Comparing latitudinal and upstream–downstream gradients: life history traits of invasive mosquitofish

Aim Variation of life history traits along spatial gradients is poorly understood in invasive species and particularly in freshwater fish. We aimed to examine life history variation in a highly invasive fish (Gambusia holbrooki) along latitudinal and upstream–downstream river gradients and to assess the effects of age on this variation. We hypothesized similar responses in populations inhabiting environments more favourable to this species (lower latitudes and lower reaches of rivers). Location European rivers from southern Spain to southern France. Methods We sampled mosquitofish from the lowest reaches of ten river basins along 6° of latitude in the Mediterranean region and seven sites along the upstream–downstream gradient in three of the rivers. We examined abundance, population structure, size‐at‐age and other life history traits along these gradients. Results As hypothesized, lower reaches and lower latitudes both resulted in higher reproductive effort and lower body condition of mosquitofish. However, these patterns explained low per cent variation, were nonlinear and strongly depended on fish age. Independently of fish size, age groups differed in reproductive effort, in the gonadal weight–size relationship and its variation along spatial gradients. Mean size‐at‐age (or overall body size) did not vary with latitude (so the intra‐specific version of Bergmann’s rule or its converse does not apply) and in contrast increased upstream in rivers. Main conclusions Our findings suggest that for life history traits of freshwater organisms, river longitudinal variation plays a role as important as climate, with often differential effects. Our results also illustrate the poor knowledge of spatial variation of many life history traits, which precludes the understanding and prediction of biological invasions in a rapidly changing world.     

Age structure, growth, mortality, and density of belugas (Delphinapterus leucas) in the Canadian Arctic: responses to environment?

Environmental constraints on life-history traits are expected to increase with seasonality in resources such as food and appropriate breeding habitat. Seasonality is highest at polar latitudes, where environmental constraints can be stronger than biotic factors, such as density and its effect on intraspecific competition. In this study, the age structure, body-length distribution, mortality, and density were studied and compared among five beluga populations of the Canadian Arctic: eastern Beaufort Sea (EBS), Baffin Bay (BB), Cumberland Sound (CS), western (WHB), and eastern Hudson (EHB) Bay, to test the prediction that density-dependent effects on these life-history traits should be inversely related to latitude. Growth, but not mortality, showed a significant positive relationship with latitude. Winter density also increased with winter latitude, consistent with the prediction of greater risk of mortality associated with density-independent effects, such as ice entrapment in winter. Age distributions differed among populations, with animals harvested at the highest-latitude population (EBS) being the oldest and attaining the longest adult body lengths, compared to lower-latitude populations (WHB and EHB). The latitudinal variation in growth, adult body size, and winter density is congruent with the hypothesis that environmental seasonality may impose stronger constraints on life-history traits of beluga with increasing latitude.     

Altitudinal variation of demographic life-history traits does not mimic latitudinal variation in natterjack toads (Bufo calamita)

In anuran amphibians, age- and size-related life-history traits vary along latitudinal and altiudinal gradients. In the present study, we tested the hypothesis that altitudinal and latitudinal effects cause similar responses by assessing demographic life-history traits in nine Bufo calamita populations inhabiting elevations from sea level to 2270 m. Skeletochronologically determined age at maturity and longevity increased at elevations exceeding 2000 m, but female potential reproductive lifespan (PRLS) did not increase with altitude, as it did with latitude. Integrating the available evidence, it was found that lifetime fecundity of natterjacks decreased at the upper altitudinal range because PRLS was about the same as in lowland populations but females were smaller. In contrast, small size of northern females was compensated for by increased PRLS which minimised latitudinal variation of lifetime fecundity. Thus, this study provides evidence that altitudinal effects on life-history traits do not mimic latitudinal effects. Life-history trait variation along the altitudinal gradient seems to respond directly to the shortening of the annual activity period. As there is no evidence for increasing mortality in highland populations, reduced lifetime fecundity may be the ultimate reason for the natterjacks' inability to colonise elevations exceeding 2500 m.     

