The distribution of Branchiostoma senegalense (Acrania,Branchiostomidae) in the off-shore shelf region off North West Africa

During investigations on the macrobenthos between 17° N and 26° N on the North West African continental shelf, abundant stocks of Branchiostoma were found off Spanish Sahara (23° N-25° N), on the d'Arguin Bank (21° N-20° N) and off Gambia (12° N-13° N). The lancelets were identified as Branchiostoma senegalense (WEBB, 1955) by means of statistical analyses. The lancelet populations occur at dephts down to about 40 m. Deeper regions are probably avoided because of the excessively high detritus content. Favourable environmental factors such as temperature, composition of the sediment and food supply permit high lancelet abundancies. Up to 9000 animals'm² were found in the population off Spanish Sahara. Rough calculations showed that the lancelet population comprises about 6 × 10¹² individuals with a biomass of 1.5 million tons. The potential natality amounts to about 45 × 10¹⁵ larvae a year.     

Geographic variation in photoperiodic diapause induction and diapause intensity in Sericinus montelus (Lepidoptera: Papilionidae)

Abstract Due to the risk of extinction and ornamental value of the swallowtail butterfly, Sericinus montelus Gray (Lepidoptera: Papilionidae) in China, knowledge about local adaptations is important for the conservation and economical utilization of the species. In the present study, photoperiodic diapause induction and diapause intensity of S. montelus populations from Jiamusi (46°37′N), Beijing (40°15′N), Zibo (36°48′N), Fangxian (32°36′N), Wuhan (30°33′N) and Huaihua (27°33′N) were characterized at 25°C. Logistic regression analysis revealed a significant population × hours of light interaction, confirming that photoperiodic responses varied among populations. The critical photoperiod was positively correlated with latitude and increased toward the north at a rate of about 1 h for each 6.67 degrees of latitude. Survival analyses indicated that survival time of diapausing pupae before adult eclosion differed significantly among populations at 25°C and 16 : 8 L : D h. The mean duration of pupal diapause was also positively correlated with latitude. Our study reveals geographic variation in the critical photoperiod for diapause induction and in diapause intensity of S. montelus. These results provide useful information for our general understanding about seasonal adaptation in insects and may also be used to predict how geographic populations respond to climate warming.     

Latitudinal differences in temperature effects on the embryonic development and hatchling phenotypes of the Asian yellow pond turtle,Mauremys mutica

The effect of incubation temperature on embryonic development and offspring traits has been widely reported for many species. However, knowledge remains limited about how such effects vary across populations. Here, we investigated whether incubation temperature (26, 28, and 30 °C) differentially affects the embryonic development of Asian yellow pond turtle (Mauremys mutica) eggs originating from low‐latitude (Guangzhou, 23°06′N) and high‐latitude (Haining, 30°19′N) populations in China. At 26 °C, the duration of incubation was shorter in the high‐latitude population than in the low‐latitude population. However, this pattern was reversed at 30 °C. As the incubation temperature increased, hatching success increased in the low‐latitude population but slightly decreased in the high‐latitude population. Hatchlings incubated at 30 °C were larger and righted themselves more rapidly than those incubated at 26 °C in the low‐latitude population. In contrast, hatchling traits were not influenced by incubation temperature in the high‐latitude population. Overall, 30 °C was a suitable developmental temperature for embryos from the low‐latitude population, whereas 26 and 28 °C were suitable for those from the high‐latitude population. This interpopulation difference in suitable developmental temperatures is consistent with the difference in the thermal environment of the two localities. Therefore, similarly to posthatching individuals, reptile embryos from different populations might have evolved diverse physiological strategies to benefit from the thermal environment in which they develop. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114 , 35–43.     

Environmental adaptation and genetic variations in geographically isolated Emma field crickets Teleogryllus emma (Orthoptera: Gryllidae)

The Emma field cricket, Teleogryllus emma (Ohmachi & Matsuura), distributed between 43°N and 30°N in the Japanese archipelago, is univoltine and overwinters in the egg stage. Its eggs hatch on the slope of the Oishi Dam (38.03°N, 139.57°E, 160–170 m a.s.l.) in late June, adults begin emerging from late August, and oviposition lasts until early October. Oviposition is limited to the period when the water level of the Oishi Dam is low. The period from egg hatching to adult emergence is approximately 1 month shorter than that of the T. emma population on the Arakawa riverside (38.09°N, 139.57°E, 29 m a.s.l.), which is approximately only 7 km from the Oishi Dam. The egg and body sizes of T. emma on the slope of the Oishi Dam were smaller than those of T. emma on the Arakawa riverside, and the egg and nymphal periods were shorter; these variations were inherited by the next generation of T. emma. The egg period, nymphal period and head width of T. emma on the dam slope correspond to those of the populations near 40°N. Several traits of the T. emma population on the dam slope were naturally selected by adapting to the isolated environment, resulting in the genetic variations. However, their variations were small and the period after isolation is short, suggesting that it is in the early stages of speciation.     

