Climatic Correlates of Body Size in European Tenebrionid Beetles (Coleoptera: Tenebrionidae)
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Org Divers Evol (2014) 14:215–224 DOI 10.1007/s13127-013-0164-0 ORIGINAL ARTICLE Climatic correlates of body size in European tenebrionid beetles (Coleoptera: Tenebrionidae) Simone Fattorini & Roberto Lo Monaco & Andrea Di Giulio & Werner Ulrich Received: 17 June 2013 /Accepted: 4 December 2013 /Published online: 29 December 2013 # Gesellschaft für Biologische Systematik 2014 Abstract Tenebrionidae are one of the largest families of the second hypothesis, we regressed mean body size of beetles and are known for their adaptations to hot and dry European country faunas against climatic characteristics. We climates. An increase in body size also increases the volume/ found a strong increase in body size in southern faunas surface area ratio, which reduces transpiration, and hence experiencing hot and dry climates. Therefore, increase in body water loss. If an increase in body size is an important adapta- size is not a major adaptation in tenebrionid evolution, but tion in tenebrionids to cope with increasing aridity, we expect climate is an important filtering factor that determines a prev- a correlation between body size and climatic gradients in the alence of larger species in southern Europe. major tenebrionid clades. Alternatively, we can postulate that arid climates do not drive body size evolution, but rather Keywords Biogeography . Body size . Europe . Darkling select, from a wider fauna containing species of any size, beetles . Macroecology those that have larger bodies. In this case we expect that drier regions will host faunas that contain, on average, larger spe- cies. To test the first hypothesis, we correlated inter-specific Introduction body size variation in the main tenebrionid clades with cli- matic gradients in Europe. We found only weak trends. To test The family Tenebrionidae is one of the largest of Coleoptera, comprising about 19,000 known species (Aalbu et al. 2002). Adult tenebrionids exhibit a diversity of form possibly ex- Electronic supplementary material The online version of this article (doi:10.1007/s13127-013-0164-0) contains supplementary material, ceeding that of any other family of beetles. Tenebrionidae which is available to authorized users. occur in all major zoogeographical regions and are strongly represented also in hot deserts, where other insects are scarce. S. Fattorini Azorean Biodiversity Group (CITA-A) and Platform for Enhancing In general, tenebrionid species inhabiting environments char- Ecological Research & Sustainability (PEERS), University of the acterized by high temperatures and low precipitations exhibit Azores, Angra do Heroísmo, Terceira, Açores, Portugal a number of well-known morphological, physiological and behavioral adaptations to cope with the risk of overheating S. Fattorini (*) Department of Biotechnology and Biosciences, University of Milano and dehydration, like subelytral cavity, sand-walking and Bicocca, Piazza della Scienza 2, 20126 Milan, Italy sand-swimming modifications, wax bloom covering the in- e-mail: [email protected] tegument to minimize water loss, drinking of fog water, active uptake of atmospheric water, use of metabolic water, high R. Lo Monaco : A. Di Giulio Department of Sciences, University of Roma Tre, Viale G. Marconi specialized osmoregulation processes, etc. (see Fattorini 446, 00146 Rome, Italy 2000, 2008 for reviews). A. Di Giulio An increased body size in insects living in arid environ- e-mail: [email protected] ments, in either cold or warm regions, has also been interpreted repeatedly as an adaptation to reduce water loss, W. Ulrich because an increase in the volume/surface area ratio reduces Ecology and Biogeography, Nicolaus Copernicus University in Toruń, Lwowska 1, 87-100 Toruń, Poland transpiration (Chown 1993;Hadley1994). In fact, it has been e-mail: [email protected] suggested, on anecdotal evidence, that tenebrionids living in 216 S. Fattorini et al. warm and arid environments tend to be particularly large promoting the prevalence of large species in arid areas. (Marcuzzi 1960), but this issue has been largely unexplored. If this is correct, we expect the average body size of the At the intraspecific level, Doyen and Rogers (1984)found species that constitute a fauna to increase with increasing some clinal variation in body size in a tenebrionid species temperatures and decreasing precipitation in the area living in western North American sand dunes, but the factors where that fauna lives. involved in these spatial variations remained undetected. Krasnov et al. (1996) found variation in body size with eleva- To explicitly test these two hypotheses, we used variation tion in certain (but not all) tenebrionid species inhabiting the in