Monogenean parasites of introduced pumpkinseed Lepomis gibbosus (Centrarchidae) in the Danube River Basin

The pumpkinseed, Lepomis gibbosus, a centrarchid fish native to eastern North America, was introduced into Europe at the end of the 19th century. Lepomis gibbosus now represents one of the most successful of introduced fish species, having spread widely throughout many European countries. In this study, we collected monogenean parasites of L. gibbosus from four sites in the Danube River Basin. We recorded four monogenean species: Gyrodactylus sp., probably acquired in the area of introduction, and Onchocleidus similis, O. dispar and Actinocleidus recurvatus, species introduced together with their host. Onchocleidus similis dominated the parasite community at all sampling sites. Actinocleidus recurvatus has only been reported from southern Europe to date and, therefore, this is the first report of A. recurvatus from Central Europe and the Danube River Basin. We observed high morphological variability in both anchor pairs of A. recurvatus. Only in O. similis was there a positive correlation observed between haptor metric traits and fish host length. Differences in metric traits between native and introduced O. similis populations may reflect a difference in fish host size, the introduced fish host achieving a smaller size than fish from native populations. A detailed analysis of microhabitat distribution indicated a preference for the second gill arch for both dominant species O. similis and A. recurvatus, with dissimilar site segregation.     

Latitudinal population differentiation in two species of Solidago (Asteraceae) introduced into Europe

Solidago altissima and S. gigantea were introduced from North America to Europe ~250 yr ago and are now considered aggressive weeds in abandoned fields and conservation areas. We studied patterns of genetic differentiation in these two species along their present latitudinal range in Europe (44-61 degrees N). Two generations of clonally propagated ramets from randomly selected genets of 24 populations of each species were grown in a common-garden experiment at latitude 47 degrees N from 1991 to 1992. Both species showed significant variation among populations in morphological and life-history characters: at this southern location, plants from northern populations were smaller and flowered earlier than plants from southern populations. The gradient of clinal variation was more pronounced in the second year of cultivation than in the first and was steeper in S. altissima than in S. gigantea. Within-population variation among genotypes was significant tot most characters in the case of S. altissima. Phenological rate (reciprocal of days to flowering) and size at maturity showed a significant negative correlation among populations bot not among genotypes within populations, indicating that genetic trade-offs may occur at one but not another infraspecific level. We suggest that the pattern of among-population variation reflects rapid adaptive population differentiation after introduction of the species to Europe.     

Photoperiod affects compensating developmental rate across latitudes in the damselfly Lestes sponsa

1. Although there is a great deal of theoretical and empirical data about the life history responses of time constraints in organisms, little is known about the latitude‐compensating mechanism that enables northern populations' developmental rates to compensate for latitude. To investigate the importance of photoperiod on development, offspring of the obligatory univoltine damselfly Lestes sponsa from two populations at different latitudes (53°N and 63°N) were raised in a common laboratory environment at both northern and southern photoperiods that corresponded to the sites of collection. 2. Egg development time was shorter under northern photoperiod regimes for both populations. However, the northern latitude population showed a higher phenotypic plasticity response to photoperiod compared with the southern latitude population, suggesting a genetic difference in egg development time in response to photoperiod. 3. Larvae from both latitudes expressed shorter larval development time and faster growth rates under northern photoperiod regimes. There was no difference in phenotypic plastic response between northern and southern latitude populations with regard to development time. 4. Data on field collected adults showed that adult sizes decreased with an increase in latitude. This adult size difference was a genetically fixed trait, as the same size difference between populations was also found when larvae were reared in the laboratory. 5. The results suggest phenotypic plasticity responses in life history traits to photoperiod, but also genetic differences between north and south latitude populations in response to photoperiod, which indicates the presence of a latitudinal compensating mechanism that is triggered by a photoperiod.     

Geographical variability in life‐history traits of a midslope dogfish: the brier shark Deania calcea

Deania calcea (n = 420) were collected from the catch of deep‐water trawlers in the southern and eastern scalefish and shark fishery in southern Australia during the years 2008–2011. The total length (L_T) range varied between sexes, females being larger (n = 264; 280–1530 mm) than males (n = 156; 310–921 mm). The reproductive cycle in this population is non‐continuous and asynchronous. The estimated L_T at which 50% of males are mature is 807 mm and is 914 mm for females. Populations of D. calcea in higher latitudes appear to mature at a larger size than conspecifics in lower latitudes, in both the northern and southern hemispheres. Litters ranged from three to 10 embryos with a 1:1 sex ratio, but litter size does not increase with maternal L_T. Deania calcea shows geographical variability in its biological parameters and gathering information on life‐history traits of populations is vital to understand the trade‐offs made by this species in response to environmental conditions and to predict intraspecific spatial differences. Such information is a basis for specific spatial management to protect populations from excessive fishing.     