Effects of ambient temperature and of temperature acclimation on nitrogen excretion and differential catabolism of protein and nonprotein resources in the intertidal snails,Littorina saxatilis (Olivi) and L. obtusata (L.)

Nitrogenous excretion in two snails, Littorina saxatilis (high intertidal) and L. obtusata (low intertidal) was studied in relation to temperature acclimation (at 4° and 21°C), including total N excretion rates, the fraction of urea in N excretion, corresponding O:N ratios and the partitioning of deaminated protein between catabolic and anabolic processes at 4°, 11° and 21°C. Aggregate N excretion rates in both species showed no significant compensatory adjustments following acclimation. Total weight specific N excretion rates at 21°C were higher in standard 3 mg L. saxatilis (739 ng N mg⁻¹ h⁻¹) than standard 5 mg L. obtusata (257 ng N mg⁻¹ h⁻¹) for snails acclimated to 21°C. Comparisons of Q₁₀ values of total weight specific N excretion to Q₁₀ values for weight specific oxygen consumption ({xxV}O₂) between 4° to 11 °C and 11° to 21°C indicated that, while total rates of catabolic metabolism ({xxV}O₂) and protein deamination in L. obtusata were essentially parallel, the relationship between N excretion and {xxV}O₂ in L. saxatilis revealed the partitioning of a larger share of deaminated protein carbon into anabolism at 4° and 21°C than at 11°C. Urea N accounted for a larger share of aggregate N excreted in L. saxatilis than in L. obtusata, but in both species urea N is a greater proportion of total N excreted when acclimated at 4°C (urea N: ammonia N ratio range: 1 to 2.15) than in snails acclimated to 21°C (urea N: ammonia N ratio range: 0.46 to 1.39). Molar O:N ratios indicate that the proportion of metabolism supported by protein catabolism is greater in L. saxatilis (O:N range: 2.5–8.4) than in L. obtusata (O:N range: 7.3–13.0). In both species, regardless of acclimation temperature, the O:N ratios are generally lowest (high protein catabolism) at 4°C and highest at 21°C.     

Heat coma as an indicator of resistance to environmental stress and its relationship to ocean dynamics in the sea skaters,Halobates (Heteroptera: Gerridae)

Abstract The tolerance to temperature increase was tested for Halobates individuals collected during two cruises in the western tropical Pacific Ocean (MR‐06‐05‐Leg 3, December 21, 2006–January 12, 2007, 0°N‐8°N; KH‐06‐02‐Leg 5, August 18–31, 2006, 12°N–17°N). High temperature coma experiments were conducted on adults and 5th instar larvae. On average, H. sericeus (distributed in the wide latitude zone of 5°N–40°N), H. germanus (distributed in the moderate latitude zone of 0°N–35°N) and H. micans (distributed mainly in the lower latitudes around the equator) were on average paralyzed at 35.6°C (SD: 0.89), 32.9°C (SD: 2.17) and 31.6°C (SD: 2.60), respectively (P= 0.035). According to the current dynamics during the cruise, the colony of H. sericeus at one station (5°N 137°E) may have been transferred from the northern area of 14°N by three currents (North Equatorial Current, Mindanao Current and North Equatorial Counter Current) to the area of 5°N 138°E. Extremely high heat resistance was shown by the adults of H. germanus in the sea area around the equator. Dynamic current and air movements in this area around the equator, that is a “warm seawater pool”, could be hypothesized to be related to the high resistance to heat shown in this study.     

