Ecological Entomology (2019), 44,249–254 DOI:10.1111/een.12701

An interspecific test of Bergmann’s rule reveals inconsistent body size patterns across several lineages of water (Coleoptera: )

SUSANA PALLARÉS,1 MICHELE LAI,2 PEDRO ABELLÁN,3 IGNACIO RIBERA4 and D AV I D S Á N C H E Z - F E R N Á N D E Z 1 1Instituto de Ciencias Ambientales, Universidad de Castilla-La Mancha, Toledo, , 2Università degli Studi di Cagliari, Cagliari, , 3Departmento de Zoología, Universidad de Sevilla, Sevilla, Spain and 4Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), , Spain

Abstract. 1. Bergmann’s rule sensu lato,theecogeographicpatternrelatinganimals’ body size with environmental temperature (or latitude), has been shown to be inconsis- tent among taxa. Body size clines remain largely unexplored in aquatic , which may show contrasting patterns to those found in terrestrial groups because of the physiological or mechanical constraints of the aquatic environment. 2. Bergmann’s rule was tested using data on body size, phylogeny and distribution for 93 species belonging to four lineages of dytiscid water beetles. The relationship between size and latitude was explored at two taxonomic resolutions – within each independent lineage, and for the whole dataset – employing phylogenetic generalised least-squares to control for phylogenetic inertia. The potential infuence of habitat preference (lotic versus lentic) on body size clines was also considered. 3. Within-lineage analyses showed negative relationships (i.e. converse Bergmann’s rule), but only in two lineages (specifcally in those that included both lotic and lentic species). By contrast, no relationship was found between body size and latitude for the whole dataset. 4. These results suggest that there may be no universal interspecifc trends in latitudinal variation of body size in aquatic insects, even among closely related groups, and show the need to account for phylogenetic inertia. Furthermore, habitat preferences should be considered when exploring latitudinal clines in body size in aquatic taxa at the interspecifc level. Key words. Aquatic insects, biogeography, habitat, inland waters, latitude, lentic, lotic, phylogeny.

Introduction patterns among closely related species in endotherm (Blackburn et al., 1999), but the same latitudinal cline has been Body size is related to many physiological, life-history and eco- observed in ectotherm taxa, at both the inter- and intraspecifc logical traits, and thus has important effects on ftness and is ulti- levels (Vinarsky, 2014), leading to an extended use of the term mately linked to the spatiotemporal distribution and abundance ‘Bergmann’s rule’ in the literature (Meiri, 2011). of animals (Chown & Gaston, 2010). One of the oldest and most In insects, the generality and direction of body size patterns are debated ecogeographical patterns of body size is Bergmann’s far from consistent across taxa (Shelomi, 2012), in part because rule (BR) (Bergmann, 1847), which refers to size increase the taxonomic resolution and the phylogenetic component of with decreasing temperature or increasing latitude. It has been size variation are not often considered, despite their known interpreted that the rule originally referred to interspecifc strong effects (Chown & Gaston, 2010). In aquatic insects, which remain surprisingly unexplored in comparison with ter- Correspondence: Susana Pallarés, Instituto de Ciencias Ambientales, restrial ones, the few studies of geographic variation in size are Universidad de Castilla-La Mancha, Campus de Toledo, Av. Carlos III, at assemblage level (Vamosi et al., 2007; Zeuss et al.,2017)or 45071, Toledo, Spain. E-mail: [email protected] intraspecifc, the latter showing different patterns in different