Are high-latitude individuals superior competitors? A test with <Emphasis Type="Italic">Rana temporaria</Emphasis> tadpoles

Species with a wide distribution over latitudinal gradients often exhibit increasing growth and development rates towards higher latitudes. Ecological theory predicts that these fast-growing genotypes are, in the absence of trade-offs with fast growth, better competitors than low-latitude conspecifics. While knowledge on key ecological traits along latitudinal clines is important for understanding how these clines are maintained, the relative competitive ability of high latitude individuals against low latitude conspecifics has not been tested. Growth and development rates of the common frog Rana temporaria increase along the latitudinal gradient across Scandinavia. Here we investigated larval competition over food resources within and between two R. temporaria populations originating from southern and northern Sweden in an outdoor common garden experiment. We used a factorial design, where southern and northern tadpoles were reared either as single populations or as mixes of the two populations at two densities and predator treatments (absence and non-lethal presence of Aeshna dragonfly larvae). Tadpoles from the high latitude population grew and developed faster and in the beginning of the experiment they hid less and were more active than tadpoles from the low latitude population. When raised together with high latitude tadpoles the southern tadpoles had a longer larval period, however, the response of high latitude tadpoles to the competition by low latitude tadpoles did not differ from their response to intra-population competition. This result was not significantly affected by density or predator treatments. Our results support the hypothesis that high latitude populations are better competitors than their low latitude conspecifics, and suggest that in R. temporaria fast growth and development trade off with other fitness components along the latitudinal gradient across Scandinavia.     

Latitudinal variation in seed weight and flower number in Prunella vulgaris

Studies of seed-weight variation across altitudinal and latitudinal gradients have led to conflicting hypotheses regarding the selective value of this traint in relation to the length of the growing season. Growing-season length may also influence the evolution of seed number, and population differentiation in seed weight may be constrained by a negative genetic correlation between seed weight and seed number within populations. We examined variation in seed weight and an estimate of seed number (flower number) and the covariance of these traits among populations of Prunella vulgaris at five latitudes between northern Michigan and South Carolina. We measured seed weight and flower number in native habitats and in a common environment to determine the extent to which patterns observed in the field reflect genetic differentiation. We observed no genetically based variation in seed weight across the latitudinal gradient, although genetic variation among populations within a latitude was observed. In contrast to the lack of variation in seed weight, flower number increased clinally from northern Michigan to Tennessee in a common environment. Population mean flowering date in a common environment was successively later from north to south. Later-flowering individuals appear to achieve a larger size before flowering and consequently possess more resources for seed production. This difference may account for the greater flower production of late-flowering, southern populations. Independence of population mean seed weight and flower number across the latitudinal gradient suggests that population differentiation in seed weight has not been constrained by a trade-off between seed size and number within populations.     

The relationship between geographic variation in clutch size and migration pattern in the Yellow Wagtail

Clutch size in the Yellow Wagtail increases by about one egg per 19° of latitude throughout Europe, but at a given latitude larger clutches are laid in western than in eastern Europe. In eastern Asia there is evidence of a reverse latitudinal cline, in which clutch size is smaller at higher latitudes, and considerably smaller than in Europe at equivalent latitudes. These trends suggest that smaller clutches are laid by populations with access to extensive wintering areas in east Africa and south-east Asia, whereas larger clutches are laid by populations with more restricted wintering areas in west Africa and India. Higher winter mortality in the latter populations may reduce breeding density, leading to less competition for resources and allowing larger clutches to be produced.     