Temperature‐dependent developmental model of Neoseiulus californicus (McGregor) (Acari,Phytoseiidae)

The developmental time and survival of immature stages of Neoseiulus californicus were studied at nine constant temperatures (12, 16, 24, 24, 28 32, 36, 38 and 40°C), 60–70% RH, and a photoperiod of 16 : 8 (L : D) h. The total mortality of immature N. californicus was lowest at 24°C (4.5%) and highest at 38°C (15.2%). The total developmental time decreased with increasing temperature between 12°C (18.38 days) and 32°C (2.98 days), and increased beyond 32°C. The relationship between the developmental rate and temperature was fitted by five nonlinear developmental rate models (Logan 6, Lactin 1, 2 and Briere 1, 2). The nonlinear shape of temperature development was best described by the Lactin 1 model (r² = 0.98). The developmental variation of each stage was well described by the three‐parameter Weibull distribution model (r² = 0.91–0.93). The temperature‐dependent developmental models of N. californicus developed in this study could be used to determine optimal temperature conditions for its mass rearing, to predict its seasonal population dynamics in fruit tree orchards or greenhouse crops, or to develop a population dynamics model of N. californicus.     

Adaptive latitudinal variation of the duration and thermal requirements for development in the ground beetle Amara communis (Panz.) (Coleoptera, Carabidae)

The data are obtained on development time at six constant temperatures (12, 14, 16, 18, 20, 22°C) and thermal requirements for preimaginal development in a ground beetle Amara communis from Arkhangelsk (64°34′N) and St. Petersburg (59°53′N). The larval and pupal development times were found to be significantly shorter in the Arkhangelsk than in the St. Petersburg population under all temperatures. As a result, total preimaginal development appeared to be shorter by 6.2–6.6% in the Arkhangelsk population. The regression lines of the larval, pupal and total (egg-to-adult) development rate on temperature for the Arkhangelsk population run above and steeper than the respective lines for the St. Petersburg population. Both populations share the similar values of the thermal thresholds (7.2–8.2°C). This explains faster preimaginal development in the northern population under all temperatures above the threshold. Thus, the slope of the regression lines increases, i.e., the sum of degree-days decreases, whereas the thermal threshold for development exhibited no distinctive changes from south to north in this species. Adults from Arkhangelsk reared in the experiments appeared heavier on the average in comparison with those from St. Petersburg, especially at 18–22°C. Temperature did not significantly affect adult weight, except the fact that the beetles were slightly heavier at 20 and 22°C. Consequently, the well-known “temperature-size rule” is violated in this species. Relative growth rate in larvae of A. communis increased considerably with temperature rise from 14 to 22°C. It was significantly higher in the beetles from Arkhangelsk at 18–22°C. There were no differences in larval growth rate between the two populations at 14 and 16°C.     

Geographic variation in winter freezing susceptibility in the eggs of the European pine sawfly (Neodiprion sertifer)

Abstract 1 The European pine sawfly, Neodiprion sertifer (Geoffroy) (Hymenoptera, Diprionidae), frequently defoliates Scots pine (Pinus sylvestris L.) forests in northern Europe. It overwinters as an egg. It has been proposed that the high egg mortality caused by low winter temperatures limits the occurrence of outbreaks to the southern part of Fennoscandia. 2 In this study, variation in freezing avoidance by egg supercooling between four Finnish populations (originating between latitudes 60°N and 69°N) of N. sertifer was tested by differential thermal analysis. Offspring of 20 females within each population were selected for the study. The freezing avoidance of parasitized eggs was also examined. 3 The northernmost Inari population was found to be the cold hardiest, and the southernmost (Hanko) was the least hardy population. The within‐population variation between females was greatest in the population from Inari, and the next greatest in the one from Hanko. The inland populations in Eastern Finland had the smallest within‐population variation in freezing avoidance. 4 The high variation in freezing avoidance of eggs will enable N. sertifer to adapt to the predicted climate change and to spread its distribution northwards. This may also change the risk for outbreaks in this area. Parasitized eggs froze at higher temperature than healthy eggs. This observation indicates that N. sertifer may experience reduced egg parasitism in certain winter climate conditions.     

Symbiotic growth of indigenons white clover (Trifolium repens) with local Rhizobium leguminosarum biovar trifolii