© 2018 The Royal Entomological Society 249 250 Susana Pallarés et al. taxa: from the typical BR (e.g. Hassal et al.,2014)orU-shaped unable to cope with the strong drag forces produced by the water clines (e.g. Johansson, 2003) to the converse BR (i.e. decrease fow (Bournaud et al., 1992; Ribera & Nilsson, 1995). There- of size with latitude; e.g. Shama & Robinson, 2009). fore, whereas large sizes are generally absent in lotic waters, the Bergmann (1847) suggested that a more effcient heat con- full variability of sizes can be found in lentic waters. Consider- servation in large versus small organisms (because of the lower ing these physical and dispersal constraints of lotic species, we surface to volume ratio) could be the mechanism underlying the might expect that, in general, the temperature–size relationship latitudinal increase of body size. However, this mechanism is must be clearer for lentic species. However, the annual num- not applicable to ectotherms, because large size also slows heat ber of generations as well as other factors at local scale could gain, which could be as important as decreasing heat loss. Then, also infuence such a relationship, such as, for example, the anumberofalternativemechanismstoexplainobservedclines geographical and temporal variations in oxygen or temperature, in ectotherms have been proposed (see Blackburn et al.,1999; which are generally higher in small, shallow lentic waters than Chown & Gaston, 2010; Vinarsky, 2014 for detailed reviews). in lotic systems (Batzer & Boix, 2016). Briefy, these are based on the infuence of temperature on Among aquatic insects, diving beetles (Dytiscidae) have been growth rate (temperature–size rule; Atkinson, 1994), or a pos- proposed as good models to explore body size variation along itive relationship between size and dispersal ability (migration environmental gradients because of their considerable variation ability hypothesis; Blackburn et al.,1999)orbetweensizeand in body and geographic range size, even among closely related starvation resistance (Calder, 1984; Lindstedt & Boyce, 1985). species (Vamosi et al.,2007).Theavailabilityofwell-resolved Concerning the converse BR, it has been suggested that shorter phylogenies for different lineages of this group (Abellán & Rib- seasons (and the consequent shorter time available for growth era, 2011) provides a unique opportunity to study biogeographic and development) (Mousseau, 1997; Chown & Gaston, 2010) patterns across independent ‘evolutionary replicas’, controlling or lower availability of resources at high latitudes (Atkinson for phylogenetic inertia. Here, we explored the relationship &Sibly,1997)leadtoadecreaseinbodysize.ConverseBR between body size and latitude in four monophyletic lineages clines have been also attributed to the heat-dependent growth of diving beetles across a wide latitudinal range, accounting for rates and metabolic rates of ectotherms (Makarieva et al.,2005; the potential infuence of taxonomic resolution, habitat prefer- Winterhalter & Mousseau, 2008). However, the relationship ence and phylogenetic effects on body size clines. between size and latitudinal-correlated factors in insects could be infuenced by voltinism, because, as the number of genera- tions year–1 increases, less time per generation is available for Material and methods growth (Zeuss et al.,2017).Therefore,giventhemultipleenvi- Study group ronmental and biotic factors and individual traits directly or indi- rectly related with size, empirical evidence of such mechanisms Our dataset includes four monophyletic lineages, comprising a is generally scarce, especially for aquatic ectotherms. total of 93 dytiscid species (Supporting information, Table S1), In the aquatic environment, physiological or mechanical con- from which morphological, distributional and phylogenetic data straints could result in patterns of body size variation that are are available from previous studies: 27 species of the sub- different from those found in terrestrial animals (e.g. Zeuss aeneus group, an almost exclusively lentic lineage consisting of et al.,2017).Indeed,meta-analysesbyForsteret al. (2012) and 33 recognised species with generally large geographical ranges Horne et al. (2015) showed that (intraspecifc) temperature–size (Nilsson & Hájek, 2018); 20 of the western Mediterranean responses (conforming to BR) were stronger in aquatic than clade of Deronectes,anexclusivelyloticlineagewith24known in terrestrial species. It has been suggested that the balance species (García-Vázquez et al., 2016); 17 of Graptodytes,a between oxygen supply and demand, as an important driver genus with 21 recognised species (Ribera & Faille, 2010); and of the temperature–size response, might strengthen such a 29 of the planus group (genus Hydroporus; Ribera response in the aquatic environment, as oxygen is less readily et al.,2003;Nilsson&Hájek,2018),whichincludes51species. available in water than in air (Atkinson, 1995; Verberk et al., The latter two groups include lentic and lotic species. Most of 2011). Other indirect factors that might play a role are, however, the species studied have a Palearctic distribution, but some of frequently overlooked, such as species’ preference for lentic them are also present in the Nearctic region (Larson et al.,2000) or lotic waters. The contrasting stability between these habi- (Table S1). tat types (at evolutionary timescales) is known to select dif- The total length of these species was obtained from Scheffer ferentially for traits related to dispersal ability (Ribera, 2008): et al. (2015) and distributional data (latitudinal centroids and lentic insects are generally better dispersers than their lotic rela- maximum latitude) were obtained from Abellán and Ribera tives and therefore have broader and more northern distribution (2011). ranges (e.g. Hof et al.,2006;Abellán&Ribera,2011;Pinkert et al., 2018). If dispersal ability is positively correlated with body size in insects with a similar body structure and biol- Data analyses: Bergmann’s rule tests ogy (see Rundle et al.,2007),BRclinesinlineageswithboth lotic and lentic species could actually refect differential disper- We tested the relationship between body size and latitude sal capacities between species specialised in each habitat. On at two different taxonomic resolutions: (i) within each lin- the other hand, lotic waters may impose stronger physical con- eage; and (ii) for the whole dataset, pooling the four lineages. straints on body size than lentic habitats, as large insects are Phylogenetic generalised least squares (PGLS) were used

© 2018 The Royal Entomological Society, Ecological Entomology, 44,249–254 Bergmann’s rule in water beetles 251

Table 1. Results of phylogenetic generalised least squares (PGLS) testing the relationship between average size and central latitude for the whole dataset and each lineage, respectively.

