Conservation biology is frequently referred to as a “crisis discipline“, a status which doesn’t appear to be changing any time soon. Like any response to a crisis, biologists of all walks of life operate under a prioritisation scheme – how can our finite resources be best utilised to save as much biodiversity as possible? This approach requires some knowledge of both current vulnerability and future threat – we need to focus our efforts on those populations and species which are most at-risk of extinction in the near (often immediate) future.
As regular readers of The G-CAT are likely aware, my first ever scientific paper was published this week. The paper is largely the results of my Honours research (with some extra analysis tacked on) on the phylogenomics (the same as phylogenetics, but with genomic data) and biogeographic history of a group of small, endemic freshwater fishes known as the pygmy perch. There are a number of different messages in the paper related to biogeography, taxonomy and conservation, and I am really quite proud of the work.
To my honest surprise, the paper has received a decentamount of media attention following its release. Nearly all of these have focused on the biogeographic results and interpretations of the paper, which is arguably the largest component of the paper. In these media releases, the articles are often opened with “…despite the odds, new research has shown how a tiny fish managed to find its way across the arid Australian continent – more than once.” So how did they manage it? These are tiny fish, and there’s a very large desert area right in the middle of Australia, so how did they make it all the way across? And more than once?!
The Great (southern) Southern Land
To understand the results, we first have to take a look at the context for the research question. There are seven officially named species of pygmy perches (‘named’ is an important characteristic here…but we’ll go into the details of that in another post), which are found in the temperate parts of Australia. Of these, three are found with southwest Western Australia, in Australia’s only globally recognised biodiversity hotspot, and the remaining four are found throughout eastern Australia (ranging from eastern South Australia to Tasmania and up to lower Queensland). These two regions are separated by arid desert regions, including the large expanse of the Nullarbor Plain.
As one might expect, the formation of the Nullarbor Plain was a huge barrier for many species, especially those that depend on regular accessible water for survival. In many species of both plants and animals, we see in their phylogenetic history a clear separation of eastern and western groups around this time; once widely distributed species become fragmented by the plain and diverged from one another. We would most certainly expect this to be true of pygmy perch.
This is where the real difference between everything else and pygmy perch happens. For most species, we see only one east and west split in their phylogenetic tree, associated with the Nullarbor Plain; before that, their ancestors were likely distributed across the entire southern continent and were one continuous unit.
Not for pygmy perch, though. Our phylogenetic patterns show that there were multiple splits between eastern and western ancestral pygmy perch. We can see this visually within the phylogenetic tree; some western species of pygmy perches are more closely related, from an evolutionary perspective, to eastern species of pygmy perches than they are to other western species. This could imply a couple different things; either some species came about by migration from east to west (or vice versa), and that this happened at least twice, or that two different ancestral pygmy perches were distributed across all of southern Australia and each split east-west at some point in time. These two hypotheses are called “multiple invasion” and “geographic paralogy”, respectively.
So, which is it? We delved deeper into this using a type of analysis called ‘ancestral clade reconstruction’. This tries to guess the likely distributions of species ancestors using different models and statistical analysis. Our results found that the earliest east-west split was due to the fragmentation of a widespread ancestor ~20 million years ago, and a migration event facilitated by changing waterways from the Nullarbor Plain pushing some eastern pygmy perches to the west to form the second group of western species. We argue for more than one migration across Australia since the initial ancestor of pygmy perches must have expanded from some point (either east or west) to encompass the entirety of southern Australia.
So why do we see this for pygmy perch and no other species? Well, that’s the real mystery; out of all of the aquatic species found in southeast and southwest Australia, pygmy perch are one of the worst at migrating. They’re very picky about habitat, small, and don’t often migrate far unless pushed (by, say, a flood). It is possible that unrecorded extinct species of pygmy perch might help to clarify this a little, but the chances of finding a preserved fish fossil (let alone for a fish less than 8cm in size!) is extremely unlikely. We can really only theorise about how they managed to migrate.
What does this mean for pygmy perches?
Nearly all species of pygmy perch are threatened or worse in the conservation legislation; there have been many conservation efforts to try and save the worst-off species from extinction. Pygmy perches provide a unique insight to the history of the Australian climate and may be a key in unlocking some of the mysteries of what our land was like so long ago. Every species is important for conservation and even those small, hard-to-notice creatures that we might forget about play a role in our environmental history.
Emotion and spirituality are concepts that inherently seem at odds with the fundamentally stoic, empirical nature of scientific research. Science is based on a rigorous system of objectivity, repeatability and empiricism that, at face value, appears to completely disregard subjective aspects such as emotion, spirituality or religion. But in the same way that this drives the division of art from science, removing these subjective components of science can take away some of the personal significance and driving factors of scientific discipline.
Emotions as a driving force in science
For many scientists, emotional responses to inquiry, curiosity and connection are important components of their initial drive to study science in the first place. The natural curiosity of humanity, the absolute desire to know and understand the world around us, is fundamental to scientific advancement (and is a likely source of science as a concept in the first place). We care deeply about understanding many aspects of the natural world, and for many there is a strong emotional connection to our study fields. Scientists are fundamentally drawn to this career path based on some kind of emotional desire to better understand it.
