A simple rule that unites geographical range evolution across terrestrial and marine environments.
Above: Holacanthus ciliaris (left) is broadly distributed, from the state of Florida (USA) to Santa Catarina (southern Brazil), whereas Hyplopectrus providencialis is endemic to the Caribbean islands of San Andrés and Providencia. Photographs by Osmar J. Luiz..
If one were to ask the above question to biogeographers, the answer would likely be no. Each species is unique, and geographical distributions seem idiosyncratic and perhaps too dependent on the arbitrary nature of geographical barriers. However, a recent study in our research group seemed to point in another direction: in the case of terrestrial vertebrates, their geographical limits closest to the poles evolved substantially faster than limits closest to the equator. Indeed, those differences were far from subtle, with high-latitude limits evolving 1.6–4 times faster than their low-latitude counterparts. Interestingly, the same pattern was shared across organisms with drastically different life-histories, from snakes to carnivores. In our featured paper on Journal of Biogeography, we set out to test whether this difference was also found in the marine realm. We analyzed a massive dataset including over five thousand reef fish species from around the world and repeated the analyses at varying phylogenetic levels (families vs. orders), as well as between different ocean basins. The vast majority of our analyses were consistent with the expected rate variation between high- and low-latitude limits for reef fish, whereas those that failed to do so might have been affected by the relatively small number of species in those particular taxa.
Editors’ Choice article: (Free to read online for a year.)
Pie, M.R., Divieso, R., Caron, F.S., Siqueira, A.C., Barneche, D.R. and Luiz, O.J. (2021), The evolution of latitudinal ranges in reef-associated fishes: Heritability, limits and inverse Rapoport’s rule. J Biogeogr. https://doi.org/10.1111/jbi.14150
What could be the mechanism underlying such differences in rates of evolution between high- and low-latitude limits? One possibility is that organismic, physiological processes could provide an intrinsic bias, such that adaptation to warmer conditions would be inherently more difficult to attain than adaptation to colder conditions. There is some evidence based on physiological and artificial selection studies of some taxa that indeed support this idea. However, if this is true, it would only push the question one step back: why would organisms show this asymmetry in their capacity to evolve different range limits in the first place? The short answer is that we don’t know, particularly because we just recognized that this phenomenon even existed. One possible mechanism involves the spatial differences in climatic conditions. Regions farther from the equator are not only colder, but almost invariably more seasonal. Therefore, on average, organisms of a given species that are nearest to the poles experience a broader range of environmental conditions than those nearest to the equator. As a consequence, low- and high-latitude range limits could correspond to cold- and hotspots of climatic adaptation. Alternatively, as the low-latitude tends to overlap with more species as a consequence of the latitudinal gradient in species diversity, the higher rate of evolution in the limit closest to the poles might be due to the relatively lower influence of interspecific competition in constraining their geographical distributions. Regardless of the mechanism, exploring further the drivers of variation in the rates of evolution of range limits might be a particularly exciting area for future research, particularly by exploring whether they are also found in other organisms, such as plants and invertebrates. In addition, the fact that such a universal pattern remained unnoticed for so long underscores how much we have yet to learn about the drivers of species distributions, particularly at long temporal scales.
Marcio R. Pie
Associate professor, Department of Zoology, Universidade Federal do Paraná, Brazil
I would like to thank Raquel Divieso (@raqueldivieso) and Fernanda Caron (@fercaron) for providing valuable feedback on this blog post.