Biopedia

Natural selection is not just one phenomenon, but can be spliced into different types depending on what its action results in. Today’s episode will examine disruptive selection, stabilising selection and directional selection; what they are, what their effects on populations are and some examples we see in the natural world.

Sources for this episode: 1) Allaby, M., (2020), A Dictionary of Zoology (Oxford Quick Reference), 5th edition, Oxford, Oxford University Press. 2) Cain, M. L., Bowman, W. D. and Hacker, S. D. (2011), Ecology (Second Edition). Sunderland, Massachusetts, Sinauer Associated Ltd 3) Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited. 4) Hine, R. (2019), A Dictionary of Biology (Oxford Quick Reference), 8th edition, Oxford, Oxford University Press. 5) Thain, M. and Hickman, M. (2014), Dictionary of Biology (Eleventh Edition). London: Penguin Books Ltd.

Cultured cells are useful, but have their limitations. For instance, B cells- white blood cells which produce antibodies- have a limited lifespan in vitro, meaning their use for making antibodies commercially is limited. The solution to this is the topic of today’s episode: the hybridoma.

Sources for this episode: 1) Fullick, A. and Coates, A. (ed. Ryan, L.) (2016), GCSE AQA Biology (Third Edition). Oxford: Oxford University Press. 2) Madigan, M. T., Martinko, J. M., Dunlap, P. V. and Clark, D. P. (2009), Brock Biology of Microorganisms (12th Edition, International Edition), San Francisco: Pearson Benjamin Cummings Ltd. 3) Thain, M. and Hickman, M. (2014), Dictionary of Biology (Eleventh Edition). London: Penguin Books Ltd.

Perhaps you’ve never thought much about bonsai trees. However, their existence does raise some biologically relevant questions. For instance, how is a bonsai tree created? Moreover, as we’ll see in today’s episode, they have also been considered as a tool in conservation…

Sources for this episode: 1) Cain, M. L., Bowman, W. D. and Hacker, S. D. (2011), Ecology (Second Edition). Sunderland, Massachusetts, Sinauer Associated Ltd. 2) The Editors, Encyclopaedia Britannica (2021), Bonsai (online) [Accessed 15/06/2021, 18/08/2021 and 19/08/2021]. 3) Joshi, A. R. and Joshi, K. (2009), Bonsai: A Technique for Conservation of Species, Bonsai and Conservation 1(1): 3-4. 4) Perrott, R., Synge, P. M. and Herklots, G. A. C., Encyclopaedia Britannica (2020), Gardening (online) [Accessed 18/08/2021]. 5) Wyman, D. (1954), Japanese dwarfed trees. Arnoldia 14(1): 1-7. 6) Author unknown, RHS Gardening (date unknown), Bonsai (online) [Accessed 15/06/2021 and 18/08/2021].

We’re going to explore a particular kind of hybridisation today- the kind that produces grolar bears. As the name might suggest, this refers to the offspring of a grizzly bear and a polar bear. Its existence- and that of cases like it- also allow us to put something called the biological species concept under scrutiny…

Sources for this episode: 1) Cain, M. L., Bowman, W. D. and Hacker, S. D. (2011), Ecology (Second Edition). Sunderland, Massachusetts, Sinauer Associated Ltd. 2) Callaway, E., New Scientist (2010), Neanderthal genome reveals interbreeding with humans (online) [Accessed 03/08/2021]. 3) Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited. 4) Cooke, F., Dingle, H., Hutchinson, S., McKay, G., Schodde, R., Tait, N. and Vogt, R. (2008), The Encyclopedia of Animals: A Complete Visual Guide (p.370). Sydney: Weldon Owen Pty Ltd. 5) Wei-Haas, M., National Geographic (2018), Ancient Girl’s Parents Were Two Different Human Species (online) [Accessed 03/08/2021]. 6) Author unknown, BBC Newsround (2021), Have you ever heard of a ‘pizzly’ bear? (online) [Accessed 02/08/2021]. 7) Author unknown, Understanding Evolution (berkeley.edu), (date unknown), Misconceptions about evolution (online) [Accessed 03/08/2021].8) Author unknown, WWF (date unknown), Top 10 facts about polar bears (online) [Accessed 03/08/2021].

