Irwin, J. T. nd Lee, R. E. Jr 2003. Cold winter microenvironments conserve energy and improve overwintering survival and potential fecundity of the goldenrod gall fly, Eurosta solidaginis. -Oikos 100: 71 -78.We studied the influence of two overwintering microenvironments on survival and potential fecundity of goldenrod gall flies, Eurosta solidaginis (Fitch) (Diptera, Tephritidae). These freeze-tolerant larvae overwinter above the snow on standing goldenrod stems (elevated) or below the snow on broken stems (ground-level). When covered by snow, the ground-level larvae were well insulated and thus protected from the lowest temperatures of the winter, but, because they were warmer, they consumed more energy than their elevated counterparts. The ground-level group also experienced greater warming from the soil during sunny spring days, and their galls were less prone to drying than their elevated counterparts. By winter's end the groundlevel larvae exhibited significantly lower rates of emergence (83.5% vs 93.0%) and reduced potential fecundity (274 9 11 eggs/female vs 336 9 17 eggs/female). Models of seasonal energy use indicate that these differences were due to higher metabolic rates in the ground-level microenvironment due to insulation by snow and warming from the soil, which reduced the energy available for morphological development and egg production in the spring. We conclude that colder winter microenvironments can have a strong positive effect on overwintering ectotherms, particularly those that rely on energy stores accumulated during the autumn to produce eggs in spring. The enhanced reproductive output of insects overwintering in colder microenvironments may be a selective force promoting the evolution of increased cold-hardiness.

The moor frog Rana arvalis is a lowland species with a broad Eurasiatic distribution, from arctic tundra through forest to the steppe zone. Its present-day range suggests that glacial refugia of this frog were located outside southern European peninsulas. We studied the species-wide phylogeographical pattern using sequence variation in a 682 base pairs fragment of mtDNA cytochrome b gene; 223 individuals from 73 localities were analysed. Two main clades, A and B, differing by c. 3.6% sequence divergence were detected. The A clade is further subdivided into two subclades, AI and AII differing by 1.0%. All three lineages are present in the Carpathian Basin (CB), whereas the rest of the species range, including huge expanses of Eurasian lowlands, are inhabited solely by the AI lineage. We infer that AII and B lineages survived several glacial cycles in the CB but did not expand, at least in the present interglacial, to the north. The geographical distribution and genealogical relationships between haplotypes from the AI lineage indicate that this group had two glacial refugia, one located in the eastern part of the CB and the other probably in southern Russia. Populations from both refugia contributed to the colonization of the western part of the range, whereas the eastern part was colonized from the eastern refugium only. The effective population size as evidenced by theta(ML) is an order of magnitude higher in the AI lineage than in the AII and B lineages. Demographic expansion was detected in all three lineages.

Although the range dynamics of North American amphibians during the last glacial cycle are increasingly better understood, the recolonization history of the most northern regions and the impact of southern refugia on patterns of intraspecific genetic diversity and phenotypic variation in these regions are not well reconstructed. Here we present the phylogeographic history of a widespread and primarily northern frog, Rana sylvatica. We surveyed 551 individuals from 116 localities across the species' range for a 650-bp region of the NADH dehydrogenase subunit 2 and tRNA(TRP) mitochondrial genes. Our phylogenetic analyses revealed two distinct clades corresponding to eastern and western populations, as well as a Maritime subclade within the eastern lineage. Patterns of genetic diversity support multiple refugia. However, high-latitude refugia in the Appalachian highlands and modern-day Wisconsin appear to have had the biggest impact on northern populations. Clustering analyses based on morphology further support a distinction between eastern and western wood frogs and suggest that postglacial migration has played an important role in generating broad-scale patterns of phenotypic variation in this species.

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SUMMARYThe physiological responses supporting freeze tolerance in anurans are well known, but the evolution of this trait remains little studied. This is the first common-garden study of geographic variation in cryoprotective responses to freezing and the degree of freeze tolerance. We studied the gray treefrogs(Hyla versicolor and H. chrysoscelis) from sympatric sites in Minnesota, Indiana and Missouri. Patterns in the literature suggest that northern frogs produce more cryoprotectants upon freezing, but we found no geographic variation in cryoprotective responses or degree of freeze tolerance. The concentration of glucose produced upon freezing was higher than previously reported for this species (liver: 475 μmol g–1dry mass). Unfrozen frogs had high levels of glycerol (liver: approx. 150μmol g–1 dry mass), and did not produce more upon freezing. Liver glycogen content (concentration multiplied by liver mass) was highest in frogs from Minnesota and Missouri, and was stored in preference to lipids in Minnesota frogs, possibly to provide energy for the longer northern winters. Minnesota frogs accumulated more ice (53.4±1.8%) after freezing to–2.5°C than Indiana frogs (45.5±3.3%). The two species differed in body size but not in any of the physiological parameters measured. We conclude that these populations show no adaptive variation in freeze tolerance and that comparing published studies may be misleading because of different acclimation and feeding regimes.