Body Size Clines Research Articles

Water temperature and season length interact to explain a rare non‐linear ecogeographic cline in body size

AbstractAimAdult body size often exhibits patterns across large‐scale environmental gradients, creating ecogeographic clines. However, the form of body size clines varies across taxonomic groups, with linear and non‐linear patterns in body size observed in nature. Non‐linear body size clines have received less study, and questions remain about how environmental gradients interact to produce non‐linear clines. We examined the body size of the American horseshoe crab (Limulus polyphemus), a widely distributed marine arthropod, and evaluated the hypothesis that temperature and active season length can interact multiplicatively to result in a dome‐shaped distribution.LocationFourteen states in the United States of America and three Mexican states, representing the entire geographic range of the species.MethodsWe compiled environmental data and body size measurements from more than 49,000 individual horseshoe crabs. For each location, we extracted from the literature or calculated from raw data the mean male prosoma width and the mean female prosoma width. We applied a general additive modelling (GAM) approach to characterize the body size cline, test a hypothesis regarding temperature and season length, and explore evidence for the influence of additional environmental factors.ResultsModel results indicate temperature and season length could act multiplicatively to produce dome‐shaped clines, and these findings align with and quantify previous anecdotal reports of a strong dome‐shaped body size cline across latitude for horseshoe crabs.Main ConclusionsActive season length appears to become relatively more influential on horseshoe crab body size in the northern part of their range, while temperature effects per se appear to dominate in southern latitudes. For horseshoe crabs, the pattern of size variation is consistent with the predictions of Optimal Resource Allocation models, but more study is needed to elucidate mechanistic underpinnings. Considering climate change projections, results from our study suggest future shifts in horseshoe crab body sizes.

Systematics and biogeography of Anoura cultrata (Mammalia, Chiroptera, Phyllostomidae): a morphometric, niche modeling, and genetic perspective, with a taxonomic reappraisal of the genus.

The nectar-feeding bats of the genus Anoura are widely distributed in the Neotropics, but are most speciose in the Andes. Anoura cultrata is a rare mid-elevation bat occurring in South and Central America. It is thought to be one of the few bat species exemplifying a latitudinal cline in body size. We address three systematic and biogeographic questions: 1) is the geographic variation in A. cultrata continuous, as argued to justify its current monotypic status? 2) do ecogeographic barriers to dispersal affect such variation? and 3) how do the genetic divergence and biogeography of the species compare to those of other members of the genus? To answer these questions, we used morphometric analyses, ecological niche modeling, and DNA barcoding. We divided the samples of A. cultrata into six geographic groups, delimited by topographic depressions separating mountain systems. We did not find significant correlations between body size and the geographic coordinates within five groups. Therefore, we conclude that ecogeographic barriers to dispersal between the regions occupied by such groups influenced morphometric variation in A. cultrata, and that despite its general north to south reduction in body size, the species does not show continuous clinal variation. A recent phylogenetic study of the genus Anoura concluded that it contains seven valid species. Our DNA barcoding analysis and morphological examination indicated that at least 10 species should be recognized, including A. peruana distinct from A. geoffroyi, and A. aequatoris and A. luismanueli distinct from A. caudifer. Moreover, we show that Central and South American populations of A. cultrata differ from each other at least at the subspecific level, thus we respectively refer to them as A. cultrata cultrata and as A. c. brevirostrum. Similarly, we refer to Central American and Mexican populations of 'A. geoffroyi' as A. peruana lasiopyga, and to their South American counterparts as A. p. peruana. The range of the latter subspecies reaches northeastern Venezuela. The Andes from southern Colombia to northern Peru appear to be the ancestral range of the genus.