Latitudinal influence on gametogenesis and host–parasite ecology in a marine bivalve model

Reproduction and parasites have significant impacts on marine animal populations globally. This study aimed to investigate the associative effects of host reproduction and a host–parasite interplay on a marine bivalve, along a geographic gradient of latitude. Cockles Cerastoderma edule were sampled from five European sites (54°N to 40°N), between April 2018 and October 2019. A histological survey provided data on trematode (metacercaria and sporocyst life stages), prevalence, and cockle stage of gametogenesis to assess the influence of a latitudinal gradient on both interplays. Sex ratios at the northernmost sites were skewed toward females, and spawning size was reduced at the lower latitudes. Trematode infection did not follow a latitudinal gradient. Localized site‐related drivers, namely seawater temperature, varied spatially, having an impact on cockle–trematode interactions. Spawning was related to elevated temperatures at all sites. Prolonged spawning occurred at southern latitudes, where seawater temperatures were warmer. Trematode prevalence and the impact of trematodes on gametogenesis were found to be spatially variable, but not latitudinally. Therefore, it is not possible to determine the likelihood of boom and bust events in cockles, based on the latitudinal location of a population. In terms of sublethal impacts, it appeared that energy was allocated to reproduction rather than somatic growth in southern populations, with less energy allocated to reproduction in the larger, northern cockles. The demonstrated spatial trend of energy allocation indicates the potential of a temporal trend of reduced cockle growth at northern sites, as a result of warming sea temperatures. This awareness of the spatially varying drivers of populations is crucial considering the potential for these drivers/inhibitors to be exacerbated in a changing marine environment.     

Parasites of the shore crab Carcinus maenas (L.): implications for reproductive potential and invasion success

The European shore crab, Carcinus maenas, is one of the most successful marine invasive species. Its success has been in part attributed to the loss of parasites, rekindling an interest in host-parasite interactions and impacts on host fitness in this crab. In the present study, we investigated C. maenas populations from Europe, South Africa and Australia for parasites, and assessed their impact on the fitness of male crabs. For the shore crab, testes weight along with success in mating competition is traded off against other life-history traits. We therefore used this parameter as an indicator both for reproductive fitness and a possible resource trade-off in response to parasite infestation. In the native range, crabs infested with Sacculina carcini showed significantly lower testes weight than uninfected crabs. However, helminth parasites did not generally cause reduced testes weights. Crab populations from South Africa and Australia were either parasitized at very low prevalences, or were completely parasite free. However, no population level effect of this parasite release was reflected in testes weight. These findings do not support a severe fitness impact of helminth parasites on C. maenas, which questions the role of parasites on its population dynamics, both in the native area and for invasive success.     

Influence of latitudinal variation in environmental gradients and population structure on the demography of a widespread pelagic fish, <Emphasis Type="Italic">Arripis trutta</Emphasis> (Forster, 1801)

Knowledge of the influence of both spatial and temporal environmental gradients on life history traits and population demographics is a critical requirement in the management of exploited fish populations. This study examined variation in the demographics of Arripis trutta, an economically-important pelagic fish species with a broad latitudinal distribution in the waters of coastal south-eastern (SE) Australia, a region dominated by the influence of the East Australian Current (EAC). A validated ageing protocol was first developed using sectioned sagittal otoliths, which in turn permitted examination of latitudinal variation in A. trutta growth, size compositions and age compositions. The von Bertalanffy growth function parameters for A. trutta in SE Australia were estimated to be L _∞?=?63.20?±?0.37 cm fork length (FL), k?=?0.26?±?0.01 yr^?1 and t _o?=??0.14?±?0.03 yr, with a maximum estimated age of 12.7 years. Growth was shown to be faster with decreasing latitude likely due to a simple relationship with the latitudinal gradient in water temperature; fastest growth occurring in northern NSW and slowest growth occurring in Tasmania. Latitudinal patterns in growth were remarkably similar to those previously reported for this species, despite age being estimated using scale readings some 40 years ago. This consistency in latitudinal growth patterns of a temperate fish can be attributed to the life history-related movements undertaken by A. trutta in this region. This temporally-consistent movement pattern is supported by the spatial gradient in the size and age composition of A. trutta sampled from different latitudes in both the current and historical research, whereby numbers of large and old fish increase progressively from Tasmania to northern NSW. These results highlight the need to consider the potential for spatial size- or age-structuring in the development of sampling designs and interpretation of results for any study examining spatial or temporal variation in demographic parameters of exploited fish populations.     