2 Group Predictor Slope ± SD d.f. FP-value R !† All species Latitude −0.015 ± 0.020 1 1.412 0.238 Habitat type 0.571 ± 0.944 1 2.983 0.088 Latitude × habitat type −0.004 ± 0.023 1 0.035 0.853 Full model 0.227 0.049 0.969 (P < 0.001) Ilybius Latitude −0.016 ± 0.041 1 0.145 0.707 0.007 0.670 (P = 0.004) Deronectes Latitude 0.004 ± 0.010 1 0.203 0.658 0.011 0.977 (P = 0.003) Hydroporus (all) Latitude −0.029 ± 0.015 1 7.540 0.011 Habitat type 0.800 ± 0.687 1 19.619 <0.001 Latitude × habitat type −0.004 ± 0.018 1 0.056 0.814 Full model <0.001 0.537 0.988 (P = 0.028) Hydroporus (lotic) Latitude −0.025 ± 0.018 1 2.011 0.194 0.200 0.920 (P = 0.162) Hydroporus (non-lotic) Latitude −0.034 ± 0.008 1 17.142 <0.001 0.502 1 (P = 0.002) Graptodytes (all) Latitude −0.064 ± 0.018 1 3.061 0.104 habitat −1.844 ± 0.763 1 3.751 0.075 Latitude × habitat type 0.056 ± 0.021 1 7.600 0.016 Full model 0.018 0.526 0 (P = 1) Graptodytes (lotic) Latitude −0.064 ± 0.027 1 5.769 0.074 0.591 0 (P = 1) Graptodytes (non-lotic) Latitude −0.004 ± 0.006 1 0.506 0.495 0.053 1 (P = 0.035)

†Maximum likelihood-estimated Pagel’s !;inparentheses,P-values of the test assessing whether it differed from zero (i.e. no phylogenetic signal). to control for phylogenetic inertia. For the analyses within Results lineages, the phylogenetic trees from Abellán and Ribera (2011) were used. For the pooled dataset, we combined the Average and maximum body size and central and maximum phylogenies of the four lineages in a global tree, using the most latitudes were strongly correlated for all the lineages (Table S2), recent family-level phylogeny for Dytiscidae (Désamoré et al., so we report only the relationships between average body size 2018) as a base tree representing the evolutionary relationships and central latitude (but see Table S3 for results for maximum among lineages (see Fig. S1). The depth of each clade tree size and maximum latitude). in the global tree was set from the age of each lineage, as Phylogenetic generalised least-squares for the whole dataset provided in Abellán and Ribera (2011). While this meta-tree showed no signifcant relationships between size and either lati- approach has a number of limitations, it provides an - tude or habitat, or their interaction (Tables 1 and S3). The differ- tional phylogenetic hypothesis based on the currently available ent lineages were clearly clustered by (mainly) size and latitude, data suitable for comparative analysis (Funk & Specht, 2007). especially for Ilybius, the largest and most northerly distributed The phylogenetic signal of the regressions’ residuals was group (Fig. 1a). Within-lineage analyses revealed no consistent assessed by maximum-likelihood estimated values of Pagel’s patterns across the different groups. No signifcant relationships were found in Ilybius or Deronectes,whereasaveragesizeand lambda (!; Pagel, 1999) and likelihood ratio tests to determine whether it differed signifcantly from zero (i.e. from a model central latitude showed a signifcant relationship in Hydroporus as well as maximum size and maximum latitude in Graptodytes assuming that patterns of body size variation are independent (Tables 1 and S3), negative in both cases (i.e. following a con- of phylogeny). verse BR) (Fig. 1b,c). This pattern showed a strong signifcant To account for the potential infuence of habitat, we included phylogenetic signal in Hydroporus (Table 1). it and the interaction with latitude as predictors for those anal- In Graptodytes and Hydroporus species, the two lineages yses including species with different habitat preferences (i.e. that include both lentic and lotic species, body size was also the whole dataset, Graptodytes and Hydroporus lineages). For signifcantly related to habitat (Tables 1 and S3). When the simplicity, and because the main size constraints are presum- relationship between body size and latitude was tested separately ably expected in lotic species (Ribera & Nilsson, 1995), we for species grouped by habitat, the converse BR cline only held considered two habitat categories: lotic specialists and the rest for non-lotic specialist species of Hydroporus,withasignifcant (including both lentic specialists and non-specialists). Addition- phylogenetic signal (Tables 1 and S3). ally, when habitat was signifcant, we ftted separate PGLS mod- els for each habitat category. All analyses were performed for both average size and central Discussion latitude, and maximum size and maximum latitude, in rv. 3.3.3 (R Core Team, 2017). We used a single datapoint for each The currently available data show that latitudinal clines in body species, as intraspecifc variation of size in diving beetles is size are much less consistent across insects (and ectotherms relatively low in relation to interspecifc variation (see Larson in general) than endothermic taxa (Shelomi, 2012; Vinarsky, et al.,2000andTableS1). 2014). Here, we found no support for BR in the studied lineages,