To study a possible adaptation of the symbiosis between white clover (Trifolium repens L.) and Rhizobium leguminosarum biovar trifolii with regard to light and temperature at northern latitudes, local seed populations of white clover and isolates of R. leguminosarum biovar trifolii from 3 different latitudes in Norway, 58°48'N, 67°20'N and 69°22'N, were used. The commercial cultivar Undrom was used as a reference plant. The experiments were done at 18 and 9°C under controlled conditions in a phytotron during the natural growing season at 69° 39'N. Growth of the plants was evaluated by number and size of leaves, dry matter production and total N-content. At 18°C the white clover plants were harvested twice while at 9°C there was only one growth period. The results from first harvest at 18°C and total growth at 9°C, showed that white clover populations from northern Norway had a lower growth potential than the population from the south and cv. Undrom. This difference was not apparent in the second growth period at 18°C. Growth of the plants from seeds to first harvest was enhanced by mineral nitrogen compared to plants dependent on Rhizobium only. However, after a second growth period dry weight and total nitrogen content of the plants with nitrogen fixation were comparable to the plants receiving mineral nitrogen. Statistical analysis showed that the most important factor for the variation in dry matter production was the plant population. Within the populations at 9°C and at first harvest at 18°C, there were no significant differences in dry matter production with different Rhizobium inoculum. In the second growth period at 18°C, different inoculum gave significantly different amount of dry matter within a population. The results showed a significant interaction between plant population and Rhizobium inoculum, and the results indicated that plants from the north gave higher yield when nodulated by Rhizobium from the north than from the south.     

Competitive success of southern populations of Betula pendula and Sorbus aucuparia under simulated southern climate experiment in the subarctic

Global warming has been commonly accepted to facilitate species’ range shifts across latitudes. Cross‐latitudinal transplantations support this; many tree species can well adapt to new geographical areas. However, these studies fail to capture species’ adaptations to new light environment because the experiments were not designed to explicitly separate species’ responses to light and temperature. Here we tested reaction norms of tree seedlings in reciprocal transplantations 1,000 km apart from each other at two latitudes (60°N and 69°N). In contrast to past studies, we exposed our experimental plants to same temperature in both sites (temperature of 60°N growing site is recorded to adjust temperature of 69°N site in real time via Internet connection) while light environment (photoperiod, light quality) remained ambient. Shoot elongation and autumn coloration were studied in seedlings of two deciduous trees (Betula pendula and Sorbus aucuparia), which were expected to respond differently to day length. Sorbus as a member of Rosaceae family was assumed to be indifferent to photoperiod, while Betula responds strongly to day length. We hypothesized that (1) southern and northern populations of both species perform differently; (2) southern populations perform better in both sites; (3) autumn phenology of southern populations may delay in the northern site; (4) and Sorbus aucuparia is less dependent on light environment. According to the hypotheses, shoot elongation of northern population was inherently low in both species. An evolutionary consequence of this may be a competitive success of southern populations under warming climate. Southern population of B. pendula was delayed in autumn coloration, but not in growth cessation. Sorbus aucuparia was less responsive to light environment. The results suggest that light provides selection pressure in range shifts, but the response is species dependent.     

Effects of temperature and elevated CO2 on cell division in shoot meristems: differential responses of two natural populations of Dactylis glomerata L.

The aim was to establish whether temperature and/or elevated [CO₂] (-700 μmol mol^?1) affects the cell doubling time (cdt) in the different zones of the shoot apex of two natural populations of Dactylis glomerata originating in Portugal (38° S3′ N) and in Sweden (63° 09′ N). In the Portuguese population at ambient [CO₂], only the pith rib meristem (PRM) exhibited a significant shortening of cdts from 10 to 30 °C. Elevated [CO₂] resulted in a significant shortening of cdt, particularly in the PRM where cdt was reduced 4-8- and 6-1-fold at 10 and 20 °C, respectively, but only 2-fold at 30 °C. In the Swedish population at ambient [CO₂], there were no consistent temperature-dependent alterations to cdt and this population was less responsive to elevated [CO₂] than the Portuguese population. Nevertheless, elevated [CO₂] resulted in a significant shortening of the cdt for some of the zones; the maximum reduction occurred in the PRM at 30 °C. We concluded that in the shoot apex of the Portuguese population, and most notably in the PRM, 10 and 20 °C were non-optimal temperatures for cell division, whilst the Swedish population was relatively buffered against temperature change. Elevated [CO₂] resulted in substantially greater reductions in cdts in the shoot meristem of the Portuguese population than in that of the Swedish population.     

ESTERASE VARIATION AND GENETIC STRUCTURE IN THREE GEOGRAPHIC POPULATIONS OF SITODIPLOSIS MOSELLANA (GEHIN) (DIPTERA: CECIDOMYIIDAE) IN WESTERN CHINA*