What drives the evolution of body size in ectotherms? A global analysis across the amphibian tree of life

AbstractAimThe emergence of large‐scale patterns of animal body size is the central expectation of a wide range of (macro)ecological and evolutionary hypotheses. The drivers shaping these patterns include climate (e.g. Bergmann's rule), resource availability (e.g. ‘resource rule’), biogeographic settings and niche partitioning (e.g. adaptive radiation). However, these hypotheses often make opposing predictions about the trajectories of body size evolution. Therefore, whether underlying drivers of body size evolution can be identified remains an open question. Here, we employ the most comprehensive global dataset of body size in amphibians, to address multiple hypotheses that predict patterns of body size evolution based on climatic factors, ecology and biogeographic settings to identify underlying drivers and their generality across lineages.LocationGlobal.Time PeriodPresent.Major Taxa StudiedAmphibians.MethodsUsing a global dataset spanning 7270 (>87% of) species of Anura, Caudata and Gymnophiona, we employed phylogenetic Bayesian modelling to test the roles of climate, resource availability, insularity, elevation, habitat use and diel activity on body size.ResultsOnly climate and elevation drive body size patterns, and these processes are order‐specific. Seasonality in precipitation and in temperature predict body size clines in anurans, whereas caecilian body size increases with aridity. However, neither of these drivers explained variation in salamander body size. In both anurans and caecilians, size increases with elevational range and with midpoint elevation in caecilians only. No effects of mean temperature, resource abundance, insularity, time of activity or habitat use were found.Main ConclusionsPrecipitation and temperature seasonality are the dominant climatic drivers of body size variation in amphibians overall. Bergmann's rule is consistently rejected, and so are other alternative hypotheses. We suggest that the rationale sustaining existing macroecological rules of body size is unrealistic in amphibians and discuss our findings in the context of the emerging hypothesis that climate change can drive body size shifts.

Beyond latitude: Temperature, productivity and thermal niche conservatism drive global body size variation in Odonata

AbstractAimSo far, latitudinal body size clines have been discussed primarily in the context of thermoregulation, sensu Bergmann. However, body size patterns are ambiguous in ectotherms, and this heterogeneity remains poorly understood. We tested whether Bergmann's rule and the resource availability rule, which states that energetic requirements determine species body size, apply to damselflies and dragonflies (Odonata). Furthermore, we hypothesized that the contrasting effects of thermoregulation and resource availability (e.g., productivity) can obscure the overall gradient in body size variation.LocationGlobal.Time periodContemporary.Major taxa studiedOdonata.MethodsUsing data for 43% of all odonate species described so far, we tested our hypotheses in phylogenetically and spatially comparative analyses at assemblage and species levels. For the distribution data, we integrated expert range maps and ecoregional ranges based on all available occurrence records. To distinguish between long‐term and evolutionarily recent responses of environmental drivers in body size, we constructed a phylogenetically informed classification of all odonate species and decomposed the body size into its phylogenetic and specific components for our subset of species.ResultsWe documented a weak positive relationship between body length and latitude but found strong and contrasting effects for temperature between dragonflies and damselflies and consistent positive effects for productivity that explained 35–57% of body size variation. Moreover, we showed a strong phylogenetic signal in sized‐based thermoregulation that shaped the distribution of dragonflies, but not of damselflies.Main conclusionsWe concluded that temperature, productivity and conservatism in size‐based thermoregulation synergistically determine the distribution of ectotherms, while the taxon‐specific importance of these factors can lead to contrasting and weak latitude–size relationships. Our results reinforce the importance of body size as a determinant of species distributions and responses to climate change.

Unveiling the environmental drivers of intraspecific body size variation in terrestrial vertebrates