© 2018 The Royal Entomological Society, Ecological Entomology, 44,249–254 252 Susana Pallarés et al.

altitudinal gradient working with a large dataset of tropical moths. We furthermore found a strong phylogenetic signal in body size variation, which is common in insects, highlighting the importance of accounting for phylogenetic relatedness (Chown & Gaston, 2010). Few interspecifc studies of BR in aquatic insects are available for comparison with the patterns found here, but the closest one, by Vamosi et al. (2007) (also on dytiscids), found a positive relationship between the proportion of large species with latitude, contrary to the trends (or lack of them) observed here within specifc lineages. However, that study was done at the assemblage level (i.e. the body sizes of all dytiscid species were pooled within each grid cell) and was restricted to a geographic political region (southern Alberta, Canada). Thus, because of the different taxonomic and spatial resolutions, and for the reasons outlined earlier, these results are not directly comparable. One of the physiological mechanisms proposed to explain size patterns in aquatic ectotherms is based on the fact that aero- bic performance in the aquatic environment is worse in warmer habitats, because oxygen demand exceeds supply, constraining size at lower latitudes (Verberk et al.,2011).Makarievaet al. (2005) proposed that the interactions between metabolic rates, growth and temperature are behind the size decrease with tem- perature (BR) in aquatic organisms (e.g. Chapelle & Peck, 1999) and the opposite pattern (i.e. converse BR) in terrestrial ones (e.g. Ashton & Feldman, 2003), as oxygen concentrations in aquatic environments are lower than the atmosphere. However, Fig. 1. Relationships between average body length and central lati- we found the converse BR in two of the studied aquatic groups. tude for the whole dataset (a), average body length and central latitude Because of the respiratory mode of dytiscids (both adults and for Hydroporus species (b), and maximum body length and maxi- larvae) by a physical compressible gill that needs to be renewed mum latitude for Graptodytes species (c). Regression lines of signif- at the surface, they are highly dependent on atmospheric air, icant relationships are shown (continuous for all species; dashed for whereas O2 exchange with surrounding water is supposed to be lentic and mixed-habitat species). [Colour fgure can be viewed at minimal (Calosi et al., 2007). Thus, body size patterns in aquatic wileyonlinelibrary.com]. insects with this respiratory mode could be driven by similar metabolic constraints to those on terrestrial rather than aquatic and inconsistent latitudinal patterns of body size at the two ectotherms. However, no empirical evidence supports this idea. taxonomic resolutions explored, as well as among the different In part, the inconsistent patterns among the studied lineages lineages. could refect different constraints imposed by habitat type on No signifcant relationship between body size and latitude was both size and distribution, which have typically been ignored detected when data from the four lineages were pooled; however, when studying body size patterns in the aquatic environment. two of the studied lineages (Hydroporus and Graptodytes) Here, signifcant relationships between size and latitude were showed a converse BR cline when assessed independently. The only found in lineages that include lentic and lotic species (i.e. frst important point to be drawn from these results is the Hydroporus and Graptodytes)and,amongthese,therelationship importance of considering well-defned, complete taxonomic was only signifcant for species with lentic or indistinct habitat units when examining biogeographic patterns in body size. It preference. Lotic species in our dataset were mostly restricted to was not our goal to examine body size trends at the family level, lower latitudes, a pattern that has previously been attributed to given the limited extent of our size and distribution dataset and the well-supported hypothesis that they have lower propensity the lack of a comprehensive phylogeny at such level. However, for dispersal than lentic ones (Abellán & Ribera, 2011). On our analyses show that body size patterns (or the absence of the other hand, size variability was higher between lentic than them) observed when different taxonomic groups are pooled between lotic species. The largest species in our dataset were arbitrarily may be confounded by inconsistent patterns among lentic or with indistinct habitat preference (Fig. 1), which might lower taxonomic groups. Other studies have found similar be related to the physical constraint on size imposed by the inconsistencies, such as those on latitudinal body size clines currents in running water (Ribera & Nilsson, 1995). Therefore, in bees (Gérard et al., 2018) or size variation in Lepidoptera it is likely that, because size and dispersal are constrained in lotic along elevational gradients (e.g. Hawkins & DeVries, 1996; species, the latitudinal body size clines we found in Hydroporus Brehm & Fiedler, 2004). However, Brehm et al. (2018) found and Graptodytes species actually refect the size gradient of aconsistentpatternofbodysizeincreasealonganextensive lentic (or mixed-habitat) species.

