G is for Gorilla phylogeography
Today, more than ever, we need to understand where animals currently live and where they have lived in the past, for example our work on endangered species such as the western lowland gorilla. Only then we are to make educated decisions for their conservation under pressures such as climate and land use change. We need to understand their ‘vagility’ — the extent to which a species can spread within an environment.
The scientific study of the geographical distribution of animals is called zoogeography. But zoogeography involves so much more than simply plotting the distribution of animals onto a map. As a branch of biology, zoogeography aims to explain the causes, effects and interactions of the geographical ranges of animals. This approach can be further divided into ‘ecological zoogeography’, which attempts to understand present-day factors, both biotic (relations with other organisms) and abiotic (the role of climate, geology and other physical factors) affecting the distribution of animals, and ‘historical zoogeography’ (the more traditional view), which is concerned with understanding the origin, extinction and dispersal of animals in a geological timescale.
At Canterbury Christ Church University we can trace our pedigree in zoogeography to Alfred Russel Wallace, a British naturalist, explorer, geographer, biologist and anthropologist. Born in 1823, he is known for his work on the theory of natural selection which he jointly published with Charles Darwin in 1858. An avid explorer, Wallace spent years travelling and collecting specimens, many from places not yet explored by western society. During his expedition in 1854 through the Malay Archipelago (now known as Malaysia and Indonesia), he collected over 125,000 specimens. It was from this expedition that Wallace recognised a distinctive pattern between the distribution of animals from the Australian and Asian regions, which led him to propose a boundary line dividing the two regions. This line later became known as Wallace’s Line, and in 1876 Wallace published his classic text, The Geographical Distribution of Animals, which included the first map of global terrestrial zoogeographic regions. Wallace divided the world into six zoogeographic realms and regions and considered the ancestral relationships of species. This work became the cornerstone of modern biogeography and Wallace is often quoted as the father of biogeography.
With scientific advancements in evolutionary theory and in molecular biology and genetics, coupled with increasing computational power, modern phylogenetics emerged as a means to visualise, analyse and quantify the evolutionary relationships among species, based on the hypothesis that all living organisms share a common ancestor. Like many disciplines in biology, zoogeography has been reinvigorated by the use of ‘phylogenetic methods’ (relating to the evolutionary development and diversification of a species or group of organisms), DNA sequencing and genotyping, and geographical information systems (GIS) to study patterns of diversity and distributions of animals, further driven by concerns of global biodiversity loss. Current consensus, combining data on geographic distributions and phylogenetic relationships of amphibian, bird and mammal species, reveals twenty distinctive zoogeographical regions within in eleven larger realms.
Just like the diversity and distribution of species around the globe is not random, the diversity within species and populations is also non-random, and those spatial patterns can be discovered and studied. ‘Phylogeography’ is concerned with the spatial distribution of genealogical lineages (‘family connections’) and the genetic diversity of populations and aims to understand the historical and ecological reasons for this, often linking geological climatic changes, isolation-by-distance or dispersion, natural selection in divergent climates, demographic events like population expansions or contractions, and movement of genes across land- and seascapes.
Seen as a subdiscipline of biogeography, phylogeography can easily be applied to studying animals. In her PhD project, Dr Jaimie Morris and her supervisor Dr Rodrigo Vega used a phylogeographic approach to study the geographic distribution of genealogical lineages of western lowland gorillas, evaluated the genetic diversity within and among modern wild and captive gorilla populations, and compared them with historical gorilla populations using museum samples (Fig. 1A). They discovered that the captive gorilla population is more genetically diverse than originally thought and that it has retained a large proportion of genetic diversity found in historical populations (Fig. 1B). Contrary to expectations, they found no evidence of geographic regional divisions in the historic population of western lowland gorillas, which can be explained by their ‘vagility’ (the extent to which an organism or taxon can spread) and large geographic range in the rainforests of equatorial western Africa.
Geographic, genetic and demographic knowledge of wild and past populations is fundamental for the management of captive populations and is of vital importance for the conservation of endangered species. With natural populations continuing to decline, maintaining genetic variation in captive populations is a conservation priority. Research that focuses on the genetic viability of captive populations provides conservation managers with additional knowledge to make informed captive breeding decisions that consider the genetic health of captive populations and avoid inbreeding and informs reintroduction programmes. The results presented by Morris and Vega are therefore good news for the captive breeding and reintroduction programmes led by The Aspinall Foundation. By taking multidisciplinary approaches combining data from geographic and genetic research, modern zoogeographers can draw more informed conclusions regarding the historical and present-day distributions and relationships among and between species and can make good use of this information to make science-based decisions to try tackle the loss of biodiversity in a rapidly changing world.
Dr Jaimie Morris obtained her PhD in Biological Science from Canterbury Christ Church University in 2021. Having worked as the Wilder Kent Education Officer at the Kent Wildlife Trust, she is now the Education Officer at The Wildwood Trust.
Dr Rodrigo Vega is a Senior Lecturer in Biology at Canterbury Christ Church University interested in evolutionary biology, phylogeography and population genetics for conservation biology — see his research on phylogeographic structure of the pygmy shrew listed below.
Further reading:
Davies, J.L. (1961) ‘Aim and method in zoogeography’, Geographical Review, 51(3), pp. 412–417.
Holt, B.G., Lessard, J-P., Borregaard, M.K. et al. (2013) ‘An update of Wallace’s zoogeographic regions of the world’, Science, 339(6115), pp. 74–78.
Vega, R., et al. (2020) Phylogeographic structure of the pygmy shrew: revisiting the roles of southern and northern refugia in Europe, Biological Journal of the Linnean Society 129: 901–917.
Hickerson, M.J., Carstens, B.C., Cavender-Bares, J. et al. (2010) ‘Phylogeography’s past, present, and future: 10 years after Avise, 2000’, Molecular Phylogenetics and Evolution, 54(1), 291–301.
Morris, J. (2020) Genetic and morphological analyses of historic and contemporary populations of western lowland gorilla: a multidisciplinary approach for the conservation of a critically endangered primate, PhD Thesis, Canterbury Christ Church University.
