Evidence for association of chromosomal form and development time from complex clines and geographic races in the grasshopper Caledia captiva (Orthoptera: Acridadae)

Evidence for an association between chromosomal form and development time in the grasshopper Caledia captiva (F.) was obtained through comparison of two geographic taxa and analysis of a complex latitudinal cline within one of the taxa. Northern populations of the Moreton taxon possess a metacentric genome and are slow-developing. In contrast, the Torresian taxon, distributed throughout northern, coastal Australia, a region of pronounced seasonality in rainfall, and southern populations of the Moreton taxon, which inhabit a region of pronounced seasonality in temperature, Soth have an acrocentric genome and are fast-developing. The convergence of chromosomal form and development time between Torresian and southern Moreton populations appears to be driven by convergence in life history. Seasonality limits grasshoppers to one generation per year and favours fast development. The transition between relatively acrocentric southern Moreton populations and relatively metacentric northern Moreton populations is gradual but not monotonic. Instead, a shift to a bivoltine life history in the middle of the transect occurs and is associated with shifts in both development time and chromosomal form. These results imply an adaptive role for chromosomal form, although the causative link between chromosomal variation and variation in development time remains to be established.     

Latitudinal clines in life-history variables of anadromous brown trout in Europe

Based on published data, we reviewed clinal variations in life-history characteristics of anadromous brown trout Salmo trutta from 102 European rivers at latitudes between 54 and 70° N. Growth rate in fresh water, mean smolt age, mean sea age at first sexual maturity, proportion of repeal spawners among adults, longevity, and length of adult life span exhibited latitudinal clines. Brown trout grew faster in fresh water, smolted and matured younger, lived fewer years but spawned more times in the south than in the north. The life-history traits studied were often correlated. Longevity, smolt age and sea age at maturity were negatively and smolt length and proportion of repeat spawners among adults were positively correlated with growth rate in fresh water. Longevity was positively correlated with smolt age and sea age at maturity. The latter also increased with increasing smolt age. None of these significant correlations among life history variables, except for those between smolt age and parr growth and proportion of repeat spawners and parr growth, are latitudinal effects. We do not know to what extent the latitudinal variation in life–history traits reflects phenotypic plasticity and to what extent it is caused by inherited differences among populations.     

Latitudinal variation in wild populations of Drosophila melanogaster: heritabilities and reaction norms

Large amounts of genetic variation for wing length and wing area were demonstrated both within and between Drosophila melanogaster populations along a latitudinal gradient in South America. Wing length and wing area showed a strong positive correlation with latitude in both wild flies and laboratory-raised descendants. Large population differences were observed for heritability and coefficient of variation of these two traits, whereas relatively small population differences were found for development time, viability, pupal mortality, sex ratio and their norms of reaction to four developmental temperatures. No clear-cut latitudinal clines were established for these life-history characters. These results are discussed in the light of Bergmann's Rule and the relation between larval development and adult body size.     

Patterns of size variation in bees at a continental scale: does Bergmann's rule apply?

Body size latitudinal clines have been widley explained by the Bergmann's rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann's rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142 008 distribution records of 615 bee species at 50 × 50 km (CGRS) grids across the West Palearctic. We then applied generalized least squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann's rule. However, considering bee genera separately, four genera were consistent with Bergmann's rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann's cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a ‘season length effect’ (i.e. shorter foraging season) is a potential driver of the converse Bergmann's cline particularly in bumblebees.     

Investigating latitudinal clines for life history and stress resistance traits in Drosophila simulans from eastern Australia

Latitudinal clines have been demonstrated for many quantitative traits in Drosophila and are assumed to be due to climatic selection. However, clinal studies are often performed in species of Drosophila that contain common cosmopolitan inversion polymorphisms that also show clinal patterns. These inversion polymorphisms may be responsible for much of the observed clinal variation. Here, we consider latitudinal clines for quantitative traits in Drosophila simulans from eastern Australia. Drosophila simulans does not contain cosmopolitan inversion polymorphisms, so allows the study of clinal selection on quantitative traits that are not confounded by associations with inversions. Body size showed a strong linear cline for both females and males. Starvation resistance exhibited a weak linear cline in females, whereas chill-coma recovery exhibited a significant nonlinear cline in females only. No clinal pattern was evident for development time, male chill-coma recovery, desiccation or heat resistance. We discuss these results with reference to the role inversion polymorphisms play in generating clines in quantitative traits of Drosophila.     

Re-establishment of clinal variation in flowering time among introduced populations of purple loosestrife (Lythrum salicaria, Lythraceae)

Range expansion during biological invasion requires that invaders adapt to geographical variation in climate, which should yield latitudinal clines in reproductive phenology. We investigated geographic variation in life history among 25 introduced populations of Lythrum salicaria, a widespread European invader of North American wetlands. We detected a strong latitudinal cline in initiation of flowering and size at flowering, which paralleled that reported among native populations. Plants from higher latitudes flowered earlier and at a smaller size than those from lower latitudes, even when raised in a uniform glasshouse. Early flowering was associated with greatly reduced reproductive output, but this was not associated with latitudinal variation in abundance, and probably did not result from a genetic correlation between time to and size at flowering. As introduction to North America c. 200 years ago, L. salicaria has re-established latitudinal clines in life history, probably as an evolutionary response to climatic selection.     

Evolution of Rotifer Life Histories

When compared to most other multicellular animals, rotifers are all relatively small, short-lived and fast-reproducing organisms. However among and within different rotifer species there is a large variation in life history patterns. This review accounts for such variation in rotifers, with a strong focus on monogonont rotifers. As the life cycle of monogonont rotifers involves both asexual and sexual reproduction, life history patterns can be examined on the level of the genetic individual, which includes all asexual females, sexual females and males that originated from one resting egg. This concept has been applied successfully in many areas, for example in predicting optimal levels of mictic reproduction or sex allocation theory. The benefits and implications of the view of the genetic individual are discussed in detail. Rotifer life histories can also be viewed on the level of physiological individuals. A large part of this review deals with the life histories of individual amictic females and addresses life history traits like body size, egg size and resource allocation patterns. It asks which trade-offs exist among those traits, how these traits change under the influence of environmental factors like food availability or temperature, and whether these changes can be interpreted as adaptive.     

Conservation Implications of Behaviour and Growth of the Lake Sturgeon, Acipenser fulvescens, in Northern Ontario

We investigated the age, growth and population structure of lake sturgeon in the Groundhog and Mattagami rivers, northern Ontario, Canada. Age, estimated from counts of annuli in pectoral fin rays, ranged from 1 to 69 years (y) in the 327 fish examined. Growth, expressed as an increase in fork length and calculated from a von Bertalanffy growth equation, slowed from a peak of about 3.9cmyear^-1during the early juvenile period (<9y) and approached an asymptote beyond 90y (FL=141.549[–e^-0.043(t–4.901)]). A length–mass equation (log M=3.07 log FL–2.26) and conversion factors for fork and total length (FL=0.97 TL–1.154) from our study ranged from 14.5 to 142cm (fork length), 15.5 to 158cm (total length) and 20 to 19730g (live mass) for 1177 individuals. We found no evidence for spawning or recruitment to the population in our study area. Population age and length structure were strongly bimodal, and growth rate appears to have slowed over the past decade. We discuss the possible environmental correlations and conservation implications of this age (size) distribution.