© 2018 The Royal Entomological Society, Ecological Entomology, 44,249–254 Bergmann’s rule in water beetles 253

Voltinism has also been shown to be an important constraint Atkinson, D. (1994) Temperature and organism size – a biological law on body size at macroecological scales. For example, a positive for ectotherms? Advances in Ecological Research, 25,1–54. size–latitude relationship was reported in univoltine Odonata Atkinson, D. (1995) Effects of temperature on the size of aquatic at the assemblage level, but this was negative for multivol- ectotherms: exceptions to the general rule. Journal of Thermal tine species (Zeuss et al.,2017).Theseauthorssuggestedthat Biology, 20,61–74. Atkinson, D. & Sibly, R.M. (1997) Why are organisms usually bigger because multivoltine species (or populations) have less time in colder environments? Making sense of a life history puzzle. Trends per generation available for growth than univoltine ones, multi- in Ecology and Evolution, 12,235–239. voltine species should be smaller than univoltine species, and, Batzer, D. & Boix, D. (2016) Invertebrates in Freshwater Wetlands. among the latter, larger sizes can be reached in cold areas. Springer, Cham, . Unluckily, the lack of life-cycle data for most of the studied Bergmann, K.G.L.C. (1847) Über die Verhältnisse der wärmeokönomie species does not allow testing of this hypothesis. der Thiere zu ihrer Grösse. Göttinger Studien, 3,595–708. Our results suggest that there may be no universal interspecifc Blackburn, T., Gaston, K.J. & Loder, N. (1999) Geographic gradients trends in latitudinal variation of body size across aquatic insect in body size: a clarifcation of Bergmann’s rule. Diversity and groups and, therefore, these cannot be explained by a single Distributions, 5,165–174. universal mechanism, but are instead driven by complex inter- Bournaud, M., Richoux, P. & Usseglio-Polatera, P. 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© 2018 The Royal Entomological Society, Ecological Entomology, 44,249–254 Electronic supplementary material A An interspecific test of Bergmann’s rule reveals inconsistent body size patterns across several lineages of water beetles (Coleoptera: Dytiscidae) Susana Pallarés, Michele Lai, Pedro Abellán, Ignacio Ribera & David Sánchez-Fernández Table S1: Taxa included in the different studied lineages with data on body size, habitat and geographic range. Codes; Distribution: PL= Palearctic, NA=Nearctic; maxLat: maximum latitude; minLat: minimum latitude; LatC: latitude of centroids

