ECR feature: Vicente García-Navas on diversification in dasyurid marsupials

Vicente is an evolutionary ecologist and is currently a postdoc at the University of Zurich. He is largely interested in patterns of lineage diversity and eco-morphologies. Vicente shares his recent work on the interplay between competition, divergence time, and geographic range overlap on the diversification of dasyurid marsupials in Australia.

Name. Vicente García-Navas

Personal links. Twitter | ResearchGate | Website

Institute. University of Zurich, Switzerland (UZH)

Academic life stage. Postdoc

Major research interests. My ongoing research lies at the interface between ecology and evolution, addressing how temporal and spatial patterns of eco-morphological and lineage diversity are influenced by biotic and abiotic factors and their interactions. I try to incorporate contemporary (local) processes into “tree thinking” allowing joint testing of ecological and evolutionary processes. I am interested in how phenotypic traits evolve, how species richness accumulates, how the rate of evolution differs among lineages and over evolutionary time, and the mechanisms driving these varying rates of change.

Pictures of Triodia (spinifex) clumps and sandy substrates along the Canning Stock route in Western Australia. Triodia is a large genus of hummock-forming bunchgrass endemic to Australia. Triodia hummocks constitute the main habitat of some Sminthopsis species like the sandhill dunnart S. psammophila (pictures: Mike Westerman).

Current study system. I use vertebrate radiations as model systems with special emphasis on taxonomic groups that diversified in Australia and nearby islands. This island-continent constitutes a very suitable scenario for studying diversification dynamics at a regional scale. Marsupials account for over half of Australia’s land mammals and are well represented in the totality of environments that can be found across this continent. Consequently, this taxonomic group has prompted a large body of research. However, little is known about the role of biotic interactions in shaping coexistence patterns in marsupials. There is paucity of studies focused on interspecific competition among members of this speciose group.

Recent publication in Journal of Biogeography. García-Navas, V., Kear, B.P., Westerman, M. (2020) The geography of speciation in dasyurid marsupials. Journal of Biogeographydoi/abs/10.1111/jbi.13852 [Access here]

Motivation behind this work. Unlike other more striking and iconic Australasian radiations, dasyurid marsupials have received relatively little attention. This lack of research might (at least partially) be due to low morphological specialization in this mammalian taxon, which makes it less intuitively appealing for diversification studies. However, we have previously showed that patterns of both phenotypic disparity and speciation in dasyurids exhibited an early burst followed by a slowdown. It is likely that the extinction of thylacinids and the spread of arid habitats spurred this radiation of insecto-carnivorous mammals giving rise to that early burst signal. In this paper, we were interested in the effects of competition and divergence time on morphological dissimilarity (in terms of body mass and molar row length) and geographic range overlap between species at different scales. Most community phylogenetic studies do not consider biogeographic history and regional-scale processes despite growing recognition that these influence contemporary community patterns. Consequently, incorporating perspectives on clade-level evolution into studies of community assembly constitutes a fundamental challenge for the progress of this field.

One of the most emblematic Australian species; two Tasmanian devils Sarcophilus harrisii at Traunna Wildlife Park in Tasmania (picture: Mike Westerman).

Key methodologies. We examined the relationship between species co-occurrence patterns and morphological similarity at two spatial scales. Although local and regional scale analyses should ideally be applied in tandem, few studies have addressed both perspectives simultaneously. Specifically, we first tested whether speciation in this group has been largely allopatric at regional scale, as previously shown in other mammalian families. Secondly, where species coexist, we tested whether this sympatry might have been facilitated by morphological divergence at local scale through character displacement. For this purpose, we used a novel approach developed by M. Borregaard, node-based analysis (, which quantifies the distributional divergence between daughter lineages descending from the same node and allows obtaining a better insight of the phylogenetic structure of assemblages at large scale. At local scale, we used co-occurrence data from 83 communities in order to test whether co-existing species are more morphologically divergent that those that do not coexist or do so not preferentially. 

