So, given that I have just started this blog, I feel it is only appropriate to introduce (briefly and as interestingly as possible) a basic overview of what my PhD over the next three years will entail-besides I have always loved the idea of science communication. So lets jump right in!
Are you familiar with the term coevolution? Many people have some idea of what it refers to and there is a basic definition which I will explain a little further on, but the interesting part is that despite having had a formal definition for decades we have relatively few examples of exactly how this coevolution between species drives diversification (i.e.increases the number of species). Well, I should rather say we have few convincing examples of co-evolutionary diversification occurring in nature. The fact is that coevolution makes perfect ecological sense- because for all the complexity that exists on planet earth organisms have never, and will never evolve or speciate (the development of a new species over time) in isolation. Much of the variety in species is a direct result of the complex interactions between species, i.e. coevolution. Where coevolution is defined as:
“reciprocal evolutionary change among interacting species driven by natural selection” (1)
What this means is that when say, a pollinator visits a flower- Its picks up some of the pollen in the process of feeding which it then transports to another flower of the same species. It is obviously of benefit to the plant to have its pollen distributed and it achieves this by producing a sugary nectar or floral oil which attracts the pollinator and is then subsequently fed on by this animal. However, the plant also needs to maximise the number of pollinators it attracts (to be successful and survive) and it does this by developing mechanisms which limit the amount of nectar that can be consumed per visit of the pollinator. Some examples (as you will see later in this post) include the development of modified floral structures such as spurs which house the nectar in difficult to reach places. What then happens is that the pollinators must also undergo adaptations if possible (by the process of natural selection) to still gain access to their sugary reward. Examples include lengthened proboses (feeding mouthparts) and insect foreleg length.
Given that there are millions of species, surely the evolutionary trajectory of one species would have influenced another? and would then, as a result of natural selection improve the rate at which new species are formed in either or both of the interacting taxa. The short answer is yes. The difficulty then arises when you go about trying to test for this as there must be some sort of mechanism which can be used to determine coevolution between two taxa and indeed if these interactions increase the rate at which new species are formed This is where my research comes in.
Creating a “family” tree or Phylogeny
Over the next three and a bit years I will get the opportunity to look at this question by undertaking a study of which the broad aim is, to investigate the ecological drivers of species diversification in Diascia (Twinspurs) species across the Drakensberg Alpine Centre (DAC-Figure 1) and the Cape floristic region (CFR) in South Africa. The Diascia or twinspurs get their name from the extraordinary twin spurs that extend from the base of each flower, creating something quite spectacular!
This work will luckily (YAY!) involve a fair amount of field work where I will have to go out and collect as many species from the genus as is possible (plus they are beautiful little flowers!, see Figure 3-5 below) and then sequence their DNA to create a phylogeny (Family tree of how the species are related and how they split). I do not want to go too much into the details but one of the very interesting components of this work will look at if life history strategy (i.e. perennial -has a life cycle of more than 2 years versus annual-complete life cycle in a year) played a role in how the genus historically dispersed across the landscape and how the different species came to be. In the DAC most Diascia seem to be perennial while in the cape they are annual species.
The coevolution between the bees and the flower
There has been research done previously, showing that the spurlength of these flowers is strongly correlated to the foreleg length of the bee to access the floral oil, i.e. different species of Rediviva (Figure 6)-solitary oil-collecting bees, pollinate different species of twinspur. I will be looking at how the interactions between these two genera might have contributed to the number of species we see in each today (Bees- ~ 26 species all found only in SA; Twinspurs-~ 70 species). To do this I will have to have a look at if the fitness (ability of the organism to survive and reproduce) of the species is influenced by the other (4). One way we can do this is to see if there is a relationship between the spur length in the flower and bee foreleg length to seed set and seed viability of the plant (because the foreleg length and spur length have been demonstrated to be traits that are evolving in conjunction-coevolution).
Well that is a very broad and basic introduction to some of the things that my PhD will involve. I will likely include more detailed aspects of each different section mentioned above (and not included in this summary) over the course of the next few years. I hope you enjoyed reading this!
I am excited to head out into the field to get started and of course to become a happy snappy, taking as many photos as I can of the gorgeous mountain scenery and the different parts of the country I visit.
Comment below if you would like anymore information or just if you enjoyed my long-winded introduction to my life for the next few years 😀
Stick along for the ride!
(1) Losos, J.B., Baum, D.A., Futuyma, D.J., Hoekstra, H.E., Lenski, R.E., Moore, A.J., Peichel, C.L., Schluter, D., Whitlock, M.C. (Eds.), 2013. The Princeton Guide to Evolution. Princeton University Press, Princeton ; Oxford.
(2) Armstrong, A.J., Brand, R.F., 2012. Invertebrates on isolated peaks in the uKhahlamba-Drakensberg park world heritage site, South Africa. Koedoe 54, 1–10. doi:10.4102/koedoe.v54i1.1082
(3) Steiner, K.E., Whitehead, V.B., 1990. Pollinator Adaptation to Oil-Secreting Flowers–Rediviva and Diascia. Evolution 44, 1701–1707. doi:10.2307/2409348
(4) Althoff, D.M., Segraves, K.A., Johnson, M.T.J., 2014. Testing for coevolutionary diversification: linking pattern with process. Trends in Ecology & Evolution 29, 82–89. doi:10.1016/j.tree.2013.11.003