Group Taxon average lenght Min length Max length range length range/average lengthHabitat Distribution maxLat minLat LatC Ilybius sunaeneus Ilybius aenescens 9.15 8.50 9.80 1.30 0.14 lentic PL 70.70 45.65 59.09 Ilybius sunaeneus Ilybius angustior 8.85 7.50 10.20 2.70 0.31 lentic NA PL 75.53 32.27 58.91 Ilybius sunaeneus Ilybius anjae 10.24 9.88 10.60 0.72 0.07 lentic PL 69.97 42.77 56.58 Ilybius sunaeneus Ilybius apicalis 9 8.00 10.00 2.00 0.22 lentic PL 55.06 27.89 40.37 Ilybius sunaeneus Ilybius ater 13.75 13.00 14.50 1.50 0.11 lentic PL 69.72 36.69 56.17 Ilybius sunaeneus Ilybius biguttulus 9.65 8.80 10.50 1.70 0.18 lentic NA 51.58 31.76 41.78 Ilybius sunaeneus Ilybius chishimanus 11.065 10.30 11.83 1.53 0.14 lentic PL 66.40 43.07 56.61 Ilybius sunaeneus Ilybius cinctus 8.5 7.50 9.50 2.00 0.24 lentic PL 55.58 23.66 43.93 Ilybius sunaeneus Ilybius crassus 11.25 10.00 12.50 2.50 0.22 lentic PL 70.70 46.85 59.77 Ilybius sunaeneus Ilybius discedens 8.065 7.10 9.03 1.93 0.24 lentic NA PL 69.81 39.67 56.26 Ilybius sunaeneus Ilybius fenestratus 11 10.00 12.00 2.00 0.18 lentic PL 70.66 41.55 56.95 Ilybius sunaeneus Ilybius fraterculus 10 9.30 10.70 1.40 0.14 lentic NA 61.15 32.94 46.10 Ilybius sunaeneus Ilybius fuliginosus 10.75 10.00 11.50 1.50 0.14 lentic PL 73.71 36.27 56.13 Ilybius sunaeneus Ilybius guttiger 9.35 8.70 10.00 1.30 0.14 lentic PL 70.66 44.01 57.39 Ilybius sunaeneus Ilybius lateralis 7.85 7.50 8.20 0.70 0.09 lentic PL 58.04 45.70 52.29 Ilybius sunaeneus Ilybius meridionalis 11.1 10.60 11.60 1.00 0.09 lentic PL 45.14 35.39 40.82 Ilybius sunaeneus Ilybius minakawai 8 7.80 8.20 0.40 0.05 lentic PL 54.42 45.89 50.33 Ilybius sunaeneus Ilybius nakanei 11.1 10.90 11.30 0.40 0.04 lentic PL 49.31 41.41 44.38 Ilybius sunaeneus Ilybius obtusus 9.5 9.00 10.00 1.00 0.11 lentic PL 63.27 30.14 48.46 Ilybius sunaeneus Ilybius picipes 8.75 8.00 9.50 1.50 0.17 lentic NA PL 72.94 38.83 58.65 Ilybius sunaeneus Ilybius pleuriticus 11.4 10.20 12.60 2.40 0.21 lentic NA 63.79 39.53 51.16 Ilybius sunaeneus Ilybius poppiusi 10.325 9.96 10.69 0.73 0.07 lentic PL 70.81 46.13 57.47 Ilybius sunaeneus Ilybius quadriguttatus 11.35 10.50 12.20 1.70 0.15 lentic PL 65.43 36.46 51.19 Ilybius sunaeneus Ilybius quadrimaculatus 10.3 9.50 11.10 1.60 0.16 lentic NA 62.43 36.24 52.34 Ilybius sunaeneus Ilybius similis 11.25 10.50 12.00 1.50 0.13 lentic PL 65.43 46.80 55.84 Ilybius sunaeneus Ilybius subaeneus 10.85 9.20 12.50 3.30 0.30 lentic NA PL 76.06 39.91 59.42 Ilybius sunaeneus Ilybius vittiger 7.65 6.80 8.50 1.70 0.22 lentic NA PL 72.97 53.70 63.47 Deronectes W Mediterranean Deronectes algibensis 5.1 4.90 5.30 0.40 0.08 lotic PL 36.73 36.02 36.40 Deronectes W Mediterranean Deronectes aubei 4.35 4.10 4.60 0.50 0.11 lotic PL 48.71 42.15 45.43 Deronectes W Mediterranean Deronectes bicostatus 4.6 4.20 5.00 0.80 0.17 lotic PL 43.58 39.00 41.32 Deronectes W Mediterranean Deronectes brannanii 4.65 4.40 4.90 0.50 0.11 lotic PL 39.93 39.29 39.62 Deronectes W Mediterranean Deronectes costipennis 4.15 4.00 4.30 0.30 0.07 lotic PL 43.71 40.02 42.32 Deronectes W Mediterranean Deronectes delarouzei 4.35 4.00 4.70 0.70 0.16 lotic PL 43.16 41.63 42.53 Deronectes W Mediterranean Deronectes depressicollis 4.45 4.00 4.90 0.90 0.20 lotic PL 38.74 36.75 37.66 Deronectes W Mediterranean Deronectes doriae 4.3 4.10 4.50 0.40 0.09 lotic PL 41.86 36.84 39.85 Deronectes W Mediterranean Deronectes fairmairei 4.9 4.40 5.40 1.00 0.20 lotic PL 47.36 29.83 37.50 Deronectes W Mediterranean Deronectes ferrugineus 5 4.70 5.30 0.60 0.12 lotic PL 43.64 39.99 41.91 Deronectes W Mediterranean Deronectes fosteri 4.9 4.60 5.20 0.60 0.12 lotic PL 42.74 42.09 42.38 Deronectes W Mediterranean Deronectes hispanicus 5.35 4.90 5.80 0.90 0.17 lotic PL 44.32 35.42 39.89 Deronectes W Mediterranean Deronectes lareynii 5 4.70 5.30 0.60 0.12 lotic PL 43.01 41.36 42.16 Deronectes W Mediterranean Deronectes moestus 4.55 4.10 5.00 0.90 0.20 lotic PL 47.66 29.47 18.78 Deronectes W Mediterranean Deronectes opatrinus 5.35 5.10 5.60 0.50 0.09 lotic PL 46.77 36.19 41.65 Deronectes W Mediterranean Deronectes platynotus 4.15 3.80 4.50 0.70 0.17 lotic PL 53.34 39.70 46.52 Deronectes W Mediterranean Deronectes sahlbergi 3.85 3.50 4.20 0.70 0.18 lotic PL 41.33 36.17 38.88 Deronectes W Mediterranean Deronectes semirufus 4.65 4.30 5.00 0.70 0.15 lotic PL 46.50 37.44 41.97 Deronectes W Mediterranean Deronectes theryi 5.1 4.70 