Back in episode 49, I mentioned the Great American Interchange, which took place three million years ago when North America and South America collided and were connected by the isthmus of Panama. However, I largely glossed over it as it was only of tangential relevance to the topic of the Wallace Line. So, today, let’s correct that oversight and explore the Great American Interchange…

Sources for this episode: 1) Domingo, L., Tomassini, R. L., Montalvo, C. I., Sanz-Pérez, D. and Alberdi, M. T. (2020), The Great American Biotic Interchange revisited: a new perspective from the stable isotope record of Argentine Pampas fossil mammals, Scientific Reports 10(1): 1608. 2) Marshall, L. G., Webb, S. D., Sepkoski, J. J. and Raup, D. M. (1982), Mammalian Evolution and the Great American Interchange, Science 215(4538): 1351-1357. 3) Weir, J. T., Bermingham, E. and Schluter, D. (2009), The Great American Biotic Interchange in birds, Proceedings of the National Academy of Sciences 106(51): 21737-21742. 4) Author unknown, Wikipedia (date unknown), Great American Interchange (online) [Accessed 15/06/2021 and 13/08/2021]. 5) Author unknown, Wikipedia (date unknown), δ13C (online) [Accessed 10/08/2021]. 6) Author unknown, Wikipedia (date unknown), δ18O (online) [Accessed 10/08/2021].

Photosynthesis has proven a useful tool in life’s arsenal, but it isn’t perfect. This is because one of its enzymes- RuBisCo for short- is not equipped to deal with our oxygenated world and as such sometimes creates toxic by-products which the organism then has to expend energy to deal with. However, some plants have evolved strategies to deal with this issue. Instead of simply working with vanilla-flavoured C3 photosynthesis, they have switched to alternative strategies known as C4 or CAM photosynthesis…

Sources for this episode: 1) Cain, M. L., Bowman, W. D. and Hacker, S. D. (2011), Ecology (Second Edition). Sunderland, Massachusetts, Sinauer Associated Ltd. 2) Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited. 3) Hirst, K. K., ThoughtCo (Updated 13/11/2019), Adaptations to Climate Change in C3, C4 and CAM Plants (online) [Accessed 27/07/2021]. 4) Thain, M. and Hickman, M. (2014), Dictionary of Biology (Eleventh Edition). London: Penguin Books Ltd.

Altruism- or actions by organisms which ultimately provide a benefit to other organisms- have been puzzling evolutionary scientists since Darwin’s time. As such, attempts have been made to explain how this phenomenon comes about. One of these explanations is the subject of today’s episode- kin selection and Hamilton’s rule. Now, I am not going to go into the arguments and evidence for and against it, which is probably a topic for future episodes. For now, it’s probably best to say that my previous studies on the topic have taught me that there is a tangible divide within biology on this topic…

Sources for this episode: 1) Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited. 2) Dugatkin, L. A. (2007), Inclusive Fitness Theory from Darwin to Hamilton, Genetics 176(3): 1375- 1380. 3) The Editors, Encyclopaedia Britannica (2018), Kin selection (online) [Accessed 18/06/2021]. 4) Herron, J. C. and Freeman, S. (2015), Evolutionary Analysis (Fifth Edition, Global Edition). Harlow: Pearson Education Limited. 5) Oshaka, S., OUPblog (Oxford University Press, 2015), Kin selection, group selection and altruism: a controversy without end? (online) [Accessed 17/06/2021]. 6) Thain, M. and Hickman, M. (2014), Dictionary of Biology (Eleventh Edition). London: Penguin Books Ltd.

If Alfred Russell Wallace (1823- 1913) is thought of at all, he is an after-thought to his far more famous counterpart Charles Darwin and the theory of natural selection. However,he has also had an impact in other fields. Today, we’ll be exploring the Wallace Line and Wallace’s contribution to zoogeography.