the body size of European tenebrionids. Tenebrionids are Negev Desert—the largest individuals occurring at low and widespread across Europe and their distribution is strongly warmer sites. They interpreted this trend as a possible adap- conditioned by climatic factors (Fattorini and Baselga 2012; tation for thermoregulation, because larger individuals have Fattorini and Ulrich 2012a, b). To test the aforementioned small surface/volume ratio and absorb relatively less direct hypotheses about the effects of temperature and precipitation shortwave and visible radiation, being thus in a better situation gradients on tenebrionid body size, we used two complemen- than smaller individuals at high ambient temperatures. Finally, tary approaches. To test the first (adaptive) hypothesis, we in a study that mixed intra- and inter-specific variation, De Los regressed the body size of each species against the mean Santos et al. (2000) found that, in the genus Hegeter of values of temperatures recorded from the areas inhabited by Tenerife Island, individuals from the lower zones adopted that species. We conducted separate analyses for taxonomi- globular and robust forms, possibly to avoid moisture and cally homogeneous groups to disentangle true adaptation from temperature stress. lineage turnover (Olson et al. 2009; Homburg et al. 2012). To All these studies on Tenebrionidae have been conducted at test the second (filtering) hypothesis, we calculated values of local scale and were focused on population variations, where- the mean body size of local faunas (sensu Penev 1996), i.e., as no research has been performed to test variation in body the mean of the body size of the species that live in each area, size among species at broad spatial scale. Studies on other and correlated these mean values with temperature values of arthropod taxa (e.g., Peat et al. 2005; Entling et al. 2010; each area (see Knouft 2004 for a similar approach). Ulrich and Fiera 2010) suggested that large body size is With this second approach, we tested if colder regions host favored by high temperature and low precipitation. species are, on average, larger than those inhabiting warmer Therefore we can expect large-scale spatial variation in tene- areas. The idea is that temperatures select species according to brionid body size across Europe. In fact, two main hypothesis body size from a common pool. Thus, we assume the whole can be evoked to explain the observation that the largest European fauna as a common pool of species from which tenebrionids tend to occur in hot and dry areas: northern countries were colonized after the last Pleistocene glaciations (Fattorini and Ulrich 2012b). If higher tempera- (1) Trend of increasing body size with temperature is a tures and low precipitation favor species with larger body size, consequence of an adaptive increase in size to cope with we expect a positive correlation between the mean body size increasing aridity. of the species that compose a fauna of a given area and the According to this interpretation, within each clade, climatic conditions of that area. species living in warmer and dryer areas should be larger than their counterparts living in colder and more humid places. Thus, on a large geographical scale, we expect, Materials and methods within each clade, an inter-specific cline of increasing body size with increasing temperatures and decreasing The current taxonomic division into species and subspecies, as precipitation among species of a given clade. applied to the tenebrionids of Europe, is arguably arbitrary. (2) Faunas inhabiting warmer and drier areas contain, on Recent morphological (Trichas 2008; Condamine et al. 2011; average, larger species because of filtering processes that Ferrer 2008, 2011) and molecular (Pons et al. 2004;Soldati favor, from the various clades that occur in each region, and Soldati 2006;Stroscioetal.2011) analyses showed that species having larger body size. populations traditionally classified as subspecies are really In this case, we expect that there is no clear trend in ‘evolutionarily significant units’ (sensu Ryder 1986), usually body size variation within each particular clade, and that demanding a species status. Thus, we considered both species faunas include species that may have any size, although and subspecies as terminal taxonomic units. Species and sub- certain faunas should be characterized by the prevalence species will be referred to as ‘species’ for simplicity. Further, of large-sized species. If large-sized species are favored the present paper includes the former family Lagriidae as a in warmer and drier areas, they will be a prevalent subfamily within the Tenebrionidae. In consideration of the component of the local fauna in such areas but not in highly derivative and specialized characters of Alleculinae others.