We use aquatic insects, particularly water beetles, to explore a range of fundamental and applied topics in ecology and evolution. Recent studies have explored the biology of rarity, underwater gas exchange, and the evolution of salinity tolerance, often within the context of global change.
Water beetles and rarity
Most species on earth are rare, sometimes being restricted to very small areas of the world, and often occurring in very low numbers. This is well known. What is not so well known is why most species are rare. Work led by Prof David Bilton at Plymouth University, is helping to provide some answers to this question, and also helping us to understand how rare and common species may respond to future climate change.
There are three main ideas as to why related species show dramatically different range sizes; these relate to evolutionary age (i.e. how long a species has had to spread), dispersal limitation (i.e. how good a species is at moving to new places) and fundamental niche breadth (i.e. the range of environmental conditions a species can tolerate). Work at Plymouth University has evaluated the relative importance of these three factors amongst closely related rare and common species, and demonstrated that there is often a fundamental link between niche breadth, in the form of ecophysiology (temperature tolerance, immune responses and metabolic plasticity) and range size. Put simply, how common or rare a species is can often be accurately predicted from its physiological abilities. Species with narrower temperature tolerances, for example, are far more restricted, and it is these species which seem likely to be the most vulnerable to on-going climatic changes.
We have studied a number of clades of closely related species of European water beetles which vary dramatically in their geographical range size, from species restricted to areas in southern Europe to those which are found from the Mediterranean to northern Sweden. The ability to tolerate temperature extremes was a very good predictor of the geographical range size of species, far more so than how good these species are at flying from place to place, or how long ago they evolved. As with much of the biota of Europe, these beetles survived ice ages in southern Europe, moving north as the climate warmed 12,000 years ago. Present-day widespread species are those which have been able to retain their southern range boundaries, and expand north, something which requires relatively high tolerance to both heat and cold. Species with narrower temperature tolerances are far more restricted, and it is these species which seem likely to be the most vulnerable to ongoing climatic changes. As well as having limited temperature tolerance, these rare species also have limited ability to adjust their tolerance windows as temperatures change. Given that climate warming will also lead to a reduction in the availability of suitable aquatic habitats in Mediterranean areas, such restricted species would appear to be doubly threatened in the future.
Pallares, S., Arribas, P., Bilton, D.T., Millan, A., Velasco, J. & Ribera, I. 2017. The chicken or the egg? Adaptation to desiccation and salinity tolerance in a lineage of water beetles. Molecular Ecology DOI: 10.1111/mec.14334.
García-Vázquez, D., Bilton, D.T., Foster, G.N. & Ribera, I. 2017. Pleistocene range shifts, refugia and the origin of widespread species in Western Palaearctic water beetles. Molecular Phylogenetics and Evolution 114: 122–136.
Cioffi, R., Moody, J.A., Millan, A., Billington, R. & Bilton, D.T. 2016. Physiological niche and geographical range in European diving beetles (Coleoptera: Dytiscidae). Biology Letters12: 20160130.
Verberk, W.C.E.P. & Bilton, D.T. in 2015. Oxygen limited thermal tolerance is seen in a plastron breathing insect, and can be induced in a bimodal gas exchanger. Journal of Experimental Biology 218: 2083-2088.
Verberk, W.C.E.P. & Bilton, D.T. 2013. Respiratory control in aquatic insects dictates their vulnerability to global warming. Biology Letters 9: 20130473.
Arribas P., Abellán P., Velasco J., Bilton D.T., Millán A. & Sánchez-Fernández D. 2012. Evaluating drivers of vulnerability to climate change: a guide for insect conservation strategies. Global Change Biology 18: 2135–2146.
Arribas, P., Velasco, J., Abellán, P., Sánchez-Fernandez, D., Andújar, C., Calosi, P. Millán, A., Ribera, I. & Bilton, D.T. 2012. Dispersal ability rather than ecological tolerance drives differences in range size between lentic and lotic water beetles (Coleoptera: Hydrophilidae). Journal of Biogeography 39: 984-994.
Sánchez-Fernández, D., Aragón, P., Bilton, D.T. & Lobo, J.M. 2012. Assessing the congruence of thermal niche estimations derived from distribution and physiological data. A test using diving beetles. PloS ONE 7: e48163.
Verberk, W.C.E.P., Bilton, D.T., Calosi, P. & Spicer, J.I. 2011. Oxygen supply in aquatic ectotherms: Partial pressure and solubility together explain biodiversity and size patterns. Ecology 92: 1565–1572.
Calosi, P., Bilton, D.T., Spicer, J.I., Votier, S. & Atfield, A. 2010. What determines a species' geographical range? Thermal biology and latitudinal range size relationships in European diving beetles (Coleoptera: Dytiscidae). Journal of Animal Ecology 79:194–204.
Calosi, P., Bilton, D.T. & Spicer, J.I. 2008. Thermal tolerance, acclimatory capacity and vulnerability to global climate change. Biology Letters 4: 99-102.