Latitudinal compensation in female reproductive rate of a geographically widespread reef fish

Latitudinal variation in fitness-related traits has often been attributed to local adaptation to climates. In poikilotherms including fishes, lower temperatures and shorter reproductive seasons at high latitudes would be expected to cause a reduction in annual reproductive output of an individual. Theories of latitudinal compensation predict that organisms at high latitudes should evolve compensatory responses for these climatic effects. Therefore, latitudinal compensation in female reproductive rate (egg production rate), that individuals from high latitudes produce eggs at higher rates than those from lower latitudes, is likely to occur. I tested this hypothesis with a latitudinally widespread reef fish Pomacentrus coelestis that is a multiple batch spawner, from three different localities, from temperate to subtropical waters, within Japan. I used common-environment experiments at three different temperatures to compare reproductive capacity among local populations. In the experiments, average inter-spawning intervals were the shortest and average size-specific clutch weight was the heaviest in fish from the most northern locality across all temperatures, showing clear latitudinal clines. Thus, the northern fish can achieve higher reproductive output per unit time both by shortening inter-spawning intervals and increasing size-specific clutch weight. Additionally, faster egg production rate of the northern fish did not result from increased food consumption. This finding suggests that gross egg production efficiency was higher in the northern fish and that northern fish had a superior capacity for reproduction within a season. These results support the prediction that latitudinal compensation occurs in the female reproductive rate of P. coelestis. As the reproductive season of this species decreases drastically with increasing latitude, the observed cline in the reproductive rate must be an adaptive response to the local selective regime, i.e., length of the reproductive season. Such latitudinal compensation in female reproductive rates may be a common pattern in latitudinally widespread fishes.     

A multivariate approach to the determination of faunal structures among European butterfly species (Lepidoptera: Rhopalocera)

Multivariate analyses of 393 butterfly species over 85 geographical areas (R- and Q-data matrices) in Europe and North Africa have produced a consistent pattern of faunal structures (units and regions). Prominent features to emerge are the latitudinal zonation of geographical units and the division of the Mediterranean into western and eastern components; southwards in Europe, endemicity increases whereas faunal structures decrease in spatial dimensions. Central Europe–from the Urals to the British Isles–forms a single large faunal structure (extent unit and region). A model has been constructed to account for Pleistocene evolutionary changes and endemism in European butterflies and for the east-west taxonomic divisions in the extent faunal structure which dominates central Europe. Periodic Pleistocene climatic changes have resulted in cycles of population extinction, isolation, evolution and migration, but the nature and timing of events has depended on the environmental tolerances of species belonging to different faunal units. During Pleistocene glaciations, southern species have been relatively static and more isolated and have evolved independently. By comparison, northern species have been more mobile and have migrated over large distances. Contact and hybrid zones among cosmopolitan species in northern Europe are probably of some antiquity. They result from persistent survival and isolation of refuge populations in the west and east Mediterranean during glacial phases; dispersal from these refuges leads to their regeneration during each interglacial.     

Temporal Variation in Population Size of European Bird Species: Effects of Latitude and Marginality of Distribution

In the Northern Hemisphere, global warming has been shown to affect animal populations in different ways, with southern populations in general suffering more from increased temperatures than northern populations of the same species. However, southern populations are also often marginal populations relative to the entire breeding range, and marginality may also have negative effects on populations. To disentangle the effects of latitude (possibly due to global warming) and marginality on temporal variation in population size, we investigated European breeding bird species across a latitudinal gradient. Population size estimates were regressed on years, and from these regressions we obtained the slope (a proxy for population trend) and the standard error of the estimate (SEE) (a proxy for population fluctuations). The possible relationships between marginality or latitude on one hand and slopes or SEE on the other were tested among populations within species. Potentially confounding factors such as census method, sampling effort, density-dependence, habitat fragmentation and number of sampling years were controlled statistically. Population latitude was positively related to regression slopes independent of marginality, with more positive slopes (i.e., trends) in northern than in southern populations. The degree of marginality was positively related to SEE independent of latitude, with marginal populations showing larger SEE (i.e., fluctuations) than central ones. Regression slopes were also significantly related to our estimate of density-dependence and SEE was significantly affected by the census method. These results are consistent with a scenario in which southern and northern populations of European bird species are negatively affected by marginality, with southern populations benefitting less from global warming than northern populations, thus potentially making southern populations more vulnerable to extinction.     