Although it’s likely a massive cliché, Contactis one of my favourite science-fiction movies for simultaneously tackling faith, emotion, rationality, and scientific progress. And no doubt any literary student could dissect these various themes over and over and discuss exactly how the movie balances the opposing concepts of faith in the divine and scientific inquiry (and the overlap of the two). But for me, the most heartfelt aspect the movie is the portrayal of Ellie Arroway: a person who is insatiably driven to science, to the point of sacrificing many things in her life (including faith). But she’s innately an emotional person; when her perspectives are challenged by her observations, it’s a profound moment for her as a person. Ellie, to me, represents scientists pretty well: passionate, driven, idealistic but rational and objective as best as she can be. These traits make her very admirable (and a great protagonist, as far as I’m concerned).
I would not, under ordinary circumstances, consider myself to be particularly sentimental or spiritual. I don’t believe in many spiritual concepts (including theism, the afterlife, or concepts of a ‘soul’), and try to handle life as rationally and objectively as I can (sometimes not very successful given my mental health). But I can’t even remotely deny that there is a strong emotional or spiritual attachment to my field of science. Without delving too much into my own personal narrative (at the risk of being a little self-absorbed and pretentious; it’s also been covered a little in another post), the emotional connection I share with the life of Earth is definitely something that drove me to study biology and evolution. The sense of wonder and curiosity at observing the myriad of creatures and natural selection can concoct. The shared feeling of being alive in all of its aspects. The mystery of the world being seen through eyes very different to ours.
Although it’s of course always better to frame an argument or present research in an objective, rational matter, people have a tendency to respond well to appeal to emotion. In this sense, presenting scientific research as something that can be evocative, powerful and emotional is, in my belief, a good tactic to get the general public invested in science. Getting people to care about our research, our study species, and our findings is a difficult task but one that is absolutely necessary for the longevity and development of science at both the national and global level.
Pretending the science is emotionless and apathetic is counterproductive to the very things that drove us to do the science in the first place. Although we should attempt to be aware of, and distance, our emotions from the objective, data-based analysis of our research, admitting and demonstrating our passions (and why we feel so passionate) is critical in distilling science into the general population. Science should be done rationally and objectively but driven by emotional characteristics such as wonder, curiosity and fascination.
All of these questions can be addressed with a combination of genetic, environmental and ecological information across a variety of timescales. However, the overall field of biogeography (and phylogeography as a derivative of it) has traditionally been largely rooted on a strong yet changing theoretical basis. The earliest discussions and discoveries related to biogeography as a field of science date back to the 18th Century, and to Carl Linnaeus (to whom we owe our binomial classification system) and Alexander von Humboldt. These scientists (and undoubtedly many others of that era) were among the first to notice how organisms in similar climates (e.g. Australia, South Africa and South America) showed similar physical characteristics despite being so distantly separated (both in their groups and geographic distance). The communities of these regions also appeared to be highly similar. So how could this be possible over such huge distances?
Dispersal or vicariance?
Two main explanations for these patterns are possible; dispersal and vicariance. As one might expect, dispersal denotes that an ancestral species was distributed in one of these places (referred to as the ‘centre of origin’) before it migrated and inhabited the other places. Contrastingly, vicariancesuggests that the ancestral species was distributed everywhere originally, covering all contemporary ranges within it. However, changes in geography, climate or the formation of other barriers caused the range of the ancestor to fragment, with each fragmented group evolving into its own distinct species (or group of species).
In initial biogeographic science, dispersal was the most heavily favoured explanation. At the time, there was no clear mechanism by which organisms could be present all over the globe without some form of dispersal: it was generally believed that the world was a static, unmoving system. Dispersal was well supported by some biological evidence such as the diversification of Darwin’s finches across the Galápagos archipelago. Thus, this concept was supported through the proposals of a number of prominent scientists such as Charles Darwin and A.R. Wallace. For others, however, the distance required for dispersal (such as across entire oceans) seemed implausible and biologically unrealistic.
A paradigm shift in biogeography
Two particular developments in theory are credited with a paradigm shift in the field; cladistics and plate tectonics. Cladistics simply involved using shared biological characteristics to reconstruct the evolutionary relationships of species (think like phylogenetics, but using physical traits instead of genetic sequence). Just as importantly, however, was plate tectonic theory, which provided a clear way for organisms to spread across the planet. By understanding that, deep in the past, all continents had been directly connected to one another provides a convenient explanation for how species groups spread. Instead of requiring for species to travel across entire oceans, continental drift meant that one widespread and ancient ancestor on the historic supercontinent (Pangaea; or subsequently Gondwana and Laurasia) could become fragmented. It only required that groups were very old, but not necessarily very dispersive.
From these advances in theory, cladistic vicariance biogeography was born. The field rapidly overtook dispersal as the most likely explanation for biogeographic patterns across the globe by not only providing a clear mechanism to explain these but also an analytical framework to test questions relating to these patterns. Further developments into the analytical backbone of cladistic vicariance allowed for more nuanced questions of biogeography to be asked, although still fundamentally ignored the role of potential dispersals in explaining species’ distributions.
Modern philosophy of biogeography
So, what is the current state of the field? Well, the more we research biogeographic patterns with better data (such as with genomics) the more we realise just how complicated the history of life on Earth can be. Complex modelling (such as Bayesian methods) allow us to more explicitly test the impact of Earth history events on our study species, and can provide more detailed overview of the evolutionary history of the species (such as by directly estimating times of divergence, amount of dispersal, extent of range shifts).
From a theoretical perspective, the consistency of patterns of groups is always in question and exactly what determines what species occurs where is still somewhat debatable. However, the greater number of types of data we can now include (such as geological, paleontological, climatic, hydrological, genetic…the list goes on!) allows us to paint a better picture of life on Earth. By combining information about what we know happened on Earth, with what we know has happened to species, we can start to make links between Earth history and species history to better understand how (or if) these events have shaped evolution.