Abstract This paper investigates the esterase variation and genetic structure in three geographic populations of Sitodiplosis mosellana (Géhin) in western China by PAGE. The localities surveyed are Gaolan (36.3°N, 103.9°E) and Wuwei (37.9°N, 102.6°E) in spring wheat region and Chang'an (34. 1°N, 108.9° E) in winter wheat region. The results suggest that the esterase is coded by two loci: Est‐1 and Est‐2. Est‐1 is coded by a plastogene producing only one band that is the fastest on the gel among all bands. The Est‐2 is duplicated loci with 8 alleles, namely, a, b, c, d, e, f, g, h, which produce altogether 8 bands in all the populations and 1–4 bands in individual samples. There are 19 zymogram types observed in the three geographic populations. Seventeen zymogram types emerge in Chang'an population, but 5 and 4 zymogram types are found respectively in Gaolan and Wuwei populations. II₂ zymogram type is the commonest in all the populations. The alleles that had the highest frequencies in all the populations are d, e, g. All 8 alleles at the Est2 were observed in Chang'an population, but only total 3 alleles‐d, e, g at the Est‐2 appeared in Gaolan and Wuwei populations. The analysis of genetic identity and cluster (UPGMA) on the alloenzyme indicates that the relationship between the two populations of spring wheat region seems to be closer, as compared with the relationship between spring wheat population and winter wheat population. It is evident that there exists some infraspecific variation caused mainly by genetic drift in S. mosellana and the gene flow among the populations possibly took place to some extent.     

Latitudinal population differentiation in phenology,life history and flower morphology in the perennial herb Lythrum salicaria

Abstract In plants with a wide distribution, phenological characters can be expected to vary clinally along climatic gradients, whereas other characters important for adaptation to local biotic and abiotic factors may vary in a more mosaic fashion. We used common‐garden experiments and controlled crosses to examine population differentiation in phenology, life history and morphology in the perennial herb Lythrum salicaria along a latitudinal transect through Sweden (57°N to 66°N). Northern populations initiated growth and flowering earlier, flowered for a shorter period, were shorter, produced more and larger winter buds, and were older at first reproduction than southern populations. Flower morphology varied significantly among populations, but was, with the exception of calyx length, not significantly related to latitude of origin. Survival in the common garden (at 63°49′N) was positively correlated with latitude of origin and the size and number of winter buds produced in the preceding year. The results suggest that the among‐population differences in phenology and life history have evolved in response to latitudinal variation in length of the growing season. Further studies are required to determine whether population differentiation in flower morphology is maintained by selection.     

Niche separation between <Emphasis Type="Italic">Encarsia dispersa</Emphasis> and <Emphasis Type="Italic">Encarsia guadeloupae</Emphasis>, two biological control agents of the spiraling whitefly <Emphasis Type="Italic">Aleurodicus dispersus</Emphasis>, in Benin,West Africa

The spiraling whitefly Aleurodicus dispersus (Russell) is an insect pest that causes substantial damage to ornamental plants, shade trees and food crops. It was first observed in Benin in 1993. Two host specific parasitoids, Encarsia dispersa and E. guadeloupae, fortuitously introduced with its host, were recovered in the second half of 1993 in Southern Benin. Survey results from 1993 to 1995 (already published) showed the decline in the population of A. dispersus due to the parasitoids, and the spread from Cotonou (6°10′N) in a northern directions of both parasitoids and their host. Results from similar field surveys from 1996 to 2003 document that the spiraling whitefly and both its parasitoids spread to Natitingou (10°20′N, 540 km) in 1995 and Bembereke (10°14′N) in 1996, whereby E. dispersa arrived within less than a year of its host and quickly became dominant in the two localities on the northern front. In subsequent years, the parasitoids established their geographical niches, with E. dispersa being more abundant (up to 89%) in the coastal south bellow latitude 7°30′N and E. guadeloupae (up to 84%) in the north between latitudes 7°30′ and 10°30′N. We conclude that the gradual replacement observed over ten years and over 500 km has to do with longitudinal shifts in the length and severity of the dry season and the higher susceptibility to these conditions by E. dispersa.     

Competition between laboratory populations of green leafhoppers,Nephotettix spp. (Homoptera: Cicadellidae)