5.50 0.80 0.16 lotic PL 34.34 30.94 32.69 Deronectes W Mediterranean Deronectes wewalkai 4.8 4.50 5.10 0.60 0.13 lotic PL 41.39 40.00 40.66 Graptodytes Graptodytes aequalis 2.55 2.30 2.80 0.50 0.20 lentic PL 41.79 32.67 37.63 Graptodytes Graptodytes atlantis 2.7 2.60 2.80 0.20 0.07 both PL 34.07 32.29 33.21 Graptodytes Graptodytes bilineatus 2.55 2.40 2.70 0.30 0.12 lentic PL 67.64 36.67 53.34 Graptodytes Graptodytes castilianus 2.55 2.30 2.80 0.50 0.20 both PL 42.95 38.34 41.42 Graptodytes Graptodytes delectus 2.55 2.50 2.60 0.10 0.04 lotic PL 28.57 27.73 28.14 Graptodytes Graptodytes eremitus 3.05 3.05 3.05 0.00 0.00 lotic PL 30.65 30.53 30.60 Graptodytes Graptodytes flavipes 2.4 2.20 2.60 0.40 0.17 both PL 64.55 31.14 42.20 Graptodytes Graptodytes fractus 1.8 1.60 2.00 0.40 0.22 lotic PL 64.55 34.42 40.39 Graptodytes Graptodytes granularis 2.25 2.10 2.40 0.30 0.13 lentic PL 67.23 38.91 53.68 Graptodytes Graptodytes ignotus 2.3 2.20 2.40 0.20 0.09 lotic PL 46.55 29.83 39.68 Graptodytes Graptodytes kuchtae 2 1.90 2.10 0.20 0.10 lotic PL 40.07 38.84 39.58 Graptodytes Graptodytes pictus 2.3 2.20 2.40 0.20 0.09 both PL 67.23 41.24 53.87 Graptodytes Graptodytes pietri 2.575 2.35 2.80 0.45 0.17 both PL 37.25 35.18 36.26 Graptodytes Graptodytes sedilloi 2.3 2.10 2.50 0.40 0.17 lentic PL 35.69 30.86 33.05 Graptodytes Graptodytes siculus 2.5 2.30 2.70 0.40 0.16 lotic PL 38.30 36.64 37.59 Graptodytes Graptodytes varius 2.4 2.30 2.50 0.20 0.08 both PL 48.80 31.14 40.45 Graptodytes Graptodytes veterator 2.7 2.60 2.80 0.20 0.07 both PL 46.70 36.00 41.35 Hydroporus planus group Hydroporus acutangulus 3.05 2.80 3.30 0.50 0.16 lentic PL 77.64 47.83 64.05 Hydroporus planus group Hydroporus analis 3.6 3.40 3.80 0.40 0.11 lentic PL 45.27 34.40 39.80 Hydroporus planus group Hydroporus basinotatus 3.25 3.00 3.50 0.50 0.15 lotic PL 38.28 32.34 35.42 Hydroporus planus group Hydroporus brancuccii 2.675 2.50 2.85 0.35 0.13 lotic PL 43.76 40.15 42.28 Hydroporus planus group Hydroporus brevis 2.5 2.30 2.70 0.40 0.16 lentic PL 72.97 52.84 62.38 Hydroporus planus group Hydroporus brucki 4.35 4.00 4.70 0.70 0.16 lentic PL 41.65 33.13 38.47 Hydroporus planus group Hydroporus compunctus 2.92 2.71 3.13 0.42 0.14 lotic PL 28.85 28.02 28.49 Hydroporus planus group Hydroporus decipiens 3.9 3.60 4.20 0.60 0.15 both PL 43.76 36.00 40.02 Hydroporus planus group Hydroporus discretus 3.2 3.00 3.40 0.40 0.13 lotic PL 63.17 26.12 44.64 Hydroporus planus group Hydroporus errans 3.65 3.50 3.80 0.30 0.08 lotic PL 34.21 27.73 31.63 Hydroporus planus group Hydroporus feryi 3.25 3.00 3.50 0.50 0.15 lotic PL 36.82 35.04 36.05 Hydroporus planus group Hydroporus foveolatus 3.75 3.50 4.00 0.50 0.13 lentic PL 50.43 40.09 45.69 Hydroporus planus group Hydroporus fuscipennis 3.2 2.90 3.50 0.60 0.19 lentic NA PL 77.57 37.13 58.49 Hydroporus planus group Hydroporus goldschmidti 3.85 3.50 4.20 0.70 0.18 lotic PL 42.54 38.21 40.68 Hydroporus planus group Hydroporus kabakovi 3.125 3.10 3.15 0.05 0.02 lentic PL 51.93 47.71 49.80 Hydroporus planus group Hydroporus kozlovskii 3.65 3.30 4.00 0.70 0.19 both PL 44.82 30.27 38.44 Hydroporus planus group Hydroporus limbatus 4.35 4.00 4.70 0.70 0.16 lentic PL 45.43 31.07 37.80 Hydroporus planus group Hydroporus lucasi 4.75 4.60 4.90 0.30 0.06 both PL 44.40 31.07 36.36 Hydroporus planus group Hydroporus lundbladi 2.94 2.86 3.02 0.16 0.05 lotic PL 32.87 32.63 32.74 Hydroporus planus group Hydroporus macedonicus 2.975 2.90 3.05 0.15 0.05 lotic PL 43.64 41.17 42.48 Hydroporus planus group Hydroporus marginatus 4.15 3.80 4.50 0.70 0.17 both PL 56.34 31.34 44.48 Hydroporus planus group Hydroporus nigrita 3.1 2.80 3.40 0.60 0.19 lentic PL 72.94 37.77 56.60 Hydroporus planus group Hydroporus pilosus 3.125 2.92 3.33 0.41 0.13 lotic PL 28.58 27.73 28.14 Hydroporus planus group Hydroporus planus 4.3 3.80 4.80 1.00 0.23 lentic PL 67.23 33.66 52.46 Hydroporus planus group Hydroporus pubescens 3.6 3.10 4.10 1.00 0.28 lentic PL 66.72 28.51 49.42 Hydroporus planus group Hydroporus sabaudus 3.35 3.00 3.70 0.70 0.21 lentic PL 51.56 36.94 46.57 Hydroporus planus group Hydroporus tessellatus 3.5 3.10 3.90 0.80 0.23 both PL 58.65 28.78 41.84 Hydroporus planus group Hydroporus thracicus 3.45 3.10 3.80 0.70 0.20 lentic PL 44.19 39.40 41.22 Hydroporus planus group Hydroporus zimmermanni 4.1 3.90 4.30 0.40 0.10 lentic PL 46.45 42.48 44.54 Electronic supplementary material B