Major results. Our study reveals that geographic isolation arising from niche conservatism (as opposed to biotic interactions including competitive exclusion) has played a pivotal role in shaping the speciation patterns of this endemic mammal radiation. The level of sympatry observed in our sample of sister species pairs was slightly higher than that generally reported amongst placental mammals. However, despite moderate levels of sympatry through time, our results indicate low rates of spatial co-occurrence between dasyurids. It supports the idea that, under certain circumstances a high degree of range overlap may not translate into real coexistence at a local scale. That is, in many cases sympatric species (in terms of broad-scale spatial overlap) are not syntopic and do not interact ecologically. By integrating approaches used to infer broad-scale, evolutionary processes and those commonly used to study ecological interactions at fine scales, we show that it is possible to obtain a comprehensive understanding of factors driving species distributions.

Unexpected challenges. I remember writing this paper while recovering from a surgery. So, I have a folder in my laptop devoted to this study called “dasyurid speciation” but, for me, this paper will always be the gallbladder paper. There is no better plan for the summer than to stay at home writing while your scars dry and doctors remove the stitches. Apart from this, the process was quite smooth. What took us the longest was to collect data on length of the lower molar row for all species. In several cases, we had to dig into grey literature to find morphological data for some poorly-known taxa (e.g. Antechinus) or request data from experts, which indicates that even in some charismatic groups like marsupials there is still a need for more natural history studies. We still lack basic information on morphology and ecology for a high percentage of mammalian species. Consequently, there is no doubt that fieldwork is still crucial for science research.  

A Northern quoll, Dasyurus hallucatus, also known as the northen native cat, in Darwin (NT). This species was first described in 1842 by the English ornithologist John Gould (picture: Mike Westerman).

Next steps of this research. This study is part of a project on diversification and phenotypic evolution in vertebrate Australasian radiations. One of the main aims of this project is trying to reconcile macroevolutionary processes acting at a continental scale with ecological processes, like competition, that are generally interpreted at smaller spatial scales. We plan to continue interpreting local coexistence patterns in light of historical processes, taking advantage of traditional field surveys and state-of-the-art techniques. We are interested in examining how local assemblages are structured over time by explicitly considering range dynamics, speciation, colonization, and local extinction rates. In this way, we will be able to ask if there is a link between diversification rates and species co-occurrence.  

If you could study any organism on Earth, what would it be? Certainly no one will find me chasing raptors or large ungulates. I don’t know why, but I have a strong preference for rodents (and rodent-like marsupials) and small birds. So, I would definitely continue studying songbirds and small mammals. They are probably easier to study than other organisms, which allows obtaining large sample sizes and even carrying out experiments in the field. In addition, they represent some of the most striking vertebrate radiations and have successfully colonized a great variety of environments exhibiting a high variability in terms of morphological and/or behavioural adaptations. Beyond this, I think it goes without saying that they are amazing creatures and, most of them, overwhelmingly cute.

Anything else you would like to share?

I did my PhD on behaviour in blue tits and then I started to apply molecular tools to address questions at a larger scale (e.g. gene flow and local adaptation between colonies). The need to answer broader questions pushed me to move from working at the individual or population level to adopt a more comprehensive approach, one that considers macroevolution using modern phylogenetic comparative methods. Thus, I have progressively expanded my interests from individual decisions and taxon-specific questions to broad-scale processes that act as biodiversity engines. I think that this winding path has provided me with a background that allows me to approach my research with a broader and more integrative perspective.

Regarding my little obsession with the Australian fauna, I remember that I enjoyed a lot watching “Taz-mania”, an animated sitcom produced by Warner Bros and starring Taz, the Tasmanian Devil, when I was a kid. This “Looney Tunes” character was popular enough for the potential of a spin-off series focused on his adventures and those of other furry creatures including wallabies, koalas and dingoes. I really think cartoons have great potential to convey respect and interest for animals!

Published by jbiogeography

Contributing to the growth and societal relevance of the discipline of biogeography through dissemination of biogeographical research.

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