Intra- and interspecific competition between laboratory populations of four green leafhoppers, Nephotettix spp. was studied in the laboratory under three different temperature regimes of 24°C, 27°C and 30°C. For the single-species population of the three tropical species, the equilibrium density increased as the temperature increased. On the other hand, for the temperature species N. cincticeps, the highest equilibrium density was at the intermediate temperature and the lowest at high temperature. Interspecific interactions between two tropical (N. virescens vs. N. nigropictus), a tropical and a temperature (N. virescens vs. N. cincticeps) and a rice-feeding and a grass-inhabiting (N. virescens vs. N. malayanus) Nephotettix species were also studied in the laboratory at the three temperature regimes. Temperature differentially affected the outcome of competition between two Nephotettix species. Between N. virescens and N. nigropictus, the latter was more successful over the former at low and intermediate temperatures, while the former was more successful at high temperature. Between N. virescens and N. cincticeps, the temperate species inhibited the growth of the tropical species at low temperature while the tropical species inhibited the growth of the temperate species at high temperature. At intermediate temperature, the population of N. virescens persisted at a slightly higher density over the population of N. cincticeps. Between the rice-feeding N. virescens and the grass-inhabiting N. malayanus, regardless of temperature the population density of the latter was greatly reduced and later became extinct while the population of the former continued its growth. These consequences of competition between two Nephotettix species conformed fairly well to those predicted by theLotka-Volterra model using demographic parameters specified for each species.     

Cover Caption

The Glanville fritillary butterfly, Melitaea cinxia, is widely distributed between approximately 35°N and 60°N in Eurasia, from the Atlantic coast to the Baikal Lake region. In China, M. cinxia is distributed in Xinjiang. The geographic populations have to face greatly different ambient temperatures. The biochemical adaptation strategy of M. cinxia is revealed in Chinese population for dealing with high temperature (see pages 758-770). Photo provided by Rongjiang Wang.     

Genetic Characteristics of Western North Pacific Sei Whales, Balaenoptera borealis, as Revealed by Microsatellites

Genetic characteristics of sei whales, Balaenoptera borealis, inhabiting the western North Pacific were analyzed at 17 microsatellite loci in a total of 89 whales obtained from the area between 37°N–45°N and 147°E–166°E in 2002 (N = 39) and 2003 (N = 50). All the loci analyzed were polymorphic over the samples, some of the loci had more than 10 alleles, indicating a high level of genetic variation within samples. No significant deviation from the expected Hardy–Weinberg genotypic proportion was observed at the 17 loci in the samples. No evidence of genetic heterogeneity in allele frequencies was observed between sexes within samples as well as between the two temporally different samples, indicating a single population of sei whales inhabiting the western North Pacific. We finally tested and demonstrated that the population appeared not to suffer from genetic bottleneck as a result of population decline from past commercial whaling.     

Variation in aboveground net primary production of diverse European Pinus sylvestris populations

On range-wide and regional scales, climate and site factors exert control over tree growth, masking the genetic basis of biomass accumulation and allocation. To determine intrinsic population differences in productivity, aboveground net primary production (ANPP) was measured in 16-year-old Scots pine from 19 geographically distinct populations grown in a common garden experiment in central Poland (52°N). The populations originated from the northern (>55°N), central (54–47°N), and southern (<45°N) European range of Scots pine. We calculated ANPP from aboveground growth components, using diameter-based allometric equations developed for this site. Average foliage, aboveground woody and total ANPP differed significantly among populations and were greater for central European populations than for the southern and northern ones. Stocking and total ANPP per tree were positively correlated to stand aboveground biomass (r ²≥0.71). The relationship between the latitude of seed origin and ANPP was curvilinear and maximum for populations originating near the planting site (52°N). ANPP declined in populations with increasing longitude eastward from the Atlantic Ocean towards the center of the continent. This study underscores the potentially large genetic control of ANPP and biomass accumulation among diverse Scots pine populations. Received: 3 January 2000 / Accepted: 29 March 2000     

Latitudinal cline in allele length provides evidence for selection in a circadian rhythm gene

Divergent natural selection across a heterogeneous landscape can drive the evolution of locally adapted populations in which phenotypic variation is fine‐tuned to the environment. At the molecular level, such processes can be inferred by identifying correlations between genetic variation and environmental variables. We demonstrate that allele length and allele frequency at a regulatory circadian rhythm gene, OtsClock1b, are highly correlated (R² = 0.86, P = 1.25 × 10^?5) with latitude (a surrogate for photoperiod) in kokanee, the freshwater resident form of sockeye salmon (Oncorhynchus nerka). Two OtsClock1b alleles were identified that differed in length by seven amino acids, with the frequency of the shorter allele increasing from 50% in southern British Columbia (49°N) to complete fixation in Alaska (62°N). No such associations were detected for neutral microsatellite loci. In addition, a kokanee population sampled from Kamchatka, Russia (55°N) fits within the North American latitudinal cline, suggesting that this pattern may be convergent across large longitudinal spatial scales. This correlation provides evidence that natural selection rather than demographic processes may drive the distribution of genetic variation at OtsClock1b in kokanee. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 869–877.