An interspecific test of Bergmann’s rule reveals inconsistent body size patterns across several lineages of water beetles (Coleoptera: Dytiscidae) Susana Pallarés, Michele Lai, Pedro Abellán, Ignacio Ribera & David Sánchez- Fernández

Figure S1. Combined phylogenetic tree of the four studied lineages. Table S2. Results of PGLS testing the relationship between average and maximum size and central and maximum latitude for the whole dataset and each lineage, respectively.

Average size – maximum size Central latitude – maximum latitude Group slope±sd p-value R2 slope±sd p-value R2 All species 0.924±0.006 <0.001 0.996 0.612±0.030 <0.001 0.822 Ilybius 0.930±0.047 <0.001 0.946 0.589±0.051 <0.001 0.859 Deronectes 0.924±0.048 <0.001 0.951 0.594±0.103 <0.001 0.641 Hydroporus 0.892±0.030 <0.001 0.969 0.525±0.042 <0.001 0.845 Graptodytes 1.123±0.054 <0.001 0.964 0.464±0.066 <0.001 0.749

Table S3. Results of linear regressions and PGLS testing the relationship between maximum size and maximum latitude for the whole dataset and each lineage, respectively.

Group Predictor slope±sd df F p-value R2 λa All species max.lat -0.011±0.013 1 0.209 0.649 hab -0.355±0.717 1 2.249 0.137 max.lat*hab 0.017±0.016 1 1.145 0.288 full model 0.007 0.972 (p<0.001) Ilybius max.lat 0.033±0.028 1 1.412 0.248 0.063 0.691 (p=0.003) Deronectes max.lat 0.008±0.016 1 0.292 0.596 0.016 0.962 (p=0.003) Hydroporus (all) max.lat -0.011±0.008 1 0.636 0.433 hab 0.913±0.504 1 18.622 <0.001 max.lat*hab -0.004±0.010 1 0.125 0.726 full model 0.437 1 (p<0.001) Hydroporus (lotic) max.lat -0.011±0.008 1 1.751 0.222 0.077 1 (p=0.066) Hydroporus (non-lotic) max.lat -0.015±0.006 1 5.381 0.033 0.240 0.997 (p=0.001) Graptodytes (all) max.lat -0.023±0.007 1 5.837 0.031 hab -0.413±0.382 1 6.651 0.023 max.lat*hab 0.016±0.008 1 3.542 0.082 full model 0.552 0 (p=1) Graptodytes (lotic) max.lat -0.023±0.010 1 5.330 0.082 0.571 0 (p=1) Graptodytes (non-lotic) max.lat -0.004±0.003 1 1.396 0.268 0.134 1 (p=0.008) a Maximum-likelihood estimated Pagel’s lambda with p-values of the test assessing whether it differs for zero (i.e. no phylogenetic signal) in parentheses. max.lat: maximum latitude, hab: habitat type