Sources for this episode: 1) Cain, M. L., Bowman, W. D. and Hacker, S. D. (2011), Ecology (Second Edition). Sunderland, Massachusetts, Sinauer Associated Ltd. 2) Camerini, J. R., Encyclopaedia Britannica (2021), Alfred Russell Wallace (online) [Accessed 10/06/2021]. 3) The Editors, Encyclopaedia Britannica (2019), Wallace Line (online) [Accessed 10/06/2021]. 4) Marshall, M., New Scientist (2021), The other humans: The emerging story of the mysterious Denisovans (online) [Accessed 11/06/2021]. 5) Scoville, H., ThoughtCo (2020), What Is the Wallace Line? (online) [Accessed 10/06/2021]. 6) Smithsonian Tropical Research Institute, Phys (2016), Recent connection between North and South America reaffirmed (online) [Accessed 10/06/2021]. 7) Tang, C. M., Encyclopaedia Britannica (2018), Tethys Sea (online) [Accessed 11/06/2021]. 8) Thain, M. and Hickman, M. (2014), Dictionary of Biology (Eleventh Edition). London: Penguin Books Ltd. 9) University of Adelaide, Phys (2013), Mysterious ancient human crossed Wallace’s Line (online) [Accessed 10/06/2021]. 10) Author unknown, Understanding Evolution (Berkeley, date unknown), Biogeography: Wallace and Wegener (online) [Accessed 11/06/2021]. 11) Author unknown, Wikipedia (date unknown), Wallacea (online) [Accessed 11/06/2021].

It’s a well-known fact that humans have 23 pairs of chromosomes- 46 chromosomes in total. However, chimpanzees have 48 chromosomes, as do the other ‘great apes’. Why is this? Well, it centres around human chromosome 2.

Sources for this episode: 1) Fullick A., Locke, J. and Bircher, P. (2015), A Level Biology for OCR A. Oxford: Oxford University Press. This is where I originally learned the chromosome numbers of horses and donkeys; however, I don’t have access to this book at the moment due to COVID. For an alternative source, see: Rodriguez, M., Understanding Genetics, The Tech Interactive (2007), Chimeras, Mosaics, and Other Fun Stuff: Why can’t mules breed? I understand that a horse and a donkey make a mule but why can’t 2 mules have a baby mule? (online) [Accessed 06/06/2021]. 2) IJdo, J.W., Baldini, A., Ward, D. C., Reeders S. T. and Wells, R. A. (1991) Origin of human chromosome 2: an ancestral telomere-telomere fusion, Proceedings of the National Academy of Sciences of the United States of America 88(20): 9051-9055. 3) Willey, J. M., Sherwood, L. M. And Woolverton, C. J. (2017), Prescott’s Microbiology, 10th edition (International Edition). New York, McGraw-Hill Education. 4) Young, W. J., Merz, T., Ferguson-Smith, M. A. and Johnston, A. W. (1960), Chromosome Number of the Chimpanzee, Pan troglodytes, Science 131(3414): 1672-1673. 5) Author unknown, Wikipedia (date unknown), Chimpanzee genome project (online) [Accessed 02/06/2021]. 6) Author unknown, WWF (date unknown) Great apes (online) [Accessed 06/06/2021].

Moving away from previous topics somewhat, we’re going to dive back into ecological theory and discuss the concept of sibling species. What is a sibling species? Well, they’re species which appear broadly very similar, but do have some differences when you get up close. As we’ll see in today’s episode, sibling species are essentially part of the process of speciation..

Sources for this episode: 1) Eisenmann, E., Amadon, D., Banks, R. C., Blake, E. R., Howell, T. R., Johnson, N. K., Lowery, G. H., Parkes, K. C. and Storer, R. W. (1973), Thirty-Second Supplement to the American Ornithologists’ Union Check-List of North American Birds, Auk 90(2): 411-419. 2) Gittleman, J. L., Encyclopaedia Britannica (2019), Species (online) [Accessed 29/05/2021]. 3) Nelson, D., OSU Bio Museum (2015), Examples of sibling species (online) [Accessed 02/06/2021]. 4) Thain, M. and Hickman, M. (2014), Dictionary of Biology (Eleventh Edition). London: Penguin Books Ltd. 5) Author unknown, Wikipedia (date unknown), Alder flycatcher (online) [Accessed 02/06/2021].