AbstractAimWhether intraspecific spatial patterns in body size are generalizable across species remains contentious, as well as the mechanisms underlying these patterns. Here we test several hypotheses explaining within‐species body size variation in terrestrial vertebrates including the heat balance, seasonality, resource availability and water conservation hypotheses for ectotherms, and the heat conservation, heat dissipation, starvation resistance and resource availability hypotheses for endotherms.LocationGlobal.Time period1970–2016.Major taxa studiedAmphibians, reptiles, birds and mammals.MethodsWe collected 235,905 body size records for 2,229 species (amphibians = 36; reptiles = 81; birds = 1,545; mammals = 567) and performed a phylogenetic meta‐analysis of intraspecific correlations between body size and environmental variables. We further tested whether correlations differ between migratory and non‐migratory bird and mammal species, and between thermoregulating and thermoconforming ectotherms.ResultsFor bird species, smaller intraspecific body size was associated with higher mean and maximum temperatures and lower resource seasonality. Size–environment relationships followed a similar pattern in resident and migratory birds, but the effect of resource availability on body size was slightly positive only for non‐migratory birds. For mammals, we found that intraspecific body size was smaller with lower resource availability and seasonality, with this pattern being more evident in sedentary than migratory species. No clear size–environment relationships were found for reptiles and amphibians.Main conclusionsWithin‐species body size variation across endotherms is explained by disparate underlying mechanisms for birds and mammals. Heat conservation (Bergmann's rule) and heat dissipation are the dominant processes explaining biogeographic intraspecific body size variation in birds, whereas in mammals, body size clines are mostly explained by the starvation resistance and resource availability hypotheses. Our findings contribute to a better understanding of the mechanisms behind species adaptations to the environment across their geographic distributions.

Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains

Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains

Oh, the places you will grow: Intraspecific latitudinal clines in butterfly size suggest a phylogenetic signal

Within an animal species, the body sizes of individuals at higher latitudes are often different from individuals at lower latitudes. For homeothermic species that maintain a relatively constant body temperature, such as mammals and birds, individuals at higher latitudes tend to be larger. For ectothermic species, such as insects, that do not retain their own body heat and which often do not maintain a relatively constant body temperature, patterns of body size with latitude are highly variable. This has led some authors to contend that patterns in even closely related species cannot be expected to be similar. Indeed, to our knowledge, no studies of invertebrates have found that more closely related species have more similar relationships between body size and latitude. Further, no studies have investigated the potential influence of diet quality on interspecific differences in these clines. We measured wing lengths of specimens (N = 1753) in eight lycaenid butterfly species and one species of the sister family, Riodinidae to determine if more closely related species have similar latitudinal trends. We also estimated the mean nitrogen content of caterpillars’ hosts to investigate whether this often‐limiting nutrient influences the strength and direction of latitudinal clines in body size. We found that four species are significantly smaller at higher latitudes, an additional species is marginally smaller at higher latitudes (p < .06), and four species had no significant relationship with latitude. We also found a strong phylogenetic signal for latitudinal clines in body size among our species, which indicates that some closely related species may have similar clines. However, the strength and direction of these clines did not depend on the estimated nitrogen content of caterpillars’ hosts. Our results indicate that mean nitrogen content of hosts may not be an important driver in latitudinal clines but that phylogenetic relationships among species should be accounted for when exploring other potential drivers of body‐size clines in invertebrate species.

Bumble bees exhibit body size clines across an urban gradient despite low genetic differentiation

Environmental heterogeneity resulting from human-modified landscapes can increase intraspecific trait variation. However, less known is whether such phenotypic variation is driven by plastic or adaptive responses to local environments. Here, we study five bumble bee (Apidae: Bombus) species across an urban gradient in the greater Saint Louis, Missouri region in the North American Midwest and ask: (1) Can urban environments induce intraspecific spatial structuring of body size, an ecologically consequential functional trait? And, if so, (2) is this body size structure the result of plasticity or adaptation? We additionally estimate genetic diversity, inbreeding, and colony density of these species—three factors that affect extinction risk. Using ≥ 10 polymorphic microsatellite loci per species and measurements of body size, we find that two of these species (Bombus impatiens, Bombus pensylvanicus) exhibit body size clines across the urban gradient, despite a lack of population genetic structure. We also reaffirm reports of low genetic diversity in B. pensylvanicus and find evidence that Bombus griseocollis, a species thought to be thriving in North America, is inbred in the greater Saint Louis region. Collectively, our results have implications for conservation in urban environments and suggest that plasticity can cause phenotypic clines across human-modified landscapes.