Using Tournament Angler Data to Rapidly Assess the Invasion Status of Alien Sport Fishes (Micropterus spp.) in Southern Africa

Fishes are one of the most commonly introduced aquatic taxa worldwide, and invasive fish species pose threats to biodiversity and ecosystem function in recipient waters. Considerable research efforts have focused on predicting the invasibility of different fish taxa; however, accurate records detailing the establishment and spread of invasive fishes are lacking for large numbers of fish around the globe. In response to these data limitations, a low-cost method of cataloging and quantifying the temporal and spatial status of fish invasions was explored. Specifically, angler catch data derived from competitive bass angling tournaments was used to document the distribution of 66 non-native populations of black bass (Micropterus spp.) in southern Africa. Additionally, catch data from standardized tournament events were used to assess the abundance and growth of non-native bass populations in southern Africa relative to their native distribution (southern and eastern United States). Differences in metrics of catch per unit effort (average number of fish retained per angler per day), daily bag weights (the average weight of fish retained per angler), and average fish weight were assessed using catch data from 14,890 angler days of tournament fishing (11,045 days from South Africa and Zimbabwe; 3,845 days from the United States). No significant differences were found between catch rates, average daily bag weight, or the average fish weight between countries, suggesting that bass populations in southern Africa reach comparable sizes and numbers relative to waters in their native distribution. Given the minimal cost associated with data collection (i.e. records are collected by tournament organizers), the standardized nature of the events, and consistent bias (i.e. selection for the biggest fish in a population), the use of angler catch data represents a novel approach to infer the status and distribution of invasive sport fish.     

Molecular and Quantitative Genetic Differentiation in Sitobion avenae Populations from Both Sides of the Qinling Mountains

Quantitative trait differences are often assumed to be correlated with molecular variation, but the relationship is not certain, and empirical evidence is still scarce. To address this issue, we sampled six populations of the cereal aphid Sitobion avenae from areas north and south of the Qinling Mountains, and characterized their molecular variation at seven microsatellite loci and quantitative variation at nine life-history traits. Our results demonstrated that southern populations had slightly longer developmental times of nymphs but much higher lifetime fecundity, compared to northern populations. Of the nine tested quantitative characters, eight differed significantly among populations within regions, as well as between northern and southern regions. Genetic differentiation in neutral markers was likely to have been caused by founder events and drift. Increased subdivision for quantitative characters was found in northern populations, but reduced in southern populations. This phenomenon was not found for molecular characters, suggesting the decoupling between molecular and quantitative variation. The pattern of relationships between F_ST and Q_ST indicated divergent selection and suggested that local adaptation play a role in the differentiation of life-history traits in tested S. avenae populations, particularly in those traits closely related to reproduction. The main role of natural selection over genetic drift was also supported by strong structural differences in G-matrices among S. avenae populations. However, cluster analyses did not result in two groups corresponding to northern and southern regions. Genetic differentiation between northern and southern populations in neutral markers was low, indicating considerable gene flow between them. The relationship between molecular and quantitative variation, as well as its implications for differentiation and evolution of S. avenae populations, was discussed.     

Northward range expansion requires synchronization of both overwintering behaviour and physiology with photoperiod in the invasive Colorado potato beetle (Leptinotarsa decemlineata)

Photoperiodic phenological adaptations are prevalent in many organisms living in seasonal environments. As both photoperiod and growth season length change with latitude, species undergoing latitudinal range expansion often need to synchronize their life cycle with a changing photoperiod and growth season length. Since adaptive synchronization often involves a large number of time-consuming genetic changes, behavioural plasticity might be a faster way to adjust to novel conditions. We compared behavioural and physiological traits in overwintering (diapause) preparation in three latitudinally different European Colorado potato beetle (Leptinotarsa decemlineata) populations reared under two photoperiods. Our aim was to study whether behavioural plasticity could play a role in rapid range expansion into seasonal environments. Our results show that while burrowing into the soil occurred in the southernmost studied population also under a non-diapause-inducing long photoperiod, the storage lipid content of these beetles was very low compared to the northern populations. However, similar behavioural plasticity was not found in the northern populations. Furthermore, the strongest suppression of energy metabolism was seen in pre-diapause beetles from the northernmost population. These results could indicate accelerated diapause preparation and possibly energetic adjustments due to temporal constraints imposed by a shorter, northern, growth season. Our results indicate that behavioural plasticity in burrowing may have facilitated initial range expansion of L. decemlineata in Europe. However, long-term persistence at high latitudes has required synchronization of burrowing behaviour with physiological traits. The results underline that eco-physiological life-history traits of insects, such as diapause, should be included in studies on range expansion.