens.

For scientists interested in mammals, it has been known for a long time that since the mammalian brain pretty much fills up all the braincase, endocasts provide a very faithful representation of the relative sizes of different brain regions and can thus deliver otherwise unknowable information on the evolution of brains. For example, investigations of the endocasts of many early primates reveal a small brain with relatively large olfactory bulbs, hinting at early primates being highly-dependent on their sense of smell, with the visual centers becoming more prominent as primates evolved further (Silcox et al., 2009, 2010).

Mammal brains are probably the most exciting to study due to the unique presence of the isocortex, the result of an encephalisation process. The first sign of an isocortex can be found in the endocasts of early mammals (Luo et al., 2001), but not in the endocasts of theraspid ancestors of mammals (Kemp, 1982).

archaeopteryx_brain

Endocast of Archaeopteryx. Source: Alonso et al. (2004)

Of course, endocasts are found in all craniates, so they can be useful for any group with a skull. Dinosaur palaeontologists are fond of using them to find out whatever they can about their animals’s brains. The most popualr dinosaur endocast is Stegosaurus‘s laughably ridiculous 60cm³ brain. But there are more serious dinosaur endocast facts that can be thrown around. For example, Rogers (1999) made a virtual endocast of an allosaur and found its brain was arranged more like a crocodile’s than a bird’s, a similarity since corroborated by several other dinosaur endocasts – although as you move into the close avian relatives, like the Archaeopteryx whose endocast is imaged above, the brain becomes bird-like (Alonso et al., 2004). Carnivorous dinosaurs also tend to have relatively large olfactory bulbs, which can be useful for both detecting prey (predators) and decaying carcasses (scavengers).

shuyu

Reconstructed brain of Shuyu zhejiangensis. Source: Gai et al. (2011)

The picture above shows the virtual endocast of Shuyu zhejiangensis, an early galeaspid fish from the Silurian of China. In other words, you are looking at what the brain of a 430 million year old fish looked like. If that’s not an awesome testament to the prowess of modern palaeontology, I don’t know what is.

As I said before, endocasts are not perfect. They are not casts of the brain, but merely of the impression made by the outermost layer of the brain on the inside of the skull. Endocasts do not hold a candle to studies of actual brains. However, what I have tried to show in this post is that even with a fossil record subject to unavoidable, uncountable losses, there are ways to gain an otherwise unattainable direct look into the evolution of an unfossilisable organ like the brain.

References:

Alonso PD, Milner AC, Ketcham RA, Cookson MJ & Rowe TB. 2004. The avian nature of the brain and inner ear of Archaeopteryx. Nature 430, 666-669.

Falk D, Hildebolt C, Smith K, Morwood MJ, Sutikna T, Jatmiko, Saptomo EW, Bundsen B & Prior F. 2006. Response to Comment on “The Brain of LB1, Homo floresiensis. Science 312, 999.

Gai Z, Donoghue PCJ, Zhu M, Janvier P & Stampanoni M. 2011. Fossil jawless fish from China foreshadows early jawed vertebrate anatomy. Nature 476, 324-327.

Holloway RL. 2010. Human Brain Endocasts, Taung, and the LB1 Hobbit Brain. In: Broadfield D, Yuan M, Schick K & Toth N (eds.). The Human Brain Evolving: Paleoneurological Studies in Honor of Ralph L. Holloway.

Kemp TS. 1982. Mammal-Like Reptiles and the Origin of Mammals.

Luo Z-X, Crompton AW & Sun A-L. 2001. A New Mammaliaform from the Early Jurassic and Evolution of Mammalian Characteristics. Science 292, 1535-1540.

Martin RD, MacLarnon AM, Phillips JL, Dussubleux L, Williams PR & Dobyns WB. 2006. Comment on “The Brain of LB1, Homo floresiensis. Science 312, 999.

Rogers SW. 1999. Allosaurus, crocodiles, and birds: Evolutionary clues from spiral computed tomography of an endocast. The Anatomical Record 257, 162-173.

Silcox MT, Dalmyn CK & Bloch JI. 2009. Virtual endocast of Ignacius graybullianus (Paromomyidae, Primates) and brain evolution in early primates. PNAS 106, 10987-10992.

Silco MT, Benham AE & Bloch JI. 2010. Endocasts of Microsyops (Microsyopidae, Primates) and the evolution of the brain in primitive primates. Journal of Human Evolution 58, 505-521.








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