Temperature strongly correlates with regional patterns of body size variation in Mediterranean small pelagic fish species

In this study, we consider the applicability of Bergmann’s rule to the populations of small pelagic fish species in the Mediterranean Sea. Under Bergmann’s rule, body size increases with decreasing temperature and increasing latitude. Although this macroecological pattern in body sizes is well established for many taxa of endotherms and ectotherms, it remains not universal and the proposed mechanisms underlying it are multiple and still lack consensus. We explored here the occurrence of geographical body size clines using measurements of average body sizes of 10 species collected in pelagic trawl hauls carried out during acoustic surveys in the Mediterranean Sea. Bergmann’s rule was evaluated by correlating body sizes with latitude and temperature for each species while accounting for potential confounding variables and sampling bias. For 5 species, namely anchovy, sardine, Atlantic chub mackerel, bogue, and blue jack mackerel, we demonstrate that they follow a Bergmann’s rule, with a decline in average body size by about 3.01, 3.43, 3.67, 3.82, and 3.76 % per 1°C of warming respectively, although this did not translate with an increase in size with latitude. The adherence of these 5 pelagic fish to Bergmann’s rules strongly suggests that temperature is a major determinant of their body sizes and enables them to act as sentinel species for identifying the drivers and consequences of warming in the Mediterranean ecosystems.

Ecogeographical patterns of body size differ among North American paper wasp species

Species with widespread distributions frequently show clines in body size across broad geographic areas. These clines may be the result of “ecogeographical rules” that describe spatial patterns of phenotypic differences driven by environmental variation. Intraspecific variation in body size, and the mechanisms causing this variation, have been poorly described in social wasps. This study examined ecogeographical patterns of body size for 12 native species and one non-native species of North American paper wasps (genus: Polistes) using body size measurements from > 14,000 pinned museum specimens. Intraspecific body size was correlated with latitude, elevation, and broadscale climate variation. However, the direction of this relationship was idiosyncratic across species, with Bergmann’s clines and converse Bergmann’s clines equally represented. There was no evidence of a phylogenetic signal in the direction of the cline between body size and the environment. Within species, the worker caste and the reproductive caste showed the same direction of response between body size and latitude, although for most species the reproductive caste was larger than the worker caste. Intraspecific variation in body size appears to be driven by differences in the response among species to similar environmental variables but the mechanisms causing this variation remain unknown.

Impact of landscape fragmentation and climate change on body size variation of bumblebees during the last century

Body size is a key parameter of organism fitness. While the impact of climate change on body size has received increasing attention, the long‐term consequences of landscape fragmentation are still poorly known. These two major global threats may potentially induce opposite trends: the decrease of body size in warmer environments (e.g. individuals developing faster) or the selection of larger individuals in fragmented habitats (e.g. large individuals more capable of reaching distant patches).We assessed the relationship between temperature and landscape fragmentation with mean body size during the last century, within four European regions (Austria, Belgium, England and above the Arctic circle in Scandinavia) and among queens of five bumblebee species. At the regional scale, we first analysed the variation over time of body size and the two hypothesised drivers, temperature and landscape fragmentation. Then, at the local landscape scale, we tested whether body size varied according to these drivers irrespective of the region. At the regional level, we observed a statistically clear increase of queen body size corresponding to an increase of landscape fragmentation (i.e. in Belgium and England). There was no increase of size when fragmentation did not increase (i.e. in Austria and above the Arctic Circle). Temperature also increased through time in all regions. At the local landscape scale, we found that all species were impacted by changes in both climate and landscape fragmentation but show different trends. The body size of the two largest species significantly increased at landscape level with higher fragmentation while body size of the two smallest species decreased with higher fragmentation. We highlight that, in a context of global changes, landscape fragmentation can also be a major driver of body size clines. Depending on the dispersal abilities of species, larger species could be positively selected for and overcome landscape fragmentation.

Body size of ectotherms constrains thermal requirements for reproductive activity in seasonal environments

Body size may influence ectotherm behaviour by influencing heating and cooling rates, thereby constraining the time of day that some individuals can be active. The time of day at which turtles nest, for instance, is hypothesized to vary with body size at both inter- and intra-specific levels because large individuals have greater thermal inertia, retaining preferred body temperatures for a longer period of time. We use decades of data on thousands of individual nests from Algonquin Park, Ontario, Canada, to explore how body size is associated with nesting behaviour in Painted Turtles (Chrysemys picta (Schneider, 1783); small bodied) and Snapping Turtles (Chelydra serpentina (Linnaeus, 1758); large bodied). We found that (i) between species, Painted Turtles nest earlier in the evening and at higher mean temperatures than Snapping Turtles, and (ii) within species, relatively large individuals of both species nest at cooler temperatures and that relatively larger Painted Turtles nest later in the evening compared with smaller Painted Turtles. Our data support the thermal inertia hypothesis and may help explain why turtles in general exhibit geographic clines in body size: northern environments experience more daily variation in temperature, and larger size may evolve, in part, for retention of preferred body temperature during terrestrial forays.

Revisiting classic ecogeographical rules, using a widely distributed mouse species (Apodemus draco)

Abstract Ecogeographical rules predict an association between specific adaptive morphological/physiological traits and latitude, elevation or cooler climates. Such ecogeographical effects are often expressed most clearly in widely distributed species due to continuous selective adaptation occurring over their geographic range. Based on 40 population sampling sites of 116 adult individuals (female, ; male, ) across an elevational range of 191–2573 m, we tested whether morphological traits accorded with predictions of Bergmann’s rule, Allen’s rule and Hesse’s rule for the South China field mouse (Apodemus draco). The effects of elevation on body size, appendage length and heart size were tested by fitting Linear Mixed-Effects Models. None conformed to Bergmann’s, Allen’s or Hesse’s rule. Clines in body size opposed Bergmann’s rule, and foot and snout length ratios opposed Allen’s rule. We conclude that South China field mice, a widely distributed species, exhibit an acute thermoregulation mechanism in which in colder conditions body sizes decrease – as opposed to altering heart sizes or surface area to volume ratios – requiring less energy to regulate body temperatures. Also, there was a stronger selective pressure to increase partial appendage lengths (i.e., foot and snout) to adapt to the specific environment (e.g. longer period of snow cover, up to 2573 m) rather than on a general shortening of appendages to cope with colder conditions.

Heat stress reduces growth rate of red deer calf: Climate warming implications.

Climate models agree in predicting scenarios of global warming. In endothermic species heat stress takes place when they are upper their thermal neutral zone. Any physiological or behavioural mechanism to mitigate heat stress is at the cost of diverting energy from other physiological functions, with negative repercussions for individual fitness. Tolerance to heat stress differs between species, age classes and sexes, those with the highest metabolic rates being the most sensitive to stressing thermal environments. This is especially important during the first months of life, when most growth takes place. Red deer (Cervus elaphus) is supposedly well adapted to a wide range of thermal environments, based on its worldwide distribution range, but little is known about the direct effect that heat stress may have on calf growth. We assessed the effect that heat stress, measured by heat stress indices and physical environment variables (air temperature, relative air humidity, wind speed and solar radiation), have on calf and mother body weights from calf´s birth to weaning. We used 9265 longitudinal weekly body weight records of calf and mother across 19 years in captive Iberian red deer. We hypothesised that (i) heat stress in hot environments has a negative effect on calf growth, especially in males, as they are more energetically demanding to produce than females; and that (ii) the body weight of the mother through lactation should be negatively affected by heat stress. Our results supported hypothesis (i) but not so clearly hypothesis (ii). By weaning (day 143) calves growing under low heat stress environment grew up to 1.2 kg heavier than those growing in high heat stress environment, and males were more affected by heat stress than females. The results have implications in animal welfare, geographical clines in body size and adaptation to climate change.

Elevational partitioning in species distribution, abundance and body size of Australian alpine grasshoppers (Kosciuscola)

AbstractChanges in the physical environment with elevation can influence species distributions and their morphological traits. In mountainous regions, steep temperature gradients can result in patterns of ecological partitioning among species that potentially increases their vulnerability to climate change. We collected data on species distributions, relative abundance and body size for three grasshopper species of the genus Kosciuscola (K. usitatus, K. tristis and K. cognatus) at three locations within the mountainous Kosciuszko National Park in Australia (Thredbo, Guthega and Jagungal). All three species showed differences in their distributions according to elevation, with K. usitatus ranging from 1400 to 2000 m asl, K. tristis from 1600 to 2000 m asl and K. cognatus from 1550 to 1900 m asl. Decreasing relative abundance with increasing elevation was found for K. usitatus, but the opposite pattern was found for K. tristis. The relative abundance of K. cognatus did not change with elevation but was negatively correlated with foliage cover. Body size decreased with elevation in both male and female K. usitatus, which was similarly observed in female K. tristis and male K. cognatus. Our results demonstrate spatial partitioning of species distributions and clines in body size in relation to elevational gradients. Species‐specific sensitivities to climatic gradients may help to predict the persistence of this grasshopper assemblage under climate change.

Differences in Mobility and Dispersal Capacity Determine Body Size Clines in Two Common Alpine-Tundra Arthropods.

The Arctic is projected to be severely impacted by changes in temperature and precipitation. Species react to these changes by shifts in ranges, phenology, and body size. In ectotherms, the patterns of body size clines and their underlying mechanisms are often hard to untangle. Mountains provide a space-for-time substitute to study these shifts along multiple spatial gradients. As such, mobility and dispersal capacity might conceal reactions with elevation. We test this influence on body size clines by comparing two common arthropods of the alpine tundra. We find that high mobility in the lycosid spider Pardosa palustris blurs elevational effects. Partially low mobility at least during development makes the carabid beetle Amara alpina more susceptible to elevational effects. Specific life-history mechanisms, such as brood care in lycosid spiders and holometabolic development in carabid beetles, are the possible cause.

Integrative taxonomic analysis reveals a new species of Leptobrachium (Anura: Megophryidae) from north-eastern Cambodia and central Vietnam

ABSTRACT Species boundaries within the red-eyed Leptobrachium of southern Indochina have been uncertain. Leptobrachium pullum and L. mouhoti from upper and lower elevations, respectively, of the Langbian Plateau of southern Vietnam and eastern Cambodia differ in body size but have relatively low interspecific mitochondrial DNA divergence, leading to speculation that these might represent a single species with an elevational cline in body size. The recent discovery of an allopatric high-elevation population of red-eyed Leptobrachium on the Kon Tum Plateau (= Central Highlands) of north-eastern Cambodia and central Vietnam has been referred to both species, and to a putatively undescribed species. We examine variation in morphology of adults and tadpoles, mitochondrial DNA, 11 nuclear genes and advertisement calls, and show corroborating lines of evidence for the existence of three species of red-eyed Leptobrachium in southern Indochina. Although the three species are reciprocally monophyletic in mitochondrial DNA, their shallow mitochondrial DNA divergences are not mirrored by morphology, advertisement calls, or – in part – nuclear DNA, and probably reflect past mitochondrial introgression rather than recent speciation. The Central Highlands taxon is described herein as a new species. http://www.zoobank.org/urn:lsid:zoobank.org:pub:CE6650AF-D9FB-40F4-8A2E-9B4E23AAC205

Shift in size of bumblebee queens over the last century.

Species can respond differently when facing environmental changes, such as by shifting their geographical ranges or through plastic or adaptive modifications to new environmental conditions. Phenotypic modifications related to environmental factors have been mainly explored along latitudinal gradients, but they are relatively understudied through time despite their importance for key ecological interactions. Here we hypothesize that the average bumblebee queen body size has changed in Belgium during the last century. Based on historical and contemporary databases, we first tested if queen body sizes changed during the last century at the intraspecific level among four common bumblebee species and if it could be linked to global warming and/or habitat fragmentation as well as by the replacement by individuals from new populations. Then, we assessed body size changes at the community level, among 22 species, taking into account species population trends (i.e. increasing, stable or decreasing relative abundance). Our results show that the average queen body size of all four bumblebee species increased over the last century. This size increase was significantly correlated to global warming and habitat fragmentation, but not explained by changes in the population genetic structure (i.e. colonization). At the community level, species with stable or increasing relative abundance tend to be larger than declining species. Contrary to theoretical expectations from Bergmann's rule (i.e. increasing body size in colder climates), temperature does not seem to be the main driver of bumblebee body size during the last century as we observed the opposite body size trend. However, agricultural intensification and habitat fragmentation could be alternative mechanisms that shape body size clines. This study stresses the importance of considering alternative global change factors when assessing body size change.

Contrasting patterns of population structure at large and fine geographical scales in a migratory avian disturbance specialist of braided river ecosystems

AbstractAimTo understand the population structure and its potential drivers at different spatial scales in a migratory bird, the black‐fronted tern (Chlidonias albostriatus), a specialist of the spatially and temporally dynamic environments of braided rivers.LocationNew Zealand.MethodsWe used a three‐pronged approach based on 17 microsatellites, two mitochondrial loci (cytochrome b/control region) and phenotypic data (head‐bill length, bill depth, wing length, weight). We determined large‐scale genetic structure throughout the whole breeding range (approx. 150,000 km2), calculated genetic divergence of breeding colonies and tested for isolation‐by‐distance between colonies. We investigated the level of fine‐scale genetic structure based on spatial autocorrelation analyses and assessed the presence of a body size cline based on phenotypic data. Lastly, we compared phenotypic divergence (PST) and the level of divergence by genetic drift (FST) among breeding colonies to test for underlying mechanisms of population differentiation.ResultsNuclear and mitochondrial DNA showed that across their range black‐fronted terns were effectively panmictic, with low genetic divergence between breeding colonies overall and no isolation‐by‐distance. However, at fine geographical scales black‐fronted terns accrued significant genetic structure for distances up to 75 km, primarily driven by males, indicating more frequent female dispersal. Furthermore, a phenotypic cline in accordance with Bergmann's rule was evident. PST exceeded FST in three traits, suggestive of local adaptation.Main conclusionsSignificant fine‐scale structure can be present in highly mobile, specialist species while not affecting spatial structures at larger scales. Hence, methodologies applied to both whole landscapes and local scales are important to appropriately estimate connectivity in dynamic metapopulations and investigate the processes behind connectivity. Conservation management will need to include protecting currently uninhabited patches to facilitate natural colonization of suitable habitat. For black‐fronted terns, managing whole catchments throughout the entire breeding range would be preferable to managing single patches.

Robustness of latitudinal life-cycle variations in a cricket Dianemobius nigrofasciatus (Orthoptera: Trigonidiidae) in Japan against climate warming over the last five decades

Recent climate warming is expected to have changed the phenology of organisms. The cricket Dianemobius nigrofasciatus (Matsumura) (Orthoptera: Trigonidiidae) has univoltine and bivoltine life cycles in northern and southern regions of Japan, respectively, because of latitudinal variation in the growing season length. Its adult body size increases with decreasing latitude, and decreases at a latitude where the number of annual generations increases. The present study aims to examine whether the range of the bivoltine life cycle has expanded northward due to climate warming. We compared a latitudinal saw-tooth body size cline between the 1960s and the 2010s. The body size showed a latitudinal saw-tooth cline in adults collected in recent years, as it did in adults collected five decades ago. However, no significant difference was observed between these two clines, suggesting that the bivoltine life cycle has not expanded in the last five decades. These results contrast to those recently reported in a closely related species, Polionemobius mikado (Shiraki) (Orthoptera: Trigonidiidae), in which the turning points of the saw-tooth cline had shifted northward in the last four decades. The stable latitudinal distribution of life cycles in D. nigrofasciatus might result from the different photoperiodic regulation of growth rate involved in the different responses to climate warming.